Tribological behaviors of precipitation-strengthened Al_0.8NbTaTiM_0.2 (M = Ni, Cr) refractory high entropy alloys in a wide temperature range

Refractory high entropy alloys (RHEAs) have attracted considerable attention as promising candidates for high-temperature structural and wear-resistant applications. In this study, the microstructural evolution and wide-temperature tribological behaviors of newly designed precipitation-strengthened Al_0.8NbTaTiM_0.2 (M = Ni, Cr) RHEAs were systematically investigated. Structural analyses revealed that the Al_0.8NbTaTiNi_0.2 alloy formed a dual-phase constitution of BCC and σ phases, while Al_0.8NbTaTiCr_0.2 effectively suppressed σ-phase precipitation and facilitated the formation of AlCr₂. The Al_0.8NbTaTiCr_0.2 alloy exhibited higher hardness, attributed to the synergistic effects of precipitation strengthening and enhanced solid-solution strengthening. Wear results showed that the Al_0.8NbTaTiCr_0.2 alloy achieved lower coefficient of friction and wear rates from room temperature to 800 °C. At room temperature, its superior wear resistance originated from the higher hardness and the uniform dispersion of fine precipitates, which suppressed fatigue and adhesive wear. At high temperatures, the formation of dense and stable oxide tribo-layers enriched in Al₂O₃ and TiO₂ further improved its wear resistance. These findings demonstrate that tailoring phase constitution via Cr-alloying is an effective strategy to optimize the tribological performance in RHEAs, providing guidance for the development of advanced high-temperature wear-resistant materials.