Relation procédé-microstructure-propriétés de tubes sans soudure de Ti–3Al–2,5V laminés à pas de pèlerin

Abstract : Cold pilgered Ti-3Al-2.5V alloy tubes are used in a stress relieved condition in commercial and military aircraft since the late 20th century. Despite the extensive use of these tubes, some aspects of the relations between processing and properties are still misunderstood, restricting the possibilities for the development of new products. The key properties are the tensile yield stress and elongation, the Contractile Strain Ratio (CSR) and the fatigue resistance. While early studies have shown how the pilgering process impacts texture and some of the effects of texture on these properties, public literature dismisses the effects of recovery and recrystallization, which both occur during the various annealing treatments of the transformation schedule. To fill this gap, this work focuses on the fine characterization of the local microstructures and textures of tubes produced in industrial trials. EBSD maps presented in this work show that the stress relieving treatment produces discontinuous recrystallization with variable local kinetics depending on the heterogeneity of the deformed condition, which is caused by the high anisotropy of the hexagonal alpha phase. The recrystallized fraction Rx is shown to influence the tensile deformation behavior, as anomalous yield point phenomena are more pronounced when Rx increases. Under the studied conditions, strong recrystallization is shown to produce fine equiaxe grains and a weak texture although without significant modification of the deformation texture components. This result suggests that grain growth is inhibited by the beta phase present in the microstructure. This work also analyses the influence of the sequences of deformation and recrystallization on the final texture and microstructure. It was confirmed that texture can be modified by the ratio of thickness to diameter reduction and that texture determines the CSR. The latter result is well reproduced in crystal plasticity simulations. The microstructural analysis of a wide range of tube dimensions suggested that the sizes of recrystallized grains in the final microstructures can be tailored through the choice of the overall strain path. Finally, the fatigue behavior of tubes with similar microstructure and different texture were studied under internal pulsed pressure tests. The results suggest that tangentially textured tubes are more tolerant to surface damages and crack propagation at high and medium stress amplitudes. The radial textures, however, improve the endurance limit under the conditions of these trials
Document type :
Theses
File URL :
http://docnum.univ-lorraine.fr/prive/DDOC_T_2012_0423_BAYONA_CARRILLO.pdf
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https://hal.univ-lorraine.fr/tel-01754604
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Submitted on : Friday, March 30, 2018 - 9:54:43 AM
Last modification on : Tuesday, May 28, 2019 - 3:40:14 PM

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  • HAL Id : tel-01754604, version 1

Citation

Nicolas Bayona-Carrillo. Relation procédé-microstructure-propriétés de tubes sans soudure de Ti–3Al–2,5V laminés à pas de pèlerin. Autre. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0423⟩. ⟨tel-01754604⟩

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