1. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
2. Wuhan Material Protection Research Institute Co., Ltd., Wuhan 430030, China
The key to improve the resistance of aluminide coatings to high temperature oxidation and hot corrosion is to clarify the microstructure and formation mechanism of aluminide coatings. In this study, the aluminide coating was deposited on the surface of nickelbased superalloy Mar-M-247 by chemical vapor deposition. The microstructure and formation mechanism of aluminide coating were characterized and analyzed by using the material thermodynamics simulation software JMatPro and scanning electron microscope. The results showed that the aluminide coating on the surface of Mar-M-247 superalloy had a double layer structure, the outer layer consisted of a single β-NiAl phase, and the inner layer was mainly composed of β-NiAl phase, σ phase and μ phase. A large amount of Ni in Mar-M-247 superalloy diffused outwards to the surface of the alloy and reacted with Al in the environment to form the β-NiAl phase of outer layer of the aluminide coating. The contents of γ-Ni phase and γ-Ni3Al phase in superalloy were reduced due to the large outward diffusion of Ni element. When the volume fraction of Ni elements in the superalloy is reduced to 55%, 52% and 38%, respectively, the μ phase, β-NiAl phase and σ phase are sequentially precipitated in the superalloy. Finally, when the volume fraction of Ni in the superalloy is reduced to 32%, the superalloy is completely transformed into the inner layer of aluminide coating composed of β-NiAl, σ phase, μ phase and a small amount of carbide phase MC.