Fatigue behavior of sylramic-iBN/BN/CVI SiC ceramic matrix composite in combustion environment

Fatigue behavior of Sylramic-iBN/BN/CVI SiC CMC was investigated under tension–tension fatigue using a test facility which simulated simultaneously both loading and combustion conditions of hot-section components of gas turbine engines. Combustion environment was created using a high-velocity oxygen fuel gun to impinge combustion flame on one side of specimen subjected to fatigue to simulate the real situation. The flame-impinged surface of specimen was heated to average temperature of 1250, 1350, or 1480 °C. Ultimate tensile strength of CMC was about 270 MPa at 1480 °C under combustion environment. Fatigue life diagram was established at stress ratio of 0.1 and frequency of 1 Hz. The CMC survived up to 25 h at 46 and 33 % of ultimate tensile strength under combustion at 1250 and 1350 °C, respectively. However, it could not survive 25 h at 1480 °C under combustion fatigue environment even with no stress on the specimen due to degradation/erosion of the material. Microscopic analysis of fracture surface showed oxidation of BN interface, which was more on flame side than other side. Fracture surfaces showed oxide formation over matrix, fibers, and/or fiber/matrix interphase causing embrittlement and thereafter failure of CMC.