MoSi₂/SiC HIGH TEMPERATURE ANTI-OXIDATION COMPOUND COATING ON CARBON/CARBON COMPOSITES AND ITS ANTI-OXIDATION BEHAVIOUR

The high temperature anti-oxidation compound gradient MoSi₂/SiC coating on carbon/carbon composites was prepared by a new complex process of two-stage holding temperature burying and sealing.The suitable gradient framework of the coating is SiC transiting layer,SiC compacting layer,MoSi₂/SiC double phase layer and outer layer containing mainly MoSi₂ from the inner to the outer of the coating.The oxidation mass loss rate of the unsealed coating prepared for longer holding time at the high temperature stage is less.The oxidation mass loss rates of the unsealed coating at 1200℃ and 1300℃ are larger than those at 1400℃ and 1500℃ in air.The surface of the coating is sealed with Si ( OC₂H₅ ) ₄, and the formed SiO₂ in gel fills the cracks and covers the coating.Oxidated at 1500℃ in air for a given time, the specimen with unsealed coating loses the mass,and the specimen with sealed coating gains the mass.The mass gain of sealed coating is 1.28% after oxidation at 1500℃ in air for 52 hours.The sealing improves the anti-oxidation of the coating greatly.