Microstructure and properties of Cf/SiC composites with thin SiCN layer as fiber-protecting coating

Cf/SiC composites were prepared first by chemical vapor infiltration for formation of SiCN coating on the fiber surface, then by polymer infiltration and pyrolysis for SiC densification process. The effect of SiCN content on microstructure and mechanical properties of the composites was investigated. As the content of deposited SiCN increased, the density of the composites gradually increased. Simultaneously, the bending strength and proportional limit stress were also improved. When the preform density after SiCN deposition reached about 1.01 g/cm3, the ultimate bending strength and proportional limit stress of the final densified composites were enhanced to 386 MPa and 302 MPa, respectively. The fracture behavior of the fabricated composites was totally changed after SiCN deposition. Long fiber pullout dominated the fracture surfaces for composites with deposited SiCN, while for the one without fiber coating no fiber pullout was observed.