The Co diffusion in B2-type ordered material was investigated for 7 compositions of between 40.9 and 52.6at%Al, at 5 temperatures of between 1423 and 1623K, by using a diffusion couple method. The Co diffusion coefficients at each temperature had their minimum value at the stoichiometric composition, while their activation energies and pre-exponential factors were greatest at this composition. The activation energies decreased slowly, with Ni content, on the Ni-rich side but decreased steeply with Al content on the Al-rich side. This behavior was explained in terms of diffusion mechanisms; assuming a triple-defect mechanism at the stoichiometric composition, an antisite bridge mechanism on the Ni-rich side and a next-nearest neighbor jump mechanism with structural Ni vacancies.

Co Diffusion in a B2-Type Ordered NiAl Compound. Y.Minamino, Y.Koizumi, N.Tsuji, T.Yamada: Journal of the Japan Institute of Metals, 2002, 66[2], 67-74