Multi-layer CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC oxidation protective coating for carbon/carbon composites

•CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC coating was prepared on C/C composite surface.•B-modified SiC prepared with 10 wt.% B has the best oxidation protection at 1173 K.•The coating can protect C/C composites for 30 h at 1173 K and 200 h at 1873 K.•The coating can endure 30 thermal cycles between 1873 K and room temperatures.

To further improve the oxidation resistance of coating for carbon/carbon (C/C) composites, a multi-layer CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC coating was prepared on the surface of C/C composites by pack cementation and chemical vapour deposition method, respectively. The microstructures, oxidation and thermal shock resistance of the coating were studied. The influence of B content in pack powder on the microstructure and oxidation resistance of B-modified SiC coating was also investigated. The results show that the B-modified SiC coating prepared with 10 wt.% B exhibited the best oxidation protection ability for C/C composites at 1173 K. The multi-layer coatings could protect the C/C composites at 1173 K for 30 h and 1873 K for 200 h, and endure 30 thermal cycles between 1873 K and room temperatures. The oxidation resistance and thermal shock resistance is mainly attributed to their dense structure and self-sealing property.