Effect of Si additions on the oxidation behavior of AlMo0.5NbTiVSix refractory high-entropy alloys at 1073 K

In this study, AlMo_0.5NbTiVSi_x (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) refractory high-entropy alloys were fabricated by vacuum arc-melting, and the effects of Si on the oxidation resistance were systematically investigated. The results indicate that the oxidation behavior of alloys without Si addition primarily involved metal-gas interface reactions and solid-solution diffusion through the oxide layer. After the introduction of the Si element, Si formed the M₅Si₃-type intermetallic compound phase with Ti and Nb attributed to their strong bonding ability and acted as a short-circuit diffusion channel, contributing to the accelerated corrosion of oxygen on the interior of the alloy during the oxidation process. In addition to the metal-gas interface reaction and solid-solution diffusion through the oxide layer, the oxidation behavior of Si-containing RHEAs in our study also comprised the influence of the phase interface, suggesting that the nucleation sites of the oxide included the phase interface between BCC and M₅Si₃ phase. High Si content was not conducive to the antioxidant performance of RHEAs. Furthermore, the oxidation products and mechanisms of AlMo_0.5NbTiVSi_x alloys were discussed from a thermodynamic perspective.