The diffusion of Pt was investigated, in compounds with compositions of 43.7 to 51.9at%Al, at 1373 to 1673K by using diffusion couple methods. The diffusion coefficients exhibited a large concentration-dependence, of valley-shape, with the diffusivity having its minimum value near to the stoichiometric composition and increasing with deviations from stoichiometry. On the other hand, the activation energy had its maximum value near to stoichiometry. The value decreased slightly with Ni content on the Ni-rich side, but decreased sharply with increasing Al content on the Al-rich side. The diffusion of Pt in NiAl occurred mainly via the triple defect mechanism at stoichiometry, via the anti-site atom-bridge mechanism in considerably non-stoichiometric Ni-rich samples and via the next-nearest neighbour jump mechanism (with constitutional Ni vacancies) in non-stoichiometric Al-rich samples.

Pt Diffusion in B2-Type Ordered NiAl Intermetallic Compound and its Diffusion Mechanisms. Y.Minamino, Y.Koizumi, N.Tsuji, M.Morioka, K.Hirao, Y.Shirai: Science and Technology of Advanced Materials, 2000, 1[4], 237-49