Oxidation sequence modulation induced superior high-temperature tribological performance of Ti-Hf-Nb-V refractory high entropy alloy fabricated through directed energy deposition

To fulfill the demands of applications under severe operational conditions, alloys should possess outstanding wear resistance at elevated temperatures. A Ti-Hf-Nb-V based refractory high entropy alloy (RHEA) was successfully produced using the directed energy deposition (DED) technique, which avoided the formation of fatal defects and showcased well-performed mechanical properties across a broad temperature spectrum. Strategic design of the oxidation sequence enabled the early formation of oxide nanolayers, which can form a polycrystalline oxide nanocoating under a complex stress condition to drastically reduce the wear rate from 2.69 × 10^–4 mm³·(N·m)⁻¹ at room temperature to 6.90 × 10^–7 mm³·(N·m)⁻¹ at 600 °C. These results indicate that the application of additive manufacturing to fabricate RHEAs with superior wear resistance at high temperatures paves the way for the development of functional coatings designed to withstand extreme conditions.