Crack morphology and distribution of SiC coating on carbon/carbon composites

Due to the mismatch of the thermal expansion coefficient between the coating and carbon/carbon composites, coating cracks inevitably appeared when the coating was cooled from the production temperature to the ambient temperature. To study the coating crack configuration, single-layer and double-layer SiC coatings on carbon-felt C/C composite and intertexture C/C composite were prepared, and the crack morphology and distribution were investigated. The optical microscope and scanning electron microscope were used to discuss the crack morphology and distribution, to explain the relationship of the coating cracks with the thermal stress on the coating and substrate defects. The XRD method was conducted to analyze the ingredient of single-layer and double-layer SiC coating, to describe the relationship of different types of SiC coating structure with the coating cracks. The results showed that the crack distribution and spacing were related to the fiber direction of substrate. With the increase of coating thickness, the number of cracks decreased. The intrinsic defects on the substrate would cause through-the-thickness cracks in the coating.