Abstract
For H-charged, highly deformed Ni3Fe alloys the method of magnetic aftereffect (MAE) in combination with thermal desorption was applied in order to study the short- and long-range diffusion processes of H in the temperature range 4·2–500 K. The H-induced MAE relaxation maximum at T = 140K, yielding an activation enthalpy Q vol reor = 0·36 ± 0·01 eV and a preexponential factor τ0 of 1·7 × 10−12±1S, can be attributed to H hopping processes between interstitial sites in the dislocation-free lattice of the f.c.c. Ni3Fe alloy. In plastically deformed Ni3Fe with a high dislocation (⊥) density a low-temperature flank between T = 40 and 130K is additionally observed, yielding an activation enthalpy Q ⊥ reor spectrum extending from 0·17 to 0·32 eV. This broad spectrum is assigned to H hopping processes at or near the core of the dislocations. An analysis of isochronal and isothermal H desorption measurements, employing the Meechan-Brinkman evaluation method, shows that H atoms with a large Q ⊥ reor, that is, low short-range mobility, dissociate from dislocations at lower temperatures than H atoms with a high short-range mobility. A maximum binding enthalpy Q bind of 0·14 ± 0·02 eV for H to dislocations was obtained. Furthermore, the activation parameters Q vol desorp = 0·44 ± 0·02 eV and D 0 = 1·2 × 10−16±1m2s−1 for long-range hydrogen diffusion and desorption were determined, revealing a surface barrier enthalpy Qbarr of 0·08 ± 0·02 eV. Taking these data into consideration, we propose a potential model for H diffusion at or near dislocations as well as in the dislocation-free volume of f.c.c. Ni3Fe alloys.