A. Lindsay Greer University of Cambridge
Cynthia A. Volkert University of Goettingen
Kenneth F. Kelton Washington University
TT1: Structure of Liquids and Glasses
Monday PM, December 01, 2008
Room 103 (Hynes)
9:30 AM - **TT1.1
Ordering in Liquid State: Metallic Melts and Mesoscopic Colloidal Suspensions.
Dieter Herlach 1 , Dirk Holland-Moritz 1 , Ina Klassen 1 , Thomas Palberg 2 , Patrick Wette 1 Show Abstract
1 Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, DLR, Köln Germany, 2 Institut für Physik, Johannes-Gutenberg Universität Mainz, Mainz Germany
The liquid state of metals is in most cases the parent phase for the preparation of metallic materials. Efforts are directed to understand and describe the entire pathway of a system going from ordering in liquid state to nucleation and crystal growth in order to develop a predictive capability for solidification processing. In non-transparent metals processes as ordering in liquid, formation of solid-liquid interfaces and crystal nucleation are not accessible for direct observation. Therefore, transparent colloidal suspensions are frequently discussed as model systems for metals. The particles in colloids are several orders of magnitude larger than atoms in metals and their relaxation behavior is very sluggish compared to atomic systems.In the present work we present investigations of short-range ordering in liquid metals utilizing elastic neutron scattering. The results of these investigations are compared to measurements on colloidal suspensions in liquid state applying Ultra Small Angle X-ray Scattering. Colloidal suspension and metallic melt are studied far away from equilibrium. Deviations from equilibrium are measured by the difference of particle number densities of metastable and stable liquid in colloidal suspensions and by the undercooling below the melting temperature of metals as achieved by containerless processing. The measured structure factors of both physically different systems are analyzed using the same formalism. The investigations reveal icosahedral short-range order in fluid phase of colloidal suspensions and pure liquid metals as well. The icosahedral short-range order becomes more pronounced with increasing deviations from equilibrium. The experiments demonstrate that in both systems topological effects control ordering in liquid state. Obviously, electrons are of minor importance with respect to structural ordering in pure metals.Support by Deutsche Forschungsgemeinschaft within grants HE1601/23, HE1601/24, Pa459/14, Pa459/16 is gratefully acknowledged.
10:00 AM - TT1.2
Density Maximum of Supercooled Liquid Silicon.
Masahito Watanabe 1 , Masayoshi Adachi 1 , Akitoshi Mizuno 1 Show Abstract
1 Department of Physics, Gakushuin University, Tokyo Japan
Study of structural properties of supercooled liquid metals has been recently progressed by using the evitation technique, which can provide stable supercooled states on contamination-free conditions by containerless melting. Using the diffraction method combined with the levitation technique, icosahedral short-range order (ISRO) was observed in undercooled metallic melts such as Ni, Fe and others. On the other hand, for the case of liquid Si(l-Si), the structure of liquid state is different from the metals since the l-Si has the structure with small number of first-shell coordination. However, the different temperature dependence l-Si structure has been reported in the supercooled region [1,2,3]. Therefore, we must investigate the density and the structure of supercooled l-Si. To investigate the density and the structure of supercooled l-Si, we use the elctromagnetic levitation (EML) technique to keep supercooled state with highly supercoolings. The density of supercooled l-Si must be precisely measured, therefore we newly developed the measurements method of electromagnetic levitated liquid with reduced the surface oscillations using a static magnetic fields. In normal EML technique, since levitated liquid droplets have surface oscillation with large amplitudes, the density of levitated liquid droplet has large error values in temperature dependence data due to the asymmetry of surface oscillation of levitated liquid droplets. Since our new technique of the measurement of l-Si density can reduce the surface oscillation effects, we can obtain precise temperature dependence of l-Si density. We also performed first-principle molecular dynamics (FPMD) simulations of supercooled l-Si to investigate the precise structure of supercooled l-Si with comparing with the previous high-energy x-ray diffraction experiments combined with the EML technique . The structure of l-Si from FPMD results quite agreed with experimental data of high-energy x-ray diffraction method and also agreed with the density of l-Si obtained by present experiments and previous report data. Based on these things, we are discussed about supercooled l-Si structure and also about existence of density maximum which is well known in the water at 4°C. Therefore, in highly supercooled liquid the tetrahedral coordinated atoms would make to difficult to from bulk amorphous Si from supercooled liquid state. However, if we will achieve more highly supercooled liquid state below 1200K, the liquid state has large density state, so we will be able to make bulk amorphous Si from the liquid state. S. Ansell et al., J. Phys.: Condens. Matter 10 (1998) L73. H. Kimura et al., Appl. Phys. Lett., 78 (2001) 604. N. Jakse et al., Appl. Phys. Lett. 83 (2003) 4734. M. Watanabe et al., Faraday Discuss. 136 (2007)279. K. Higuchi et al., Meas. Sci. Technol. 16 (2005) 381.
10:15 AM - TT1.3
Liquid-liquid Phase Transition in Supercooled Silicon: Structural, Electronic and Dynamical Aspects.
Noel Jakse 1 Show Abstract
1 , Grenoble Institute of Technology, Saint Martin d'Hères France
Despite the occurrence of advanced materials in recent years, silicon still keeps the leadership in semiconductor technology. Most technological applications begin with crystalline silicon wafers elaborated from the melt, and amorphous silicon made from slightly supercooled melts. The properties of normal and supercooled liquid silicon are therefore of importance for the manufacturing process. Unusual behavior of the density in the supercooled liquid states, as deep as 200 K below the melting point, was observed leading researchers to consider plausible the existence of a liquid-liquid transition at even lower temperature, unfortunately out of reach to state-of-the-art experimental facilities. Therefore, the absence of direct evidence from experiments has prompted to look for it using numerical simulations [1,2]. We have proposed a new mixed approach by combining efficiently classical and first-principles molecular dynamics, giving a strong support to the existence of a transition between a high density liquid to a low density liquid near 1050 K, regardless of a specific empirical interaction model . We were able to clarify the nature of atomic and electronic structures of both the high and low density phase, which were incorrectly described from early classical simulations. Our finding indicates the liquid-liquid transition is accompanied by an enhancement of the local tetrahedral structure and is not characterized by a semimetal to semiconductor transition. Concerning the dynamical aspects, simulations evidence the presence of a boson peak in the THz frequency range in the low density liquid and a fragile-to-strong crossover across the liquid-liquid phase transition. The analysis of the collective excitations shows that its origin might be due to a hybridization of the longitudinal and transverse acoustic modes localized on the nanometer scale and could be attributed to collective vibrations of connected tetrahedral . N. Jakse, S. Krishnan, E. Artacho, T. Key, L. Hennet, B. Glorieux, A. Pasturel, D. L. Price, M.-L. Saboungi, Appl. Phys. Lett. 83, 4734 (2003)  S. Sastry and C. A. Angell, Nat. Mater. 2, 739 (2003); S. S. Ashwin, U. V. Waghmare and S. Sastry, Phys. Rev. Lett. 92, 175701 (2004). N. Jakse and A. Pasturel, Phys. Rev. Lett. 99, 205702 (2007). N. Jakse and A. Pasturel, Phys. Rev. Lett. (to be published 2008).
10:30 AM - TT1.4
Solidification of Bulk Metallic Glass-forming Alloys Observed by Time-resolved X-ray Diffraction Combined with Levitation Technique.
Toshihiko Akimoto 1 , Akitoshi Mizuno 1 , Masahito Watanabe 1 , Shinji Kohara 2 , Masaki Takata 2 3 , Yoshihiko Yokoyama 4 Show Abstract
1 Physics, Gakushuin University, Tokyo Japan, 2 , JASRI/SPring-8, Hyogo Japan, 3 , SPring-8/RIKEN, Hyogo Japan, 4 Material Research, Tohoku University, Miyagi Japan
10:45 AM - TT1:Structure
11:15 AM - TT1.5
X-ray Scattering of Liquid and Vitreous (B2O3)1-x(H2O)x.
Ralf Bruning 1 , Justine Galbraith 1 , Katherine Braedley 1 , Frederick Adurodija 1 2 Show Abstract
1 Physics Department, Mount Allison University, Sackville, New Brunswick, Canada, 2 , HelioVolt Corporation, Austin, Texas, United States
The structures of liquid water and vitreous B2O3 have been studied extensively. Limited information is available for vitreous and liquid mixtures in this system, in which a random network of hydrogen bonds gradually replaces a random network of covalent bonds. These compounds are encountered as liquids e.g. when boron-oxide based flame-retardants are heated, when minerals form  and in fluxes. Glasses can be obtained by quenching in the range x ≤ 0.50 . Here we report the wide-angle x-ray scattering by the liquid phase in the composition range from x = 0.4 to x = 1.0 (pure water) at temperatures just above the liquidus. Samples were contained in thin-walled capillaries that withstand the liquidus vapor pressure of up to 0.7 MPa. The first sharp diffraction peak (FSDP) of the liquid attains a maximum at x=0.71, a lower water concentration relative to the crystalline layer compoundB(OH)3 with x=0.75. Remarkably, at x=0.42 the FSDP of the liquid phase is considerably higher than the FSDP of the corresponding glass. This suggests that the glass has a high degree of structural frustration of glasses near the limit of the glass forming range, whereas the liquid is free to assume a locally layered structure. C. Schmidt, R. Thomas and W. Heinrich, Boron speciation in aqueous fluids at 22 to 600°C and 0.1 MPa to 2 GPa, Geochim. Cosmochim. Acta 69, 275 (2005). R. Brüning and S. Patterson, Thermal and structural properties of B2O3-H2O glasses, J. Mater. Res. 18, 2494 (2003).
11:30 AM - TT1.6
On the Determination of Ti Local Structure in Glasses from Ti K-edge XANES.
Nan Jiang 1 , Dong Su 1 , John Spence 1 Show Abstract
1 , Arizona State University, Tempe, Arizona, United States
The pre-edge features of Ti K-edge x-ray absorption near-edge structure (XANES) have been widely used as fingerprints for qualitatively or even quantitatively identifying Ti coordination in materials, for which it is not feasible to apply diffraction techniques, such as amorphous and nanoparticle samples. Recently, there has been a tendency to use the Ti K-edge XANES to quantify the fractions of Ti coordination in amorphous materials. All the simplified quantification attempts are called into question, when we consider that the peak positions and peak intensity vary among compounds even with the same coordination. In this work, we have carried out a theoretical analysis of the dependence of the Ti K-edge XANES pre-edge shape on various geometrical parameters, including coordination, symmetry, Ti – O bond length and bond angle. We begin with density functional theory (DFT) calculations based on the local density approximation for several typical Ti compounds, which provide an interpretation of Ti K-edge XANES in the pre-edge region. This is followed by a detailed discussion of the dependence of the pre-edge peak intensity upon the distortion of the Ti octahedron, where the Ti – O bond lengths, bond angles and inversion symmetry were taken into account, based on calculations using the real-space full multiple-scattering theory. For simplicity, we developed an embedded cluster model, in which a small slightly distorted Ti polyhedron was embedded into a large undistorted cluster obtained from the experimental crystal structure. It is found that the greatest impact on the pre-edge features arises from a reduction in Ti – O bond length, rather other parameters, such as symmetry, coordination and angles. Therefore, we should be cautious about using the Ti pre-edge peak(s) to determine Ti coordination. This work is funded by the NSF DMR-0603993.
11:45 AM - **TT1.7
A Topological Assessment of Binary and Ternary Metallic Glasses.
Daniel Miracle 1 , Dmitri Louzguine 2 , Larissa Louzguina 2 , Akihisa Inoue 2 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio, United States, 2 Advanced Institute of Materials Research, Tohoku University, Sendai Japan
12:15 PM - TT1.8
Coexistence of Three Distinct Amorphous Structures in an Al89La6Ni5 Metallic Glass.
