High temperature oxidation and ablation behaviors of HfB₂-SiC/SiC coatings for carbon/carbon composites fabricated by dipping-carbonization assisted pack cementation

To improve the uniformity and the content of HfB₂ in HfB₂-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 HfB₂-SiC/SiC coatings with a mosaic structure and high content of HfB₂ were prepared by a novel dipping-carbonization assisted pack cementation methods (DPC[sbnd]HS/S). In contrast, a HfB₂-SiC/SiC coatings were also fabricated by pack cementation (PC[sbnd]HS/S). Results revealed that the oxidation and ablation protective performances of the DPC[sbnd]HS/S coatings were superior to those of PC[sbnd]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[sbnd]HS/S coated specimen was 1.62 μm/s, which was much lower than that of PC[sbnd]HS/S coated specimen (3.08 μm/s).