Mechanical properties of SiCf/SiC composites with h-BN interphase formed by the electrophoretic deposition method

Abstract

Silicon carbide fiber–reinforced silicon carbide (SiCf/SiC) composites have been expected to be used as next-generation heat resistant structural materials with high reliability. The fiber/matrix interface for SiCf/SiC composites plays an important role for toughening and strengthening, and it is important to form the optimal interphase for SiCf/SiC composites. In this study, hexagonal-boron nitride (h-BN), which shows better oxidation resistance than carbon, was selected as the interphase for SiCf/SiC composites, and h-BN coating was formed on low-conductive SiC fibers by the electrophoretic deposition (EPD) method using flaked h-BN suspension prepared by wet-jet milling. Unidirectional SiCf/SiC composites with the BN interphase formed by the EPD method were prepared by polymer impregnation and pyrolysis (PIP) method, and their mechanical properties were evaluated. The uniform h-BN interphase was successfully formed on the low-conductive SiC fibers by EPD when thin polypyrrole (Ppy) coating, that is, conductive polymer, was formed on the SiC fibers. The h-BN coating became denser by heat-treatment at 1000°C, and the h-BN coating deposited tightly on the SiC fibers was confirmed. It was demonstrated that the SiCf/SiC composites with the uniform and relatively dense h-BN interphase formed by EPD using flaked h-BN particles exhibited pseudo-ductile fracture behavior with large amount of fiber pullout and higher fracture energy.