Microstructure evolution and oxidation mechanism of HfB2-SiC coating on SiC-coated C/C composites at 1173 K and 1773 K

Abstract

HfB2-SiC coatings with 30–60 wt% HfB2 additions were prepared by slurry-dipping on SiC-coated C/C composites for investigating their oxidation behavior at low (1173 K) and high (1773 K) temperatures. With the increase of HfB2 content, more B2O3 glass was produced in the coating and the coating became denser during oxidation at 1173 K. 50 wt% HfB2-SiC coating can protect C/C composites for 494 h against oxidation, which was attributed to the formation of the dense borosilicate glass with high thermal stability as an oxygen barrier layer. After oxidation at 1773 K, 30 wt% HfB2-SiC coating provided the longest protection time (460 h) for C/C composites among 30–60 wt% HfB2-SiC coatings. A few Hf-oxides inhibited the volatilization of SiO2 glass as the main phase in the 30 wt% HfB2-SiC coating after oxidation. As for other coatings with higher content of HfB2, the violent oxidation of HfB2 particles made more bubbles produced, resulting in the poor oxidation resistance at 1773 K.