Microstructural effect on moisture-induced embrittlement of the Ni3(Si,Ti)-based alloys

The microstructures of Nb-added Ni3(Si,Ti) alloys with Nb-containing second-phase dispersions were characterized by an optical microscope, an X-ray diffraction and a scanning electron microscope (attached with a wavelength dispersive spectroscope). Next, the effects of Nb-containing second-phase dispersions on the moisture-induced embrittlement of Nb-added Ni3(Si,Ti) alloys were investigated at room temperature as a function of strain rate by tensile testing in air, and by fractographic observation. Finely distributed Nb-containing second-phase dispersions were shown to be effective in reducing the moisture-induced embrittlement of Ni3(Si,Ti) alloys in spite of the increased yield strength. The suppression of the moisture-induced embrittlement was associated with the transition from intergranular fracture to transgranular fracture mode. The possible mechanisms accounting for the beneficial effect of Nb-containing second-phase dispersions on the moisture-induced embrittlement of Nb-added Ni3(Si,Ti) alloys were discussed in association with dynamic interaction of hydrogen with the microstructure and chemistry of Nb-containing second-phase dispersions.