Slip localization and hydrogen embrittlement of alloy 718

In this study, detailed electron microscopy characterization was employed to investigate the plastic deformation behavior and related hydrogen induced embrittlement of a nickel-based superalloy UNS N07718 (Alloy 718). Transmission Electron Microscopy (TEM) analysis demonstrated that dislocations with slip systems of 〈110〉{111} operate in a localized manner during plastic deformation. Dislocation slip localization is further revealed by high resolution digital image correlation and Electron Channeling Contrast Imaging (ECCI) techniques, where planar dislocation boundary traces (DBTs) are observed. Both postmortem analysis of the hydrogen charged sample after slow strain rate (SSR) tension and in-situ SSR tension in a Scanning Electron Microscope (SEM) show that cracks tend to initiate and propagate along the DBTs, where dislocation slip localization happens. This phenomenon is rationalized by the evident nucleation of nanoscale voids along the dislocation boundaries, especially at the intersections between non-parallel dislocation boundaries. Hydrogen enhanced localized plasticity, which associates with intensive hydrogen-dislocation interaction, is suggested to be the dominant reason for the hydrogen embrittlement of Alloy 718.