The compositional and temperature dependences of Ni self-diffusion was investigated in single crystals which had various compositions. The radiotracer technique was applied at 1200 to 1630K, using 63Ni. At lower temperatures (1050 to 1200K), the diffusion profiles were analyzed by means of secondary ion mass spectrometry; using highly-enriched stable 64Ni. An unexpected compositional dependence was observed. The Ni diffusivity was almost the same for Al-rich and stoichiometric compositions while, on the Ni-rich side, a marked increase in diffusivity occurred with increasing Ni content. Between 1050 and 1500K, the Ni self-diffusion coefficients exhibited almost linear Arrhenius dependences. The effective activation enthalpy was found to be equal to about 3.0eV atom in Al-rich, stoichiometric and slightly Ni-rich alloys. In samples with higher Ni contents, a decrease in activation enthalpy with increasing Ni content was observed. Atomistic calculations, using empirical embedded-atom potentials, were carried out in order to explain the experimental results. A comparison of experimental data and calculated results supported the operation of the triple-defect diffusion mechanism in NiAl; although other mechanisms could also play an appreciable role.

The Ni Self-Diffusion in NiAl - an Experimental Investigation of the Temperature and Composition Dependences and Atomistic Simulation of Diffusion Mechanisms. S.V.Divinski, S.Frank, C.Herzig, U.Södervall: Solid State Phenomena, 2000, 72, 203-8