Symposium Organizers
Amit Misra Los Alamos National Laboratory
T. John Balk University of Kentucky
Hanchen Huang Rensselaer Polytechnic Institute
Maria Jose Caturla Universitat d'Alacant
Christoph Eberl University of Karlsruhe
EE1/NN1: Joint Session: In-situ Nanomechanics
Session Chairs
Monday PM, December 01, 2008
Room 200 (Hynes)
9:00 AM - EE1.1/NN1.1
SEM In situ Compression of Silicon Nanowires.
William Mook 1 , Rudy Ghisleni 1 , Karolina Rzepiejewska-Malyska 1 , Samuel Hoffmann 1 , Laetitia Philippe 1 , Johann Michler 1
1 , Swiss Federal Laboratories for Materials Testing and Research (EMPA), Thun Switzerland
Show AbstractSilicon nanowires have created a great deal of interest for over a decade due to their enhanced electrical properties when compared to bulk values. These structures also show size-dependent mechanical properties and since they can determine the reliability of many nanodevices and nanosystems, it necessary to quantify their elastic and plastic mechanical response to externally applied loads. This, however, is experimentally challenging due to the length scales involved. Therefore uniaxial compression experiments have been performed in situ with a high resolution scanning electron microscope (SEM) on single crystal silicon nanowires with diameters ranging from 100 nm to 1 μm. A flat-punch indenter can be positioned above the structure of interest with nanometer precision without modifying it due to deformation from mechanical scanning. Compressions are then run under displacement-control at 1 nm/s. By observing the deformation and contact area throughout the experiment engineering stress-strain curves can be extracted from the load-displacement data. Nanowire compressive strength is compared to silicon micropillar compression experiments and to silicon wires in bending.
9:15 AM - EE1.2/NN1.2
SEM In situ Micropillar Compression - Room Temperature Ductile to Brittle Transition of Si, GaAs, InP Semiconductors.
Johann Michler 1 , Fredrik Oestlund 1 , Karolina Rzepiejewska-Malyska 1 , William Mook 1 , Klaus Leifer 2 , Rudy Ghisleni 1
1 , Swiss Federal Laboratories for Materials Testing and Research (EMPA), Thun Switzerland, 2 Electron Microscopy and Nanoengineering, Department of Engineering Science, Uppsala University, Uppsala Sweden
Show AbstractCurrent fabrication technology is capable of producing micro- to nano-meter scale structures. The mechanical response of such structures has been shown to depend upon length scales such as pillar diameter. These findings contradict the classical laws of mechanics which assume that mechanical properties are independent of sample size. This contradiction has fostered an increasing number of investigations into mechanical size effects in order to accurately design and fabricate devices at these scales. In an effort to characterize and understand the mechanical behaviour dependence on the size, an investigation on single crystal semiconductor micropillars is presented. Single crystal silicon, gallium arsenide, and indium phosphide micropillars were fabricated by a focused ion beam (FIB) technique. The diameter of the pillars ranged from 200 nm to 10 μm with a length to diameter aspect ratio of three. The micropillars’ mechanical response was investigated by uniaxial compression tests performed with a diamond flat punch using an in situ SEM nanoindenter instrument.Engineering stress-strain curves as a function of pillar diameter are presented. The results show that all the investigated semiconductor materials exhibited a brittle to ductile transition with a decrease in pillar diameter. The deformation mechanism that is responsible for the plasticity is shown to be the formation of Shockley partial dislocations. The decrease of the projected pillar diameter on the crystal slip plane below the equilibrium distance (proportional to the stacking fault energy) between the leading and trailing partial dislocation controls the transition from a brittle to ductile behavior.
9:30 AM - EE1.3/NN1.3
In-situ Investigation of Nano-scale Plasticity in Cubic and Tetragonal Crystals via Homogeneous Deformation of Nano-Pillars.
Julia Greer 1 , Ju-Young Kim 1 , Steffen Brinckmann 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States
Show AbstractStrength of crystalline materials at reduced dimensions is important for fabrication and reliability of devices at nanometer scales such as MEMS and NEMS, bio-cell sensors, and fuel cells. Plastic flow stress of crystals, a size-independent property for bulk, is found to strongly depend on sample size as it is reduced to nano-scale. To investigate plasticity under homogeneous deformation, we have developed an in-situ micro-deformation methodology, where nano-pillars are mechanically deformed in a one-of-a-kind instrument, SEMentor, which merges the strengths of SEM and Nanoindenter, and offers the advantage of measuring mechanical response of nano-scale materials while capturing video frames throughout the deformation process. We present for the first time results of compression and tension tests performed in-situ inside SEMentor, where load-displacement data is correlated with real-time slip step formation on the surface of the deforming specimens. We perform a new robust technique for stress-strain calculation based on load-displacement data. We also report mechanical strengths of uniaxially-deformed single crystalline nano-pillars with different crystallographic structures (Au, Al, In, Mo) and compare them with one another. Our experiments demonstrate pronounced differences in the behavior of individual structures, and possibly plasticity mechanisms are discussed. We find that although all crystals show an increase in flow stress with decreasing diameter in a power-law fashion, the slopes of these size effects vary with the material, and the ratio between the observed maximum flow stress and the theoretical strength vary significantly.
9:45 AM - EE1.4/NN1.4
Quantitative In Situ Tensile Testing of 1D Nanostructures.
Daniel Gianola 1 , Reiner Moenig 1 , Oliver Kraft 1 2 , Cynthia Volkert 3
1 Institute for Materials Research II, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 , University of Karlsruhe, Karlsruhe Germany, 3 Institut für Materialphysik, Universität Göttingen, Göttingen Germany
Show AbstractPlasticity in extremely small volumes is fundamentally different than in large materials; the law of averages gives way to discrete processes that dominate the response. Probing the mechanical response and uncovering the underlying deformation mechanisms of diminishingly small structures at the micro- and nanoscale requires new strategies and approaches that circumvent difficulties associated with handling, gripping, loading, and measuring small specimens. The need for in situ experiments that give a one-to-one correlation between mechanical response and deformation morphology is exacerbated by the fact that electron optics are needed to image and manipulate nanostructures. Tensile experiments are the preferred modality at larger scales since they apply a homogeneous stress state and are less sensitive to boundary conditions, easing interpretation. Meanwhile, results obtained using the popularly employed techniques at the nanoscale (e.g. nanoindentation, micro-compression testing) are clouded by these unresolved issues. Here we describe quantitative in situ tensile experiments on 1D nanostructures in a dual-beam scanning electron microscope (SEM) and focused ion beam (FIB). Specimen manipulation, transfer, and alignment are performed using an in situ manipulator, independently-controlled positioners, and the FIB. Gripping of specimens is achieved using electron-beam assisted Pt deposition. Local strain measurements are obtained using digital image correlation of SEM images taken during testing. Examples showing results for single-crystalline metallic nanowires and nanowhiskers, having diameters between 30 and 300 nm, will be presented in the context of size effects on mechanical behavior, the theoretical strength of crystals, and the influence of defects on the accommodation of plasticity in small volumes.
10:00 AM - **EE1.5/NN1.5
Observation of Size-Dependent Plasticity by In Situ SEM and TEM.
Gerhard Dehm 1 2
1 Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben Austria, 2 Materials Physics, University of Leoben, Leoben Austria
Show AbstractThe continuing trend of miniaturizing materials in many modern technological applications has led to a strong demand for understanding the complex mechanical properties of materials at small length scales. This talk focuses on the recent understanding of the size-dependent plasticity in face-centered cubic metals with dimensions of several microns down to some tens of nanometers. At that length scale sophisticated measurement approaches are required with the advantage of in situ microscopy techniques providing both, control of the deformation experiment and insight in the underlying deformation mechanisms. Size effects of the flow stresses are compared for “wires” and thin films on compliant or stiff substrates. The interpretation of the results is based on recent insights on dislocation nucleation, glide band formation, and dislocation mobility stemming from in-situ SEM and TEM studies of single-crystalline and polycrystalline samples. The results are discussed with the attempt to explain the size effects in straining experiments at small length scales.Acknowledgement: Significant contributions from D. Kiener, R. Pippan, S.H. Oh (Leoben), M. Legros (Toulouse), and P. Gruber (Stuttgart) are acknowledged.
10:30 AM - EE1/NN1:joint
BREAK
11:00 AM - EE1.6/NN1.6
In Situ Examination of Nanoscale Deformation of Thin Film Bridges within a Scanning Electron Microscope.
Erik Herbert 1 , Arnold Lumsdaine 1 , R. Brian Peters 1 , Warren Oliver 1
1 , Agilent Technologies, Oak Ridge, Tennessee, United States
Show AbstractUsing a high precision nanoindentation head, a new technique has recently been developed to determine the elastic modulus and residual stress of a free-standing doubly-clamped thin film bridge [1]. A desire to examine the impact of certain anomalies in the experimental results (possibly occurring due to misalignment of the tip of the nanoindentation head with the surface of the bridge or due to adhesion of the tip with the surface of the bridge) motivates an examination of the experiment within a scanning electron microscope (SEM). A linear feedthrough mechanism has been developed to position the indentation head within the SEM chamber for precise targeting of the thin film bridge sample (placed on the SEM sample stage). This configuration also allows for the examination of the multi-dimensional deformation state of the bridge when the indentation head contact occurs offset from the center of the bridge.[1]E.G. Herbert, W.C. Oliver, M. P. de Boer, and G.M. Pharr, “Measuring the Elastic Modulus and Residual Stress of Free-Standing Thin Film Bridges by Nanoindentation,” 2007 MRS Spring Meeting, 2007.
11:15 AM - **EE1.7/NN1.7
A New Perspective on Nano-Mechanics: Quantitative Deformation Test in the TEM
Zhiwei Shan 1 , A. Minor 2 3 , J. Nowak 1 , S. Syed Asif 1 , O. Warren 1
1 , Hysitron Inc., Eden Prairie, Minnesota, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , University of California , Berkeley, California, United States
Show AbstractIt is often a challenge to measure accurately the mechanical properties of nanostructures and nanomaterials on account of their extremely small physical dimensions. Recently, we have developed an in situ TEM nanomechanical testing apparatus. This device enables one to acquire quantitative mechanical data while simultaneously recording the microstructural evolution of the materials during deformation, developing a one-to-one relationship between an imposed stress and an individual deformation event. In this talk, we report on the current progress in the application of this in situ TEM device for measuring the mechanical behavior of individual single crystal nickel and metallic glass (MG) pillars. Prior to the deformation tests, the Focused Ion Beam (FIB) fabricated nickel pillars were observed to contain a high density of defects. However, quite unexpectedly, the defects density was observed to decrease dramatically during the deformation process and, in some cases, even resulted in a dislocation-free crystal. The phenomena which we termed as “mechanical annealing” is the first direct observation of the dislocation starvation mechanism and sheds new light on the unusual mechanical properties associated with submicron- and nano- scale structures (Shan et al, Nature Materials, 2008). The compression tests on Cu-Zr-Al MG pillars revealed the intrinsic ability of fully glassy MGs to sustain large plastic strains, which would otherwise be preempted by catastrophic instability in macroscopic samples and conventional tests (Shan et al, PRB, 2008).
11:45 AM - EE1.8/NN1.8
In- Situ Observation of Deformation Characteristics in Nanotwinned Copper Pillars.
Vinay Sriram 1 , Jia Ye 2 3 , Andrew Minor 2 3 , Jenn-Ming Yang 1
1 Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States, 2 National Centre for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States
Show AbstractThe semiconductor industry is currently moving towards integration of “air gap” technology beyond the 32nm node. A major concern in the introduction of air gap technology is the mechanical integrity, reliability and stability of the vias and interconnects line structures. A new method based on In-situ Transmission Electron Microscopy nanocompression testing of copper pillars which are of the same size scale of vias, interconnects will be presented. Copper pillars having nanotwined boundaries and nanocrystalline grains were tested by this technique. We show direct evidence that twin boundaries can withstand extensive plastic deformation and still retain their structure when compared to regular grain boundaries. The deformation mechanisms of twin boundaries predicted by Molecular Dynamic (MD) simulations has been verified by real-time TEM analysis. Quantitative in-situ stress measurements for deformation twinning are in close agreement with those reported by first principle based calculations.
12:00 PM - EE1.9/NN1.9
In Situ TEM Nanocompression Testing of Gum Metal.
Elizabeth Withey 1 , Andrew Minor 2 , Jia Ye 2 , Shigeru Kuramoto 3 , Daryl Chrzan 1 , John Morris 1
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Toyota Central R&D Laboratories, Inc., Nagakute Japan
Show Abstract“Gum Metal” is a newly developed β-Ti alloy that, in the cold-worked condition, has exceptional elastic elongation and high strength. The available evidence suggests that Gum Metal does not yield until the applied stress approaches the ideal strength, and then deforms by mechanisms that do not involve conventional dislocation plasticity. To study its behavior, submicron-sized pillars of solution-treated and cold-worked Gum Metal were compressed in situ in a quantitative compression stage in a transmission electron microscope. Quantitative load vs. displacement data was correlated to real-time images to determine a pattern of deformation that agrees with previous results from ex situ nanoindentation.
12:15 PM - EE1.10/NN1.10
Thermal Behavior of Gold Nanoparticles on Pyrite and Arsenopyrite Surfaces.
Niravun Pavenayotin 1 , Qiangmin Wei 2 , Yanbin Chen 1 , Lumin Wang 1 2
1 Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractDiffusion of gold nanoparticle on pyrite (FeS2) and arsenopyrite (FeAsS) surfaces was studied under in-situ TEM. The gold nanoparticles were deposited onto the surfaces by sputtering of gold TEM grids by ion milling. The gold nanoparticles have a uniform size of approximately 2 nm in diameter. The samples were heated up using a hot stage in the TEM to 100, 200, 300, 400, 500 and 550°C. The movement and characteristics of the nanoparticles were monitored by in situ TEM. The gold nanoparticles coalesce and grow by Oswald’s ripening as the temperature rises. At 500°C, pyrite starts to decompose into amorphous Fe and S. Gold particles on the decomposed surface are driven together and form particles as large as 30 nm in diameter while at the same temperature the gold particles in arsenopyrite are less than 20nm in diameter. Some of the solid gold nanoparticles on pyrite surface also melt and form a film-like morphology. Arsenopyrite does not decompose until 550°C. The gold particles that reside on top of the amorphous decomposed region are immobile. The particles on the crystalline surface grow at a fast rate and visibly mobile on the surface. The differences in the diffusion behavior of gold nanoparticles on two different pyrites will be explained.
12:30 PM - **EE1.11/NN1.11
Revealing the Deformation Processes Responsible for Controlling Mechanical Properties.
Ian Robertson 1
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractTransmission electron microscopes have played a critical role in building our knowledge base regarding dislocations, dislocation-obstacle interactions and microstructural evolution as a function of deformation history. Past usage yielded primarily snapshots of the microstructure, leaving the pathways by which it was attained to be deduced. Development of straining stages for use in electron microscopes, cameras for capturing the reaction dynamics and computer technology and software for image processing have enabled observation of dislocation processes in real time and at the spatial resolution of the instrument. Provided the impact of the thin film geometry and the stress state are appreciated, this technique can and has been used to provide visual and quantitative information about dislocation reactions and processes. The results of these studies are now being incorporated into physically-based models for predicting the mechanical properties. Recent developments in stage design provide the capability to measure the macroscopic response and to simultaneously observe the deformation behavior, thus, providing the opportunity to correlate microscopic processes with a macroscopic property. In this talk, examples of applications of standard and new straining stages will be used to illustrate how these tools have advanced our understanding of dislocation reactions and processes and how this insight has been used to yield new models.
EE2: Anomalous Nanomechanical Behavior
Session Chairs
Monday PM, December 01, 2008
Room 200 (Hynes)
2:30 PM - **EE2.1
Stress-coupled Grain Boundary Migration in Nanocrystalline Thin Films.
Kevin Hemker 1 , John Sharon 1 , Timothy Rupert 2 1 , Daniel Gianola 3 1
1 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Materials Sci & Eng, MIT, Boston, Massachusetts, United States, 3 , KIT, Karlsruhe Germany
Show AbstractStress-coupled grain boundary migration has recently been manifest in observations of stress-assisted room temperature grain growth in nanocrystalline metals. Of particular interest to this study are micro-tensile experiments involving nanocrystalline thin films that highlight the fact that the mechanical behavior of these films is not only different that bulk materials but dynamic as well. The observation of stress-assisted grain growth in these nanocrystalline thin films cannot be described by traditional grain growth driving forces and appears to be a direct experimental observation of stress-coupled grain boundary motion. This stress-coupled grain boundary motion appears to be highlighted in nanocrystalline films because of their unusually high flow stresses.
3:00 PM - EE2.2
Diffusion Induced Stresses in Nanostructured Materials for Energy Conversion and Storage.
Yang-Tse Cheng 1 2 , Mark Verbrugge 1
1 , GM R&D Center, Warren, Michigan, United States, 2 Department of Chemical and Materials Engineering, University of Kentucky, Louisville, Kentucky, United States
Show Abstract3:15 PM - EE2.3
First Observation of Hollow Silver Nanotubes.
Maureen Lagos 1 2 , Fernando Sato 1 , Jefferson Bettini 2 , Varlei Rodrigues 1 , Douglas Galvao 1 , Daniel Ugarte 1 2
1 Applied Physics, State University of Campinas, Campinas, Sao Paulo, Brazil, 2 , LNLS, Campinas, Sao Paulo, Brazil
Show AbstractMetallic nanowires (NWs) have been object of many theoretical and experimental studies in the last years. In nanostructures, the atomic arrangements may be different from macroscopic matter, mainly due to the role of surface energy. In fact the stretching of metal junctions has revealed quite surprising metastable structures such as suspended atomic chains and helical wires. In this work we report the first experimental observation of the formation of the smallest possible square cross-section hollow silver nanotubes during elongation of Ag nanocontacts as revealed by real time atomic resolution transmission electron microscope (HRTEM). Silver NWs were produced inside the HRTEM (JEM-3010 URP 300kV, 0.17 nm point resolution). Firstly, holes are opened in a self-supported metal film by focusing the electron beam and, nanometric bridges are formed between neighboring holes. These constrictions evolve, elongate and break. This process is recorded with a high sensitive camara (Gatan 622SC, 30 frames/s). We have analyzed the NW structural stability by total energy ab initio calculations using the well-known SIESTA code. We have used norm-conserving pseudo potentials (PP)and atomic orbitals as a basis set. We have used the PP built on Troullier-Martins scheme in a local density approximation (LDA). The theoretical analysis suggests that the formation of these metastable hollow structures requires a combination of minimum basis size and high gradient stress generating a soft structure capable of absorbing a huge tensile deformation when high stress is applied.
3:30 PM - **EE2.4
Unusual Mechanical Behaviors Of Nanocrystalline Metals - Effect Of Size And Heterogeneity Of Microstructure.
Jagannathan Rajagopalan 1 , Taher Saif 1
1 Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractNano-grained thin metal films exhibit substantially different mechanical behaviors compared to their bulk, coarse-grained counterparts due to their unique dimensional and microstructural constraints. We have experimental evidence showing that nanocrystalline freestanding thin metal films (aluminum and gold films, grain size of 50-80 nm) recover a large fraction of their plastic strain after unloading, under macroscopically stress-free conditions. This recovery is time and temperature dependent with three distinct activation energies, possibly linked to three impurities in the films. The same films with larger grain sizes (200 nm) show strong Bauschinger effect during unloading, even at large overall tensile stresses. At an intermediate grain size (150 nm), they exhibit both Bauschinger effect and strain recovery upon unloading. We hypothesize that these unusual and seemingly unrelated phenomena are the consequence of the interplay between the small grain size of these films and the microstructural heterogeneity (size and texture variations of individual grains) – a paradigm that has not been explored in much detail. We carry out in situ Transmission Electron Microscopy (TEM) of these films while their macroscopic stress-strain response is measured, using a novel micro mechanical stage. TEM analysis shows first evidence of a dislocation mediated, and thermally assisted, mechanism for both strain recovery and Bauschinger effect in nano-grained thin films.
4:30 PM - **EE2.5
Time-Dependent Deformation of Thin Aluminum and Gold Films.
Richard Vinci 1 , Xiaojun Yan 1 , Walter Brown 1 , Yuan Li 2 , John Papapolymerou 2
1 Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractTime-dependent deformation of thin metal films can lead to failure in a number of microelectromechanical devices. Even at room temperature, creep and stress relaxation can be rapid and large, and can continue for months. In this regime, small changes in temperature can have significant effects on the rate and extent of deformation. In an effort to characterize the time-dependent behavior of thin metal films we present experiments and models addressing the stress relaxation observed in micrometer-thick sputtered Al and electroplated Au membranes at room temperature. It is shown that relaxation can be due to both inelastic processes (creep plasticity) and to anelastic processes (fully elastic but with delayed response). However, under certain conditions it is possible to induce a state in which the behavior is purely anelastic, allowing separation of the two contributions to the more general case. Linear viscoplastic and viscoelastic models are presented that enable prediction of the film’s mechanical behavior under monotonic relaxation conditions and under complex cyclic loading, both for the purely anelastic state and for the mixed inelastic-anelastic state.
5:00 PM - EE2.6
Creep Deformation Behavior of Nanocrystalline Copper Doped with Antimony.
Rahul Rajgarhia 1 , Ashok Saxena 1 , Douglas Spearot 1
1 , University of Arkansas, Fayetteville, Fayetteville, Arkansas, United States
Show AbstractNanocrystalline materials are prone to premature grain growth causing the loss of its superior mechanical properties attributed to its low grain size. Recent theoretical and molecular dynamics simulation results have shown promising results of stabilizing the microstructure by including impurity atoms (dopants) at the grain boundaries. In this study, nanocrystalline copper doped with 0.2 and 0.5 at.% antimony is studied under the influence of elevated temperatures and mechanical stress. At these low concentrations, Sb completely segregates to grain boundaries in Cu without forming precipitates or secondary phases. The Cu-Sb alloy is prepared by casting in an induction arc furnace followed by equal channel angular extrusion process (ECAE) that causes grain size refinement. The TEM images of heat treatment analysis at 250 C for 1 hour show that the microstructure of the nanocrystalline samples with Sb remain unchanged whereas extensive grain growth is observed in pure Cu. Also, the combined effect of stress and temperature, using creep deformation tests, on the microstructure of the nanocrystalline Cu-Sb and pure Cu materials are discussed.
5:15 PM - EE2.7
Void Formation Mechanism of Nanocrystalline Cu Alloys During Uniaxial Relaxation Test.
