Dynamic properties of major shear bands in Zr-Cu-Al bulk metallic glasses

We present a systematic investigation of shear-band dynamics as a function of chemical composition in the ZrxCu90-xAl10 (x = 45-65) metallic glass system. We investigate aging dynamics in the non-serrated flow regime, shear-band velocities in the serrated flow regime, the transition between these two flow modes, and the transition from ductile to brittle behavior. We find that the activation energy for shear-band propagation is largely determined by the underlying time scales of the shear process, and that temperature-dependent stress drops only play a minor role. The activation energy as a function of composition can be linked to the bonding strength between the fastest diffusor, Cu, and its coordinating atoms, represented by the ratio of strong Cu-Zr to weaker Cu-Cu bonds. This indicates that the resistance to accelerated shear, i.e. the apparent activation barrier, is primarily controlled by a chemical nearest-neighbor effect. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.