Structural processes that initiate shear localization in metallic glass

For crystalline metals, the structural carriers (dislocations and twins) of plasticity have been well characterized. In contrast, the structural processes responsible for the localized shear flow in amorphous metals remain poorly understood. Using molecular dynamics simulations, we illustrate here how the shear localization initiates in a Cu-Zr metallic glass. We identify the breakdown of full icosahedral clusters as a structural signature of the initiation of shear localization, which is demonstrated to be a spontaneous and autocatalytic instability propagating with a velocity close to the speed of sound. Structural disorder induced softening precedes thermal softening as the origin of the shear banding. Once the deformation band penetrates across the entire sample, the already-rejuvenated structure inside allows the entire band to collectively slip as a whole, to grow the shear offsets on both sides of the sample. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.