Abstract
The role of grain boundaries in Fe on hydrogen diffusion has been investigated by electrochemical permeation tests using ultrafine-grained Fe produced by high-pressure torsion (HPT) processing. Permeation tests were also conducted on cold-rolled and water-quenched Fe to understand the trapping effect of dislocations and vacancies. Hydrogen diffusion was delayed in all these discs. However, the delay mechanism in the HPT-processed disc was different from that in rolled and water-quenched Fe. Grain boundaries do not act as trapping sites but slow the diffusion. The diffusion coefficients of hydrogen were significantly decreased by HPT processing on account of the high activation energy for hydrogen diffusion in grain boundaries.
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