Antagonist softening and hardening effects of hydrogen investigated using nanoindentation on cyclically pre-strained nickel single crystal

Distinct Evidence of Hydrogen-Enhanced Defect Formation on Pre-Strained Nickel Alloy 625 during In Situ Electrochemical Nanoindentation Test

“…Thus, for 5% pre-strained material, either the probed area is defect-free or, due to very high localized stress generated under the indenter, the defect strength is nullified. Similar findings have been reported for cyclically pre-strained pure nickel with a dislocation density comparable to our measured value [6,15]. On the other hand, the 20% pre-strain sample exhibits an increased hardness value (11% larger) when compared to the undeformed sample.…”

“…H-induced resistance to dislocation motion, and the interpretation of the solid solution hardening mechanism with hydrogen, is considered as an alloying element and was also reported by Ogawa et al [28]. Similar results were reported during in situ testing of the cyclically pre-strained pure nickel [15] and in the discrete dislocation dynamics computer simulation [29]. When the potential is changed to anodic, the hardness of the undeformed sample has not completely recovered to the same level as that in air (6% increase).…”

“…H-induced hardening can be further explained in such a way that the H solute accumulates around the edge components of a dislocation loop or dipole and can exert a pinning effect which resembles a Cottrell atmosphere. An increase in the constraint to dislocation motion is the result of the pinning effect [13,15,27]. H-induced resistance to dislocation motion, and the interpretation of the solid solution hardening mechanism with hydrogen, is considered as an alloying element and was also reported by Ogawa et al [28].…”

“…While considerable research in nanoindentation has focused on assessing the hydrogeninduced changes in nanomechanical properties of well-annealed ductile materials [12][13][14], information regarding the hydrogen effect on pre-strained materials is still scarce [6,15,16]. In this work, we have designed an experiment that captures the hydrogen effect on the material response after two hours of cathodic charging, while the nanomechanical properties obtained after one hour of anodic discharging provide insights into the aftereffects of hydrogen-affected microstructure changes.…”

An In-Situ Electrochemical Nanoindentation (ECNI) Study on the Effect of Hydrogen on the Mechanical Properties of 316L Austenitic Stainless Steel

“…In addition, the electrolyte used was an aqueous electrolyte with very low viscosity, which promotes a fast track for hydrogen bubbles to escape the solution. This can possibly result in very different hydrogen concentration and diffusion in the material compared to other works and the HELP-related softening mechanisms [62]. Though the lattice friction has been enhanced by the introduction of hydrogen, this was modeled only until the onset of plastic deformation, where the massive dislocation motion and the associated dislocation-hydrogen interaction during motion was less pronounced.…”