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Modélisation des évolutions microstructurales par changement de phases dans les alliages de titane [bêta] - métastables

Abstract : A model has been developed which is able to predict the kinetics of beta alpha transformation in industrial multi component titanium alloys during complex heat treatments. The model is based on: (i) a simple geometric representations of the different morphologies commonly observed in these alloys (parent grains, allotriomorphs (at grain boundaries), colonies and intragranular precipitates); (ii) analytical nucleation and growth laws for each morphology of phase; (iii) the assumption of local equilibrium at interfaces, handled within the CalPhaD framework; (iv) averaged solute balances in each morphology. Diffusion of solutes in both phases is considered. We thus obtain the transformation kinetics as well as mean size parameters and mean chemical composition for each morphology of the product phase (at grain boundaries, colonies and intragranular precipitates. Calculations performed are at first presented for a ternary TiVO alloy emphasizing the potentialities of the model. The relationships between growth conditions, role of diffusion in each phase, and chemical composition for each morphology are analyzed upon isothermal holdings, cooling from the beta phase field and more complex cooling-heating sequence. The model is further used on the Ti17 industrial and results are compared to experimental transformation kinetics and microstructures.
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Paolo Di Napoli. Modélisation des évolutions microstructurales par changement de phases dans les alliages de titane [bêta] - métastables. Autre. Institut National Polytechnique de Lorraine, 2010. Français. ⟨NNT : 2010INPL070N⟩. ⟨tel-01749487⟩



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