純ニッケルおよび銅ニッケル合金の引張破壊に及ぼす内部水素の影響と温度依存性

抄録

To elucidate hydrogen embrittlement (HE) of pure Ni and Cu‒Ni alloy, slow strain rate tensile (SSRT) tests of hydrogen (H)-charged specimens were conducted at room temperature (RT) and 77 K. At RT, the tensile properties of both pure Ni and Cu‒Ni alloy were degraded, accompanied by the formation of intergranular (IG) facets (pure Ni) and flat fracture surfaces (Cu–Ni alloy), both of which are brittle fracture morphologies. Beneath the flat fracture surface of Cu–Ni alloy, numerous internal cracks were detected. The electron backscatter diffraction (EBSD) analysis revealed that these internal cracks were initiated along grain boundaries (GBs), implying that the flat fracture surface in H-charged Cu–Ni alloy originated from IG cracking, and therefore, the HE of Cu–Ni alloy was attributed to the occurrence of IG cracking as well as that of pure Ni. In contrast to the SSRT tests at RT, at 77 K, although pure Ni still showed the hydrogen-induced ductility loss with the formation of IG fracture surface, Cu–Ni alloy showed no degradation with ductile microvoid coalescence fracture even in the presence of hydrogen. This difference in HE behavior at 77 K implies that the dominating mechanism to cause the HE is not the same between pure Ni and Cu–Ni alloy.