Dislocation relaxation peaks involving hydrogen drag in deformed Ni-H alloys

The internal friction and modulus changes in pure and hydrogenated nickel are measured after plastic deformation at frequencies of 2 Hz and 30 kHz. The hydrogen dissolution strongly diminishes a Bordoni-type peak (B peak) but develops a Snoek–Köster-type peak (SK peak) at a temperature well above the B peak. The SK peak increases in height and shifts toward higher temperature with increasing hydrogen concentration up to 1600 at. ppm. It has an effective activation enthalpy of 0.50±0.05 eV. An analysis of the concentration dependence of the peak shift suggests that this peak is caused by dislocations dragging pairs of hydrogen atoms, rather than isolated ones, segregated in the vicinity of the dislocations. A simple model is proposed which involves both dislocation pinning and impurity drag with changes in temperature. It explains well the observed correlation between the B peak and the SK peak as well as the conservation of their total relaxation strength with changes in the hydrogen concentration.