SUMMARY

The interaction of hydrogen with dislocations in steels has long been believed to be the root cause of observed environmental embrittlement phenomena. Previous approaches to explain H effects have been focused on developing mechanism based models of the interaction of H fields with dislocations, with recent consideration of vacancies. We study the underlying atomic processes governing phenomena related to proposed models in three sections. First we find the distribution of H around a dislocation and present an algorithm for the sampling of this distribution. Sampled structures are then used in atomistic calculations to study the screening potential of H fields on dislocation-dislocation interactions. Next, a model is proposed for the production of vacancies in persistent slip bands due to annihilation of edge dislocation segments. This model is implemented upscale into an existing CP UMAT. Last, the collective interaction of H, vacancies, and dislocation is studied. The formation energy of H-vacancy clusters is calculated by molecular statics and by a hybrid molecular dynamics / Monte Carlo method. The goal here is to better understand the structure and statistical distribution of clusters. This information will then be used to study the pinning strength of H-vacancy clusters and the stability of such clusters with respect to absorption by moving dislocations.