Oxidation behavior of Cansas 3303 SiC fiber-reinforced composites with an interconnected SiC and dispersed Si matrix prepared by LSI process

SiC_f/SiC composites fabricated by liquid silicon infiltration (LSI) possess high strength and thermal conductivity, making them attractive for thermal-structural applications in aircraft engines. Unlike dense SiC_f/SiC with a single SiC matrix that forms a protective oxide layer, LSI-derived composites contain a multiphase SiC-Si matrix, and their oxidation response remains unclear, particularly in systems where the matrix consists of continuously formed SiC from the C-Si reaction, dispersed residual Si, and small amounts of impurities. In this study, the oxidation behavior of LSI SiC_f/SiC composites is examined in air at 1204, 1315, and 1400 °C, focusing on surface oxide evolution, internal microstructure, and residual mechanical properties. At 1204 and 1315 °C, different oxidation rates of SiC and Si generated a dense, wave-like oxide layer, with flexural strength retention above 92 % after 100 h. In contrast, at 1400 °C, severe cracking and spallation of the oxide scale lead to significant Si depletion, pore formation, and the diffusion of Si toward the BN interphase. Consequently, flexural strength retention dropped to 78 %, indicating that high-temperature degradation is dominated by oxidation-induced damage and Si-related erosion.