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Modélisation d’évolutions microstructurales dans les alliages de titane

Abstract : The present study is mainly about the calculation of β → α + β transformation kinetics and the prediction of resulting microstructures in three industrial titanium alloys Ti17, Ti6242 and Ti6246 and a ternary alloy TiMoO during isothermal heat treatments, by pursuing the development of TITAN model, developed by Di Napoli (2010). A study of the sensitivity of the model to several input parameters is first presented, distinguishing two temperature domains: the domain of morphologies at the grain boundaries αgb + αwgb , and the domain of the intragranular morphology αwi. Among these parameters: the critical thickness of appearance of awgb morphology and the spacing between the lamellae, in order to determine a dataset for the different alloys and temperatures studied; the σββ grain boundary energies, which have a significant influence on the nucleation and growth of the three α phase morphologies; the aspect ratio of the αwi spheroids, which varies according to the isothermal holding temperature; the thermodynamic parameters and diffusivities of the alloying elements, which control the thermodynamic equilibrium, and whose study allowed to highlight complex evolutions. The influence of the isothermal holding temperature and the alloy composition on phase transformation kinetics has also been addressed. These studies allowed to establish a calculated TTT of Ti17 alloy, in agreement with the experimental results.
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Sarah Tioual-Demange. Modélisation d’évolutions microstructurales dans les alliages de titane. Science des matériaux [cond-mat.mtrl-sci]. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0293⟩. ⟨tel-02559513⟩

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