Hydrogen diffusion and trapping in FCC alloys: a quantitative approach based on experimental data and numerical analysis
Résumé
In the framework of hydrogen embrittlement of metals and alloys, stress corrosion cracking as well as irradiation-assisted stress corrosion cracking mechanisms, hydrogen may be the central actor enhancing decohesion and crack onset or propagation. By direct contact with H2 molecules or by water dissociation, occurring for instance during a corrosion process, some hydrogen is taken up by the alloys and diffuses into the metallic matrix in interstitial sites. Recent original experimental works on Inconel A690, based on permeation in PWR primary water conditions, show that the hydrogen source term is, even at very low corrosion rates, non-null. Some of this hydrogen can also be trapped at defects such as dislocations, precipitates, vacancies, cavities, interfaces etc. The role of this trapped hydrogen will not be discussed but in order to model the system as close as possible to reality, good understanding and characterization of hydrogen trapping parameters is necessary. Since the localization of hydrogen in the material is most probably the major parameter playing on local sensitivity of the alloy to hydrogen embrittlement, a good knowledge or simulation of hydrogen distribution, based on both microstructural characterization and trapping kinetic constants will provide a closer knowledge on potential local failures or rupture of the materials.
Based on coupling experimental works carried out on fcc model materials with modeling, I will try to show how relevant trapping parameters can be estimated and how it can feed simulations for experimental design or extended applications. Characterization of trapping at dislocations, carbides and cavities will form the main body of the presentation. Results will be discussed in terms of actual available literature data and potentialities for future works.