Abstract

Molecular dynamics simulations were carried out to investigate the influence of annealing process at glass transition temperature (Tg) on the atomic structure of a model Cu-Zr bulk metallic glass (BMG), especially icosahedral short- and medium-range orders (SRO and MRO). Analysis of SRO and MRO is done on voronoi tessellation, bond angle distribution and connectivity of clusters. It is found that the amount of icosahedral content of the system is significantly increased in a well relaxed structure. Since such SROs construct MROs via the icosahedral polyhedron connections, the size of MROs becomes larger as the annealing time is getting longer, and eventually make a huge cluster which can be considered as a rigid backbone. While we considered four connection types of vertex-, edge-, face-, and volume-sharing, the huge cluster in the relaxed samples mainly involve volume-type connection and exhibits a remarkable athermal plasticity that great stiffness and great yield strength compared to the as-quenched samples. In addition, the bond-angle distribution of annealed sample shows sharp peaks at specific bond angles which is an evidence of crystallized Laves-phase formed by icosahedral atoms, however the peaks are to be broaden after loading, which indicates decreasing amount of icosahedral content and their shape distortion. These results suggest that icosahedral content in a bulk metallic glasses plays a key role to determine the mechanical properties such as rigidity and maximum stress carrying capacity.