Role of atomic-scale chemical heterogeneities in improving the plasticity of Cu-Zr-Ag bulk amorphous alloys

The addition of minor elements to binary amorphous alloys often results in simultaneous improvement in plasticity and strength. This is particularly the case for alloy systems that promote atomic-scale compositional separation during quenching. Considering that plasticity and strength are two contrasting properties originating from different atomic-scale structures characterized by short-range orders (SROs), this experimental observation at first seems contradictory when viewed from an SRO perspective. We performed comparative studies on (Cu0.5Zr0.5)(100-x)Ag-x amorphous alloys using experiments and molecular dynamics (MD) simulations to elucidate how these two mutually exclusive properties can be realized at the same time. MD simulations showed that while the addition of Ag promotes the formation of stable icosahedral orders responsible for improved strength, it also encourages the formation of weak/unstable Ag-bearing polyhedra that mitigate strain localization. In this study, the mechanistic origin of the enhanced plasticity is assessed by introducing a new descriptor that can quantitatively evaluate the characteristics of Ag-bearing polyhedra in terms of their size, softness, population, and spatial uniformity. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.