Effect of hydrogen on nanomechanical properties of Inconel 625 studied using in-situ electrochemical nanoindentation technique

In-situ electrochemical nanoindentation (ECNI) experiment is performed to probe the nanomechanical properties of Inconel 625 alloy under a hydrogen environment. The hydrogen effect on various stages of the load-displacement (LD) plot is quantified. The pop-in load, which indicates the onset of a homogenous dislocation nucleation event, is reduced with hydrogen charging, which augers well with the 'Defactant' concept. The hydrogen solute hinders dislocation glide during pop-in (reduced pop-in width), and the resultant glide resistance force is found to be linearly dependent on dissolved hydrogen concentration. We have also quantified the hydrogen-reduced activation barrier for the secondary source by examining the secondary elastic hardening stage from LD data. Hydrogen charging-induced slip line formation and nanohardness variation at different polarizations are explained using a simple diffusion-desorption model. Furthermore, the electron channeling contrast imaging technique is used to study the dislocation patterns around the indents in air and in the hydrogen environment to shed light on the difference in plastic behavior.