Enhancement of Oxidation Resistance of Continuous-Fiber-Reinforced Ceramic Composite by Using C-B-Si Fiber-Coating and SiC Surface-Coating

Continuous fiber-reinforced composite with an amorphous Si-N-C matrix was prepared by a polymer impregnation pyrolysis method by using C-B-Si coated silicon nitride fiber as reinforcement. This composite had a fairly high oxidation resistance due to the self-formed seal of B2O3-SiO2 upon oxidation of the C-B-Si fiber-coating. Chemical vapor deposited (CVD) SiC was coated on the composite to further enhance its oxidation resistance. The composite using mono-layered C-B-Si fiber-coating without surface-coating showed a strength decrease from 1136 to 635MPa upon oxidation at 1473K for 720ks. SiC surface coating of 10μm thickness on the composite improved its strength after oxidation to 814MPa. The composite using three-layered C-B-Si fiber-coating showed negligible strength decrease from 979 to 846MPa even without surface-coating. On this better composite, the SiC surface-coating did not improve the oxidation resistance, but decreased the mass gain by oxidation to half.