Jan Schroers, Yale University
Ralf Busch, Universitaet des Saarlandes
Wei-Hua Wang, Institute of Physics, CAS
Nobuyuki Nishiyama, Tohoku University
Symposium Support Materion Corporation
PX Services SA
II2: Structure and Deformation II
Monday PM, December 02, 2013
Hynes, Level 1, Room 107
2:30 AM - *II2.01
Atomistic Origin of Viscosity in the Liquid
Takeshi Egami 1 2
1University of Tennessee Knoxville USA2Oak Ridge National Laboratory Oak Ridge USAShow Abstract
Viscosity is one of the most important parameters to characterize a liquid. In the supercooled state as temperature is lowered it increases rapidly, by as much as 15 orders of magnitude or more, before the sample reaches the glassy state. The microscopic origin of viscosity and the reason why it increases so much in the supercooled region have long been a subject of intense debate because it is a key question regarding the formation of a glass. Recently we found that the origin of viscosity at high temperatures is the local configurational fluctuations. We have shown that the Maxwell relaxation time, tau;_M (= eta;/G, where eta; is viscosity and G is the high-frequency shear modulus), is equal to the time-scale of local configurational excitation (LCE), tau;_LC, defined as the time to lose or gain one nearest neighbor . Thus a macroscopic quantity, tau;_M, is directly related to a microscopic quantity, tau;_LC. This relation, however, breaks down below the crossover temperature, TA, where viscosity shows a super-Arrhenius behavior. We found that this is because transverse phonons are localized above TA, so that LCEs cannot communicate each other and thus they are independent of each other. Below TA they communicate through the dynamic stress field they create, resulting in tau;_M > tau;_LC. This explains the super-Arrhenius behavior and rapid increase in viscosity as temperature approaches Tg, the glass transition temperature. These results represent a view of atomic dynamics in the liquid state very different from the conventional one. We are currently working on the experimental verification of the relation, tau;_M = tau;_LC, using inelastic neutron and x-ray scattering.
 T. Iwashita, D. M. Nicholson and T. Egami, Phys. Rev. Lett., 110, 205504 (2013).
3:00 AM - *II2.02
Structure and Properties of the Backbone of Metallic Glasses
Howard Sheng 1
1Geroge Mason University Fairfax USAShow Abstract
The properties of metallic glasses depend on their structures. Here we demonstrate the existence of backbone structures in metallic glasses through computational studies focusing on metal-metalloid systems. The backbone of metallic MGs distinguishes itself by its topological and chemical ordering in the medium range. The atomic-level structure of the backbone can be best described with the concept of tetrahedral cluster packing, where the packing of local structural motifs is highly efficient. The backbone structure is found to be inherited from the supercooled liquid, and shows no signs of spatial growth during the glass transition. The spatial extension and dimensionality of the backbone is highly correlated with geometrical frustration limit of cluster packing. By applying metadynamics to alter the structure of the backbone, new glasses with distinct energetics and structures is found. The existence of backbones has profound effects on the properties of metallic glasses. We further shed light on (1) the heterogeneous relaxation dynamics of the supercooled liquid by correlating it with the formation of the backbone structure; and (2) the devitrification process of metallic glasses and the destabilization of the backbone.
3:30 AM - II2.03
Systematic Mapping of Icosahedral Short-Range Order in a Melt-Spun Zr36Cu64 Metallic Glass Using Scanning Electron Nano-Diffraction
Amelia Liu 1 2 Melissa Neish 3 2 Georgie Stokol 2 Genevieve Buckley 2 Lachlan Smillie 4 2 Martin de Jonge 5 Ryan Ott 6 7 Matthew Kramer 6 7 Laure Bourgeois 1 8
1Monash University Clayton Australia2Monash University Clayton Australia3University of Melbourne Melbourne Australia4Australian National University Canberra Australia5Australian Synchrotron Clayton Australia6Ames Laboratory Ames USA7Iowa State University Ames USA8Monash University Clayton AustraliaShow Abstract
Despite the lack of long-range order in metallic glasses (MGs) it is thought that significant localized atomic ordering exists. At the length scale of nearest-neighbor arrangements, the short-range atomic order (SRO) is dictated by efficient atomic packing in clusters or polyhedra . The packing of these quasi-equivalent clusters then gives rise to a distinct medium-range atomic order (MRO). ZrxCu100minus;x MGs have good glass-forming abilities over many compositions . Modeling studies of this system using molecular dynamics [3, 4] and reverse Monte Carlo  have identified the dominant SRO as Cu-centered icosahedral clusters using Voronoi analysis [3, 5] and a cluster template method . The incidence of icosahedra increases with increasing Cu [3, 5]. The short-range stability of icosahedral clusters in the liquid  contributes greatly to the slowing structural dynamics at the glass transition . Icosahedral clusters in the models demonstrate a strong spatial correlation compared to other polyhedra, suggesting a string-like icosahedral MRO  that might determine strength and brittleness.
In the present study we measure and map the magnitude of angular correlations in an array of scanning electron nano-diffraction (SEND) patterns obtained from a Zr36Cu64 glass . By tuning the coherence length of the electron probe to the size of the SRO clusters in the glass, the angular symmetries in the SEND patterns reflect prominent symmetries of the SRO clusters. We statistically analyze the incidence of prominent two, six and ten-fold symmetries in the SEND patterns of this glass, and identify the predominant SRO in these materials as icosahedral clusters, consistent with many modeling studies [3,4,5]. By mapping the magnitude of these symmetries we infer that the MRO in this material consists of face-sharing or interpenetrating icosahedra in keeping with efficient space-filling. This novel technique of mapping the strength of angular correlations in SEND patterns is a promising direct method to probe the structure of disordered materials .