Junya Inoue 1 , Yosuke Fujii 1 2 , Toshihiko Koseki 1
1 Materials Engineering, The University of Tokyo, Tokyo Japan, 2 , SONY, Miyagi Japan
Show AbstractVoid formation in nanocrystalline Cu alloys during uniaxial relaxation experiment was quantitatively studied to clarify the effect of alloying elements to the void formation process in nanocrystalline Cu. Cu alloy films (Cu-Sn and Cu-Ag) with various thickness were deposited on heat-resistant polyimide substrates by electron beam physical vapor deposition (EB-PVD) method. On the top and bottom surfaces of the Cu layer, Ta layers were deposited to suppress the surface diffusion of Cu during the relaxation test. The Cu alloy films were annealed after the deposition to achieve complete grain growth to the size equivalent to the film thickness at the temperature of 460K in a vacuum of 1.0x10-5Pa for 12h. A uniform uniaxial tensile strain was induced in the films by applying a constant radius of curvature to the polyimide substrate. Isothermal microstructural evolution as well as void formation in the films was studied at elevated temperature, 460K.No apparent initial voids were found in EB-PVD films after annealing the samples at 460K, while stress-induced voids were found initiated at the grain boundary triple points at various levels of applied strain below that equivalent to the maximum ultimate strength of nanocrystalline Cu with identical grain size reported by others. The voids were found to nucleate without incubation time, and the nucleation rate was highly dependent on the applied strain. No severe plastic deformation, such as dislocation pile up or mechanical twinning, could be found in the films with a thickness less than 300nm even at the stress level almost equivalent to the tensile strength. The results indicate that the microvoiding is the predominant accommodation process in this range of grain sizen, stress and temperature. By introducing an approximate void formation model, the void growth and the effect of stress relaxation to the void nucleation were examined. Resulting model shows a reasonable agreement with the experimentally observed number density and area fraction of voids for various strain levels and grain sizes. The application of the model to the void formation process in Cu alloys revealed the effect of alloying elements to the void nucleation rate and void growth rate separately. From the microstructural investigation, the difference in the segregation behavior of alloying elements was found responsible to the observed trends in the suppression of the void formation process by the alloying elements.
5:30 PM - EE2.8
Strain Recovery Driven by Grain-boundary Diffusion for Nanocrystalline Thin Films.
Xiaoding Wei 1 , Jeffrey Kysar 1
1 Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractPlastic strain in metals is typically considered to be irreversible. However plastic strain in nanocrystalline materials can be recovered over a period of time via diffusive mechanisms. In this study, free-standing nanocrystalline Cu films of submicron thickness with an average grain size of about 40 nm are mechanically loaded via a plane-strain bulge test in order to obtain the stress-strain behavior. During loading, the specimens are deformed with a significant plastic strain after which the specimens are left at room temperature. The specimens recover their plastic strain in a period of time that can range from a few minutes to a few days depending upon the magnitude of the induced plastic strain as well as the number of strain recovery cycles. We will present results of multiple cycles of plastic deformation and recovery as well results of the rate of recovery of the plastic strain. There are two characteristic strain rates that occur during plastic strain recovery. A model of the plastic strain recovery that invokes various diffusive mechanisms will be presented as a possible explanation for the phenomenon.
5:45 PM - EE2.9
Mechanical Behavior Associated with Heterogeneous Grain-boundary Diffusion and Sliding in Nanocrystalline Materials.
Yujie Wei 1 , Allan Bower 1 , Huajian Gao 1
1 Engineering Division, Brown University, Providence, Rhode Island, United States
Show AbstractTo improve our understanding of deformation mechanisms in materials with small characteristic microstructures, like nanocrystals and thin films, we consider a mesoscopic continuum model of a two-dimensional assembly of grains separated by sharp grain boundaries. In this model, the crystal deforms plastically by grain boundary diffusion, grain-boundary sliding, as well as grain interior dislocation activities described by single crystal plasticity. Some of the phenomena found in this study include:(a) If the diffusivity changes abruptly in the grain-boundary network, the transient stress distribution in response to an applied load develops crack-like stress concentrations. The stress concentrations develop at a rate determined by the fast diffusion coefficient, and subsequently relax at a rate determined by the slow diffusion coefficient [1].(b) Creep deformation by heterogeneous grain-boundary diffusion is partially recoverable [2], which could explain the recent experiments published in Science by Rajagopalan, Han, and Saif [3].(c) Coble creep changes character under heterogeneous grain-boundary diffusion exists [1].(d) There is a transition from sliding and diffusion dominated creep in relatively small grain sized nanocrystals at low strain rates to plasticity dominated flow in nanocrystals with larger grain size deformed at higher strain rates [4] and [5].Refereces:[1] Wei, Bower, Gao, J. Mech. Phys. Solids, 2008;56:1460. [2] Wei, Bower, Gao, Scripta. Mat., 2007;57:933. [3] Rajagopalan, Han, Saif, Science 2007;315:1831. [4] Wei and Gao, Mat. Sci. Eng. A 2008;478:16. [5] Wei, Bower, Gao, Acta Mater.2008;56:1741.
Symposium Organizers
Amit Misra Los Alamos National Laboratory
T. John Balk University of Kentucky
Hanchen Huang Rensselaer Polytechnic Institute
Maria Jose Caturla Universitat d'Alacant
Christoph Eberl University of Karlsruhe
EE3: Fatigue, Fracture & Tribology
Session Chairs
Chris Eberl
Nikhil Koratkar
Tuesday AM, December 02, 2008
Room 200 (Hynes)
9:30 AM - **EE3.1
Fatigue Deformation of Nanocrystalline and Ultrafine-grained Ni Alloy.
Sheng Cheng 1 , Peter Liaw 1 , Xun-li Wang 2 , Alexandru Stoica 2 , Hahn Choo 1
1 Dept of Materials Science and Engineering, University of tennessee, Knoxville, Tennessee, United States, 2 Neutron scattering science division, Oak ridge national laboratory, knoxville, Tennessee, United States
Show AbstractGrain size of metals plays an important role in their deformation mechanism. It also applies to fatigue deformation. However, the fatigue deformation of nanocrystalline and ultrafine-grained metals was not extensively studied, and many issues remain unsolved. We have recently performed fatigue studies on a range of materials with grain size from nanocrystalline to ultrafine-grained to conventional coarse-grained samples under both tensile and compressive loading modes. We used in situ and ex situ neutron diffraction and synchrotron X-ray diffraction to study the lattice strain as well as the intergranular strain evolutions during fatigue tests. From the lattice strains as well as intergranular strain evolution, we show a clear grain size-related mechanism in fatigue. Different influential mechanisms will be discussed. This work is supported by the National Science Foundation International Materials Institutes (IMI) Program (DMR-0231320) and Major Research Instrumentation (MRI) Program (DMR-0421219) with Dr. C. Huber and Dr. C. Bouldin as the Program Directors, respectively.
10:00 AM - EE3.2
Effect of Cyclic Loading and Microhardness Indentation on the Microstructural Stability of Nanotwinned Cu Samples with Highly Aligned Twin Interfaces.
C. Shute 1 , B. Myers 1 , S. Xie 1 , A. Hodge 2 , T. Barbee 3 , Julia Weertman 1
1 , Northwestern University, Evanston, Illinois, United States, 2 , University of Southern California, Los Angeles, California, United States, 3 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractThe effects on the microstructure of cyclic loading and of microhardness indentation on high purity nanotwinned Cu samples were examined. Samples were made by a laminate process using magnetron sputtering. The foil consists of long micron-width columnar grains containing nanotwins spaced about 40-50 nm apart with their interfaces aligned perpendicular to the growth direction. Transverse cuts of the thick foil samples (170 um) by FIB technique showed that the twins were remarkably stable under tension-tension fatigue except under the highest stress tested (450 MPa maximum stress amplitude, in the LCF regime). HREM pictures showed the appearance of some incoherent regions on the twin interfaces, development of high internal strains and dislocations in the twin interiors. Indentation of a foil surface caused significant disruption of the columnar grain boundaries, appearance of a shear band, large incoherent regions on twin interface boundaries, and extensive regions of very high internal strain. The highly aligned nanotwins, unlike equiaxed nanocrystalline or UFG Cu, present quite a stable microstructure.*The TEM, FIB and SEM work was performed in the EPIC facility of NUANCE Center, supported by NSF-NSEC, NSF-MRSEC, Keck Foundation, State of Illinois, and Northwestern University.
10:15 AM - EE3.3
Damage Behavior of Al Thin Films Fatigued at Ultra-high Frequencies.
Diana Courty 1 , Chris Eberl 1 , Werner Ruile 2 , Oliver Kraft 1 3
1 izbs, University of Karlsruhe, Karlsruhe Germany, 2 , EPCOS AG, Munich Germany, 3 IMF2, Forschungszentrum Karlsruhe, Karlsruhe Germany
Show AbstractComponents used in radio frequency communication are typically stressed at frequencies in the GHz-regime. We perform fatigue tests at ultra-high frequencies in metallizations using testing devices that reach cycle numbers up to 10^14 in one day to investigate the reliability of such thin film devices. Fatigue effects, such as the formation of voids and extrusions that result in a frequency shift or in short circuits, respectively, are observed in the polycrystalline metallization.In more detail, we have used patterned Al/Cu thin films of a thickness of approximately 200 nm on a piezoelectric substrate, which are subjected to an AC electric field that leads to cyclic strains in the film/substrate system. Transmission Electron Microscopy is used to study the possible role of dislocations and to determine the mean grain size, which is in the order of 100 nm. No long range dislocation structures were observed in the fine grained material. Extrusions and voids that form in the stressed metal film are analyzed quantitatively by Scanning Electron Microscopy and are correlated to the frequency shift which represents an easily accessible fatigue criterion. For a quantitative correlation, the modeling focuses on the influence of damage on the frequency. By means of finite element simulation, the influence of void size, density and position in the metal conductor lines is explored. These simulations are part of a physically based life time model which is currently being developed.
10:30 AM - EE3.4
Study the High-cycle-fatigue Behavior of a Nano-precipitate Strengthened Alloy by In-situ Neutron-diffraction Experiments.
E-Wen Huang 1 , Wei-Ren Chen 2 , Michael Hofmann 3 , Chih-Pin Chuang 4 , Sven Vogel 5 , Peter Liaw 1 , Lee Pike 6
1 Materials Science & Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Neutron Scattering Sciences Division, Spallation Neutron Source, Oak Ridge National Laboratory , Oak Ridge, Tennessee, United States, 3 Spec-Stress, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Garching Germany, 4 Department of Engineering and System Science, National Tsing Hua University, Hsinchu Taiwan, 5 Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 6 Technology Engineering, Haynes International Inc., Kokomo, Indiana, United States
Show AbstractIn this study, a theoretical model of the nano particle deformation under a tension-tension high-cycle-fatigue experiment and a tension test is proposed for investigating the structural properties of precipitation-strengthened metallic alloys using the in-situ neutron-diffraction technique. The model is based on the macroscopic stress-strain curves incorporating with atomic-scale responses measured by the in-situ neutron-diffraction experiments. A newly-developed corrosion-resistant nickel-based alloy, HASTELLOY® C-22HSTM, is selected to demonstrate the applicability of this model and a complementary texture investigation is used to gauge its validity. The alloy contains the strengthening nano precipitates, which are treated as a set of polydisperse hard ellipsoids and their spatial arrangement, given by the inter-precipitate structure factor, is calculated by a stochastic phenomenological approach using small-angle neutron-scattering experiments accompanied by TEM measurements. In comparison with the fracture surfaces, the different deformation mechanisms of the nano precipitates under two types of tensile loadings have been characterized by the evolution of the lattice strain and peak-profile, extracted from in-situ neutron-diffraction profile fitting.ACKNOWLEDGMENTSThe National Science Foundation (NSF), International Materials Institutes (IMI) Program (DMR-0231320), supports this research. Dr. Carmen Huber is the Director of the IMI program. The Department of Energy’s Office of Basic Energy Science funds the Lujan Neutron Scattering Center at Los Alamos Neutron Science Center (LANSCE). The Los Alamos National Security LLC under the DOE Contract DE-AC52-06NA25396 operates the Los Alamos National Laboratory. Haynes International provides the alloys.
10:45 AM - EE3.5
Suppression on Fatigue Crack Growth in Carbon Nanotube Composites.
Nikhil Koratkar 1 , Catalin Picu 1 , Wei Zhang 1
1 Mechanical Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractFatigue is one of the primary causes for catastrophic failure in structural materials. In this study, we report an order of magnitude reduction in the fatigue crack propagation rate for an epoxy system with the addition of ~0.5% weight of multiwalled carbon nanotube (MWNT) additives. The fatigue suppression performance of the nano-composite was found to be the most effective at low stress intensity factor amplitudes. Using fractography analysis and fracture mechanics modeling we show that the crack suppression is caused by a crack bridging phenomena which results in an effective crack closing stress due to the frictional pull-out of nanotube-fibers in the wake of the crack tip. Using this model, we show that the suppression of crack growth can be further optimized by reducing the nanotube diameter, by increasing the number density of nanotubes that bridge the crack and by increasing the pull-out length of the nanotubes. Control experiments with nanotubes of different diameters, lengths and dispersion quality confirmed the model predictions. These results demonstrate that carbon nanotubes can significantly enhance the fatigue-life of structural polymers that are susceptible to damage in the form of cracks. One of the limitations of fatigue suppression using carbon nanotube additives is that the crack growth rates can be effectively suppressed only at low values of the stress intensity factor. We show that the reason for this is the shrinkage of the nanotube (fiber) bridging zone in the wake of the crack tip which occurs at the high stress intensity factors. We demonstrate that this problem can be overcome by using amine-functionalized multiwalled carbon nanotubes (A-MWMT). The reason is that the A-MWNT interact covalently with the epoxy matrix which prevents pull-out of the nanotubes. Instead we find that the A-MWNT additives change the structure/morphology of the local epoxy in the interphase zone which encapsulates the A-MWNT. The modified epoxy within this interphase zone has a relatively lower cross-link density compared to the bulk and is prone to 'Crazing' which significantly enhances the energy dissipation and dramatically slows the crack growth rates across the full range/spectrum of applied stress intensity factors. We report over 20-fold reduction in crack growth rates for the A-MWNT/epoxy composite compared to the neat epoxy over the full range of stress intensity factor amplitudes. In this way addition of A-MWNT to the epoxy fundamentally changes the material's fatigue behavior due to the altered molecular scale morphology of epoxy within the interface zone (that encapsulates the nanotubes) as compared to the bulk, which allows crazing to take place in an otherwise brittle material.
11:30 AM - **EE3.6
Effects of Grain Refinement on Lifetime and on Damage Evolution under Repeated Contact in Nanostructured Metals.
Ruth Schwaiger 1 2
1 IMF2, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 IZBS, University Karlsruhe, Karlsruhe Germany
Show AbstractIn structural applications, materials may be subjected to conditions in which cyclic contact loading inevitably occurs. This may lead to contact fatigue effects which are critical to assess the overall usefulness of nanocrystalline materials but have not yet been investigated systematically on the nanoscale.This talk will describe our studies on sliding contact and normal contact fatigue behaviors of nanocrystalline metals, with average and total range of grain sizes well below 100 nm. Cyclic contact deformation was induced in Ni samples having different grain sizes by repeatedly indenting the surface of the specimens and by repeatedly sliding a tip over the surface. The mechanical behavior as well as the evolution of damage in nanocrystalline Ni during repeated contact were systematically compared with ultrafine-crystalline and microcrystalline materials in order to gain a broader perspective on the effects of grain size on contact fatigue.
12:00 PM - EE3.7
Tribology of a Nanocrystalline Alloy across the Hall-Petch Breakdown.
Timothy Rupert 1 , Christopher Schuh 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractNanocrystalline alloys exhibit generally desirable wear properties, but the extreme conditions produced during sliding or abrasive wear can lead to evolution of the nanostructure and properties. This talk addresses the tribological response of nanocrystalline Ni-W alloys across a range of grain sizes spanning the Hall-Petch breakdown. Both cyclic sliding and abrasive wear are studied in electrodeposited coatings with grain sizes ranging from 3 to 40 nm, to understand the influence of microstructure and mechanical properties on wear resistance. The experiments reveal evidence of a dynamic nanostructure where grain boundary character evolves under sliding loading, which in turn alters the mechanical response. The effect of a grain size gradient on tribological response is also discussed.
12:15 PM - EE3.8
Connecting Plasticity and Fracture in Brittle Materials.
Douglas Stauffer 1 , Aaron Beaber 1 , William Gerberich 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show Abstract12:30 PM - EE3.9
Brittle and Ductile Failures of Silicon Nanowires under Tension Simulation.
Keonwook Kang 1 , Wei Cai 1
1 , Stanford University, Stanford, California, United States
Show AbstractWe performed molecular dynamics study of tension simulations of small diameter silicon nanowires (D < 10nm) grown along [110] direction and found that their brittle or ductile failure behavior depends on their size and temperature. A dislocation dynamics model is developed to explain the size and temperature effects on the failure behavior of nanowires observed in atomistic simulations. Results are also compared with recent tensile experiments on silicon nanowires.
12:45 PM - EE3.10
Deformation Mechanisms in Nanocrystalline Pd and Pd-Zr Thin Films.
Rudolf Baumbusch 1 , Patric Gruber 1 , Tanja Ulyanenkova 2 , Tanja Filatova 2 , Stephen Doyle 3 , Anna Castrup 4 , Juergen Markmann 5 , Joerg Weissmueller 4 , Tilo Baumbach 2 3 , Horst Hahn 4 , Oliver Kraft 1
1 Institut für Zuverlässigkeit von Bauteilen und Systemen, University of Karlsruhe, Karlsruhe, Baden-Württemberg, Germany, 2 Laboratorium für Applikationen der Synchrotronstrahlung, University of Karlsruhe, Karlsruhe, Baden-Württemberg, Germany, 3 Institut für Synchrotronstrahlung, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Baden-Württemberg, Germany, 4 Institut für Nanotechnologie, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Baden-Württemberg, Germany, 5 Fachrichtung 7.3 -Technische Physik, Universität des Saarlandes, Saarbrücken, Saarland, Germany
Show AbstractEE4: Thin Films, Multilayers and Nanocomposites: Mechanics and Radiation Effects
Session Chairs
Yang-Tse Cheng
Dan Gianola
Tuesday PM, December 02, 2008
Room 200 (Hynes)
2:30 PM - **EE4.1
Deformation and Fatigue of Nanoscale Multilayer Metallic Composites.
David Bahr 1 , Nicole Overman 1 , Cory Overman 1 , Ioannis Mastorakos 1 , Firas Akasheh 2 , Hussein Zbib 1
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 , Tuskegee University, Tuskegee, Alabama, United States
Show AbstractMultilayer metallic thin films, where film thicknesses are on the order of 10 to 100 nm, have been shown to have substantially elevated strengths over their constituent materials. This presentation focuses primarily on Nb/Cu at thicknesses of 20/20 nm, and the testing methodology used to compare the effects of uniaxial and biaxial stress states on the deformation and fatigue of the systems. The films are deposited via sputtering on silicon wafers, and form discreet layer structures. The mechanical response of the films were tested using two complementary techniques; nanoindentation and bulge testing. Bulge testing was used to determine the residual stress in these films, approximately 30 MPa. The composite elastic modulus was measured using both techniques, and found to correlate well between the two systems. The plasticity of these films was assessed using both techniques. The hardness of the Nb/Cu films was approximately 5 GPa. Alterations in the bulge test geometry, ranging from rectangular membranes that produce effectively uniaxial strain conditions, to square membranes that form biaxial stress states, but have significant stress concentrations, and more complex tailored shapes selected using high strain finite element modeling of the structures that localize the stress concentrations away from the etched window structures used to form the test specimens will be compared with an etched “dimple” structure that leads to a stress concentration in the center of the window. This presentation will discuss and compare the experimental techniques required to assess the properties of these extremely strong films. Plastic deformation is shown to occur during bulge testing either at regions of microstructural variations, such as an anomalously large grain, or these controlled stress concentration sites. With a best practices condition for non-unaxial bulge testing, low cycle, high strain fatigue testing using the bulge test is shown to be a viable method for biaxial loading conditions. Evidence of strain softening in these conditions is presented. Finally, the experimental conditions will be related to simulations of deformation using dislocation dynamics of the multilayer structures.
3:00 PM - EE4.2
Deformation in Multilayers at Elevated Temperatures.
Sandra Korte 1 , David Dunstan 2 , William Clegg 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Physics Department, Queen Mary, University of London, London United Kingdom
Show AbstractMultilayers made of InGaAs are of interest due to their use in optoelectronic devices. Formation of dislocations can result in failure of the entire device and therefore an exact understanding of the onset of yield in these systems is important.Nanoscale superlattices of heteroepitaxially grown InxGa1-xAs of different compositions were characterized by means of nanoindentation and micropillar compression in order to identify the pressure at the onset of yield. Using a new nanoindentation system under protective atmosphere to prevent oxidation this was done over a range of temperatures from room temperature to 500°C. In layered systems the mechanical properties are partly determined by whether or not flow is confined to indiviual layers or occurs continuously over a number of layers. In order to identify the overall deformation mechanism in InGaAs superlattices, in-situ micropillar compression and indentation inside a transmission electron microscope was used to observe flow within and across layers during deformation.In order to predict yield in heteroepitaxial multilayers, the system parameters layer thickness, coherency strains and mechanical properties of the constituent layers need to be known. Nanoindentation at room and elevated temperatures was employed to obtain mechanical data on the solid solution InGaAs over the relevant compositional range and incorporated into a model predicting the measured multilayer properties.
3:15 PM - EE4.3
Radiation Damage and He Solubility at Coherent and Incoherent Interfaces.
Dhriti Bhattacharyya 1 , Osman Anderoglu 1 , Michael Demkowicz 2 , Igor Usov 2 , Richard Hoagland 2 , Amit Misra 1
1 MPA-CINT, Los Alamos National Laboraotry, Los Alamos, New Mexico, United States, 2 MST-8, Los Alamos National Laboraotry, Los Alamos, New Mexico, United States
Show Abstract3:30 PM - **EE4.4
Elasto-plastic Transition in High Strength Nanocomposite Wires and Composite Micro-pillars Studied by In-situ Deformation under X-rays.
Ludovic Thilly 1 , Robert Maass 2 , Marc Legros 4 , Steven Van Petegem 2 , Pierre-Olivier Renault 1 , Vanessa Vidal 5 , Jean-Baptiste Dubois 1 3 , Florence Lecouturier 3 , Helena Van Swygenhoven 2
1 PHYMAT, University of Poitiers, Futuroscope France, 2 , Paul Scherrer Institute, Villigen Switzerland, 4 , CEMES, Toulouse France, 5 , CROMeP, Albi France, 3 , LNCMP, Toulouse France
Show AbstractCopper-based high strength nanocomposite wires are prepared by severe plastic deformation (Accumulative Drawing and Bundling process) for the windings of high pulsed magnets. The process leads to a multi-scale Cu matrix containing up to N=854 (52.2 106) continuous parallel Nb filaments or tubes with diameter down to few tens nanometers. After heavy strain, the multiscale Cu matrix is nanostructured and the Nb reinforcing phase is strongly refined. The resulting macroscopic strength is in excess from rule of mixture predictions calculated from bulk coarse-grained counterparts: an ultimate tensile strength up to 2 GPa is reached at 77K.In-situ tests have been performed under synchrotron radiation on nanocomposite wires containing Nb nanotubes. The evolution of elastic strains and peak profiles versus applied stress evidences the co-deformation behavior with different elasto-plastic regimes: the Cu matrix exhibits size effect in the finest channels while the Nb nanotubes remain elastic up to the macroscopic failure, with a strong load transfer from the Cu matrix onto the Nb nanotubes. During multiple loading-unloading cycles, the macroscopic stress-strain curve evidences strong hysteresis that could be independently followed in the different phases via the measurement of elastic strains: internal stresses are building-up because of large yield stress mismatch in the nanocomposite structure. This Bauschinger effect can be related to the dislocation storage in the different phases (APL 90 (2007), 241907). The elasto-plastic transition is also studied in the different phases, in particular the microplastic to macroplastic transition with respect to microstructure size.In addition, in-situ compression of Cu-Nb micro-pillars (containing a single Nb filament surrounded by Cu grains) has been performed under synchrotron micro-beam: the evolution upon loading of the Cu and Nb Laue peaks gives additional information on the elasto-plastic transition and the effect of interfaces on the plasticity of these nanomaterials.
