INTERDIFFUSION BEHAVIOR IN AN ALUMINIDE COATED NICKEL-BASE ALLOY AT 1150 deg C

摘要

The interdiffusion behavior between an aluminum-rich beta-NiAl coating and a model Ni-Cr-Al gamma-Ni + gamma ft-Ni_3Al substrate was studied at 1150 deg C for times of up to 6500 min. The resulting microstructural changes basically involved two major stages: beta homogenization causing coating enlargement and then subsequent recession of the beta layer. In the early stages of homogenization, the inward diffusion of chromium from the interdiffusion zone into the substrate and the outward diffusion of nickel from the substrate into the coating induced the formation of a beta+gamma region at the coating/substrate interface. Moreover, chromium exhibited uphill diffusion in the Ni-rich beta region of the coating during the early stages of homogenization. With time, the outer beta-layer completely homogenized, and the influence of chromium diffusion decreased whilst the outward diffusion of nickel and inward diffusion of aluminum became predominant. Further depletion of chromium and aluminum, coupled with nickel enrichment, caused the beta to transform to gamma ft. The compositions within the interdiffusion zone changed with time but were in accordance with the equilibrium Ni-Cr-Al phase diagram. Interpretation of the complex interdiffusion behavior was aided by the application of diffusion paths.