 D. B. Miracle, Nature Mat., 3, 697 (2004).
 N. Mattern, A. Schöps, U. Kühn, J. Acker, O. Khvostikova, and J. Eckert, J. Non-Cryst. Solids, 354, 1054 (2008).
 Y. Q. Cheng, H. W. Sheng, and E. Ma, Phys. Rev. B, 78, 014207 (2008).
 X. W. Fang, C. Z. Wang, Y. X. Yao, Z. J. Ding, and K. M. Ho, Phys. Rev. B, 82, 184204 (2010).
 M. Li, C. Z. Wang, S. G. Hao, M. J. Kramer, and K. M. Ho, Phys. Rev. B, 80, 184201 (2009).
 F. C. Frank, Proc. R. Soc. Lond. A, 215, 43 (1952).
 A. C. Y. Liu, M. J. Neish, G. Stokol, G. A. Buckley, L. A. Smillie, M. D. de Jonge, R. T. Ott, M. J. Kramer, and L. Bourgeois, Phys. Rev. Lett., 110, 205505 (2013)
3:45 AM - II2.04
Production of Bulk Amorphous Steels from Cast Iron Scraps
Bengi Yagmurlu 1 M. Vedat Akdeniz 1 Amdulla O. Mekhrabov 1
1Middle East Technical University Ankara TurkeyShow Abstract
Bulk amorphous steels (BAS&’s) are one of the promising advanced materials with superior mechanical and physical properties compared with their crystalline counterparts. These unique properties make BAS&’s suitable candidates for structural applications. Although there are diverse production techniques from high purity constituent elements, however no research have been published about the synthesis of BAS&’s from scrap materials via commercially available production techniques. According to this perspective, the usage of steel scraps as a base material in the production of BAS&’s had to be investigated.
In this study, the BAS&’s consisting of cast iron scrap (having 3.5 - 4.5% C) with elemental addition (Cr, Mo, B, Ln (=Lanthanides), Y, V, W) were produced by arc melting equipped with suction casting unit as well as conventional centrifugal casting machine. In this ongoing research, 2.5 mm thick amorphous samples with having wide supercooled liquid region (Tg = 545.2°C, Tx = 663.1°C, Tm = 1136.5°C, Trg = 0.48 and ΔTx = 117.9°C), were produced with conventional centrifugal casting machine. The effects of alloying additions on physical, mechanical and structural properties were investigated. Nanocrystallization characteristics and kinetics will also be studied by annealing the BAS&’s in the vicinity of Tg and Tx temperatures. Both amorphous and nanocrystallized samples will be characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimerty (DSC), vibrating sample magnetometer (VSM) and mechanical testing methods.
4:30 AM - *II2.05
Atomic Scale Signatures of Deformation and Cavitation in Metallic Glass: Toward a Microscopic Theory of the Brittle-Ductile Transition
Michael L. Falk 1 Pengfei Guan 1 Sylvain Patinet 1
1Johns Hopkins University Baltimore USAShow Abstract
Molecular dynamics simulation can be used to test the microscopic assumptions of constitutive theory. We have applied these techniques to investigate theories of cavitation and deformation in metallic glass. The rate of cavitation was measured in systems subjected to various degrees of hydrostatic loading. We observed two regimes of cavitation, an early regime in which classical nucleation theory holds and a later regime in which shear transformation zone (STZ) activity interferes with the cavitation process. This leads to interesting questions regarding how cavitation and STZ activation compete within the fracture process zone to determine metallic glass ductility. Furthermore we have applied MD techniques to attempt to identify STZ activation in metallic glass under differently oriented shear loading. Attempts to correlate STZ activity with normal mode analysis of the structure have proven inconclusive, but the orientation dependence of the STZ activity reveals important characteristics of the STZs and the history dependence of their distribution.
5:00 AM - *II2.06
Atomic-Scale Characterization of Shear Bands in Metallic Glasses: Tracer Diffusion, Free Volume and Nanocrystal Development
Gerhard Wilde 1
1University of Munster Munster GermanyShow Abstract
Deformation in glasses proceeds differently than in crystalline materials due to the absence of defined lattice planes and due to the absence of line defects with discrete Burgers vectors. Experiments have shown that deformation exceeding the elastic range is mostly localized in plate-like mesoscopic defects, so-called shear bands. Although the occurrence of shear bands during plastic deformation of metallic glasses is well known, their actual physical properties remain fairly unknown. Here, experimental data on the rate of atomic diffusion within shear bands has been obtained using the radiotracer method on post-deformed specimens. The experimental results indicate unambiguously that the diffusivity is largely enhanced as compared to volume diffusion in the same metallic glass at identical temperatures. This result is also discussed with respect to nanocrystal formation in shear bands.
In order to analyze the local properties of glassy matter within the shear band regions, a new approach based on analytical transmission electron microscopy methods has been developed. In fact, this approach allows to quantitatively determine the local mass density, composition and structural states with nanometer resolution. Thus, shear bands and the surrounding matrix can be analyzed separately and comparatively. In addition, to analyze the shear band propagation and interaction on a mesoscopic scale, digital image correlation in combination with the application of nanoscale marker patterns and scanning electron microscopy detection have been utilized. The experimental results are discussed with respect to the underlying mechanism during the early stages of shear band activation.
5:30 AM - II2.07
Shear Offset and Temperature Rise in Bulk Metallic Glasses
Stephanie Slaughter 1 Xiaojun Gu 2 Felicitee Kertis 1 Wendelin J. Wright 2 3 Todd Hufnagel 1
1Johns Hopkins University Baltimore USA2Bucknell University Lewisburg USA3Bucknell University Lewisburg USAShow Abstract
Although it is well known that significant heating can occur in active shear bands, the degree of heating and the circumstances under which heating occurs remain controversial. We have used the fusible tin coating method to detect shear band heating in amorphous Zr57Ti5Cu20Ni8Al10 loaded under quasi-static uniaxial compression. By lithographically patterning the tin coating into 15 µm wide lines we can measure the shear offset as a function of position along a shear band, and simultaneously assess the amount of heat release by measuring the distance away from the shear band that melting of the tin is observed. These observations are further correlated with high-rate load data acquired with a piezoelectric load cell and high-rate video, which allow a precise determination of the time scale associated with the shearing events. On samples loaded to fracture we observe evidence of melted tin consistent with significant heat release. On samples where loading was halted prior to fracture we see no evidence of melted tin, despite the presence of shear offsets up to ~6 µm on some shear bands. We discuss the implications of these observations for our understanding of thermal evolution in shear bands, including the possibility that there is less heat released than current models predict.
