Topological and chemical short-range order and their correlation with glass form ability of Mg-Zn metallic glasses: A molecular dynamics study

Abstract

Mg-based metallic glasses are promising materials for biodegradable implants. Understanding atomistic mechanism behind glass formation in these glasses plays a critical role in developing them for future applications. In the present work, we perform a set of molecular dynamics simulations to study structural origin behind glass form ability of Mg-based Mg-Zn metallic glasses at a wide range of compositions. Pair distribution function, Voronoi tessellation and dynamical analysis were adopted to characterize local structures in these glasses. Structural analysis was performed considering both topological and chemical short-range orders. It was found that structure of Mg-Zn metallic glasses could be best described from the perspective of solute-centered clusters. Zn-centered icosahedra, which have the highest symmetry among all local clusters, are preferred in all compositions and its population reaches nearly 28% regardless of the overall chemical composition. The stability of this local cluster depends at high extent to the chemical short-range order around Zn atoms. At favorable composition, that is equivalent to nearly ideal icosahedron geometry, Zn-centered icosahedra would have highest stability and lowest dynamic, which could hinder atoms involved in these clusters from redistribution and/or crystallization. The results offer a good explanation of experimentally observed maximum glass form ability at Mg70Zn30 composition in Mg-Zn system. It could open a door for the engineering of metallic glass alloys compositions for the optimal glass form ability by means of numerical simulations without involving expensive experimental procedures.