By systematically investigating the relaxation behavior of a model metallic glass based on the extensive molecular dynamics (MD) simulations combined with the dynamic mechanical spectroscopy method, a pronounced ultra-low temperature peak on the loss modulus spectrum was discovered for the first time in MD simulations. It was found that the relation peak occurs at a much lower temperature than the typical temperature for the conventional beta relation peak as reported in the literature. According to the atomic displacement analysis, we unravel that the reversible atomic motions, rather than the thermal vibrations or local structural rearrangements, mainly contribute to this relaxation peak. We further identify the atomic level mechanism of this fast relaxation process by characterizing the local geometrical anisotropy. Furthermore, by tracing the dynamic behaviors of these "reversible" atoms, we demonstrate the intrinsic hierarchy of the local relaxation modes, which are triggered by atomic vibrations and gradually developed to the reversible and irreversible atomic movements. Our findings shed light on a general picture of the relaxation processes in metallic glasses.
Crystallization of metallic glass as a grain-boundary nucleated process: experimental and theoretical evidence for the grain structure of metallic glasses
We use coherent X-rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. The rich diversity of this behavior reflects a complex energy landscape, giving rise to a unique type of gla…
The activation energy (E_A) spectra of potential energy landscape (PEL) provides a convenient perspective for interpreting complex phenomena in amorphous materials; however, the link between the E_A spectra and other physical properties in metallic glasses is still mysterious. By systematically probing the E_A spectra for numerous metallic glass samples with distinct local geometric ordering, which correspond to broad processing histories, it is found that the shear modulus of the samples are strongly correlated with the arithmetic mean of the E_A spectra rather than with the local geometrical…
Upon cooling, glass-forming liquids experience a two-step relaxation associated to the cage rattling and the escape from the cage, and the following decoupling between the \b{eta}- and the α-relaxations. The found decoupling behaviors have greatly changed the face of glassy physics and materials studies. Here we report a novel dynamic decoupling that the relaxation function changes gradually from a single-step to a two-step form as temperature declines through the stress relaxation of various metallic glasses in a broad time and temperature range below glass transition temperature (Tg). Such a…
New metallic glasses containing La or Ce have been introduced that have dynamic properties bordering on extremes of conventional metallic glasses. This provides opportunity to test trends or correlations established before in molecular and polymeric glass-formers if exist the same exist in the broader family of metallic glasses. Due to the drastically different chemical and physical structure of metallic glass-formers than soft matter, there is no guarantee that any correlation found in the latter will hold in the former. If found, the result brings metallic glasses closer to the much wider cl…
We theoretically investigate high-pressure effects on the atomic dynamics of metallic glasses. The theory predicts compression-induced rejuvenation and the resulting strain hardening that have been recently observed in metallic glasses. Structural relaxation under pressure is mainly governed by local cage dynamics. The external pressure restricts the dynamical constraints and slows down the atomic mobility. In addition, the compression induces a rejuvenated metastable state (local minimum) at a higher energy in the free energy landscape. Thus, compressed metallic glasses can rejuvenate and the…
In the present investigation the glass forming ability of Ce65Al25Co10 metallic glass has been reported. It was successfully synthesised using melt spinning techniques. The existence of amorphous phase in Ce65Al25Co10 alloy have been proved using X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The thermal analysis of the synthesised sample using differential scanning calorimetry (DSC) shows a glass transition around 371 K, thus confirms existence of glassy phase at room temperature. The hardness of the synthesised sample at different load have been demonstrated…
We show the correlation between nanoscale structural heterogeneity and mechanical property and glass forming ability of Zr-based metallic glasses (MGs). Detailed parameters of medium range ordering (MRO) that constitutes the structural heterogeneity, including the type, size, and volume fraction of MRO domains determined using 4-dimensional scanning transmission electron microscopy, directly correlate with the ductility and glass forming ability of Zr-Cu-Co-Al MGs. Mesoscale deformation simulation incorporating the experimentally determined MRO confirms that the diverse types and sizes of MRO …
