Mechanical Properties of Porous SiC f /SiC Composites Modified With Epoxy Resin and Pyrolytic Carbon at 300–700°C

Porous SiC f /SiC composites were modified by epoxy resin infiltration (SiC f /SiC‐EP) and phenolic resin infiltration followed by pyrolysis (SiC f /SiC‐PyC). Their physical properties, thermal degradation behavior, microstructure, and flexural performance were investigated after oxidation at 300–700°C. The untreated SiC f /SiC‐EP composite exhibited a flexural strength of 1013.07 MPa, which decreased to 657.15 MPa at 400°C and 182.23 MPa at 700°C. This deterioration was associated with epoxy degradation, increased pore connectivity, and reduced matrix continuity. In contrast, SiC f /SiC‐PyC exhibited a nonmonotonic response, with strength decreasing from 440.42 MPa to 165.90 MPa at 400°C, recovering to 395.27 MPa at 500°C, and declining to 138.55 MPa at 700°C. The temporary recovery coincided with increased fiber pull‐out and a more tortuous fracture morphology, suggesting changes in crack–interface interactions. Localized carbon oxidation and residual‐stress relaxation may contribute, although their roles remain unverified. TG–DTG analysis revealed mass losses of approximately 12% and 5% for SiC f /SiC‐EP and SiC f /SiC‐PyC composites, respectively, while XRD detected no new crystalline phases. These findings link mechanical degradation to pore and interfacial evolution.