Here an investigation was made of how large vacancy concentrations affect intrinsic and interdiffusion coefficients, using B2-NiAl as an example and calculating all of the parameters that entered into a phenomenological description of interdiffusion from first principles, including thermodynamic factors, the effect of a concentration dependent volume, intrinsic diffusion and interdiffusion coefficients. It was found that in Al-rich alloys, characterized by high vacancy concentrations, the thermodynamic factor of Al was larger than that of Ni by several orders of magnitude, while in Ni-rich alloys, where the vacancy concentration was very low, they were identical. Similarly, the effects of changing cell volume on intrinsic diffusion coefficients were very different for Al and Ni for the alloy compositions in which the vacancy concentration was high. Comparison of calculated interdiffusion coefficients with experimentally measured values showed acceptable agreement in Ni-rich alloys but poor agreement in Al-rich alloys.

The Effect of Large Vacancy Concentration on Intrinsic and Interdiffusion Coefficients: a First-Principle Study of B2-NiAl. Q.Xu, A.Van der Ven: Acta Materialia, 2011, 59[3], 1095-104