Affinement de microstructures de métaux par des déformations plastiques extrêmes

Abstract : For several years, Severe Plastic Deformation (SPD) processes have been developed to refine the microstructure of metals in order to obtain ultrafine grains (UFG). This refinement attributes improved properties (ex: yield stress) to the material. The overall geometry of the material remains unchanged. That is why these processes are specific for a given geometry. For this purpose, a process recently initiated at the LEM3, the so called HPTT – High Pressure Tube Twisting – is designed to nanostructure tubular samples. A tube is confined by applying a hydrostatic pressure of several GPa and large friction forces are generated. A shear strain (> 4) is finally applied in the tube thickness. In this thesis, an experimental device was developed and used to produce UFG materials. Finite element and analytical studies have been carried out to understand the stress and strain state in the tube wall. The obtained ultrafine grains IF (Interstitial-Free) steel was characterized to determine the evolution of the microstructure (SEM-EBSD), textures (X-rays) and the mechanical behavior (compression tests). For a better understanding of the fragmentation phenomena, a polycrystal code involving lattice curvature as the main element leading to refinement of the microstructure was used and compared with experimental measurements. This work is concluded by a study on the limited grain size achievable by SPD processes
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Submitted on : Thursday, March 29, 2018 - 12:55:10 PM
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Arnaud Pougis. Affinement de microstructures de métaux par des déformations plastiques extrêmes. Autre. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0332⟩. ⟨tel-01750798⟩

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