4:30 PM - EE4.5
Effect of Ion Irradiation on Mechanical Deformation of Low-Density Nanoporous Materials.
K. Lord 1 , Sergei Kucheyev 1 , J. Satcher 1 , A. Hamza 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractMechanical properties of porous solids exhibit a strongly superlinear dependence on the material density. Hence, ultralow-density nanoporous solids have poor mechanical properties, and this remains the major factor limiting many potential energy-related applications of these materials. For example, silica aerogels with densities below ~100 mg/cm3 typically have a very low Young’s modulus of ~1 MPa. Here, we use ion irradiation to manipulate mechanical properties of low-density nanofoams. In particular, we study dose dependencies and effects of electronic and nuclear energy loss on the mechanical properties of nanoporous silica monoliths (aerogels) with densities below ~350 mg/cm3. We use depth-sensing indentation with various indenter geometries (spherical, pyramidal, and flat punches) to measure Young’s modulus, crushing pressure, fracture toughness, and brittleness of nanofoams. Our results show that ion bombardment could be used to improve the foam connectivity and, hence, the mechanical response of low-density nanoporous solids. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
4:45 PM - EE4.6
Modeling of Effects of Ion Energy and Mass on Self-Organized Nanostructure Formation During Ion-beam Implantation.
Kun-Dar Li 1 2 , Alejandro Perez-Bergquist 2 , Qiangmin Wei 1 , Lumin Wang 1 2
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractIon beam is an important technique for achieving controlled modification of surface and near-surface regions. One of the recent developments in ion beam processing has focused on the studies of self-organized nanostructure created after ion-implantation. Various surface morphologies have been produced by focused ion beam (FIB), e.g. ripple, cellular, nanodot or nanofiber patterns. In addition to material properties, temperature and other experimental parameters, e.g., ion energy and ion mass play a crucial influence on the formation of self-organized nanostructures. In this study, a 3D theoretical model has been developed to study the effects of ion energy and ion mass on the formation of these structures during ion-beam bombardment. We adopted a phase field approach which integrates the production and elimination rates of vacancies considering ion sputtering, recombination with interstitials and redeposition of sputtered atoms with the free energy of mixing and interfacial energy as the driving force for vacancy diffusion. The depth profile of vacancy production along the depth of an irradiated matrix is considered as approximately Gaussian in shape according to the Monte-Carlo calculation by SRIM code. With increasing ion energy while all other parameters treated as constant, the number of vacancies produced and the depth of the peak vacancy concentration will increase. The simulated surface morphologies transformed from cellular nano-holes into a nanofiber structures. While the implanted ion mass increases, the number of vacancies produced increases and the depth of the peak vacancy concentration decreases. The simulated morphologies change from nanofibers, nanowall-like structures into open and/or embedded hole structure. The simulated morphologies are consistent with experimental observations achieved under comparative experimental conditions. Our model provides a distinct numerical approach to predict results or direct experimental designs to form a desired nanostructure by ion beam technology.
5:00 PM - EE4.7
Nanospire Formation by Heavy Ion Beam Irradiation of Oxide Multilayer Surfaces.
Cynthia Reichhardt 1 , Marylin Hawley 1 , David Devlin 1 , Kurt Sickafus 1 , Igor Usov 1 , James Valdez 1 , Youngqiang Wang 1
1 T-12, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract5:15 PM - EE4.8
Nano Nickel Composites for High-Temperature LIGA/MEMS-Applications.
Manel Haj-Taieb 1 , Klaus Bade 2 , Siriyara Jagannatha Suresha 3 , Kevin Hemker 3 , Jarir Aktaa 1
1 intitute for Matirials research II, Forschungszentrum Karlsruhe GmbH, Eggenstein-Leopoldshafen Germany, 2 Institute for Microstructure Technology , Forschungszentrum Karlsruhe GmbH, Eggenstein-Leopoldshafen Germany, 3 Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractFor high temperature LIGA/MEMS applications the often applied ED-Nickel is limited by its remarkable microstructural instability connected with a loss of mechanical strength even at intermediate temperature (300-400 °C). To increase strength at higher temperatures (> 300 °C) a second phase could be introduced which shall hinder the recrystallization during high temperature exposures. Here, the objective is to fabricate such materials with added phases: Ni-Al2O3 ODS (oxide dispersion strengthened) and Ni-Al composites by electrodeposition and characterize them by microtesting experiments. As electrolytes two ammonia citrate electrolytes with different chemical compositions and dispersed nano-sized alumina or aluminium particles (nm or µm) were used.The deposited Ni-Al2O3 layers were investigated by SEM and FIB to verify the incorporation of the oxide particles into the nickel matrix. The chemical composition of the electroplated material was determined by EDX. The latter investigations demonstrated the successful incorporation of the Al2O3 nano particles into the layers with ~3 weight-%. In addition the micro-hardness of the as-deposited Ni-Al2O3 measured on the cross-section increases up to ~500 HV which is larger than the micro-hardness of pure Nickel (<300 HV), which confirms the strengthening effect. Ni-Al2O3 layers on copper-substrate have been annealed in the temperature ranges of 300-600 °C for two hours. The micro-hardness remains unchanged at intermediate temperatures (300 and 400 °C). At higher temperatures, e.g. 600 °C, the micro-hardness decreases to a value still higher than the value of pure nickel in the as-deposited state. These enhancements are probably due to the pinning of the grain boundaries and dislocations by the nano particles increasing the microstructural stability improving mechanical properties. These effects have been studied more closely with microtensile tests carried out on LIGA fabricated ODS-microspecimens at different temperatures. TEM investigations will be presented in order to show the localization of the particles in the microstructure.The nickel layers with the nano-sized aluminium particles are compact without voids and also with lower roughness whereas depositions with µm-sized particles yielded non compact layers. At the moment electrodeposited layers have been heat-treated at different annealing temperatures and durations in order to achieve a fine scale γ’-precipitation in the nickel-matrix. The content of the γ’-phase have been determined using XRD. The microstructure of the composite has been characterized using TEM. The results of these investigations available so far will be presented in addition.
5:30 PM - EE4.9
Bauschinger Effect in Unpassivated Freestanding Metal Films.
Jagannathan Rajagopalan 1 , Jong Han 1 , Taher Saif 1
1 Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractThe mechanical behavior of unpassivated freestanding metal films, subjected to uniaxial tension, was measured during several loading-unloading cycles. The results show that the stress-strain response of these films deviates substantially from linear elastic behavior during unloading, even at large overall tensile stresses. For example, in aluminum films (thickness 210-400 nm, grain size ~ 200 nm) the deviation from elastic behavior, indicative of reverse plasticity, starts at stresses as high as 150 MPa during unloading. As a result of this Bauschinger effect, the plastic strain in these films after unloading is often less than 50% of the expected value. Similar trends are seen in gold films, but the effect is less pronounced. The current understanding is that only passivated metal films, where reverse deformation is assisted by back stresses from dislocation pile-ups at the film/passivation layer interface, should exhibit Bauschinger effect. The Bauschinger effect observed in these unpassivated films thus suggests an alternate mechanism, which appears to result from the coupling of small grain size and heterogeneity of the microstructure. During loading, relatively larger grains deform plastically and relax their stresses whereas the stresses in smaller elastically deforming grains keep increasing, leading to a build up of internal stresses. During unloading, the internal stresses induce reverse plastic deformation in the larger grains leading to Bauschinger effect. This alternate mechanism of Bauschinger effect is supported by observations from in situ straining experiments in TEM.
5:45 PM - EE4.10
Kinetics of the Plastic Deformation of Gold during Nanoindentation.
Vineet Bhakhri 1 , Robert Klassen 1
1 Mechanical & Materials Engineering, The University of Western Ontario, London, Ontario, Canada
Show AbstractTwo stage indentation tests, involving a constant-loading rate stage, where the indentation shear strain rate γ*ind is very high, followed by a constant-load stage, where the γ*ind is low were performed on annealed and 20% cold-worked Au at 300 K to investigate the effect of indentation depth and initial dislocation density on the time-dependent plastic deformation process. Indentation data were analysed in terms of an obstacle-limited dislocation glide mechanism. The apparent obstacle activation energy ΔGo during low γ*ind associated with the constant-load stage was of the order of 0.16 μb3 and was neither a function of initial indentation depth, from h0 = 200 to 2000 nm, nor degree of cold-work. The apparent activation volume, V*, of the deformation process follows the same dependence upon dislocation density and effective indentation stress regardless of h0 or the degree of cold-work. The data from the indentation tests display linear dependence of inverse apparent activation area,1/Δa*, upon effective indentation shear stress,τind_eff, however the mechanical activation work, ΔW, which is the reciprocal of the slope of the 1/Δa* versus τind_eff trend, is larger during the high γ*ind constant-loading rate stage than during the low γ*ind constant-load stage of the tests. We observe also that ΔW is not a function of the initial depth, over the range from 200 nm to 2000 nm, or the material condition (i.e. the degree of cold-work). This suggests that more mechanical energy must be applied to the mobile dislocations to overcome obstacles in the microstructure during the high γ*ind compared to during low γ*ind.The dislocation structure within the indentation plastic zone of “crept” and “uncrept” indentations of h0 = 400 nm was investigated with TEM performed on foils cut from beneath the indentations using FIB micromachining. TEM observations indicate that during the high γ*ind stage (i.e. the “uncrept” indentation) of the test individual dislocations are visible throughout the indentation plastic zone while the dislocations recover into well developed cells during the subsequent one-hour low γ*ind stage (i.e. the “crept” indentation) of the test. The combined results of this investigation indicate that larger mechanical activation work, ΔW, is dissipated during constant loading rate indentation due to the large amount of work-hardening of the material in the rapidly expanding indentation plastic zone. The plastic zone expands at a much slower rate during constant-load indentation and the dislocation structure has the opportunity to recover by rearrangement into lower energy dislocation cell configurations.
EE5: Poster Session: Nanomaterials, Mechanical Behavior and Radiation Effects
Session Chairs
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - EE5.1
Microstructure, Mechanical, and Chemical Properties of Nanoporous Gold Films.
Dongyun Lee 1 , Jinwoo Ahn 1 , Hae-Sung Kim 1
1 Nanomaterials Engineering, Pusan National University, Busan Korea (the Republic of)
Show AbstractNanoporous thin film of pure gold, which is comprised of nanosized pores and ligaments regularly distributed across the volume of the film, was fabricated by dealloying technique. To obtain this film, multi-layers of two pure metals (gold and silver) with buffer layers (Cr or Ti) were deposited on silicon substrate by several deposition methods, thermal evaporation, e-beam evaporation, or sputtering system, and then the films were heat treated at elevated temperatures to attain homogeneous solid solution of Au-Ag alloy films. Dealloying was then performed to accomplish fabricating nanoporous gold films on silicon substrate. Dealloying was achieved in either concentrated/diluted nitric acid, HNO3 or controlled electrolyte with various chemical substances, like Perchloric acid, HClO4, or HNO3. Pore size and regularities of the films were verified under Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray (EDX). Crack-free nanoporous gold films on hard substrate (Si) were fabricated by well controlled electrochemical dealloying process in specific range of alloying compositions. Mechanical properties of the films were investigated by nanoindentation; the primary results of mechanical tests show the elastic modulus and hardness of nanoporous gold films on Si substrate are about 10 GPa and 200 MPa, respectively. Implications for the performance of the nanoporous gold under certain environments containing sulfur, hydrogen, or carbon dioxides are discussed.
9:00 PM - EE5.10
Crystallization-induced Stress in Phase Change Random Access Memory.
Minghua Li 1 , Jianming Li 1 , Qiang Guo 2 , Luping Shi 1 , Yi Li 2 , Tow Chong Chong 1 3
1 , Data Storage Institute, Agency for Science, Technology and Research (A*STAR), 5 Engineering Drive 1, Singapore 117608 Singapore, 2 Department of Materials Science and Engineering, National University of Singapore, 7 Engineering Drive 1, Singapore, 117576 Singapore, 3 Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 119260 Singapore
Show AbstractGeSbTe (GST) alloys are of much interest as non-volatile Phase Change Random Access Memory (PCRAM) elements, based on their fast and repeatable switching performances. The structure reversible phase change provides the two logic states, which are represented by the crystalline phase (low resistivity) versus the amorphous phase (high resistivity). In addition to the huge resistivity change, the phase change process is accompanied by a significant volume change due to the difference of the density between the amorphous and the crystalline phases.This in turn results in large stresses during operation of the PCRAM device. The stress can generate defects and directly affect the performance and durability of the device. Practically, it is usually desirable to get large resistance difference with less stress upon crystallization. For this purpose, we have study the crystallization-induced stress in different PCRAM cell structures. A typical PCRAM cell consists of not only phase change material, but also electrode material for electrical contact and dielectric material for thermal isolation. It is well known that the thermal-induced phase change behaviors depend strongly on the cell structure. Stress generation and relief are also affected by the electrode and dielectric materials used, as well as the cell structure design. In this paper, the GST phase change films integrated with TiN/TiW electrode layer and SiO2/ZnS-SiO2 dielectric layer are employed for stress evolution study. The effects of the dimension and stacking structure are addressed.Thermal-electrical simulation yields temperature profile for a particular PCRAM cell structure. Apart from the deformation caused by conventional thermal-mechanical effect, additional strain induced by crystallization plays a more important role to stress evolution as the crystallization-induced volume change can reach 5 ~ 9% according to experimental results. Therefore, the density change during PCRAM operation is taken into consideration in the thermal-mechanical simulation. The results show that the high level of stress is generated in the interface between the GST film and neighbor layer. Less stress during PCRAM operation can be achieved by optimizing the electrode and dielectric materials and the cell structure. It is expected that the stress evaluation method developed in this paper is very useful for PCRAM device design.
9:00 PM - EE5.11
Local Distortion Analyses of CNT by Scanning Probe Microscopy with X-ray Excitation Source: Visualization of Electron Traps on Distorted CNT.
Masashi Ishii 1 2 , Eric Whittaker 2 , Brian Towlson 2 , Kenji Sakurai 1 , Bruce Hamilton 2
1 Quantum Beam Center, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan, 2 Photon Science Institute, The University of Manchester, Manchester United Kingdom
Show AbstractNew electric devices using a carbon nano tube (CNT) as an electron channel have been demonstrated by a number of researchers. For construction of functional circuits from the CNT devices, basic structural components such as a cross and branch of CNTs are necessary for electric connections. However, in the components fabricated by stacking and sticking, unexpected distortions are introduced into the CNTs. A heavy load during the processes changes shape and electronic properties of CNTs, resulting in disconnection or deceleration of the electron flow.In this study, we developed a diagnostics of the fatal distortion in the CNT networks. The advantages of this technique, i.e., scanning probe microscopy with x-ray excitation source are element selectivity and nano scale spatial resolution. With this technique, we can clarify the chemical components, electronic states and nano scale distribution of the distortions.On the x-ray irradiated sample surface, inner-shell excitation and following electron relaxation are induced. If the x-rays excite a distorted CNT with localized electrons, a relaxation process different from undistorted parts is expected; the core-holes owing to the inner-shell excitation are occupied by the localized electrons in the valence, resulting in electron delocalization at this site. The process corresponds with photo ionization of the distorted CNT. If the photo ionization state has a relatively long lifetime of ~ms, we can observe the state by a scanning probe detecting electrostatic force (Electrostatic force microscopy, EFM). [1]An EFM system is combined with x-ray beamlines at Synchrotron radiation facilities (APS, SRS, and Diamond), and stacked CNTs on silicon dioxide substrate are observed by EFM under the x-ray irradiation. The main results are as follows. (1) CNTs with switchable EFM signal by x-ray photon energy at C K-edge are found. (2) The switchable EFM signal is coming from distinctive CNTs, i.e, strongly compressed and torsional CNTs. (3) Mapping of the fatal distortions in a single CNT wire can be achieved. These results indicate element selectivity, distortion sensibility, and nano scale spatial resolvability involved in this technique. We will discuss about nano-spectroscopy by changing the x-ray photon energy.[1] M. Ishii, B. Hamilton, N. R. J. Poolton, N. Rigopoulos, S. De Gendt, and K. Sakurai, Appl. Phys. Lett. 90, 063101 (2007).
9:00 PM - EE5.13
Pulsed Excimer Laser-induced Fragmentation of Indium Tin Oxide Nanoparticles.
Douglas Dukes 1 , Shannon Johnson 1 , Linda Schadler 1 , Yong Huang 2 , Douglas Chrisey 1
1 Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Mechanical Engineering, Clemson University, Clemson, South Carolina, United States
Show AbstractThe use of a pulsed KrF excimer laser focused on or below the surface of a nanoparticle solution as a means to induce nanoparticle fragmentation of Indium Tin Oxide (ITO) nanoparticles is employed in this study. Prior literature shows that this technique causes cavitation of the solution and fragmentation of nanoparticles within, yielding a reduction in both primary and secondary particle size. We have expanded prior work to encapsulate a multi-variable study of laser energy density, energy deposited per solution volume, and particle concentration. The goal of this study is to determine optimal processing conditions to yield controlled and reduced size distributions as well as to understand the production and nucleation of cavitation under a wide range of conditions. Preliminary results employing transmission electron microscopy of the irradiated ITO nanoparticle solutions reveal that the particle diameter is reduced from ~40nm to ~5nm. While the overall solution size distribution is increased, the resulting fragmented particles are quite monodisperse. New polycrystalline particle geometries, larger than the as-received particles, were also observed, but account for <1% of the particles in solution. The formation mechanism of these new particle geometries is under investigation and may be linked with laser/particle interactions that produce cavitation. Numerical simulations of the cavitation process were performed by studying the laser energy absorption process and subsequent nanoparticle formation resulting from the laser energy absorption-induced shock wave. The simulation demonstrated that selecting a proper combination of laser fluence and particle properties can control the fragmented particle size and its size distribution. The results of this study have broad implications for reducing the size of any nanoparticle system, regardless of crystallinity, in a controllable manner.
9:00 PM - EE5.14
Impact of He Ion Irradiation on the Microstructure and Hardness of Sputtered Cu/V Nanolayers.
Engang Fu 1 , Jesse Carter 2 , Greg Swadener 3 , Amit Misra 3 , Lin Shao 2 , Xinghang Zhang 1
1 Department of Mechanical Engieering, Texas A&M University, College Station, Texas, United States, 2 Department of Nuclear Engineering, Texas A&M University, College Station, Texas, United States, 3 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractSputter-deposited Cu/V nanolayers with individual layer thickness, h, varying from 1 to 200 nm were subjected to helium ion irradiation at room temperature. At a peak dose level of 5 displacement per atom (dpa), when h is reduced from 50 to 2.5 nm, average helium bubble density decreases by a factor of 3-4, accompanied by a 2-3 times reduction in lattice expansion, as revealed by cross-sectional transmission electron microscopy experiments. The magnitude of radiation hardening decreases with decreasing layer thickness, and becomes negligible when h is 2.5 nm or less. A similar hardening trend is observed in specimens radiated with different doses. Radiation hardening seems to reach saturation when peak dose is 5 dpa or greater. This study indicates that nearly immiscible Cu/V interface spaced a few nm apart can effectively reduce the concentration of radiation induced point defects and thus may improve the radiation tolerance comparing to monolithic Cu or V alone.
9:00 PM - EE5.15
Hardening in Al/Nb and Fe/W Multilayers Induced by Helium Ion Irradiations.
Nan Li 1 , Jesse Carter 2 , Haiyan Wang 3 , Engang Fu 1 , Amit Misra 4 , Lin Shao 2 , Xinghang Zhang 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Nuclear Engineering, Texas A&M University, College Station, Texas, United States, 3 Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 4 Materials Physics and Application Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe report on the evolution of microstructure and mechanical properties of sputter-deposited Al/Nb and Fe/W multilayers subjected to helium ion irradiations. Radiations were performed by using 100 keV He+ ions with a dose of 6×1016/cm2. Helium bubbles, 1-2 nm in diameter, were observed in multilayers. Dependence of radiation hardening on individual layer thickness, h, is in great contrast in the two systems. In Fe/W system, radiation hardening increases with decreasing h till 5 nm, and is negligible at even smaller layer thickness. In Al/Nb system, radiation hardening is barely detectable when h is > 25 nm, whereas the hardening is significant at smaller h. Analysis indicates that He bubbles, dislocation loops and high density interstitials are the major factors for hardness enhancement in Fe/W. Potential mechanisms of radiation hardening in the two different systems are compared.
9:00 PM - EE5.16
In-situ Surface Characterization of Mechanical and Electronic Behavior During Ion-induced Nanostructure Synthesis.
D. Rokusek 1 , C. Wagener 1 , M. Nieto-Perez 2 , J. Allain 1
1 Nuclear Engineering, Purdue University, West Lafayette, Indiana, United States, 2 , CICATA-IPN, Queretaro, Queretaro, Mexico
Show Abstract9:00 PM - EE5.17
Softening and Nano-foaming of Amorphous Carbon Films via Electron Beam Irradiation.
Tatsuhiko Aizawa 1 2 , Eiji Iwamura 3 , Takuhiko Uematu 4
1 , AsiaSEED-Institute, Tokyo Japan, 2 , Osaka Prefecture University, Osaka Japan, 3 , Arakawa Chemical Co. Ltd, Osaka Japan, 4 , Tokyo Metropolitan Induatrial Research Institute, Tokyo Japan
Show Abstract9:00 PM - EE5.18
Nanoscale Morphological Evolution of Pyrolytic Carbon Surface under Ag Ion Irradiation.
Yanbin Chen 1 , Rongsheng Zhou 1 , Lumin Wang 1 2
1 Nuclear Engineering & Radiology Department, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science & Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - EE5.2
Molecular Level Detection of Heavy Metal Ion Using Coral-like Macroporous Gold.
Hero Kim 1 , Younghun Kim 1
1 Chemical Engineering, Kwangwoon University, Seoul Korea (the Republic of)
Show AbstractSince porous materials have uniform pore size, regular pore distribution and large surface area, they have been used extensively in research concerning such materials as adsorbents, catalysts, and molecular sieves. With interest increasing in nano/bio-sensors, metallic porous materials are increasingly being looked at for use in electro(chemical) applications due to their biocompatibility, conductivity, stability, and high surface-to-volume ratio. Porous gold in particular is believed to be a good candidate as a substrate for batteries, sensors, and catalysts, while gold-conjugated protein has been proposed for use in sensing electrode systems. In most cases, porous gold materials are prepared by a dealloying process, which is a kind of corrosion process to selectively remove the least noble element within an alloy, resulting in a porous material of the more noble element. For example, immersion of a commercially available white-gold alloy (Ag/Au) in nitric acid selectively removes the silver atoms leaving behind the free-standing porous gold network. This method has the merit of easy fabrication of an ultrathin, porous gold membrane made by hammering, but the dealloying step generally is a resource-consuming process.In this study, to obtain submicron-sized porous material, porous gold was prepared by the templating method using both stearic acid (or its salt) and aluminum alkoxide for the template. While stearic acid usually is used as porogen in the preparation of nanoporous alumina, herein it acted as a reinforcement agent for the reverse network (i.e., alumina structure) of porous gold. For preparation of porous alumina using stearic acid, calcined alumina shows a solidified smooth surface with a framework porosity, which represents the porosity contained within the uniform channels of a templated framework. In addition, when the salts of stearic acid (e.g., magnesium stearate) are used as a surfactant, the resulting alumina has both a well-developed textural and framework porosity and shows a solidified, coarse surface. As a proof-of-concept test, the molecular level detection of heavy metal ion (Hg2+) was carried out.
