Effect of Al content on the structure and oxidation resistance of Y and Al modified silicide coatings prepared on Nb–Ti–Si based alloy

Several Y and Al modified silicide coatings containing different Al contents were prepared on an Nb–Ti–Si based alloy by pack cementation technique. The microstructure and oxidation resistance of these coatings were investigated. The existence of Al in the coatings was in the form of solid solutions in (Nb, X)Si2 outer layer and forming Al-rich inner layer. A suitable content of Al in the coatings improved their oxidation resistance at 1250 °C for promoting the formation of SiO2 preferentially, while an excess of Al in the coatings imposed an adverse effect for destroying the integrality of the SiO2 scale.

► Y and Al modified silicide coatings containing different Al contents were prepared.
► The microstructures of the coatings containing different Al contents were studied.
► The Al content in the coatings imposed a significant influence on their oxidation.
► The effect mechanism of Al on the oxidation of the coatings was investigated.