Doping B or C to improve the wear resistance of (Ti42.5Zr42.5Nb10Ta5)93Mo7 refractory high-entropy alloy via grain boundary plasticization

RHEAs exhibit low room-temperature ductility, which severely restricts their processing and industrial applications. In this work, the high strength (Ti_42.5Zr_42.5Nb₁₀Ta₅)₉₃Mo₇ was selected as the base alloy and grain boundary engineering through doping B and C was utilized to achieve an optimal balance between mechanical properties and wear resistance. The tensile strength and plasticity of the (Ti_42.5Zr_42.5Nb₁₀Ta₅)₉₃Mo₇ refractory high-entropy alloys (RHEAs) are simultaneously enhanced with the addition of 0.05 at.% B or 0.05 at.% C. The effects of doping B or C on tribological properties of the (Ti_42.5Zr_42.5Nb₁₀Ta₅)₉₃Mo₇ RHEAs sliding against Si₃N₄ balls under different sliding distance were systematically investigated. The results show that B or C segregates at grain boundaries (GBs) and enhance the GB cohesion, thus significantly improving the strength and plasticity of RHEAs. After doping 0.05 at.% B, the yield strength increases from 956 MPa to 983 MPa and the elongation increases from 1.81 % to 4.97 %. Specifically, the yield strength is 1047 MPa for the alloy doped with 0.05 at.% C, and the elongation skyrockets to 26.51 %. The RHEA-C alloy exhibits the lowest wear rate under different sliding distance due to its highest strength and optimal plasticity. Additionally, the wear rates of the three RHEAs decrease firstly and then increase with increasing sliding distance from 18 m to 144 m. After 18 m sliding, the wear mechanism is severe abrasive wear, adhesive wear and slight oxidation wear. As the sliding distance increased to 108 m, the wear mechanism of the alloy is mainly dominated by oxidative wear, resulting in the best wear resistance, but the cracks and spalling pits occur in the oxide layer as the sliding distance further increased. The RHEAs designed in this work are applicable to numerous industries, including defense, transportation, and aerospace due to its good mechanical properties and wear resistance.