水素チャージした純Niにおける塑性ひずみ発達および転位組織

抄録

Hydrogen embrittlement susceptibility of stainless steels decreases with an increase of Ni equivalent (Ni_eq), which is an index of FCC phase stability. However, when Ni_eq exceeds 50 mass%, the hydrogen embrittlement susceptibility increases. To consider this subject, we investigated effects of hydrogen on plastic strain evolution and dislocation structure in an industrial pure nickel (Ni_eq=100 mass%). Tensile tests were performed at room temperature in air after hydrogen charging with 100 MPa-high pressure gas at 250°C. We measured plastic strain distribution and grain orientation spread (GOS) using digital image correlation (DIC) and electron backscatter diffraction (EBSD), and also observed dislocation structure using electron channeling contrast imaging (ECCI). The tensile elongation of the uncharged specimen was 60%, and the fracture surface consisted of dimples. However, the elongation of the hydrogen charged specimen was 10% and the fracture surface showed an intergranular surface. The relationships of GOS – plastic strain in both specimens showed a linear correlation. Dislocation cells were recognized at 10% strain in both specimens.