Microstructure and oxidation behavior of MoSi₂-based coating on carbon/carbon composites

MoSi₂-based oxidation protective coating was fabricated on carbon/carbon (C/C) composites by combining pack cementation and supersonic atmospheric plasma spraying techniques. This work firstly studied the effect of spraying power on the phase composition of MoSi₂ coating. Proper power at 50–55 kW could suppress the phase transition and powder oxidation of MoSi₂ during spraying, which facilitated the coating densification. In addition, the static oxidation behavior of MoSi₂-based coating at 900 °C, 1200 °C and 1500 °C was systematically investigated, and its oxidation resistance at 1500 °C was better than 900 °C and 1200 °C. More specifically, the MoSi₂-based coating continued to reduce mass during the oxidation at 900 °C without significant mass addition, and the mass loss rate rapidly increased with the promotion of oxidation process, eventually showing a large mass loss percentage. However, it exhibited varying degrees of mass gain during oxidation at 1200 °C and 1500 °C, and the ultima mass loss percentage was relatively low. The mass gain phenomenon is correlated with the produced SiO₂ glass scale covering on the coating surface, while the mass loss behavior may be attributed to the immoderate depletion of MoSi₂-based coating and the considerable evaporation of gaseous products accompanied by the oxidation reaction ongoing.