Notched bars of bulk metallic glasses, Pd$_{40}$Ni$_{40}$P$_{20}$ and Zr$_{52.5}$Cu$_{17.9}$Ni$_{14.6}$Al$_{10}$Ti$_{5}$, were deformed under 3-point bending conditions, resulting in the formation of shear bands before failure. The immediate environment of shear bands was investigated in detail using fluctuation electron microscopy to extract information on the strain-induced modifications of the medium-range order (MRO) and its lateral extension. Characteristic material-independent gradients were observed for the tensile and compressive sides of the samples indicating the impact of the local stress state on the MRO. Our results reveal an upper limit of a few microns for the lateral extension of the shear-affected environments of shear bands.
Micro- or minor alloying of metallic glasses is of technological interest. An originally ductile Pd-based monolithic bulk metallic glass (Pd$_{40}$Ni$_{40}$P$_{20}$) was selectively manipulated by additions of Fe or Co. The alloying effects were extreme, showing either exceptional ductility upon Co addition or immediate catastrophic failure upon Fe addition when tested under uniaxial compression or 3-point bending. The amorphous structure was characterized prior to deformation with respect to its medium-range order (MRO) using variable resolution fluctuation electron microscopy (VR-FEM). We ob…
Spin-charge conversion via inverse spin Hall effect (ISHE) is essential for enabling various applications of spintronics. The spin Hall response usually follows a universal scaling relation with longitudinal electric resistivity and has mild temperature dependence because elementary excitations play only a minor role in resistivity and hence ISHE. Here we report that the ISHE of metallic glasses shows nearly two orders of magnitude enhancements with temperature increase from a threshold of 80-100 K to glass transition points. As electric resistivity changes only marginally in the temperature r…
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…
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 …
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…
Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle transitions, is not yet available. Here we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elasto-plastic crack tip instability for sufficiently relaxed…
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.
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…
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…
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 …
Crystallization of metallic glass as a grain-boundary nucleated process: experimental and theoretical evidence for the grain structure of metallic glasses
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.
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 develop a generic strategy and simple numerical models for multi-component metallic glasses for which the swap Monte Carlo algorithm can produce highly stable equilibrium configurations equivalent to experimental systems cooled more than $10^7$ times slower than in conventional simulations. This paves the way for a deeper understanding of thermodynamic, dynamic, and mechanical properties of metallic glasses. As first applications, we considerably extend configurational entropy measurements down to the experimental glass temperature, and demonstrate a qualitative change of the mechanical res…
Residual stress engineering is very widely used in the design of new advanced lightweight materials. For metallic glasses the attention has been on structural changes and rejuvenation processes. High energy scanning X-ray diffraction strain mapping reveals large elastic fluctuations in metallic glasses after deformation under triaxial compression. Microindentation hardness mapping hints to a competing hardening-softening mechanism after compression and further reveals the complementary effects of stress and structure modulation. Transmission electron microscopy proves that structure modulation…
Plastic deformation of metallic glasses performed well below the glass transition temperature leads to the formation of shear bands as a result of shear localization. It is believed that shear banding originates from individual stress concentrators having quadrupolar symmetry. To elucidate the underlying mechanisms of shear band formation, microstructural investigations were carried out on sheared zones using transmission electron microscopy. Here we show evidence of a characteristic signature present in shear bands manifested in the form of sinusoidal density variations. We present an analyti…
A recent paper by Juntao Huo et al [Chin. Phys. Lett. 39 (2022) 0464011] reported a correlation between the entropy of mixing (and the corresponding energy state) and the thermal stability and mechanical parameters, for three Zr-Ti-Cu-Ni-Be metallic glasses (MG) including a high-entropy one (HEMG). The authors dismissed a possible compositional contribution to the variations of the thermal stability and mechanical parameters studied.
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）
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 …
We report on and characterize, via molecular dynamics (MD) studies, the evolution of the structure of Cu50Zr50 and Cu64Zr36 metallic glasses (MGs) as temperature is varied. Interestingly, a percolating icosahedral network appears in the Cu64Zr36 system as it is supercooled. This leads us to introduce a static length scale, which grows dramatically as this three dimensional system approaches the glass transition. Amidst interpenetrating connections, non-interpenetrating connections between icosahedra are shown to become prevalent upon supercooling and to greatly enhance the connectivity of the …
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…
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…
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.
