Internal friction in nickel containing hydrogen effect of relaxation and trapping of dislocations by hydrogen

The influence of hydrogen is investigated on internal friction in nickel (α phase, no hydride). After work hardening at 77 K, and during a slow rise in temperature, an irreversible peak centred at 110 K appears on specimens treated with hydrogen, followed by a second reversible peak whose maximum is around 230 K. The former is associated with the precipitation of hydrogen towards the dislocations, the kinetics of which obey laws of the Cottrell type (t2/3). The hydrogen migration energy is abnormally low: 0.19 eV. As in the case of the alloys PdH and NbH, this anomaly might be due to a quantum effect. These results are in agreement with those obtained from mechanical tests. The second peak can be compared with a Debye peak characterising a phenomenon with a single relaxation time (U = 0.22 eV; τ = 106 s−1), which seems to be due to the movement of hydrogen atoms near the dislocations.