The diffusion and permeability of H was investigated at 150 to 400C, and 300torr. At temperatures above 200C, the diffusivity was highest in tempered martensite and lowest in ferrite. At temperatures below 200C, both the diffusivity and permeability decreased sharply in tempered martensite. A decrease in the diffusion rate, with increasing dislocation density, indicated the existence of a critical temperature at which the dislocation effect upon H mobility changed. This temperature, which corresponded to the Peierls-Nabarro critical temperature, ranged from 150 to 250C; depending upon the metal structure. At low temperatures, the activation energy was equal to 14.5kcal/mol for tempered martensite. At high temperatures, it was equal to 3.7kcal/mol. In body-centered cubic metals, H diffusion occurred via tetrahedral and octahedral voids as well as via dislocations.

N.S.Borisova, L.M.Ammosova: Fiziko-Khimicheskaya Mekhanika Materialov, 1976, 12[5], 10-4

Table 73

Effect of Pd upon H Diffusion in AISI4130