Hydrogen suppression of dislocation cell formation in micro and nano indentation of pure iron single crystals

The influence of hydrogen on dislocation mobility in pure single crystal iron subjected to micro- and nanoindentation testing perpendicular to the (100) plane has been analysed using electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) and simulated using the self-consistent kinetic Monte-Carlo (SCkMC) method. The nanoindentation load curve for the hydrogen free sample has two major constant load pop-ins, and multiple smaller pop-ins, whereas the hydrogen charged material has only one pop-in but with a longer loading release. A well-defined cell structure was observed below the indenter in the hydrogen free condition, but the dislocations were homogenously distributed in the hydrogen charged sample. The SCkMC simulations showed that it is difficult for dislocations to glide out of the primary slip plane after hydrogen charging compared with the hydrogen free sample under the present loading conditions.