Using a combination of high-resolution scanning and transmission electron microscopy, the basic mechanisms of hydrogen-induced intergranular fracture in nickel have been revisited. Focused-ion beam machining was employed to extract samples from the fracture surface to enable the examination of the microstructure immediately beneath it. Evidence for slip on multiple slip systems was evident on the fracture surface; immediately beneath it, an extensive dislocation substructure exists. These observations raise interesting questions about the role of plasticity in establishing the conditions for hydrogen-induced crack initiation and propagation along a grain boundary. The mechanisms of hydrogen embrittlement are re-examined in light of these new results.
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