Berlin 2018 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 3: Topical session (Symposium MM): Hydrogen in Materials
MM 3.2: Topical Talk
Montag, 12. März 2018, 10:45–11:15, H 0107
Hydrogen-assisted failure in Ni-based superalloy 718 studied under in situ hydrogen charging: The role of localized deformation in crack propagation — Zahra Tarzimoghadam1, •Dirk Ponge1, Jutta Klöwer2, and Dierk Raabe1 — 1Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — 2VDM Metals GmbH, Altena, Germany
We investigated hydrogen embrittlement (HE) of Ni-base superalloy 718 after different heat treatments by slow strain rate tensile testing under continuous electrochemical hydrogen charging. Hydrogen-assisted cracking mechanisms were studied by electron backscatter diffraction (EBSD) analysis and electron channeling contrast imaging (ECCI). Fracture in hydrogen-charged samples was dominated by localized deformation. Non-uniform hydrogen concentrations and plastic instabilities arise at the impingement of slip bands on grain boundaries and at intersecting slip lines. Transgranular cracking was caused by shear localization assisted by hydrogen-enhanced localized plasticity (HELP) along slip planes. Intergranular cracking was due to grain boundary triple junction cracking, slip-localization at grain boundaries, and delta/gamma interface cracking. Observations on the overaged state confirmed that the delta-phase promotes HE by initializing micro-cracks from delta/gamma interfaces. Hydrogen-enhanced strain-induced vacancy (HESIV) mechanism also assisted the ductile intergranular and transgranular fracture. The failure mechanism is explained based on hydrogen-enhanced formation of strain-induced vacancies, nano-void nucleation and coalescence during deformation.