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Elaboration, caractérisation structurale et mise en forme d'alliages de magnésium vitreux

Abstract : The amorphous structure of metallic glasses results in high mechanical properties at room temperature, high hardness and strength, large elastic deformation domain, but also interesting forming capacity in their supercooled liquid region. Because of their out of equilibrium state, a crystallisation can develop during a heat treatment and lead to the formation of a glass/crystallites composite, for which properties are changed. We investigate in this thesis the Mg based bulk metallic glasses family, mainly in the Mg-Cu-RE system (RE = Rare Earth): from their elaboration by copper mold injection casting, through their structural characterisation, by DSC, X-ray diffraction and microscopy, their mechanical characterisation, mainly by compression, in amorphous and partially crystallised states, to their forming by extrusion. Samples are obtained in the form of amorphous rods up to 9mm diameter. At room temperature, despite a macroscopic brittle behaviour, fracture stresses higher than 800MPa can be measured. In the vicinity of the glass transition temperature, at about 150°C, a great forming capacity is highlighted, associated to Newtonian flows and low viscosities. The crystallisation mainly deteriorates the mechanical properties of the glass, especially by a weakening at room temperature and by the progressive degradation of forming capacities at high temperatures. Nevertheless, the high thermal stability of the glass is sufficient to keep the amorphous state during the forming operations, allowing the elaboration of multi-materials metallic glass/light alloy.
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Submitted on : Thursday, June 18, 2009 - 9:56:55 AM
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Sylvain Puech. Elaboration, caractérisation structurale et mise en forme d'alliages de magnésium vitreux. Matériaux. Institut National Polytechnique de Grenoble - INPG, 2008. Français. ⟨tel-00396419⟩

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