Correlation between Dynamics and Atomic Structures in Cu-Zr Metallic Glasses

Abstract

The atomic structures of metallic glasses (MGs) are very sensitive to the cooling rates. Most molecular dynamics (MD) simulations suffer from the ultrahigh cooling rates on the order of 1010–13 K/s, where the as-prepared models are hardly given enough time to relax. In this work, an extended sub-T g annealing up to 1.8 µs was applied to a Cu64.5Zr35.5 MG in order to reduce the effect of the high cooling rate used in MD simulations. The effective cooling rate after the sub-T g annealing is derived to be 2×108 K/s, which is about two orders of magnitude lower than the cooling rates used in conventional MD simulations. The icosahedral short-range order and the Bergman-type medium range order (BMRO) are significantly enhanced after the annealing. The interpenetrating, face-, edge- and vertex-sharing schemes of connections among icosahedra are found to be enhanced after annealing. The network formed by the interpenetrated ICO centers clearly shows a transition from string-like to star-like in morphology. The diffusing atoms are found to be outside icosahedral SRO and BMRO for most of the simulation time. Our result supports the scenario that there are both liquid- and solid-like regions in MGs. The solid-like regions form the backbone while the liquid-like regions provide diffusion channels of the glassy structure.