Modeling the influence of hydrogen on Ni201 plastic behavior through integration of experimental observations and multiobjective optimization

Hydrogen is a promising alternative to traditional fossil fuels due to its abundance, high energy density, and clean energy profile. However, hydrogen can degrade the mechanical properties of materials, hindering its widespread implementation. This work develops a crystal plasticity finite element (CPFE) model to assess the influence of hydrogen on the macroscale behavior of pure nickel, Ni201. The model is based on existing mechanisms, including hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced strain-induced vacancies (HESIV), as well as the defactant theory, which attempts to explain these mechanisms within a thermodynamic framework. Monotonic tensile tests were performed at hydrogen concentrations of 0, 3000, 4000, and 5000 appm, from which yield strength, initial work hardening, and work hardening rate evolution were extracted to inform development of the crystal plasticity constitutive equations. The model parameters were calibrated using a state-of-the-art multiobjective UNSGA-III algorithm. Although the model assumes a uniform distribution of hydrogen and does not incorporate time-dependent processes such as ingress and diffusion, it captures the non-linear increasing trend of the three abovementioned metrics as a function of hydrogen concentration.