The intrinsic diffusivities of both components and the activation volume for interdiffusion in the B2 type NiAl phase were measured at 1473 to 1773K. The activation volume for interdiffusion in 40 to 49at%Al was found to be almost constant at 1.0V0 (where V0 was the molar volume of the alloy) at 1473 to 1773K; thus suggesting that divacancies contributed to the diffusion. Near to 43at%Al, the diffusion mechanism for Al atoms was most likely the triple defect mechanism, with an activation energy of 320kJ/mol, while that of Ni atoms was probably the anti-structure bridge mechanism with the smaller activation energy of 240kJ/mol. However, at 50.5at%Al, the Al atoms diffused via the nearest-neighbor mechanism with the smaller activation energy (260kJ/mol), whereas Ni

atoms probably diffused via the next-nearest neighbor jump related to the triple defect with the larger activation energy (360kJ/mol).

Diffusion Mechanisms in B2 NiAl Phase Studied by Experiments on Kirkendall Effect and Interdiffusion under High Pressures. R.Nakamura, K.Fujita, Y.Iijima, M.Okada: Acta Materialia, 2003, 51[13], 3861-70