9:00 PM - EE5.21
Effect of Gamma Irradiation on Carbon Nanotubes and Their Composites with Nanodiamond.
Sanju Gupta 1 , A. Schuttler 1 , M. Muralikiran 1
1 ECE, UMC, Columbia, Missouri, United States
Show AbstractSevere environmental tolerability is the prime factor in the development of novel space materials exhibiting excellent physical properties accompanied by lightweight, reusability, and multifunctional capabilities. Diamond is known for radiation hardness besides several outstanding physical properties and hence it is preferable in harsh environments. Carbon nanotubes (CNTs) are also of great interest owing to their unsurpassable physical and structural (high aspect ratio) properties. It is believed that across the main radiation environments including heavy ions, gamma and proton radiation, different types of nanoscale materials may outperform their conventional counterparts, where the improvement is attributed to nanoscale functional entity and apparent radiation resiliency [1-3]. For ‘harsh’ radiation environment applications, it is critical to demonstrate their structural integrity and optimal performance. We studied both the single- and multiwalled nanotubes (SWNT and MWNT) and their composites with nanodiamond forming true trigonal- tetragonal nanocomposites. These materials were spin cast on Si wafers and subjected to gamma radiation (5, 10 and 100 Mrads) from 60Co nuclide with dose rate of ~ 1.5 Mrad/h. They were analyzed prior to and post-irradiation in terms of morphology, microscopic structure and physical properties using electron microscopy, micro-Raman spectroscopy, and electrical (I-V) measurements to establish property-structure-processing relationship. It is found that the SWNT composites are relatively more robust than MWNT and intermediate of MWNT composites. Although the structure and dynamics of defects in carbon nanostructures remain elusive, this investigation imparts insights into the nature of gamma radiation induced events in nanotubes and nanocomposites for a) short-term space mission; b) radiation hard programmable logic circuits; c) radiation dosimeters; and d) radiation pressure sensors. The results are evaluated in terms of the structural transformation/ irregularities and to identify the radiation interaction mechanism at nanoscale. It is found that single-walled nanotubes improved their radiation resilience with nanodiamond and they become comparable to multi-walled nanotubes. Furthermore, they reach a state of damage saturation. The findings are discussed in terms of radiation-induced microscopic defects aggregation, bonding re-arrangement, and/or amorphization collectively known as Wigner effect deduced from the position and intensity of D and G bands in micro-Raman spectra which are also compared with traditional graphite. The author (SG) acknowledges Dr. V. Padalko (Alit Co. Ukr) for nanodiamond material. This work is financially supported by MU Research Council. [1] S. Gupta, R. J. Patel, N. Smith, Mater. Res. Soc. Symp. Proc. 863, Q6.3-Q6.9 (2005). [2] S. Gupta, R. J. Patel, J. Raman Spectr. 38, 188 (2007). [3] V.M. Ayres, B.W. Jacobs, M.E. Englund, et.al. Diam. and Relat. Mater. 15, 1117 (2006).
9:00 PM - EE5.22
The Influence of Annealing Temperature on the Phase Separation of Magnetron Sputtered Ti0.2Al0.8N Thin Films.
Ramaseshan Rajagopalan 1 , Feby Jose 1 , Sitaram Dash 1 , Arup Dasgupta 2 , Saroja Saibaba 2 , Sridhar Kalavathi 3 , Ashok Kumar Tyagi 1
1 Surface Science Section, Indira Gandhi Centre for Atomic Research , Kalpakkam, Tamil Nadu, India, 2 Physical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil nadu, India, 3 XS&CG Section, Indira Ghandi Centre for Atomic Research, Kalpakkam, Tamil Nadu, India
Show AbstractOver the years titanium aluminum nitride (Ti1-xAlxN) (where, x ~ 0.6) has been under active investigation as promising alternative to binary coatings for cutting and forming tools because of its superior oxidation resistance and lower thermal conductivity[1, 2]. But this compound with higher Al (x=0.8) is not being studied extensively for the splitting of its composition from a single phase. In this paper we report the results of the influence of thermal annealing on the formation of two phase mixtures for the above mentioned composition for the fundamental point of view. Ti1-xAlxN films were deposited on SS-304LN at a constant pressure of 1x10-2 mbar, substrate temperature of 773K with RF (Ti) and DC (Al) magnetrons. The rate of deposition was maintained at 8 nm/min by suitably adjusting the power of the magnetrons and other parameters. Annealing experiments were carried out at different temperatures starting from 873K to 1173K in nitrogen atmosphere. GIXRD technique is used to identify the structural modifications in the films. TEM technique is used to analyze these films for the structure and morphology. Nanoindentation technique is used to measure the hardness of these films.The single phase Ti1-xAlxN films splitted in to TiAlN and AlN with hexagonal phase. Cross sectional TEM is used to understand the crystallite size as well as the phase analysis with the help of selected area diffraction. Very small crystallites of hexagonal AlN dispersed in an amorphous matrix in the as deposited condition. During annealing, these crystallites act as nucleation centers of AlN as a major phase. The indentation hardness decreased from 30GPa (as deposited) to 18GPa during the annealing at 1073K. The hardness of as deposited films is high due to its amorphous nature with a dispersion of AlN crystallites. The compressive residual stress of the film has been considerably reduced with the annealing process which decreased the hardness of this film. Reference:1.P.H.Mayrhofer et al, Self-organized nanostructures in the Ti-Al-N system, Applied Physics Letters, 83 (2003) 2049.2.Feby Jose, R. Ramaseshan, S. Dash, S. Rajagopalan and A.K. Tyagi, Significance of aluminum on hardness of Titanium Aluminum Nitride deposited by magnetron co-sputtering. International Journal of Applied Ceramic Technology (Accepted).
9:00 PM - EE5.23
Mechanical Behavior of Nano-scale FCC Thin Films using Resonance System.
Seungmin Hyun 1 , Jungmin Park 1 , Hak Joo Lee 1 , Chiwon Ahn 2 , Jaeyong Song 3 , Walter Brown 4
1 , Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of), 2 , National NanoFab Center, Daejeon Korea (the Republic of), 3 , Korea Research Institute of Stasndards and Science, Daejeon Korea (the Republic of), 4 , Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractWe have used a resonance system to measure the mechanical stress changes of nano-scale thickness Al thin films as a function of temperature and time. The resonance system is designed to measure stress changes of nanoscale thick film by measuring the resonance frequency of the film that is electrostatically actuated. The changes in resonance frequency during the measurement are directly related to the stress changes in films. The Al films were prepared by DC magnetron sputtering and evaporation onto 160nm thick silicon nitride membrane that is surrounded a thick Si frame. The dimension of the film on membrane is 2 x 12 mm2 or 3 x 12 mm2. The resonance frequency of 80nm thick Al film is in the range of 40,000 Hz to 48,000 Hz during thermal cycling up to 280 oC. The corresponding stress of the film during thermal cycle changes from -150 MPa to 300 MPa. The stress changes in Al films during thermal cycle are due to thermal expansion differences with a thick Si frame. The stress evolution in as-deposited film during a thermal cycle reveals dramatic stress changes above 180oC and stress relaxation behavior of the film at room temperature is also observed after thermal cycle. The thermo-mechanical behavior and stress relaxation behavior of nano scale thin films that depend on film thickness and deposition conditions will be presented. This presentation will also include the mechanical behavior of nano-cluster FCC films that are deposited by nanocluster deposition system
9:00 PM - EE5.24
The Mechanical and Wear Resistant Properties of ‘Duplex’ WC-17Co Nanocrystalline Coatings Sprayed by the HVOF Technique.
Gobinda Saha 1 2 , Tahir Khan 1 , Larry Glenesk 1 2
1 Department of Mechanical & Manufacturing Engineering, University of Calgary, Calgary, Alberta, Canada, 2 R&D, Hyperion Technologies Inc., Calgary, Alberta, Canada
Show Abstract9:00 PM - EE5.25
Co-Electrodeposited Ni / Sic Nano-Grain Thin Films for Enhanced Fatigue Lifetimes.
Angela Feldhaus 1 , Sean Hearne 2 , Brad Boyce 2 , Adam Rowen 2
1 Physics, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Labs, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - EE5.26
Fatigue and Frictional Sliding Response of Nanostructured Copper.
Nairong Tao 1 2 , Lei Lu 1 2 , Ming Dao 1 , Subra Suresh 1
1 Materials Science & Engineering, MIT, Cambridge, Massachusetts, United States, 2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang China
Show AbstractFor nanocrystalline metals, with grain size typically smaller than 100 nm, it was found that the frictional sliding and damage evolution are dominated by material strength rather than grain size, whereas the resistance to failure under stress-controlled fatigue is closely related to its grain size. It is also known that the strengthening effect of nano-scale twin boundaries is similar to that of grain boundaries. However, the effects of nano-scale twins on the frictional sliding and fatigue behaviors are still not well understood. The objective of this study is to investigate the effect of nano-scale twin bundles on friction evolution and damage accumulation. The bulk nanostructured Cu is prepared by dynamic plastic deformation (DPD) at liquid nitrogen temperature. The typical microstructure of the DPD Cu with a strain of 200% was characterized by 33% volume of nano-scale twin/matrix lamellae with an average twin thickness of 49 nm embedded in the nanocrystal matrix with an average grain size of 78 nm. The coefficient of friction and the scratch profile of the DPD Cu are studied by repeated nanoscratch tests at different scratch speeds. The cyclic frequency effects on the fatigue behaviors are also systematically investigated. Based on the microstructural comparison before and after scratch/fatigue tests, possible mechanisms for the nanoscale twin induced friction and fatigue variations are discussed.
9:00 PM - EE5.27
Strength Enhancements of Nanoscale Multilayers for MEMS Electrodes in Oxidizing Environments.
Aikaterini Bellou 1 , Rachel Schoeppner 1 , David Bahr 1
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractPt thin films are used as electrodes in Micro-electro-mechanical systems (MEMs) in high temperature and oxidizing environments. Lead zirconate titanate films (PZT) are often deposited on a Pt thin film by a sol-gel technique which includes annealing of the Pt film at 600 C, pyrolysis of the PZT layer at 375 C and crystallization of the PZT layer at 700 C in an oxidizing environment. During the crystallization of the PZT the structures are subjected to rapid thermal annealing and quenching, which can lead to high residual stresses due in part to plastic flow in the Pt electrodes. Multilayered structures as electrodes should improve the electrode strength, and improve the mechanical performance of the film system. For this study Mo was layered with Pt using sequential DC sputtering to deposit a total of 4 layers. The thickness of the Mo film was varied between 35 and 100 nm, whereas the Pt film was kept constant at 100 nm, thus changing the bilayer period of the structure. Pt and Mo show significant solubility and can also form intermetallics. This provides both strengthening mechanisms that operate in bulk materials, like solid solution hardening, and structural variation on the nano scale, the layer thickness, that can control the mechanical behavior. In order to investigate the initial thermal stability of these films some samples were annealed at 475 C for 1 hour. The modulus and hardness of both the as deposited and heat treated films were measured using continuous stiffness indentation measurements. Scanning electron microscopy was used to correlate the microstructure to the observed mechanical behavior in each case. Although a significant change in the microstructure occurs after annealing, where the thickness of the Mo layer significantly increases, the impact on the mechanical properties was small. XPS analysis was used to further investigate the film chemistry, and shows that during annealing oxidation of the Mo layer occurs. Additional studies of thermal stability of Pt/Mo multilayers at higher temperatures to simulate the actual MEMs processing and the effects on the mechanical properties will be discussed. Finally, the strength and residual stress in PZT films deposited on the multilayered structures after the rapid thermal annealing and shock, due to the very high cooling rates at the end of the sol-gel deposition, will be compared to those on the pure Pt electrode.
9:00 PM - EE5.28
Effects of Linear Confinement at Sub-micron Length Scales on the Morphology and Properties of Thermoplastic Polymers.
Elizabeth Welsh 1 , Michael Sennett 1 , Peter Stenhouse 1
1 Natick Soldier Center, US Army RDEC, Natick, Massachusetts, United States
Show Abstract9:00 PM - EE5.29
Study of Microstructure, Texture and Mechanical Properties of Heavily Cold Worked TiTaNb Alloy and the Effect of Annealing.
Arup Dasgupta 1 , Kinkar Laha 1 , R. Kayalvizhi 1 , S. Raju 1 , S. Murugesan 1 , Saibaba Saroja 1 , V. Subramanya Sarma 2 , M. Vijayalakshmi 1
1 Materials Development and Characterisation Group, Indira Gandhi Centre for Atomic Research , Kalpakkam, Tamil Nadu, India, 2 Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show AbstractThe Ti-5Ta-1.8Nb has been shown by us to posses an outstanding corrosion resistance in a highly hostile oxidizing media such as the boiling concentrated nitric acid. [1 and references therein]. The α-β Ti alloys are well known for their high specific strength and very high ductility but a relative low yield strength. The objective of this work is to attain a high value of yield strength while retaining the ductility. This can be achieved by suitable themo-mechanical processing. The processing conditions, microstructure and microtexture and mechanical properties will be presented in this paper. The starting material was well annealed and yielded polygonal α-Ti grains with average diameter of about 8µm. The material was then rolled to 20, 50, 65, 75 and 85% at room and cryogenic temperatures. Under 85% room temperature rolling, the finest grains measured about 150nm in width while those for 85% cryo-rolling were even finer while crystallite sizes were reduced to about 40 nm as measured from FWHM of XRD peaks. It was observed that the Vicker’s macrohardness increased from 140HV for the starting material to about 265 HV for the 85% RT-rolled material and to about 280 for the 85% Cryo-rolled material; exhibiting a power-law behavior for the increase. It was also observed that the 85% RT-rolling was equivalent to only about 65% of Cryo-rolling indicating higher degree of plastic strain at lower temperature. The detailed mechanical properties of these materials are being evaluated through tensile testing. XRD studies showed an increase followed by decrease of lattice strain with increase of cold working both at room and cryo temperatures. It was also observed that the relative intensities of the (00.2) and (10.1) peaks vary with the degree of deformation as well as the temperature which is a signature of deformation texture. The alloy exhibits deformation texture of type (0002)//rolling plane of α-Ti grains due to the cold working. The 85% RT rolled and 85% Cryo-rolled materials were subjected to annealing for various time durations so as to achieve materials with differed amounts of recrystallised grains. Macro-hardness studies have shown lowering of hardness with increase of annealing time at 500oC as a result of recrystallisation. Tensile testing results of some of these annealed specimens will also be presented in the paper. Differential Scanning Calorimetry (DSC) is also being employed to identify the recovery and recrystallisation temperatures and mechanisms. Evolution of crystallographic texture as a result of deformation and recrystallisation is also presently being studied by Electron Back Scatter Diffraction (EBSD) technique. [1] "Study of Surface Morphology in Welds of Ti-5Ta-1.8Nb Alloy Exposed to 11.5 M Boiling Nitric Acid" Arup Dasgupta, T. Karthikeyan, S. Saroja, V.R. Raju, M. Vijayalakshmi, R.K. Dayal and V.S. Raghunathan, Jrl. Mater. Engg. Perform. Vol. 16 (2007) pp. 800-806.
9:00 PM - EE5.3
Highly Compliant Nanoporous Gold with Environment-Dependent Elastic Modulus.
Steven Choi 1 , Dorota Artymowicz 2 , Felicia Pop 2 , Steven Nunnari 2 , Mark Kortschot 2 , Steven Thorpe 1 2 , Roger Newman 2 1
1 Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada, 2 Chemical Engineering, University of Toronto, Toronto, Ontario, Canada
Show AbstractElectrolytic de-alloying of Ag-Au alloys produces nanoporous gold whose ligament size depends on the starting alloy composition, the electrolyte, and the electrode potential, as well as the temperature. Dissolution of silver and surface diffusion of gold jointly create the nanoporous morphology. By starting with an alloy containing 23 at.% gold and optimizing the de-alloying procedure to prevent shrinkage cracking, a highly compliant product is produced, with Young’s modulus as low as 50 MPa in the wet state as determined by foil bending and platen-compression techniques. Remarkably, the compression modulus of this material increases by up to 7 times on drying. This change is irreversible when drying is carried in flowing dry nitrogen or for long times in dry air. However, if drying is carried out for short times in a mildly humid environment, such that adsorbed water is retained on the pore surfaces, the modulus still increases but reverts to its former value when the material is re-wetted. The results are discussed in terms of surface stress and other, more exotic, effects in the scattered gold nanowires that dominate the mechanics of the material. When the gold content of the starting material is increased to 28 at.%, and especially if de-alloying is carried out at a more oxidizing potential (as used by others in the literature), the material adopts a much higher modulus in the GPa range and the effect of wetting and drying is small or absent.
9:00 PM - EE5.30
Local Investigations of Deformed Aluminum Samples by Electrochemical Impedance Spectroscopy.
Aurelien Perron 1 , Halina Krawiec 2 , Olivier Politano 1 , Vincent Vignal 1
1 ICB, UMR 5209 CNRS, Universite de Bourgogne, Dijon France, 2 Department of Foundry Engineering, AGH University of Science and Technology, Krakow Poland
Show AbstractIn ambient air, pure aluminum (Al) forms extremely thin but dense natural oxide layers. These films consist of a thin amorphous Al2O3 layer, which is estimated at about 20 Å to 100 Å [1]. Thin Al oxide films have technological applications in microelectronics and catalysis, and for protection against wear and corrosion. For these applications, previous investigations (experimental and numerical) were done to characterize the thickness, structure, morphology, chemical composition and the microstructure of the oxide films [2,3]. The electrochemical behaviour of pure Al was investigated by using classical and local experimental techniques [4-5]. For example, electrochemical impedance spectroscopy (EIS) was widely used to obtain mechanistic information on the passive behaviour of Al [6] and to characterize porous Al oxide films [7]. To our knowledge, no works were performed to quantify the influence of applied strain on the electrochemical response of passive Al specimens at the microscale.In this study, the electrochemical behaviour of pure Al (99,998 % Al foil, Puratronic, Alfa-Aeasar 11372) was studied by means of local EIS based on the use of microcapillaries (280 mm diameter). Experiments were carried out in 0.1 M Na2SO4 solution at the open circuit potential value. Bode and Nyquist plots obtained on polished samples were compared to those obtained on strained samples (after +3% plastic strain). In addition, impedance curves were fitted by using equivalent circuits to model the behaviour of two systems and to highlight the influence of the density of slip bands on the impedance data. Note that results obtained at low frequency range were discussed.Finally, the results obtained with EIS were compared to variable charge molecular dynamics on polycrystalline Al samples under strain. The simulations used the electrostatic plus potential model, which is composed of an embedded atom method potential and an electrostatic term [8]. The simulated samples contained 16 grains with a mean size of 5nm and the oxidations were performed at 600K under a constant oxygen pressure (1 atm). Both approaches exhibit a good qualitative agreement. In particular we observed the decrease of the resistivity (i.e. the increase of the concentration defects) in the oxide film with the applied strain.References[1] H.H. Uhlig, R.W. Revie, Corrosion and Corrosion Control, John Wiley & Sons, (1985) p. 341.[2] A. Hasnaoui, O. Politano et al., Surface Science 579 (2005) 47.[3] L.P.H. Jeurgens, W.G Sloof. et al., Surface Science 506 (2002) 313.[4] P.L. Cabot, F.A. Centellas, J.A. Garrido et al.,Electrochimica Acta 36 (1991) 179.[5]. N. Birbilis, R.G. Buchheit, Journal of The Electrochemical Society 152 (2005) B140.[6] J.H.W. De Wit, H.J.W. Lenderink, Electrochimica Acta 41 (1996) 1111.[7] J.A. Gonzalez, V. Lopez et al., Journal of Applied Electrochemistry 29 (1999) 229.[8] F.H. Streitz, J.W. Mintmire, Physical Review B 50 (1994) 11996.
9:00 PM - EE5.31
Integrated Experimental, Atomistic, and Microstructurally-Based Finite-Element Investigation of the Dynamic Compressive Behavior of High Strength Al-Cu-Mg-Ag Alloys.
Khalil Elkhodary 1 , Lipeng Sun 2 , Douglas Irving 2 , Donald Brenner 2 , William Lee 1 , Bryan Cheeseman 4 , Guruswami Ravichandran 3 , Mohammed Zikry 1
1 Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 4 Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, Maryland, United States, 3 Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, California, United States
Show Abstract9:00 PM - EE5.32
Characterization of Local Deformation Microstructure in Ferrous Lath Martensite by using Micro-sized Specimens.
Yuichiro Ogawa 1 , Akinobu Shibata 2 , Chiemi Ishiyama 2 , Masato Sone 2 , Yakichi Higo 2
1 Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama Japan, 2 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan
Show Abstract Martensitic steel, especially lath martensite, has overwhelming significance because it appears in most commercial steels. Lath martensite is a characteristic structure in queched steels with a low alloy content. The transformation of a parent austenite grain into lath martensite was characterized as a grain subdivision on different length scales. A prior austenite grain is divided into packets (the group of laths with the identical habit plane), and each packet is subdivided into blocks (the group of laths with the identical orientation). These microstructures may have a significant influence on the deformation behavior of lath martensite, because boundaries between these microstructures are high angle boundaries. Therefore, there are many studies concerning with the deformation microstructures of lath martensite. However, it was difficult to estimate the effect of these microstructures on the deformation behavior in detail because previous studies used bulk-sized specimens which contain a large number of these microstructures. To overcome this difficulty, we fabricated the micro-sized specimens containing only one kind of specific microstructures (packet boundaries (high angle), block boundaries (high angle), or lath boundaries (low angle)), and compared the each deformation microstructure in detail. Furthermore, bending deformation was carried out to observe the local deformation microstructure with different strains directly. An Fe-23 mass% Ni alloy was used in the present study. The as-quenched specimen is a full lath martensite structure. After orientation analysis by electron backscattered diffraction pattern (EBSD), the micro-cantilever beam-type specimens (10 x 10 x 50 micro meter), which contain only one kind of specific microstructure (packet boundaries (high angle), block boundaries (high angle), or lath boundaries (low angle)), were fabricated by Focused Ion Beam (FIB) machining. Bending test was carried out using a testing machine for micro-sized specimens with a displacement resolution of 5 nm and a load resolution of 10 micro N. The deformation microstructures near the fixed end of the specimens were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After the bending test, a large number of straight shear bands appeared in the area near the fixed end of the specimen containing only lath boundaries (low angle boundaries). Furthermore, in the TEM observation, lath boundaries between adjacent laths partly disappeared in the area near the specimen surface (strain is large). Because as-quenched lath martensite contains a high density of dislocations, the pre-existing dislocations in lath martensite presumably interact with lath boundaries, resulting in the disappearance of lath boundaries. In the presentation, the deformation microstructure with block or packet boundaries will be shown and compared with each deformation microstructure in detail.
9:00 PM - EE5.33
Plasticity in Ceramics at Small Scales and Elevated Temperatures.
Sandra Korte 1 , William Clegg 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractUniaxial compression tests on micropillars have attracted great interest as a means of studying flow in small volumes of material. However, work so far has focused on the deformation behaviour of metals or metallic glasses at room temperature. As the dimensions of a specimen made from a macroscopically brittle material are reduced, a brittle-to-ductile-transition is generally observed as the volume becomes sufficiently small that it becomes difficult to obtain sufficient elastic energy in the body to generate an area of crack surface. This allows the deformation of brittle materials to be studied under much simpler conditions than can be obtained in nanoindentation. Using a high-temperature nanoindentation setup, it is shown that the brittle/ductile transition temperature increases as the pillar diameter increases and that, in conjunction with transmission electron microscopy, the deformation behaviour of brittle materials can be characterized.
