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• HfB 2 -SiC/SiC coatings with a mosaic structure was fabricated. • Oxidation at 1700 °C and cyclic ablation behaviors of the coating were investigated. • The mass loss was 1.65% after oxidation at 1700 °C for 156 h. • The linear ablation rate of the DPC HfB 2 -SiC/SiC coated specimen was 1.62 μm/s. To improve the uniformity and the content of HfB 2 in HfB 2 -Si-based ceramic coating and alleviate the damage of substrate, and then enhance the high-temperature (1700 °C) oxidation and cyclic ablation resistances of carbon/carbon composites, a close-knit double layer HfB 2 -SiC/SiC coatings with a mosaic structure and high content of HfB 2 were prepared by a novel dipping-carbonization assisted pack cementation methods (DPC HS/S). In contrast, a HfB 2 -SiC/SiC coatings were also fabricated by pack cementation (PC HS/S). Results revealed that the oxidation and ablation protective performances of the DPC HS/S coatings were superior to those of PC HS/S coatings. After 30 thermal cycles between 1500 °C and room temperature, the mass gain of the coated sample was 0.78%, and the mass loss was 1.65% after oxidation at 1700 °C for 156 h. Moreover, under an oxyacetylene torch ablation for 180 s (3 cycles), the linear ablation rate of the DPC HS/S coated specimen was 1.62 μm/s, which was much lower than that of PC HS/S coated specimen (3.08 μm/s). [ABSTRACT FROM AUTHOR]

A SiCnws/HfCSiC coating was fabricated by a two-step chemical vapor deposition. After introducing SiC nanowires, the fracture toughness of HfCSiC coating increases by 228%. After ablation under oxyacetylene torch for 60s, a bone-like HfO2reticular structure was formed in the central ablation area. Interestingly, a novel HfSiO wire-drawing phenomenon was happened in the transition area of ablated SiCnws/HfCSiC coating, providing a new toughness mechanism under ablation environment. Moreover, HfO2precipitated from HfSiO glass wires to generate nanocrystalline grains during ablation, which explains the formation of bone-like HfO2reticular structure observed from central ablation area.