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PhD M/F Phase-field modelling of irradiation damaged in metallic alloys

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Français - Anglais

Date Limite Candidature : mercredi 13 juillet 2022

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General information

Reference : UMR8207-CORHEN-001
Date of publication : Wednesday, June 22, 2022
Scientific Responsible name : THUINET Ludovic
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

In nuclear power plants, alloys under irradiation are maintained in out-of-equilibrium conditions which can accelerate or even induce modifications in their microstructures. This is due to the generation in large quantity of point defects (vacancies, self-interstitials) or clusters of defects which can interact with microstructural defects (grain boundaries, dislocations, cavities, ...). In addition, these point defects can drag with them or on the contrary repel the solutes present in the alloy via flux couplings which results in chemical segregation within the material and ultimately changes their properties. In recent years, numerical simulation, notably at the atomic scale, allowed to better understand the phenomena involved in the irradiation of a material, but this type of modelling is often limited in space and time. Continuous scale models of the phase field type have therefore been developed to simulate microstructural evolutions on the grain scale, but it is only very recently that this type of approach has been applied to the prediction of irradiation damage [1]. In the UMET laboratory (Unité Matériaux et Transformations, UMR CNRS 8207), a phase-field calculation code dedicated to this type of application has been developed [2,3], in particular to predict changes in chemical composition induced by irradiation near grain boundaries or dislocations in alloys [4,5].
The present project aims to challenge the modelling and simulation of the interactions between solutes and microstructural defects in irradiated alloys via phase-field methods. One application of high technological importance is the prediction of radiation induced segregation (RIS) near microstructural defects like dislocations and grain boundaries. Indeed, despite some tremendous progress done to investigate this phenomenon so far at different length scales, numerous experimental results concerning RIS remain poorly understood. Recently, some new encouraging results have been obtained on Fe-Cr alloys using a phase-field code developed in the UMET laboratory and then we propose in this PhD to use this code to simulate RIS profiles in other model alloys in order to explain the high diversity of experimental results.

The objectives of this subject are the following:

(i) To improve some aspects of the phase field code. In particular, so far, it has been assumed that point defects are generated at a constant and uniform rate, which is quite far from actual irradiation conditions. It is therefore necessary to better describe the radiation source term in the code.

(ii) To calculate the chemical segregation of solutes near grain boundaries and dislocation loops in model materials (Fe-Cr, Ni-Cr, Ni-Fe, …) representative of the alloys used in the nuclear industry. For this purpose, a parameterization for each model alloy will have to be determined properly from atomic-scale simulations or the literature and concerns the thermodynamic parameters (activity coefficients of the atomic species, equilibrium compositions of the point defects), the elastic parameters and the kinetic parameters, related to the diffusion of the point defects and atomic species (Onsager coefficients) and to the mobility of the dislocations.

(iii) To better describe the microstructural defects. In particular, grain boundaries are often described as simple planar defects. Such a description ignores the fact that the grain boundary structure and character have an impact on the radiation induced segregation. Some attempts in the literature to refine their description exist and we will focus parts of our efforts in that direction.

Work Context

This thesis subject is funded by the NEEDS program (Nuclear, energy, environment, waste, society) of the CNRS. Its start is ideally scheduled for October 1, 2022. It will be carried out at the Materials and Transformations Unit (UMET - UMR CNRS 8207, Lille) in collaboration with EDF and the CEA.
The laboratory "Unité Matériaux Et Transformations" was created in January 2010 following the merger of four former laboratories of the Lille campus. The UMET laboratory now hosts a large portion of the research in Materials Science of the the Université de Lille. The laboratory includes approximately 80 professors and assistant professors, and CNRS researchers, 40 technical and administration staff, 60 PhD students, and 15 temporary contracts researchers or emeritus faculty.
There are six research groups:
Matériaux Moléculaires et Thérapeutiques
Earth and Planetary Materials
Métallurgie Physique et Génie des Matériaux
Polymer Systems Engineering
Interface Processes and Hygiene of Materials.
All work on materials science, but with different applications.

Additional Information

The candidate is expected to have a strong motivation to do programming and numerical simulation applied to the study of complex physical metallurgy phenomena, such as those encountered under irradiation. The candidate must therefore have solid knowledge of materials science and experience in programming and simulation.
Interested candidates are invited to send the following documents:
- CV
- Application letter with a brief description of why the candidate wants to pursue research studies and is interested by the thesis subject
- 2 recommendation letters

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