Effect of Hydrogen on Creep in High-Purity Ni-16Cr-9Fe Alloys at 360°C

Environmentally assisted cracking involves synergistic interactions between corrosion and deformation processes. This study focused on providing insight into the influence of the environment on the time-dependent deformation behavior of an ultra-high-purity Ni-16Cr-9Fe alloy in argon, dissociated hydrogen, and water environments at 360°C. Results from experiments conducted in dissociated hydrogen or primary water showed more enhancements in both primary and secondary creep than those conducted in argon. Experiments begun in argon gas exhibited positive strain transients when dissociated hydrogen gas was introduced during steady-state creep. These results indicate a strong effect of hydrogen on the primary and transient creep behavior of this alloy at 360°C. This environmentally enhanced creep behavior is attributed to a mechanism involving dislocation contraction based on the hydrogen-enhanced localized plasticity model. This reasoning is supported by detailed experiments that revealed lower internal stresses and activation areas in primary water than in argon. Changes in the primary creep behavior attributable to hydrogen are consistent with a change in the work-hardening behavior. An increase in the steady-state creep rate is likely attributable to a combination of mechanisms that involve hydrogen.