Effect of long-time annealing at high temperature on the microstructure and mechanical properties of different types of SiC fibers

SiC fibers play a crucial role in ceramic-matrix composites due to their excellent high-temperature resistance. To analyze the high temperature stability of different types of SiC fibers, this work investigated three typical SiC fibers (KD-II, KD-S, KD-SA) after being annealed at 1600 °C and 1800 °C for 1 h ∼ 200 h, respectively. For annealing at 1600 °C, the decomposition of the SiCxOy phase and grain growth were the main reasons for strength degradation in KD-II and KD-S fibers, while the KD-SA fiber maintained good thermal stability due to its large grain size. For long-time annealing at 1800 °C, obvious Si sublimation in the three fibers, leading to appearance of skin-core structure, resulted in obvious strength decline. This phenomenon was more pronounced over 1800 °C. These results in this work could be helpful guidance for the preparation of higher performance SiC fibers and SiCf/SiC composites.