Abstract
In the present work positron lifetime spectroscopy was employed for investigation of hydrogen-induced defects in Pd. Well annealed polycrystalline Pd samples were electrochemically charged with hydrogen and the development of defects with increasing hydrogen concentration was investigated.
At low concentrations (alpha-phase region, x(H) < 0.017 H/Pd) hydrogen loading introduced vacancies surrounded by hydrogen atoms and characterized by a positron lifetime of approximate to 200 ps. When the hydrogen concentration exceeded 0.017 H/Pd the alpha-phase transformed into the hydrogen rich alpha'-phase.
This generated dislocations characterized by a positron lifetime of approximate to 170 ps. Dislocations can accommodate a large volume mismatch between the alpha and the alpha'-phase.
Hardness testing revealed that absorbed hydrogen made Pd harder. In the alpha-phase region hardness increased due to solid solution hardening caused by dissolved hydrogen.
Dislocations created by the alpha to alpha'-phase transition caused strain hardening which led to an additional increase of hardness.