Effect of grain boundary nature and connectivity on the diffusion of hydrogen in heterogeneous materials : numerical study

Overview & Synopsis

Anticipating hydrogen embrittlement requires knowledge of the effect of different time and spatial scales within diffusion and trapping processes in the material's microstructure. In this work, we examine the impact of various types of triple junctions (TJ) and grain boundaries (GB) and their connectivity on the diffusion of hydrogen. First, we propose four algorithms to control the distribution of TJ fractions depending on a given fraction of Random grain boundaries. Then, using finite element modeling, we investigate the effects of triple junction distribution on hydrogen diffusivity. We discover remarkable relationships between grain boundary connectivity and the effective diffusion coefficient by quantifying grain boundary networks in 2D idealized microstructures. In addition, greater diffusivity is reflected in nanocrystalline materials. Our results prove to reproduce GB connectivity paths by compelling the distribution. Furthermore, 2D reconstructed EBSD microstructures were simulated and compared to experimental data. Following that, 3D simulations of idealized microstructures were performed, and the effects of triple junction connectivity were investigated. We show that there is strong correlation between the connectivity of the triple junction and the effective diffusion coefficient, particularly in nanocrystalline materials. 3D simulations approach the experimental results more accurately as the impact of the connectivity of TJs is included.