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

摘要

The interdiffusion behavior between an aluminum-rich β-NiAl coating and a model Ni-Cr-Al γ-Ni+γ'-Ni_3Al substrate was studied at 1150℃ for times of up to 6500 min. The resulting microstructural changes basically involved two major stages: β homogenization causing coating enlargement and then subsequent recession of the β 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 β+γ region at the coating/substrate interface. Moreover, chromium exhibited uphill diffusion in the Ni-rich β region of the coating during the early stages of homogenization. With time, the outer β-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 β to transform to γ'. 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.