Unveiling the high-temperature oxidation behavior of Ti-V-Nb-Mo-Al refractory high entropy alloy: A combined experimental and computational study

The high-temperature oxidation behavior of two refractory high-entropy alloys (RHEAs), Ti₃₅V₃₅Nb₁₀Mo₂₀ (Al0 RHEA) and Ti₃₅V₃₅Nb₁₀Mo₂₀Al₅ (Al5 RHEA), was systematically investigated through both experimental methods and first-principles calculations. Al0 RHEA exhibits severe oxidation at 1000 ℃, characterized by significant weight gain and the formation of porous, cracked oxide layers due to the volatilization of MoO₃ and V₂O₅ and the growth of needle-like oxides. In contrast, the addition of Al improves oxidation resistance in Al5 RHEA, which forms a continuous, dense, and adherent oxide layer. First-principles calculations indicate that Ti has the highest oxygen affinity and dominates initial oxygen adsorption, but the resulting TiO₂ is loosely packed and insufficient for protection. The composite oxide AlNbO₄ exhibits unique “integrator and stabilizer” functions. The addition of Al promotes the formation of composite oxide AlNbO₄, which combines loose TiO₂ particles and improves the overall stability and integrity of the oxide layer. Furthermore, the formation of AlNbO₄ contributes to a more balanced Pilling–Bedworth ratio (PBR), which helps alleviate internal stress accumulation during oxidation and enhances the adhesion and mechanical stability of the oxide layer.