Title: Packing Efficiency of Hard Sphere Mixtures and Glass-forming Ability of Metallic Glasses

Author (Talk): Kai Zhang, Yale University

Abstract:

Hard-sphere models provide quantitatively accurate descriptions of physical properties in systems where steric, repulsive interactions are dominant. Bulk metallic glasses (BMGs) are prepared by thermally quenching liquid alloys at sufficiently fast rates such that they bypass crystallization, and instead form amorphous solids. Despite their optimal mechanical properties, the applications of BMGs are still constrained by the high cost and small casting thickness. The glass-forming ability (GFA) of a BMG is defined by the critical cooling rate Rc below which the system begins to crystallize and understanding what factors may affect GFA is crucial for developing better BMGs. We perform molecular dynamics simulations to compress hard sphere mixtures into jammed packings as a function of the compression rate R, size ratio alpha, and the number fraction x of small particles to determine the connection between the GFA and the packing efficiency. We found for systems with alpha > 0.8 that do not de-mix, Rc degreases strongly with the difference between the average packing fraction of the amorphous packings and random crystal structures at Rc.