Mechanical behaviors of bulk metallic glasses (BMGs) including heterogeneous and homogeneous deformation are interpreted by phenomenological shear transformation zones (STZs) model. Currently, information about STZs, i.e. size and density, is only extracted by fitting model equation to the data obtained from macroscopic mechanical tests. This is inadequate since structural features of STZs theory cannot be assessed. Here, we develop anisotropic pair distribution function (PDF) method for directly characterizing mechanical response of deformation defects. Our results reveal the physical picture…
Planar flow casting (PFC) is a method that can be used to make thin, long, and wide metallic alloy foils by extruding molten liquid through a thin and wide nozzle and immediately quenching on a moving roller. The quenching rates are high enough that amorphous metallic glasses may be formed which have many desirable properties for a wide variety of applications. This paper reviews how PFC processes were developed, examines the typical operability range of PFC, and reviews the defects that commonly form. The geometrical similarities between PFC and slot coating process are apparent, and this pap…
Micro-alloying was performed using additions of Co and Fe to monolithic Pd40Ni40P20 bulk metallic glass to study selectively the influence on the plastic behavior in uniaxial compression and three-point bending tests. The corresponding Poisson's ratios were determined by ultrasonic measurements. The microstructure of the individual bulk metallic glasses was characterized by electron microscopy, X-ray diffraction and calorimetry. A plastic strain of 13% was found for the Co addition (1 at.%), whereas the Fe addition (0.6 at.%) led to immediate failure after reaching the elastic limit. Surprisin…
Magnetism prediction is of great significance for Fe-based metallic glasses (FeMGs), which have shown great commercial value. Theories or models established based on condensed matter physics exhibit several exceptions and limited accuracy. In this work, machine learning (ML) models learned from a large amount of experimental data were trained based on eXtreme gradient boosting (XGBoost), artificial neural networks (ANN), and random forest to predict the magnetic properties of FeMGs. The XGBoost and ANN models exhibited comparably excellent predictive performance, with R^2 >= 0.903, mean absolu…
We study correlations of non-affine displacement during simple shear deformation of Cu-Zr bulk metallic glasses in molecular dynamics calculations. In the elastic regime, our calculations show exponential correlation with a decay length that we interpret as the size of a shear transformation zone in the elastic regime. This correlation length becomes system-size dependent beyond the yield transition as our calculation develops a shear band, indicative of a diverging length scale. We interpret these observations in the context of a recent proposition of yield as a first-order phase transition.
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…
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…
A relation between the freezing temperature ($T^{}_{\rm g}$) and the exchange couplings ($J^{}_{ij}$) in metallic spin-glasses is derived, taking the spin-correlations ($G^{}_{ij}$) into account. This approach does not involve a disorder-average. The expansion of the correlations to first order in $J^{}_{ij}/T^{}_{\rm g}$ leads to the molecular-field result from Thouless-Anderson-Palmer. Employing the current theory of the spin-interaction in disordered metals, an equation for $T^{}_{\rm g}$ as a function of the concentration of impurities is obtained, which reproduces the available data from …
Metallic glasses are known to have a remarkably robust yield strength, admitting Weibull moduli as high as for crystalline engineering alloys. However, their post-yielding behavior is strongly varying, with large scatter in both flow stress levels and strains at failure. Using x-ray tomography we reveal for the first time how a strain-dependent internal evolution of shear-band cavities underlies this unpredictable post yielding response. We demonstrate how macroscopic strain-softening coincides with the first detection of internal shear-band cavitation. Cavity growth during plastic flow is fou…
The interaction of shear bands with crystalline nanoprecipitates in Cu-Zr-based metallic glasses is investigated by a combination of high-resolution TEM imaging and molecular-dynamics computer simulations. Our results reveal different interaction mechanisms: Shear bands can dissolve precipitates, can wrap around crystalline obstacles, or can be blocked depending on size and density of the precipitates. If the crystalline phase has a low yield strength, we also observe slip transfer through the precipitate. Based on the computational results and experimental findings, a qualitative mechanism ma…
During the solidification of Al-Sm metallic glasses the evolution of the supercooled liquid atomic structure has been identified with an increasing population of icosahedral-like clusters with increasing Sm concentration. These clusters exhibit slower kinetics compared to the remaining clusters in the liquid leading to enhanced amorphous phase stability and glass forming ability (GFA). Maximum icosahedral-ordering and atomic packing density have been found for the Al90Sm10 and Al85Sm15 alloys, respectively, whereas minimum cohesive energy has been found for the Al93Sm7 which is consistent with…
Metallic glasses are excellent candidates for biomedical implant applications due to their inherent strength and corrosion resistance. Use of metallic glasses in structural applications is limited, however, because bulk dimensions are challenging to achieve. Glass-forming ability (GFA) varies strongly with alloy composition and becomes more difficult to predict as the number of chemical species in a system increases. Here we present a theoretical model - implemented in the AFLOW framework - for predicting GFA based on the competition between crystalline phases, and apply it to biologically rel…
