Abstract
Hydrogen embrittlement is a critical concern in precipitation-hardened nickel-based alloys and is typically evaluated using slow strain rate tensile (SSRT) tests, as outlined in NACE TM0198 Appendix C. This study investigated the influence of counter electrode (CE) characteristics on hydrogen charging behavior under these conditions. The evaluated CEs included platinum and two types of mixed metal oxide-coated titanium (MMO-Ti), each tested at low and high CE-to-WE area ratios (AR). Alloy 718 specimens were hydrogen-charged via cathodic polarization at −5 mA·cm-² in a 0.5 mol·L-1 H2SO4 solution at 40 °C, deaerated with nitrogen. Hydrogen uptake was quantified by thermal desorption analysis (TDA), while CE degradation was assessed by ICP-MS. XPS was used to detect redeposition of CE elements on the specimen surface. Although none of the evaluated CEs behaved as fully inert under the test conditions, their electrochemical stability varied significantly. Platinum showed clear signs of dissolution and redeposition, whereas MMO-Ti plates exhibited lower degradation and no evidence of species transfer to the working electrode. Hydrogen uptake was significantly affected by the CE material: specimens charged with MMO-Ti CEs absorbed up to seven times more hydrogen than those charged with platinum. These findings underscore the need for stricter specification of CE configurations in hydrogen charging protocols, not only for SSRT but also for other long-duration mechanical testing methodologies.