| Abstract Scope |
We used in situ tensile straining experiments to investigate the role of hydrogen (H) in crack initiation in Ni-based alloy 725. In our experiments, we varied different hydrogen charging conditions: electrochemical charging and high-temperature thermal charging. Our experiments reveal no tendency for H to enhance localized slip, and no necessity of slip for crack initiation. With electrochemical charging, cracks initiate at regions with localized slip when hydrogen content is low or more ubiquitously at higher concentrations, but mostly on the surface. Conversely, thermal charging leads to a predominance of secondary cracks in the sample interior without many surface slip traces. We ascribe these differences to the variance in internal hydrogen distribution and, possibly, to the degree of confinement on crack tip plasticity. Comprehending these mechanisms is pivotal for reliable lifetime predictions of components operating in H-rich environments, and for future development of novel, HE-resistant alloys. |