It was pointed out that the high degree of ordering at stoichiometry suggested that the interdiffusion coefficient for this compound should exhibit a minimum at that composition. However, published data showed that the minimum interdiffusion coefficient occurred at between 48 and 49at%Al. Diffusion-couple measurements were carried out here, using single-phase NiAl wafers, at 700 to 1000C. The measured concentration profiles were analyzed in terms of the lattice mole fraction. This yielded the interdiffusion coefficients as a function of composition and temperature. It was found that, for all of the temperatures which were studied, the interdiffusion coefficients went through a minimum at the stoichiometric composition; with a corresponding maximum in the activation energies which were obtained from the temperature dependence of the interdiffusion coefficients.

An Interdiffusion Study of a NiAl Alloy using Single-Phase Diffusion Couples. S.Kim, Y.A.Chang: Metallurgical and Materials Transactions A, 2000, 31[6], 1519-24