Guoqiang Li 1 , Konstantin Borisenko 1 , Yixin Chen 1 , Duc Nguyen-Manh 2 , Evan Ma 3 , David Cockayne 1 Show Abstract
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 , EURATOM/UKAEA Fusion Association, Abingdon United Kingdom, 3 3Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
Metallic glasses have been attracting much attention due to their ultra-high strength, hardness and elasticity . However, most metallic glasses usually show very poor plasticity which hampers industrial applications where reliability is important. Al-La-Ni metallic glass with high Al content, however, exhibits good plasticity, making it a good candidate for studying the plasticity of metallic glasses . Knowledge of atomic structure is fundamental to understanding the material’s properties. In this study, RDF analysis based on electron diffraction  has been used to determine the local structure of chosen small volumes in an Al89La6Ni5 (at%) metallic glass, and atomic models have been refined against the RDF data using the reverse Monte Carlo (RMC) method and density functional theory (DFT) calculations.Al89La6Ni5 metallic glass ribbons 5 mm in width and 30 μm in thickness were prepared by melt spinning. TEM samples were made out of these ribbons by electropolishing and were then studied using a JEOL-3000F field emission gun transmission electron microscope. Selected area diffraction (SAD) was collected from different local areas with the scattering vector q (=4πsinθ/λ) up to 20 Å^-1. During the collection, considerable effort was taken to keep the microscope in identical electron optical conditions so that the RDFs were comparable. The RDFs were then extracted from the SAD patterns using procedures described in . The RDFs were used to refine atomic models using RMC accompanied by DFT calculations.We have found that RDFs from different local areas show three distinct amorphous structures with the experimental first/second peaks located at 2.76/3.32 Å, 2.90/3.46 Å, and 2.96/3.55 Å (all +/- 0.02 Å ), which, as shown in Fig. 1, are referred to as Type A, B, and C, respectively. Type A is the majority phase in Al89La6Ni5 metallic glass. DFT calculations suggest the Al-Al-Al-Ni rings are preferred structure in Type A, but not frequent in Type C. The RMC refinements have shown only a slight increase in the Al-Al distance and a larger increase in the Al-La distances, with similar trends observed in the DFT calculations. The increase in these distances is accompanied by shortening of the Al-Ni first neighbour contacts and reduction of Ni coordination number. The coexistence of three distinct amorphous states in Al89La6Ni5 is important to understand the nature of metallic glasses and their macroscopic properties such as plasticity.ReferenceA. L. Greer and E. Ma, MRS Bulletin 32, 611 (2007).A. Inoue, and A. Takeuchi, Mater. Trans. JIM 43, 1892 (2002).D. J. H. Cockayne, and D. R. McKenzie, Acta. Cryst. A 44, 870 (1988).
12:30 PM - TT1.9
Effect of Transition Metal Micro-additions on The Structure of Al88-xY7Fe5TMx Glasses.
Kisor Sahu 1 2 , Lydia Longstreth-Spoor 1 2 , Nicholas Mauro 1 2 , Karyn Bondi 1 2 , Michael Miller 3 , Kenneth Kelton 1 2 Show Abstract
1 Department of physics, Washington University in Saint Louis, Saint Louis, Missouri, United States, 2 Center for Material Innovation, Washington University in Saint Louis, Saint Louis, Missouri, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
We have reported earlier that transition metal micro-additions in Al88-xY7Fe5TMx based alloys improve glass formability and change the transformation character upon devitrification. In particular a 0.5% Ti micro-addition suppresses the nucleation of the primary phase, increasing the crystallization temperature and producing a measurable glass transition, thus making it a better glass. Such a significant impact from so small an addition of Ti is intriguing. To better understand the role of Ti, atom probe tomography data were obtained for both the base glass (Al88Y7Fe5) and the one containing the Ti micro-addition (Al87.5Y7Fe5Ti0.5). These data show the presence of large regions of essentially pure Al, surrounded by the transition metals. A statistical analysis demonstrates that spatial distribution of pure Al-region is nearly random, consistent with the high Al concentration of the alloy. The most interesting observation is that the as-quenched base glass is phase separated into high and low Al regions that are ~ 40 nm apart, suggesting that the Al-rich regions are preferred sites for crystallization of α-Al, thus explaining the high nucleation rates needed to produce the amorphous/nanostructured devitrified composite. The pair distribution function constructed for the distribution of α-Al in the devitrified glass gives the characteristic distance of the diffusion zone. Connections between the length scales of the phase separation and the diffusion zone are explored. Importantly, the phase separation is suppressed in the glass containing the Ti micro-addition, explaining their easier glass formability and greater stability.*Supported by the US Air Force Office of Scientific Research under contract FA9550-05-1-0110 and the National Science Foundation under grant DMR-06-06065. Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by Basic Energy Sciences, U.S. Department of Energy.
12:45 PM - TT1.10
In-situ Neutron Scattering Studies of Elastic Deformation of Bulk Metallic Glasses.
Dong Ma 1 , A. Stoica 1 , Xun-li Wang 1 , Zhaoping Lu 1 2 Show Abstract
1 Neutron Scattering Science division, Oak ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology of Beijing, Beijing China
TT2: Frans Spaepen Colloquium
Monday PM, December 01, 2008
Room 103 (Hynes)
2:30 PM - **TT2.1
On the Structure and Motion of the Semiconductor Crystal-Amorphous Interface.
Michael Aziz 1 Show Abstract
1 Harvard School of Engrg. & Appl. Sci., Harvard University, Cambridge , Massachusetts, United States
Frans Spaepen's ideas about the structure and motion of the semiconductor crystal-amorphous interface stimulated the development of a substantial body of knowledge about these topics today. This talk will trace some of these ideas from conception to state of the art.
3:00 PM - **TT2.2
Thermodynamics of Solid Surfaces with Application to Nucleation.
Robert Cammarata 1 2 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
The thermodynamics of surfaces has been one of many areas of materials science that Frans Spaepen has made many important contributions. Examples include the structure and energetic of grain boundaries, measurement of the interface stress in solid-solid interfaces, and the influence of surface thermodynamics properties on nucleation. The framework that he has used is based on that developed by J. Willard Gibbs. When Gibbs considered solid-fluid surfaces he restricted his attention to single component solids. Certain issues arise that can make attempts to extend his approach to surfaces involving multicomponent solids problematic. It will be suggested that many of these difficulties can be overcome using the concept of thermodynamics availability applied to surfaces. Availability is a measure of the maximum work that can be extracted from a system under environmental constraints and has been used primarily to analyze nonequilibrium flow processes. However it will be shown that it also useful when considering the equilibrium behavior of nonuniform systems such as those involving an interfacial region between a multicomponent crystalline or amorphous solid and a fluid. A discussion of surface availability applied to the thermodynamics of nucleation will be given where it will be shown that such an approach is necessary in order to properly obtain the expression the reversible work to form a critical nucleus during solidification.
3:30 PM - **TT2.3
Influence of Non-equilibrium Surface Conditions on Thin Film Stress Evolution.
Eric Chason 1 Show Abstract
1 Div of Engineering, Brown U, Providence, Rhode Island, United States
The evolution of stress during thin film growth (either amorphous or polycrystalline) is controlled by a dynamic competition among many different mechanisms . Some of these, such as the conversion of free surfaces into interfaces, result in tensile stresses. Others, such as the insertion of atoms into the boundaries between clusters, can relax the stress or lead to compressive stress generation. The interaction of these kinetic processes with the evolving microstructure leads to a complex sequence of tensile and compressive stress states during the growth of the film. We will discuss real-time wafer curvature measurements of stress focused on understanding the mechanisms controlling the residual stress. In the first case, we will discuss measurements of electrodeposited Sn which was studied because the atomic mobility is very high compared to other systems. We find that the transients during growth interrupts completely relax the stress in the film, independent of the layer thickness. The results are interpreted in terms of a model in which the non-equilibrium surface conditions drive atoms into and out of the grain boundary. Because the grain boundaries break the symmetry of the crystal, they provide a source or sink for atoms which can change the density of the film and create residual stress. In the second case, we will discuss a model for why the steady-state compressive stress changes to tensile stress as the film becomes thicker (seen in amorphous  and polycrystalline films). The increasing roughness of the surface can act to decrease the effectiveness of the compressive mechanism that inserts atoms into the region between clusters and shift the balance toward the creation of tensile stress.  F. Spaepen, “Interfaces and stresses in thin films”, Acta Mater. 48, 31 (2000). J.A. Floro, P.G. Kotula, S.C. Seel, D.J. Srolovitz, “Origins of growth stresses in amorphous semiconductor thin films”, Phys. Rev. Lett. 91, 096101 (2003).
4:00 PM - TT2:FransSpaepen
4:30 PM - **TT2.4
Multifunction Nanoparticle-Nanowire/Nanotube Composites: Interface Physics and Chemistry.
Li-Chyong Chen 1 Show Abstract
1 Center for Condensed Matter Sciences, National Taiwan University , Taipei Taiwan
For most practical devices, heterogeneous structures and phases with different functionalities are involved. Therefore, understanding the physics and chemistry of the interfaces and junctions is crucial for ultimate device performance. Noble-metal nanoparticles (NPs) having different shape, size and geometric arrangement have shown many interesting properties, including surface plasmon resonance (SPR) and catalysis. Nanoscale engineering and strategies that exemplify these novel properties and their applications will be presented, specifically in two cases: (1) encapsulating Au NPs inside amorphous silica nanowires and (2) dispersing Pt-Ru NPs on the arrayed carbon nanotubes. For the first case, a micro-reactor approach for fabricating Au nanoparticle chain encapsulated by dielectric nanowire matrix will be illustrated. The Au@SiOx nanopeapods exhibit pronounced SPR absorption. More remarkably, a two-terminal device based on an ensemble of Au@SiOx nanopeapods shows a strong wavelength-dependent and reversible photoresponse under light illumination, while no photoresponse is observed for the plain silica nanowires. This result manifests the potential of using Au nanopeapodded silica nanowires as color-selective nanoswitches and sensors [Nature Mater. 5, 102 (2006)]. For the second case, an efficient and simple route to disperse Pt–Ru NPs onto bamboolike nitrogen-containing carbon nanotubes (CNx NTs) grown directly on the carbon cloth will be presented. It was found that nitrogen incorporation, while causing some deformation of CNT, helps nucleation and growth of catalytic metal on CNT with site and size controllability. The Pt–Ru NPs, with an average size of 2-3 nm, supported by the CNx NTs–carbon cloth composite electrode exhibit high electrocatalytic activity, which can be attributed to substantial increase in surface area, fast electron-transfer kinetics, and low interfacial barriers. Moreover, our synthetic technique for CNx NTs-Pt-Ru nanocomposites is highly efficient in loading precious metal, in that we obtain a similar power performance with only one tenth of loading, in comparison to that of the conventional method, thus, enabling a significant cost-reduction in fuel cells.
5:00 PM - **TT2.5
Crystal Nucleation, Amorphous Phase Density, and Formation of Metallic Glasses.
Carl V. Thompson 1 3 , Yi Li 2 3 , Qiang Guo 3 , Johannes Kalb 1 4 Show Abstract
1 Materials Science and Engineering, M.I.T., Cambridge, Massachusetts, United States, 3 , Singapore-MIT Alliance, Singapore Singapore, 2 Mateials Science and Engineering, University of Singapore, Singapore Singapore, 4 , Intel Corporation, Santa Clara, California, United States
Formation of a metallic glass requires that nucleation of crystalline phases be avoided. This kinetic constraint often correlates with thermodynamically defined compositions with high reduced glass transition temperatures. It has also been suggested that ease of glass formation correlates with liquid compositions having dense structures, and consequent high viscosities and low diffusivities. However, both experimental and theoretical studies have so far failed to establish the latter correlation. We have made systematic deflection measurements using micro-cantilevers and a combinatorial-deposition method to show a clear correlation between glass-forming ability and the density change upon crystallization. This has been demonstrated over a broad compositional range and with unprecedented compositional resolution. Experiments were carried out using the Cu-Zr binary alloy system as a model. Three distinct peaks in the packing density of the amorphous phase were found to correlate with specific maxima in the critical thickness for glass formation. The implications of these results in terms of suppression of crystal nucleation will be discussed.
5:30 PM - **TT2.6
Anelasticity and Flow in a Metallic Glass and in its Shear-Bands.
Michael Atzmon 1 2 , Adam Ganuza 2 , Dongchan Jang 1 , Koteswararao Rajulapati 1 Show Abstract
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
Metallic glasses have been known to flow at temperatures near the glass transition temperature, Tg. We have recently observed significant time-dependent deformation in amorphous Al86.8Ni3.7Y9.5, both reversible and irreversible, at room temperature, well below Tg. Using both nanoindentation and macroscopic bend stress relaxation measurements, we have identified several distinct anelastic processes. Cold rolling greatly increased the amplitude of time-dependent processes with long time constants. Faster processes, having time constants of the order of seconds, decreased in amplitude. In separate experiments, the flow at shear bands was observed by monitoring the effect of applied stress on the evolution of individual surface steps, at the intersection of shear bands with the free surface. In the discussion of our observations, the concepts of Spaepen’s free-volume based model of flow [F. Spaepen, Acta Metall. 25, 407 (1977)] will be employed.
TT3: Poster Session: Local Structure and Dynamics in Amorphous Systems I
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - TT3.1
Intruder Dynamics on Vibrofluidized Granular Surfaces.
Alexander Wissner-Gross 1 2 Show Abstract
1 Department of Physics, Harvard University, Cambridge, Massachusetts, United States, 2 Center for the Environment, Harvard University, Cambridge, Massachusetts, United States
Granular fluids have received significant attention for their transport characteristics within rigid boundaries. In this work, we study the potential for amorphous granular beds themselves to serve as elastic boundaries for transport and manipulation of surface particles. In particular, we measure the effect of the mass and diameter of an intruding particle, supported and tossed by a periodic vibrofluidized granular bed, on its horizontal self-diffusivity using a two-dimensional hard-sphere molecular dynamics simulation. Intruder mass and diameter scaling exponents are fitted and found to be consistent with dominant Stokes drift. Intruder types favorable for manipulation applications are identified.
9:00 PM - TT3.10
Nanometer Scale Atomic Structure in Zr-based Bulk Metallic Glass.
