Hydrogen diffusion in ultrafine-grained palladium: Roles of dislocations and grain boundaries

Diffusion behavior of hydrogen in ultrafine-grained palladium (Pd) is investigated by electrochemical permeation tests. The ultrafine-grained structure is produced by severe plastic deformation through high-pressure torsion (HPT). The diffusion behavior is compared with an annealed state with a coarse-grained structure and a cold-rolled state with dislocations and subgrain structures.

Hydrogen permeation is analyzed in absorption step and desorption step at five different temperatures in the range of 15–35 °C. Hydrogen diffusion is retarded due to hydrogen trapping by dislocations. Grain boundaries act as rapid diffusion paths for hydrogen so that hydrogen diffusion is enhanced in the HPT-processed Pd samples with the ultrafine-grained structures.

This article originally appeared in Acta Materialia, 107, 2016, Pages 168–177.