[en] Highlights: • 3D phase-field modeling is developed to investigate the deformation of MG nanowires. • The surface defects significantly affect the mechanical properties of nanowires. • Multiple shear bands are initiated from the surfaces of nanowires with D < 50 nm. - Abstract: It is very challenging to investigate the deformation mechanisms in micro- and nano-scale metallic glasses with diameters below several hundred nanometers using the atomistic simulation or the experimental approaches. In this work, we develop the fully three-dimensional phase-field model to bridge this gap and investigate the sample size effects on the deformation behaviors of metallic glass nanowires. The initial deformation defects on the surface are found to significantly affect the mechanical strength and deformation mode of nanowires. The improved ductility of metallic glass nanowires could be related with the multiple shear bands initiated from the nanowire surfaces

[en] Research highlights: → Effects of atomic bonding conditions at the interface on shear banding. → Effects of residual stresses on shear banding. → Modes of shear banding and cracking in the composites. - Abstract: Different modes of shear banding in bulk metallic glass (BMG) matrix composites are identified from the systematic simulation studies based on a mesoscopic phase-field model for deformation in glassy alloys. We characterize the interaction between shear band and crystalline reinforcements by considering the residual stress and atomic bonding condition at the interface between BMG-matrix and the reinforcement. The simulation demonstrates that compressive residual stress assists to impede the shear bands propagating toward the reinforcements, while tensile residual stress accelerates such process. In addition, the effect of atomic bonding at the interface on shear banding is investigated by the simulation. The relations between the fracture toughness and the residual stress and atomic bonding condition at the interface are quantitatively determined.

[en] An approach is developed to investigate the deformation behavior of hexagonal close-packed (hcp) nanocrystalline (nc) cobalt by computer simulations. The microstructures are modeled by a grain growth theory, and the mechanical deformation behavior is investigated using molecular dynamics simulation in nc-cobalt samples with an average grain size of 10 nm. The deformation mechanisms are found to involve both full and partial dislocation activities. Despite the small stacking fault energy of nc-cobalt, surprisingly the deformation twinning is not prevalent in the model cobalt sample. The simulation suggests that unlike the easy twinning events in coarse-grained hcp metals, deformation of nanocrystalline cobalt is primarily controlled by partial dislocation slips and stacking faults. The continuous accumulation of deformation faults eventually leads to hcp to face-centred cubic allotropic phase transformation during tension and compression of nc-cobalt

[en] Highlights: • An atomistic approach has been developed to predict the glass forming ability (GFA) in Zr–Cu–Al ternary alloy system. • Both of the thermodynamic and structure-dependent kinetic effects to glass formation have been taken into account. • The first-principles calculation and molecular dynamics simulation have been performed. • The approach predicts the best glass former in the model Zr–Cu–Al alloy system. • The predicted GFA is consistent with various experimental results. - Abstract: Prediction of composition-dependent glass-forming ability (GFA) remains to be a key scientific challenge in the metallic-glass community, especially in multi-component alloy systems. In the present study, we apply an atomistic approach to predict the trend of GFA effectively in the Zr–Cu–Al ternary alloy system from alloy compositions alone. This approach is derived from the first-principles calculations based on the density-functional theory and molecular dynamic (MD) simulations. By considering of both the thermodynamic and atomic-structure induced kinetic effects, the predicted GFA trend from this approach shows an excellent agreement with experimental data available in this alloy system, manifesting its capability of seeking metallic glasses with superior GFA in ternary alloy systems

[en] Recently, we have revealed that the atomic packing in both metallic liquids and supercooled liquids can be described globally by the spherical-periodic order (SPO), while the global feature of the glassy solids can be characterized by the local translational symmetry (LTS) imposed on the SPO (Liu XJ, et al. Phys Rev Lett 2010;105:155501). In this study, we have conducted a systematic study of the effects of chemical compositions and radiation resources on the evolution of pair distribution function (PDF) profiles in the model Zr-Cu and Zr-Cu-Al glass-forming systems, by theoretical atomistic simulations coupled with synchrotron X-ray scattering experiments. Our results indicate that the global symmetry feature is held very well even in some complex cases, as long as their short-range orders can be carefully identified.