We report nano-scale mechanical heterogeneity of a metallic glass characterized by dynamic atomic force microscopy. Apparent energy dissipation with the variation of ~12%, originating from non-uniform distribution of local viscoelasticity, was characterized. The correlation length of heterogeneous viscoelasticity was measured to be ~2.5{\pm}0.3 nm, which is well consistent with the dimension of shear transformation zones for plastic flow. This study provides the first experimental observation on the nano-scale mechanical heterogeneity in a metallic glass, and may fill the gap between atomic mo…
Cycling of a metallic glass between ambient and cryogenic temperatures can induce higher-energy states characteristic of glass formation on faster cooling. This rejuvenation, unexpected because it occurs at small macroscopic strains and well below the temperatures of thermally induced structural change, is important, for example, in improving plasticity. Molecular-dynamics simulations elucidate the mechanisms by which thermal cycling can induce relaxation (reaching lower energy) as well as rejuvenation. Thermal cycling, over tens of cycles, drives local atomic rearrangements progressively eras…
Avalanche behaviors, characterized by power-law statistics and structural relaxation that induces shear localization in amorphous plasticity, play an essential role in deciding the mechanical properties of amorphous metallic solids (i.e., metallic glasses). However, their interdependence is still not fully understood. To investigate the influence of structural relaxation on elementary avalanche behavior, we perform molecular-dynamics simulations for the shear deformation test of metallic glasses using two typical metallic-glass models comprising a less-relaxed (as-quenched) glass and a well-re…
The atomic theory of elasticity of amorphous solids, based on the nonaffine response formalism, is extended into the nonlinear stress-strain regime by coupling with the underlying irreversible many-body dynamics. The latter is implemented in compact analytical form using a qualitative method for the many-body Smoluchowski equation. The resulting nonlinear stress-strain (constitutive) relation is very simple, with few fitting parameters, yet contains all the microscopic physics. The theory is successfully tested against experimental data on metallic glasses, and it is able to reproduce the ubiq…
Studying the primary α- and secondary β-relaxation process has contributed significantly to the understanding of the structure and rheology of metallic glasses. In this letter, we report on a third relaxation mechanism indicated by a maximum in the loss modulus at low temperatures, which we term γ-relaxation. Contrary to the α- and β-relaxation mechanisms, this irreversible, low energy excitation causes a macroscopic rejuvenation, which we assign to non-affine atomic rearrangements in the matrix that are driven by thermal stresses during cooling. Observed in three different glassy alloys, the …
The lack of thermal stability, originating from their metastable nature, has been one of the paramount obstacles that hinder the wide range of applications of metallic glasses. We report that the stability of a metallic glass can be dramatically improved by slow deposition at high temperatures. The glass transition and crystallization temperatures of the ultrastable metallic glass can be increased by 51 K and 203 K, respectively, from its ordinary glass state. The ultrastable metallic glass also shows ultrahigh strength and hardness, over 30 % higher than its ordinary counterpart. Atomic struc…
An atomistic understanding of annealing embrittlement is a longstanding issue for metallic glasses, which is still lacking due to the insurmountable gap between the thermal history of atomic models and laboratory-made samples. Here, based on a thermal-cycling annealing method that can vary the effective quenching rate over ten orders of magnitude, we perform an atomistic study of the ductile-brittle transition in a ternary model metallic glass, which can be keyed to the annealing embrittlement in bulk metallic glasses. We reveal that thermal annealing can effectively obliterate thermally activ…
The structural, vibrational, and electronic properties of Ni$_{40}$Pd$_{40}$P$_{20}$ bulk metallic glass have been studied using ${\it ab\,initio}$ molecular-dynamics simulations and total-energy optimization. Structural analyses of the resulting ${\it ab\,initio}$ models show the presence of few to no P-P bonds and two main building blocks, consisting of tricapped trigonal prism (TTP) and capped square anti-prism (CSAP) with P as the center of these blocks. The computed Pd and Ni K-edge spectra of extended x-ray absorption fine structure (EXAFS) are found to be in good agreement with experime…
In metallic glasses a clear correlation had been established between plasticity or ductility with the Poisson ratio and alternatively the ratio of the elastic bulk modulus to the shear modulus, K/G. Such a correlation between these two macroscopic mechanical properties is intriguing and is challenging to explain from the dynamics on a microscopic level. Such a microscopic explanation is provided in this paper.
