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Formation de structures de grains dans des Alliages a solidification dendritique - Modélisation couplée automates cellulaires et éléments finis

Abstract : The solidification of metallic alloys gives rise to the formation of columnar or equiaxed dendritic grain structures. A segregation of prime importance for the prediction of the material properties is associated with the spatial distribution of this structure. A mode) has been developed for the study of the influence of the formation of the grains structure on segregation. It couples a cellular automaton (CA) method with a finite element (FE) method. The CA method simulates the development of the grains while the FE method solves the conservation equations that govern the evolution of the macroscopic variables. The coupling scheme between the CA and FE methods is defined to account for the movement of the grains, the approximation of a fixed sol id being used within the FE method. The various parts of this coupling scheme have been numerically validated. We have also developed a boundary layer approach which gives us the possibility to easily calculate the dendrite tip growth velocity. The fall of NH4CI crystals agrees with the measured grain sizes and, partially, with the sedimentation velocities. The simulation of the Hebditch and Hunt experiment on the solidification of lead-tin ingots shows a destabilization at the growth front due to the transition from a constrained to an unconstrained growth regime. This leads to the formation of segregated channels. The orientation of the segregated channels is shown to depend on the crystallographic orientation of the columnar structure. For an equiaxed structure, the grain size modifies the amplitude of the mesosegregations. In this way the influence of the grains structure on the mesosegregation is modelled. The comparisons with experimental results indicate that the mode) would benefit from an extension that calculates more precisely the internai solid fraction of the grains.
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Gildas Guillemot. Formation de structures de grains dans des Alliages a solidification dendritique - Modélisation couplée automates cellulaires et éléments finis. Matériaux. Institut National Polytechnique de Lorraine, 2004. Français. ⟨tel-01445968⟩

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