Energy Materials 2017: Materials for Oil and Gas and AMREE Oil & Gas III: Hydrogen Effects on Materials in Energy
Sponsored by: Chinese Society for Metals
Program Organizers: Indranil Roy, Schlumberger; Chengjia Shang, University of Science and Technology Beijing

Tuesday 2:00 PM
February 28, 2017
Room: 14A
Location: San Diego Convention Ctr

Session Chair: Hani Elshahawi, Shell Exploration & Production, Co. ; Partha Ganguly, Baker Hughes

2:00 PM  Keynote
Hydrogen-assisted Failure in Ni-base Superalloy 718 Studied under In-situ Hydrogen Charging: The Role of Localized Deformation in Crack Propagation: Z. Tarzimoghadam1; Dirk Ponge1; J. Klwer2; Dierk Raabe1; 1Max-Planck-Institut fr Eisenforschung GmbH; 2VDM Metals GmbH
    We investigated hydrogen embrittlement (HE) of Ni-base superalloy 718 in different heat treatment conditions by tensile testing at slow strain rate (10-4 s-1) under continuous electrochemical hydrogen charging. Hydrogen-assisted cracking mechanisms were studied via 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 {111} slip planes. Intergranular cracking was due to grain boundary triple junction cracking, slip-localization at grain boundaries, and d/g-matrix interface cracking. Observations on the overaged state of alloy 718 with different precipitation conditions for and g phases confirmed that d-phase promotes HE by initializing micro-cracks from d/g interfaces. Moreover, hydrogen-enhanced strain-induced vacancy (HESIV) mechanism also assisted the ductile intergranular and transgranular fracture. The failure mechanism was explained based on hydrogen-enhanced formation of strain-induced vacancies and concurrent nano-void nucleation and coalescence during plastic deformation.