Oxidation Behavior of Spark Plasma Sintered Compacts of MoSiBTiC Powder Produced by Gas Atomization

The first generation MoSiBTiC alloy with the nominal composition of 65Mo–5Si–10B–10Ti–10C in at% exhibits excellent high temperature creep resistance and specific strength for application at the temperature up to at least 1300°C. But the oxidation behavior should also be paid attention to since it is a big issue for such Mo-based alloys and could be well affected by the microstructure at the material surface. In this study, gas atomized MoSiBTiC powder was used to produce the compact by spark plasma sintering (SPS) method, and a relative density of almost 100% was achieved. Compared to the conventional arc-melted MoSiBTiC alloy, also prepared in this work, SPS compact showed greatly refined microstructure and a small compositional change during the process. By the microstructure refinement, the oxidation performance of the SPS compact slightly deteriorated at 800°C but improved at 1100 °C. Moreover, the effect of microstructure refinement on the oxidation behavior at a higher temperature such as 1500 °C is not remarkable. This distinction at the three temperatures is considered to be attributed to different reasons. Surface modification using the pack cementation method was also applied to the SPS compact to further improve the high-temperature oxidation resistance. With the development of an approximately 100 µm thick silicide layer on the top surface, the sample exhibited remarkably enhanced oxidation resistance at the temperature up to at least 1300 °C.