Metallic glasses response to the mechanical stress in a complex and inhomogeneous manner with plastic strain highly localized into nanoscale shear bands. Contrary to the well-defined deformation mechanism in crystalline solids, understanding the mechanical response mechanism and its intrinsic correlation with the macroscopical plasticity in metallic glasses remains long-standing issues. Through a combination of experimental and theoretical analysis, we showed that the shear banding process in metallic glasses exhibits complex chaotic dynamics, which manifests as the existence of a torus destro…
Bulk metallic glasses (BMGs) are produced by rapidly thermally quenching supercooled liquid metal alloys below the glass transition temperature at rates much faster than the critical cooling rate R_c below which crystallization occurs. The glass-forming ability of BMGs increases with decreasing R_c, and thus good glass-formers possess small values of R_c. We perform molecular dynamics simulations of binary Lennard-Jones (LJ) mixtures to quantify how key parameters, such as the stoichiometry, particle size difference, attraction strength, and heat of mixing, influence the glass-formability of m…
We report excess specific heat in a series of metallic glass forming liquids. It is found that the excess specific heat relative to glass at glass transition temperature Tg is constant and close to, where R is gas constant. In the typical Pd40Ni10Cu30P20 metallic glass forming liquid, the excess specific heat is independent of temperature. A quantitative description of the excess specific heat is built up. The atomic translational diffusion is the origin of the excess specific heat. The results provide a fundamental understanding to the glass transition in metallic glasses.
The relaxation dynamics of glass-forming systems shows a multitude of features that are absent in normal liquids, such as non-exponential relaxation and a strong temperature-dependence of the relaxation time. Connecting these dynamic properties to the microscopic structure of the system is very challenging because of the presence of the structural disorder. Here we use computer simulations of a metallic glass-former to establish such a connection. By probing the temperature and wave-vector dependence of the intermediate scattering function we find that the relaxation dynamics of the glassy mel…
The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu46Zr54, Ni80Al20, Ni33.3Zr66.7, and Pd82Si18. Resulting cumulative coordination numbers (CN) show that metallic liquids have a dimension of d = 2.55 +/- 0.06 from the center atom to the first coordination shell and metallic glasses have d = 2.71 +/- 0.04, both less than 3. Between the first and second coordination shells, both phase…
Transmutation-accelerated sampling method for multi-component ZrCu(Al) metallic glasses
NOMATEN Centre of Excellence, National Center for Nuclear Research（NOMATEN卓越中心，国家核研究中心）；Univ. Lyon, INSA-Lyon, CNRS, LaMCoS, UMR 5259（里昂大学，里昂国立应用科学学院，法国国家科学研究中心，LaMCoS实验室）；Laboratoire de Mécanique des Solides, CNRS, Ecole Polytechnique（固体力学实验室，法国国家科学研究中心，巴黎综合理工学院）；Aalto University（阿尔托大学）
Using inelastic neutron scattering and molecular dynamics simulations on a model Zr-Cu-Al metallic glass, we show that transverse phonons persist well into the high-frequency regime, and can be detected at large momentum transfer. Furthermore, the apparent peak width of the transverse phonons was found to follow the static structure factor. The one-to-one correspondence, which was demonstrated for both Zr-Cu-Al metallic glass and a 3-dimensional Lennard-Jones model glass, suggests a universal correlation between the phonon dynamics and the underlying disordered structure. This remarkable corre…
Motivated by results of the topological theory of glasses accounting for geometric frustration, we develop the simplest possible continuum mechanical model of defect dynamics in metallic glasses that accounts for topological, energetic, and kinetic ideas. The model is aimed towards the development of a microscopic understanding of the plasticity of such materials. We discuss the expected predictive capabilities of the model vis-a-vis some observed physical behaviors of metallic glasses.
NOMATEN Centre of Excellence, National Center for Nuclear Research（国家核研究中心 NOMATEN 卓越中心）；Center for Complexity and Biosystems, Department of Physics "Aldo Pontremoli", University of Milan（米兰大学物理学院复杂性与生物系统中心）；Saarland University, Chair of Metallic Materials（萨尔兰大学金属材料讲席）；Glass and Time , IMFUFA, Department of Science and Environment, Roskilde University（罗斯基勒大学科学与环境学院 IMFUFA 玻璃与时间）；Department of Materials Science, Montanuniversität Leoben（莱奥本矿业大学材料科学系）；Erich Schmid Institute of Materials Science, Austrian Academy of Sciences（奥地利科学院埃里希·施密德材料科学研究所）；Department of Materials Science and Engineering, Johns Hopkins University（约翰斯·霍普金斯大学材料科学与工程系）；Department of Mechanical Engineering, Johns Hopkins University（约翰斯·霍普金斯大学机械工程系）；Department of Physics and Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文学系）；Hopkins Extreme Materials Institute, Johns Hopkins University（约翰斯·霍普金斯大学霍普金斯极端材料研究所）；Technical University of Berlin, Chair of Metallic Materials（柏林工业大学金属材料讲席）
We report that both shear and bulk moduli, not only shear modulus, are critical parameters involved in both homogeneous and inhomogeneous flows in metallic glass. The flow activation energy (ΔF) of various glasses when scaled with average molar volume Vm, which is defined as flow activation energy density ρ_E =ΔF/Vm, can be expressed as: D=(10G+K)/11 . The extended elastic model is suggestive for understanding the glass transition and deformation in metallic glasses.
