Effect of temperature on static fatigue behavior of self-healing CMC in humid air

Static fatigue tests at 100 MPa with unload-reload cycles were performed at 500, 550, 650 and 800 °C in air + 10 %vol·H2O on a self-healing ceramic matrix composite (SH-CMC) with a pyrocarbon interphase. The self-healing matrix was multi-layered and deposited by chemical vapor infiltration (CVI) based on the Si-B-C system. During static fatigue tests, damage was monitored during the tests with acoustic emission (AE) and electrical resistance (ER). AE demonstrated that crack initiation primarily takes place during loading for all test conditions. Evolution of ER, strain and modulus demonstrated that failure was primarily driven by interphase degradation at constant load due to unsealed cracks at temperatures below 550 °C. In these conditions, crack sealing is prevented by boria volatilization and interphase degradation takes place due to both interphase oxidation and recession of the boron carbide phase surrounding the interphase.