Effect of substrate characteristics on interdiffusion coefficients of Ni and Al atoms in β-NiAl phase of aluminide coatings

Interdiffusion coefficients at 950degreesC and 1050degreesC are calculated by Wagner analysis method as a function of composition of beta-NiAl phase. The beta-NiAl phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients in beta-NiAl phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometric beta-NiAl phase, the interdiffusion coefficients in beta-NiAl phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of beta-NiAl phase.