Dynamic compression has been used to synthesize liquid metallic hydrogen at 140 GPa (1.4 million bar) and experimental data and theory predict Al2O3 might be a metallic glass at ~300 GPa. The mechanism of metallization in both cases is probably a Mott-like transition. The strength of sapphire causes shock dissipation to be split differently in the strong solid and soft fluid. Once the 4.5-eV H-H and Al-O bonds are broken at sufficiently high pressures in liquid H2 and in sapphire (single-crystal Al2O3), electrons are delocalized, which leads to formation of energy bands in fluid H and probably…
This review deals with the kinetic and thermodynamic fragility of bulk metallic glass forming liquids. The experimental methods to determine the kinetic fragility, relaxation behavior and thermodynamic functions of undercooled metallic liquids are introduced. Existing data are assessed and discussed using the Vogel-Fulcher-Tammann equation and in the frameworks of the Adam-Gibbs as well as the Cohen-Turnbull free volume approach. In contrast to pure metals and most non glass forming alloys, bulk glass formers are moderately strong liquids. In general the fragility parameter $D^{*} $ increases …
We applied an efficient methodology to separate vibrational and configurational entropies in bulk metallic glasses by means of molecular dynamics simulation based on a combination of non-equilibrium adiabatic switching and reversible scaling methods. This approach involves calculating the vibrational free energy using the Einstein crystal as a reference for the solid phase and the recently proposed Uhlenbeck-Ford model for the fluid phase. This methodology has the advantage that it does not require a crystalline solid phase for separating the entropies. Therefore, in principle, it is applicabl…
The glass transition remains unclarified in condensed matter physics. Investigating the mechanical properties of glass is challenging because any global deformation that may result in shear rejuvenation requires an astronomical relaxation time. Moreover, it is well known that a glass is heterogeneous and a global perturbation cannot explore local mechanical/transport properties. However, an investigation based on a local probe, i.e. microrheology, may overcome these problems. Here, we establish active microrheology of a bulk metallic glass: a probe particle driven into host medium glass. This …
Physically vitrifying single-element metallic glass requires ultrahigh cooling rates, which are still unachievable for most of the closest-packed metals. Here, we report a facile synthetic strategy for creating mono-atomic palladium metallic glass nanoparticles with a purity of 99.35 +/- 0.23 at% from palladium-silicon liquid droplets using a cooling rate below 1000 K/s. In-situ environmental transmission electron microscopy directly detected the leaching of silicon. Further hydrogen absorption experiment showed that this palladium metallic glass expanded little upon hydrogen uptake, exhibitin…
We theoretically investigate the temperature dependence of the reversible structural relaxation time and diffusion constant of metallic glasses under pressure. The compression not only changes the glassy dynamics, but also generates a metastable state along with a higher-energy state where the system can rejuvenate. The relaxation times for forward and backward transitions in this two-state system are nearly identical and much faster than the relaxation time without accounting for barrier-recrossing. At ambient pressure, the expected irreversible relaxation process is recovered, and our numeri…
The structural description for the intriguing link between the fast vibrational dynamics and slow diffusive dynamics in glass-forming systems is one of the most challenging issues in physical science. Here, in a model of metallic supercooled liquid, we find that local connectivity as an atomic-level structural order parameter tunes the short-time vibrational excitations of the icosahedrally coordinated particles and meanwhile modulates their long-time relaxation dynamics changing from stretched to compressed exponentials, denoting a dynamic transition from subdiffusive to hyperdiffusive motion…
Recent computational and laboratory experiments have shown that the brittle-ductile transitions in metallic glasses such as Vitreloy1 are strongly sensitive to the initial effective disorder (or "fictive") temperature. Glasses with lower effective temperatures are weak and brittle; those with higher effective temperatures are strong and ductile. The analysis of this phenomenon presented here examines the onset of fracture at the tip of a slightly rounded notch as predicted by the shear-transformation-zone (STZ) theory of spatially varying plastic deformation. The central ingredient of this ana…
Cryogenic rejuvenation in metallic glasses reported in Ketov et al 's experiment (Nature(2015)524,200) has attracted much attention, both in experiments and numerical studies. The atomic mechanism of rejuvenation has been conjectured to be related to the heterogeneity of the glassy state, but the quantitative evidence is still elusive. Here we use molecular dynamics simulations of a model metallic glass to investigate the heterogeneity in the local thermal expansion. We then combine the resulting spatial distribution of thermal expansion with a continuum mechanics calculation to infer the inte…
A comparative study on as cast and annealed rare earth bulk metallic glass (BMG) with composition Tb36Sm20Al24Co20 has been carried out by magnetization measurements. The as cast amorphous sample shows non-ergodic magnetization but does not show the behavior expected from magnetic glass. After annealing, the partially crystallized BMG shows this magnetic glass behavior. This is confirmed by the established measurement protocol of cooling and heating in unequal fields (CHUF).
