Nickel is an important material for the development of a hydrogen society. While it exhibits excellent performance against hydrogen in alloys, the hydrogen sensitivity increases for the pure material. This study aims to elucidate the mechanism of hydrogen embrittlement in nickel by investigating changes in dislocation density induced by tensile strain. Tensile tests were conducted on flat dog-bone-shaped specimens, applying strains of 1%, 5%, 10%, 15%, 20%, 30%, 40%, and up to breaking. The central sections of these deformed specimens were analyzed using X-ray diffraction. Dislocation densities were calculated from the obtained data using the Direct-Fitting/modified Williamson-Hall (DF/mWH) method. The results revealed that the addition of hydrogen reduced the breaking strain, and the stress-strain curves indicated that specimens exposed to hydrogen exhibited higher stress at equivalent strain levels. Furthermore, longer hydrogen exposure times intensified the effects of hydrogen on the mechanical behavior, confirming the time-dependent nature of hydrogen embrittlement. Based on the calculated dislocation densities, specimens exposed to hydrogen exhibited significantly higher dislocation densities compared to the hydrogen-free counterparts. Prolonged hydrogen charging time is considered to significantly increase the rate of dislocation density, thereby contributing to the reduction in fracture strain.
HAYASHI et al. (Wed,) studied this question.