Jinwoo Hwang 1 , Hongbo Cao 1 , Paul Voyles 1 Show Abstract
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
We have used fluctuation electron microscopy (FEM) to show that there is a significant degree of medium range order (MRO) at a 1 nm length scale in ternary bulk metallic glass (BMG), Zr54Cu38Al8. By using electron scattering simulations from atomic structural models constructed by hand on the computer, we concluded that this order could be consistent with clusters of Al-centered icosahedra. We now present the results of a more comprehensive, less biased approach to simulating the structure of this material using Reverse Monte Carlo (RMC) modeling. Using a RMC code adapted from Biswas, Atta-Fynn, and Drabold, we have constructed models that are consist with both FEM data and RDF data measured using high-angle, energy-filtered electron diffraction on samples from the same cast ingot. Including FEM data means that our RMC model is consistent with MRO data, as well as the short range order diffraction or x-ray absorption data more commonly used. This should significantly increase the uniqueness of the output structure. Understanding the structural motifs, including MRO, in these models may shed light on their properties, such as their ability to avoid crystallization, and their plastic deformation through shear banding.
9:00 PM - TT3.12
Spinodal Decomposition of Ni-Nb-Y Metallic Glasses.
Norbert Mattern 1 Show Abstract
1 , Leibniz_Institute IFW Dresden, Dresden Germany
The preparation of phase-separated glasses requires modifying an alloy with high glass-forming ability by addition of elements having a strong demixing tendency to one of the constituents. Then, phase separation and structure formation may take place during quenching in the liquid, or in the metastable undercooled liquid, respectively. The ternary phase diagram Ni-Nb-Y exhibits a miscibility gap in the equilibrium liquid. The critical temperature of liquid-liquid phase separation decreases with increasing Ni content. For rapidly quenched Ni-Nb-Y glasses the thermodynamic properties essentially determine the formed microstructure of the glasses. The influence of chemical composition and preparation conditions like cooling rate and casting temperature of the melt will be discussed. Early stages of decomposition are obtained by rapid quenching for compositions with high Ni contents (70at.%). Strongly correlated chemical fluctuations with a nanometer length scale were observed in the as-quenched state. The fluctuation lengths range from 5 to 12 nm depending on the actual composition of the glass. The frozen in early stages of decomposition occur in the deeply undercooled melt due to the reduction of the critical temperature of liquid-liquid phase separation with the Ni content. In situ small angle X-ray scattering at elevated temperatures gives evidence of the spinodal character of the decomposition in the supercooled liquid state.
9:00 PM - TT3.13
The Effect of Cooling Rates on the Apparent Fragility of Bulk Metallic Glasses.
Zachary Evenson 1 , Isabella Gallino 1 , Ralf Busch 1 Show Abstract
1 Materials Science and Engineering, Saarland University, Saarbrücken Germany
The effect of various enthalpic states on the glass transition of the Zr57Nb5Al10Cu15.4Ni12.6 and Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 bulk metallic glass forming alloys are studied. The amorphous samples are heated into the supercooled liquid region using Differential Scanning Calorimetry (DSC) and cooled back down into the glassy state using series of different cooling rates Ci. The relative shifts in the glass transition region are assessed by determining the onset glass transition temperature Tg upon re-heating with a series of heating rates Ri. Analysis of the fictive temperature Tf was is carried out using methods adopted by Moynihan  and Angell . The data are modelled assuming a Vogel-Fulcher-Tammann (VFT) type behavior in the structural relaxation time τ. Shifts in the glass transition region are observed as being influenced, in part, by the thermal histories of the samples. These changes also showed evidence of an apparent increase in the kinetic fragility parameter, D* for lower cooling rates. The VFT fits are compared with viscosity data obtained by three point beam bending and rotating cup viscometry, where a crossover in kinetic fragilities was observed from the low to high-temperature regions. This strong-to-fragile transition is thought to be attributed to the increase in entropy through the destruction of short-range order as the high-temperature region is reached. C. T. Moynihan, A. J. Easteal, and M. A. DeBolt. Dependence of the Fictive temperature of glass on cooling rate. Journal of the American Ceramic Society, 59:12–16, 1976. V. Velikov, S. Borick, and C. A. Angell. Molecular glasses with high Fictive temperatures for energy landscape evaluations. Journal of Physical Chemistry B, 106:1069–1080, 2002.
9:00 PM - TT3.14
Improved Bond Valence Models for Ion Transport Pathways in Glasses.
Stefan Adams 1 Show Abstract
1 Mater. Science and Eng. , Nat. University of Singapore, Singapore Singapore
9:00 PM - TT3.17
Shape Effects on the Geometric Packing in Two-dimensional Monodisperse Granular Media.
Bjoern Arnold 1 , Ayse Turak 1 , Alejandro Diaz-Ortiz 1 , Helmut Dosch 1 Show Abstract
1 , Max Planck Institute for Metals Research, Stuttgart Germany
Shape can play a critical role in the collective dynamics and packing of granular materials. Using particles of various aspect ratios, random geometric packing was investigated for two-dimensional monodisperse systems. Analysis of the real-time fluctuations in the local order during agitation was performed using a combination of shaking experiments and theoretical modeling. The Lubachevsky-Stillinger model was employed for the two-dimensional numerical simulations, with volume, force and contact network distributions analyzed using Voronoi foams. These frictionless simulations were compared with experiments for plastic beads of various shapes and surface friction coefficients.
9:00 PM - TT3.19
Clustering in the Liquid Phase of Aluminum-4.8 at%Silicon Alloy. An ab initio Simulation.
J. Andres Díaz-Celaya 1 , Ariel Valladares 1 , R. Valladares 2 , Alexander Valladares 2 Show Abstract
1 Materia Condensada, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, México, D.F., Mexico, 2 Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
9:00 PM - TT3.2
Microstructure of Pd-Ni-P Metallic Glass Film Fabricated by Electroless Alloy Plating.
Akinobu Shibata 1 , Yoshihide Imamura 2 , Masato Sone 1 , Chiemi Ishiyama 1 , Yakichi Higo 1 Show Abstract
1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan, 2 Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama Japan
Due to the unique properties in comparison with crystalline materials, such as high strength, high corrosion resistance, and good soft magnetic properties, there have been many studies concerning with not only fundamental but also application researches on these materials. Unlike the conventional amorphous materials, there is a supercooled liquid region (between the glass transition and crystallization temperatures) in metallic glass. The super cooled liquid region can be used to remove internal stress, or to fabricate micro components easily. Furthermore, because of its amorphous structure, metallic glasses remain isotropic even when specimen sizes decrease to be micro or nano meter order. Thus, metallic glass films are very important materials for micro-machine or micro-electro mechanical system (MEMS). Recently, we proposed a novel fabrication method of Pd-Ni-P metallic glass films by electroless alloy plating. The present study investigated the microstructure of Pd-Ni-P metallic glass film fabricated by electroless alloy plating. The substrates were a film of pure Cu or Al. Electroless alloy plating was conducted with a mixture of Pd and Ni-P electroless plating solutions at temperatures within a range from 303 to 333K. The heat flow was measured by differential scanning calorimetry (DSC) after dissolving the substrate. The structural analysis was conducted by X ray diffraction (XRD), and the microstructure was observed by transmission electron microscopy (TEM). The compositions of the fabricated Pd-Ni-P films can be effectively controlled by adjusting the mixture ratio of the plating solution or the plating temperature. XRD showed that the Pd-Ni-P film has an amorphous structure. Furthermore, Pd-Ni-P film exhibits a glass transition followed by a crystallization during continuous heating. Thus, we confirmed that the Pd-Ni-P film is metallic glass. However, in contrast to the homogeneous, featureless microstructure in conventional bulk metallic glasses, the fabricated Pd-Ni-P film does not have a uniform microstructure and consists of isolated dark regions surrounded by bright regions in TEM micrograph. Both of these regions were confirmed to be amorphous structure from diffraction pattern. This non-uniform microstructure could be attributed to the inhomogeneous distribution of free volume accompanying electroless alloy plating reaction. In the presentation, the crystallization behavior from this non-uniform microstructure will also be shown.
9:00 PM - TT3.20
Atomic Structure of Zr-Cu Glasses Probed by Neutron and Synchrotron X-ray Diffractions.
Dong Ma 1 , A.d. Stoica 1 , Xun-li Wang 1 , Matthew Kramer 2 Show Abstract
1 , oak ridge national laboratory, Oak Ridge, Tennessee, United States, 2 , Ames National Laboratory, ames, Iowa, United States
9:00 PM - TT3.21
Nitrogen Induced Amorphization of Crystallized Fe-Si-B-Cu-Nb Amorphous Powders.
Jun Hyun Han 1 , Jae Pyoung Ahn 2 , Do Hyeon Kim 3 , Kyu Hwan Oh 3 , Seung Hee Han 1 Show Abstract
1 , Division of Materials Science & Technology, Korea Institute of Science & Technology, Seoul Korea (the Republic of), 2 , Advanced Analysis Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 , School of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
9:00 PM - TT3.22
Interatomic Bond Enthalpies in Metallic Glasses.
James Dahlman 1 , Daniel Miracle 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patt AFB, Ohio, United States
9:00 PM - TT3.3
Surface Tension of Liquid Al-Cu Alloys.
Julianna Schmitz 1 , Jürgen Brillo 1 , Ivan Egry 1 Show Abstract
1 Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51170 Köln Germany
In order to study the interaction of liquid Al-Cu alloys with differently oriented single crystalline sapphire surfaces, knowledge of the surface tension γ of the melt is a necessary prerequisite. Hence, this thermophysical property was measured for the entire Al-Cu system as a function of temperature and composition.To avoid contamination of the sample from contact with container walls, measurements were performed in an electromagnetic levitation furnace using the oscillating drop method. A fast digital CMOS-camera (400 fps) recorded images of the oscillating sample and the surface tension was determined from an analysis of the frequency spectrum.Precise data with |Δγ/γ|<7% were obtained in a broad temperature range. A linear temperature dependence of γ with a negative temperature gradient was found for all compositions whereas the surface tension monotonically decreases with an increase of the aluminium concentration. The observed behaviour with respect to both, temperature and concentration, is in agreement with thermodynamic model calculations using the regular solution approximation.
9:00 PM - TT3.4
Direct Evidence of a Local Multi-shell Icosahedral Cluster in a Zr70Cu25Pt5 Metallic Glass.
Eiji Abe 1 , Hiroto Minamide 1 , Junji Saida 2 , Tadakatsu Ohkubo 3 Show Abstract
1 Dept. of Materials Engineering, University of Tokyo, Tokyo Japan, 2 , Tohoku University, Sendai Japan, 3 , NIMS, Tsukuba Japan
Understanding a thermodynamical stability of metallic glass phases in terms of their local structures has been the longstanding central issue. A key local configuration is believed to be a form of icosahedral clusters, for which several progresses have been made in recent years both from theory and experiments. On this regard, Zr70Cu(30-x)Ptx alloys are an interesting glass-forming system, since they form a metastable icosahedral quasicrystalline phase during the crystallization, implying that local icosahedral configurations are already exist in the glass state . In the present work, we have investigated the local atomic structure of a Zr70Cu25Pt5 metallic glass phase using high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). A remarkable compositional modulation at a few nanometer scales is directly observed for the first time; namely the modulation due to Cu-rich and Zr-rich regions within the amorphous structure. Individual Pt atoms can be seen as the brightest Z-contrast dots, which are found to be mostly distributed within the Zr-rich regions. Some characteristic ring-contrasts are frequently observed both in the phase-contrast HRTEM and Z-contrast STEM images. We show that, based on a simulation of phase-contrast/Z-contrast atomic images, these local contrasts are reasonably interpreted as a mulit-shell icosahedral cluster constructed by (mostly) Zr and Pt atoms. Here we note in particular that we find that the smallest icosahedral clusters with 13 atoms cannot reproduce the observed contrasts. On these basis, we provide direct evidences of a local structural similarity between the glass and QC phases in the Zr-Cu-Pt alloys; shell-inflating local atomic order in accordance with icosahedral symmetry.
9:00 PM - TT3.5
Structural Influences on Metallic Glass Relaxation.
Garth Wilks 1 2 , Daniel Miracle 1 Show Abstract
1 Materials & Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH, Ohio, United States, 2 , General Dynamics Inc., Dayton, Ohio, United States
Variations in constitution and processing route (cooling rate and subsequent annealing) in ribbons made from the Al-La-Ni system are used to probe the deformation activation energy spectra for material conditions via bend stress relaxation. Deviations in spectra between conditions are rationalized in terms of “defect” states predicted by the Efficient Cluster Packing model that contribute to local free volume fluctuation and act as sites for unit shear process nucleation.
9:00 PM - TT3.6
Liquid Structures of Metallic Glass-forming Binary Zr Alloys.
