Abstract: Up-and-coming high-temperature materials, refractory high entropy alloys, are suffering from lower oxidation resistance, restricting their applications in the aerospace field. In this study, two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication (EBF³). Finer and short-range ordering structures were observed in the remelted sample, whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases. High-temperature cyclic and isothermal oxidation tests at 1000 °C were carried out. The total weight gain after 60 h of cyclic oxidation decreased by 17.49 % and 30.46 % for the remelted and deposited samples, respectively, compared to the as-cast state. Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples. A multilayer oxide consisting of TiO₂+Al₂O₃+SiO₂+AlNbO₄ was studied for its excellent oxidation resistance. The oxidation behavior of rutile, corundum and other oxides was analyzed using first principles calculations and chemical defect analysis. Overall, this research, which introduces novel treatments, offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.

Key words: Refractory high entropy alloy, Oxidation, Electron beam freeform fabrication, Multilayer oxide, First principles calculations