Size effects in metallic glass

Li, J.*; Shimizu, Futoshi ; Ogata, Shigenobu*

Shear bands form in most bulk metallic glasses (BMGs) within a narrow range of uniaxial strain . We propose this critical condition corresponds to embryonic shear band (ESB) propagation, not its nucleation. To propagate an embryonic shear band, the far-field shear stress must exceed the quasi steady-state glue traction of shear-alienated glass until the glass-transition temperature is approached due to frictional heating, at which point ESB matures as a runaway shear crack. The incubation lengthscale necessary for this maturation is predicted to be nm for Zr-based BMGs, below which sample-scale shear localization does not happen. Molecular dynamics simulations with up to 20-million atoms have directly verified the aged-rejuvenation-glue-liquid (ARGL) shear band structural model and "march-to-melting" instability, which occurs with a characteristic incubation timescale of ps and lengthscale of nm.