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 degrees C, 1200 degrees C and 1500 degrees C was systematically investigated, and its oxidation resistance at 1500 degrees C was better than 900 degrees C and 1200 degrees C. More specifically, the MoSi2-based coating continued to reduce mass during the oxidation at 900 degrees 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 degrees C and 1500 degrees 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.