Identification des relations entre microstructure et propriétés de tolérance aux dommages d’alliage de titane de type αβ

Abstract : Weight reduction are required in order to reduce ecological footprint of aeronautic transports, therefore, the current study is about interactions between microstructures and damage tolerance properties of αβ titanium alloys. Thus, a better understanding of these relationships could allow to offer potential improvement solutions of fatigue crack propagation resistance properties of these alloys through microstructure control. In this purpose, this thesis studies focus on the generation of various lamellar microstructures from initial bimodal microstructures. Damage tolerance properties of these different microstructures have then been compared by crack propagation tests, highlighting strong properties differences between bimodal and lamellar microstructures. However, the characteristic parameters of lamellar microstructures do not seem to have any influences on these properties. Furthermore, two crack propagation regime have been identified in lamellar microstructures, separated by a visible transition on the crack propagation versus stress intensity factor curves. In particular it is shown that better resistance of lamellar microstructures can be attributed to higher closure effects and crack deflections linked to crystallographic propagation, especially in the “lowspeed” regime. Further studies then aimed to link that propagation regime change to deformation mechanism at crack tips. SEM in-situ testing on micro-sample collect at crack tips on crack propagation macro-sample allows observation of differences in plasticity localization before and after transitions, which bring to the suggestion of a scenario explaining this change in regime propagation.
Keywords : TA6V ELI
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Vincent Renon. Identification des relations entre microstructure et propriétés de tolérance aux dommages d’alliage de titane de type αβ. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2019. Français. ⟨NNT : 2019ESMA0012⟩. ⟨tel-02348970⟩

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