Yield point of metallic glass

Shear bands form in most bulk metallic glasses (BMGs) within a narrow range of uniaxial strain ey @ 2%. We propose this critical condition corresponds to embryonic shear band (ESB) propagation, not its nucleation. To propagate an ESB, the far-field shear stress s1 Eey/2 must exceed the quasi-steady-state glue traction sglue of shear-alienated glass until the glass transition temperature is approached internally due to frictional heating, at which point ESB matures as a runaway shear crack. The incubation length scale linc necessary for this maturation is estimated to be 10 nm for Zr-based BMGs, below which sample size-scale shear localization does not happen. In shear-alienated glass, the last resistance against localized shearing comes from extremely fast downhill dissipative dynamics of timescale comparable to atomic vibrations, allowing molecular dynamics (MD) simulations to capture this recovery process which governs sglue. We model four metallic glasses: a binary Lennard-Jones system, two binary embedded atom potential systems and a quinternary embedded atom system. Despite vast differences in the structure and interatomic interactions, the four MD calculations give ey predictions of 2.4%, 2.1%, 2.6% and 2.9%, respectively. 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.