Akitoshi Mizuno 1 , Toshihiko Akimoto 1 , Masahito Watanabe 1 , Shinji Kohara 2 , Masaki Takata 2 3 Show Abstract
1 , Gakushuin University, Tokyo Japan, 2 , JASRI/SPring-8, Hyogo Japan, 3 , SPring-8/RIKEN, Hyogo Japan
Recent studies on local structure of bulk metallic glasses (BMGs) have shown evidence supporting the formation of icosahedral short range ordering (ISRO) in their atomic arrangements. The formation of ISRO was also suggested even in binary glassy alloys such as Zr-Cu, Zr-Ni and Zr-Pd alloys. As is well known, the glass-forming ability of metallic alloys depends on the combination of the elements and the composition. Therefore, we have analyzed liquid structures of the binary Zr-TM (TM=Cu, Ni, Pd) alloys as a function of composition by using high-energy x-ray (E=113 keV) diffraction. A conical nozzle levitation (CNL) technique was applied to achieve a containerless condition to avoid any contamination and hence to obtain reliable structure data of high temperature melts. Obtained structure factor, S(Q), for liquid Zr50Pd50 alloy agreed with the S(Q) estimated by a hard sphere model for a random mixture. Meanwhile, a shoulder was found at high-Q side of the second peak of S(Q) for Zr70Cu30 alloy, which was similar to that observed in the glassy state of Zr70Cu30 alloy. This shoulder implies the formation of ISRO in the liquid alloy. Compared to dependences of the S(Q) on the Zr concentration of Zr-Cu alloys and Zr-Pd alloys, liquid Zr-Ni alloys show an apparent difference of the S(Q) between the Zr70Ni30 and the Zr50Ni50 alloys, which can be associated with the formation of the chemical short range ordering. The detailed liquid structure analyses using the reverse Monte Carlo (RMC) simulation will be presented.
9:00 PM - TT3.7
Experimental and Ab Initio Studies of the Molten Zr2Ni Compound.
S. Hao 3 , Matthew Kramer 1 2 , C. Wang 3 , K. Ho 3 1 , S. Nandi 3 1 , A. Kreyssig 1 , A. Goldman 3 1 , V. Wessels 4 , K. Sahu 4 , R. Hyers 5 , K. Kelton 4 , S. Canepari 5 , J. Rogers 6 Show Abstract
3 Department of Physics, Iowa State University, Ames, Iowa, United States, 1 Ames Laboratory USDOE , Iowa State University, Ames, Iowa, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 4 Department of Physics, Washington University, St Louis, Missouri, United States, 5 Mechanic Engineering, University of Massachusetts, Amherst, Massachusetts, United States, 6 , NASA Marshall Space Flight Center, Huntsville, Alabama, United States
High energy X-ray diffraction and ab initio molecular dynamics (MD) simulations demonstrate that the short-range order (SRO) in the deeply undercooled Zr2Ni liquid is quite nuanced. The 2nd diffuse scattering peak in the total structure factory sharpens with supercooling, revealing a shoulder on the high-q side that is often taken to be a hallmark of increasing icosahedral order. However, a Voronoi tessellation indicates that only approximately 4% of all the atoms are in an icosahedral-type environment. In contrast, a Honeycutt-Andersen analysis indicates that a much higher fraction of the atoms are in an icosahedral (15-18%) or distorted icosahedral (25-28%) environment. Interestingly, in both cases, the ordering changes little over the 500K of cooling. The Voronoi tessellation analysis indicates that the configuration from the most deeply supercooled simulations at 1173 K, shows few topological similarities in the first shell clusters with those of the stable C16 compound, even though the partial pair distributions are similar. Upon decreasing the temperature from 1673 to 1173 K, which represents ~ 120 K undercooling, we observed an increase in the population of Zr in Ni-centered clusters but no significant change in topology of the Zr-centered clusters.
9:00 PM - TT3.8
Dynamic Singularity in Multicomponent Glass-Forming Metallic Melts.
Mavila Chathoth Suresh 1 Show Abstract
1 I. Physikalisches Institut, University of Goettingen, Goettingen, Neidersachen, Germany
9:00 PM - TT3.9
Phase Formation in Ti45Zr38-xHfxNi17 Liquids and Solids.
V. Wessels 1 , K. Sahu 1 , V. Huett 1 , S. Canepari 6 , A. Goldman 2 3 , R. Hyers 6 , M. Kramer 5 3 , J. Rogers 4 , K. Kelton 1 Show Abstract
1 Physics, Washington University, St. Louis, Missouri, United States, 6 Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts, United States, 2 Physics and Astronomy, Iowa State University, Ames, Iowa, United States, 3 , Ames Laboratory USDOE, Ames, Iowa, United States, 5 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 4 , NASA Marshall Space Flight Center, Huntsville, Alabama, United States
Hafnium and zirconium are very similar, with almost identical sizes and chemical bonding characteristics. However, they behave differently when alloyed with Ti and Ni. A sharp phase formation boundary near 18-21 at.% Hf is observed in rapidly-quenched and as-cast Ti45Zr38-xHfxNi17 alloys. Rapidly-quenched samples that contain less than 18 at.% Hf form the icosahedral quasicrystal phase, while samples containing more than 21 at.% form the 3/2 rational approximant phase. In cast alloys, a C14 structure is observed for alloys with Hf lower than the boundary concentration, while a large-cell (11.93 Å) FCC Ti2Ni-type structure is found in alloys with Hf concentrations above the boundary. To better understand the role of Hf on phase formation, the structural evolution with supercooling and the solidification behavior of liquid Ti45Zr38-xHfxNi17 alloys (x=0, 12, 18, 21, 38) were studied using the Beamline Electrostatic Levitation (BESL) technique using 125keV x-rays on the 6ID-D beamline at the Advanced Photon Source, Argonne National Laboratory. For all liquids primary crystallization was to a BCC solid solution phase; interestingly, an increase in Hf concentration leads to a decrease in the BCC lattice parameter in spite of the similarity of Zr and Hf. A Rietveld analysis confirmed that as in the as-cast alloys, the secondary phase that formed was the C14 below the phase formation boundary and a Ti2Ni-type structure at higher Hf concentrations. Both the liquidus temperature and the reduced undercooling change sharply on traversing the phase formation boundary concentration, suggesting a change in the liquid structure. Structural information from a Honeycutt-Anderson index analysis of reverse Monte Carlo fits to the S(q) liquid data will be presented to address this issue.*Supported by the National Science Foundation under grant DMR-06-06065 and by NASA under contracts NNX07AK27G and NNM04AA01G
A. Lindsay Greer University of Cambridge
Cynthia A. Volkert University of Goettingen
Kenneth F. Kelton Washington University
TT4: Dynamics: Relaxation and Crystal Nucleation
Tuesday AM, December 02, 2008
Room 103 (Hynes)
9:30 AM - TT4.1
Complex Fluids in Nanocapillaries.
Denis Morineau 1 , Ronan Lefort 1 , Remi Busselez 1 , Regis Guegan 2 , Gilbert Chahine 1 3 , Mohammed Guendouz 4 , Jean-Marc Zanotti 4 , Bernhard Frick 5 Show Abstract
1 Institute of Physics, CNRS - University of Rennes 1, Rennes France, 2 Institut des Sciences de la Terre, CNRS - University of Orléans, Orleans France, 3 Laboratoire Léon Brillouin, CEA-Saclay, Gif-sur-Yvette France, 4 Laboratoire d’Optronique, University of Rennes 1, Lannion France, 5 , Institut Laue-Langevin, Grenoble France
The manipulation of fluids in nanochannels has become a crucial issue for many foreseen applications in advanced nanomaterials and biotechnology . Fundamental questions arise from the unexpected behaviors of fluids confined in capillaries of nanometric dimension, which rule out the validity of some approaches derived from the physics of liquids at the macro or microscopic scale.Intensive experimental studies of molecular liquids have shown that confinement on a nanometric scale considerably modifies the structure, phase behavior and molecular dynamics. Recently, much effort has focused on the unusual dynamical properties of low-molecular weight liquids and glassforming systems in mesoporous solids. It reveals a complex entanglement of low dimensionality, finite size and surface effects .In this field, a current challenge is to extend the knowledge of nanoconfined liquids to more complex fluids such as soft-matter or solutions of biological interest. The aim of the present contribution is indeed to present some original features that are observed, when the confined system is tuned from pure globular liquids to anisotropic mesogenic molecules or multi-component glassforming bioprotectant solutions .References :R. Busselez et al., Int. J. of Nanotechnology. 5, 867-884 (2008)See recent reviews : C. Alba-Simionesco et al., J. Phys.: Condens. Matter 18, R15 (2006); M. Alcoutlabi and G. B. McKenna, J. Phys.: Cond. Mat. 17, R461 (2005). R. Guégan et al., Phys. Rev. E 73 (1), 011707 (2006); R. Guégan et al., J. Chem. Phys. 126 (6), 1064902 (2007); D. Morineau et al., ILL Annual Report Scientific Highlights (2007).
10:00 AM - **TT4.3
Local Structure and Dynamics in Metallic Glasses.
Takeshi Egami 1 2 Show Abstract
1 MSE/Physics, University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
As the successor of the legacy of David Turnbull Frans Spaepen’s work continued and expanded the frontier of materials science in glasses and liquids. The impact of his work is wide and deep, on the mechanical properties in particular. The central idea for describing the local structure and dynamics of amorphous systems is the “free-volume”. This idea initiated in the analysis of the hard-sphere systems, and was modified and improved by Turnbull and Spaepen. However, the original concept by Turnbull and Cohen is less successful for metallic liquids than for molecular liquids, as was pointed out in their 1959 paper . In our view this is because metallic glasses are less hard-sphere-like than molecular liquids. We have developed a parallel idea focusing more on the harmonic nature of the interatomic potential, rather than its repulsive, hard-sphere nature. We show that the dynamics of the nearest neighbor shells, described in terms of the atomic-level stresses, is nearly harmonic at high temperatures, satisfying the equipartition theorem. As temperature is lowered, however, the nearest neighbor shells start to interact each other, crossing over from a simple liquid to a correlated liquid, and finally freeze into a glassy state. These crossover behaviors can be explained in terms of the digitization of the neighbor environment and the critical shear and volume strains for local topological instability. The glass transition temperature thus calculated show excellent agreement with the experimental data . The concept is now expanded to elucidate melting and mechanical behaviors. M. H. Cohen and D. Turnbull, J. Chem. Phys. 31, 1164 (1959). T. Egami, S. J. Poon, Z. Zhang and V. Keppens, Phys. Rev. B, 76, 024203 (2007). Work supported by the Basic Energy Sciences, Department of Energy through DE-AC05-00OR-22725
10:30 AM - **TT4.4
The Response of Metallic Glasses and Glass Forming Liquids to Applied Stress.
William (Bill) Johnson 1 Show Abstract
1 Materials Science, California Institute of Technology, Pasadena, California, United States
Metallic glasses and associated liquids are inhomogeneous on atomic length scales and characterized by disordered atomic configurations and properties which vary in space on a nanoscale. Under applied stress, the material exhibits an average macroscopic response which can be used to determine apparent shear and bulk moduli, G and B. Strictly speaking, the quasi-static shear modulus of a liquid (or glass) vanishes since average macroscopic shear stresses on a strained sample always relax on a sufficiently long time scale. The time scale for stress relaxation, τα = α-relaxation time, is determined by cooperative atomic rearrangements involving tens or hundreds of atoms. The configurational rearrangements slow dramatically as the glass transition is approached. This results in a finite “isoconfigurational” shear modulus, GI , at frequencies ω >> τα-1, or using Maxwell’s relaxation time, ω >> GI/η(T), where η(T) is the viscosity. Ultrasonic measurements are used to measure GI in both glasses and undercooled liquids at temperature well above Tg. We discuss the interpretation of the measured GI in several respresentative BMG’s, its relationship atom interactions and thermodynamic properties, and its role in the elasticity and flow behavior of metallic glasses and liquids. We show that when GI is viewed as a function of the total enthalpy or potential energy of the system, a relation emerges in which G(h) (or G(e)) fall on a single universal curve for the glassy, liquid, and crystalline states of the system.
11:00 AM - TT4: Dynamics
11:30 AM - TT4.5
Direct and Indirect Evidence for Fragile to Strong Transitions in Zr- Based Alloys.
Tobias Schmitt 1 , Christopher Way 1 , Sven Raedersdorf 1 , Isabella Gallino 1 , Ralf Busch 1 Show Abstract
1 Materials Science and Engineering, Saarland University, Saarbrücken Germany
The viscosities of six bulk metallic glass forming Zr-based melts of different complexity have been measured in the equilibrium liquid state. The viscosity vs. shear rate behaviour of the three quintary (Vitreloy105, Vitreloy106, Vitreloy106a), two quarternary (Vitreloy101, Zr65Cu17.5Ni10Al7.5) and one ternary (Zr60Cu25Al15) alloys have been studied above their respective liquidus temperatures in a custom built Couette concentric cylinder viscosimeter. Earlier, in the Be bearing Vitreloy 1, shear thinning behavior as well as a strong to fragile transition in the undercooled liquid had already been observed .The actual study shows that for all tested alloys a fragile state was present above the liquidus temperature, like in Vitreloy 1 with fragility parameters of about D*=10 and a weak shear thinning behavior. Results from parallel low temperature studies by three point beam bending show that they are much stronger liquids in the vicinity of the glass transition with D* higher than 20, this being a strong indication for a strong to fragile transition between the glass transition and the liquidus temperature also in these alloys. Comparable to the behavior of the fragile state of Vitreloy1 shear thinning exponents varying between 0.8 and 1 have been found for the tested alloys. To directly confirm the strong to fragile transition, studies are done in the supercooled liquid regions of the respective alloys. However, like in Vitreloy 1 the fragile to strong transition seems to also promote crystallisation and only a small temperature and time window is available to observe the transition in the supercooled liquid directly. C. Way, P. Wadhwa und R. Busch, Acta Mater. 55, 2977 (2007).