5:45 AM - II2.08
Nanocompression Studies on Metallic Glass Nanoparticles by In-situ Compression Test
Jinwoo Kim 1 Hyejung Chang 2 Eunsoo Park 1
1Seoul National University Seoul Republic of Korea2Korea Institute of Science and Technology Seoul Republic of KoreaShow Abstract
Mechanical properties in nano-sized metallic glasses have been widely investigated to clearly understand the fundamental deformation mechanism of metallic glasses. In particular, the change of yield strength and the occurrence of deformation mode transition (heterogeneous to homogeneous) with sample size reduction have been reported in previous experimental studies through the nanopillar test results. Research on nano-mechanical responses of metallic glasses could lead to an in-depth understanding of the deformation mechanism related to the nucleation and propagation of shear bands. However, during the pillar fabrication using focused ion beam for nanopilar test, Ga+ ion beam damage on pillar surface is difficult to avoid and the fabrication takes relatively long for multiple pillar preparations. To avoid the drawbacks of nanopillar tests, in the present study we performed nanocompression tests of metallic glass nanoparticles. In our experiments, metallic glass nanoparticles have been fabricated by the dealloying technique from phase separated metallic glasses. From the two-amorphous alloys with droplet structure, the reactive matrix phase has been selectively dissolved by chemical process. The shape of the remaining particle phases was clearly spherical, and the sizes of fabricated particles have distribution in 40~300 nm diameter range. The effect of particle size on mechanical properties of fabricated amorphous particles has been investigated from the compression test using in-situ compression tester with electron microscope imaging. Due to the distinct morphology of particles compared to that of nanopillars, the stress-strain relations from particle compression test results are derived based on contact mechanics theory and contact area calculation. The electron beam irradiation effect during in situ compression test will be also reported, with a focus on unloading process response of nanoparticles. These results provide us with insights on evaluation of nano-mechanical properties and understanding of fundamental deformation mechanism of metallic glasses.
II1: Structure and Deformation I
Monday AM, December 02, 2013
Hynes, Level 1, Room 107
9:30 AM - *II1.01
Eshelby Inclusions and Dilatation in Hard-Sphere Colloidal Glasses
Frans Spaepen 1 Katharine E. Jensen 1 David A. Weitz 1
1Harvard University Cambridge USAShow Abstract
Tracking of the individual particles by confocal microscopy during deformation of a colloidal glass makes it possible to follow the local strain tensor as a function of the macroscopically imposed strain. Autocorrelation of this strain field reveals the distinct quadrupolar character of a sheared Eshelby inclusion. The volume-strain product of these inclusions is similar to that measured experimentally in metallic glasses. Weaker quadrupolar autocorrelations are also observed in undeformed, quiescent colloidal glasses, which indicates that Eshelby shear modes are already thermally active. The shear modulus of a colloidal glass can be measured from the probability distribution of the thermally activated shear strain energy density. As expected for these dense hard-sphere glasses with a large pressure head above them, the shear modulus increases strongly with depth (from 1 to 6 Pa). Deformation causes the shear modulus throughout the sample to drop uniformly to 1-2 Pa. After the deformation stops, the modulus relaxes back to its original profile. In dense hard-sphere systems, the modulus is a sensitive probe of the density, and hence these experiments can be used to track the small density changes associated with the deformation process.
10:00 AM - *II1.02
Nonlinear Mechanical Response of Metallic Glasses
Mo Li 1 2
1Georgia Institute of Technology Atlanta USA2Tsinghua University Beijing ChinaShow Abstract
While elastic behavior of metallic glasses are well known and documented, nonlinear response remains largely untouched, especially its relation to symmetry change and yielding. Considering that the elastic limit is typically 2-3% , one must consider the nonlinear effect into consideration in mechanical properties for most metallic glasses. In this work, we show that indeed, nonlinear effect can not be ignored as shown by the large third order elastic constants. And furthermore, we show the emergence of symmetry breaking in metallic glasses caused by external loading which is exhibited in the change of the elastic constants. The nonlinear elasticity allows us also to look into the very question of the theoretical strength of metallic glasses. We show that the tensile and compressive strength can reach E/5 and E/7 respectively, where E is the Young's modulus. Other implications of the nonlinear elastic responses in the overall mechanical properties of metallic glasses will be discussed.
10:30 AM - II1.03
Origin of the Universal Elastic Strain Limit of Bulk Metallic Glasses
Jun Ding 1 Yongqiang Cheng 2 Evan Ma 1
1Johns Hopkins University Baltimore USA2Oak Ridge National Laboratory Oak Ridge USAShow Abstract
All bulk metallic glasses exhibit a large and almost universal elastic strain limit. Here we show that the magnitude of the yield strain of the glass state can be quantitatively derived from a characteristic property of the flow state typical in running shear bands (the root cause of yielding). The strain in the shear flow is mostly plastic, but associated with it there is an effective elastic atomic strain. The latter is almost identical for very different model systems in our molecular dynamics simulations, such that the corresponding yield strain is universal at any given homologous temperature.
10:45 AM - II1.04
Irradiation of Model Lennard-Jones Glasses and Its Effect on the Potential Energy Landscape: Structure and Plasticity
Peter M Derlet 1 Dan J Magagnosc 2 Dan Gianola 2
1Paul Scherrer Institute PSI-Villigien Switzerland2University of Pennsylvania Philadelphia USAShow Abstract
Multiple primary-damage-state cascade simulations were performed on a well
relaxed 50/50 binary model glass. As a function of the number of primary
knock-on atoms (PKAs), the resulting atomic-scale structure was characterized
in terms of the first and second derivatives of the potential energy landscape.
Local quantities such as volume, stress and Kelvin elastic moduli were
investigated, as well as the vibrational properties of the evolving structure.
Structural excitations were also investigated using the Activation-Relaxation-Technique (ART),
giving barrier energy distributions as a function of PKA number. The work finds that
on average the glass's structural features change little and rapidly saturate with respect
to increasing PKA number, with the main effect being a change in the pressure (and therefore volume)
as well as shift of the ART-derived barrier energies to lower values. These
results are discussed in terms of their implication to plasticity for small-scale
bulk metallic glass samples.
11:30 AM - *II1.05
Correlation between the Thermodynamic and Kinetic Fragilities of Metallic Glass Forming Liquids
Isabella Gallino 1
1Universitamp;#228;t des Saarlandes Saarbramp;#252;cken USAShow Abstract
In contrast to pure metals and most non-glass forming alloys, metallic glass formers are moderately strong liquids. In general, the kinetic fragility increases with the complexity of the alloy with differences between the alloy families, e.g. noble-metal based alloys being more fragile than Zr-based alloys. Experimental kinetic and thermodynamic data are assessed for several bulk metallic glasses-forming and analyzed using the Vogel-Fulcher-Tammann (VFT) equation and the Adam-Gibbs (AG) approach. The thermodynamic temperature where the configurational entropy vanishes in the AG-approach is the same temperature where viscous flow becomes infinite in the VFT-kinetic model, suggesting the same microscopic origin and rigorously connecting the kinetic and thermodynamic aspects of fragility. Moreover, the stronger the glass, the larger is the AG-free enthalpy barrier to cooperative rearrangements, advocating the concept that in strong liquids the flow events are more localized and therefore higher activation barriers need to be overcome.