9:00 PM - EE5.34
First-principles Calculations of Adhesive Behavior at Metal/oxide Incoherent Interface.
Daisuke Matsunaka 1 , Yoji Shibutani 1
1 , Osaka University, Osaka Japan
Show AbstractMetal/oxide interfaces are important components in advanced applications such as microelectronics devices, photovoltaic devices, composites, coatings, sensors, catalysts, etc. The functions and properties of metal/oxide interfaces play a key role in the performance of such applications. Moreover, the metal/oxide interface must possess the adequate thermodynamic mechanical stability under the particular conditions of the application. In order to investigate adhesive behavior at the interface between dissimilar materials, first-principles calculation is a valid method assuming no a priori type of chemical bonding. However, almost exclusively in previous calculations using a slab of crystal layers, the coherent interface approximation is imposed in the supercell, i.e., the change in the lattice constant across heterophase interfaces is neglected, and thus effects of misfit are not adequately evaluated. Recently, several studies using extended slab models have shown the interfacial bonding nature is strongly dependent on the interfacial atomic configuration. In this study, we carry out first-principles calculations of incoherent metal/oxide interfaces with large misfit, Cu/MgO(001) and Ni/MgO(001), based on the density functional theory (DFT). In order to consider the large misfit of incoherent interfaces, we adopt the coincidence boundary slab model by extending the supercell parallel to interface. It is shown that interfacial strain and bonding characteristics are inhomogeneous at incoherent interfaces, depending on local atomic configurations. In regions where a metal atom is located near an O atom, the misfit is compensated as the metal layer is stretched to the period of MgO. The adhesion behavior at the O-atop site has a covalent and ionic bonding characteristic. On the other hand, in regions where a metal atom is situated near a Mg atom, the metal layer is hardly strained and the atomic geometry remains incoherent. The metal-Mg adhesive interaction are mediated by the image-charge electron accumulation induced above the Mg atoms, which is absent in DFT results using the Mg-atop coherent structure. We also show that effects of the interfacial strain as well as the metal-Mg interaction on the adhesive energy are significant for accurate estimation of the stability of incoherent metal/oxide interfaces.
9:00 PM - EE5.4
Controlling Nanoporosity During Impact and Solidification of Molten Droplets via Surface Roughness Modification – Implications for Adhesion.
Meng Qu 2 , Jose Colmenares 2 , Andrew Gouldstone 1
2 Materials Science and Engineering, SUNY Stony Brook, Stony Brook, New York, United States, 1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractHigh velocity (100 m/s) impact of liquid droplets on a flat surface can cause nucleation of nanoscopic bubbles, due to gas supersaturation under very high impact pressure (1-3 GPa) and rapid (10 ns) depressurization. We previously showed that when spreading and solidification into splats follows, bubbles ‘solidify’ into pores of less than 100 nm diameter, and have gave empirical relations between impact conditions (substrate material, velocity) and pore morphology. In this study, we varied the solid surface roughness before droplet impact. We hypothesized that roughness two orders smaller than droplet size would increase bubble nucleation rate by providing more heterogeneous sites, whereas roughness of order droplet size would decrease nucleation rate, by decreasing impact pressure (driving force for supersaturation.) These hypotheses proved correct, and were supported by computational fluid dynamics models. In addition, we hypothesized that bubbles would reduce splat/substrate adhesion significantly. This was proven correct by systematic Ni splat pull-off tests on surfaces of different roughness. These results suggest a fundamental, nano-scale reason for the effectiveness of surface roughening before spray-based coating processes, and also the potential for controlled or patterned nanoporosity via varying surface conditions.
9:00 PM - EE5.5
Effects of Thermal Treatment and Loading Conditions on the Mechanical Behavior of Ultra-Low-Dielectric-Constant Mesoporous Amorphous Silica Films.
M. Rauf Gungor 1 , James Watkins 2 1 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Amherst, Massachusetts, United States, 2 Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Amherst, Massachusetts, United States
Show AbstractHigh-performance microelectronic devices require ultra-low-dielectric-constant (ULK) dielectric materials in order to reduce the capacitive coupling between the closely spaced interconnect lines. These ULK materials must also satisfy certain integration requirements, such as a minimum mechanical strength: this is particularly important to ensure the structural integrity of the device under thermomechanical loading conditions characteristic of semiconductor manufacturing processes, chip packaging, and device service. Among new ULK dielectric materials, porous amorphous silicas have significant advantages due to their compatibility with current semiconductor manufacturing technologies. In this presentation, we report results of molecular-dynamics (MD) simulations aiming at a fundamental understanding of the mechanisms that govern the mechanical behavior of mesoporous amorphous silica (a-SiO_2) film structures, as well as prediction of the response of such structures to various mechanical loading conditions. The normal-density a-SiO_2 structures are prepared through MD starting from a beta-cristobalite crystal and following a thermal processing sequence that includes melting, rapid quenching, and a thermal annealing schedule. We have generated regular mesoporous structures through introduction of a regular array of spherical pores with nanometer-scale diameter into the normal-density a-SiO2 matrix and subsequent thermal annealing to ensure proper structural relaxation. We present a systematic analysis of the mechanical response of these regular mesoporous a-SiO2 structures to applied strains within the elastic limit near room temperature based on isostrain MD simulations employing large-size computational supercells. We compute the elastic moduli and analyze structural stability under tensile and compressive strains as a function of density (ranging from 70% to 90% of the normal density) and pore diameter. We find that the Young modulus depends on density according to a sublinear power-law scaling relationship and decreases with decreasing mesopore size. Upon uniaxial compression, an elastic instability is triggered in structures with less-than-critical density or mesopore size, leading to rupture. In addition, we analyze the anelastic characteristics of the mechanical behavior based on nanosecond-scale MD simulations of dynamic deformation experiments in both tension and compression under high strain rates, ranging from 10^8 to 10^10 s^-1. Furthermore, we analyze the effects of thermal treatment near the glassy transition temperature on structural stability and mechanical strength.
9:00 PM - EE5.7
In situ Monitoring of the Structural Changes in Boron Carbide under Electric Fields.
Varun Gupta 1 , Giovanni Fanchini 1 , Adrian Mann 1 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe absence of a plastic phase in boron carbide and its failure at shock impact velocities just above the Hugoniot elastic limit (HEL) has been the subject of several experimental investigations for decades [1-3]. Nevertheless, a real time study that could provide valuable insight into why B4C fails prematurely in dynamic tests and extreme environments is still missing. By applying pulses of increasing voltage and simultaneously monitoring changes with Raman spectroscopy, it is possible to observe not only the onset of carbon segregation but also the degree of sp2 clustering in real time. In this work, in situ monitoring of the transformation of B4C under electric field using Raman spectroscopy is reported. Application of electric fields up to 5000 V/cm leads to local segregation of carbon, indicated by the appearance of Raman D and G peaks. At low electric fields (<3000 V/cm) the segregated carbon is amorphous, while at higher fields aromatic sp2 clustering is observed. Electrical measurements as a function of temperature are used to complement the Raman measurements. The results demonstrate that it is possible to induce transformations in boron carbide using electric fields that are comparable with those obtained under shock and nanoindentation [4]. 1. M. W. Chen, J. W. McCauley, and K. J. Hemker, Science, 299, 1563-1566 (2003). 2. V. Domnich, Y. Gogotsi, M. Trenary, and T. Tanaka, Applied Physics Letters, 81 [20] 3783-3785 (2002).3. G. Fanchini, J. W. McCauley, and M. Chhowalla, Physical Review Letters, 97, 035502 (2006).4. G. Fanchini, V. Gupta, A. B. Mann and M. Chhowalla, “In situ Monitoring of the Structural Changes in Boron Carbide under Electric Fields,” Journal of the American Ceramic Society (2008).
9:00 PM - EE5.8
High Pressure Structural Modifications and Equation of State of LaCrO3 and La0.75Ca0.25CrO3.
Maulik Patel 1 , Amol Karandikar 1 , Gautam Mukherjee 1 , V. Vijayakumar 1 , Avesh Tyagi 2 , Andrea Lausi 3 , Edoardo Busetto 3
1 High Pressure Physics Division, Bhabha Atomic Research Center, Mumbai, Maharashtra, India, 2 Chemistry Division, Bhabha Atomic Research Center, Mumbai, Maharashtra, India, 3 , ELETTRA, Sincrotrone Trieste, Trieste Italy
Show Abstract9:00 PM - EE5.9
Degradation of Mechanical Strength of Vertically Aligned Carbon Nanotubes at Growth Interface Joints at High Temperatures.
Feng Jin 1 , Scott Little 1 , Yan Liu 1
1 , Ball State University, Muncie, Indiana, United States
Show Abstract
Symposium Organizers
Amit Misra Los Alamos National Laboratory
T. John Balk University of Kentucky
Hanchen Huang Rensselaer Polytechnic Institute
Maria Jose Caturla Universitat d'Alacant
Christoph Eberl University of Karlsruhe
EE6: Deformation Mechanisms at Small Length-scales
Session Chairs
Julia Greer
Ludovic Thilly
Wednesday AM, December 03, 2008
Room 200 (Hynes)
9:30 AM - **EE6.1
In-Situ Mechanical Testing Shedding Light on Deformation Mechanisms.
Helena Van Swygenhoven 1 , Steven Van Petegem 1 , Robert Maass 1 , Christian Brandl 1 , Peter Derlet 1
1 ASQ/NUM – Materials Science & Simulation, Paul Scherrer Institut, Villigen PSI Switzerland
Show AbstractPerforming mechanical testing in-situ in the Swiss light source has revealed unprecedented details on the fundamentals and the dynamics of plastic deformation mechanisms in confined volumes. In-situ powder diffraction is particularly interesting for studying nanocrystalline metals, whereas in-situ Laue can reveal the dynamics in single crystal plasticity in micron-sized objects.Recent results obtained during in-situ mechanical testing of electrodeposited Ni and NiFe are presented. These types of materials are characterized by a high rms-strain, which partly recovers in the early stages of plastic deformation, demonstrating the presence of large micro-plastic strains before the onset of macro-plasticity. Furthermore the different behaviour of peak position and peak width during tensile/compressive, constant strain rate tests and during creep tests are presented. The findings are discussed in terms of recent results obtained from molecular dynamics simulations suggesting cross-slip and in terms of diffraction patterns calculated from computational configurations.In-situ white beam Laue micro diffraction combined with a 2-D mapping has been applied to investigate the initial microstructure of undeformed Au, Ni, Cu and NiTi single crystal micro- pillars fabricated by focused ion beam milling. Various microstructural features have been evidenced ranging from strain gradients to misorientations at pillar base extending well into the pillar body, all features from which it is known that they contribute to classical hardening. The results are discussed in terms of the observed smaller is stronger.
10:00 AM - EE6.2
Compressive Stress-strain Response of Mo-alloy Single Crystal Micro-pillars Prepared by Directional Solidification Techniques.
Hongbin Bei 1 , Sanghoon Shim 1 2 , E. George 1 2 , G. Pharr 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractA new technique for producing single crystal micro-pillars that does not involve FIB milling has been used to make micro-pillars of a Mo(Ni,Al) alloy with sizes ranging from 0.3 to 1.5 μm. The technique involves directional solidification of eutectic alloys to produce long-aspect-ratio fibrous composites followed by etching away of the matrix to expose the fibers as free-standing micro-pillars. By pre-straining the composite in compression prior to etching away the matrix, the initial dislocation structure in the pillars can be systematically varied. Results are presented that document the influences of pre-strain on the mechanical behavior. It is found that, at one extreme, the as-grown pillars (0% pre-strain) behave like dislocation-free materials with yield strengths approaching theoretical strength, independent of size. At the other extreme were pillars pre-strained 11%, which behaved like bulk materials, with reproducible stress-strain curves, relatively low yield strengths, stable work hardening, and no size dependence. At intermediate pre-strains (4-8%), the stress-strain curves were stochastic and exhibited considerable scatter in strength. This scatter decreased with increasing pre-strain and pillar size, suggesting a transition from discrete to collective dislocation behavior.This research was sponsored by the U.S. Department of Energy: Division of Materials Sciences and Engineering (HB and EPG); the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program (SS); and the SHaRE User Facility, Division of Scientific User Facilities, Office of Science (GMP).
10:15 AM - EE6.3
Influence of Gamma Radiation on Strengthening Size Effects in LiF Micron-Scale Single Crystals.
Edward Nadgorny 1 , Dennis Dimiduk 2 , Michael Uchic 2 , Peter Shade 3 , Christopher Woodward 2
1 Physics, Michigan Technological University, Houghton, Michigan, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 3 Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
Show AbstractIt is well known that high-energy radiation considerably changes the mechanical properties of materials. In particular, for the present study the yield stress increased ten-fold in LiF single crystals irradiated by a 60Co gamma-radiation source. However, we recently observed surprising results in micron-scale LiF samples prepared from as grown and irradiated crystals: the two sample sets obey practically identical “size-effect” strengthening when tested by microcompression, so that the flow stress reaches an unusually high value (~600-MPa range in 1 μm samples) independent of whether the samples are prepared from gamma-irradiated or unirradiated bulk crystals. In this study, we present a detailed comparison of these two groups of samples regarding their mechanical behavior and avalanche-flow properties, which are very similar to those observed in metals and intermetallics. We find that both qualitative and quantitative differences do exist in larger samples but almost disappear in 1 μm samples. The data are analyzed using a new statistical approach to the power-law observed in micron-sized samples. The new findings support an earlier proposed model of size-limited dislocation generation. Several possible explanations of the observed effects are presented and compared.
10:30 AM - EE6.4
Lattice Rotation in Tensile Tested Cu Micropillars: A Synchrotron Microdiffraction Experiment.
Nicolas Vaxelaire 1 , Jozef Keckes 2 , Stéphane Labat 1 , Daniel Kiener 2 , Cristian Mocuta 3 , Gerhard Dehm 2 , Olivier Thomas 1
1 , CNRS, IM2NP (UMR 6242), Faculté des Sciences et Techniques, Campus St Jérome, 13 397 Marseille Cedex France, 2 , University of Leoben, Departement Materials Physics and Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstr. 12,A -8700 Leoben Austria, 3 , European Synchrotron Radiation Facility, Grenoble France
Show AbstractThe mechanical properties of single crystal metals with micron and submicron dimensions has spurred a lot of research in recent years. The possibility to strain under tension micron-sized single crystal Cu pillars has been demonstrated recently [1]. In this work we have investigated lattice rotation in a Cu micropillar previously tested under tension (total strain 10 (?) %) along [-234] crystallographic axis. The tensile sample was shaped with Focused Ion Beam with the resulting dimensions of 20x2x2 µm^3. Monochromatic (E=8.4 keV) microdiffraction was performed on the 111 Cu reflection at ID01 beamline at ESRF. Beam focusing was achieved with 27 Be refractive lenses. Beam size was 1x3 microns and beam divergence was around 0.04x0.04 mrad^2. The diffracted signal was recorded with a 1340x1300 pixel CCD camera which give an 0.005° average angular resolution in our working conditions. Scanning along the pillar together with rocking the incidence angle yields detailed information on the rotation of the crystal lattice give some numbers and strain gradients. These results will be discussed with respect to the appearance of slip bands and dislocation activity.[1] D. Kiener, W. Grosinger, G. Dehm, R. Pippan, A further step towards an understanding of size-dependent crystal plasticity: In-situ tension experiments of miniaturized single crystal copper samples, Acta Mater 56 (2008) 580-592.
10:45 AM - EE6.5
Indentation Size Effects in Single Crystal Copper as Revealed by Synchrotron X-ray Microdiffraction.
Gang Feng 1 2 , Arief Budiman 2 3 , Nobumichi Tamura 3 , Jamshed Patel 2 3 , William Nix 2
1 Mechanical Engineering, Villanova University, Villanova, Pennsylvania, United States, 2 Materials Science & Engineering, Stanford University, Stanford, California, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractFor a Cu single crystal, we find that indentation hardness increases with decreasing indentation depth, a phenomenon widely observed before and called the indentation size effect (ISE). To understand the underlying mechanism, we measure the lattice rotations in indentations of different sizes using white beam X-ray Microdiffraction (µXRD); the indentation-induced lattice rotations are directly measured by the streaking of X-ray Laue spots associated with the indentations. The magnitude of the lattice rotations is found to be independent of indentation size, which is consistent with the basic tenets of the ISE model. Using the µXRD data together with an ISE model, we can estimate the effective radius of the indentation plastic zone, and the estimate is consistent with the value predicted by a finite element analysis. Using these results, an estimate of the average dislocation densities within the plastic zones has been made; the findings are consistent with the ISE arising from a dependence of the dislocation density on the depth of indentation.
11:30 AM - EE6.6
Effects of Nanoscale Deformation Volume on the Mechanical Behavior of Nanoporous Noble Metals.
Ye Sun 1 , T. John Balk 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show Abstract11:45 AM - EE6.7
The Strength of Nanoporous Gold: Strain Gradient and Intrinsic Size Effects.
Brian Derby 1 , Rui Dou 1
1 Materials Science, University of Manchester, Manchester United Kingdom
Show AbstractDeformation models for nanoporous foams must account for the effects of strain gradients. We have developed a mechanism based model, based on conventional models for the deformation of macroscopic foams, that includes the influence of strain gradients. This predicts two regimes for the deformation of nanoporous gold with a transition that depends on foam relative density and ligament size. We have used this model to analyse experimental data for the strength of nanoporous gold with a range of microstructures. Our model shows that the strength of nanoporous gold is controlled by two independent size effects. One of these can be accurately modelled using strain gradient concepts, the other is an intrinsic size effect. Using the model to account for the effects of strain gradients, we are able to produce a prediction for the intrinsic size effect on strength as a function of ligament diameter in nanoporous gold. Thus we show that this intrinsic size effect is identical to that reported for the compressive yield strength of single crystal gold nanorods and nanowires.
12:00 PM - EE6.8
TEM Characterization of Deformation and Failure Mechanisms in Cu/Nb Nanoscale Composites.
Nathan Mara 1 , Dhriti Bhattacharyya 2 , Pat Dickerson 1 , Richard Hoagland 1 , Amit Misra 2
1 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractCu/Nb nanolayered composites have recently been shown to possess interfacial characteristics that render them resistant to ion irradiation damage. The ability of interfaces to act as sinks for defects such as dislocations also provides for enhanced mechanical behavior. In our recent work, Cu/Nb nanoscale multilayered composites have shown ultra-high strength as well as high ductility using a variety of mechanical test methods (nanoindentation, tensile testing, and micropillar compression). Individual layer thicknesses tested range from 100 nm to 5 nm, with flow stresses (5 nm Cu/Nb case) of nearly 3 GPa, and deformation during micropillar compression in excess of 20%. Through the use of Focused Ion Beam (FIB) milling, post-deformed microstructures of micropillars are examined via Transmission Electron Microscopy (TEM). Formation of shear bands, as well as homogeneous deformation of over 10% true strain is evident at individual layer thicknesses as low as 5 nm. The microstructure within the shear band exhibits large plastic deformation and grain rotation relative to the compression axis, and the layered structure remains continuous even after local strains in excess of 70%. Plastic behavior of these materials at large plastic strains will be discussed in terms of interfacial effects on dislocation motion. It was found that total plasticity to failure in nanoscale multilayered composites was limited only by the onset of instability due to mechanical testing geometry.
12:15 PM - EE6.9
Modeling the In situ TEM Deformation of CdS Nanospherical Shells.
Matthew Sherburne 1 , Hillary Green 1 , Daryl Chrzan 1 2
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractRecently, it has become possible to test the mechanical properties of nanostructures while viewing the entire process within a transmission electron microscope. Experiments performed by Shan et al.4 indicate that hierachically structured CdS nanospherical shells, in which the nanoshells themselves are composed of multiple nanograins, can be compressed by as much as 20% of their diameters before fracturing in a brittle fashion. A finite element model for the process was developed and used to analyze the stress state within the shells at the failure point and indicate that the shear stresses within the shell approach 2.2 GPa at the point of failure. This large shear stress prompted the computation of the ideal shear stress for CdS using density functional based total energy method. The computed ideal shear strength for CdS is 3.1 GPa. Remarkably, the stresses within the shell approach 71% of the ideal strength of the material. This unusual strength is attributed to the heirarchical structure of the nanospheres. This research is supported by the Director, Office of Science, Office of Basic Energy Sciences (BES), of the US Department of Energy under Contract No. DE-AC02-05CH11231 and National Science Foundation under Grant No. DMR 0304629.4 Z. W. Shan et al., submitted for publication.
12:30 PM - EE6.10
Activation Volume and Mobile Dislocation Density of Ultrafine-grained Cu with Nano-scale Twin Lamellae.
Lei Lu 1 2 , Ming Dao 1 , Subra Suresh 1
1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang China, 2 Materials Science & Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractIt is known that twin boundaries (TBs) behave similarly to grain boundaries (GBs) as obstacles to the motion of dislocations during the plastic deformation. On the other hand, the nanoscale twins also promote the rate sensitivity for the flow stress. However, most previous strain rate change tests were usually single transition ones, which neither allows a determination of mobile dislocation density in the solid and the dislocation velocity, nor yields information about dislocation multiplication. The objective of the present study is to explore the activation volume and mobile dislocation densities by means of repeated transient tests, stress relaxation tests, for the electrodeposited ultra-fine grained Cu with different densities of nanoscale twins. The observed high density of mobile dislocations suggested that the TB-medicated deformation mechanism is fundamentally different from the conventional forest dislocations cutting mechanism in coarse-grained and GB-mediated dislocation activities in nanocrystalline fcc metals. A clear twin thickness (λ) dependence on the activation volume is found for the nt-Cu samples, viz. a reduction in λ results in a noticeable reduction in activation volume to about 10 b3 (when λ~15 nm). Applying the twin-boundary affected zone (TBAZ) model, the theoretical predictions are found to correspond well with the size-dependent trend of the activation volume versus twin thickness (λ).
12:45 PM - EE6.11
Formation of Nanostructures in Al and Al–Mg Alloys Subjected to Severe Plastic Deformation.
Hans Roven 1 , Manping Liu 1 , Maxim Murashkin 2 , Ruslan Valiev 2 , Ascar Kilmametov 2 , Tamas Ungar 3 , Levente Balogh 3
1 Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim Norway, 2 Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa Russian Federation, 3 Department of Materials Physics, Eötvös University, Budapest Hungary
Show AbstractEE7: Nanomechanical Testing and Characterization
Session Chairs
Wednesday PM, December 03, 2008
Room 200 (Hynes)
2:30 PM - **EE7.1
In-situ Mechanical Testing at the Micro-scale.
Paul Shade 2 , Robert Wheeler 3 , Michael Uchic 1 , Dennis Dimiduk 1 , Yoon-Suk Choi 3 , Hamish Fraser 2
2 Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States, 3 , UES, Inc., Dayton, Ohio, United States, 1 , Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States
Show Abstract3:00 PM - EE7.2
In-Situ Laue Micro-Compression: Yield and Hardening in Gold Pillars.
