Medium range order evolution in pressurized sub-Tg annealing of Cu64Zr36 metallic glass

Abstract

Molecular dynamics (MD) simulations have been widely used to study the structure of metallic glasses (MGs) at atomic scale. However, ultrafast cooling rates in MD simulations create structures that are substantially under-relaxed. In this study, we introduce long-term pressurized annealing up to 1μs slightly below the glass-transition temperature, Tg, in MD simulation, which effectively relaxes the structure of Cu64Zr36 MG toward experimental conditions. It is found that applying hydrostatic pressure up to 2GPa relaxes the MG to low-energy states whereas higher pressures retard relaxation events. In the sample annealed at 2GPa pressure, equivalent cooling rate reaches to 3.7×107K/s, which is in the order of melt spinning experiments. Furthermore, the correlation between structural relaxation and medium-range structures formed by interpenetrating connection of icosahedra is studied. Clustering coefficient analysis shows that in the samples prepared at high cooling rates, interpenetrating icosahedral networks are fragmented. However, as the glass relaxes toward real conditions, a unified network develops throughout the glassy structure, which acts as a solid-like backbone. The morphology of such a network differs from string-like fashion proposed in the previous studies.