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 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 homogeneous dislocation nucleation through the reduction of dislocation line energy and stacking fault energy were proposed as the reasons. The dependence of pop-in behaviors on 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 pop-in load and nanohardness during hydrogen egress were assessed according to the different amounts of residual hydrogen in the corresponding affected zone. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.