Mechanical property and hydrogen permeability of ultrafine-grained Pd–Ag alloy processed by high-pressure torsion

A process of high-pressure torsion (HPT) was used to produce an ultrafine-grained Pd–Ag alloy, and to improve mechanical property and hydrogen permeability simultaneously. Hardness values of the HPT-processed sample were much higher than those of a cold-rolled sample which is strengthened by dislocation accumulation. Additionally, in contrast to the degradation of hydrogen permeability in the cold-rolled sample due to a high density of dislocations which act as trapping sites of hydrogen atoms, the hydrogen permeability in the HPT-processed sample was improved due to a high density of high-angle grain boundaries which act as a fast diffusion path. The ultrafine-grained structure in the Pd–Ag alloy was retained during permeation testing at 300 °C due to the addition of silver.