The diffusivity and solubility of H in annealed or cold worked polycrystalline material were determined, at temperatures ranging from 10 to 60C, by using electrochemical permeation techniques. It was found that the diffusivity increased slightly with increasing grain size, and there was an enhanced H solubility at grain boundaries. Cold-working resulted in lower diffusivities (figures 18 and 19), caused an increase in H solubility and changed the absorption from endothermic to exothermic. This behavior was explained in terms of a H-trapping process which involved imperfections, such as dislocations, faults, lattice vacancies and sub-grain boundaries, which were introduced by cold working.

Y.Sakamoto, A.Miura: Journal of the Japan Institute of Metals , 1978, 42[4], 331-7

Figure 18

Diffusivity of H in Ni

(Cathodic current density. Circles: 10mA/cm2,

filled squares: 30mA/cm2, open squares: 50mA/cm2)

Figure 19

Diffusivity of Fe in Ni

(circles: annealed [850C, 2h], open squares: annealed [500C, 1h],

filled squares: as cold-worked)