Microstructural changes of aluminized Alloy 617 during high-temperature aging

In this study, aluminized Alloy 617 was prepared by Al-pack cementation of high temperature high Al activity process. The microstructure evolution and microstructural changes of aluminide coating were investigated after Al-pack cementation and high-temperature aging. The aluminide coating was composed of Ni-aluminide layers, such as δ-Ni 2Al 3, β-NiAl, Cr 2Al, Al 3 + x Mo 1 − x , and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the δ-Ni 2Al 3 to the β-NiAl because of outward Ni diffusion from substrate. The Cr 2Al and the Al 3 + x Mo 1 − x were dissolved during aging. On the other hand, the α-(Cr, Mo) particles were precipitated during aging due to the low solubility of alloying elements in the β-NiAl. The β-NiAl newly formed by the outward Ni diffusion during aging and resulted in the formation of the inter-diffusion zone. The inter-diffusion zone consisted of β-NiAl, Ni 3(Al, Ti), Cr-rich M 23C 6 carbide, and sigma phases. ► Aluminide coating was successfully formed on Alloy 617 by Al-pack cementation. ► Microstructure evolution of aluminide coating was investigated. ► Aluminide coating was discussed about microstructure and phase changes during aging. ► Formation mechanism and phases of inter-diffusion zone were analyzed and discussed.