Effect of hydrogen on nanomechanical properties in Fe-22Mn-0.6C TWIP steel revealed by in-situ electrochemical nanoindentation

In-situ electrochemical nanoindentation was applied to study the effect of hydrogen on the mechanical properties of Fe-22Mn-0.6C TWIP steel at the nanoscale. Distinctive behaviors in three defined grain orientations: (001), (101), and (111) were investigated in a sequence of air, hydrogen ingress, and hydrogen egress processes. The obvious pop-in load drop caused by introducing hydrogen was analyzed using the classical dislocation theory in combination with the "Defactant" model, wherein hydrogen-enhanced homogenous dislocation nucleation through the reduction of the dislocation line energy and the stacking fault energy were proposed as the reasons. The dependence of pop-in behaviors on the crystallographic orientations was also discussed. Tabor relation-based models were applied to analyze the nanohardness increment, which was related to the hydrogen-enhanced lattice friction and the hydrogen-reduced plastic zone size. The different recovery behaviors of the pop-in load and nanohardness during hydrogen egress were assessed according to the different amounts of residual hydrogen in the corresponding affected zone.