12:00 PM - *II1.06
Structural Transitions in Metallic and Semiconducting Glassformers: Some Phenomenological Relationships
Charles Austen Angell 1
1Arizona State University Tempe USAShow Abstract
One of the more surprising developments in the area of metallic glassformers in recent years has been the suggestion by Zhang et al (J.Chem. Phys. 133, 014508 (2010). that a large number of metallic glassformers exhibit some sort of structural transition, manifested as a change from fragile liquid character at high temperature to strong liquid character at lower temperature approaching the glass transition. This behavior was previously considered a characteristic only of certain highly anomalous "tetrahedral liquids" like water, silica, BeF2 and elemental silicon. That such phenomena may also be associated with metal-to-semiconductor transitions was suggested long ago by Turnbull and coworkers in relation to silicon phenomenology, and then confirmed by the simulations of Grabow, Sastry and their coworkers.
In the metallic glassformer case, of course, the transition cannot be assigned to any electron localization phenomenon, while in the water and silica cases, there is no hint of delocalized electrons, so we must search for some more general explanation. We find this in the phenomenology of the glassformer analog class of materials called the rotator phases, which also exhibit the pattern of behavior known as strong/fragile in the case of liquids. However, in the case of plastic crystals the "strong" extreme can be associated with the occurrence of order-disorder ("lambda") transitions at higher temperatures. These critical phenomena have a well-understood theoretical underpinning, and it will be suggested that they might be relevant to the metallic glassformer behavior as well. In liquids, the transition may be damped out before becoming critical, or may be prempted by a first order transition, which might signal a sudden crystallization. In the case of certain model liquids, there is a true critical point, at which two liquids of the same composition but different density, become indistinguishable. We link these ideas to known anomalies in supercooled liquid Te, and As2Te3, and wonder if they might find practical manifestation in the fast switching phenomena of "phase change" materials. (Angell, in Physics and Applications of Disordered Materials (editor M. Popescu) pp 1-18 (2002)).
12:30 PM - II1.07
Thermodynamic and Kinetic Studies of Pt-Base Bulk Metallic Glass Forming Alloys
Isabella Gallino 1 Giulia dalla Fontana 2 Oliver Gross 1 Livio Battezzati 2 Ralf Busch 1
1Saarland University Saarbruecken Germany2Universitaamp;#8217; di Torino Torino ItalyShow Abstract
Master alloys of composition Pt57.3Cu14.6Ni5.3P22.8, Pt42.5Cu27Ni9.5P21, and Pt60Cu16Co2P22 have been produced by melting the raw elements in an induction furnace. The master alloys have been consequently purified by melting them under a flux of B2O3 and used to cast bulk metallic glass specimens, of 3 mm thickness, using a tilt-casting device and Cu-molds. For each alloy composition, thermophysical properties, both thermodynamic and kinetic, have been measured using differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA), respectively. The specific heat capacities of the liquid, crystalline and glassy states are measured in DSC and the excess and configurational entropy functions of the undercooled liquid are thereafter determined. Equilibrium viscosities below the glass transition are measured using a three-point beam-bending method and the kinetic fragility parameters are determined using the empirical Vogel-Fulcher-Tamman equation. Additionally, the temperature dependence of the equilibrium viscosity is analyzed with the Adam-Gibbs configurational entropy model and an activation barrier for cooperative rearrangement are determined. Particular attention has been devoted to how these properties change with the alloy group, composition and complexity.
12:45 PM - II1.08
In situ Heating Transmission Electron Microscopy Study of Metallic-Glass Thin Films
Li He 1 Jinn P. Chu 2 Yen-Chen Chen 2 Chia-Lin Li 2 Peter K. Liaw 3 Paul M. Voyles 1
1University of Wisconsin-Madison Madison USA2National Taiwan University of Science and Technology Taipei Taiwan3University of Tennessee Knoxville USAShow Abstract
We have used in-situ heating in the scanning transmission electron microscope (STEM) to measure the structural evolution and glass transition temperature Tg of ZrCuAlNi bulk metallic glass thin films deposited by sputtering. Annealing at 400 °C for 2 hours increases the Zr and Cu compositional fluctuations from around 3 at. % to about 10 at. % measured with sub-nanometer electron probes on 20 nm thick Zr51Cu32Al9Ni8 films. When Zr and Cu atoms are more separated, two distinct diffraction maxima appear, indicating that the short-range order becomes less homogeneous above 350 °C. The degree and type of the medium-range order structure also shift above 400 °C. All of these correlated changes in composition and structure begin well below the Tg, and grow more pronounced until the onset of crystallization above the glass transition. Tg of Zr53Cu29Al12Ni6 was measured in situ using the plasmon peak energy, Ep, in electron energy loss spectroscopy (EELS). Ep is sensitive to the specific volume, V, through the number density of valence electrons. V derived from Ep as a function of temperature up to 500 °C shows two linear regions. The low temperature region corresponds to a volume thermal expansion coefficient α of 5 × 10-5 K-1. At high temperatures, α = 4 × 10-4 K-1. The intersection of the two lines gives Tg = 490 °C. This value is higher than the calorimetric Tg of 470 °C, pointing to the importance of obtaining a true reference temperature for the thin TEM sample, not just the thermocouple on the TEM sample holder. Efforts to combine this technique and temporal fluctuation electron microscopy to study nanoscale structural relaxation near Tg will also be discussed.
We acknowledge support from the National Science Foundation (LH and PMV DMR-0905793 and PKL DMR-0909037, CMMI-0900271, and CMMI-1100080).
Jan Schroers, Yale University
Ralf Busch, Universitaet des Saarlandes
Wei-Hua Wang, Institute of Physics, CAS
Nobuyuki Nishiyama, Tohoku University
Symposium Support Materion Corporation
PX Services SA
Tuesday PM, December 03, 2013
Hynes, Level 1, Room 107
2:30 AM - *II4.01
What Can Nanocrystalline Alloys Teach Us About Glass Forming?
