純NiおよびNi-Fe合金の水素脆化について

抄録

In order to clarify the mechanism of hydrogen embrittlement in nickel and nickel-iron alloys, tensile tests at various temperatures and strain rates were carried out using thin specimens occluded with hydrogen in the form of solid solution and hydride.
Embrittlement occurred over the whole investigated temperature range of −196 to +100°C, revealing two maxima near −50°C and ambient temperatures. In lower testing temperatures where the hydride is stable, supersaturated hydrogen in the form of solid solution is segregated to grain boundaries or high triaxial stress fields, precipitating hydride during the tensile test. Embrittlement near −50°C decreases with the increase in iron content and strain rate, since they make hydride precipitation difficult. On the other hand, in the higher testing temperature range where the hydride is unstable, embrittlement is accelerated not only by the generation of structural damage like surface cracks caused by the decomposition of the unstable hydride but also by the segregation of the hydrogen to regions of triaxial stresses around the damage. Embrittlement of this type occurs more pronouncedly during aging at 20°C; the ductility of hydrogenated metals decreases with hydride decomposition, showing a minimum when the hydride has been decomposed completely.
Hydrogen embrittlement is considered to take place by two distinct causes; one is precipitation of brittle hydride, and the other is the clustering of hydrogen around the metallographic damage introduced by hydride decomposition.