Contribution à la conception d’alliages de nickel résistants à la fragilisation par l’hydrogène

In this thesis, strategies for mitigating hydrogen embrittlement (HE) are investigated. A first approach relies on the design of model alloys combined with experimental investigations to examine the role of γ' precipitates in hydrogen trapping, as well as their impact on HE. Two alloys with distinct γ/γ′ misfits were designed using a combination of thermodynamic calculations, regression models and a genetic algorithm. Experimental results revealed a significant delay in hydrogen diffusion in both alloys due to the presence of hydrogen traps. The alloy with low misfit showed less trapping but a more effective diffusion retardation. The second approach uses ab initio calculations to understand the influence of alloying elements on HE. These calculations focus on surface energy, the unstable stacking faults energy and the electronic density of states. Hydrogen embrittles all the alloys studied, decreasing surface energy and increasing unstable stacking fault energy. Furthermore, a correlation between the number of d-electrons in the alloying elements, the density of states at the Fermi level and susceptibility to HE was observed, providing insights for the design of hydrogen-resistant alloys.