Effect of aluminum addition on the elevated-temperature wear resistance of Ti₄₀Zr₄₀Nb₁₀Ta₁₀ refractory high-entropy alloys

The tribological behavior of Ti₄₀Zr_40-xNb₁₀Ta₁₀Al_x (x = 0, 5, 8 and 10) refractory high-entropy alloys were systemically investigated from RT to 800 °C, focusing on the correlation between the composition, microstructure, and wear performance. Al addition promotes the formation of a B2 phase, resulting in a gradual increase in microhardness. Wear results show that Al addition increases the wear rate at room temperature but decreases it at high temperature. At room temperature, the addition of Al promotes the preferential formation of Al₂O₃ on the alloy surface, but the oxide film formed through oxidation induced by local flash temperatures is thin and easily peels off under load, failing to protect the alloy and thereby deteriorating its wear resistance. Conversely, at elevated temperatures, Al enables the alloy to withstand severe oxidation, forming a thicker oxide layer on its surface that effectively reduces the friction coefficient and wear rate. The Al-10 alloy exhibits excellent high-temperature wear resistance. The superior performance is attributed to the formation of an amorphous-nanocrystalline composite tribo-layer after Al addition, acting as a protective barrier to mitigate wear-induced damage.