11:45 AM - TT4.6
Elastic-constant Fluctuation in Metallic Glasses from Both Inelastic X-ray Scattering and Ultrasonic Measurements.
Tetsu Ichitsubo 1 , Eiichiro Matsubara 1 Show Abstract
1 Dept. of Mater. Sci. & Eng., Kyoto University, Kyoto Japan
The correlation between the complex relaxation processes in glasses and the glassy structure has attracted much attention for understanding the nature of glasses. Among the several relaxation processes, we consider that the Johari-Goldstein beta relaxation is a key for the metallic-glass structure. Recently, we reported that the beta relaxation that occurs near the glass transition temperature under megahertz-order vibration field deteriorates the structure of bulk metallic glasses. The partially crystallized microstructure of a Pd-based metallic glass under sub-megahertz vibration strongly indicates that the atomic motions associated with the beta relaxation are localized. Based on our experimental results, we proposed the microstructural model of metallic glasses that consists of strongly-bonded regions surrounded by weakly-bonded regions. To confirm the validity of the model, we have employed the experimental technique in combination with inelastic x-ray scattering and ultrasonic measurements. Here, we show experimentally that the sound velocity of nanometer wavelength (of acoustic phonons) exceeds that of millimeter wavelength (the ultrasound velocity in a macroscopic scale) for a Pd-based metallic glass completely frozen far below the glass transition temperature. This is a clear evidence that nanoscale elastically harder regions exist in the glass matrix and, hence, elastically softer regions are also present so as to realize the macroscopic elasticity. In addition, the propagation length of longitudinal acoustic phonons in Pd-Ni-Cu-P (PNCP) glass is much shorter than that in Zr-Al-Ni-Pd (ZANP) and Zr-Cu-Al (ZCA) glasses, and the propagation length of these glasses steeply increases at a certain Q (wavenumber) value; each value is found to be in order as Q_PNCP < Q_ZANP ~ Q_ZCA. This critical Q value corresponds to the characteristic domain size in glasses. Thus, the periodicity of elastic-constant fluctuation in Zr-based metallic glasses is shorter than that in Pd-based glasses. The evaluation of the distribution of elastic inhomogeneity in a rigid glass would provide us with significant clues to clarify the mechanism of mechanical deformation as well as structural stability.
12:00 PM - **TT4.7
Relaxation Dynamics and Stability of Metallic Glasses.
Ho Chen 1 Show Abstract
1 , Baiyee Consultant, Lebanon, New Jersey, United States
There have been series of investigations on the relaxation dynamics of metallic glasses since the early development in 1970's and 1980's. Recently, there have renewed interests on studies of mechanical dynamic relaxation at the glass transition region, and their implication on plastic flow and stability of bulk metallic glasses. In this review, I will present dynamic mechnical properties and thermal enthalpy relaxation in the glass transition regime, as well as in the glassy state well below Tg for a number of metallic glasses. Calorimetric measurements of glassy alloys have revealed the sort of secondary relaxation, or Bata-relaxation, is seen clearly for many ternaly alloys but is nearly absent in binary alloys. The distinct Beta-relaxtion peak at temperature well bellow Tg contributes to the reversible behavior in the pseudo-equilibrium states. Internal friction measurements in the glass transition region reveal two distinct loss modulus peaks, separated by ~ 20K in temperature scans. In frequency sacns, the primary, Tg Alpha-relaxation occuring at lower frequency and the subTg-Alpha-relaxation appearing as a shoulder at higher frequency. The Tg Alhpa-peak is rather narrow, being only slightly broader the the Debye peak, while the shoulder, subTg Alpha-peak shows abroad asymetric distribution spectrum. The subTg-relaxation is anelastic in nature, and do not attribute to macroscopic flow. The possible microstrure dynamics of these relaxations and their implications to the plactic flow, enhanced diffusivity and the stability of metallic glasses are discussed.
12:30 PM - TT4.8
Transformation Kinetics of Supercooled Liquid Ag into its Crystalline Phase.
Wai Lun Chan 1 , Robert Averback 1 , David Cahill 1 , Yinon Ashkenazy 2 Show Abstract
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
We study the solidification of supercooled liquid Ag melted by femtosecond laser. Third-harmonic light generation is used to monitor the depth of the liquid layer as a function of time. The amount of the undercooling is controlled by varying the thickness of the Ag thin film deposited on a dielectric substrate. We are able to measure the solidification velocity as a function of temperature down to 0.6 Tm, where Tm is the melting temperature. The solidification velocity increases rapidly between Tm and 0.85 Tm, but it stabilizes at around 100 ms-1 with further decrease in temperature. The temperature-dependence of the solidification rate suggests that the transformation kinetics in pure metal cannot be explained by a simple collision-limited model as previously suggested; the solidification velocity is significantly lower than the prediction of the model as the temperature approaching the glass transition temperature. Our experimental results are in good agreement with MD simulations, which are also presented.
12:45 PM - TT4.9
Mechanisms of Crystal Nucleation from Undercooled Liquids.
Lujian Peng 1 , James Morris 1 2 , Y. Lo 3 Show Abstract
1 Materials Science and Engineering, the University of Tennessee, Knoxville, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , National Sun Yat-Sen University, Kaohsiung Taiwan
The classical theory of crystal nucleation from undercooled liquid provides a strong conceptual framework, yet lacking a clear quantitative verification. Even in model systems, such as the Lennard-Jones system, questions of the mechanisms of transformation and of the stability of the liquid state at moderate undercoolings remain [Trudu et al., Phys. Rev. Lett. 97, 105701 (2006)]. We have performed molecular dynamics simulations of homogenous crystal nucleation in a large Lennard-Jones system and made quantitative comparisons with classical nucleation theory. No fitting parameters are necessary, as all quantities (including solid-liquid interfacial free energy) are accurately determined from separate simulations. In contrast with recent reports, no spinodal effect has been shown at moderate undercoolings; however, spinodal-like behavior appears at lower temperatures. Once transient effects are accounted for, at moderate undercoolings, we obtain reasonable quantitative agreement between our simulations results and classical nucleation theory. A crossover is observed between behavior dominated by the transient-time, and behavior dominated by steady-state nucleation. Finite-size studies demonstrate the importance of the transient time. We compare with similar simulations in a model of Al, which shows no spinodal-like behavior. This research has been sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-00OR-22725 with UT-Battelle.
TT5: Atomistic Modeling
Tuesday PM, December 02, 2008
Room 103 (Hynes)
2:30 PM - TT5.1
Molecular Dynamics Characterization of Icosahedral Order in Undercooled Copper.
Massimo Celino 1 Show Abstract
1 , ENEA - CR Casaccia, S. Maria di Galeria (Rome) Italy
No consensus there is on the role played by the icosahedral short range order on the stability of undercooled simple metals. Furthermore, experiments are not in agreement on the nature of the local icosahedral structures. The stability of undercooled copper is analyzed by performing classical molecular dynamics simulations based on an empirical interatomic potential. Icosahedral order is quantified in terms of a common neighbor analysis in several conditions of temperature and pressure. It is possible to show that not only perfect but also defective icosahedra, embedded in a disordered matrix, partecipate to stabilize the atomic structure preventing crystallization.
2:45 PM - TT5.2
Glass Forming Ability and Short-Range Order in Cu-Zr Alloys: an Ab Initio Molecular Dynamics Study.
Alain Pasturel 1 Show Abstract
1 , CNRS, Grenoble France
The understanding of the extraordinary glass forming ability of metallic alloys  is a long standing issue from the fundamental point of view as well as engineering side, and a comprehensive analysis of the thermodynamic, structural and kinetic properties at the atomic level is needed. For this purpose, we address the important question of the glass forming ability in connection with the short-range order in binary bulk metallic glasses by means of first principles molecular dynamics simulations. We have considered the evolution of the short-range order and dynamic properties of CuxZr1-x glass forming alloys as a function of composition x. We have found that the Cu-Zr alloys have a high degree of icosahedral short-range order already in the liquid state. Our results further reveal a predominance of the fivefold symmetry around Cu atoms is close to the icosahedral one, while the local environment of Zr atoms displays a more complex Frank-Kasper based-polytetrahedral symmetry. The viscosity shows a strong dependence with composition with a maximum at x=64 . From the evolution of the viscosity as a function of temperature at this composition, we have inferred the fragility parameter, which lies in the same range than some ternary bulk metallic glass formers . Our analysis clearly supports the scenario in which alloys having good glass forming ability show a pronounced ISRO already in the stable liquid . W. H. Wang, C. Dong, and C. H. Shek, Mat. Sci. Eng. R44, 45 (2004); A. Inoue, Acta Mater. 48, 279 (2000).  A. Pasturel and N. Jakse, Phys. Rev. B (to be published 2008).  N. Jakse and A. Pasturel, Appl. Phys. Lett. (to be published 2008). H. Tanaka, J. Phys.: Condens. Matter, 15, L491 (2003).
3:00 PM - TT5.3
Structural Ordering, Relaxation and Dynamical Heterogeneity in Glass-forming Metallic Liquids.
Howard Sheng 1 , Yongqiang Cheng 2 , Evan Ma 2 Show Abstract
1 Computational and Data Sciences, Geroge Mason University, Fairfax, Virginia, United States, 2 Materials Sci. Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Slow dynamics is bound to take place when a liquid enters its supercooled region. In recent years, structural mechanisms for slow dynamics have been one of the research focuses in condensed matter physics. For bulk glass forming metallic liquids, there is also a great need to uncover the interplay between structure, dynamics and glass forming ability. One of the challenges in the study of metallic liquids involving multi-components is the lack of accurate description of complicated inter-atomic interactions, which is important in controlling the formation of metallic glasses. In this presentation, we first make an effort to develop high-fidelity many-body interaction potentials for several archetypal BMG forming alloys, such as Zr-Cu-Al, Zr-Cu-Ag, and Pd-Ni-P, based on extensive first-principles calculations. Metallic glasses generated in computer simulation employing these interatomic potentials exhibit structural information, mechanical responses and other physical properties that match excellently with those of laboratory-made samples. We then proceed to systematically investigate the dynamics of the supercooled metallic liquids, as well as their underlying structural origin. Our results reveal that hierarchical structural ordering, involving the formation of immobile atomic clusters, percolation, and growth of backbone structure, is responsible for the slow dynamics and the consequent viscosity/fragility changes important for the formation of bulk metallic glasses.
3:15 PM - TT5.4
Does Anisotropy Promote Glass-forming Ability?
Corey O'Hern 1 2 , Carl Schreck 2 , Jan Schroers 1 Show Abstract
1 Department of Mechanical Engineering, Yale University, New Haven, Connecticut, United States, 2 Department of Physics, Yale University, New Haven, Connecticut, United States
We have investigated the influence of anisotropic interactions on the glass-forming ability of model binary alloys using molecular dynamics simulations. Anisotropy was included by either employing angle-dependent interaction potentials among soft (Lennard-Jones) particles or by studying the limit of hard-ellipsoids. In the simulations, we calculate the critical quench rate for crystallization as a function of anisotropy. We connect changes in the critical quench rate to the amount of short-range translational and orientational order found in the glass. These results reveal that anisotropic interactions can promote the glass-forming ability of alloys and other glassy materials.
3:30 PM - TT5.5
Atomistic Modeling of Poisson Ratio Effects in Metallic Liquids and Glasses.
James Morris 1 2 , Rachel Aga 1 , Takeshi Egami 2 1 , Valentin Levashov 2 Show Abstract
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
The Poisson ratio of a glass has recently been argued to correlate with a number of other properties of the glass and its associated liquid, including the ductility of the glass and the “fragility” of the supercooled liquid. However, there is little fundamental understanding of these correlations. We have constructed an atomistic model that allows us to tune the Poisson ratio, keeping the cohesive energy, bulk modulus, and lattice constant of the T=0 crystalline phase fixed. This model demonstrates that a number of properties are directly affected by the Poisson ratio of the glass. An increase in the Poisson ratio (from ~0.25 to ~0.3) dramatically improves the stability of the disordered phase. The melting temperature drops nearly 30%, due in large part to a lower enthalpy of the liquid phase. The diffusion barrier drops by a comparable amount. We demonstrate the existence of two “crossover” behaviors, similar to those observed in other simulations. At lower temperatures is the “mode-coupling” transition, which we associate with the conventional glass transition. At higher temperatures, a second crossover behavior occurs, above which the liquid behaves in a “normal” fashion. In the high temperature regime, energy fluctuations and pressure fluctuations are highly correlated. As the temperature drops through the upper crossover temperature, the heat capacity increases. The correlation between energy fluctuations and pressure fluctuations also drop. We present studies of the relationship of this transition to the breakdown of Stokes-Einstein behavior that links diffusion and viscosity. We also discuss these crossovers in terms of the concept of liquid “fragility,” and the relationship between fragility and Poisson ratio.This research has been sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-00OR-22725 with UT-Battelle.
