DEN : Thesis SL-DEN-15-0368

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Research field

Solid state physics, surfaces and interfaces / Solid state physics, chemistry and nanosciences

Title

Theoretical study of the role of magnetism on properties of defects in iron based alloys

Abstract

Iron based alloys such as steels play an important role as structural materials for numerous technological applications, in particular, for the nuclear reactors. Within this frame, an accurate knowledge of properties of structural defects (e.g. vacancies and self-interstitial atoms), and their interaction with impurities and alloying elements in the steels is essential. These properties have a direct impact on the microstructural and mechanical behavior of the materials.



Up to date, extensive theoretical studies have devoted to the understanding of various properties of defects in steels, employing quantum mechanics based methods. Most of these studies are mainly focused on the energetic and kinetic features, such as the stability and mobility of structural defects and of solute atoms, as well as their nucleation properties.



However, the iron based alloys often show a complex structural-magnetic phase diagram. Many properties of these alloys, and particularly of the defects closely depend on the magnetic state of the materials. For instance, experimental data show a clear change of the diffusion coefficients of vacancies and solutes as a function of the underlying magnetic structure. Also, the magnetism strongly dictates the change of chemical short-range order as a function of Cr concentration in Fe-Cr alloys. It is therefore indispensable to better understand and quantify the magnetic effects, including the impact of the magnetic disorder induced by the temperature and the magnetic transitions. The latter features represent a significant challenge from a theoretical point of view, and are currently attracting extensive effort worldwide.



The aim of this thesis is to understand the interplay between the magnetism and defects/impurities in an iron-based allo, that is, how the presence of defects will break the local magnetic order, and how the magnetism may modify the stability, diffusion and segregation properties of point defect, defect clusters and nano-precipitates.



To this end, a theoretical approach using multiscale modeling will be developed. "Ab initio" studies based on electronic structure calculations will be performed to accurately investigate key magnetic properties. Then, effective interaction models, which are more efficient in terms of computational time, will be parameterized on the obtained DFT data. These models, coupled with Monte Carlo simulations will allow studies of magnetic-defect interplay as a function of temperature, and enables to get closer to realistic materials working conditions.

Location

Département des Matériaux pour le Nucléaire
Service de Recherches Métallurgiques Physiques
Service de Recherches de Métallurgie Physique
Centre : Saclay
Starting date : 01/10/2015

Contact person

Chu Chun FU
CEA / DEN/DMN/SRMP/SRMP
CEA/Saclay, Bat. 520, piece 116
Phone : +3 31 69 08 29 32

University / Graduate School

Paris 6 Pierre-et-Marie-Curie
Physique et Chimie des Matériaux - Paris VI -

Thesis supervisor

Cyrille BARRETEAU
CEA / DSM/IRAMIS/SPCSI/LNOSC
CEA/Saclay

F-91191, Gif-sur-Yvettes


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