Irradiation by energetic particles affects the physical (especially mechanical and thermal) and chemical (corrosion resistance) properties of materials. To understand the changes in properties, it is necessary to observe and characterise the microstructure on different time and size scales (from the point defect of nanometric size to the newly formed grain trhough objects of intermediate size such as dislocation loops or cavities). For this purpose, various experimental characterisation techniques (microscopies, spectrometries, spectroscopies...) are available.

An alternative to the experimental methods consists in modelling the microstructural evolutions induced by irradiation by means of calculations at the atomic scale, in particular by molecular dynamics. We use an original method consisting of accumulating point defects (vacancies and interstitials) in a crystal and observing the evolution of the atomic structure under this continuous input of defects. Using this technique, we have obtained good results for the structural evolution of uranium oxide and iron (cubic centred) under irradiation. In this internship, we wish to tackle metals with a face-centred cubic structure, in particular nickel. Indeed, for this material, we have experimental characterisation of crystals irradiated with ions showing a rich and complex behaviour in terms of defect population and the latter varies in particular with the irradiation depth. We suspect that this variation is due to a change with depth in the relative amount of surviving vacancies and interstitials.

The internship will therefore involve the use of the molecular dynamics defect accumulation method on nickel. Various aspects of this method will be studied, in particular the effect of varying the relative amount of vacancies and interstitials injected into the structure. The possible effect of the presence of surfaces and the relaxation rate of atomic structures will also be discussed in order to distinguish between mechanical instabilities of the structure and its kinetic evolutions.

The analysis of these calculations is based on an observation of the structures obtained which poses subtle problems of defect detection (how many defects are there and of what nature?). We will compare classical methods of defect detection by simple criteria with advanced methods developed in the laboratory using artificial intelligence and machine learning.

This internship is conceived as a first step for a thesis that will broaden the subject by including other calculations as well as an experimental part of irradiations of nickel and alloys and associated observations (transmission electron microscopy, diffraction, etc.).

Materials science or solid state physics master.