Construction of a ceramic coating with low residual stress on C/CA composites for thermal protection at ultra-high temperatures

Carbon fiber reinforced carbon aerogel (C/CA) composites are promising candidates for thermal protection at ultra-high temperatures. However, the poor anti-oxidative performance and difficulties in preparing a dense and crack-free coating without damaging the substrate have limited their use in oxidizing environments. Here, we have prepared a dense SiC coating on C/CA by chemical vapor deposition under the assistance of a SiC gradient layer derived from in-situ ceramization of the CA matrix. By courtesy of the gradual compaction and composition, the SiC bilayer coating with 440 μm thickness is crack-free and has low residual stress. Resultantly, the coating has a high interfacial bonding strength of 6.79 MPa due to the difficult crack initiation and propagation as well as the limited strain localization. The coated C/CA shows good ablation resistance with a linear ablation rate of 0.62 μm/s at 1900 °C for 600 s and remarkable thermal insulation with a large temperature drop of 930 °C in 10 mm thickness. The strategy of a combination of dense CVD and gradient ceramization layers can be extended to other components with excellent high temperature properties such as ZrC, HfC, which will facilitate the improvement of the ablation performance of C/CA in ultra-high temperatures.