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-Ni2Al3, β-NiAl, Cr2Al, Al3 + xMo1 − x, and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the δ-Ni2Al3 to the β-NiAl because of outward Ni diffusion from substrate. The Cr2Al and the Al3 + xMo1 − 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, Ni3(Al, Ti), Cr-rich M23C6 carbide, and sigma phases.