Using molecular dynamics simulations with embedded atom model potential, we study structural evolution of ${\rm Cu_{64.5}Zr_{35.5}}$ alloy during the cooling in a wide range of cooling rates $γ\in(1.5\cdot 10^{9},10^{13})$ K/s. Investigating short- and medium-range order, we show that structure of ${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass essentially depends on cooling rate. In particular, a decrease of the cooling rate leads to a increase of abundances of both the icosahedral-like clusters and Frank-Kasper Z16 polyhedra. The amounts of these clusters in the glassy state drastically increase a…
Supercooled liquids exhibit spatial heterogeneity in the dynamics of their fluctuating atomic arrangements. The length and time scales of the heterogeneous dynamics are central to the glass transition and influence nucleation and growth of crystals from the liquid. We report direct experimental visualization of the spatially heterogeneous dynamics as a function of temperature in the supercooled liquid state of a Pt-based metallic glass, using electron correlation microscopy with sub-nanometer resolution. An experimental four point space-time intensity correlation function demonstrates a growin…
Metallic glasses have so far attracted considerable attention for their applications as bulk materials. However, new physics and applications often emerge by dimensional reduction from three dimension (3D) to two dimension (2D). Here, we study, by molecular dynamics simulations, how the liquid-to-glass transition of a binary Cu50Zr50 MG is affected by spatial dimensionality. We find clear evidence that crystal-like structural ordering controls both dynamic heterogeneity and slow dynamics, and thus plays a crucial role in the formation of the 2DMG. Although the 2DMG reproduces the dynamical beh…
A quinary (La0.5Ce0.5)65Al10(Co0.6Cu0.4)25 alloy with superior glass-forming ability (GFA), identified by the formation of fully glassy rod of 32 mm in diameter by tilt-pour casting, was reported. By comparing with the GFA of quarternary (La0.5Ce0.5)65Al10TM25 and ternary Ln65Al10TM25 alloys (Ln = La or Ce; TM = Co or Cu), we suggest that the strong frustration of crystallization by utilizing the coexistence of La-Ce and Co-Cu to complicate competing crystalline phases is helpful to construct BMG component with superior GFA.
Although experiments can offer some fingerprints of the atomic structure of glasses (coordination numbers, pair distribution function, etc.), atomistic simulations are often required to directly access the structure itself (i.e., the positions of the atoms). On the one hand, molecular dynamics (MD) simulations can be used to generate by quenching a liquid - but MD simulations remain plagued by extremely high cooling rates. On the other hand, reverse Monte Carlo (RMC) modeling bypasses the melt-quenching route - but RMC often yields non-unique glass structures. Here, we adopt the force-enhanced…
Boson peak and beta-relaxation are two intrinsic and markedly different dynamic modes of glasses, and their structural origins are long-standing issues. Through tuning atomic packing of a model metallic glass with microalloying of different types of elements, we find that low-temperature boson heat capacity peak evolves hand in hand with high-temperature beta-relaxation. A linear correlation between the boson peak temperature and the activation energy of beta-relaxation is disclosed. The coupling of the boson peak and the beta-relaxation indicates their common structural origin of the loosely …
In this paper, we present a thorough stress analysis of the Cu-Zr metallic-glass composite with embedded B2 particles subject to a martensitic transformation. Within the framework of the Eshelby theory, we are able to explain, in a quantitative manner, (1) the formation of three types of shear bands with distinct morphologies as observed experimentally in the severely deformed Cu-Zr metallic-glass composite and (2) the work hardening ability of the Cu-Zr metallic-glass composite as related to the coupled effects of elastic back stress and elastic mismatch caused by the martensitic transformati…
Using molecular dynamics simulation, we study the plastic zone created during nanoindentation of a large CuZr glass system. The plastic zone consists of a core region, in which virtually every atom undergoes plastic rearrangement, and a tail, where the density distribution of the plastically active atoms decays to zero. Compared to crystalline substrates, the plastic zone in metallic glasses is significantly smaller than in crystals. The so-called plastic-zone size factor, which relates the radius of the plastic zone to the contact radius of the indenter with the substrate, assumes values arou…
