ABSTRACT
Dislocation behavior in iron has been observed dynamically in vacuum and hydrogen gas using in situ deformation in an environmental cell of a high voltage electron microscope. The velocities of screw and edge dislocations increased with increasing hydrogen gas pressure in the environmental cell. Dislocation multiplication was also enhanced by the hydrogen atmosphere. These observations directly demonstrate that iron is softened by hydrogen. It is concluded that the main cause of the softening is the decrease of the strain field of moving dislocations and their interactions with solute atoms by the atmosphere of hydrogen which moves with the dislocations.
