Micromechanical modelling of coupled crystal plasticity and hydrogen diffusion
H. u. Hassan, K. Govind, A. Hartmaier.
Hydrogen transport behaviour in metals is greatly influenced by the mechanical stress and the underlying microstructural features. In this work, a micromechanical model based on coupled crystal plasticity and hydrogen diffusion is developed and applied to model hydrogen diffusion and storage in a polycrystalline microstructure. Particular emphasis is laid on mechanical influences on hydrogen transport, invoked by internal stresses and by trapping of dislocations generated by plastic strains. First, a study of a precharged material is carried out where hydrogen is allowed to redistribute under the influence of mechanical loading. These simulations demonstrate to which extent hydrogen migrates from regions with compressive strains to those with tensile strains. In the next step, the influence of plastic prestraining on hydrogen diffusion is analysed. This prestraining produces internal residual stresses in the microstructure, that mimic residual stresses introduced into components during cold working. Lastly, a series of permeation simulations is performed to characterise the influence of hydrogen trapping on effective diffusivity. It is shown that the effective diffusivity decreases with stronger traps and the effect is more prominent at a larger predeformation, because the trapped hydrogen concentration increases considerably. The reduction of effective diffusivity with plastic deformation agrees very well with experimental findings and offers a way to validate and parameterise our model. With this work, it is demonstrated how micromechanical modelling can support the understanding of hydrogen transport on the microstructural level.
Numerical modeling of the hydrogen distribution in the microstructure under no-flux boundary condition (top image) and the influence of biaxial strain on the effective diffusivity (bottom image). Initial and boundary conditions are given on the left side and results on the right side.