Abstract
Hydrogen-grain-boundaries interactions and their role in intergranular fracture are well accepted as one of the key features in understanding hydrogen embrittlement in a large variety of common engineer situations. These interactions implicate some fundamental processes classified as segregation, trapping and diffusion of the solute which can be studied as a function of grain boundary configuration. In the present study, we carried out an extensive analysis of four grain-boundaries based on the complementary of atomistic calculations and experimental data. We demonstrate that elastic energy has an important contribution on the segregation energy which cannot be simply reduced to a volume change and need to consider the deviatoric part of strain. Additionally, some significant configurations of the segregation energy depend on the long-range elastic distortion and allows to rationalize the elastic contribution in three terms: hydrostatic short range elastic energy, deviatoric short range elastic energy and long-range elastic energy. By investigating the different energy barriers involved to reach all the segregation sites, the antagonist impact of grain boundaries on hydrogen diffusion and trapping process was elucidated. The segregation and migration energies are two fundamental parameters in order to classify the grain-boundaries as a trapping location or short-circuit for diffusion. The conclusions of this work were then compared to the different experimental results obtained at several scales on different configurations of pure nickel (polycrystals and bicrystals) in order to identify a relationship between this new classification of grain boundaries and the processes of intergranular fracture assisted by hydrogen.