The effect of HfB2 content on the oxidation and thermal shock resistance of SiC coating

SiC coatings modified by HfB2 were synthesized by in-situ reaction at 2173-2373 K. The effect of HfB2 content on the oxidation and thermal shock resistances of the modified SiC coatings was investigated. HfSiO4, the oxidation products of HfB2 during oxidation test, dispersed uniformly in the coating and efficiently promoted crack deflection and termination. Therefore, a proper amount of HfB2 is helpful for improving the oxidation resistance of the SiC coating, while excessive quantity of HfB2 caused some defects in the coating due to its coefficient of thermal expansion (CTE) mismatches with that of the substrate. 18.2 wt% HfB2 modified SiC coating has the best oxidation resistance. Compared to the SiC coating without HfB2, the mass losses of SiC coating modified by 7.3 wt% and 18.2 wt% HfB2 decreased by 67.5% and 76.8% after oxidation, respectively. Moreover, the mass loss of the modified sample declined just by 25.2%, 25.8% after thermal cycle, respectively. But SiC coating modified by 31.5 wt% HfB2 has worse resistance behavior to oxidation and thermal shock than SiC coating.