Ductile to brittle transition of fracture of a Zr-based bulk metallic glass: Strain rate effect

Quasi-static and dynamic tensile experiments were conducted on a Zr-based bulk metallic glass at room temperature. A significant ductile-to-brittle transition was identified with increasing strain rate, based on the changes in the macroscopic fracture mode from shear to normal tension and in the microscopic fracture feature from vein patterns to fine dimples and/or nanoscale periodic corrugations. According to the Mohr-Coulomb criterion, it is revealed that such a transition is due to the competition between the intrinsic critical shear and tensile strengths at different strain rates. Microscopically, the strain-rate induced transition is attributed to the change in the motion of local atomic groups from shear transformation zone to tension transformation zone, in which the characteristic volume of shear transformation zone is a key parameter. (C) 2016 Published by Elsevier Ltd.