Sliding and deformation of metallic glass: experiments and MD simulations

Abstract

The sliding behavior of metallic glass (MG) was studied using pin-on-disk tests and molecular dynamics (MD) simulations. Friction coefficients and wear rates of a Zr–Ti–Cu–Ni–Be alloy were similar to those reported for ductile materials, e.g., normal crystalline metals; i.e., exceptional friction and wear characteristics of bulk MG were not observed. Sliding caused plastic deformation, transfer, mechanical mixing and reamorphizing of devitrified material. In vacuum, a softer layer developed adjacent to the interface. In air, an additional harder layer appeared when oxidation products were incorporated into the near-surface material. MD simulations involved a two-component 2D amorphous system. Simulations of tensile tests showed elastic/perfectly plastic response, strain rate dependence, void formation and shear bands. Simulations of sliding showed decreased density near the interface, suggesting an increase in free volume during shear, but neither voids nor shear bands. Subsurface displacement profiles were similar to those reported in experiments on crystalline materials and were consistent with flow patterns expected for flow near a boundary. The MD results on mechanical mixing suggest relevance to other processes, including mechanical alloying, friction welding, formation of nanocrystals, erosion and deformation at high strain rates.