3:45 PM - TT5.6
Computing Transition Pathways in Bulk Activated Processes and Viscosity of Supercooled Liquids.
Akihiro Kushima 1 , Xi Lin 2 , Ju Li 3 , Xiaofeng Qian 1 , Jacob Eapen 4 , John Mauro 5 , Phong Diep 5 , Sidney Yip 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Boston University, Brookline, Massachusetts, United States, 3 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 4 , North Carolina State University, Raleigh, North Carolina, United States, 5 , Corning Incorporated, Corning, New York, United States
4:00 PM - TT5:Modeling
TT6: Reactions and Crystallization
Tuesday PM, December 02, 2008
Room 103 (Hynes)
4:30 PM - **TT6.1
Effect of Rapid Heating on Transient Phase Formation During Self-Propagating Reactions in Metallic Multilayers.
Todd Hufnagel 1 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Metastable solid phases can be produced by rapid quenching from the liquid state, which limits the time available for diffusion and nucleation and growth of competing phases. Similar effects can be expected due to rapid heating, but most studies of phase transformations involving interdiffusion of chemical species have been performed either isothermally or at moderate heating rates (~1 K/s). In this talk, we discuss the influence of rapid heating (~10^6 K/s) on phase formation during self-propagating reactions in metallic multilayers. The reaction front is only ~100 µm wide and moves at ~1 m/s, but using time resolved synchrotron x-ray microdiffraction we can follow the sequence of phase formation in detail. For example, we show that the intermediate phases formed during self-propagating reactions in Al/Ni multilayers are different from those formed at lower heating rates, even though the final phases are the same. In situ characterization is essential, as other means of studying self-propagating reactions (such as quenching the reaction followed by ex situ analysis) provide different - and potentially misleading - results. We will interpret our observations in light of the effect of heating rate on the competitive nucleation and growth of the various intermetallic phases.
5:00 PM - TT6.2
The Size Distribution of Microstructure Formed by Time-Dependent Nucleation and Growth.
David Wu 1 , J. Chiu 1 Show Abstract
1 , Institute of High Performance Computing, Singapore Singapore
5:15 PM - TT6.3
Crystallization Pathways and Competing Multiscale Order Parameters in Metallic Glasses.
Xun-Li Wang 1 , Michael Miller 2 , Alexandru Stoica 1 , Ling Yang 1 , Dong Ma 1 , Zhao-Ping Lu 4 2 , Matthew Kramer 3 , Thomas Proffen 5 Show Abstract
1 Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology of Beijing, Beijing China, 3 Department of Materials Science and Engineering, Ames Laboratory and Iowa State University, Ames, Iowa, United States, 5 Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
One of the fascinating questions with regard to metallic glasses is the unusually high density of nucleation sites during crystallization. To answer this question we have carried out a systematic study of the crystallization process in a quinary Zr-Cu-Ni-Al-Ti bulk metallic glass, using DSC, synchrotron and neutron diffraction and small angle scattering, and atom probe tomography. By resolving the kinetics with in-situ synchrotron and neutron diffraction, we observed a two-stage consecutive nucleation process. A quasicrystal like phase formed first, followed by a second transformation into the tetragonal Zr2Ni phase. Real-space imaging by atom probe tomography shows that the nano-scale crystalline particles have a core-shell structure, which explains very well the interference peak observed in small angle neutron and synchrotron scattering experiments. Composition analysis indicates that both the core and shell are of the composition Zr2M, with M=Ni, Cu, Al. Meanwhile, Ti atoms are rejected from the core and shell. Our study suggests that crystallization in metallic glasses is driven by the nano-scale composition fluctuation, with crystalline particles nucleating from the solute-centered clusters that formed due to strong chemical bonding. The in-situ diffraction data also provided important clues on how these solute-centered clusters link up to form long-range order during crystallization.This research was supported by Office of Basic Energy Sciences, U.S. Department of Energy under Contract DE-AC05-00OR22725 with UT-Battelle, LLC.
5:30 PM - TT6.4
Crystallization Processes in Bulk Metallic Glass Forming Alloys.
Golden Kumar 1 , Jan Schroers 1 Show Abstract
1 Mechanical Engineering, Yale University, New Haven, Connecticut, United States
5:45 PM - TT6.5
Strain-rate Induced Crystallization in a Metallic Glass.
Chris Glomb 1 , Diana Farkas 1 , Chelsey Zacherl 1 , Alejandro Pacheco 2 Show Abstract
1 Materials Science, Virginia Tech, Blacksburg, Virginia, United States, 2 Engineering Science and Mechanics, Virginia Tech, Blacksburg, Virginia, United States
Virtual tensile tests of a model metallic glass were performed at different strain rates using molecular dynamics simulations. The evolution of shear transformation zones is studied, and we show that strain induced crystallization occurs with a direct correlation between the location of shear transformation zones and nucleation sites for the crystalline phase. The strain rate dependence of the phenomenon was studied, yielding an activation volume of the order of the atomic volume.
TT7: Poster Session: Local Structure and Dynamics in Amorphous Systems II
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - TT7.10
Laser Peening of Bulk-Metallic Glasses.
Feng Jiang 1 , Wenhui Jiang 1 , Yingfeng Guan 1 , Yueying Wu 1 , Philip Rack 1 , Peter Liaw 1 , Hahn Choo 1 2 Show Abstract
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Laser peening is used to treat the surface of bulk-metallic glasses. When a high-power laser beam passes through the water, it results in a shock-wave emission and cavitation-bubble generation. Large forces are induced, and localized deformation areas occur on the surface of the bulk-metallic-glass sample, when the bubbles collapse on the surface. The results show that the size and number of bubbles are dependent on the energy density of the beam, the number of the pulses, and the distance between the sample and the origin point where the beam begins to interact with the water. In deed, the shear bands have been observed around the bubble mark on the surface of the samples and the hardness of the deformation area is lower than that of the untreated area.
9:00 PM - TT7.11
Ab Initio Molecular Dynamics Studies of Liquid ZrxCu1-x.
Shaogang Hao 1 , Cai-Zhuang Wang 1 , Kai-Ming Ho 1 Show Abstract
1 , Ames Laboratory USDOE, Ames, Iowa, United States
We have carried out ab initio molecular dynamics (MD) simulations to investigate the local order, packing density, and diffusivity in liquid ZrxCu1-x as a function of Zr composition. Structure analysis demonstrates that Zr atoms tend to segregate in the liquid when Zr composition decreases. We also found that liquid Zr35Cu65 has the lowest diffusivity, which could be due to its highest local packing density. Voronoi tessellation analysis indicates that although liquid Zr20Cu80 exhibits highest population of icosahedral-like clusters among the liquid samples in our simulations, the spatial correlation among these icosahedral-like clusters is the strongest in the liquid Zr35Cu65. Comparison of our simulation results with experiments will be discussed.
9:00 PM - TT7.12
Mechanical and Fatigue Behavior of Ca65Mg15Zn20 Bulk-Metallic Glass.
Gongyao Wang 1 , Peter Liaw 1 , Oleg Senkov 2 , Daniel Miracle 2 Show Abstract
1 MSE, university of Tennessee, Knoxville, Tennessee, United States, 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio, United States
The compression behavior of a Ca65Mg15Zn20 bulk-metallic glass (BMG) was studied at strain rates of 10-4 s-1, 10-3 s-1, and 10-2 s-1 in air at room temperature. The specimens showed no macroscopic plasticity. Small pieces of material spalled from the sample free surfaces during compression and they fractured by exploding into many very small pieces after about 1.5 - 2.0% elastic strain. The nominal compressive strength increased from 300 to 409 MPa when the applied strain rate increased from 10-4 to 10-2 s-1. The Vickers hardness of the Ca65Mg15Zn20 BMG was about 1.42 GPa. Compression-compression fatigue experiments were performed at a stress ratio of R = 0.1. The fatigue limit was found to be about 140 MPa after 106 cycles. The fatigue fracture was similar to that under monotonic-compressive experiments, and demonstrated shear-fracture and splitting-fracture modes. The fracture strength was inversely proportional to the fracture time.We would like to acknowledge the financial support of the National Science Foundation: (1) the Division of the Design, Manufacture, and Industrial Innovation Program, under Grant No. DMI-9724476, (2) the Combined Research-Curriculum Development (CRCD) Programs, under EEC-9527527 and EEC-0203415, (3) the Integrative Graduate Education and Research Training (IGERT) Program, under DGE-9987548, (4) the International Materials Institutes (IMI) Program, under DMR-0231320, and (5) the Major Research Instrumentation (MRI) Program, under DMR-0421219, to the University of Tennessee, Knoxville, with Dr. D. Durham, Ms. M. Poats, Dr. C. J. Van Hartesveldt, Dr. J. Giordan, Dr. D. Dutta, Dr. W. Jennings, Dr. L. Goldberg, Dr. C. Huber, and Dr. C. R. Bouldin as Program Directors, respectively. Work at the Air Force Research Laboratory (AFRL) was conducted through the AFRL on-site contract No. FA8650-04-D-5233 and through an AFOSR Task (01ML05-COR, Dr. J. Fuller, Program Manager).
9:00 PM - TT7.13
Crystallization of HfO2-based Thin Layers Deposited by Sputtering.
Anna Vila 1 , Joaquim Font 1 , Antonis Olziersky 1 , Carlos Magana 1 , Jordi Arbiol 1 , Pedro Barquinha 2 , Luis Pereira 2 , Elvira Fortunato 2 , Rodrigo Martins 2 , Juan Morante 1 Show Abstract
1 Electronics, University of Barcelona, Barcelona Spain, 2 CENIMAT, New University of Lisbon, Lisbon Portugal
9:00 PM - TT7.14
Capillary Interactions Between Silica Particles in Organic Solvents.
Dobrin Bossev 1 , Garfield Warren 1 Show Abstract
1 Physics, Indiana University , Bloomington, Indiana, United States
9:00 PM - TT7.15
MD Simulations of Na2O-GeO2 Glass as a Function of Temperature and Composition.
Natalia Gorska 1 , John Kieffer 1 Show Abstract
1 MSE, University of Michigan, Ann Arbor, Michigan, United States
9:00 PM - TT7.16
Influence of Modifier Cation Mixing on the Structure and Mechanical Properties of Simulated Soda-lime Silicate Glasses.
Arun Upadhyay 1 , John Kieffer 1 Show Abstract
1 Materials science and engineering, University of Michigan, Ann Arbor, Michigan, United States
9:00 PM - TT7.17
Using the Interplay Between Thermodynamics and Kinetics to Control the Crystallinity in Polymer Nanofibers.
Chris Snively 1 Show Abstract
1 , University of Delaware, Newark, Delaware, United States
We have previously demonstrated that it is possible to kinetically trap thermodynamically metastable crystalline forms in semicrystalline polymers by employing electrostatic processing techniques. Here, we extend this concept to the processing of amorphous and semicrystalline polymer blends. The crystalline properties of many polymer blend systems have been studied during standard solution or melt processing techniques. Electrostatic processing offers the unique ability to study how the interplay of thermodynamics and kinetics affects the final properties of the polymer fibers. Specific examples that will be presented include poly(vinylidene fluoride) / poly(methyl methacrylate), poly(caprolactone) / poly(methyl methacrylate), and poly(ethylene glycol) / poly(vinyl acetate) blends.
9:00 PM - TT7.18
Controlling the Reactivity in Thin Film Photopolymerization via Molecular Order.
Chris Snively 1 Show Abstract
1 , University of Delaware, Newark, Delaware, United States
We have shown that 1,2-disubstituted ethylenes, which are a class of compounds that have typically been thought of as being nonpolymerizable, can be polymerized to high molecular weight within a reasonable amount of time, typically within minutes to hours. This polymerization was found to occur only in the amorphous phase. Here, we explore a wider variety of monomers to determine the effect of order on polymerization. It was observed that the reaction kinetics were widely variable, depending on whether the film was in the crystalline or amorphous state. We provide an explanation of this disparity of kinetic parameters based upon the molecular structure of the monomers in question.
9:00 PM - TT7.2
Electron-beam Induced Crystallization of Lanthanum Oxide Nanoparticles.
