Étude multi-échelles de l'hétérogénéïté et de l'anisotropie de la déformation plastique: cas des aciers TWIP et du Ti-[alpha]

Abstract : Dislocation glide and twinning mechanisms occur and interact during plastic deformation of many materials, often leading to diverse behaviors. The role of both mechanisms on heterogeneity and anisotropy of plastic deformation is discussed in this thesis through a multiscale study of two materials with strong industrial potential: an austenitic steel displaying the TWIP (TWinning Induced Plasticity) effect, and commercially pure alpha-titanium. If in both cases, dislocation glide remains the dominating mechanism to accommodate plastic deformation, the role of each mechanism is still not well understood. Materials characterization consists of tensile tests at room temperature (macroscopic scale) associated with high resolution local extensometry and acoustic emission measurements (mesoscopic scales), as well as microstructure analyses. It is shown that plastic instability which takes place in the studied TWIP steel appears progressively, long before the critical strain for the onset of stress serrations on deformation curves. Moreover the role of twinning seems to be essential for the mechanism of plastic instability. Concerning alpha-titanium, a three-stage character of strain hardening in tension conditions is highlighted with an inverse effect of strain-rate regarding the tensile direction in relation with the initial texture (rolling or transverse direction). Twinning seems to play here only a secondary role. To explain these observations it is conjectured that the strain-rate sensitivity of stress is different for prismatic and pyramidal glide. Finally, this hypothesis is compared to the estimation of active slip systems based on the slip lines analysis at different strain levels
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Amandine Roth. Étude multi-échelles de l'hétérogénéïté et de l'anisotropie de la déformation plastique: cas des aciers TWIP et du Ti-[alpha]. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0078⟩. ⟨tel-01750801⟩

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