Characterization of BN interface and its effect on the mechanical behavior of SiCf/SiC composites

The boron nitride (BN) interface of SiC fiber-reinforced SiC matrix (SiCf/SiC) composites was fabricated by chemical vapor infiltration (CVI) using BCl3 and NH3 as precursor. The microstructure and chemical composition of the BN interface were characterized. The influence of the coating thickness on the tensile behavior of SiCf/SiC composites was then evaluated. The BN interface synthesized at 800 degrees C has a low degree of crystallization and displays a quasi-isotropic microstructure. The ratio of element B to element N is near 1 and the oxygen content is about 10%. Meanwhile, the electron structure of B, N atoms near the SiC fiber surface have more sp2 hybridi-zation state. Increasing the BN interface thickness exerts a critical role in decreasing the interfacial sliding stress which improves the tensile strength and toughness of SiCf/SiC composites. The optimal thickness of the BN interface is about 670 nm and further increasing the thickness exhibits little improvement on the mechanical properties of SiCf/SiC composites.