Jonathan Winterstein 1 , C. Barry Carter 1 Show Abstract
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Rare-earth oxides are being used to modify the behavior of ion conductors, to change the sintering characteristics of oxides and non-oxides and even to dope glass. In nanoparticle form they have great potential in fuel-cell applications, as catalysts or in optically active devices. Amorphous lanthanum oxide nanoparticles form as the initial precipitates from an aqueous solution, consistent with the so-called Ostwald’s step rule. Under electron irradiation in the transmission electron microscope (TEM) the particles rapidly crystallize into an FCC-structured metastable phase and after further irradiation transform into the equilibrium hexagonal phase. The FCC phase has only been formed previously at high temperatures and high pressures. Agglomerates of very small FCC crystallites (each ~1 2 nm in diameter) form within a single, initially amorphous, particle. Other changes occur to the microstructure depending on the extent of irradiation. The structure and chemistry of the amorphous and crystalline particles are investigated in situ with electron diffraction, high-resolution TEM and electron energy loss spectroscopy (EELS).
9:00 PM - TT7.22
Size-Independent Strength and Deformation Mode in Compression of a Pd-based Metallic Glass.
Brian Schuster 1 2 , Qiuming Wei 3 , Todd Hufnagel 2 , Kaliat Ramesh 2 Show Abstract
1 Weapons and Materials Research Directorate, US Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States, 2 , The Johns Hopkins University, Baltimore, Maryland, United States, 3 , University of North Carolina at Charlotte, Charlotte, North Carolina, United States
We present quasi-static, room temperature compression data for Pd40Ni40P20 metallic glasses, with specimen sizes ranging from sub-micron to several millimeters in diameter. We observe no change in deformation mode over this range. At all sizes, plastic flow is localized in shear bands, which are accompanied by sudden strain bursts. This metallic glass shows only a modest increase in strength in going from bulk to micrometer-sized specimens. We show that stress gradients in tapered specimens can complicate measurement of the yield strength of metallic glasses in microcompression. Estimates of yield strength based on the minimum cross-sectional area implicitly assume that yielding is controlled by a maximum effective shear stress criterion. An alternative is the shear plane yield criterion, in which the minimum shear stress on the shear band trajectory determines yield. Application of this criterion in tapered micro-specimens reinforces the notion that metallic glasses possess relatively size-independent mechanical properties.
9:00 PM - TT7.23
Spatial Correlations in the Plastic Strain in Model Metallic Glasses.
Craig Maloney 1 2 , Mark Robbins 2 Show Abstract
1 Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland, United States
The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Spatial correlations in the strain field are highly anisotropic and show apparent power-law behavior with a dramatic angular dependence of the effective scaling exponent. The strongest correlations are for wavevectors roughly perpendicular to the line of maximum resolved shear stress with systematic deviations from this which can be understood in terms of a Mohr-Coulomb effect. These results shed light on the nature of the yielding transition, supporting the notion that the dense steady flowing state is effectively critical in the slow-driving limit, and provide important, testable predictions for experiments on sheared amorphous materials such as bubble rafts, foams, emulsions, granular packings, etc., which can directly access the particle displacements.
9:00 PM - TT7.24
Elasticity, Thermal Expansion and Compressive Behavior of MgCuTb Bulk Metallic Glass.
Gong Li 1 Show Abstract
1 , Yanshan University, Qinhuangdao China
9:00 PM - TT7.3
Diffusion in Silicate Glasses and Melts: the Redox Reactions.
Benjamin Cochain 2 1 , Daniel Neuville 1 , Olivier Pinet 2 , Pascal Richet 1 Show Abstract
2 CEA, CeA Valhro SECM-LDMC, Marcoule France, 1 PMM-IPGP-CNRS, IPGP-CNRS, Paris, 75000, France
Diffusion in silicate melts plays a fundamental role in all magmatic processes in nature as well as in the glass industry. Of particular importance is the diffusivity contrast that occurs between the so-called network-former (e.g., Si, Al, B) and network-modifier (e.g., alkali and alkaline-earth) cations. Whereas the diffusivities of all these cations tend to converge at the high-temperature limit, a strong decoupling is observed when the glass transition is observed. Scaling with the viscosity of the melt, the diffusivity of oxygen and network-former cations then becomes much lower than that of network-modifier cations. This decoupling exerts a very strong influence on the kinetics and mechanisms of redox reactions. In redox reactions, diffusion of oxygen is the rate-limiting factor only at superliquidus temperatures whereas at lower temperatures, the kinetics of these reactions is controlled instead by diffusion of alkaline-earth or alkaline cations coupled to a flux of electron holes. For iron redox reactions, we have investigated these effects quantitatively from the glass transition up to 2100 K by in situ X-ray absorption Near Edge Structure (XANES) experiments at the iron K-edge. Near the glass transition, similar kinetic experiments have yielded the same results. To rationalize in a simple way the observations made, we have introduced the concept of redox diffusivity from the time required to achieve redox equilibrium at a given temperature. Comparisons of these redox diffusivities with the diffusivities of oxygen, network-forming and network-modifying cations then allow one to distinguish the temperature range where a given redox mechanism predominates. The results obtained in this way for a variety of alkali iron alumino-boro-silicates will be presented.
9:00 PM - TT7.4
Enhanced Toughness and Fatigue Life due to Microstructure Control of a Metallic Glass in-situ Matrix Composites.
Maximilien Launey 1 , Douglas Hofmann 2 , Jin-Yoo Suh 2 , William Johnson 2 , Robert Ritchie 1 3 Show Abstract
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Keck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, California, United States, 3 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
9:00 PM - TT7.5
Solid State Joining of Bulk Metallic Glass via Mechanically Assisted Diffusion.
Nicholas Hutchinson 1 , K. Flores 1 Show Abstract
1 , The Ohio State University, Columbus, Ohio, United States
Bulk metallic glasses are an important and expanding classification of metallic materials that exhibit exceptional mechanical properties. Limitations in the size and complexity of shapes that can be constructed from bulk metallic glasses restrict their widespread use as structural materials. One method of expanding the application of bulk metallic glasses is through the development of a commercially viable joining technique. We examine a solid state technique which combines Joule heating and pressure across the interface to form a joint through a mechanically assisted diffusion process. Our prior investigation of this technique indicated that the effectiveness of the joining process, as measured by the percentage of the interface area exhibiting cohesive failure when pulled in tension, increases with decreasing joining pressure. However, the strength of this joined material exhibits the opposite trend. In the present work we evaluate the effect of surface preparation on joint formation as well as expand on the study of joining pressure. The microstructure of the joint interface is also characterized in detail via SEM, XRD and TEM. Experimental results and process optimization will be discussed.
9:00 PM - TT7.7
Rapid Crystallization Behavior of a Zr-based Bulk Metallic Glass During Laser Processing.
Hongqing Sun 1 , Katharine Flores 1 Show Abstract
1 Materials Science and Engineering, the Ohio State University, Columbus, Ohio, United States
Due to the advantages of large thermal gradients and fast heating and cooling rates, laser deposition is a useful technique for the creation and study of metallic components with amorphous or uniquely tailored, highly non-equilibrium microstructures. In the present work, we use the Laser Engineered Net Shaping (LENSTM) process to deposit Zr-based (Zr58.5Cu15.6Ni12.8Al10.3Nb2.8) metallic powders on glassy substrates of the same nominal composition and examine the resulting structural changes in both the deposit and underlying substrate. Highly localized laser heating during single-layer deposition results in the formation of an amorphous melt zone surrounded by a crystalline heat affected zone (HAZ). The extent and morphology of the HAZ depend on the laser heat input, with very little crystallization observed for heat inputs less than ~7 J/m2. At higher heat inputs, numerous different crystal morphologies are observed within the HAZ. Transitions in morphology are observed as a function of distance from the interface with the melt zone. Under all processing conditions, the majority of the HAZ consists of tightly packed crystalline domains and/or roughly spherical crystals with dimensions on the order of 10 μm. The large size and significant spacing between crystals, particularly at the bottom of the HAZ, suggests that the crystallization process is dominated by growth rather than nucleation. Finite element modeling of the laser heating process indicates that crystallization is observed in regions where the peak temperature exceeds 900 K, while the heating rate is on the order of 103 K/s. The durations of the heating (dT/dt > 0) and annealing (T > Tg) events in the HAZ are on the order of 0.5 s and 2 s, respectively. Rapid cooling within the HAZ (~103 K/s) after the laser passes limits the time above 900 K to ~0.01 s. Combined with the observed crystal dimensions, this suggests a crystal growth rate of ~10-3 m/s, consistent with published results for a different Zr-based glass.
A. Lindsay Greer University of Cambridge
Cynthia A. Volkert University of Goettingen
Kenneth F. Kelton Washington University
TT8: Beyond Metallic Systems
Wednesday AM, December 03, 2008
Room 103 (Hynes)
9:30 AM - **TT8.1
Metallic Glassformers with Liquid-liquid Transitions, and a Second Fictive Temperature.
C Austen Angell 1 Show Abstract
1 Chemistry, Arizona State University, Mesa, Arizona, United States
10:00 AM - TT8.2
Universal Origin for Thermo-Mechanical Anomalies in 3- and 4-Coordinated Glass Formers.
Liping Huang 2 , John Kieffer 1 Show Abstract
2 Chemical Engineering, North Carolina State University, Raleigh, North Carolina, United States, 1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Anomalous thermo-mechanical behaviors in glasses such as the increase elastic moduli upon heating, the decrease upon compression, negative thermal expansion, etc., have been known for some time to exist for silica. We were able to elucidate the underlying mechanisms using MD simulations based on a charge-transfer multiple-coordination potential, designed to describe systems that undergo reactions and structural transitions. Thermo-mechanical anomalies have been much less frequently observed in 3-coordinated glasses. However, the modulus of boron oxide in the molten state does exhibit a minimum and an anomalous increase at high temperatures. Recently, we were able to reproduce this behavior in simulations and can now explain this anomaly as well. As a consequence of the underlying mechanism we identified, we furthermore predict that the anomalous behavior in boron oxide re-surfaces at room temperature when the glass is subject to tensile deformation, and that two previously unknown crystalline polymorphs exist for this compound. In summary, we find that upon compressing or expanding both tetrahedral and trigonal glasses, mechanically or thermally, these undergo reversible structural transitions by invoking mechanisms similar to those responsible for the transformations between different polymorphs of the crystalline counterparts of these materials. Accordingly, the thermo-mechanical anomalies have the same origin for both 3-coordinated and 4-coordinated glasses, and this phenomenon appears to be universal for all major network formers. Huang and Kieffer, PRB 69, 224203 (2004) Huang and Kieffer, PRB 74, 224107 (2006)
10:15 AM - **TT8.3
Towards Universal Memories? Exploring the Potential of Ultra-fast Crystallization Processes in Phase Change Materials.
Matthias Wuttig 1 Show Abstract
1 Physics of Novel Materials RWTH , Institute of Physics Aachen University of Technology , Aachen Germany
Phase change media are among the most promising materials in information technology. There are already employed in rewriteable optical data storage, where the pronounced difference of optical and electrical properties between the amorphous and crystalline state is used for data storage. This unconventional class of materials is also the basis of a storage concept to replace flash memory and hopefully could even compete with dynamic random access memories in certain fields. In this talk the relevant material properties of phase change media will be discussed together with unsolved scientific issues and the potential of phase change based storage concepts. It will be demonstrated that only a small group of covalent semiconductors with octahedral coordination has the required unconventional property combination of high optical and electrical contrast and fast crystallization kinetics. The origin of this pronounced stoichiometry and structure dependence will be explained on the basis of advanced computations and a variety of experiments.
10:45 AM - TT8:Non-Metal
11:15 AM - **TT8.4
Glass Transition in Polymers Studied by Positron Life Time Spectroscopy and Mechanical Spectroscopy.
Reiner Kirchheim 1 Show Abstract
1 Institut fuer Materialphysik, University of Goettingen, Goettingen Germany
11:45 AM - TT8.5
Experimental Observation of the Crystallization of Hard Sphere Colloidal Particles under Gravity.
Ingo Ramsteiner 1 , Katherine Jensen 1 , David Weitz 1 , Frans Spaepen 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
The phase behavior of hard spheres is a well studied problem in the field of statistical physics. Especially the crystallization transition at sufficiently high volume fractions keeps intriguing physicists - on the one hand because the entropy-driven ordering phenomenon seems counterintuitive, and on the other because colloidal particles mimic the phase behavior of atomic systems at experimentally convenient time and length scales.Gravity is often neglected in numerical simulations or compensated in experiments by density matching the colloidal suspension. However, the influence of gravity on the phase behavior of hard spheres is not only highly interesting from a fundamental point of view. It is also crucially important for the understanding of colloidal sedimentation and the growth of colloidal (photonic) crystals. Inspired by recent computer simulations , we have performed a confocal laser scanning microscopy study of the crystallization by sedimentation of 1.5µm colloidal silica spheres from a dilute homogeneous suspension. When the bottom of the sample cell is a hard wall, we observe a discontinuous crystallization of the first two layers simultaneously, followed by layerwise further growth of the crystal. This is also seen in recent numerical simulations. If we replace the smooth wall by a lithographically structured template , we observe layerwise growth from the very first layer on.This project illustrates how the advantages of numerical and physical simulations complement each other. Marechal and Dijkstra, Phys.Rev.E 75 (2007) 61404 van Blaaderen, Ruel and Wiltzius, Nature 385 (1997) 321
TT9: Deformation of Metallic Glasses I
Wednesday PM, December 03, 2008
Room 103 (Hynes)
12:00 PM - **TT9.1
The Flow State in Metallic Glasses.
