Internal friction peaks in cold-worked and hydrogen-charged nickel

Internal friction measurements are made on deformed and hydrogenated Ni at frequencies of 2 Hz, 800 Hz, and 30 kHz over the temperature range between 4.2 and 373 K. Two kinds of relaxation peaks Pd and PdH accompanied by clear ΔM effects are commonly observed. Pd peak is generated at low temperature only by plastic deformation in uncharged Ni. Electrolytic charging with hydrogen suppresses this peak but instead induces PdH peak at a temperature well above Pd peak. On aging (outgassing) at temperatures between room temperature and 473 K, Pd further diminishes temporarily, but recovers to the original height thereafter; conversely, PdH first grows to a maximum height and then decays. These aging characteristics are related with nonuniform distributions of hydrogen in the samples. A good proportionality exists between the maximum height of PdH and the height of Pd before H charging. In fully annealed samples where Pd is absent, PdH is not generated evidently by H charging. From these results, it is concluded that Pd peak is ascribable to the dislocation relaxation peak of the Bordoni type, while PdH peak to the cold-work peak involves the interaction between hydrogen atoms and dislocations.