Robert Maass 1 , Steven Van Petegem 1 , Peter Derlet 1 , Helena Van Swygenhoven 1
1 ASQ/NUM – Materials Science & Simulation, Paul Scherrer Institut, Villigen PSI Switzerland
Show AbstractCompression of micron sized pillars has evidenced an enhanced flow stress and strain hardening strengthening with decreasing pillar diameter. To provide further understanding of the mechanistic background for such size affected plasticity an in-situ setup combining both micro-compression and Laue micro-diffraction has been developed [Phys. Rev. Lett. 99, 145505 (2007)], and shown to provide detailed insight into the microstructure [Appl. Phys. Lett. 89, 151905 (2006), Scripta Mat. 59, 471 (2008)] and also correlating stress-strain data with diffraction peak evolutions [Appl. Phys. Lett. 91, 131909 (2007), Appl. Phys. Lett. 92, 071905 (2008)].In this work we study the deformation behaviour of single crystal Au micropillars oriented for single slip, paying attention to the very early part of loading and to strain hardening observed at larger strains. Already at small strains peak broadening and peak position measured in the central part of the pillar, evidence a pronounced dislocation activity that involves crystal rotation, however using a slip system that produces little measurable strain in the compression direction. After having reached about 50MPa, a distinct change in the direction of the lattice rotation is observed, corresponding with dislocation activity on the slip system with the highest Schmid factor. At higher strains differences in the strain hardening rates are observed among the pillars and correlated with different slip system activity. The results are discussed in terms of the strain hardening mechanism and different criteria for yield based on the Laue information are derived.
3:15 PM - EE7.3
High Temperature, Controlled Atmosphere Nanoindentation.
Jeffrey Wheeler 1 , James Dean 1 , T. Clyne 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractNanoindentation has major advantages in terms of specimen size and the capacity to study the behaviour of localised regions. However, its application at high temperature has been severely limited, although it has been used to investigate creep at room temperature [1]. This limitation has primarily arisen because it is normally carried out in air, or possibly with inert gas shrouding. Unfortunately, this cannot bring the oxygen partial pressure below ~5-10 mbar at best. Maximum indentation temperatures have thus been ~400C with diamond tips (limited by tip erosion, i.e. oxidation), or ~750C with sapphire tips (limited by tip hardness). There is also the possibility of specimen oxidation. There have thus been virtually no (instrumented) nanoindentation studies at very high temperatures (>~800C), although flat punch indentation [2] and testing after exposure to extreme conditions [3] have been explored.Information will be presented on a novel nanoindentation system recently commissioned in the Gordon Laboratory in Cambridge. This comprises a combined MicroTest and NanoTest system, supplied by MicroMaterials Ltd., located in a customised vacuum chamber. The indenter can be operated under vacuum, with oxygen partial pressures below 0.1 microbar, or after backfilling with inert gas, in which case the oxygen partial pressure depends on gas purity, but would typically be 10-30 microbar. Such pressures ensure that diamond tip erosion rates remain low. Tip shape has been measured via AFM over the course of several high temperature indentation sessions, in order to monitor oxidative ablation rates. It has been confirmed that these rates can be kept below levels of concern at temperatures of up to ~1000C. This is consistent with data available in the literature for diamond erosion rates as a function of temperature and oxygen partial pressure.Best practice procedures are described for sensor calibration at high temperature, under vacuum or argon atmospheres, and thermal drift phenomena are also outlined. Required equilibration times for various measurements, e.g. dynamic hardness, indentation, and creep, are briefly described. Some illustrative data are presented for the creep behaviour of pure Ni as a function of temperature. It is also shown that, under the conditions concerned, the thickness of the oxide film formed on the specimen was below the level at which it would be likely to interfere with the measurements.References[1]R. Goodall and T.W. Clyne, Acta Mater., 54, 5489-5499 (2006).[2]R. Montanari et al, J. Nucl. Mater. 367-370, 648-652 (2007).[3]H. Ogiwara et al, J. Nucl. Mater. 367-370, 428-433 (2007).
3:30 PM - EE7.4
Optimizing High Temperature Nanoindentation in Inert Atmospheres.
Jonathan Trenkle 1 , Corinne Packard 1 , Christopher Schuh 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHigh temperature nanoindentation is an emerging technique for measuring properties of structural materials at relevant service or processing temperatures, and for investigating thermally activated deformation phenomena. At temperatures >300°C, the oxidation rates for many engineering materials are accelerated owing to rapid diffusion and higher chemical activity. Limiting testing to temperatures below 200°C or to materials with little or no reactivity with the air is exceedingly restrictive, and therefore it is desirable to explore testing in inert atmospheres. Using a custom high temperature nanoindentation apparatus based on the Ubi1 nanoindenter (Hysitron, Inc. Minneapolis, MN), we have characterized the performance of the system in several environments and in various configurations, paying particular attention to the thermal drift response. Though a single configuration is not advantageous for all situations, an optimum configuration can be selected based on the requirements of a particular test. In this presentation, we illustrate some of these “best practices” through specific examples including property evaluation of fused silica and aluminum up to 500°C, and a study of rheological behavior in a metallic glass in the superplastic forming regime. The results presented will be useful in the future design and optimization of high temperature nanoindentation experiments.
3:45 PM - EE7.5
Advanced Instrumented Micro-hardness at Ultra-High Temperatures and Acoustic Emission to Detect Crack Initiation of Ceramic Coatings.
Norm Gitis 1 , Alex Meyman 1 , Vishal Khosla 1 , Suresh Kuiry 1
1 , CETR, Inc., Campbell, California, United States
Show AbstractExperimental evaluation of micro-mechanical properties of high-temperature ceramic coatings under extreme conditions (up to 1000 °C in inert atmosphere) is discussed in details. Traditional micro-hardness tests of coatings consist of indentation and post-test indent analysis. The paper demonstrates that the instrumented indentation using in-situ multi-sensing technology may be advantageous in both repeatability and a number of measured parameters over classical hardness methods. Instrumented micro-indentations were performed on ceramic alloys at four temperatures 20, 350, 700 and 1000 °C, three tests per each to show the repeatability. The indent depths were kept under 10‰ of the film thickness to produce substrate-independent data. For reference, we performed scratch-hardness tests of the same materials at the same temperatures. The results showed dramatic changes in both hardness and Young’s modulus of the materials with temperature. All the indentation and scratch tests were done in the universal materials tester UMT-3V by CETR. The tester includes multiple sensors, measuring in-situ normal load, lateral (friction) force, indentation depth, temperature, contact high-frequency acoustic emission, contact electrical resistance, etc. It can be used to measure and compare micro-hardness on any scale (Rockwell, Vickers, Knoop, instrumented, etc.) without sample removal.The paper also correlates acoustic emission data to the load at which the crack formation starts. The megasonic acoustic emission works generally well with brittle and hard materials, and is a very sensitive technique.Further work in progress will show that the technique of instrumented hardness and multi sensing technology can be of particular use to predict the behavior of the materials as a function of temperature for an extended range of compositions.
4:30 PM - **EE7.6
Quantification of Geometrically Necessary Dislocations Beneath Small Indents of Different Depths Using EBSD Tomography.
Eralp Demir 1 , Dierk Raabe 1 , Stefan Zaefferer 1
1 , Max-Planck-Institut fuer Eisenforschung, Duesseldorf Germany
Show AbstractWe study the link between the indentation size effect and the density of geometrically necessary dislocations (GNDs) through the following approach: Four indents with different indentation depth and hardness are placed in a Cu single crystal using a conical indenter with spherical tip. The deformation-induced lattice rotations are monitored in 3D below the indents at 50 nm resolution using a tomographic electron back scatter orientation microscope in conjunction with a focused ion beam instrument for serial sectioning (3D EBSD). From the EBSD data we calculate the first order gradients of strain and from these the GND densities below the four indents. This approach allows us to directly quantify in one set of experiments both the mechanical parameters (depth, hardness) and the lattice defects (GNDs) that are held responsible for the indentation size effect.
5:00 PM - EE7.7
3D Measurements of Strain and Dislocation Gradients in Mo nano-pillars via Polychromatic Microdiffraction.
Rozaliya Barabash 1 2 , H. Bei 1 , G. Ice 1 , W. Liu 3 , J. Tischler 1 , E. George 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States, 3 , Advanced Photon Source, Argonne, Illinois, United States
Show AbstractSpatially resolved strain distributions in the NiAl matrix and the ~550-nm Mo fibers of a NiAl-Mo eutectic were investigated by micro-beam X-ray diffraction. Position sensitive d-spacings for the individual phases were obtained from Laue patterns. For embedded Mo fibers, the measured elastic strain is consistent with the predicted thermal mismatch strain between the NiAl and Mo phases. However, when the NiAl matrix is etched back to expose Mo micro-pillars, the d-spacing increases to that of unconstrained Mo, indicating release of the compressive residual strain in the Mo fibers.
5:15 PM - EE7.8
Strain Hardening Behaviors within Different Texture Components of a Cu Thin Film: A Synchrotron X-ray Diffraction Study.
Aaron Vodnick 1 , Shefford Baker 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIn-situ x-ray diffraction is a convenient characterization tool to probe the mechanical behavior of materials at elevated temperatures and in controlled environments. For highly textured thin metal films, diffraction allows the mechanical response of different texture components to be probed individually and in real time. This is of interest because obtaining the details of deformation mechanisms within each texture constituent separately is key to understanding failure mechanisms for the film as a whole. However, significant interactions between texture components due to elastic anisotropy have made detailed analyses of deformation behaviors difficult. Here, a simple analysis is introduced which applies displacement boundary conditions to each texture components in order to calculate the required plastic strains, and therefore changes in dislocation density, within each texture component during thermal cycling of a thin Cu film. From this analysis emerges an improved picture of anelastic behavior and strain hardening within thin metal films.
5:30 PM - EE7.9
Understanding Phase Transformation Behaviour in Silicon through In-situ Electrical Probing under Cyclic Loading Conditions.
Naoki Fujisawa 1 , Simon Ruffell 1 , Jodie Bradby 1 , James Williams 1
1 Electronic Materials Engineering, Australian National University, Australian National University, Australian Capital Territory, Australia
Show AbstractIndentation-induced phase transformations in both crystalline silicon (c-Si) and amorphous silicon (a-Si) have attracted considerable recent interest. During indentation loading, the diamond cubic Si-I phase transforms to a metallic Si-II phase when the pressure reaches ~11 GPa and to either high pressure poly-crystalline Si-XII and Si-III phase or a-Si on unloading, depending on the unloading conditions. A statistical correlation has been found between the occurrence of a sudden decrease of the indentation displacement or ‘pop-out’ during unloading and the formation of the Si-XII/Si-III phases in the unloaded material. If no pop-out event occurred during unloading, the final structure of the unloaded material was predominantly amorphous. In this study, a crystalline silicon wafer has been cyclically loaded by an electrically conductive Berkovich indenter to a constant peak load. During the cyclic indentation, a constant positive voltage was applied across the sample stage to enhance electrical current flow through the sample and the indenter tip. Cyclic indentations of crystalline silicon showed interesting mechanical behaviour depending on the end phase that resulted from the previous cycle. For an a-Si end phase the subsequent reloading was hysteretic. However, after a pop-out event, the load-displacement hysteresis decreased dramatically and progressively with increasing cycle number until a fully elastic reload/unload response occurred. This indicates that, whereas the a-Si retransforms readily to Si-II upon reloading, the more mechanically stable mixed Si-XII/Si-III phase, once formed in the indent volume, does not retransform to Si-II up to the maximum indentation load applied. Furthermore, the hysteresis loop area of a reload/unload cycle effectively represents the amount of energy needed to retransform the a-Si volume, and we show that it may be used to indicate the amount of the a-Si remaining in the indent volume at the start of a particular cycle. Based on our results, we propose that small amounts of the a-Si in the indent volume, through transformation to Si-II in the fully reloaded condition, were being sequentially replaced by small volumes of the mechanically stable Si-XII/Si-III phases during the unloading of each cycle, without ‘pop-out’. However, following ‘pop-out’, when the Si-XII/Si-III phases dominated the residual indent volume, subsequent cycles quickly converted the remaining a-Si to these high pressure crystalline phases.
5:45 PM - EE7.10
On the Effect of a General Residual Stress State in Indentation and Hardness Testing.
Norbert Huber 1 , Juergen Heerens 1
1 Institute of Materials Research, GKSS Research Centre Geesthacht, Geesthacht Germany
Show AbstractMeasurement of local mechanical properties and their distribution by micro hardness or nanoindentation testing is an important and widely used approach. However, materials of technical relevance have in many cases non-homogeneous residual stress fields. For example, thin films typically show a uniform biaxial stress state, while in and around welds a more complex stress state is present that can vary from a pure shear to equibiaxial stress state within a few millimetres across the weld. The residual stresses superimpose the stress field from an indentation experiment and do therefore not allow measuring the mechanical behaviour of the volume of interest without influencing the result. From the work of Tsui et al. (1996) it is known that this effect is nonlinear and can be significant, in particular for equibiaxial stress states. Beside numerical approaches, analytical models were proposed by different groups for equibiaxial stress states (Suresh and Giannakopoulos, 1998, Carlsson and Larsson, 2001). The model of Lee and Kwon (2004-2006) is able to deal with a general residual stress state but can not account for the well-known nonlinearities. In this paper a simple analytical model is proposed that allows predicting the different nonlinear behaviour of the hardness plotted versus the stress for a general residual stress state. It is shown how the observed effects are caused by the von Mises flow rule in combination with the high hydrostatic pressure underneath the indenter tip. The model has been extensively validated by finite element simulations as well as spherical indentation of uniaxially pre-stressed bending bars made of the aerospace alloy Al2025-T351. As a by-product of the model an inverse analysis allows to identify the strength of the material at very large strains of about 80%. This will be exemplarily demonstrated using our own data as well as the data from Tsui et al. for the aluminium alloy 8009.As a result of this theoretical model, it is possible to estimate the error in indentation measurements based on the uncertainty in the stress ratio and strength of the material. Large areas exist, where the effect of residual stresses is below 5% and therefore can be neglected. However, there are also areas producing errors of up to 30% and more if the residual stress field is not taken into account. As the major part of the parameter space has only a low sensitivity, a reverse analysis towards a residual stress measurement from hardness testing will be afflicted with significant uncertainties. This is in particular true in nanoindentation experiments, where the experimental scatter can be very large. Considering on the other hand the simplicity of residual stress measurement by X-ray diffraction it can be concluded that the model will be very useful to correct the effect of arbitrary residual stress fields in hardness and indentation experiments.
Symposium Organizers
Amit Misra Los Alamos National Laboratory
T. John Balk University of Kentucky
Hanchen Huang Rensselaer Polytechnic Institute
Maria Jose Caturla Universitat d'Alacant
Christoph Eberl University of Karlsruhe
EE8/W10: Joint Session: Computational Nanomechanics I - Dislocations & Radiation Effects
Session Chairs
Thursday AM, December 04, 2008
Constitution B (Sheraton)
9:15 AM - **EE8.1/W10.1
Surface Controlled Dislocation Multiplication in Metal Micro-pillars.
Wei Cai 1 , Christopher Weinberger 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractUnderstanding plasticity and strength of crystalline materials in terms of the dynamics of microscopic defects has been a goal of materials research in the last seventy years. The size-dependent yield stress observed in recent experiments of sub-micrometer metallic pillars provides a unique opportunity to test our theoretical models, allowing the predictions from defect dynamics simulations to be directly compared with mechanical strength measurements. While easy escape of dislocations from sub-micrometer pillars is expected and provides a plausible explanation of the observed size-effect, we predict the opposite to be true in body-centered-cubic (BCC) pillars through a series of Molecular Dynamics and Dislocation Dynamics simulations. Under the combined effects from the image stress and the atomistic core, a dislocation nucleated from the surface of a BCC pillar generates one or more dislocations moving in the opposite direction before it exits from the surface. The process is repeatable so that a single nucleation event is able to produce a much larger amount of plastic deformation than that in face-centered-cubic (FCC) pillars. This self-replication mechanism calls for a different explanation of the size-dependence of yield stress in FCC and BCC pillars.
9:45 AM - **EE8.2/W10.2
Mechanisms of Size-dependent Crystal Flow Gleaned from Three-dimensional Discrete Dislocation Simulations.
Satish Rao 1 , Dennis Dimiduk 2 , Michael Uchic 2 , Triplicane Parthasarathy 1 , Christopher Woodward 2
1 Materials and processes Division, UES Inc., Dayton, Ohio, United States, 2 Materials and Manufacturing Directorate, Wright-patterson Air Force labs, WPAFB, Ohio, United States
Show AbstractRecent experimental studies discovered that micrometer-scale face-centered cubic crystals show strong strengthening effects, even at high initial dislocation densities. We use large-scale 3-D discrete dislocation simulations (DDS) to explicitly model the deformation behavior of FCC Ni microcrystals in the size range 0.25 – 20 micron under both single-slip and multi-slip conditions. The study shows that two size-sensitive athermal hardening processes, beyond forest hardening, are sufficient to develop the dimensional scaling of the flow stress, stochastic stress variation, flow intermittency and, high initial strain-hardening rates, similar to experimental observations for various materials. One mechanism, source-truncation hardening, is especially potent in micrometer-scale volumes. A second mechanism, termed exhaustion hardening, results from a break-down of the mean-field conditions for forest hardening in small volumes, thus biasing the statistics of ordinary dislocation processes. Effects of thermally activated cross-slip of screw-oriented dislocations on the stress-strain behavior of microcrystals of Ni is also discussed.
10:15 AM - EE8.3/W10.3
Anisotropic Diffusion of Point Defects in Metals under a Biaxial Stress Field.
Wai Lun Chan 1 , Robert Averback 1 , Yinon Ashkenazy 2
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractWe study the diffusion anisotropy (DA) of point defects in fcc and bcc metals induced by a biaxial stress field. The study shows that the DA strongly depends on the crystal structure and the crystallographic direction in which the stress is applied. For example, interstitials in fcc metals diffuse faster in the plane of the stress than normal to it when the stress is applied to the (001) plane, but they diffuse slower when the stress is applied in the (111) plane. In contrast, applied biaxial stress in the (001) plane of a bcc metal has no effect on the DA. These results can be explained by considering the interaction of the defects in their saddle point configurations with the external field together with the constraints imposed by the crystal structure on the defect jump directions. Our calculations show that the DA can be significant in a number of practical situations where large numbers of non-equilibrium defects and high stress is presence, e.g. irradiation-induced creep, solute segregation in irradiated alloys, and stress creation during ion bombardment.
10:30 AM - EE8.4/W10.4
Atomistic Simulation Studies of Indentation into Cu-Ni and Cu-Nb Multi-layers.
Sergey Medyanik 1 , Shuai Shao 1
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractNanoscale multilayered metallic structures often exhibit very high strength levels. This strengthening has been attributed to the presence of interfaces between dissimilar materials that serve as barriers to dislocation propagation. In this work, we present atomistic simulation studies of dislocation nucleation and propagation in nanoscale multilayered metallic systems (Cu-Ni and Cu-Nb). Nanoindentation model is used to generate dislocations at and near the surface. Interaction of the propagating dislocations with coherent and incoherent types of interfaces is analyzed. In the case of coherent Cu-Ni interface dislocations that initiate in Cu layer propagate through the interface into Ni. However, the interface acts as an obstacle for dislocation propagation and leads to a higher dislocation density near the interface. In the case of incoherent Cu-Nb interface dislocations that initiate in Cu do not propagate into Nb even at very high indentation depths and tend to accumulate in copper near the interface. We provide further analysis of the results focusing on the mechanisms for strengthening in the nanoscale multilayered metallic systems due to the presence of interfaces.
10:45 AM - EE8.5/W10.5
Heterogeneous Deformation and Dislocation Dynamics in Cu Single Crystal Micropillars under Compression.
Sreekanth Akarapu 1 , Hussein Zbib 1 , David Bahr 1
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractThe size dependent deformation of sub-micron Cu single crystals with thickness ranging from 0.2 to 2.5 microns subjected to uniaxial compression was studied using a Multi-scale Discrete Dislocation Plasticity (MDDP) approach. MDDP is a hybrid elasto-visco plastic simulation model which couples 3D discrete dislocation dynamics at the micro-scale with macroscopic plastic deformation. The stress-strain behavior exhibited plastic yielding in discrete strain bursts conforming qualitatively to experimental observations. An explanation to the observed macroscopic strain bursts is given by investigating the associated dislocation mechanisms. The operation of dislocation arm was identified as the prominent mechanism causing plastic deformation. The critical stress to bow an average minimum dislocation arm length is responsible for the observed size dependent response of the single crystals. Hardening rates, similar to that shown experimentally, are shown to occur under relatively constant dislocation densities, and are shown to be linked to the bowing of arms and the addition of pinning sites, and not through dislocation starvation mechanisms. Crystal rotation during compression was predicted in the simulation, and is in accord with published results observed in electron backscatter diffraction experiments
11:30 AM - **EE8.6/W10.6
Designing Heterophase Interfaces for Radiation Damage Resistance.
Michael Demkowicz 1 , Richard Hoagland 1 , John Hirth 2 , Amit Misra 2
1 MST-8: Structure-Property Relations Group, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 MPA-CINT: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe couple atomistic and continuum modeling with experiments to understand the connection between the structure of heterophase interfaces and the role they play as sinks for radiation-induced point defects. The insights we gain allow us to construct a general model of the effect of interfaces on radiation damage reduction and to propose strategies for the informed, interface structure-driven design of radiation tolerant nanocomposites.We acknowledge the support of the LANL Directed Research and Development program, a LANL Director's fellowship, and the DOE Office of Basic Energy Sciences.
12:00 PM - EE8.7/W10.7
Effects of Grain Size on Defect Evolution.
Yongfeng Zhang 1 , Hanchen Huang 1
1 Mechannical Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractGrain boundaries play a critical role to and evolution of radiation-produced defects. Several groups have examined the production and evolution of cascades in nanograins at the atomic level. In an effort to avoid the random production of cascades, particularly when only few cascades are produced in each simulation, we here examine the evolution of uniformly produced vacancies and interstitials in nanograins. Using classical molecular dynamics simulations, our results show that grain boundaries absorb more interstitials than vacancies, leaving the grains interiors to be vacancy rich. For crystals with small grain size, grain boundary absorption dominates defect annihilation. When grain size is smaller than 20 nm, most interstitials end up at grain boundaries and no interstitial clusters exist inside the grain after 100 ps. Beyond 20 nm, interstitial clustering becomes important.
12:15 PM - EE8.8/W10.8
Accelerating Copper Dissociated Dislocations to Transonic and Supersonic Speeds.
Paulo Branicio 1 , Hélio Tsuzuki 2 , José Rino 2
1 Materials Theory and Simulation Laboratory, Institute of High Performance Computing, Singapore Singapore, 2 Departamento de Física, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil
Show Abstract12:30 PM - EE8.9/W10.9
Atomic Scale Study of Effect of Nano-voids on Mechanical Properties of Nanocrystalline Metals.
Avinash Dongare 1 , Arunachalam Rajendran 2 1 , D. Brenner 3 , Mohammed Zikry 1
1 Mechanical Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , U. S. Army Research Office, Raleigh, North Carolina, United States, 3 Materials Science, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract12:45 PM - EE8.10/W10.10
Multi-physics Modeling for Dislocation and Hydrogen Coupled Evolution in BCC Iron.
