The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we employ a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically-based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hydrogen effects on crack tip field behavior and enable exploration of hydrogen embrittlement mechanisms.

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Hydrogen embrittlement is a long-standing issue in engineering structural applications with a multitude of competing hypotheses and theories. Despite advances in experimental and computational capabilities, common understanding of contributing phenomena has not yet been achieved. Accordingly, models are varied and limited in scope, even for a given material system. A more complete understanding of hydrogen-related damage across multiple length and time scales is still an open challenge. In the present report, lower length scale simulations and arguments are used to motivate a mesoscale crystal plasticity model that can inform crack tip field evolution and fatigue crack growth rates. The fully coupled chemo-mechanical framework describes and simulates the complex interplay between hydrogen, hydrogen traps, vacancies, dislocations, vacancy complex stabilization by hydrogen, and damage in the form of nanovoid sheets. The model is implemented at a crack tip using a finite element framework to simulate the influence of hydrogen on deformation and fatigue damage development of face-centered cubic (FCC) austenitic stainless steel 316L (SS316L), a structural material important in energy applications. Accounting for hydrogen and hydrogen-related damage across multiple length scales in this way facilitates study of hydrogen embrittlement that can be related to experimental observations and historical attributions of hydrogen effects on deformation and damage in FCC metals and alloys.

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