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.