Co diffusion in a B2-type ordered NiAl compound

Abstract

Co diffusion in a B2-type ordered NiAl compound was investigated at seven compositions between 40.9 at%Al and 52.6 at%Al at five temperatures from 1423 K to 1623 K, using a diffusion couple method. The Co diffusion coefficients at each temperature have a minimum value at the stoichiometric composition, while their activation energies and pre-exponential factors reveal maximum values at this composition. The activation energies decrease gently with the Ni content in the Ni-rich side, but decrease steeply with the Al content in the Al-rich side. The interpretation of this behavior is discussed in terms of the diffusion mechanisms; the triple defect mechanism at stoichiometric composition, the antisite bridge mechanism in the Ni-rich side, and the next nearest neighbor jump mechanism with the structural Ni vacancies.