Preparation and high-temperature properties of skin–core structure SiC ceramic fibers

A new type of skin–core structure SiC ceramic fibers was prepared from polycarbosilane by employing the curing process of alternating air and vacuum atmosphere periodically at thermal oxidation temperature. High-temperature degradation characteristics and mechanism of the skin–core structure SiC fibers were investigated at temperature from 1473 to 1773 K in air and nitrogen atmosphere, respectively. The ceramic fibers took place passive oxidation reaction in air atmosphere and underwent active oxidation in nitrogen. The main crystal phase of the high-temperature-treated ceramic fibers in air was α-cristobalite. By contrast, the α-cristobalite and β-SiC phases can be detected in nitrogen atmosphere. Compared with traditional fine diameter SiC ceramic fibers, this novel skin–core structure made the SiC ceramic fibers form thinner ring-like layer in nitrogen which was beneficial to the integrity of microstructure and retain strength. The surface defect which was formed by high-temperature exposure had significant influence on mechanical performance. The ceramic fibers lost the strength completely at 1673 K under air atmosphere, while the strength can still be maintained about 0.48 ± 0.06 GP at 1773 K in nitrogen. The skin–core structure was conducive to maintaining the high-temperature mechanical properties in oxygen-free atmosphere.