Heather A. Murdoch 1 Michael Gibson 1 Christopher A. Schuh 1
1MIT Cambridge USAShow Abstract
Efforts to stabilize nanocrystalline metals through alloying share both a philosophical goal and some empirical similarities with glass forming science. The basic premise, namely that the local atomic clusters in an alloyed grain boundary may be similar to those in a comparably alloyed glass, suggests that grain boundary segregation and glass formation would have similar physical roots. Hence, thermodynamic models developed to describe the energy of grain boundaries should be able to shed a new perspective on the glass forming ability of binary alloys. In this talk we explore this analogy quantitatively for both equilibrium and non-equilibrium processing scenarios, with emphasis on its relation to classical heuristics for predicting glass forming ability: atomic size difference, heat of mixing, etc.
3:00 AM - *II4.02
An Assessment of Ternary Bulk Metallic Glasses: Correlations between Structure, Glass Forming Ability and Stability
Dan Miracle 1 Dmitri Louzguine-Luzgin 2 3 Larissa Louzguina-Luzgina 2 3 Kevin Laws 4 Akihisa Inoue 2 3
1Materials and Manufacturing Directorate Dayton USA2WPI Advanced Institute of Materials Research, Tohoku University Sendai Japan3Institute of Materials Research, Tohoku University Sendai Japan4School of Materials Science and Engineering, University of New South Wales Sydney AustraliaShow Abstract
The influence of atomic structure on glass-forming ability and thermal stability in ternary metallic glasses is assessed for a broad range of ternary metallic glasses. Over 1000 ternary BMGs from over 100 ternary systems reported in the literature are studied. The atomic structure is quantified for each alloy using the efficient cluster-packing model, and the local atom packing efficiency is quantified around all three elements in the glass. Other data taken from the literature for these glasses includes density, maximum amorphous thickness, and thermal stability parameters such as glass transition temperature, crystallization temperature, melting temperature and liquidus temperature. Correlations are made between the atomic structure, and especially local atomic packing efficiency, with amorphous thickness and thermal stability. Topological similarities and differences between the best ternary BMGs are identified, and preferences for particular combinations of radius ratios and for solute-rich vs solute-lean glasses are reported. The full range of glasses studied, along with the detailed characterization of atomic structures, give clear trends and new insights into the nature of glass-forming ability in ternary glasses.
3:30 AM - II4.03
Can Packing Efficiency Predict Glass-Forming Ability?
Kai Zhang 1 2 Yanhui Liu 1 2 Jan Schroers 1 2 Mark D. Shattuck 4 5 Corey O'Hern 1 2 3
1Yale University New Haven USA2Yale University New Haven USA3Yale University New Haven USA4The City College of the City University of New York New York USA5The City College of the City University of New York New York USAShow Abstract
The glass-forming ability (GFA) or critical cooling rate of metal alloys determines the maximum thickness of metallic glass samples. Understanding the key physical properties that determine the GFA is essential for developing stronger and less costly bulk metallic glasses (BMGs). However, it is still extremely difficult to predict the GFA of multi-component alloys, and BMG design is currently a trial-and-error process. One heuristic guiding principle is that the GFA is enhanced for systems with densely packed amorphous structures. However, we find that the jammed packing fraction varies by less than one per cent over a wide range of size ratios and stochiometries in amorphous packings of binary and ternary hard-sphere mixtures. We also search for the competing crystalline phases in binary and ternary hard-sphere mixtures over the same range of size ratios and stochiometries using novel genetic algorithms, Monte Carlo and molecular dynamics simulations. We find that the packing fraction of the dense crystalline structures is a complex and non-monotonic function of the size ratio and stoichiometry. We will determine the extent to which the packing fraction and vibrational entropy of the crystalline structures influence the GFA.
3:45 AM - II4.04
Non-Integer Power-Law Scaling of Density in Metallic Glasses
Qiaoshi Charles Zeng 1 2 Wendy Mao 1 2
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Different matter usually has different densities, which is closely relevant to their atomic packaging. Packing problem is a long-standing scientific challenge and has relevance in a wide range of scientific and practical fields.1 Metallic glass (MG)2 with non-directional metallic bonding shows exciting potential for applications and also provides a realistic model system for random sphere packing. Efficient packing (maximizing density) of atoms and/or clusters can stabilize a system and has been revealed to be the basic of mysterious atomic structure in MGs.3,4 Thus the density as a key constrain for modeling plays a essential role to understand the atomic structure and glass forming ability of MGs.4,5 By tuning the density of a MG using integrated multiple in situ high pressure techniques including x-ray diffraction, ultrasonic sound velocity measurements and full field nano x-ray transmission microscopy, we rigorously established a power-law relationship with a power D ~ 2.51 scaling the global density with the atomic level structural information (principal diffraction peak position, 1/q1) in MGs. This study with high quality data provides compelling evidence of the “universal” non-third power-law scaling in MGs, which will put an end to the intense debate in this field.6 The unusual 2.51 power-law oversets our anticipation of a third power-law based on our common sense of random packing in Euclidean space. Our results will have important implications not only in the practical measurements of density or any those involving a change in length scale under various environments, but also in understanding the real atomic packing in MGs and even more general packing problems.
1 C. Song, P. Wang, and H. A. Makse, Nature 453 (7195), 629 (2008); F. Zamponi, Nature 453 (7195), 606 (2008).
2 A. L. Greer and E. Ma, MRS Bull. 32 (8), 611 (2007); W. H. Wang, Adv. Mater. 21 (45), 4524 (2009).
3 J. D. Bernal, Nature 185 (4706), 68 (1960).
4 D. B. Miracle, Nature Mater. 3 (10), 697 (2004); H. W. Sheng, W. K. Luo, F. M. Alamgir et al., Nature 439 (7075), 419 (2006); D. B. Miracle, Acta Mater. 54 (16), 4317 (2006).
5 Y. Li, Q. Guo, J. A. Kalb et al., Science 322 (5909), 1816 (2008); L. Yang, G. Q. Guo, L. Y. Chen et al., Phys. Rev. Lett. 109 (10), 105502 (2012).
6 D. Ma, A. D. Stoica, and X. L. Wang, Nature Mater. 8, 30 (2009); Y. Q. Cheng and E. Ma, Prog. Mater. Sci. 56 (4), 379 (2011); A. R. Yavari, A. Le Moulec, A. Inoue et al., Acta Mater. 53 (6), 1611 (2005); P. Chirawatkul, A. Zeidler, P. S. Salmon et al., Phys. Rev. B 83 (1), 014203 (2011); O. F. Yagafarov, Y. Katayama, V. V. Brazhkin et al., Phys. Rev. B 86 (17), 174103 (2012); N. Mattern, M. Stoica, G. Vaughan et al., Acta Mater. 60 (2), 517 (2012).
