Influence of Grain Boundary Penetration of Oxygen on Hydrogen Embrittlement of Nickel

Abstract

In order to make clear the influence of vacuum annealing of specimens on intergranular hydrogen embrittlement of nickel, tensile properties and surface cracking along grain boundaries of specimens cathodically charged with hydrogen were examined. Specimens were annealed either in vacuum or in dry hydrogen gas before hydrogen charging. High susceptibility to intergranular hydrogen embrittlement and cracking of the surface was observed in specimens annealed in vacuum. Specimens annealed in hydrogen exhibited a significantly low susceptibility; they fractured in a predominantly transgranular mode, accompanied by a marked local contraction. The deleterious effect of vacuum annealing on the embrittlement was presumed to be due to the penetration of oxygen along grain boundaries during vacuum annealing. The penetration depth of oxygen was evaluated to exceed 2 mm in 10.8×10⁻³ s anneal at 873 K. These observations would have an important implication regarding hydrogen embrittlement of nickel and its alloys, since the effect of vacuum annealing has been disregarded in previous researches.