Internal friction in cold worked and hydrogen charged nickel single crystals

Internal friction measurements were performed on plastically pre-deformed ultrapure nickel single crystals. Bordoni and Niblett-Wilks relaxation was observed. From the activation enthalpy of the Bordoni relaxation, 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 were 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 relaxation vanished nearly completely. The experiments indicate an influence 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.