Microstructure and grain-boundary spectrum of ultrafine-grained nickel produced by severe plastic deformation

The effect of severe plastic deformation on the evolution of the microstructure and the grain-boundary ensemble in ultrafine-grained (UFG) nickel is studied. Torsion under quasi-hydrostatic pressure can produce a uniform UFG structure such that both the microstructure and grain-boundary ensemble are statistically uniform over the whole volume of a sample. The experimental results on relaxation processes in the UFG nickel produced by both severe plastic deformation and electrodeposition are presented. The grain-growth kinetics in the UFG nickel produced by equal-channel angular pressing is studied. The grain-growth activation energy is found to coincide with the activation energy of grain-boundary self-diffusion. The experimental results on the evolution of the grain-boundary spectrum upon annealing of the UFG nickel produced by torsion are described. The activation energy and stored enthalpy for the UFG nickel are measured by differential scanning photometry.