A ZrSi 2 -ZrC-SiC/SiC double layer coating was prepared on the surface of carbon/carbon (C/C) composites by pack cementation. The microstructure, oxidation and thermal shock resistance of the coating were studied. These results show that the outer coating is mainly composed of ZrSi 2 , ZrC, SiC and Si respectively. Oxidation tests were conducted in air at 1173 K for 100 min and 1773 K for 67 h and a weight decrease of 0?37 and 0?12% were recorded. After 20 times thermal shocks between 1773 K and room temperature, the weight of the coated specimens increased by only 0?12%. The excellent thermal shock resistance is attributed to the aptness to oxidation of the minor phases distributing in the gaps among the SiC particles and the coarseness of the coating.

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In order to improve the ablation properties of C/C composites, HfC-based coatings with different mass ratios of SiC were deposited on the surface of SiC-coated carbon/carbon composites by supersonic atmospheric plasma spraying. The morphologies and microstructures of the HfCbased coatings were characterised. The ablation resistance test was carried out by oxyacetylene torch. The results show that the as-prepared coatings are multiphase coatings consisting of HfC, HfO 2 , SiC and SiO 2 . The structure of different coatings is dense. After ablation for 60 s, the ablation centre region of coating is smooth without obvious microcrack and pinhole, and no interlaminar crack can be observed at the cross-section. An Hf-Si-O compound oxide layer is generated on the surface of coating, which is beneficial for protecting the C/C composites from being ablated. Meanwhile, the further generated HfSiO 4 can play a pinning effect, which can prevent crack extension.

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