Excellent wear resistance in a low density (FeCoNi)87Al5Ti8 high entropy alloy at high temperatures: Role of self-protective multi-layer oxides

The FeCoNiAlTi-based high-entropy alloy (HEA) system has been explored for its exceptional strength and ductility at ambient temperatures. However, its mechanical and tribological performance at elevated temperatures remains largely unexplored. In this study, low-density (~7.6 g/cm3) (FeCoNi)87Al5Ti8 high-entropy alloy (HEA) was developed by induction melting followed by thermal processing and systematically evaluated for its wear resistance at both ambient and elevated temperatures. The alloy exhibited wear rates of 1.5 × 10-5 mm3/Nm at room temperature and a remarkably low wear rate in the order of 10-7 mm3/Nm at 700 °C. The outstanding wear resistance observed in this alloy is attributed to the presence of a coherent nano-lamellar FCC/L12 structure and the formation of a robust, wear-resistant multicomponent tribo-oxide layer, underlain by protective mixed-oxide layers at the subsurface, effectively suppressing oxidation and wear at 700 °C. Nanoindentation and scratch tests reveal that the tribo-oxide layer exhibits approximately a 100% increase in hardness and a ~32% reduction in scratch depth compared to the base alloy, indicating mechanical robustness. The (FeCoNi)87Al5Ti8 alloy could be a promising candidate for wear and oxidation resistant applications up to 700 °C.