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Etude de l'effet d'une déformation plastique préalable sur les transformations de phases dans les alliages modèles : CuCr et FePd

Abstract : The application of severe plastic deformation on metal alloys usually leads to the reduction of the grain size and the formation of a high density of defects (dislocations, vacancies, grain boundaries, etc.), pushing systems far from thermodynamic equilibrium. This can affect the stability of microstructures and influence the mechanisms of phase transformations. The aim of this work is to understand the effect of prior plastic deformation on two kinds of phase transformations: precipitation and ordering. For this, two model alloys were chosen: CuCr1 and Fe50Pd50. For the CuCr1, the early stages of the Cr precipitation in Cu were first investigated in the undeformed state. Atom Probe Tomography and Transmission Electron Microscopy clearly show the coexistence of three kinds of Cr rich precipitates. Both their structure and composition were investigated in detail. The precipitation kinetic was modeled on the basis of thermodynamic arguments, taking into account the different energy terms, i.e. driving force, elastic energy and interfacial energy, which come into competition during the Cr precipitation in Cu. The large deformation (by rolling) of the CuCr1 alloy leads to an acceleration of the precipitation kinetic due to the heterogeneous nucleation of Cr precipitates on dislocations. For the Fe50Pd50 alloy, the effect of deformation by High Pressure Torsion on the ordering mechanism was investigated. Transmission Electron Microscopy observations showed that the ordering process in the ultrafine grained state is associated with the recrystallization. The ordered domains nucleate at grain boundaries and grow at the expense of non-recrystallized grains. It should be noted that, a record coercive field was obtained for this alloy in the nanostructured state.
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Submitted on : Tuesday, December 6, 2011 - 11:24:56 AM
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  • HAL Id : tel-00648671, version 1

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Abdelahad Chbihi. Etude de l'effet d'une déformation plastique préalable sur les transformations de phases dans les alliages modèles : CuCr et FePd. Science des matériaux [cond-mat.mtrl-sci]. Université de Rouen, 2011. Français. ⟨tel-00648671⟩

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