The bulk, grain boundary and phase boundary self-diffusivities of Ni in Ni3Al-based alloys, which also contained Cr, Mo, Hf, Ta and B, were studied at temperatures ranging from 750 to 1100C. Sectioning techniques and auto-radiography were used to determine the concentration profiles. The resultant diffusion data showed that, at temperatures ranging from 750 to 950C, intercrystalline boundaries made a dominant contribution to the overall diffusion. It was found that the grain boundary diffusion coefficients were 4 to 5 orders of magnitude higher than those for bulk diffusion, while the activation energies were 25 to 30% lower. The phase boundary diffusion coefficients were 3 to 4 orders of magnitude higher than the bulk values, and the activation energies were 10% lower. An increase in the Al content resulted in a decrease of the diffusivity in both grain and phase boundaries.

B.S.Bokstein, S.Z.Bokstein, I.T.Spitsberg: Intermetallics, 1996, 4[7], 517-23