A thermal activation model to describe the plasticity of bulk metallic glasses (Derlet and Maaß, Phil. Mag. 2013, DOI: 10.1080/14786435.2013.826396) which uses a distribution of barrier energies and some aspects of under-cooled liquid physics is developed further. In particular, a log-normal distribution is now employed to describe the statistics of barrier energies. A high temperature mean-field description of homogeneous macro-plasticity is then developed and is shown to be similar to a thermal activation picture employing a single characteristic activation energy and activation volume. In m…
The first report of phase separation in metallic glass has attracted significant attention due to their unique micro-structural variations of amorphous phases at different domain size. In the continuation of this the view is to understanding the genesis of phase separation in Ce based metallic glass. In this paper, we present extensive investigations with particular reference to low concentration of Ga in Ce-Al-Ga metallic glass. Micro-structural characteristics and indentation behavior of melt spun Ce75Al25-xGax metallic glass has been investigated by X-ray diffraction (XRD) and Transmission …
At temperatures well below their glass transition, the deformation properties of bulk metallic glasses are characterised by a sharp transition from elasticity to plasticity, a reproducible yield stress, and an approximately linear decrease of this stress with increasing temperature. In the present work it shown that when the well known properties of the under-cooled liquid regime, in terms of the underlying potential energy landscape, are assumed to be also valid at low temperature, a simple thermal activation model is able to reproduce the observed onset of macro-scopic yield. At these temper…
Bartsch et al. [A. Bartsch, K. Raetzke, A. Meyer, and F. Faupel, Phys. Rev. Lett. 104, 195901 (2010)] reported measurements of the diffusivities of different components of the multi-component bulk metallic glass Pd43Cu27Ni10P20. The diffusion of the largest Pd and the smallest P were found to be drastically different. The Stokes-Einstein relation breaks down when considering the P constituent atom, while the relation is obeyed by the Pd atom over 14 orders of magnitude of change in Pd diffusivity. This difference in behavior of Pd and P poses a problem challenging for explanation. With the ass…
We demonstrate a remarkable equivalence in structure measured by total X-ray scattering methods between very small metallic nanoparticles and bulk metallic glasses (BMGs), thus connecting two disparate fields, shedding new light on both. Our results show that for nanoparticle diameters <5 nm the structure of Ni nanoparticles changes from fcc to the characteristic BMG-like structure, despite them being formed from a single element, an effect we call nano-metallic glass (NMG) formation. However, high-resolution TEM images of the NMG clusters exhibit lattice fringes indicating a locally well-orde…
Metallic glasses deform elastically under stress. However, the atomic-level origin of elastic properties of metallic glasses remain unclear. In this paper using {\em ab initio} molecular dynamics simulations of the Cu$_{50}$Zr$_{50}$ metallic glass under shear strain, we show that the heterogeneous stress relaxation results in the increased charge transfer from Zr to Cu atoms, enhancing the softening of the shear modulus. Changes in compositional short-range order and atomic position shifts due to the non-affine deformation are discussed. It is shown that the Zr subsystem exhibits a stiff beha…
Measurements of Ag radiotracer diffusion in shear bands of deformed bulk metallic glass, Pd40Ni40P20, [Joachim Bokeloh, Sergiy V. Divinski, Gerrit Reglitz, and Gerhard Wilde, Phys. Rev. Lett. 107, 235503 (2011).] have found a colossal enhancement of diffusion coefficient by more than eight orders of magnitude than in undeformed Pd40Ni40P20. Suggestion was made by Bokeloh et al. that enhanced diffusion occurs in high-mobility pathways originating from some excess free volume distribution inside the shear bands. Although plausible, this qualitative suggestion does not allow quantitative calculat…
Universality in materials deformation is of intense interest: universal scaling relations if exist would bridge the gap from microscopic deformation to macroscopic response in a single material-independent fashion. While recent agreement of the force statistics of deformed nanopillars, bulk metallic glasses, and granular materials with mean-field predictions supports the idea of universal scaling relations, here for the first time we demonstrate that the universality extends beyond the statistics, and applies to the slip dynamics as well. By rigorous comparison of two very different systems, b…
