The design of non-classical materials, such as multifunctional energetic materials and/or the synthesis of high pressure phases rely on the understanding of the mechanisms responsible for shock-induced reactions in powder mixtures. The critical reactant powder configurational changes and mechanical mixing processes necessary for reaction initiation have yet to be determined. Consequently, shock-induced reactions have only been observed in select material systems under certain conditions, and remain an uncontrolled phenomenon. Shock-induced reactions in nickel and aluminum powder mixtures are investigated in this work through the use of instrumented gas-gun experiments performing time-resolved pressure and shock velocity measurements to determine the pressure-volume (P-V) shock compressibility (Hugoniot) of the mixture, from which evidence of reaction is inferred through deviations from the inert shock response calculated on the basis of mixture theory. The role of particle size and morphology on non-diffusional mixing and chemical reactivity is explored by conducting similar tests on micron-scale powders of spherical and plate-like (flake) shape. Recovery experiments performed just below the reaction threshold provide information about the densification and mixing behavior between reactants. Discrete-component numerical simulations of the shock-compression of powder mixtures are performed to reveal the micromechanics of particle deformation, and mechanisms of mass-flow and mixing that can lead to the formation of reaction products. The results obtained from time-resolved measurements, recovery experiments, and numerical simulations are coupled to model the linkages between starting powder configuration, mechanically-driven mixing, and chemical reactivity. The knowledge gained from this investigation will lead to understanding of reaction mechanisms, and the control over reaction initiation threshold, time and exothermicity, in addition to characteristics of reaction products formed. The scientific understanding attained will advance the design and application of multifunctional materials for next generation energetic applications, and/or the synthesis of novel materials.

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La micro fusion laser d'un lit de poudre (SLM) permet la réalisation de pièces complexes avec des microstructuresfines. Cette technologie présente de nombreux avantages mais se heurte encore à une faible disponibilité des poudres d'alliages. En SLM, la pièce est d'abord conçue par CAO (conception assistée par ordinateur), puis construite couche par couche avec un faisceau laser commandé par un ordinateur. Dans ce cadre, le travail effectué dans cette thèse a consisté à étudier et à développer une nouvelle méthode pour réaliser des pièces en alliages et en composites à partir de mélanges de poudres élémentaires, ouvrant ainsi la voie à une grande variété de compositions.Au niveau expérimental le choix s'est porté sur le système aluminium-silicium avec différentes teneurs en silicium (12, 18 et 50% en poids). L'effet de l'ajout d'un champ magnétique statique a aussi été proposé comme un outil supplémentaire de contrôle de la microstructure.Dans le processus de fabrication de pièces par SLM la puissance du laser et la vitesse de balayage déterminent au premier chef la densité, la microstructure, la composition des phases et les propriétés mécaniques du produit. Une analyse systématique de l'effet de ces paramètres sur l'alliage Al - Si fabriqué par SLM à partir de mélanges de poudres est présentée. Des alliages ont été ainsi obtenus pour plusieurs domaines de composition visés correspondant à des applications pratiques (structures légères, système tribologique, emballage électronique, ...).Les microstructures fines obtenues grâce à la solidification rapide des matériaux fondus conduit à des propriétés quise comparent de façon favorable à celles obtenues avec les techniques classiques d'élaboration et de mise en oeuvre. / As a new manufacturing technology, Selective laser melting (SLM) has a large potential in the manufacturing of complex parts with ultrafine microstructure.Selective laser melting has many significant advantages over traditional manufacturing methods but still faces a low availability of powder materials. With SLM, the part is firstly designed via 3D computer-aided design (CAD)), then built layer-by-layer with a high energy computer-controlled laser beam The work done in this study was therefore aiming at developing a new way to obtain alloys and composites directly from elemental powder mixtures with a large composition flexibility.Experimentally the choice was made of the aluminum-silicon system with several silicon contents (12, 18, 50 wt. %).Adding a static magnetic field was also considered as an additional way to control the microstructure. When parts are manufactured by SLM, laser power and scanning speed are the main parameters determining the density, microstructure, phase composition and mechanical properties. A systematic analysis of the role of these parameter on the manufacturing of Al - Si alloys by SLM from mixtures of powders was therefore conducted. Al - Si alloys with a very fine microstructure were thus obtained for several composition ranges corresponding to practical applications (lightweight structures, high wear resistance alloys, electronic packaging material, ...). The properties of the materials obtained in this way, according to the performed characterizations, compares favorably with those obtained via the conventional production technologies.