Atomic-scale mechanisms of nanoscratch response in metallic glasses at experimentally realistic cooling rates

Metallic glasses (MGs) exhibit promising tribological properties, but their atomic-scale nanoscratch response remains poorly understood because molecular dynamics (MD) simulations typically employ unrealistically fast quench rates. We address this limitation by integrating MD simulations with Monte Carlo sampling to generate Cu₅₀Zr₅₀ MGs across ten orders of magnitude in cooling rate, reaching experimentally relevant values as low as 500 K/s, unprecedented in nanoscratch simulations. Large-scale nanoindentation and nanoscratch simulations reveal a significant dependence of hardness, friction, and wear on cooling rate. Slowly cooled glasses show enhanced fivefold local order and reduced free volume, leading to higher load-bearing capacity and altered frictional behavior. We uncover the atomic-scale mechanism: structural relaxation raises shear-activation barriers and transitions from diffuse to highly localized shear transformation zones. This work provides the first atomistic resolved picture into nanoscratch behavior in MGs prepared at experimental cooling rates, establishing a predictive link between processing, structure, and nanofriction.