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.