Relationship of defects and mechanical performance of high‐crystalline SiC fibers after ultra‐high‐temperature annealing

Abstract Silicon carbide (SiC) fibers are widely utilized as critical reinforcements in high‐temperature structural composites; however, the relationship between microscopic defects and mechanical performance after ultra‐high‐temperature annealing remains a mystery. In this work, the near‐stoichiometric high‐crystalline SiC fiber (named as F‐III) were subjected to various annealing conditions to clarify the relationship. The F‐III fiber exhibits excellent thermal stability, with the tensile strength retention of 107.8% and 97.2% after annealing at 1800°C for 50 h and 1900°C for 1 h, respectively, under Ar atmosphere of atmospheric pressure. High‐pressure annealing can prevent the formation of graphite shell and decrease the pores/free carbon size to enhance the operating temperature of SiC fibers, resulting in the tensile strength retention as high as 105.6 % after annealing at 2000°C for 5 h. Interestingly, the transgranular fracture mode of SiC fibers is caused by the presence of randomly distributed pores, approximately 2–4 nm in size, within the β‐SiC grains. The tensile strength of SiC fibers is primarily governed by the thickness of graphite shell and the core pores/free carbon size, with the former having a more significant influence. These findings are helpful to provide a theoretical foundation for developing ultra‐high‐temperature‐resistant SiC fibers.