Fatigue behavior of 2D C/SiC composites in water-vapor containing environment at 1300°C

Tension-tension fatigue experiments were conducted at room temperature and in water vapor containing environment at 1300°C, using a stress ratio of 0.1 at sinusoidal frequency of 3 Hz. The results show that the fatigue limit (based on 10⁵ cycles) in the above two environments are 244.8 MPa and 90.8 MPa, respectively. Oxidation is the dominant damage mechanism. Based on the microstructure observation of the fracture surfaces, it is concluded that in water-vapor containing environment at 1300°C, sufficiently high stress remarkably weakens the sealing effect of SiO₂, which enables the oxidizing species to diffuse through the coating cracks caused by the applied stress. The higher the applied stress, the higher the gaseous diffusivity, the shorter the composite fatigue life.