Properties evolution and damage mechanism of SiC/SiC composites after thermal shock at 1300 °C

SiC/SiC composites in aerospace applications are exposed to a variety of thermal conditions, in particular, thermal stress due to rapid heating and cooling. Therefore, it is crucial to investigate and evaluate the resistance of SiC/SiC composites to repeated temperature cycling. This paper investigates the evolution of properties and damage mechanisms of 2D and 2.5D SiC/SiC composites after different thermal shock cycles at 1300 °C. It was found that SiC/SiC composites exhibit a temporary weight increase at the beginning of the thermal shock cycle. Subsequently, the weight decreases and stabilizes as the number of thermal shocks increases. After 10–30 thermal shocks at 1300 °C, the density of SiC/SiC composites decreases while the porosity increases. The fracture behavior of SiC/SiC composites remains the same as that of the initial composites, with 2D SiC/SiC composites exhibiting pseudo-tough fracture and 2.5D SiC/SiC composites exhibiting brittle fracture. The residual strength of the SiC/SiC composites decreased slightly while the residual modulus remained stable. This is related to the reaction of the SiC, and BN with water and oxygen at high-temperature. The thermal shock damage of SiC/SiC composites is anisotropic and is influenced by the structure of the fiber preforms. This is due to the difference in thermal expansion coefficients of the components within the composites and the structural properties of the fiber preforms.