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

In this study, AlMo0.5NbTiVSix (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 AlMo0.5NbTiVSix alloys were discussed from a thermodynamic perspective.