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Impact de la concentration en hydrogène sur les processus de dissolution et de passivation d’un acier inoxydable austénitique

Abstract : Different processes can lead to hydrogen absorption on the surface of the materials and can decrease their inherent materials properties, especially their surface characteristics. Interactions between these modifications and corrosion processes have to be more thoroughly studied. In this context, this work aims to investigate the role of hydrogen absorption on the dissolution and passivation mechanisms of the AISI 316L. First, the total absorbed hydrogen concentration has been quantified after an electrochemical charging process. Then, we evaluated the different hydrogen states in the material and its distribution from surface to the bulk. Results suggest a strong concentration gradient and allows to estimate both an apparent coefficient of diffusion and a local hydrogen concentration. In addition, we observed that the local hydrogen increased hardness enhanced the dislocations density and induced an occasionally phase transformation to martensite (γ→ε). In the second time, the influence of hydrogen on anodic processes on the AISI 316L have been investigated. For that purpose, electrochemical tests have been conducted and show an increase of anodic kinetics after hydrogen absorption. Hydrogen induced an increase of the passive current density while the pitting resistance is widely degraded. XPS analyses attest of a similar passive layer (thickness and composition) before and after H-charging even though EIS results show a decrease of the resistance. Inductively Coupled Plasma showed that hydrogen promotes dissolution processes. The modifications induced by hydrogen are partially reversible with hydrogen desorption. Our results illustrate that mobile hydrogen is mainly responsible for the decrease of the properties and that trapped hydrogen and / or metallurgical modifications induced by electrochemical charging have few effects on the corrosion process even they highlight the partial non-reversibility of the observed effects.
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Malo Duportal. Impact de la concentration en hydrogène sur les processus de dissolution et de passivation d’un acier inoxydable austénitique. Autre. Université de La Rochelle, 2020. Français. ⟨NNT : 2020LAROS024⟩. ⟨tel-03356122⟩

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