Hétérogénéité de la déformation plastique des monocristaux de nickel déformés à froid par ECAE

Abstract : The processing of metals through Equal Channel Angular Extrusion (ECAE) has attracted much attention within the last decade primarily because this technique has shown the potential to achieve very large strains with the final aim of obtaining ultra-fine grain microstructures in bulk polycrystalline materials. The process involves passing a billet through two channels of equal area of cross-section inclined at an angle psi, generally 90° or sometimes 120°. This imparts large deformation to the material in one pass and the process can be repeated to refine the grain size down to a value characteristic of the material. It has been shown previously that ECAE is a heterogeneous process but there is still an important lack of understanding of the phenomena involved in ECAE deformation as well as regarding the extent of this its heterogeneity. Two high purity nickel single crystals of different initial orientation were deformed by ECAE and analyzed by different techniques. Texture and microstructure evolution was examined using neutron and local X-ray diffraction, SEM, TEM, orientation imaging microscopy and optical microscopy. This work has revealed an important heterogeneity along the height of both samples due to the continuous change of the deformation mode from simple shear on top towards a complex shear deformation mode at the center at which an important friction induced deformation is added at the lower part of the samples. The initial orientation has been observed to have a great influence on the microstructure refining mechanisms by the formation of deformation heterogeneities like deformation bands and shear bands
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Daniel Goran. Hétérogénéité de la déformation plastique des monocristaux de nickel déformés à froid par ECAE. Autre. Université Paul Verlaine - Metz, 2007. Français. ⟨NNT : 2007METZ021S⟩. ⟨tel-01748977⟩

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