Segregation and precipitation in iron-chromium alloys during thermal ageing and irradiation

Iron-Chromium alloys have a peculiar thermodynamic and diffusion behavior which is due to their magnetic properties. The alloy decomposition under thermal ageing has been studied in this thesis. An atomistic kinetic model has been performed in this aim in which we have modeled in details the chemical species thermodynamic and diffusion properties. In particular, the evolution of elements diffusion properties which the ferro-paramagnetic transition has been introduced in the model. Simulated decompositions have been compared with experiments for a large range of concentrations and temperatures. A good agreement between simulations and experiments was observed and these comparisons have highlighted the ferro to paramagnetic transition key role in the concentrated alloys kinetic decomposition. This study has also evidenced that the elements diffusion at phases interfaces is responsible for the alloy decomposition kinetic in long lasting.We have also started a study of the alloy radiation induced segregation. For that purpose, atomistic kinetic model has been performed modeling defects migration through a perfect planar sink. It have been shown, I agreement with former studies, that chromium tends to segregate in the vicinity of sinks at low temperatures and deplete at high temperature. (author)