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Application of an overdamped Langevin dynamics to the study of microstructural evolutions in crystalline materials

Abstract : The macroscopic properties of metals and metal alloys are highly dependent on their microstructure. Numerical modeling is a very powerful instrument for understanding its evolution under given thermomechanical conditions. The need to understand the processes at the microscopic scale that drive phenomena such as crystal plasticity, recrystallization and phase transformations, led to a growing interest in atomistic modeling techniques such as Molecular Dynamics. This approach takes into account the discrete nature of matter and thus automatically incorporates all the processes acting on the atomic scale. However, it has strong limitations in terms of accessible time and space scales. In particular, the presence of high frequency vibrations (phonons) requires the use of integration time steps of the order of the femtosecond, which limits the time scale observed to a few nanoseconds. This thesis deals with the problematic of the time scale limit. In order to get rid of phonons, we propose the use of an overdamped Langevin dynamics. The first order in time nature of the equations used implies that vibrations are not explicitly represented. Their effect in the system evolution is integrated in the stochastic noise term. To our knowledge, it is the first time that the overdamped Langevin dynamics has been applied in this context. Consequently, the main objective of this thesis has been studying the potentialities of this method by applying it to two phenomena that govern the microstructural evolution in metals: the grain boundary migration and phase transformations.
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Carolina Baruffi. Application of an overdamped Langevin dynamics to the study of microstructural evolutions in crystalline materials. Chemical Physics [physics.chem-ph]. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS377⟩. ⟨tel-02866066⟩

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