Microstructure and oxidation resistance of carbon/carbon composites coated with Si3N4-Si/MoSi2-SiC multi-layers by slurry coating and post heat-treatment process

Si3N4-Si/MoSi2-SiC multi-coating layer was fabricated on the surface of two dimensional carbon-carbon (C/C) composites in order to improve their oxidation resistance at high temperatures. Si-6wt%Al inner layer and Si-Mo outer layer was pre-coated to C/C composites by a slurry dipping process, and then they were heat-treated at 1500degreesC for 1 hour in a vacuum and then heat-treated 1 hour in nitrogen atmosphere. Dispersed MoSi2 phase in the Si matrix and SiC interface layer between C/C composite substrate and Si/MoSi2 layer was formed by the reaction between Mo and Si and between Si and C, respectively, during heat-treatment in a vacuum. On the other hand, Si3N4 layer was formed by the reaction between liquid Si and nitrogen gas during heat-treatment in nitrogen atmosphere. The oxidation resistance of C/C composites coated with a Si3N4-Si/MoSi2-SiC multi-layer was excellent during a cyclic oxidation test at 1400degreesC up to 5 hours.