Effects of PyC shell thickness on the microstructure, ablation resistance of SiCnws/PyC-C/C-ZrC-SiC composites

SiC nanowires/pyrocarbon (SiCnws/PyC) core-shell structure toughened C/C-ZrC-SiC composites were fabricated by CLVD process, and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched. The results presented that SiCnws/PyC core-shell structure had a linear shape, and the composites became dense with the increasing PyC thickness. When the thickness of PyC shell increased from 0 to 2.4 μm, the density and thermal conductivity of the composites was improved gradually, but the coefficient of thermal expansion (CTE) decreased firstly and then increased. After the ablation test for 90 s, the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4 μm, but increased when the PyC thickness was up to 2.4 μm. Especially when the PyC thickness was 1.4 μm, the linear and mass ablation rates of the composites were 71.25 % and 63.01 % lower than those of the composites without PyC shell. The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating, improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.