Abstract
Coating performance fundamentally depends on the microstructure, which is further closely related to the diffusion behavior, especially for the diffusion coatings. Present work investigated the diffusion behavior and microstructure of the aluminide coating prepared by chemical vapor deposition (CVD) on the Inconel 718 superalloy. It was shown that the aluminide coating had a significant layered characteristic influenced by the alloy elements, where the outer layer was β-NiAl, and the beneath inter-diffusion layer consisted of TCP phases (Fe2Nb, Nb(Cr, Fe) and Cr3(Fe, Ni)2) and carbides (Nb6C5). The Y-modified coating additionally contained Y-rich phase in the outer layer, which will transform into (Y, Al)2O3 when exposed to air. Furthermore, a concentration gradient of Al in the outer layer was found, which can be associated with the outward diffusion of the alloying elements, and this phenomenon was effectively alleviated due to Y modification. The results of first-principles calculations further revealed the inhibition of Al diffusion by the substrate elements, whereas the case was opposite for Y.
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