4:30 AM - *II4.05
Ultrastable Metallic Glasses: From Short-Range Order to Medium-Range Order
Mingwei Chen 1
1Tohoku Sendai JapanShow Abstract
Multicomponent bulk metallic glasses are among the most unique and fascinating of the recently discovered materials. However, the lack of thermal stability, arising from their metastable nature and the high tendency of crystallization, has been one of the paramount obstacles that hinders the wide range of applications of metallic glasses. In this talk we will report that the stability of a metallic glass can be dramatically improved by manipulating the local atomic arrangement from short-range order to medium-range order. The glass transition and crystallization temperatures of the ultrastable glass can be increased by above 50 K and 210 K, respectively. The ultrastable metallic glass also shows ultrahigh strength and hardness, over 30 % higher than its ordinary counterpart.
5:00 AM - *II4.06
Radiation-Induced Super-Quenching and Plasticity in Metallic Glasses
Richard Baumer 1 Michael Demkowicz 1
1MIT Cambridge USAShow Abstract
Metallic glasses respond to radiation in qualitatively different ways than crystalline solids. We identify two distinctive mechanisms of radiation response in metallic glasses through a series of ½ billion-atom simulations using molecular dynamics. In the first, inter-nuclear scattering causes localized melting and quenching at rates approaching 10^14 K/s, giving rise to nanoscale “super-quenched zones” (SQZs) with exceptionally high free volume. In the second, rapid volumetric expansion in regions of localized melting generates intense stress pulses that cause polarized plastic deformation in adjacent material. Based on these insights, we construct a parameter for predicting the radiation-response of amorphous materials that may be used in the selection of metallic glasses for applications ranging from nuclear waste storage to ion beam materials modification.
5:30 AM - II4.07
Deformation-Induced Ordering of Metallic Glasses
Zhitao Wang 1 Jie Pan 1 Yi Li 1 2 Christopher A Schuh 3
1National University of Singapore Singapore Singapore2Institute of Metal Research, Chinese Academy of Sciences Shenyang China3Massachusetts Institute of Technolog Cambridge USAShow Abstract
It is considered as the nature behavior that glass deformation involve "disordering" of the structure, or the accumulation of free volume. The dominance of disordering processes is what renders the mechanical properties of glasses (metallic glasses in particular) disappointing-especially properties like toughness and ductility; this general feature of glass deformation is what makes them brittle. In this talk we explore the possibility of deformation-induced ordering in glass. Through detailed experimental work, we show that this unusual kind of deformation can occur in metallic glass at room temperature. We also discuss the physical conditions required to evoke such a process, and implications of these conditions for glass design.
5:45 AM - II4.08
Fabrication, Tuning Soft Magnetics, and Magneto-Optic Properties of BMG Based Fe66Ni6B4Nb24 Transparent Thin Films
Aadnan Ali Afridi 1 Ansar Masood 1 2 Valter Stroem 1 Anastasia Riazanova 1 Lyubov Belova 1 K. V Rao 1
1KTH Stockholm Sweden2Carl Tryggers Foundation Stockholm SwedenShow Abstract
Bulk Metallic Glass, BMGs, -as an engineering metal- is currently an area of growing interest and has focused intense research activities. Among BMGs Fe-based metallic glasses are of great interest because of their attractive soft magnetic properties with coercivity Hc less than 1 A/m, and high saturation magnetization (Ms) values. Furthermore, BMGs exhibit the best mechanical properties, which are of interest to exploit the mechanical and soft magnetic properties of these materials in the thin film form for developing special electromagnetic components and applications in the MEMS technology. We have fabricated by pulsed laser deposition very thin (5-7nm), and thick (27 to 408 nm) glassy films of composition Fe66Ni6B24Nb4 on glass and silicon substrates respectively, and studied their magnetic and magneto-optic properties at room temperature.
We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exhibit soft magnetic characteristics with low Hc, and high Ms values. The magnetic hysteretic loops of the as deposited thicker films on the silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness, and 2) the onset off a two stage process during the approach to magnetic saturation: The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (le;200oC), the thicker films can be tailored to exhibit a simple soft magnetic square loop with low Hc.
The 5-7nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation measurement technique. Very high values of FR in the range 16 to 20 deg/mu;m film thickness almost linearly dependent on the wavelengths of light in the range 405 - 611nm is observed. The observed high values of Faraday rotation over a wide range of the wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.
The studies described above at room temperature on the PLD deposited films based on Fe-based films has been made possible by using XRD, Dual beam SEM/FIB Nova 600 Nanolab, the Faraday rotation spectrometer, and room temperature vibration sample magnetometer. Preliminary room temperature domain observations carried out using Asylum research AFM and MFM system will be also discussed. These soft magnetic transparent BMG based films have then been used to develop non-invasive sensors.
* Hero-M Vinn Center of Excellence supported project.
Carl Tryggers Foundation
II5: Poster Session I
Tuesday PM, December 03, 2013
Hynes, Level 1, Hall B
9:00 AM - II5.01
Interatomic Potential to Predict the Favored and Optimized Compositions for Some Ternary Metallic Glass Formation
Jiahao Li 1 Yuanyuan Cui 1 Shizhen Zhao 1 Baixin Liu 1
1Tsinghua Unv. Beijing ChinaShow Abstract
Based on the proposed long-range n-body potential, both molecular dynamics and Monte Carlo simulations were carried out to study the ternary metallic glass formation in some bulk metallic glass forming systems containing Cu, Zr, Hf, Al and Ni, etc. In the simulations, solid solution models were employed to compare the relative stability of the solid solution versus its competing disordered state i.e. metallic glass phase, over the entire composition triangle. The simulation results not only clarified that the underlying physics of the metallic glass formation is the crystalline lattice collapsing when the solute concentration exceeds the critical solid solubility, but also predicted, for each system, a quantitative composition region, within which formation of metallic glasses is energetically favored. Furthermore, the energy difference between the initial solid solution and resulting metallic glassy phase was also derived and defined as the driving force for the crystal-to-amorphous transformation. The amount of the driving force could thus be considered as a comparative measure of the glass-forming ability. In a ternary metal system, the largest driving force could be correlated to the optimized composition, of which the metallic glass is the most stable one and likely the easiest one to be obtained in experiments. Interestingly, the predictions directly from the interatomic potentials are well compatible with the experimental observations reported so far in the literature. Consequently, the above described atomistic theory is capable of predicting the glass-forming region for the ternary metal systems and could thus be a good guidance for designing appropriate alloy compositions to produce desired ternary metallic glasses.
