Hydrogen embrittlement behavior in precipitation hardened Ni-base alloys
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2015 by Nace International. Hydrogen embrittlement (HE) of Ni-base alloys is an important concern for sour well applications and is very sensitive to microstructure of the alloys. Using tensile tests, we show that in H-charged UNS N07725 fracture is a mixture of transgranular ductile and brittle-like intergranular failure. We assess the grain boundary (GB) character using electron backscatter diffraction and perform in situ tensile testing in a scanning electron microscope, allowing for the clear identification of the microstructural features along which fracture occurs. Using this approach we confirm that the brittle-like failure is intergranular and not a direct result of slip band cracking or initiation from carbides. We also rule out the role of GB segregation in the observed HE behavior through transmission electron microscopy analysis. These results suggest that GB character may play a key role in determining susceptibility to intergranular fracture in HE. They also motivate further analysis to identify GB types that are most susceptible to intergranular failure.