Grain boundary self-diffusion in polycrystalline nickel of different purity levels

Grain boundary self-diffusion in Ni materials of two different purity levels (99.6 and 99.999 wt.%) was measured over wide temperature intervals using the radiotracer technique and applying the Ni-63 radioisotope. The diffusion experiments were performed in both Harrison's type B and type C kinetic regimes. The diffusional grain boundary width, delta, was found to be equal to 0.54 +/- 0.1 nm, that is reasonably close to the accepted value of delta = 0.5 nm in face-centred cubic metals. The purer the material, the higher the grain boundary diffusivity and the lower the corresponding activation enthalpy of self-diffusion along general high-angle grain boundaries. Using the semi-empirical approach of Borisov et al., the average energy of high-angle grain boundaries was estimated to be about 0.79 and 0.98 J m(-2) in the low- and high-purity Ni materials at room temperature, respectively. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.