Internal friction in deformed hydrogen-doped iron

The internal friction spectrum of pure iron deformed and then charged with hydrogen presents the experimentally well established hydrogen Snoek-Köster peak together with a second peak which occurs initially at about 4 K. Like the Snoek-Köster peak, this second peak requires the presence of both, hydrogen and dislocations. It is attributed to the interaction between hydrogen and preexisting geometrical kinks on the dislocations. The absence of a hydrogen Snoek-type relaxation invalidates many of the previous determinations and estimates of the diffusion coefficient of hydrogen in iron at low temperatures. Indirect proof of the long distance migration of hydrogen is given by dislocation unpinning experiments at 4 K. The subsequent repinning occurs in several stages the first of which is at 18 K.