Environmentally Assisted Cracking: Theory and Practice: Hydrogen Embrittlement
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University

Tuesday 8:30 AM
March 16, 2021
Room: RM 18
Location: TMS2021 Virtual

Session Chair: Ian Robertson , University of Wisconsin-Madison; Reiner Kirchheim, Georg-August-Universität Göttingen


8:30 AM  Invited
Hydrogen Embrittlement – A Retrospective Opinion: Ian Robertson1; 1University of Wisconsin-Madison
    The phenomenon of hydrogen embrittlement of metals has been known since the late 1800s and has been shown to occur in all but a few pure metals and their alloys. What remains in debate is the fundamental mechanism of hydrogen embrittlement with hydride-forming metals being one exception. Is the embrittlement due to hydrogen reducing the strength of metallic bonds, lowering the formation energy of defects, shielding the elastic interaction between defects, enhancing the formation of strain induced vacancies, inducing the formation of nano-hydrides at crack tips, etc? This talk will provide a critical assessment of the evidence supporting and detracting from each mechanism and will conclude with an opinion about future directions and opportunities aimed at identifying the mechanism of hydrogen embrittlement.

9:15 AM  
Discrepancy Between Hydrogen-modified Dislocation Structures in the Surface and Interior Grain: Shuai Wang1; Qingqing Sun1; 1Southern University of Science and Technology
    The study focuses on the dislocation structure evolution in surface and interior grain of pure Ni in the absence and presence of hydrogen. By combining EBSD and FIB lift-out techniques, electron-transparent foil at orientation of interest was obtained. The dislocation structure was observed at diffraction-contrast imaging condition in STEM. Diverged from the well-established dislocation pattern evolution theory, in the presence of hydrogen, the predominant dislocation structure type in surface grain was found to be always dislocation cell, which was independent of orientation. At the same strain level, the observations also indicated hydrogen has no significant effect on the size of surface dislocation cell. However, in the interior grain, hydrogen-accelerated evolution of the dislocation structure was evident. The results are attributed to different evolution process for dislocation structure in the surface and interior grains, and the hydrogen effect on surface and interior of material are discussed based on dislocation-hydrogen interaction theory.

9:35 AM  
Macroscale-based Approaches for Assessing the Influence of Hydrogen on the Deformation Behavior of Polycrystalline Ni: Zachary Harris1; Sean Agnew1; James Burns1; 1University of Virginia
    Our study seeks to leverage macroscale-based, but microstructurally-sensitive approaches to probe the influence of hydrogen on the deformation behavior of Ni-based alloys. Uniaxial tension experiments on Ni-201 charged to hydrogen contents ranging from 0 to 5000 appm are coupled with crystal plasticity simulations to specifically evaluate the effect of hydrogen on texture evolution and work hardening behavior. Results indicate that, for the strains of interest for hydrogen-assisted cracking (< 0.15), texture-based approaches are insensitive to anticipated hydrogen-induced modifications in deformation behavior. Conversely, the work hardening behavior of Ni-201 is found to be sensitive to hydrogen content, indicating that such frameworks may be useful for developing mechanistic understanding. In particular, both the dislocation storage and recovery rates are found to increase with hydrogen content, with the latter increasing strongly for concentrations greater than 4000 appm. These observations are then considered in the light of previously proposed mechanisms for hydrogen embrittlement.

9:55 AM  
Assessing the Susceptibility of Existing Pipelines to Hydrogen Embrittlement: Tim Boot1; Ton Riemslag1; Elise Reinton1; Carey Walters1; Ping Liu2; Vera Popovich1; 1TU Delft; 2INTECSEA BV
    With fossil fuels being phased out and growing global interest in a hydrogen economy, there is demand for re-purposing existing pipelines for transportation of hydrogen gas. In this study, in-situ Slow Strain Rate Tensile (SSRT) tests were performed in nitrogen and in hydrogen environments at varying pressures (0 - 100 bar) to evaluate hydrogen’s effects on the mechanical properties of an X60 base metal (polygonal ferrite/pearlite) and its girth weld (acicular ferrite/pearlite). A novel type of hollow tensile sample was designed that acts as a pipe and can be loaded with high pressure gas internally. A substantial decrease in ductility and toughness was identified for both base and weld metals even at low hydrogen pressures. Fracture surfaces were observed using SEM, showing micro-void coalescence as well as quasi-cleavage fracture characteristic of hydrogen embrittlement (HE). Susceptibility to HE was also observed in the form of secondary longitudinal and internal transverse cracks.