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Contribution to the development of a New Approach of Compound Energy Formalism (NACEF)

Abstract : In a current context of reducing energy consumption, it is necessary in many industrial fields to develop new materials such as multi-compound metal alloys. Their characterization in a purely experimental way quickly becomes impossible to realize, digital simulation tools become unavoidable. As such, the CALPHAD (Calculation of Phase Diagram) approach is the most appropriate numerical tool for thermodynamic processing of multi-constituent systems. This is a semi-empirical method for describing the Gibbs energies of the phases of a system by mathematical functions by adjusting certain parameters from a set of information relating to the equilibrium phase or the thermodynamic and structural properties. Based on the sublattice model, Compound Energy Formalism (CEF) is widely used in CALPHAD modeling to describe Gibbs energy of phases that have multiple sublattices. The work presented in this dissertation is a contribution to the development of a New Approach to Compound Energy Formalism (NACEF) that aims to increase its potential. In this thesis, the new NACEF approach is presented in the case of multi-subnet binary phases with anti-site defects. We applied NACEF in the modeling of 2 binary systems in order to demonstrate its potential and in particular its ability to make model simplifications compatible. This is the Fe-Nb system in which the Laves C14 phase has been described by the 3-sublattice model and the Co-Cr system where the σ phase has been modeled with 5 sublattices. In the last chapter, we propose an extrapolation method based on NACEF which allows to obtain an estimate of the energies of the ordered configurations of a multi-constituted phase from those of the binary configurations. The results obtained on many systems in the case of the C14 and σ phases indicate a strong correlation between the extrapolated values and those obtained by DFT.
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Submitted on : Saturday, October 17, 2020 - 12:42:34 PM
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Mohamad Badran. Contribution to the development of a New Approach of Compound Energy Formalism (NACEF). Material chemistry. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0109⟩. ⟨tel-02970053⟩



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