Effect of Y2O3 content in the pack mixtures on microstructure and oxidation resistance of B–Y modified silicide coating

B–Y modified silicide coatings were prepared on Nb–Si based alloy by pack cementation at 1300 ℃ for 10 h. The effect of Y2O3 content in the pack mixtures on microstructure and oxidation resistance of the coatings was investigated. The results show that the four coatings have similar structures, which possess a (Nb,X)Si2 outer layer and a (Nb,X)5Si3 transitional layer. Y2O3 content in the pack mixtures has an obvious effect on the Si content in the coating. The mass gains of the coatings prepared with 0.5, 1, 2 and 3 wt% Y2O3 in pack mixtures are 2.33, 1.96, 2.05 and 2.86 mg/cm2 after oxidation at 1250 ℃ for 100 h, respectively. The coating prepared with 1 wt% Y2O3 exhibits the best oxidation resistance due to the formation of a dense glass-like borosilicate scale.