Isothermal and cyclic oxidation behaviours of MoSi₂ with additions of B at 1250 °C prepared by spark plasma sintering

Mo-Si-B alloys were obtained by spark plasma sintering (SPS) using Mo-57Si-10B and Mo-52Si-15B alloy powders, and the effects of the B content and powder size on the isothermal and cyclic oxidation behaviours of the Mo-Si-B alloys at 1250 °C were investigated. A SiO₂ phase was introduced during the SPS process and the Mo-Si-B alloys consisted of a fine MoSi₂/Mo₂B₅/MoB/SiO₂ microstructure. Under isothermal and cyclic oxidation conditions, the kinetic curves of the SPS Mo-Si-B alloys exhibited parabolic time dependence on the weight gain. The increase in the nominal B caused a decrease in the incubation stage of the formation of continuously protective borosilicate layer but increased the mass gain due to the higher fluidity of the borosilicate layer. The SiO₂ phase was found to supply the borosilicate layer with a “Mechanical locking” mechanism through the spilling of the SiO₂ phase in the SPS samples, especially under the cyclic oxidation condition.