Hydrogen embrittlement of iron nanowires: investigating size and orientation dependence on loading behaviour

With the ever-increasing use and applications of nanowires it has never been more imperative to understand how environmental interactions modify their unique mechanical properties and loading behaviour. While experimental research has shown that atomic hydrogen degrades mechanical properties through hydrogen embrittlement, results are limited and often do not directly quantify the hydrogen concentration or consider small diameter nanowires. In this study, we have used molecular dynamics simulations to the study the effect of atomic hydrogen on iron nanowires with various orientations and diameters. Results demonstrate that with increasing hydrogen concentration there is a clear reduction in the elastic modulus and yield stress as compared to the hydrogen free case for all diameters and orientations considered. In addition, this reduction in mechanical properties appears to exhibit a size dependence, with larger reductions being found in nanowires with larger cross-sectional diameters. We suggest that smaller diameter nanowires, with a higher ratio of surface to bulk atoms, are more influenced by free surface atoms than lattice distortions from atomic hydrogen. As this ratio of surface to bulk atoms is decreased, the larger diameter nanowires become less affected by free surfaces and more susceptible to the effect of atomic hydrogen.