Effect of oxidation treatment on KD-II SiC fiber-reinforced SiC composites

Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites have developed into a promising candidate for structural materials for high-temperature applications in aerospace engine systems. This is due to their advantageous properties, such as low density, high hardness and strength, and excellent high temperature and oxidation resistance. In this study, SiCf/SiC composites were fabricated via polymer infiltration and pyrolysis (PIP) with the lower-oxygen-content KD-II SiC fiber as the reinforcement; a mixture of 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane (V4) and liquid polycarbosilane (LPCS), known as LPVCS, was used as the precursor; while pyrolytic carbon (PyC) was used as the interface. The effects of oxidation treatment at different temperatures on morphology, structure, composition, and mechanical properties of the KD-II SiC fibers, SiC matrix from LPVCS precursor conversion, and SiCf/SiC composites were comprehensively investigated. The results revealed that the oxidation treatment greatly impacted the mechanical properties of the SiC fiber, thereby significantly influencing the mechanical properties of the SiCf/SiC composite. After oxidation at 1300 °C for 1 h, the strength retention rates of the fiber and composite were 41% and 49%, respectively. In terms of the phase structure, oxidation treatment had little effect on the SiC fiber, while greatly influencing the SiC matrix. A weak peak corresponding to silica (SiO2) appeared after high-temperature treatment of the fiber; however, oxidation treatment of the matrix led to the appearance of a very strong diffraction peak that corresponds to SiO2. The analysis of the morphology and composition indicated cracking of the fiber surface after oxidation treatment, which was increasingly obvious with the increase in the oxidation treatment temperature. The elemental composition of the fiber surface changed significantly, with drastically decreased carbon element content and sharply increased oxygen element content.