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Traitements thermomecaniques de l'alliage de titane Ti-17. Etude expérimentale et modélisation de recristallisation de la phase Beta.

Abstract : Titanium alloys used for the manufacture of rotating parts of aircraft engines undergo complex thermomechanical processing schedules, involving usually several forging operations. The forging step in the single -phase domain plays an important role, because it governs the phase transformation that occurs during cooling or subsequent heat treatment in the two-phase α+β range, and therefore the final mechanical properties of the workpiece. Controlling the microstructural evolutions during forging in the β-domain is of prime interest to optimize the entire process of disks manufacture. A full understanding of the (continuous and geometric) dynamic recrystallization mechanisms occurring in this type of material is therefore required.In this study, the effects of temperature, strain and strain rate were investigated by hot uniaxial compression and torsion tests. The microstructures and textures were characterized using backscattering electron diffraction (EBSD). These experimental approaches were associated with the development of a physical model. In the latter, the mechanism of "continuous" dynamic recrystallization (CDRX), consisting of a progressive initial fragmentation of the grains leading to the formation of new grain boundaries, was adapted from former studies. The parameters characterizing the elementary mechanisms of CDRX (strain hardening, dynamic recovery, grain boundary migration) were determined by fitting the experimental data.The final objective of this work is to develop a metallurgical post-processor dedicated to forging operations of titanium alloys in the -phase range.
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Lois Pallot. Traitements thermomecaniques de l'alliage de titane Ti-17. Etude expérimentale et modélisation de recristallisation de la phase Beta.. Autre. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2012. Français. ⟨NNT : 2012EMSE0675⟩. ⟨tel-00849211⟩

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