Etude des mécanismes de déformation et de transformations métallurgiques en sous-couche et sur la surface usinée lors du tournage du Ti-6Al-4V avec un outil en carbure cémenté WC-Co non revêtu. Corrélation de l’intégrité matière par la surveillance de l’opération et la compréhension des mécanismes d’endommagement de l’outil.

Abstract : The scientific works presented in this thesis is taken place within the framework of an European project ACCENT which is the continuity of the ManHIRP European project (2001-2005). The main aim of these studies is the development of an experimental approach allowing of the determination of an acceptable surface integrity within the validity domain according to the cutting parameters by using the recorded monitoring signals during turning operation. The identification and the classification of the geometrical anomalies generated on the machined surface versus the cutting speed and feed rate were especially investigated. At the same time, damage on uncoated cemented carbide and evolution on process monitoring signals have conducted to a better understanding of cutting phenomena. The anomalies generated within the machined sub-surface such as the highly worked layers and “white layers” were studied with fine metallurgical analysis like the use of Castaing microprobe and transmission electron microscopy (TEM). In addition, micro-hardness and residual stresses measurements have completed the previous analysis. The knowledge of the metallurgical and mechanical states within the sub-layer have enabled to deduce the causes of their formation and to define the deformation mechanisms and the metallurgical transformations (phases and grains size) which have occurred during the machining operation. The tracking of the microstructural features related to globular alpha grains by the investigations of the images analysis have led to a better understanding of material flow according to the cutting and feed directions. Also, the dissolution phenomena of globular alpha grains occurring when the thermal loading becomes preponderant before the mechanical one has been highlighted. After these metallurgical analyses, correlations between the surface integrity and the process monitoring signals have been found. The singular evolution of the radial force signal indicates the anomalies appearance. Its amplitude is linked with the depth of the thermo-mechanically affected sub-layer of the machined surface.
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Mickael Rancic. Etude des mécanismes de déformation et de transformations métallurgiques en sous-couche et sur la surface usinée lors du tournage du Ti-6Al-4V avec un outil en carbure cémenté WC-Co non revêtu. Corrélation de l’intégrité matière par la surveillance de l’opération et la compréhension des mécanismes d’endommagement de l’outil.. Autre. Ecole nationale supérieure d'arts et métiers - ENSAM, 2012. Français. ⟨NNT : 2012ENAM0058⟩. ⟨tel-01672311⟩

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