Preparation and enhanced oxidation behavior of microalloyed Mo₅SiB₂ alloy at 1300 °C

Microalloyed Mo₅SiB₂ alloys were fabricated by spark plasma sintering (SPS). The effects of different sintering temperatures and yttrium additions on the microstructure and high-temperature oxidation behavior of the alloys were systematically investigated. For the optimum Mo-13Si-25B-0.2Y alloy sintered at 1750 °C, adding small amounts of rare-earth yttrium refined the grains to an average size of ~400 nm without reducing the Mo₅SiB₂ content. During oxidation at 1300 °C, the “fishlike” Y₂Si₂O₇ and Y₂O₃ phases were formed and anchored on the surface of the oxide layers, promoting the oxidation of silicon and accelerating the formation and coverage of the oxide protective film. Moreover, yttrium promoted the in situ deformation of a self-generated protective borosilicate glass film under high-temperature oxidation by accelerating Si oxidation. With prolonged oxidation time, viscous flow occurred to repair the internal cracks and tiny defects caused by the volatilization of MoO₃ and prevented the inward diffusion of oxygen, as evidenced by a low oxidation rate constant of 0.95 mg² cm⁻⁴ h⁻¹ at 1300 °C for 50 h in the Mo-13Si-25B-0.2Y alloy.