The influence of testing methods and microstructure on hydrogen embrittlement susceptibility of UNS(1) N07718 was assessed through slow strain rate (SSR) experiments and rising step load (RSL) testing performed in air and in a cathodic hydrogen charging test cell. The alloy was annealed and either peak-aged or over-aged to produce different strengths and precipitation conditions. The change in ductility, strength, and threshold stress intensity factor for crack growth due to hydrogen charging are compared. Over-aging resulted in superior SSR ductility ratios and higher threshold stress intensity factors compared to peak-aging. The better performance of the over-aged condition occurred despite more δ phase present at the grain boundaries, which indicates an influence of γ’ and γ” precipitation on hydrogen embrittlement resistance. Both conditions exhibited mixtures of intergranular and transgranular fracture in the embrittled region for both the SSR and RSL tests.

Subject
Scanning electron microscopy, Cathodic polarization, Test methods, Hydrogen embrittlement, Crack growth, Notches, Fracture surfaces, Intergranular cracking, Constants, Fracture, Grain boundary, Alloys, Heat treatment
Keywords:
Precipitation hardened nickel-base alloys, Hydrogen embrittlement, Slow strain rate testing, Rising step load testing, UNS N07718
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2016
Association for Materials Protection and Performance (AMPP)
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