Key words: Metallic glass, Glass-forming ability, Atomistic theory, N-body potential
1. Jan Schroers: Physics Today 66, 32-41 (2013).
2. J.H. Li, Y. Dai, X.D. Dai: Intermetallics 31, 292-320 (2012).
3. J.H. Li, S.Z. Zhao, et al. J. App. Phys. 109, 113538 (2011).
4. Y.Y. Cui, J.H. Li, et al. J. Phys. Chem. B 115, 4703-4708 (2011).
5. Y.Y. Cui, J.H. Li, et al. App. Phys. Lett. 99, 011911 (2011).
6. S.Z. Zhao, J.H. Li and B.X. Liu: J. Mater. Res. 26, 2049-2064(2011).
9:00 AM - II5.02
Physical Origin of Glass-Forming Ability of the Binary Metal Systems Clarified from Atomistic Theory
Jianbo Liu 1 JiaHao Li 1 BaiXin Liu 1
1School of Materials Science and Engineering Beijing ChinaShow Abstract
From the experimental point of view, it is generally accepted that a material&’s glass-forming ability (GFA) is usually either proportional to its critical casting thickness or inversely proportional to its critical cooling rate. However, for a metal system, differing from the situation of a specific alloy, the Glass-Forming Ability, which is one of the important scientific issues concerning the bulk metallic glass, is quantitatively denoted by the Glass-Forming Range (GFR). The GFR not only shows whether or not metallic glasses could be obtained in a system, but also indicates the alloy composition range, within which metallic glasses could be formed by some specific glass-producing techniques. It follows that the wider the GFR, the greater the GFA of a metal system. To present authors&’ view, a metal system should have its own intrinsic GFA/GFR, as the existence of the atomic configuration in a disordered state is determined by the internal characteristics of the system. The intrinsic GFA/GFR reflects the maximum possible composition range energetically favored for the metallic glass formation. We report in this paper, starting with the interatomic potentials of eight representative binary metal systems, covering various structural combinations and thermodynamics characteristics, molecular dynamics simulations using solid solution models led to establish an atomistic theory for the binary metallic glass formation. The theory not only clarifies that the physical origin of the binary metallic glass formation is the crystalline lattice collapsing while solute concentration exceeds the critical value, but also quantitatively determines, for each system, an exact composition range, within which the disordered state, i.e. formation of metallic glasses, is energetically favored. It turns out that the developed atomistic theory is well supported by the experimental observations reported so far in the literature.
9:00 AM - II5.03
Generation of Amorphous Porous Cu64Zr36: An ab initio Approach
Jonathan Galvamp;#225;n-Colamp;#237;n 1 R. M. Valladares 2 Ariel A. Valladares 1
1Instituto de Investigaciones en Materiales, UNAM Mamp;#233;xico Mexico2Facultad de Ciencias Mamp;#233;xico MexicoShow Abstract
Although some theoretical methods to generate amorphous porous structures have been devised, they are based on either experimental data or experimental procedures which lack transferability to other systems. We use our ab initio approach to generate amorphous porous Cu64Zr36 (ap-Cu64Zr36): the expanding lattice (EL) method, which has been employed previously to generate amorphous porous carbon, silicon, copper, silver and gold. In our approach the interatomic distances are proportionally increased by doubling the volume of the cell, thus halving the density and making the initial supercell metastable. We applied the EL method to two different initial configurations: a 108-atom crystalline cubic supercell (c-Cu64Zr36) and a 108-atom amorphous supercell (a-Cu64Zr36), both with an initial density of 8.06 g/cm3. After the lattice expansion, the initial supercells were subject to ab initio molecular dynamics for 500 steps at constant room temperature using a time step of 10.71 fs. Finally, the resulting structures were relaxed. Pores appeared along well-defined spatial directions. We characterized the structures by means of the pair distribution functions and the bond-angle distributions. Our results were compared with the non-porous amorphous Cu64Zr36. Due to certain difficulties that arise when obtaining microporous amorphous alloys experimentally and the lack of experimental counterparts for ap-Cu64Zr36, our results should be considered predictive. Further studies should be made in order to handle a larger number of atoms, thereby larger pores.
9:00 AM - II5.04
Uniform Tensile Plastic Deformation in a Geometrically Confined Metallic Glass Composite
Fu-Fa Wu 1 Keith C Chan 1
1Hong Kong Polytechnic University Hong Kong ChinaShow Abstract
Metallic glasses (MGs) are regarded as strong but intrinsically brittle macroscopically, exhibiting zero tensile plasticity, due to the plastic deformation being localized in a narrow shear band. By introducing a secondary soft phase such as a body-centred cubic β dendritic phase to inhibit and multiple the shear bands, the β-dendrite-reinforced MG composite (MGC) exhibits inhomogeneous elongation of the order of a few percent. Once it yields, its stress decreases continuously, leading to remarkable necking. However, when a β-dendrite-reinforced Ti-based MGC plate is confined by a commercially pure titanium (CPT) substrate, uniform tensile plastic deformation can be achieved in the MGC where the strain localization and necking is suppressed. The MGC can sustain a true tensile strain exceeding 10% without fracture. A deformation mechanism is proposed to interpret the plastic deformation of the MGC/CPT structure. The revealed significant intrinsic plasticity of the MGC suggests its potential application as an excellent coating for bulk ductile materials.
9:00 AM - II5.05
Modeling of Equilibrium Phases in Equimolar Multicomponent Systems
Daniel Joseph Miksevicius King 1 2 Simon Charles Middleburgh 2 Lyndon Edwards 2 Gregory R Lumpkin 2 Michael J Ford 1 Michael B Cortie 1
1University of Technology Sydney Australia2Australian Nuclear Science and Technology Organisation Lucas Heights AustraliaShow Abstract
High Entropy Alloys (HEAs), a novel class of material, were developed early this century in the wake of bulk metallic glass development. They are defined as alloys composed of five or more principal elements in equimolar ratios. Similar to bulk metallic glasses in many ways (including production methods), HEAs differ by displaying a crystalline structure which often takes the form of a disordered homogeneous solid solution of face centered cubic (FCC) and/or body centered cubic (BCC) packing. They display enhanced yield strengths and hardness when compared to conventional alloys at temperatures exceeding 1270K (similar to intermetallic compounds), whilst maintaining their ductility. Empirically derived thermodynamic concepts have been used to predict novel multicomponent bulk metallic glass systems. Ab-inito methods were then used to gain a mechanistic understanding of previously studied HEAs as well as to make predictions for new HEA systems. Selected four element samples of these alloys have been produced by vapour deposition techniques. XRD and electron microscopy characterization of the produced phases was carried out to guide the modeling.