Hideki Mori 1 , Hajime Kimizuka 1 , Shigenobu Ogata 1
1 Mechanical Science and Bioengineering, Osaka University, Osaka Japan
Show AbstractWe construct a numerical model of the coupled evolution of hydrogen-concentration and defect fields in iron based on a phase-field (PF) microelasticity theory, with coupling of the long-range elastic interactions and short-range chemical interactions that control hydrogen and dislocation motion. To obtain the physical parameters included in the PF free-energy functional, the interaction energy between a hydrogen atom and dislocation core, and the hydrogen-concentration dependence of misfit energy and eigenstrains are quantitatively determined using an embedded-atom-method (EAM) and density-functional-theory (DFT) calculations. Based on these data, we investigate an evolution of the hydrogen-dislocation interactions, and also a hydrogen diffusion and concentration around piled-up dislocations under applied stresses at various temperatures. It is clearly observed that the hydrogen is significantly localized and concentrated around dislocation cores, so that the remarkable difference exists in hydrogen concentration between in the bulk region and in the vicinity of dislocation cores, ranging from several weight ppm to several thousands weight ppm. Also, the spatial profile of trapped hydrogen around dislocations strongly depends on the stress field produced by dislocations. With increasing temperature, the trapped hydrogen escapes from dislocations and hydrogen concentration around dislocation cores steadily decreases. From our EAM and DFT results, the misfit energy of iron is remarkably lowered by the hydrogen impurity at high concentration. This fact brings the result that the distribution of hydrogen concentration affects the dislocation configurations mutually, and the width of dislocation core becomes broader due to the trapped hydrogen.
EE9/W11: Computational Nanomechanics II - Nanocrystals & Nanowires
Session Chairs
Thursday PM, December 04, 2008
Constitution B (Sheraton)
2:30 PM - **EE9.1/W11.1
The Limits of Strength in Materials at the Nanoscale: A Quantitative Description of Plastic Deformation in Computer Generated Nano-crystalline Cu.
Nhon Vo 1 , Robert Averback 1 , Pascal Bellon 1 , Alfredo Caro 2
1 Materials Science and Engineering, University of Illinois, Urbana-Champaign, Illinois, United States, 2 Chemistry, Materials, and Life Sciences, LLNL, Livermore, California, United States
Show AbstractUsing the concept of Richardson’s pairs developed to study turbulent flow, we construct an algorithm to quantify the contribution to plastic deformation in computer simulations of plasticity in nanophase metals originated in grain boundaries, in perfect and partial dislocations, and in formation of twins. We conclude that the competition between these mechanisms depends on strain rate and grain size. Contrary to the often-reported findings from computer simulation that metals soften as their grain sizes fall below 10-15 nm, we find an absence of such softening when the grain boundaries are suitably relaxed. Rather than “inverse” Hall Petch behavior, our calculations show that by thermally annealing the specimens prior to deformation, flow stresses either remain constant below 10 nm or even continue to increase as the grain size falls below even ~ 6 nm. These results provide a rationalization for why some experiments find an inverse Hall-Petch relationship at grain sizes below 10-20 nm while others do not, and they provide a key to resolving the long standing controversy concerning the limits of strength in materials at the nanoscale.
3:00 PM - EE9.2/W11.2
Annealing and Mechanical Response of Nanocrystalline Cu with and without Fe Impurities.
Diana Farkas 1 , Alfredo Caro 2 , Eduardo Bringa 2
1 Materials Science, Virginia Tech, Blacksburg, Virginia, United States, 2 Chemistry, Materials and Life Sciences, Lawrence Livermore National Lab, Livermore, California, United States
Show AbstractWe report fully three dimensional atomistic molecular dynamics studies of grain growth kinetics in nanocrystalline Cu of 5 nm average grain size. We observe the formation of annealing twins, including five fold twins as part of the grain growth process. The grain size and energy evolution was monitored as a function of time for various temperatures, yielding activation energy for the process. Annealing twins are formed during the grain growth process controlled by the emission of Shockley partial dislocations from the moving boundaries. We also report on the role played by Fe impurities in nanocrystalline Cu. We found a strong decrease in grain boundary mobility resulting in an enhancement of the stability of nanophase grain boundaries against annealing. Virtual tensile tests of samples with and without impurities performed using molecular dynamics techniques revealed a hardness that is unaffected by the presence of the Fe impurities.
3:15 PM - EE9.3/W11.3
Dislocation Activity Within Nanocrystalline Metals: A Molecular Dynamics Study.
Christian Brandl 1 , Erik Bitzek 1 , Peter Derlet 1 , Helena Van Swygenhoven 1
1 ASQ/NUM – Materials Science & Simulation, Paul Scherrer Institut, Villigen PSI Switzerland
Show AbstractThe use of large scale molecular dynamics to study the mechanical properties of FCC nanocrystalline (nc) metals provides a detailed picture of the atomic-scale processes during plastic deformation at room temperature. Simulations have revealed that grain boundaries can act as both sources and sinks for partial or full dislocations and that the surrounding grain boundary environment can significantly affect the motion of a dislocation as it propagates through the grain (Acta Mater. 54, 1975 (2006)). Simulations have recently revealed that cross-slip via the Fleischer mechanism occurs in nc-Al (Phys. Rev. Lett. 100, 235501 (2008)), and that the grain boundary structure is found to strongly influence when and where cross-slip occurs. It is found that cross-slip allows a dislocation to avoid local stress concentrations that would otherwise act as strong pinning sites for dislocation propagation. A statistical analysis of dislocation activity as a function of strain up to 9% total strain has also been performed (Acta. Mater. in press (2008)) revealing that (1) significant slip activity is only observed beyond the maximum flow stress whereas dislocation nucleation occurs at lower stresses indicating that propagation is the rate limiting process in simulation, (2) the resolved stress at which a slip event takes place can be correlated with the underlying dislocation process and (3) there is a distribution of critical resolved shear stresses at which slip is initiated. These results are discussed in the framework of realistic micromechanic models for nanocrystal plasticity.
3:30 PM - EE9.4/W11.4
Grain Growth of Metallic Nanocrystals: Insights from Molecular Dynamics.
Stephen Foiles 1
1 Computational Materials Science and Engineering Department, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractStructural evolution of nanograin metals critically impacts both the processing of these materials as well as their stability during use. This talk describes the evolution of the grain structure of nanograined Ni determined by molecular dynamics simulations of fully three-dimensional random grain structures with initial grain sizes ranging from 5 to 15 nm. These simulations provide important information for use in higher length scale models. In particular, we will discuss the mechanisms of twin boundary formation and the role of grain rotation in these systems.Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC0494AL85000.
3:45 PM - EE9.5/W11.5
Atomistic Modeling of the Interaction of Glide Dislocations with ‘Weak’ Interfaces.
Jian Wang 1 , Richard Hoagland 1 , John Hirth 1 , Amit Misra 1
1 , LANL, Los Alamos, New Mexico, United States
Show AbstractUsing atomistic modeling and anisotropic elastic theory, we have explored the interaction of glide dislocations with interfaces in a model Cu-Nb system. The incoherent Cu-Nb interfaces have relatively low shear strength and are referred to as ‘weak’ interfaces. Our work shows that such interfaces are very strong traps for glide dislocations and thus, effective barriers for slip transmission. The key aspects of the glide dislocation-interface interactions are as follows. (i) The weak interface is readily sheared under the stress field of an impinging glide dislocation. (ii) The sheared interface generates an attractive force on the glide dislocation, leading to the absorption of dislocation in the interface. (iii) Upon entering the interface, the glide dislocation core readily spreads into an intricate pattern within the interface. Consequently, the glide dislocations in both Cu and Nb crystals are energetically favored to enter the interface when they are located within 1.5 nm from the interface. Besides the trapping of dislocations in weak interfaces, we also discuss geometric factors such as the crystallographic discontinuity of slip systems across the Cu/Nb interfaces, which contribute to the difficulty of dislocation transmission across an interface. The implications of these findings to the unusually high strengths experimentally measured in Cu/Nb nanolayered composites are discussed.
4:00 PM - EE9/W11 joint 2
BREAK
4:30 PM - **EE9.6/W11.6
Incipient Plasticity and Creep of Nanowires, Nanopillars and Nanoparticles.
Eugen Rabkin 1 , Dan Mordehai 1 , Leonid Klinger 1 , David Srolovitz 2
1 Department of Materials Engineering, Technion, Haifa Israel, 2 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractWe report on a series of molecular dynamics simulations of the uniaxial compression of gold nanopillars and nanoparticles of various shapes and sizes. The yield stress of nanopillars observed in simulations is either a linear or parabolic function of temperature, depending on the choice of interatomic potential, nanopillar cross-section and/or nanopillar size. We suggest a simple yield nucleation criterion in which the nucleation of the first Shockley partial at the surface of a nanopillar occurs at a critical strain at the surface, which includes contributions from thermal vibration, elastic loading and thermal expansion. We demonstrate that the yield condition correctly describes the temperature dependence of the yield stress and locations of the surface nucleation sites of the Shockley partials observed in the full set of computer simulations. In the simulations of nanoparticles fixed on rigid substrate and compressed by a rigid punch, the first Shockley partials nucleate at the facet corners and at the topmost surface steps for faceted and rounded particles, respectively. The stacking faults produced by leading Shockley partial propagate toward the substrate and then spread along it. We demonstrate that plasticity is generated during the jump-in adhesive contact between the punch and the nanoparticle and discuss the geometry of the contact in terms of macroscopic theories of adhesion. We also consider the diffusional creep deformation mechanisms of nanowires and nanoparticles at the stresses below their yield stress taking into account stress-driven diffusion along the grain boundaries and punch-particle interface. Diffusion creep represents a viable deformation mechanism of gold nanoparticles at the temperatures above 500 K.
5:00 PM - EE9.7/W11.7
Predicting the Elastic Modulus of Nanowires from First-principles Density Functional Theory Calculations on Their Surface and Bulk Materials.
Guofeng Wang 1 , Xiaodong Li 2
1 Department of Mechanical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States, 2 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractNano-devices employ nanowires as their active components to generate, transmit, and convert powers and motions. Hence, the dependence of their mechanical properties on their geometric size is a very important factor in determining the performance of nanowires in those devices. So far, several different fashions of the size dependence of the elastic properties of nanowires have been revealed: (1) elastic modulus increases with the decreasing size, for examples, in Ag and Pd nanowires; (2) elastic modulus decreases with the decreasing size, for examples, in ZnO and GaN nanowires; and (3) elastic modulus shows little dependence of the size of the nanomaterials such as Au nanowires. In this work, we combined first-principles density functional theory calculations with linear elasticity theory. Using the concept of surface stress, we developed a model that is able to predict the elastic modulus of the nanowires as a function of their diameters based on the calculated properties of its surface and bulk materials. Furthermore, we applied this computation approach to Ag, Au, and ZnO nanowires. For both Ag and Au nanowires, our prediction results agree excellently with the experimental data in the literature. For ZnO nanowires, our predictions are qualitatively consistent with some of experimental data for ZnO nanobelts. Therefore, we found that surface stress plays a very important role in determining the elastic modulus of nanowires. Our finding suggests that the elastic properties of nanowires could be engineered by altering the surface stress through rational control of the adsorptions, charges, structure, and impurities in the surfaces.
5:15 PM - EE9.8/W11.8
Structural Study of the Formation of Linear Atomic Suspended Chains from Platinum Nanowires Stretching.
Pedro Autreto 1 , Fernando Sato 1 , Pablo Coura 3 , Socrates Dantas 3 , Varlei Rodrigues 1 , Daniel Ugarte 1 2 , Douglas Galvao 1
1 , State University of Campinas, Campinas/SP, São Paulo, Brazil, 3 , UFJF, Juiz de Fora, MG, Brazil, 2 , LNLS, Campinas, SP, Brazil
Show AbstractIn the last years a considerable number of experimental and theoretical studies has been devoted to metallic nanowires (NWs) and suspended atomic chains (LACs) [1]. NWs and LACs have attracted a great interest due to observation of very interesting physical phenomena, such as spin filters, quantized conductance, etc., with possible technological applications in diverse areas of nanotechnology. Atomic-size NMs generated by stretching can provide a wealth of information on the elasticity of metallic nanostructures.In this work we report results from the study of the atomistic aspects of the elongation and rupture of Pt NWs using real-time atomic-resolution transmission electron microscopy (dynamical HRTEM) and molecular dynamics (MD) simulations. We used tight-binding molecular dynamics (TB-MD) techniques with second-moment approximation (SMA), a methodology that has been proved to be very effective to study pure and alloy metallic nanostructures [2,3].We have carried out a systematic study of the structural properties of NWs and LACs formed from Pt nanostructures under simulated mechanical stretching. We have considered different crystallographic orientations ([100], [110] and [111]) for the pulling directions. Diverse parameters such as temperature, cluster size (up to ~ 400 atoms), and speed of pulling were varied in order to determine their relative importance to the LAC formation.Our results are in good agreement with the structural information data from HRTEM experiments. For defectless structures the LAC formation is statistically favored for [110], followed by [100] and [111], respectively. One interesting result is that when we have mismatched boundary grains (structures with different crystallographic orientations) this favors the LAC formation for all cases investigated. The disorder increases the probability of LAC formation and structures type “triple helix” in general appears before the final stages prior to LAC formation. It remains to be investigated whether this is a specific feature of Pt NWs or a general behavior for other metallic NWs.Work supported in part by the Brazilian Agencies CAPES, CNPq, FAPEMIG, and FAPESP.[1] N. Agrait et al, Phys. Rep. 377, 81 (2003).[2] V. Rodrigues, F. Sato, D. S. Galvão, and D. Ugarte, Phys. Rev. Lett. 99, 255501 (2007).[3] J. Bettini, F. Sato, P. Z. Coura, S. O. Dantas, D. S. Galvão, and D. Ugarte, Nature Nanotechonology 1, 182 (2006).
5:30 PM - EE9.9/W11.9
Torsion and Bending Simulations of Metallic Nanowires.
Christopher Weinberger 1 , Wei Cai 1 , William Fong 1 , Erich Elsen 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show Abstract5:45 PM - EE9.10/W11.10
Mechanisms of Dislocation Depletion in Small-volume Structures of FCC Metals.
Kedarnath Kolluri 1 , M. Rauf Gungor 1 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Amherst, Massachusetts, United States
Show AbstractRecent experimental studies on nanometer-scale face-centered cubic (fcc) metals have shown that the strength of such fcc small-volume structures increases with decreasing characteristic lengths and that the dislocation density always decreases during the application of the strain. The nearly defect-free crystal then deforms elastically until new dislocations nucleate. Furthermore, comparative studies of nanometer-scale pillars of fcc and body-centered cubic (bcc) metals showed that dislocation depletion and ultra-high strength is almost exclusive to fcc metals. This suggests that the differences in the fundamental processes of dislocation motion and dislocation-dislocation interactions between nanoscale fcc and bcc metals play an important role in determining their mechanical behavior. These fundamental atomic-scale mechanisms, however, are difficult to observe and analyze experimentally.In this presentation, we report an atomic-scale analysis of the mechanisms of dislocation depletion in small-volume structures of fcc metals, focusing on free-standing ultra-thin copper films that are subjected to biaxial tensile strain. Our study is based on large-scale molecular-dynamics simulations at constant temperature and high strain rate, using an embedded-atom-method parameterization to describe the interatomic interactions. Our analysis of the films' mechanical response to the applied tensile strain reveals three stages of deformation. During the first stage, most of the dislocations in the material are unpinned; these dislocations glide under the application of biaxial strain in such a direction that they unzip the stacking faults they bound and the dislocation networks that they are a part of. With the stacking fault area reduced, there are fewer barriers to dislocation glide in the thin films. Consequently, the remaining dislocations glide faster and farther. During the second stage, gliding dislocations interact with the stacking faults formed by other dislocations. These interactions lead to dislocation dissociation and cross-slip and they aid in dislocation annihilation. We have identified three classes of dislocation-stacking fault interactions where the stacking faults act as barriers to dislocation glide and as sources for dislocation cross-slip. As the dislocation density decreases, the thin film's strength increases significantly and its mechanical behavior is observed to be closer to that of an elastic solid. In the third deformation stage, continued application of strain leads to an increase in the film's stress and, eventually, to nucleation of new dislocations in the thin film. Dislocation nucleation and depletion through dislocation-stacking fault interactions in the thin film continue in cycles until the failure of the film.
EE10: Poster Session: Nanomechanical Behavior and Modeling
Session Chairs
Friday AM, December 05, 2008
Exhibition Hall D (Hynes)
9:00 PM - EE10.1
Anomalous Mechanical Responses of Nanoporous Structures: Surface Free Energy Effect.
Gang Ouyang 1 2 , Yan Wang 1 , Dongsheng Tang 2 , Chang Q Sun 1 , Weiguang Zhu 1
1 , School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore Singapore, 2 , College of Physics and Information Science, Hunan Normal University, Changsha 410081 China
Show Abstract9:00 PM - EE10.10
Molecular Dynamics Simulations of Mechanically-driven Phase Transformations in Nanocrystalline Nickel.
Zhiliang Pan 1 , Xiyan Zhang 2 , Xiaolei Wu 3 , Qiuming Wei 1
1 Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, Charlotte, North Carolina, United States, 2 School of Materials Science and Engineering, Chongqing University, Chongqing, Chongqing, China, 3 State Key Lab of Nonlinear Mechanics, Institute of Mechanics, CAS, Beijing China
Show Abstract9:00 PM - EE10.11
Stress Relaxation in a Nanoinclusion in Respond to Extreme Environments.
Vladimir Chaldyshev 1 , Anna Kolesnikova 2 , Alexei Romanov 1
1 , Ioffe Institute, St.Petersburg Russian Federation, 2 , Institute of Problems of Mechanical Engineering, St.Petersburg Russian Federation
Show AbstractMaterials with nanoinclusions have attracted a lot of attention due to their mechanical, electronic and optical properties. The mechanical behavior of such materials depends substantially on the mechanisms of plastic deformation of these inhomogeneous media as a whole and elementary processes of stress relaxation near an individual nanoinclusion. We consider a stressed nanoinclusion in a crystalline matrix, which is initially coherent, but may relax through local plastic deformation under an impact of heat, mechanical load, irradiation, electric or magnetic fields. The reason for the relaxation process is an increase in the mechanical energy of the inclusion, when the environment conditions are drastically changed. Based on the analysis of the mechanical fields in and around a nanoinclusion along with the material conservation law we propose a model of the local stress relaxation, in which the reduction in the total mechanical energy is achieved by formation of a satellite dislocation loop nearby the inclusion and simultaneous formation of a local or splitted misfit dislocation at the interface between the nanoinclusion and matrix. Theoretical analysis of the model for different experimental cases allow us to predict a threshold for the relaxation process and a correlation between the size of the nanoinclusion and the diameter of the satellite dislocation loop. The developed model has been verified by comparison with available experimental data. In particular, for the system of AsSb nanoinclusions in GaAs subjected to high-temperature heat treatment the model calculations were found to be in a good qualitative and quantitative agreement with observations by transmission electron microscopy.
9:00 PM - EE10.13
Modeling of Nanoimprinting of Metals by Nanotube Arrays.
Lili Li 1 , Zhenhai Xia 1 , Yanqing Yang 2
1 Department of Mechanical Engineering, University of Akron, Akron, Ohio, United States, 2 School of Materials, Northwestern Polytechnic University, Xi'an China
Show AbstractNanoimprinting is a simple technique that can generate nanometer patterns over a large area. It provides not only high resolution but is also cheap and creates high throughput nanopatterns. Directly transferring high-density nanopatterns into thin metal or other films is very attractive in the applications such as nanofiltration, and nanoscale device fabrication. In the nanoimprint process, there are two key issues: exact deformation of a film according to stamp patterns and clear separation of the stamp from the film. To achieve successful pattern transfers, it is required to understand the deformation behavior of metal films as well as effects of adhesion and friction and to investigate effects of pattern aspect ratios. We have developed a Molecular dynamics (MD) model to simulate deep nanoindentation/nanoimprinting of a copper substrate using a carbon nanotube arrays with sp3 bonds. The effect of interfacial friction on the defects of pattern transfer in nanoimprinting is analyzed by the MD model.
9:00 PM - EE10.14
Chemo-Mechanics Model of Adsorption Induced Strain in Microporous Solids.
Samir Mushrif 1 , Alejandro Rey 1
1 Chemical Engineering, McGill University, Montreal, Quebec, Canada
Show AbstractDeformation of porous carbonaceous materials during adsorption of gases is an experimentally observed phenomenon. Active carbons exhibit both, compression and dilation, at different stages of adsorption. A new model based on thermodynamics of porous continua is employed tocalculate adsorption-induced strain in a porous adsorbent, which is assumed to be linear, isotropic and poroelastic.A relationship between the strain induced in the solid and the equilibrium thermodynamic properties of the adsorbed gas is established. Experimental data of carbon dioxide adsorption-induced strain in microporous carbon adsorbents, by Yakovlev et al. [Russ. Chem. Bull. Int. Ed., 54, 2005], is used to fit the model parameters and also to validate the model.The model has potential to analyze storage and separation processes for energy and environmental material applications.
9:00 PM - EE10.15
Atomistic+Continuum Multi-scale Modeling of a Single Asperity Gold-Gold Contact in an RF MEMS Device.
Wes Crill 1 , D. Irving 1 , C. Padgett 3 , M. Zikry 2 , D. Brenner 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Department of Chemistry and Physics, Armstrong-Atlantic University, Savannah, Georgia, United States, 2 Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe gold contacts of failed RF MEMS devices often show what appear to residual structures associated with melted and re-solidified asperity tips. The cause of these features is not yet understood, but it has been suggested that the formation of nanowires during contact pull-out could be a precursor to this behavior. To understand the details of nanowire formation in gold-gold RF MEMS contacts, we have carried out simulations of the pull-apart of a single asperity contact using large-scale molecular dynamics simulations coupled to a continuum treatment of Joule heating and heat transfer. The initial asperity geometry, which was derived from a finite element fractal model of a contact blunted by plasticity, contained a 550 nm2 asperity on a 7500 nm2 substrate that is brought into contact with another flat substrate of the same size. As the contact is pulled apart, the simulations show dislocation emission in the substrate surrounding the asperity contact as well as a nanowires being drawn between the surfaces. These wires act as favorable sites from which atoms can be evaporated due to the electric field produced with an applied current. The resultant ions follow the field and are transferred to the surface below. The correlation between the nanowire formation and the field desorption mechanism will be discussed and compared to experimental structures observed for hot switching of gold MEMS. This work was supported by the Office of Naval Research and the Extreme Friction Multi-University Research Initiative sponsored by the Air Force Office of Scientific Research.
9:00 PM - EE10.16
Nanoindentation Measurement of the Elastic Modulus and Hardness of Ultra-thin Films on Substrate.
Han Li 1 , Joost Vlassak 1
1 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractDepth-sensing indentation, also known as nanoindentation is widely used for measuring the mechanical properties of solids in various forms at small scale. While the mechanics models for analyzing bulk indentations are well established, obtaining true film properties remains a challenging problem for films on substrates. Here we present data analysis procedures developed to estimate the contact area for an elastoplastic indentation of a thin film bonded to a substrate, and to derive the "true" elastic modulus and hardness of the film from indentation load, displacement, and contact stiffness data at moderate depth. These procedures are based on the application of Yu's elastic solution for the indentation of a layered half-space with a rigid conical punch in a similar manner as theOliver-Pharr method utilizes Sneddon's elastic solution for the indentation of a homogeneous half-space. This methodology has been demonstrated with good accuracy for both compliant films on stiff substrates and for thereverse combination.
9:00 PM - EE10.18
Free Edge and Heterophase Interface Effects in Nanoindentation.
