Ablation resistance enhancement of CVD-HfC on nose-shaped C/C composites by optimizing interface layer thickness and thermal stress distribution

The SiC/HfC coatings were fabricated via low pressure chemical vapor deposition on the surface of nose-shaped C/C composites to enhance their ablation resistance in extreme environments (≥2300℃). The influence of interface layer thickness on the anti-ablation and thermal stress distribution of the nose-shaped C/C composites coated with HfC was investigated. The results demonstrated that the defects were consistently generated at the top of the nose-shaped sample during ablation owing to the stress concentration at the top of nose-shaped sample. Compared with a single HfC coating, adapting a 20 μm SiC transition layer reduced the maximum stress about 23 %, leading to a reduction of mass and linear ablation rates by 49 % and 73 %, respectively. The improved anti-ablation performance can be primarily attributed to the alleviated thermal stress on nose-shaped sample through introducing transition layer with lower thermal expansion coefficient and an intermediate thickness, which mitigated the generation of cracks and inhibited delamination of oxide layer from the nose-shaped substrate.