9:00 AM - II5.09
Calculation of the Dynamic Loss Modulus for Bulk Metallic Glasses: Thermal Activation, Extreme Value Statistics and Kinetic Freezing
Peter M Derlet 1 Robert Maass 2
1Paul Scherrer Institute PSI-Villigien Switzerland2University of Gamp;#246;ttingen Gamp;#246;ttingen GermanyShow Abstract
The dynamic loss modulus of bulk metallic glasses below the glass transition
temperature is calculated using a thermal activation theory that exploits
the known properties of the potential energy landscape of the under-cooled
liquid regime. Below the glass transition temperature, the calculated loss
modulus is found to consist of two dominant components, which can be
interpreted as reflecting the underlying alpha-relaxation and beta-relaxation
processes that facilitate both micro- and macro-plasticity in these materials.
These results are discussed in terms of recent dynamical mechanical spectroscopy
experiments for a variety of well known bulk mechanical glasses.
9:00 AM - II5.10
A Crystalline-to-Amorphous-to-Crystalline (C-A-C) Transition in Cr2Ti Intermetallic Compound
Satoshi Anada 1 Takeshi Nagase 2 1 Yasuda Hidehiro 2 Mori Hirotaro 2
1Osaka University Suita Japan2Osaka University Ibaraki JapanShow Abstract
A crystalline-to-amorphous-to-crystalline (C-A-C) transition in Cr2Ti intermetallic compound was investigated by high voltage electron microscopy (HVEM). The Cr2Ti could not maintain its original crystal structure under electron irradiation, resulting in the irradiation-induced solid-state amorphization (SSA) at and below 103 K. With continued irradiation, a new non-equilibrium crystalline phase was formed from the amorphous phase. Namely, a C-A-C transition was observed under electron irradiation. The crystalline phase obtained through the C-A-C transition was identified as a bcc solid solution phase whose composition was the same as that of Cr2Ti. A typical C-A-C transition, characterized by an amorphous single phase formation through SSA and the appearance of coarse crystalline grains without the difference in the chemical composition among Cr2Ti, an amorphous phase and a bcc solid solution, was found. The origin of the C-A-C transition was discussed on the basis of a binary phase diagram and a Gibbs free energy model.
9:00 AM - II5.11
Glass Transition by Gelation in a Phase Separating Amorphous Binary Alloy
Richard E Baumer 1 Michael J Demkowicz 1
1Massachusetts Institute of Technology Cambridge USAShow Abstract
Previous studies have identified compositional medium range order (CMRO) and icosahedral short-range order (ISRO) in phase separating amorphous metal alloys. Using molecular dynamics (MD) simulations of a model phase separating amorphous metal alloy, Cu50Nb50, we show that a percolating network of ISRO forms at interfaces between compositionally enriched regions and leads to glass transition. Below the glass transition temperature, the ISRO network is mechanically stiff, imparts shear resistance, and halts coarsening of the CMRO. The ISRO network constrains the dynamics of surrounding atoms and leads to anomalous diffusion. This ISRO network and its influence on the physical properties of the system bears striking resemblance to gelation in colloidal systems, in which a system-spanning, dynamically arrested network of locally preferred structures imparts stiffness. We discuss how gelation may be relevant to glass transition in more conventional bulk metallic glasses.
9:00 AM - II5.12
Antimicrobial Properties of As-Cast and Surface-Engineered Zr-Based Bulk Metallic Glasses
Lu Huang 1 2 Elizabeth M. Fozo 3 Peter K Liaw 1 Tao Zhang 2 Wei He 1 4
1the University of Tennessee Knoxville USA2Beihang University Beijing China3the University of Tennessee Knoxville USA4the University of Tennessee Knoxville USAShow Abstract
The random packing of constituent atoms in metallic glasses (MGs) yields a unique combination of properties. Their excellent mechanical properties, high chemical stability, facile thermal formation, and metallic appearance qualify them as durable, scratch resistant, and aesthetically pleasing touch surface materials. Touch surfaces in public settings serve as reservoirs of pathogenic microbes, which can result in the transmission of infectious diseases. Current practices to prevent bacterial growth on touch surfaces include the use of disinfectants, which requires repetitive operations, and Cu alloys with their intrinsic antimicrobial properties. The efficiency of Cu alloys though can be hindered by the high cost of pure copper, its low strength and wear resistance, and its susceptibility to corrosion. MGs exhibit potential antibacterial property, owing to the presence of biocidal elements (i.e., Cu, Ag, Zn, etc) in various glass-forming compositions. In the current research, the antimicrobial ability of Cu- or Ag-bearing Zr-based MGs was investigated using dry contact assays with the gram positive bacterium Staphylococcus aureus (ATCC 6538). Number of viable adherent cells was determined by serial dilution and the spread plate method and pure Cu or Ag samples were used as controls. A significantly lower number of viable bacterial cells were found on the Zr-Al-Ni-Cu MGs after 4 hr of incubation, indicating the killing capability of the Zr-based MGs. In order to advance the antimicrobial properties of as-cast MGs, the ion implantation technique was employed to increase the surface concentration of biocidal elements. Moreover, we found that the antibacterial mechanisms of Cu or Ag lie in their ion forms. Therefore, the amounts of Cu or Ag ions released from MGs and reference samples were monitored using inductively-coupled plasma (ICP-OES). Ion release profile was established as a function of immersion time, which was directly correlated with killing efficacy.
9:00 AM - II5.14
High-Resolution Radial Distribution Functions of Pure Ion-Implanted Amorphous Silicon Measured Using Tilted-Illumination Selected Area Electron Diffraction
Amelia Liu 1 2 Timothy Petersen 2 1 Alexander Gorecki 2 Bianca Haberl 3 Jodie Bradby 3 Jim Williams 3
1Monash University Clayton Australia2Monash University Clayton Australia3Australian National University Canberra AustraliaShow Abstract
Amorphous silicon (a-Si) created by self-ion implantation is an extremely pure and reproducible form of amorphous silicon. It is 1.8% less dense than crystalline Si  and has no voids . The Si atoms are on average sightly under 4-fold coordinated, due to atomic defects . Continuous a-Si layers created by ion implantation undergo structural relaxation when annealed at low temperatures. This structural relaxation results in a reduction in average bond-angle distortion , consistent with a decrease in defect