Abstract:Determining the microstructure and elucidating the formation mechanism of aluminide coatings on Inconel 718 superalloy surfaces are crucial steps in enhancing the alloy’s resistance to high-temperature oxidation and corrosion of. In this study, aluminide coatings were deposited on Inconel 718 superalloy surfaces by chemical vapor deposition. The microstructure of the aluminide coatings was thoroughly characterized by material thermodynamics simulation software JMatPro, along with X-ray diffractometry, X-ray energy spectrometry and scanning electron microscopy. The results showed that, following a 1.5 h reaction time at 1 050 ℃, the aluminide coating exhibited a distinctive double-layered structure on the Inconel 718 surface. The outer layer consisted predominantly of the β-NiAl phase with an average thickness of 14.1 μm, while the inner layer, with an average thickness of 5.9 μm, comprised the σ phase and Laves phase. The outward diffusion of a substantial amount of Ni from the Inconel 718 superalloy to its surface led to the formation of the β-NiAl phase through a reactive process with aluminum halides in the surrounding environment. This outward diffusion resulted in a reduction of the γ-Ni phase within the superalloy . As the Ni content in the superalloy decreased to 49 at.%, the Laves phase began to precipitate in the γ-Ni phase. A further reduction to 40 at.% of Ni content initiated the precipitation of the σ phase. Ultimately, with Ni content reaching 9 at.%, the Inconel 718 superalloy underwent a complete transformation into an aluminide inner layer, comprising the σ phase and the Laves phase. These findings provide comprehensive insights into the underlying mechanisms of coating formation, offering a theoretical foundation for optimizing aluminide coating processes. Moreover, the study holds practical significance in enhancing the high-temperature stability and corrosion resistance of Inconel 718 superalloys.
