0000000000515747
AUTHOR
Nicolas Creton
A Mechano-Chemical Coupling for Hydrogen Diffusion in Metals Based on a Thermodynamic Approach
Hydrogen diffusion in metals is still an ongoing topic of research due to its technical relevance (hydrogen embrittlement, hydrogen storage...). In the last decades, significant progress in understanding the time evolution of the hydrogen concentration in solids was completed. This paper presents a modeling of hydrogen diffusion with a general and thermodynamically based diffusion concept coupled with mechanical and chemical aspects. This model was previously used to simulate the oxidation of a metal [1][2]. This concept has been upgraded to offer a thoroughly macroscopic behavior law used to simulate hydrogen diffusion in metal parts under mechanical loadings. The thermodynamic approach of…
Impact of rolling conditions on the hydriding of grade 2 titanium welded tubes
In this article, we study the impact of rolling conditions on the texture of the commercially pure titanium grade 2. In a previous work, NEOTISS in collaboration with ICB laboratory, shown that the texture highly influences the precipitation of hydrides in Titanium. In order to create different textures, Titanium sheets grade 2 are cold rolled asymmetrically and symmetrically with or without lubricant. The inverse pole figures and direct pole figures obtained allow us to deduce that symmetrical cold rolling does not change the grains orientation but generates a rotation of grains along c-axis (normal to basal plan). However, asymmetrical cold rolling leads to the formation of a new crystall…
Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids
Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The…
Influence of the U3O7 domain structure on cracking during the oxidation of UO2
Abstract Cracking is observed when a UO 2 single crystal is oxidised in air. Previous studies led to the hypothesis that cracking occurs once a critical depth of U 3 O 7 oxidised layer is reached. We present some μ-Laue X-ray diffraction results, which evidence that the U 3 O 7 layer, grown by topotaxy on UO 2 , is made of domains with different crystalline orientations. This observation was used to perform a modelling of oxidation coupling chemical and mechanical parameters, which showed that the domain patterning induces stress localisation. This result is discussed in comparison with stress localisation observed in thin layer deposited on a substrate and used to propose an interpretation…
Towards a Study of Effects on Hydrogen Diffusion into T40 Titanium Alloys
In a global study of titanium alloys behavior in specific aqueous solution (embrittlement, corrosion and corrosion under stresses), the present work focuses on hydrogen diffusion into the metal and the consequences on its microstructure. Two ways of hydrogen charging were used to investigate this issue (gaseous and cathodic charging). The final aim is to determine a fitted method to create an identified microstructure and then to perform accelerated aging tests of titanium U-Bend samples into an autoclave with a specific environment. Hydrogen absorption and formation of titanium hydride have been studied by SEM analyses and by X-ray diffraction methods.