Microstructural changes of aluminized Alloy 617 during high-temperature aging

Abstract

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 delta-Ni(2)Al(3), beta-NiA1, Cr(2)Al, Al(3+x)Mo(1-x), and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the delta-Ni(2)Al(3) to the beta-NiAl because of outward Ni diffusion from substrate. The Cr(2)Al and the Al(3+ x)Mo(1-x) were dissolved during aging. On the other hand, the alpha-(Cr, Mo) particles were precipitated during aging due to the low solubility of alloying elements in the beta-NiAl. The beta-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 beta-NiAl, Ni(3)(Al, Ti), Cr-rich M(23)C(6) carbide, and sigma phases. (C) 2011 Elsevier B.V. All rights reserved.