Fatigue durability of an environmental barrier coating–coated two-dimensional woven SiC/SiC composite at elevated temperatures in a steam environment

Sustained-peak low-cycle fatigue tests in a steam environment were conducted on uncoated and environmental-barrier-coated SiC-fiber-reinforced SiC-matrix (SiC/SiC) composites at 1204 and 1315°C with an R ratio of 0.5 at maximum stresses from 69 to 138 MPa for up to 500-h run-out or failure. The composites were fabricated by the melt-infiltration process and contained Sylramic-iBN SiC fibers. The run-out specimens were tensile tested at room temperature to measure residual tensile properties. Computed tomography, microstructural analysis, and fractography of the failed specimens were conducted. Results indicate that at a constant temperature and stress, mechanical cycling causes environmental barrier coating (EBC) damage with increasing exposure time. Moreover, at a fixed exposure time and stress, damage increases with increasing temperature. Breaching of the EBC followed by moisture-assisted damage and crack growth within the SiC/SiC substrate dictates durability of EBC SiC/SiC composites. The damage and failure mechanisms of the composites are discussed.