Enhancement of oxidation resistance of continuous-fiber-reinforced ceramiccomposite by using C-B-Si fiber-coating and SiC surface-coating

Continuous fiber-reinforced composite with an amorphous Si-N-C matrix was p repared by a polymer impregnation pyrolysis method by using C-B-Si coated s ilicon nitride fiber as reinforcement. This composite had a fairly high oxi dation resistance due to the self-formed seal of B2O3-SiO2 upon oxidation o f the C-B-Si fiber-coating. Chemical vapor deposited (CVD) SiC was coated o n the composite to further enhance its oxidation resistance. The composite using mono-layered C-B-Si fiber-coating without surface-coating showed a st rength decrease from 1136 to 635 MPa upon oxidation at 1473 K for 720 ks. S iC surface coating of 10 mum thickness on the composite improved its streng th after oxidation to 814 MPa. The composite using three-layered C-B-Si fib er-coating showed negligible strength decrease from 979 to 846 MPa even wit hout surface-coating. On this better composite, the SiC surface-coating did not improve the oxidation resistance, but decreased the mass gain by oxida tion to half.