Abstract
To provide elements of understanding of the hydrogen embrittlement of the nickel and its alloys, it is important to study the impact of the various metallurgical heterogeneities (grain boundaries, dislocations, precipitates, vacancies, etc.) on the mechanisms of hydrogen diffusion and trapping. Furthermore, it is also necessary to question the implications and consequences of the interactions between these heterogeneities and hydrogen, especially on the mechanical behaviours at different scales and hence the mechanisms of damage induced by hydrogen.
For this purpose, we have carried out several studies on pure nickel and nickel-based alloys presenting different metallurgical states (single crystals, bi-crystals, polycrystals, precipitates, etc.). Many experimental approaches (permeation, TDS, GD-OES, SKPFM, Tof-SIMS, etc.) have been performed with and without mechanical couplings. The numerous experimental results were confronted with the multiscale modelling approaches, ranging from the atomic scale (ab initio (DFT), empirical potential) to the mesoscale (finite elements method, etc.).
Among the remarkable outcomes and depending on the metallurgical state, we have identified an outstanding role of hydrogen mobility and reversible trapping on plasticity (hardening and softening), damage mechanisms, and crack initiation and propagation in hydrogenated environments. We singled out the implication of the hydrogen-vacancy interactions in the modification of the elastic properties. Also, we fathomed the role of the grain boundary character on the diffusion and trapping of hydrogen as well as on the mechanisms of fracture assisted by hydrogen.