Formation mechanism of large SiC grains on SiC fiber surfaces during heat treatment

Three low oxygen-containing SiC fibers with different surface compositions were heat-treated at high temperature in argon, and large SiC particles were observed on the surfaces of SiC fibers with oxygen-containing surface layers. The SiC particles were identified as single crystal β-SiC. The growth process, formation mechanism of these large SiC grains and their influence on fiber strength were investigated. Nano-sized SiC particles were precipitated from the decomposition of SiCxOy in the fiber surface that acted as nuclei, and these nuclei grew gradually to form large grains because of the gaseous reaction of SiO and CO. The formation of large SiC grains was related closely to the SiC fiber surface composition, which affected SiC nucleation and SiO diffusion from the core to the fiber surface. The large grains influenced the fiber strength degradation significantly and should be avoided to retain high fiber strength.