Positron-lifetime study of electrically hydrogen charged Ni, austenitic stainless steel and Fe

Positron-lifetime study has been made for the electrically hydrogen charged Ni, austenitic stainless steel (316 stainless steel), and Fe in order to investigate the structural changes due to the presence of high concentration of hydrogen atoms in the bulk, such as hydrogen-induced defects, hydrogen-induced phase transformation and so on. Increase of mean lifetime was observed for Ni and 316 stainless steel, but almost no change was observed for Fe. The introduction of a long lifetime of about 150 ps to the Ni specimen was interpreted as the generation of vacancies by the hydrogen charging. But in the case of Fe, no vacancy generation was observed probably due to the low concentration of hydrogen atoms, even by the electrical hydrogen charging. In 316 stainless steel, both the phase transformation and the generation of vacancies were observed by the presence of high concentration of hydrogen atoms in the bulk. Elastic recoil detection (ERD) method showed that the hydrogen concentration reaches about 40% (H/atom=0.4) near the surface region of 316 stainless steel, electrically hydrogen charged.