Mechanical properties of SiC_f/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.