Ali Argon 1 Show Abstract
1 Mechanical Engineering, Massachusdetts Institute of Technology, Cambridge , Massachusetts, United States
Much progress has been made in achieving robust metallic glass compositions having high melt viscosities to stifle premature crsytallization through dense atomic packing with minimal free volume. This, however, is counter-productive if the glassy product is to be subsequently plastically formed to final shape because plastic flow necessitates a flow state with a high concentration, c, of a liquid-like material fraction (free volume) of the order of c=O(0.5). This results in severe strain softening with attendant deformation instabilities and flow induced crystallization during flow. If processing is by viscous flow close to Tg at high rates, glass transition can occur, terminating processing. In the lecture many such examples will be cited in metallic glasses, amorphous silicon and even in lubricating oils that become glassy at high shear rates
12:30 PM - **TT9.2
Collective Dynamics of Shear Transformation Zones in Amorphous Metals.
Christopher Schuh 1 , Eric Homer 1 , Corinne Packard 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
The mechanism by which amorphous metals undergo shape change and redistribute deviatoric stress is the shear transformation zone, or STZ. Being local atomic shearing events on the scale of a few to a few dozen atoms, STZs are thermally activated but biased by the local stress field, and their operation redistributes stress in the surrounding material. When the temperature is high, STZs operate in a largely independent manner, and statistical flow laws can be derived to capture the ensemble average response. However, many of the most interesting mechanical phenomena in metallic glasses pertain to collective dynamics of multiple STZs in a cooperative mode. This talk will discuss progress in understanding collective STZ activity, through both simulations and experiments. First, an STZ-dynamics method of simulation is described, permitting observation of STZ operation and interaction on meaningful time and length scales. This work illustrates the manner in which STZs communicate with one another through the elastic stress field, and permits detailed analysis of complex mechanical behaviors such as shear band formation. Second, nanoscale deformation experiments using nanoindentation are discussed; these illustrate some interesting facets of collective STZ activity both in the process of yield (i.e., shear band formation) and for loading below the nominal yield point.
TT10: Deformation of Metallic Glasses II
Wednesday PM, December 03, 2008
Room 103 (Hynes)
2:30 PM - TT10.1
Broadband nanoindentation creep characterization of shear transformation zone activation during deformation in metallic glasses
Jonathan Puthoff 1 , Donald Stone 1 2 , Paul Voyles 1 2 , Joseph Jakes 1 3 , Hongbo Cao 2 Show Abstract
1 Materials Science Program, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2 Department of Materials Science and Engineering, University of Wisconsin - Madison, Madison, Wisconsin, United States, 3 , USDA Forest Products Laboratory, Madison, Wisconsin, United States
Broadband nanoindentation creep (BNC) is a new type of nanoindentation experiment which can determine material hardness across a wide range of strain rates (10–4
) from a single experiment at room temperature. These data can be used to characterize the kinetics of plastic deformation, including the free energy function (ΔG) for thermally-activated deformation. We have applied BNC in an investigation of the thermal activation of shear transformation zones (STZs) in three bulk metallic glasses in the Zr-Cu-Al system. We have found that the activation energy agrees with the functional form proposed by Johnson and Samwer , in which ΔG
– τ) / τc
, where τ is the flow stress and τc
is the flow stress at a temperature (T
) of 0 K. In the context of their model, we find that the STZ volume is in the range 100-500 atomic volumes and the activation energies for low stress deformation are 5-15 eV. Although these parameters are derived entirely from room temperature measurements, they can be used to reproduce the temperature-dependence of the flow stress. The derived τ vs. T
curves are in good agreement with the behavior expected in a wide range of metallic glasses .
 W.L. Johnson and K. Samwer, Phys. Rev. Lett. 95, 195501 (2005).
2:45 PM - **TT10.2
Frans Spaepen: Must Shear Bands be Hot?
Jeff De Hosson 1 , Dave Matthews 1 , Vasek Ocelik 1 , Paul Bronsveld 1 Show Abstract
1 Applied Physics, Un. of Groningen, Groningen Netherlands
Three glass forming alloy compositions have been chosen for ribbon production and subsequent electron microscopy studies. In-situ tensile testing with transmission electron microscopy, followed by ex-situ transmission electron microscopy and ex-situ scanning electron microscopy has allowed the deformation processes in tensile fracture of metallic glasses to be analyzed. In-situ shear band propagation has been found to be jump-like, with the jump-sites correlating with the formation of secondary shear bands. Nano-crystallization near the fracture surface is observed, however no crystallization is also reported in the same sample and the reasons for this are discussed. Both TEM and SEM observations confirm the presence of a liquid-like layer on or near the fracture surface of the ribbons. The formation of a liquid-like layer has been characterized by vein geometries and vein densities on fracture surfaces and its dependence on shear displacement is discussed. A simple model is adapted to relate the temperature rise during shear banding to the glass transition and melting temperatures and this is used to explain the variety of fracture surfaces which are developed for macroscopically identical tensile testing of metallic glasses together with features which exhibit local melting.
3:15 PM - **TT10.3
Local Structure and Dynamics in Glass Forming Alloys: Relationship with Strength and Plasticity of Bulk Metallic Glasses.
Evan Ma 1 , Yongqiang Cheng 1 Show Abstract
1 Materials Sci & Eng, Johns Hopkins University, Baltimore, Maryland, United States
3:45 PM - TT10:Deform
4:15 PM - TT10.4
A Coarse-grained Description of Localized Inelastic Deformation in Amorphous Materials.
Marios Demetriou 1 , William Johnson 1 , Konrad Samwer 2 Show Abstract
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Physics, University of Goettingen, Goettingen Germany
Amorphous materials and glasses in general are widely perceived as randomly inhomogeneous nanostructures, consisting of nanoscopic mechanical heterogeneities of varying configurational properties which result in material properties that vary spatially at the nanometer scale. These elementary “defects”, which are commonly referred to as shear transformation zones (STZ’s), are thought to represent regions of atomic cooperativity and are widely perceived as the “carriers” of plastic flow in the glassy nanostructure. Under conditions of mechanical non-equilibration (i.e. under strain rates higher than the rate of configurational relaxation), plasticity is understood to propagate through the glassy nanostructure via percolation across soft STZ’s aligned along the direction of maximum shear, thereby producing shear bands. In this presentation we will demonstrate that the sequence of STZ’s transitions that lead to localized inelastic deformation can be described by a spatially random coarse-grained model calibrated to obey the thermodynamic scaling relations that govern flow in a real glass. By means of this analysis we will further demonstrate that the evolution of the average shear modulus and potential enthalpy during shear localization is consistent with the concept of configurational hoping across a random potential energy landscape.
4:30 PM - TT10.5
Peak Width Changes in the Reciprocal- and Real-space Distribution Functions for Elastically and Plastically Deformed Cu64.5Zr35.5 Alloys.
Ryan Ott 1 , Mikhail Mendelev 1 , Matthew Besser 1 , Matthew Kramer 1 2 , Jonathan Almer 3 , Daniel Sordelet 1 Show Abstract
1 Materials and Engineering Physics, Ames Laboratory (USDOE), Ames, Iowa, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Recent studies have shown that in situ X-ray scattering is an effective technique for examining the atomic-scale deformation of metallic glasses, particularly their elastic behavior. Furthermore, the widths of the peaks in the reciprocal- and real-space distribution functions have been reported to be dependent on the elastic strain, where the change in peak widths has been attributed to the variance of the atomic-level hydrostatic stress distribution. Since previous studies have examined alloys containing 3 or more constituents, the effect of elastic straining on the peak widths is complicated by the multiple partial-pair correlations. Here we report utilizing in situ high-energy X-ray scattering and molecular dynamics (MD) simulations to examine the peak width changes in a binary Cu-Zr glass loaded in uniaxial compression and tension for the X-ray experiments and under hydrostatic pressure for the MD simulations. The X-ray results combined with the MD simulations reveal that the widths of the peaks in the reciprocal- and real-space distribution functions exhibit very different strain-state dependencies. Furthermore, the MD simulations suggest that the effect of elastic strain on the peak widths of the partial-pair correlations can vary greatly. To further explore the nature of the peak width changes during elastic and homogeneous plastic deformation, we performed constant strain-rate experiments at 425 oC. We find that the peak widths for both the reciprocal- and real-space distribution functions can be used to examine in real-time the structural disordering associated with plastic flow.
4:45 PM - TT10.6
Structural Changes Associated with Plastic Flow in a Zr-Based Bulk Metallic Glass.
Ashwini Bharathula 1 , Weiqi Luo 1 , Katharine Flores 1 , Wolfgang Windl 1 Show Abstract
1 Materials Science and Engineering, Ohio State University, Columbus, Ohio, United States
Due to exceptional properties like near-theoretical strength, large elastic range, and unusual formability above the glass transition temperature, bulk metallic glasses have tremendous potential as structural materials. However, their unique structure also gives rise to significant limitations, such as a lack of ductility due to the rapid localization of plastic flow in shear bands. Overcoming these limitations and realizing the potential of metallic glasses requires a detailed understanding of the complex relationship between the glass structure and deformation mechanisms. In the present study, we examine the structural changes induced by homogeneous deformation of a Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (nominal at%) bulk metallic glass, with particular focus on the combined effects of mass and thermal diffusion on the evolution of the glass structure. Flow behavior over a range of temperatures (300-450oC) is characterized by performing constant strain-rate and constant load experiments. The deformed specimens are examined using high resolution SEM, and structural changes are characterized via DSC and TEM. Experimental results are evaluated in light of a computational investigation of deformation in a simpler binary Zr-Cu system using Molecular Dynamics. Ab-initio electron density distributions for the structures are examined before and after the deformation. This provides insight into the structure of flow-defects which facilitate the required atomic rearrangement processes during both homogeneous and inhomogeneous flow.
5:00 PM - TT10.7
Molecular Dynamics Simulation Study of Changes in Structure of Amorphous Cu-Zr Alloys Associated with Deformation.
Mikhail Mendelev 1 , Ryan Ott 1 , Mattew Kramer 1 , Daniel Sordelet 1 Show Abstract
1 MEP, Ames Laboratory, Ames, Iowa, United States
We present the results of molecular dynamics simulations revealing changes in the structure of the amorphous Cu-Zr alloys that are associated with deformation. The simulation utilizes our Cu-Zr many-body potential, which provides very good agreement with the experimentally measured elastic constants for these alloys. First, we study the case of hydrostatic deformation and analyze how the partial and total pair correlation functions change during elastic deformation. We show that Zr-Zr nearest-neighbor distances exhibit a stronger sensitivity to an imposed hydrostatic stress than do Cu-Cu or Cu-Zr distances. Based on these results we analyze how reliable the determination of the strain tensor from diffraction data is. Next, we examine the structural changes in amorphous Cu64.5Zr35.5 during plastic deformation. In particular these changes are discussed in relation to increases in free volume and atomic mobilities in the flow-softening regime.
5:15 PM - TT10.8
New Processing Potential for Ultra-High Fracture Toughness Metallic Glass Matrix Composites.
Douglas Hofmann 1 , Jin-Yoo Suh 1 , Aaron Wiest 1 , Marios Demetriou 1 , William Johnson 1 Show Abstract
1 Materials Science, Caltech, Pasadena , California, United States
5:30 PM - TT10.9
Mechanical Behaviors of a Zr-based Bulk-metallic Glasses Subjected to Surface Severe Plastic Deformation.
Jiawan Tian 1 , Leon Shaw 2 , Yoshihiko Yokoyama 3 , Peter Liaw 1 Show Abstract
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Chemical, Materials and Biomolecular Engineering , University of Connecticut, Storrs, Connecticut, United States, 3 Advanced Research Center of Metallic Glasses , Institute for Materials Research, Tohoku University , Sendai 980-8577 Japan
The near-surface severe plastic deformation process has been successfully applied on the Zr50Cu40Al10 bulk metallic glasses (BMGs) without casuing brittle fractures. The experiment is implemented using twenty WC/Co balls to bombard the surface of the samples in a purified argon atmosphere. The plastic-flow deformation in the unconstrained sample edge was observed, which exhibits the good intrinsic ductility of the BMG materials in this experimental condition. Differential-scanning-calorimetry (DSC) and synchrotron diffraction experiments on the specimens subjected to different processing times show that possible crystallization may occur during the process. Surface hardness was improved by about 15% and begin to decrease from surface to interior after three hours of treatment, which may be attributed to the deformation-induced crystallization and/or the reduced free volume. Four-point-bending fatigue behavior has been characterized and related to the modified surface structure and the compressive residual stress induced by the surface treatment. This work is supported by the NSF combined research-curriculum development (CRCD) program under DGE-9987548 with Ms. Poats as the contract director.