Plastic deformation induced anisotropy in metallic glasses: A molecular dynamics study (original) (raw)
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Observation of structural anisotropy in metallic glasses induced by mechanical deformation
We have investigated atomic structure of a Fe 81 B 13 Si 4 C 2 metallic glass after mechanical creep deformation. We determined the structure function and pair density function resolved for azimuthal angle using x-ray scattering and a two-dimensional detector. The results are analyzed by the spherical harmonics expansion, and are compared to the often-used simple analysis of the anisotropic pair density function determined by measuring the structure function along two directions with respect to the stress. We observed uniaxial structural anisotropy in a sample deformed during creep experiment. The observed macroscopic shear strain is explained in terms of local bond anisotropy induced by deformation at elevated temperature. The bond anisotropy is a "memory" of this deformation after load was removed. We showed that use of sine-Fourier transformation to anisotropic glass results in systematic errors in the atomic pair distribution function.
Anelastic strain and structural anisotropy in homogeneously deformed Cu64.5Zr35.5 metallic glass
Acta Materialia, 2008
Using plastic deformation tests and high-energy X-ray scattering, we examined the anelastic strain and structural anisotropy in a binary Cu 64.5 Zr 35.5 metallic glass deformed homogeneously under uniaxial compression at 425°C, which is approximately 60°C below the glass transition temperature. For a sample quenched immediately after deformation, we find that the atomic structure observed by X-ray scattering is anisotropic with the average bond length parallel to the loading axis being smaller than that of an undeformed, structurally relaxed reference sample, while the average bond length normal to the loading axis is dilated relative to the same reference sample. For a different sample annealed at 425°C for 500 s immediately following deformation, the magnitude of the structural anisotropy decreases as anelastic strain is recovered. The relationship between the atomic-scale structural rearrangements that occur during annealing and the macroscopic anelastic strain recovery is discussed.
Physical Review B, 2011
In this study, we characterize the mechanical properties of Cu 64 Zr 36 nanoglasses under tensile load by means of large-scale molecular dynamics simulations and compare the deformation behavior to the case of a homogeneous bulk glass. The simulations reveal that interfaces act as precursors for the formation of multiple shear bands. In contrast, a bulk metallic glass under uniaxial tension shows inhomogeneous plastic flow confined in one dominant shear band. The results suggest that controlling the microstructure of a nanoglass can pave the way for tuning the mechanical properties of glassy materials.
Mechanics of Materials, 2013
We investigate the influence of various microstructural features on the deformation behavior of binary Cu 64 Zr 36 glasses by molecular dynamics computer simulations and discuss how and why the very same modifications established for enhancing the strengths of crystalline materials, namely the insertion of solutes, precipitates and grain boundaries, can be used for tuning the mechanical properties of metallic glasses. First, by testing bulk samples with and without open surfaces under tensile load, we show that the condensation of shear transformation zones into shear bands can occur as heterogeneous but also as a homogeneous nucleation process. Then, the influence of crystalline nanoprecipitates on shear band nucleation and propagation is investigated. Finally, we study the effect of grain size and composition on the deformation behavior of nanoglasses and nanoglass composites. The results reveal that glass-glass interfaces act as structural heterogeneities ,which promote shear band formation and prevent strain localization.
Relevance of structural defects to the mechanism of mechanical deformation in metallic glasses
Scientific Reports
It is known that deformation in disordered materials such as metallic glasses and supercooled liquids occurs via the cooperative rearrangement of atoms or constituent particles at dynamical heterogeneities, commonly regarded as point-like defects. We show via molecular-dynamics simulations that there is no apparent relationship between atomic rearrangements and the local atomic environment as measured by the atomic-level stresses, kinetic and potential energies, and the per-atom Voronoi volume. In addition, there is only a weak correlation between atomic rearrangements and the largest and smallest eigenvalues of the dynamical matrix. Our results confirm the transient nature of dynamical heterogeneities and suggest that the notion of defects may be less relevant than that of a propensity for rearrangement.
Signature of local stress states in the deformation behavior of metallic glasses
NPG Asia Materials, 2020
The design of ductile heterogeneous metallic glasses (MGs) with enhanced deformability by purposely controlling the shear-band dynamics via modulation of the atomic-scale structures and local stress states remains a significant challenge. Here, we correlate the changes in the local atomic structure when cooling to cryogenic temperature with the observed improved shear stability. The enhanced atomic-level structural and elastic heterogeneities related to the nonaffine thermal contraction of the short-range order (SRO) and medium-range order (MRO) change the characteristics of the activation process of the shear transformation zones (STZs). The experimental observations corroborated by Eshelby inclusion analysis and molecular dynamics simulations disclose the correlation between the structural fluctuations and the change in the stress field around the STZ. The variations in the inclination axes of the STZs alter their percolation mechanism, affect the shear-band dynamics and kinetics,...
Paradoxical phenomena between the homogeneous and inhomogeneous deformations of metallic glasses
Applied Physics Letters, 2009
Experiments in binary alloys demonstrate that metallic glasses exhibiting more plastic strain during homogeneous deformation tend to show lower global plasticity during inhomogeneous deformation. Testing of Cu–Zr binary alloys supports the hypothesis that the formation energy of a shear transformation zone, as extracted from the experimental data, is related to the homogeneous flow rate. We also report the microstructural aspects that control the global plasticity of metallic glasses in the light of structural disordering, softening, and shear localization.
Deformation induced structural evolution in bulk metallic glasses
Chinese Science Bulletin, 2011
The structural behavior of binary Cu 50 Zr 50 and ternary Cu 50 Zr 45 Ti 5 bulk metallic glasses (BMGs) under applied stress was investigated by means of in-situ high energy X-ray synchrotron diffraction. The components of the strain tensors were determined from the shifts of the maxima of the atomic pair correlation functions (PDF) in real space. The anisotropic atomic reorientation in the first-nearest-neighbor shell versus stress suggests structural rearrangements in short-range order. Within the plastic deformation range the overall strain of the metallic glass is equal to the yield strain. After unloading, the atomic structure returns to the stress-free state, and the short-range order is identical to that of the undeformed state. Plastic deformation, however, leads to localized shear bands whose contribution to the volume averaged diffraction pattern is too weak to be detected. A concordant region evidenced by the anisotropic component is activated to counterbalance the stress change due to the atomic bond reorientation in the first-nearest-neighbor shell. The size of the concordant region is an important factor dominating the yield strength and the plastic strain ability of the BMGs. bulk metallic glasses, high energy X-ray diffraction, deformation, structural evolution Citation: Wang G, Mattern N, Bednarčí J, et al. Deformation induced structural evolution in bulk metallic glasses.