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Déformation plastique sévère des surfaces d’alliages à faible densité par grenaillage ultrasonique : gradients de microstructures, comportements en fatigue et en tribologie

Abstract : The impact of ultrasonic shot peening on titanium and aluminium alloys is studied at room temperature and at cryogenic temperature. This process may also be called surface mechanical attrition treatment (SMAT). Fatigue strength and tribological behaviour are investigated in order to better understand the pros and cons of this process. Two titanium alloys were chosen: pure titanium in its fully α form and β-metastable titanium in its fully β form. This choice makes it possible to correlate the influence of the initial microstructure on the treatment of severe plastic deformation and on the final properties. The β-metastable titanium is sensitive to strain-induced martensitic transformation, which allows exploring the possibility of introducing martensite to the shot-peened surface to delay, for example, short crack propagation in fatigue testing. Shot peening at cryogenic temperature in this case improves the initiation of the martensitic transformation. In addition to facilitating martensitic transformation, cryogenic temperature shot peening increases the yield strength of alloys during processing, which has the effect of reducing the flow of material at the shot-peened surface. Thereby, it improves surface integrity and changes tribological and fatigue properties. Two precipitation hardenable aluminum alloys were also studied: 2024 and 7075. The purpose of this aluminium study is to compare the impact of ultrasonic shot blasting when used before or after precipitation aging. As the dislocations produced during ultrasonic shot-peening serve as preferential nucleation sites, the objective is to explore the possibility of improving (e.g. in terms of hardness) the precipitation aging by refining the size of the precipitates and increasing their density. The use of two series of aluminium should make it possible to compare the effect of the treatment on the two different alloying compositions. In addition, these two alloys show significant differences in terms of defect sensitivity, permitting to study the impact of surface integrity after ultrasonic shot-peening on mechanical properties. The study of tribological and fatigue behaviour allows to conclude about the effectiveness of these treatments under common conditions of use.
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https://hal.univ-lorraine.fr/tel-03176365
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Submitted on : Monday, March 22, 2021 - 12:19:39 PM
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  • HAL Id : tel-03176365, version 1

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Pierre Maurel. Déformation plastique sévère des surfaces d’alliages à faible densité par grenaillage ultrasonique : gradients de microstructures, comportements en fatigue et en tribologie. Science des matériaux [cond-mat.mtrl-sci]. Université de Lorraine; École de technologie supérieure (Montréal, Canada), 2020. Français. ⟨NNT : 2020LORR0182⟩. ⟨tel-03176365⟩

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