The compositional and temperature dependences of Ni self-diffusion were investigated, in single crystals having various compositions, by using 63Ni and radio-tracer techniques at 1200 to 1630K. At lower temperatures (1050 to 1200K), the diffusion profiles were analyzed by means of secondary ion mass spectrometry; using the highly enriched stable isotope, 64Ni. An unexpected compositional dependence of Ni self-diffusion was observed. The diffusivity was almost the same, to within experimental error, for the Al-rich and stoichiometric compositions while, on the Ni-rich side, a marked increase in Ni diffusivity was observed with increasing Ni content. From 1050 to 1500K, the Ni self-diffusion coefficient exhibited almost linear Arrhenius dependences. The effective activation enthalpy was found to be about 3.0eV in Al-rich stoichiometric or slightly Ni-rich alloys whereas, for compositions with larger Ni contents, a decrease in the activation enthalpy was observed with increasing Ni content. Atomistic calculations, using empirical embedded-atom potentials, supported the operation of a triple-defect diffusion mechanism; although it was possible that other mechanisms also made an important contribution.

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.Sodervall: Solid State Phenomena, 2000, 72, 203-7