Effects of thermal shock on the microstructures, mechanical and thermophysical properties of SiCnws-C/C composites

In order to understand the effects of thermal shock cycles between 1100 degrees C and room temperature on SiC nanowires reinforced carbon/carbon (SiCnws-C/C) composites, their microstructure, internal friction behavior, coefficient of thermal expansion (CTE), flexural strength and fracture morphology before and after different thermal shock cycles were studied. The results show that the fiber/matrix (F/M) interface debonding and matrix cracks are the main reasons for the increase of porosity. The SiCnws-C/C composites has the largest internal friction in the whole testing frequency after 10 thermal cycles. The CTE of the composites first decreases and then increases to some extent with the increase of the thermal cycles. The flexural strength of SiCnws-C/C composites increases by 23% after 10 thermal cycles, and then reduces to 92% of the original strength after 20 thermal cycles. The increase of flexural strength and internal friction after 10 thermal cycles is associated with the appropriate F/M interface weakening and the increased d(002) values, which also results in the decrease of CTE. Compared to C/C composites, the better thermal shock resistance of SiCnws-C/C composites is attributed to the nanoscale strengthening mechanism brought by SiC nanowires, including their pull-out and bridging.