Though extensively studied, hardness, defined as the resistance of a material to deformation, still remains a challenging issue for a formal theoretical description due to its inherent mechanical complexity. The widely applied Teter's empirical correlation between hardness and shear modulus has been considered to be not always valid for a large variety of materials. Here, inspired by the classical work on Pugh's modulus ratio, we develop a theoretical model which establishes a robust correlation between hardness and elasticity for a wide class of materials, including bulk metallic glasses, wit…
Sheared multi-component bulk metallic glasses are characterized by both chemical and structural disorder that define their properties. We investigate the behavior of the local, microstructural elastic modulus across the plastic yielding transition in six Ni-based multi-component glasses, that are characterized by compositional features commonly associated with solid solution formability. We find that elastic modulus fluctuations display consistent percolation characteristics pointing towards universal behavior across chemical compositions and overall yielding sharpness characteristics. Elastic…
The icosahedral-like polyhedral fraction (ICO-like fraction) has been studied as a criterion for predicting the glass-forming ability of bulk ternary metallic glasses, Al90Sm8X2 (X = Al (binary), Cu, Ag, Au), using ab initio molecular dynamics (AIMD) simulations. We found that the ICO-like fraction can be determined with adequate precision to explore correlations with AIMD simulations. We then demonstrated that ICO-like fraction correlates with the critical cooling rate, which is a widely used intrinsic measure of glass forming ability. These results suggest that the ICO-like fraction from AIM…
Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing the quasi-elastic asymmetric mechanical cycling method, we effectively induce the mechanical polarity of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine…
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…
By microalloying of Gd atoms with 4f electrons into CuZrAl or MgCuY glassy alloys, they display a variety of puzzling behaviors such as the characteristic of Kondo effect. The ground states of the Gd-alloyed systems are determined to have non-Fermi-liquid characteristics which derive from the strong structural disorder. The Kondo effect in these glassy alloys is attributed to the strong structural disorder. The coexistence of the Kondo effect and strong structural disorder has implications for the understanding the origin of the puzzling non-Fermi-liquid behavior.
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.
Crystallization from an amorphous atomic structure is usually seen as a spontaneous process in pursuit of a lower energy state, but for alloy systems it is often hard to elucidate because of the intrinsic structural and compositional complexity. Here, by means of electron beam irradiation, we found surface-limited, and thus size-dependent crystallization in a system of monoatomic Pd metallic glass, which is ascribed to the structural differences between the surface and the interior. The equilibrium thickness of the surface crystallization is controllable, presenting a promising approach to fab…
Experimentally resolving atomic-scale structural changes of a deformed glass remains challenging owing to the disordered nature of glass structure. Here, we show that the structural anisotropy emerges as a general hallmark for different types of glasses (metallic glasses, oxide glass, amorphous selenium, and polymer glass) after thermo-mechanical deformation, and it is highly correlates with local nonaffine atomic displacements detected by the high-energy X-ray diffraction technique. By analyzing the anisotropic pair density function, we unveil the atomic-level mechanism responsible for the pl…
The process of crystal nucleation can be accelerated or retarded by ultrasonic vibration, which is particularly attractive for the addictive manufacture and thermoplastic forming of metallic glasses, however, the effect and mechanism of oscillatory loading on the nucleation process are still elusive. By using molecular dynamics simulation, the changes in the time-temperature-transformation (TTT) curve under oscillatory external loading are systematically investigated in two typical binary alloys. A glass forming ability dependent response to the external loading is found, and the shortest incu…
Investment in brighter sources and larger detectors has resulted in an explosive rise in the data collected at synchrotron facilities. Currently, human experts extract scientific information from these data, but they cannot keep pace with the rate of data collection. Here, we present three on-the-fly approaches - attribute extraction, nearest-neighbor distance, and cluster analysis - to quickly segment x-ray diffraction (XRD) data into groups with similar XRD profiles. An expert can then analyze representative spectra from each group in detail with much reduced time, but without loss of scient…
"Micro-alloying", referring to the addition of small concentration of a foreign metal to a given metallic glass, was used extensively in recent years to attempt to improve the mechanical properties of the latter. The results are haphazard and nonsystematic. In this paper we provide a microscopic theory of the effect of micro-alloying, exposing the delicate consequences of this procedure and the large parameter space which needs to be controlled. In particular we consider two very similar models which exhibit opposite trends for the change of the shear modulus, and explain the origins of the di…
Beijing Computational Science Research Center（北京计算科学研究中心）；Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences（中国科学院宁波材料技术与工程研究所）；State Key Laboratory of Advanced Marine Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences（中国科学院宁波材料技术与工程研究所先进海洋材料国家重点实验室）；College of Materials & Environmental Engineering, Hangzhou Dianzi University（杭州电子科技大学材料与环境工程学院）；State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences（中国科学院力学研究所非线性力学国家重点实验室）；School of Engineering Science, University of Chinese Academy of Sciences（中国科学院大学工程科学学院）
