Unlocking metallic glasses ultra-low friction via high-entropy effect and oxidation

Bulk metallic glasses (BMGs) hold immense potential as micro- and nano-scale engineering materials, yet their tribological performance remains limited by metastable structures and poor friction behavior. This study achieves superior nanotribological properties in a Ti₂₀Zr₂₀Cu₂₀Hf₂₀Be₂₀ high-entropy BMG (HE-BMG) by synergistically combining high-entropy design with controlled surface oxidation, overcoming limitations of conventional BMG treatments. Nano-scratch testing revealed a 40 % reduction in coefficient of friction (from 0.2 to 0.12) and a 44 % decrease in scratch depth (from 90 nm to 50 nm) for high entropy oxide amorphous surface, alongside a 90 % elastic recovery, far surpassing the as-cast counterpart. Complementary molecular dynamics simulations and nanoindentation uncovered the dual role of the high entropy oxide amorphous surface: its ionic bonding and elevated free volume suppress ploughing and adhesion, while boosting hardness and elastic modulus. This synergy arises from the HE-BMG's uniform elemental distribution, which curbs oxygen diffusion and yields a uniquely thin yet robust oxide layer compared to traditional BMGs. These findings establish a credible framework for designing low-friction, wear-resistant BMGs, with broad implications for advanced engineering applications.