The influence of hydrogen on the development of localized plastic deformation in internally nitrided single crystals of iron

It is well known that hydrogen can severely reduce the ductility and toughness of iron and ferrous alloys. Interface embrittlement effects, possibly through reductions in the cohesion of interfaces, and hydrogen induced microstructural damage through, for example, microvoid formation, are documented mechanisms. On the other hand, it has been reported that dissolved hydrogen affects the plastic flow process itself, through interactions with dislocations, and this appears to promote localized plastic deformation which in turn leads to fracture. The purpose of the present study was to make direct use of these background studies to learn more about the possible influences of hydrogen on the localization process. The authors' procedure was to experimentally observe the influence of hydrogen on the deformation and shear band process in ductile single crystals of internally nitrided Fe-Ti-Mn alloys. Dislocation structures involved in the localization process, along with the evolution of stress levels and strain hardening rates as shear bands formed, were documented. These crystals thus offered a good opportunity to study how hydrogen dissolved in this ferrous alloy lattice would influence the development of already well characterized dislocation structures and localization processes. The experiments carried out in the present work essentially paralleled those conducted previously, wheremore » untested crystals from the same material were hydrogen charged as described below. They were subjected to similar mechanical tests and metallographic and electron microscopy study.« less