Joseph Jakes 1 2 , Chuck Frihart 1 , James Beecher 1 , Robert Moon 1 , Donald Stone 2 3
1 , USDA Forest Products Laboratory, Madison, Wisconsin, United States, 2 Materials Science Program, University of Wisconsin, Madison, Wisconsin, United States, 3 Materials Science and Engineering, Unversity of Wisconsin, Madison, Wisconsin, United States
Show AbstractIt is sometimes of interest to use nanoindentation to measure the properties of a material near a free edge or near a heterophase interface which intersects the specimen surface. Up until now, however, it has not been possible to obtain unambiguous nanoindentation data in this kind of measurement because the abrupt change in properties associated with the edge or interface introduces artifacts into the measurement even if the nanoindent does not overlap the edge or interface. In this work we demonstrate experimentally that the predominate consequence of a free edge or heterophase interface is to introduce a structural compliance (Cs) into the measurement. Like the machine compliance, Cs is independent of the size of the indent and it adds to the measured unloading compliance; but unlike the machine compliance, Cs varies sensitively as a function of position in the specimen. Cs can even be negative if the nearby phase is stiffer than the phase being tested. Therefore, Cs must be determined independently at each indent location in order for this artifact to be removed from the data analysis. To address this problem we develop an experimental approach to account for Cs in nanoindentation measurements so that the hardness and modulus can be determined with a minimum of error. We perform experiments on silicon and fused silica. Results from experiments studying edge effects are in good agreement with elasticity theory. The structural compliance varies in inverse proportion to the distance from the edge or heterophase interface. The method even works near the edge of a layered specimen.
9:00 PM - EE10.19
Estimating Uncertainty of Measurement on Instrumented Indentation Technique with Round-robin Test.
Eun-chae Jeon 1 , Joo-Seung Park 2 , Doo-Sun Choi 1 , Dongil Kwon 3
1 , Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 , Korea Agency for Technology and Standards, Gwacheon Korea (the Republic of), 3 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe instrumented indentation technique which measures indentation tensile properties attracts much interest because the technique can replace uniaxial tensile test. In virtue of many related researches, the legislation of international standard is on progress. However, the uncertainty of indentation tensile properties has never been estimated, which is essential for the legislation. It is very hard to estimate the uncertainty of the indentation tensile properties because the indentation tensile properties cannot be obtained by experimental raw data directly but by complex calibrations and calculations. A simplifying uncertainty estimation model was proposed in order to overcome this problem, and the model was verified by round-robin test (RRT) with several institutes in this study. The variables of final constitutive equations of the indentation tensile properties were regarded as experimental raw data though the variables can be obtained after the calibrations and the calculations. The average uncertainties of indentation tensile properties on instrumented indentation test from the RRT were estimated within reasonable range. The values were independent of materials’ mechanical properties, however, varied with environmental conditions. They were larger than the uncertainty on uniaxial tensile test because of measuring local properties of the instrumented indentation technique.
9:00 PM - EE10.2
Studies of the Elastic Properties of Amorphous SiO2 Nanoballs by Molecular DynamicsSimulations.
Heikki Ristolainen 1 , Antti Kuronen 1 , Kai Nordlund 1 , Masaki Fujikane 2 3 , Roman Nowak 3
1 Department of Physics, University of Helsinki, Helsinki Finland, 2 Division of Sustainable Energy and Environmental Engineering, University of Osaka, Osaka Japan, 3 Nordic Hysitron Laboratory, Helsinki University of Technology, Helsinki Finland
Show AbstractAmorphous silica (a-SiO2) is used very commonly in optical fibres and as an insulatingmaterial in silicon-based metal-oxide-semiconductor devices. As the downscaling of electroniccomponents goes further, it is essentially important to understand how the elasticproperties of the materials in them are altered in nanoscale. The strength of a macroscopicbody is mainly related to the interatomic bonds between its constituents, or in other words,its bulk energy. However, as the size of an object becomes small, its surface-to-volumeratio increases drastically, implying that the role of the surface energy on its elasticitybecomes substantial [1]. This interesting feature is commonly referred to as the nanosizeeffect.Recent indentation experiments [2] manifest a remarkable increase in Young’s modulus ofnanosized a-SiO2 balls as compared to the properties of the bulk material. In literature, thevalue of Young’s modulus for bulk a-SiO2 is 72 GPa, whilst for a 50 nm radius nanoballit was measured to be almost three times as high. This stands for a remarkable indicationof novel behaviour appearing at small scales.In order to analyse the experimental results and examine the atomistic level phenomenaresponsible for the strengthening, we use molecular dynamics simulations. By simulatingthe compression of nanoballs and using different contact models, we define the elasticproperties of perfect a-SiO2 bulk structure [3] and various sized nanoballs, and compare them to the data obtained from experiments.[1] R. E. Miller and V. J. Shenoy, Nanotechnology 11, 139-147 (2000)[2] M. Fujikane and R. Nowak, unpublished[3] K. Nordlund and F. Djurabekova, Phys. Rev. B 77, 115325 (2008)
9:00 PM - EE10.20
Influence of Indenter Geometry on the Nanoindentation-Induced Plasticity Evolution in Bulk Metallic Glasses.
Jae-il Jang 1 , Young-Wook Park 1 , Byung-Gil Yoo 1 , Byoung-Wook Choi 1 , So-Jung Kwon 1
1 Division of Materials Science and Engineering, Hanyang University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - EE10.21
Structural and Nanotribological Properties of Carbon-Implanted Silicon Scanning Probe Tips.
Papot Jaroenapibal 1 , Sean O'Connor 2 , Yun Chen 2 , Kumar Sridharan 2 , Kevin Turner 2 , Mark Lantz 3 , Bernd Gotsmann 3 , Robert Carpick 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , IBM Research GmbH, Zurich Research Laboratory, Zurich Switzerland
Show Abstract9:00 PM - EE10.22
Nanoindentation Analysis as a Two-dimensional Tool for Mapping the Mechanical Properties of Complex Surfaces.
Nicholas Randall 1
1 , CSM Instruments, Needham, Massachusetts, United States
Show AbstractInstrumented indentation (referred to as nanoindentation at low loads and low depths) has now become established for the single point characterization of hardness and elastic modulus of both bulk and coated materials. This makes it a very good technique for measuring mechanical properties of homogeneous materials. However, many composite materials comprise material phases that cannot be examined in bulk form ex-situ (e.g., carbides in a ferrous matrix, calcium silicate hydrates in cements, etc.). The requirement for in-situ analysis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. This paper will focus on new developments in the way that nanoindentation can be used as a two-dimensional mapping tool for examining the properties of constituent phases independently of each other. This approach relies on on large arrays of nanoindentations (known as grid indentation) and statistical analysis of the resulting data. Examples will be presented ranging from soft polymer blends to metal-matrix composites. Additional analysis of the influence of the separation between consecutive indentations will also be presented.
9:00 PM - EE10.23
Investigating the Applicability of Soft Metals as the Calibration Materials in Nanoindentation Measurements.
Keerthika Balasundaram 1 , Yanping Cao 1 , Dierk Raabe 1
1 , MPIE, Düsseldorf Germany
Show Abstract9:00 PM - EE10.25
Particle-Matrix Interaction in Al/AlB2 Composites Measured by Nanoindentation.
Zenon Melgarejo 1 , Pedro Resto 1 , Donald Stone 2 1 , Marcelo Suarez 3
1 Material Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering Dept., University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Dept. of Engineering Science & Materials, University of Puerto Rico-Mayagüez, Mayagüez, Puerto Rico, United States
Show Abstract9:00 PM - EE10.26
Measuring Residual Stress in Glass using Instrumented Indentation.
Thomas Buchheit 1 , Rajan Tandon 2
1 Computational Materials Science and Engineering, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Materials Reliability, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - EE10.27
High Temperature Mechanical Properties of Electroplated Ni Thin Film by Micro Tensile Testing.
Seungwoo Han 1 , Taeok Kim 2 , Seungmin Hyun 1 , Hakjoo Lee 1 , Hyunwoo Lee 2
1 Nano mechanical systems research division, KIMM, Daejeon Korea (the Republic of), 2 School of mechanical engineering, Pusan National University, Pusan Korea (the Republic of)
Show Abstract9:00 PM - EE10.28
X-ray Laue Micro Diffraction and Neutron Diffraction Analyses of Residual Elastic Strains and Plastic Deformation in a 1% Uniaxial Tensile Tested Nickel Alloy 600 Sample.
Marina Suominen Fuller 1 , Jing Chao 1 , Alison Mark 3 , Rozaliya Barabash 4 , Stewart McIntyre 1 , Rick Holt 3 , Robert Klassen 2 , Wenjun Liu 5
1 Chemistry Department, University of Western Ontario, London, Ontario, Canada, 3 Department of Mechanical and Materials Engineering, Queen's University, Kingston, Ontario, Canada, 4 Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario, Canada, 5 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe state of local and global strain within a 1% plastically strained nickel alloy 600 (A600) sample, and a control sample, were measured by diffraction using a polychromatic x-ray beam from a synchrotron source, and by using neutrons. Laue x-ray micro diffraction measurements were made at Beamline 34-ID-E at the Advanced Photon Source (APS). Neutron diffraction was carried out at the Canadian Neutron Beam Centre (CNBC). Measurements of the lattice spacing of four sets of low index crystal planes were made in five directions. The x-ray micro-diffraction provides data on the local variations in the interplanar spacing with a spatial resolution of one µm at a depth of up to 100 µm within the sample while the neutron diffraction provides data on the average interplanar spacing for each measurement direction within the bulk sample. Both the Laue x-ray micro-diffraction and the neutron diffraction data indicated that the global residual elastic strain was on the order of 1.0 x 10-4 within the 1% plastically strained sample, however the micro-diffraction data indicated that considerable grain-to-grain variability exists amongst individual components of the residual strain tensor. The x-ray Laue micro diffraction data were also used to assess the extent of local plastic deformation within the 1% plastically strained sample. Local plastic deformation resulted in some grains having significantly distorted (streaked) Bragg reflection spots compared to their neighboring grains. Seven streaked diffraction spots from one grain were simulated using the statistical analysis of streaked Laue pattern. The streaked Laue patterns are calculated taking into account atomic displacements due to superposition of displacement fields caused by all dislocations within the diffracting region. The close fit between the simulation and the measured shape of the seven spots suggests that the local plastic flow within this grain occurs by dislocation glide on two slip systems having the same Burgers vector: b=[1-1 0] and dislocation lines: τ1=[-1-1-2] and τ2=[-1-1 2] resulting in the overall rotation around the [-1-1 0] axis. At some specific locations 3D measurements with differential aperture technique were performed to get an understanding about the depth dependent distribution of geometrically necessary dislocations.Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Use of the CNBC facility was supported by the NSERC Major Resources Support Grant. The research at University of Western Ontario and Queen’s University was supported by funding from the Candu Owners Group (COG) and the Ontario Centres of Excellence (OCE) through the Collaborative Research and Emerging Materials Knowledge (EMK) programs. The research at ORNL was supported by the Division of Materials Science and Engineering, Office of Basic Energy Science U.S. Department of Energy.
9:00 PM - EE10.29
Multi-Million Atoms Molecular Dynamics Study of Combustion Mechanism of Aluminum Nanoparticle.
Weiqiang Wang 1 , Richard Clark 1 , Aiichiro Nakano 1 , Rajiv Kalia 1 , Priya Vashishta 1
1 Mork Family Department of Chemical Engineering and Materials Science, university of southern california, Los Angeles, California, United States
Show AbstractReaction of oxygen with aluminum nanoparticle under extreme environment is studied using multi-million atoms molecular dynamics (MD) simulations. In our simulations, the aluminum nanoparticle is coated with either crystalline or amorphous alumina shell and ignited by heating the aluminum core to extreme high temperatures, as is done in the experiments of flash heating aluminum nanoparticles using lasers. The metal aluminum and ceramic alumina are modeled by Voter-Chen’s EAM potential form and Vashishta et al.’s potential form, respectively. Oxidation of aluminum atoms is modeled by using a bond-order scheme, which is validated by comparing various optimized AlnOm molecular structures to those from quantum mechanical calculations. Structural and dynamical behavior, and atomic level details of the combustion of an aluminum nanoparticle are investigated. The effects of initial aluminum core temperature and alumina shell structure on the combustion efficiency and energy release rate of aluminum nanoparticle are discussed. Three mechanisms involved in the combustion of aluminum nanoparticle are observed in the simulations. These are: diffusion, ballistic transport followed by diffusion, and ballistic transport followed by coalescing of atoms into few-atom clusters.
9:00 PM - EE10.3
Meso-scale Harmonic Analysis of Homogeneous Dislocation Nucleation.
Asad Hasan 1 , Craig Maloney 1
1 Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractUnder sufficiently high loads, dislocations will be nucleated in perfect crystals. A typical scenario is the nano-indentation of a defect-free metal. An outstanding issue is the prediction of where and under what loads nucleation will occur. Many criteria have been put forward which address this question, some in terms of the local stress field, others in terms of the local tangent stiffness of the material. More recently it has been questioned whether a local criterion can be used at all [1]. We address the locality of the nucleation process via analysis of molecular dynamics simulations in terms of the vibrational eigenmodes of mesoscale regions of the crystal for various model systems.[1] R.E. Miller and D. Rodney, J. Mech. Phys. Solids 56 (4) 1203-1223, 2008.
9:00 PM - EE10.30
Utilization of Electrokinetics to Improve B4C Sintering for High Strain Rate Deformation Applications.
Joseph Buchanan-Vega 1 , Henry Cardenas 2 , Naidu Seetala 3 , Tabbetha Dobbins 1 3
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Applied Electrokinetics Laboratory, Nanosystems Engineering, Louisiana Tech University, Ruston, Louisiana, United States, 3 Physics, Grambling State University, Grambling, Louisiana, United States
Show Abstract9:00 PM - EE10.31
High Temperature Thermographic Measurements of Laser Heated Silica.
Selim Elhadj 1 , James Stolken 1 , Vaughn Draggoo 1 , Jeff Jarboe 1 , John Adams 1 , Jeff Bude 1 , Jeff Colvin 1 , Steven Yang 1 , Manyalibo Matthews 1
1 National Ignition Facility, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractPredictions of the behavior of heated materials, such as evolution of stress and morphology, require knowledge of the temperature profile and history during thermal treatment. This requirement is not surprising since the driving force for changes in the state of the heated material and the material properties are both strong function of temperature. We present in situ thermographic temperature measurements of fused silica surface heated with 4.6 and 10.6 μm laser radiation. Surface temperature measurements were obtained with μm-scale and ms resolution, and from room temperature up to ca. 2500K. Non-linear thermal diffusion model was then used to derive an effective thermal conductivity that can predict the spatial and temporal temperature evolution in the bulk and on the surface of silica. Thermocouple-based in situ temperature measurements within the bulk of silica confirmed the model predictions providing a self consistent model constrained by data. For 10.6μm laser beam diameters between 100 μm and 1 mm and for exposure times approaching steady state, the scaling behavior of temperature on spot size and laser power shows very little non-linearity, indicating minimal contribution from radiation heat transport contrary to previous predictions. Thermal conductivity estimates show reasonable agreement with classical calculations based on purely phonon transport. However, because of the longer absorption lengths below 5μm, the contribution from radiation heat transport for 4.6μm irradiated surfaces becomes significant as is observed experimentally. For all laser wavelengths and above ~1500K, the temperature rises more slowly with increasing absorbed power, indicating the onset of evaporative cooling, which was determined experimentally from thermal and pit depth data. Estimates of maximum temperatures based on pit depth data showed good agreement with temperatures derived from pyrometric measurements, indicating that the latter can effectively be used even during silica evaporation. These results, in defining the proper computational model and diagnostics, are important to improve control, and thus performance, in applications requiring local heating of silica-based glasses such as laser polishing, optical damage repair, and micro-optical fabrication.
9:00 PM - EE10.4
First Principles Study on Formation of Grain Boundaries by Severe Plastic Deformation.
Masato Yoshiya 1 , Hiroki Yoshizu 1
1 , Osaka University, Suita, Osaka, Japan
Show AbstractSevere plastic deformation (SPD) brings about the two phenomena: the increase of dislocation density and the division of existing grain, i.e., formation of new grain boundaries. Besides, small amount of impurities strongly alters these phenomena. Although each phenomenon has been extensively studied by experiments, their correlation is still unclear, since these phenomena can be observed and analyzed at each SPD cycle but many things can happen within one cycle. This is an impediment to further control the microstructure to optimize resulting mechanical properties. In the present study, first principles calculations of Al tilt grain boundaries have been carried out in a systematic way, in order to reveal atomistic mechanism of grain boundary formation due to alignment of dislocations generated by SPD process. It is found, from the systematic survey with various atomic arrangements at a given tilt angle, that, at medium to high angle tilt grain boundaries, exactly same kite-shaped atomic arrangement prevailed, exhibiting minimal grain boundary energy, and only distance between the kite-shaped polygons was changed, similarly to the dislocations at low angle tilt grain boundary. In addition, at medium to high angle tilt grain boundaries, even if structural optimization was carried out with the initial atomic arrangements in which dislocations were placed in a zigzag manner as in low angle tilt grain boundary (glide model), the optimized structure had the exactly same kite-shaped polygons. This indicates that, in spite of the difference between a dislocation and a kite-shaped polygon, energy barrier for the transfer from one to the other is small, implying that a kite-shaped polygon is easily transformed to individual dislocations under external stress. Generally, low angle tilt grain boundary is represented by alignment of dislocations while high angle tilt grain boundary is represented by CSL model. The present results show that there is not so much difference between them from energetical points of view, and thus, its mechanical properties can be understood in the extension of dislocation theories, if dislocation core region is appropriately treated.
9:00 PM - EE10.5
Mechanical Properties in Individual Carbon Nanofibers at High Temperature and High Pressure by Molecular Dynamics Simulations.
Jingjun Gu 1 , Frederic Sansoz 1
1 , The University of Vermont, Burlington, Vermont, United States
Show AbstractCarbon nanofibers (CNFs) are high-strength, high-modulus nanomaterials that open up new ways to improve the thermo-mechanical resistance of carbon-based nanocomposites used by NASA as thermal protection systems in hypersonic vehicles. The deformation and fracture mechanisms of CNFs under extremely-high temperature and pressure, however, is not fully understood, because it is experimentally very difficult to characterize the microstructure evolution and mechanical properties of CNF-based composites under such conditions. The objective of this study is to model the effects of microstructure and size on elastic and plastic behavior in an individual CNF at high-temperature using molecular dynamics simulations. Atomistic models of cone-stacked CNFs with single or multishell nanocones and different apex angles are investigated. We also use the AI-REBO interatomic potential for carbon atoms, which is found to provide a better modeling of behavior in CNFs. Fiber diameters from 2 – 30 nm and temperatures ranging from 300 K to 2000 K are systematically studied, along with the changes in plastic deformation mechanisms. The findings of this study provide a predictive understanding of size effects on high-temperature mechanical properties in CNFs, which may help optimize the design of CNF-based nanocomposites.
9:00 PM - EE10.6
First-principles Study of the Mechanical Properties of Metallic Grain Boundaries Using Local Energy Density and Local Stress Density.
Masanori Kohyama 1 , Ruzhi Wang 1 , Yoshinori Shiihara 2 , Shingo Tanaka 1 , Tomoyuki Tamura 2 , Shoji Ishibashi 2
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan, 2 Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology, Dublin 2 Ireland
Show AbstractGrain boundaries have serious effects on the mechanical properties of metallic materials as barriers of dislocation transmission or as sources or sinks of dislocations. This feature is greatly enhanced in nano- or sub-micron grained metals formed by severe plastic deformation via the procedures of ECAP or ARB [1], revealing peculiar mechanical properties such as co-existence of hardness and ductility. In such systems, grain-boundary regions dominate substantial volume ratio and there are only few movable dislocations inside grains. And thus the response or deformation of grain boundary regions for applied stresses and the dislocation nucleation at grain boundaries directly dominate the macroscopic mechanical behavior. In this way, the understanding of the primary behavior of metallic grain boundaries under various tensile or shear stresses is crucial. For this purpose, first-principles tensile or shear testing simulations of grain boundaries have made valuable contributions [2]. Recently, this kind of computations is applied to systems with impurity segregations. On the other hand, it is desirable to deal with both the electronic and mechanical properties more effectively and directly. For this purpose, recently we have developed computational codes for local energy density [3] and local stress density [4] within the framework of the PAW scheme in our QMAS (Quantum MAterials Simulator) code [5]. In this study, we apply first-principles tensile tests to coincidence tilt and twist boundaries in Al and Cu, and perform detailed analysis using local energy and stress densities. The problems of gauge-dependence in the energy and stress densities are analyzed. We have found that the interfacial bonding nature is substantially different for grain boundaries in Al and Cu, due to the different electronic structures of Al and Cu. This study was supported by MEXT program "Giant Straining Process for Advanced Materials Containing Ultra-High Density Lattice Defects", and by Next Generation Super-Computing Project, Nanoscience Program, MEXT, Japan. [1] Z. Horita et al., Adv. Mater. 17 (2005) 1599, X. Huang et al., Science 312 (2006) 249, [2] C. Molteni et al., Phys. Rev. Lett. 79 (1997) 869 ; M. Kohyama, Phys. Rev. B 65 (2002) 184107; G.H. Lu et al., ibid. 73 (2006) 224115; [3] N. Chetty and R.M. Martin, Phys. Rev. B 45 (1992) 6074; [4] A. Filippetti and V. Fiorentini, Phys. Rev. B 61 (2000) 8433; [5] S. Ishibashi, T. Tamura, S. Tanaka, M. Kohyama and K. Terakura, unpublished; http://www.qmas.jp.
9:00 PM - EE10.7
Molecular Dynamics Simulation of Straining of Nanocrystalline Palladium.
Dmitriy Bachurin 1 , Peter Gumbsch 1 2
1 , Institut für Zuverlässigkeit von Bauteilen und Systemen, Karlsruhe Germany, 2 , Fraunhofer Institut für Werkstoffmechanik, Freiburg Germany
Show AbstractGrain interior and grain boundaries contribute to a deformation of nanocrystalline materials. Previous simulations on aluminum and nickel have revealed that a change of grain size leads to a transition from intergranular deformation mechanisms, caused mainly by grain boundary sliding, to an intragrain mechanism caused by a motion of full and partial dislocations. In the present work, an Embedded Atom Method potential for palladium is used to study deformation mechanisms in nanocrystalline structures that have previously been investigated for aluminum. The 3D sample contains 100 randomly oriented grains with mean grain size of 10 nm and 4.6 millions atoms. Grain sizes are distributed from 6 to 16 nm and grain boundary misorientations are random. Molecular dynamics simulations of uni-axial straining at room temperature and different strain rates are presented.Although generalized stacking faults energy curves for palladium are very similar to nickel and therefore similar plastic deformation behaviour is expected, palladium responded to the loading by the fracturing of grain boundaries at uni-axial strain of approximately 3%. The cracks are nucleated on grain boundaries which are oriented perpendicular to the applied strain. Up to 3% of strain no partial or full dislocation passed through the entire grain. However, several partial and full dislocation embryos exist near grain boundaries. These nucleated dislocations are strongly pinned and can not break away from the grain boundaries even at high applied strain. Dislocation configurations and the first fracture events are analysed in detail.
9:00 PM - EE10.9
Atomic-scale Simulation of the Interaction between Screw and Mixte Dislocations with Nanotwins.
Marie Chassagne 1 2 , Marc Legros 2 , David Rodney 1
1 SIMAP, INP Grenoble, Saint Martin d Heres France, 2 CEMES, CNRS, Toulouse France
Show Abstract9:00 PM - EE10: poster 2
EE10.8 Transferred to EE5.34
Show Abstract9:00 PM - EE10: poster 2
EE10.32 Transferred to EE3.10
Show Abstract