Molecular hydrogen H2 is an alternative energy carrier to traditional fossil fuels, gas or oil. It meet the current energy and environmental challenges, i.e. the need to store greenhouse gases free energy produced by intermittent means such as wind turbines or solar panel. Nevertheless, its safe storage and transportation is one of the keys to its use. The containers or pipes that carry the hydrogen must be leaktight and maintain their integrity over time. Understanding and predicting the behavior of hydrogen in container/pipeline alloys and the associated mechanical degradation – such as embrittlement – is therefore crucial for the development of the hydrogen industry. These issues are also generic to all alloys exposed to a source of hydrogen, in corrosion or in the metallurgical industries where the hydrogen simply comes from contact with water, or in the oil industry where hydrogen comes from hydrogen sulphides present in hydrocarbons – oil or gas.
If many experimental works have identified hydrogen embrittlement as the origin of the degradation of alloys exposed to hydrogen, large gray areas still remain on the mechanisms at work due to experimental difficulties and the great variability of the observed phenomena. In addition, the transport and trapping of hydrogen prior to mechanical degradation are poorly known and poorly documented.
The objective of the thesis is to explore the mechanisms of hydrogen trapping / transport in austenitic materials prior to cracking in order to be able to report and explain the experimental observations.
To achieve this objective, the thesis work will be dedicated to the study of pure nickel, a model system for austenitics. The study will be carried out in two stages: (i) at the atomic scale by molecular dynamics in empirical potentials to obtain detailed information on the transport and the trapping of hydrogen then (ii) at the mesoscopic scale by chemical kinetics modeling coupled with Fick's law that are modified according to the mechanisms identified in molecular dynamics.