In this Master Thesis work, the effect of pressure on sintering of cemented carbides is investigated. Special focus hasbeen given to the residual porosity after sintering. It is well known that sintering shrinkage depends on binder phasecontent, grain size, temperature and pressure. Thus 4 different cemented carbides grades were selected. The gradeswere pressed into standard products and TRS (Tensile Rupture Strength) rods with two different shrinkage factors.These were then sintered at different pressures and temperatures. Thereafter the impact of pressure on propertiessuch as Density, Coercivity, Porosity and TRS were analyzed. The observations were further supported with Weibullprobability analysis and fracture surface analysis in SEM.It has been shown that there exists a distinct threshold pressure at which significant reduction in porosity occurs forgiven compacted densities. For 3 out of 4 cemented carbide grades it has been observed that P2 sintering pressure issufficient to meet desired product characteristics. The fourth grade required a minimum sintering pressure of P4 toachieve desired quality criteria. Moreover it has been concluded that an increased sintering pressure increasesmaterial strength, as compared to vacuum sintering, thereby reducing the amount of early failures caused by poresduring TRS test.                                    Keywords: Cemented Carbides, Pressurized Sintering, Tungsten carbide, Porosity, Vacuum sintering, TensileRupture Strength, Weibull analysis, Fracture surface analysis.

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Les alliages de titane β-métastables comme le Ti-10V-2Fe-3Al se substituent progressivement aux alliages α/β dans les applications aéronautiques du fait de leur résistance spécifique améliorée. Leurs microstructures d'emploi sont cependant complexes et multi-échelles, constituées d'une matrice β (de grains millimétriques) partiellement transformée en nodules primaires αp (micrométriques) et en lamelles secondaires αs (sub-micrométriques). Les propriétés finales peuvent être très sensibles aux variations locales de microstructures et sont souvent non maîtrisées lors du forgeage de pièces massives. De plus la matrice β qui représente ~40% du volume et qui a un comportement élastique et plastique fortement anisotrope, comme la phase α, complique la compréhension des mécanismes de déformation en jeu. Le premier objectif de cette thèse est de mettre en œuvre des techniques de caractérisation multi-échelles (la diffraction des neutrons, l'imagerie électronique couplée à l'analyse d'image et l'EBSD, la reconstruction des microtextures de haute température β/αp) pour analyser efficacement la microstructure/texture des constituants β/αp/αs et caractériser leurs hétérogénéités au sein de demi-produits et de pièces obtenues par matriçage. Les résultats permettent d'analyser la fragmentation des grains β en sous-grains, les macrozones αp, le maintien de relation d'orientation entre β/αp et l'organisation des lamelles αs en colonies ou paniers tressés, en pointant les différences de taille de domaines révélés par la cristallographie et l'imagerie standard. Le second objectif est d'appliquer cette méthodologie à l'analyse de facies de rupture d'éprouvettes présentant un comportement singulier (en traction ou en fatigue) pour caractériser les configurations microstructurales à l'origine de l'amorçage de fissures. Cette analyse a principalement été réalisée par polissage manuel du faciès couplé à des acquisitions EBSD mais également en exploitant le potentiel de l'imagerie 3D par MEB-FIB (Focus Ion Beam) et la technique TKD (Transmission Kikuchi Diffraction) sur lame mince prélevée au niveau d'un site d'amorçage par FIB. Enfin, cette étude expérimentale a été complétée par une première approche en simulation micromécanique sur une microstructure modèle 100% β. L'objectif était d'évaluer l'influence de l’anisotropie élastique de la phase β sur la genèse de contraintes d'incompatibilités dans les régimes élastique et élasto-plastique. L'ensemble des résultats contribue à une meilleure compréhension des variations de propriétés mécaniques en lien avec la microstructure locale / The β-metastable titanium alloys such as Ti-10V-2Fe-3Al are gradually replacing α/β alloys in aeronautical applications thanks to their improved specific strength. However, their microstructures are complex and multi-scale, consisting of a β matrix (of millimetric grains) partially transformed into primary αp nodules (micrometric) and secondary αs lamellae (sub-micrometric). The final mechanical properties are very sensitive to local variations of the microstructure, which are not always fully controlled during forging of massive parts. Moreover, the β matrix, which represent 40% of the volume and whose elastic and plastic behavior is strongly anisotropic (like the α phase) complicates the understanding of the mechanisms of deformation. The first objective of this thesis was to efficiently characterize the microstructure/texture of the different constituents (β/αp/αs) and their heterogeneities within half-finished products and forged parts by using techniques of multi-scale characterization (neutron diffraction, electronic imaging coupled with image analysis and EBSD, reconstruction of high temperature microtextures β/αp). As a result the fragmentation of the β grains into subgrains, the αp macrozones, the destruction of the orientation relation between β/αp and the organization of the αs lamellae in colonies or basket weave was quantified and the differences in size of domains revealed by crystallography and by standard imaging were pointed out. The second objective is to apply this methodology to the analysis of fracture surfaces of samples exhibiting singular behavior (in tension or in fatigue) in order to characterize the microstructural configurations leading to early cracking. This analysis was mainly performed by manual polishing coupled with EBSD acquisitions but also by using 3D imaging by SEM-FIB (Focus Ion Beam) and TKD (Transmission Kikuchi Diffraction) technique on a thin foil FIB-extracted from the crack initiation site. Finally, this experimental study was completed by a micromechanical simulation on a 100% β model microstructure. The objective was to evaluate the influence of the elastic anisotropy of the β phase on the genesis of incompatibility stresses in the elastic and elasto-plastic regimes. The overall results contribute to a better understanding of the variations of mechanical properties related to the local microstructure