Nanoscratching of metallic glasses -- An atomistic study

TL;DR

This study uses molecular dynamics simulations to analyze nanoscratching of metallic glasses, revealing temperature-dependent plasticity, force evolution, and damage mechanisms relevant for engineering tribological applications.

Contribution

It provides atomistic insights into nanoscratching behavior of metallic glasses, highlighting temperature effects on plasticity and damage, which were not previously detailed at this scale.

Findings

Plasticity volume increases with temperature, especially above glass transition.

Nanoscratching damage is more severe at higher temperatures.

Force and hardness evolution follow known behaviors from crystalline substrates.

Abstract

Tribological properties of materials play an important role in engineering applications. Up to now, a number of experimental studies have identified correlations between tribological parameters and the mechanical response. Using molecular dynamics simulations, we study abrasive wear behavior via nanoscratching of a Cu$_{64.5}$Zr$_{35.5}$ metallic glass. The evolution of the normal and transverse forces and hardness values follows the behavior well known for crystalline substrates. In particular, the generation of the frontal pileup weakens the response of the material to the scratching tip and leads to a decrease of the transverse hardness as compared to the normal hardness. However, metallic glasses soften with increasing temperature, particularly above the glass transition temperature thus showing a higher tendency to structurally relax an applied stress. This plastic response is analyzed focusing on local regions of atoms which underwent strong von-Mises strains, since these are the basis of shear-transformation zones and shear bands. The volume occupied by these atoms increases with temperature, but large increases are only observed above the glass transition temperature. We quantify the generation of plasticity by the concept of plastic efficiency, which relates the generation of plastic volume inside the sample with the formation of external damage, viz. the scratch groove. In comparison to nanoindentation, the generation rate of the plastic volume during nanoscratching is significantly temperature dependent making the glass inside more damage-tolerant at lower temperature but more damage-susceptible at elevated temperatures.