Connection between the packing efficiency of binary hard spheres and the glass-forming ability of bulk metallic glasses

Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Sep;90(3):032311. doi: 10.1103/PhysRevE.90.032311. Epub 2014 Sep 29.

Abstract

We perform molecular dynamics simulations to compress binary hard spheres into jammed packings as a function of the compression rate R, size ratio α, and number fraction x(S) of small particles to determine the connection between the glass-forming ability (GFA) and packing efficiency in bulk metallic glasses (BMGs). We define the GFA by measuring the critical compression rate R(c), below which jammed hard-sphere packings begin to form "random crystal" structures with defects. We find that for systems with α≳0.8 that do not demix, R(c) decreases strongly with Δϕ(J), as R(c)∼exp(-1/Δϕ(J)(2)), where Δϕ(J) is the difference between the average packing fraction of the amorphous packings and random crystal structures at R(c). Systems with α≲0.8 partially demix, which promotes crystallization, but we still find a strong correlation between R(c) and Δϕ(J). We show that known metal-metal BMGs occur in the regions of the α and x(S) parameter space with the lowest values of R(c) for binary hard spheres. Our results emphasize that maximizing GFA in binary systems involves two competing effects: minimizing α to increase packing efficiency, while maximizing α to prevent demixing.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Glass / chemistry*
  • Hardness*
  • Metals / chemistry*
  • Molecular Conformation
  • Molecular Dynamics Simulation*
  • Phase Transition*

Substances

  • Metals