INTERNAL-FRICTION IN COLD-WORKED AND HYDROGEN CHARGED NICKEL SINGLE-CRYSTALS

Internal friction measurements were performed on plastically pre-defor med ultrapure nickel single crystals. Bordoni and Niblett-Wilks relaxa tion was observed. From the activation enthalpy of the Bordoni relaxat ion, H-eff(B) (0.19 +/- 0.03) eV, the enthalpy of a single kink could be derived as H-k = 0.093 eV applying Seeger's kink-relaxation model. After the measurements under hydrogen-free conditions, the specimens w ere charged with hydrogen from gaseous phase or electrolytically. Thus , rather different hydrogen concentrations were obtained. The hydrogen loading caused an intense Snoek-Koster relaxation while the Bordoni r elaxation vanished nearly completely. The experiments indicate an infl uence of the hydrogen concentration along the dislocation lines on the activation enthalpy of the Snoek-Koster relaxation which was found as H-eff(SK) = (0.59 +/- 0.06) eV on electrolytically charged specimens.