Inconel 718の水素環境ぜい化に及ぼす炭化物の影響

抄録

Tensile properties of Inconel 718 Ni-base superalloy were investigated in high-pressure hydrogen and in argon at room temperature. The effect of Nb-Ti carbide on hydrogen environment embrittlement (HEE) of the superalloy was also examined. The results obtained are as follows:
(1) Hydrogen decreased elongation, reduction of area and ultimate tensile strength of the superalloy. HEE increased with decreasing the strain rate. Dimple rupture was mainly observed in argon, but brittle transgranular and intergranular fracture were observed in hydrogen. The crack initiation occurred at carbides both in argon and in hydrogen. Then the crack propagated in the matrix with ductile fracture in argon and with brittle fracture in hydrogen, respectively.
(2) The finite element analysis (FEA) was applied to the crack initiation of the superalloy during the monotonic tensile process with the FEA model, which contained one particle at the center surrounded by the matrix. The effect of the shape of the particle on the maximum effective stress in the particle was simulated. The maximum effective stress in the particle increased markedly with increasing the average stress above the proof stress. The increasing order of the maximum effective stress depended on the shape of the particle. It was reasonable that the maximum effective stress in the carbide is high enough to break the carbide itself. It was also expected that the control of the shape of the carbide could improve HEE of the superalloy.