Critically-Percolated, Cluster-Packed Structure in Cu–Zr Binary Bulk Metallic Glass Demonstrated by Molecular Dynamics Simulations Based on Plastic Crystal Model

Abstract

Molecular dynamics (MD) simulations based on a plastic crystal model (PCM) were performed for a Cu_0.618Zr_0.382 binary bulk metallic glass (BMG). The local atomic arrangements of the Cu_0.618Zr_0.382 BMG were demonstrated with MD-PCM under an assumption that the BMG is composed of randomly-rotated as well as distorted hypothetical clusters. The Cu-rich Cu_0.618Zr_0.382 alloy was computationally created from a tentatively-created Zr-rich Zr_0.73Cu_0.27 alloy through two steps. The first step includes the Zr_0.73Cu_0.27 alloy quenched from a liquid through conventional MD simulation, whereas the second step has a replacement of the Zr and Cu atoms in the Zr_0.73Cu_0.27 alloy with randomly-rotated icosahedral and tetrahedral clusters, respectively, and subsequent structural relaxation. The Cu_0.618Zr_0.382 alloy, thus created with MD-PCM, was formed in a noncrystalline state as a critically-percolated cluster-packed structure. The analyses with total pair-distribution and interference functions revealed that the calculation results tend to reproduce the experimental data in an as-quenched state. The results explain that the glass-forming ability of the Cu_0.618Zr_0.382 BMG is due to (1) a critically-percolated and distorted tetrahedral clusters forming a network and (2) atomistic-level inhomogeneity for the local atomic arrangements with keeping macroscopic homogeneity in terms of the chemical composition and dense random atomic arrangements.