Développement d'un modèle 3D Automate Cellulaire-Éléments Finis (CAFE) parallèle pour la prédiction de structures de grains lors de la solidification d'alliages métalliques

Abstract : Grain structure formation during solidification of metal parts has a big impact on the final mechanical and electronic properties. Besides determining the crystallographic texture, the nucleation and growth of grains are linked and interact with the appearance of thermodynamic phases and inhomogeneities in the alloy's chemical elements distribution. Grain structure is very rarely modeled on the macro scale, especially because the 2D approximation is often not justified. In this work, the nucleation and growth of each individual grain is tracked with the 3D CAFE macroscopic model. The internal microscopic structure is not explicitly solved. In order to validate the assumptions concerning this microstructure, a direct comparison has been done with a microscopic "phase field" model. That comparison led to the validation of some of the hypothesis on which the CAFE model is built. Moreover, the various data computed in microscopic models that can be used as input parameters of the macroscopic models have been identified, and the limits of each model clearly shown. Secondly, coupling with macrosegregation and thermodynamic databases was achieved, and applied to a binary tin-lead alloy. An experiment featuring macrosegregation induced by natural convection was modeled. The agreement between the experimental and the predicted cooling curves is within 1K, and the recalescence is found to be correctly predicted. The composition maps and the grain structure agree qualitatively with the experiment. The improvement due to structure tracking was demonstrated, regarding a standard finite elements resolution. It was also shown that the 3D simulation is mandatory to reach a good description. Finally, the model was implemented through an optimized parallel algorithm. This permitted to apply the CAFE model on an industrial scale polycrystalline silicon ingot, which dimensions are 0,192 x 0,192 x 2,08m. The cell size is chosen to be 250µm. In total, 4,9 billions of cells were represented, and the nucleation and growth of 1,6 million of grains were tracked.
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Tommy Carozzani. Développement d'un modèle 3D Automate Cellulaire-Éléments Finis (CAFE) parallèle pour la prédiction de structures de grains lors de la solidification d'alliages métalliques. Autre. Ecole Nationale Supérieure des Mines de Paris, 2012. Français. ⟨NNT : 2012ENMP0061⟩. ⟨pastel-00803282⟩

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