Giant configurational softening controls atomic-level process of shear banding in metallic glasses

Abstract

While the shear banding is a ubiquitous feature for metallic glasses and other disordered solids, the underlying material softening mechanism is still an open question requiring physical interpretation at atomic level. Here, through a set of atomistic simulations, we clarify the origin of flow localization, i.e., the birth of a shear band. The local thermal temperature induced by atomic vibration and configurational temperature attributed to structural disordering are proposed to quantify critical degree of thermal and configurational softening, respectively. The comparison between configurational softening and thermal softening being two potential causes for shear banding emergence is then examined at atomic scale. Numerical evidence from atomistic simulations indicates that configurational-softening-induced strain burst is the dominant instability mode as evidenced through a very large value of configurational temperature rise that commensurate with glass transition temperature. It is also found that configurational softening takes precedence over thermally activated ones. Configurational softening is thus conceivably acting as the root cause for the onset of strain localization and shear banding, while the subsequent thermal softening is its consequence. These results provide important insights into the puzzle about the material weakening mechanism underlying shear banding.