Mechanical properties and microstructure evolution of KD-SA SiC_f/BN/SiC CMCs oxidized at different temperatures

Silicon carbide fiber-reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) based on a domestic KD-SA SiC fiber were exposed to a wet oxygen atmosphere for 135 h at 800, 1100, and 1300 degrees C. The evolution of the microstructure and mechanical properties of SiCf/SiC CMCs have been systematically investigated following oxidation. For weight change, CMC-1300 showed the greatest gain (0.394%), followed by CMC-1100 (0.356%) and CMC-800 (0.149%). The volatilization of boron oxide (B2O3) combined with the slight oxidation of the SiC matrix at 800 degrees C caused crack deflection and fiber pull-out. The complete dissipation of the interphase could be found when the oxidation temperature increases to 1100 degrees C, generated a fracture surface with brittle fracture characteristics. At 1300 degrees C, crystalline SiO2 hindered oxygen diffusion, with evidence of fiber pull-out. Based on thermodynamic calculations and microscopic observations, we propose a mechanism to explain the thermal degradation of SiCf/SiC CMCs. This work offers valuable guidance for the fabrication of SiCf/SiC CMCs that are suitable for high-temperature applications.