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High modulus SiC fibers can be used in complex working environment with alternating heat and cold. In this paper, SiC fibers with various oxygen contents and crystal size were fabricated by polymer-derived ceramics routes. The effects of oxygen content and crystal size on the elastic modulus of SiC fibers were studied in detail. It was found that the elastic modulus of SiC fibers can be improved by reducing the oxygen content and increasing the crystal size of SiC fibers when the crystal size was less than 2 nm. When the oxygen content decreased from 21.5 wt.% to 11.7 wt.%, the elastic modulus of SiC fibers was increased from 131 GPa to 167 GPa. Particularly, the highest elastic modulus of CVC treated hypoxic SiC fibers is close to 200 GPa when the crystallite size is about 2 nm.

The near stoichiometric SiC fiber has been reported to play significant roles in the application of aeroengine field. An in‐depth understanding on the degradation mechanism of the fiber during its corrosion in air and under a simulated aeroengine environment (PH2O:PO2:PAr = 14:8:78 kPa) will shine a light on the performance evaluations of the near stoichiometric SiC fiber‐based materials as well as the development of their potential applications. In this study, X‐ray diffraction, scanning electron microscope, and FIB‐TEM were utilized to analyze the mechanical properties and microstructure of the fiber. After oxidation in dry air and Ar–H2O–O2 for 1 h, respectively, the fiber strength retention rate has been found to decrease with the increased oxidation temperature. The raise in oxidation temperature also led to the increase of the thickness and the crystallization rate of the oxide scale. The most different oxidation behaviors of SiC being treated under the simulated environment than in air are the lower oxidation activation energy and the higher crystallization activation energy for cristobalite. Water vapor can promote the oxidation reaction and inhibit the crystallization of cristobalite in the oxide scale. Few significant differences have been observed otherwise in the oxidation process and oxidation chromatography crystallization mechanism of fibers being treated under different conditions. The increase of oxide layer thickness and the formation of cristobalite impair the structural integrity and compactness of the oxide scale and thus lead to the deterioration of the mechanical properties of SiC fibers. Therefore, it is proposed that oxidation resistance of SiC fiber can be improved by insulating the reaction between the oxidizing agents and the SiC fiber or by increasing the crystallization temperature of cristobalite in the oxidation process and reducing the crystallization rate.

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