The magnetic after-effect and thermal desorption methods were applied to H-charged highly-deformed samples in order to study the short-range and long-range diffusion of H at temperatures ranging from 4.2 to 500K. An H-induced magnetic after-effect relaxation maximum at 140K indicated an activation enthalpy of 0.36eV and a pre-exponential factor of 1.7 x 10-12s. This was attributed to H hopping between interstitial sites in the dislocation-free lattice of this face-centered cubic alloy. In plastically deformed samples with a high dislocation density, a low-temperature flank between 40 and 130K was also observed; yielding an activation enthalpy spectrum which extended from 0.17 to 0.32eV. This broad spectrum was attributed to H hopping at, or near to, the cores of the dislocations. An analysis of isochronal and isothermal H desorption measurements showed that H atoms with a large activation energy (low short-range mobility) dissociated from dislocations at lower temperatures than did H atoms with a high short-range mobility. A maximum enthalpy of 0.14eV was deduced for H binding to dislocations. Activation parameters of 0.44eV and 1.2 x 10-6m2/s were deduced for long-range H diffusion and desorption; thus revealing a surface barrier enthalpy of 0.08eV. On the basis of the present data, a potential model was proposed for H diffusion at, or near to, dislocations as well as in the dislocation-free bulk of Ni3Fe alloys.

E.H.Büchler, M.Hirscher, H.Kronmüller: Philosophical Magazine A, 1994, 69[6], 1039-50

Table 182

Grain-Boundary Diffusivity of 51Cr in Ni-16.49Cr-7.40Fe-0.015wt%C