Le Cold Spray Basse Pression est un procédé de projection thermique émergeant de plus en plus apprécié par les industriels pour sa simplicité, son faible coût et sa polyvalence. Pour améliorer encore les caractéristiques des dépôts, des substrats en aluminium ont été préalablement texturés par laser, sous la forme de trous de dimensions variables répartis selon un motif régulier, avant d’être revêtus de cuivre. Une optimisation géométrique de la surface a alors permis d’augmenter l’adhérence de dépôts Cu/Al2O3 de +81% par rapport à un substrat brut. Ces résultats sont analysés, notamment à l’aide d’un modèle mathématique développé durant la thèse permettant de calculer l’augmentation de surface induite par la texturation. De plus, une caractérisation des contraintes résiduelles par DRX à travers l’épaisseur a mis en évidence l’uniformité des contraintes en compression dans le dépôt. Dans un second temps, des dépôts de cuivre ont été réalisés sur des substrats en composite PEEK/Carbone. La nécessité d’avoir une couche de matrice organique à la surface du composite a été mise en évidence afin d’éviter une érosion du substrat et permettre la construction du dépôt. Une stratégie de projection basée sur une variation de la granulométrie des poudres en cours de projection a également été développée afin de réduire le taux de porosité et obtenir des dépôts conducteurs électriquement. En complément de ce volet expérimental, un modèle numérique 3D en dynamique a été développé sur Abaqus/Explicit. Il permet d’étudier l’influence des paramètres de projection et de l’état de surface du substrat sur la déformation des particules lors de l’impact et les contraintes résiduelles induites. / Low Pressure Cold Spray is an emerging thermal spraying process increasingly appreciated in the industry for its simplicity, low cost and versatility. In order to enhance coatings characteristics, aluminum substrates were laser-textured with holes of varying dimensions distributed in a regular pattern before being coated with copper. An optimization of the holes dimensions led to an increase of the adhesion for Cu/Al2O3 coatings by +81% compared to a raw substrate. These results were analyzed using a mathematical model developed during the thesis allowing to calculate the surface increase induced by the laser texturing. Moreover a characterization of the residual stresses by XRD through the thickness revealed the uniformity of compressive stresses in the deposit. In a second time copper deposits were made on PEEK/Carbon composites. The need to have an organic matrix layer on the composite surface has been highlighted in order to avoid substrate erosion and allow the coating construction. A spraying strategy based on a variation of the powders granulometry being sprayed has therefore been developed in order to reduce the porosity and obtain electrically conductive coatings. In addition to this experimental aspect, a 3D dynamic model has been developed on Abaqus/Explicit. This model allowed to study the influence of the projection parameters and the substrate surface state on the particles deformation during the impact and the induced residual stresses.

As a result of the rise in processing power demands of today’s personal computers, water cooled pin fin heat sinks are increasingly being employed for the cooling of graphical processing units. Currently, these high performance devices are manufactured through high-cost, high-waste processes. In recent years, a new solution has emerged using the cold gas dynamic spray process, in which pin fins are directly manufactured onto a baseplate by spraying metallic powder particles through a mask. This process allows for a high degree of adaptability to different graphics processing unit shapes and sizes not achievable by any other process to date. One drawback of this process is that, as substrate sensitivity to heat and mechanical residual stresses requires the use of reduced spray parameters, there is reduced deposition efficiency, resulting in a fair portion of the feedstock powder being wasted. This work aims to demonstrate the feasibility of using powder recycling to mitigate this issue and compares coatings sprayed with reclaimed powder to their counterparts sprayed with as-received powder. The work demonstrates that cold gas dynamic spray is a highly flexible and economically competitive process for the production of pin fin heat sinks when using powder recycling even when spray parameters result in reduced deposition efficiency. The benefits of pin fins on heat transfer properties of flat plates used for graphical processing units is briefly addressed and demonstrated

Memoria para optar al título de Ingeniero Civil Mecánico / En el desarrollo de las industrias de manufactura se busca acelerar los procesos, en este punto la manufactura aditiva ha ayudado al progreso de la industria gracias a la creación de prototipos rápidos, con precisión, y disminución de costos, entre otros. Existen distintas formas de manufactura aditiva y aplicaciones con distintos materiales, plásticos, metales y cerámicos. Dentro de la manufactura aditiva se encuentran los procesos de proyección térmica usada típicamente con metales, donde se proyectan partículas fundidas, semifundidas o en frío. Este último es el caso de los sistemas de Cold Spray que son utilizados hoy en día para la manufactura de revestimientos, reparación de piezas mecánicas, relleno de orificios, relleno de piezas de fundición defectuosas, entre otros tipos de aplicaciones. Lo mencionado anteriormente tiene aplicaciones en el área de energía, aeroespacial, militar, automotriz, entre otros. En este proceso de manufactura se proyectan partículas metálicas, por intermedio de un gas que es calentado y acelerado mediante una tobera de Laval a velocidades supersónicas, las partículas logran su adhesión por la deformación plástica sufrida en el impacto. La presente Memoria consiste el diseño, construcción y pruebas de un sistema de Cold Spray de baja presión. Este proyecto se divide en varias etapas: Definir criterios de dise- ño, Diseño preliminar, Memoria de cálculo, Selección de componentes, Diseño y validación mediante elementos finitos, Construcción y ensamblaje, Pruebas. Luego de fabricado el sistema se realizan una serie de pruebas en cada uno de sus subsis- temas (control gas, control temperatura, movimiento y gabinete protección). Estas pruebas sirven para observar desperfectos, analizar sus posibles causas y opciones de solución. Una vez terminada la construcción y pruebas, se plantean mejoras a futuro, donde se destaca la construcción de una nueva tobera y un alimentador de partículas; así como también, la aislación de las partes mecánicas (husillos y ejes lineales), ya que éstas pueden sufrir daños o desperfectos por suciedad o polvos proyectados. Finalmente con el sistema de Cold Spray se busca realizar posteriores estudios en el ámbito de la manufactura aditiva y así conocer distintos tipos de aplicaciones según sus propiedades mecánicas.

Cold spray (CS) deposition of metals is a process involving deposition of materials in the solid or semi-solid state. It also has lower operating temperatures, and oxidation is greatly reduced in the process. The process is beneficial for refractory metals, such as tantalum, which are tough and difficult to machine. The interface between the CS powder and the substrate is the most important region for the study of mechanical properties as it is where the bonding process occurs first; studying mechanical properties at the nanoscale will give us a better idea of the mechanical properties of the coated surface. The present work investigates multiple-sprayed conventional and low-hydrogen treated tantalum powders on stainless steel substrates and also single-sprayed nitrogen-treated tantalum powders on aluminum substrate using Atomic force microscopy (AFM). It also discusses the effects of topography on the local changes in modulus. AFM is an instrument that measures the site-specific property of the sample. In this work, the local Young's modulus is studied using force-distance curves. Calibration of the AFM cantilever and the photodetector used to measure the cantilever, is a vital step before the actual process. The conventional method of calibration can cause damage to the tip as it arbitrarily penetrates into the sample creating a cantilever deflection vs. tip penetration curve, giving the sensitivity of the photodetector. AFM is highly dependent on topographical features as the cantilever tip-sample interaction can vary, causing variations in the property mapped. This work, however uses a non-contact method of calibration which saves the cantilever tip from potential damages, saving the results from the detrimental effects of tip topography. The work also discusses the effects of local sample deformation and volume of tip-surface contact on local changes in Young's modulus at the interface of coating and substrate. This work uses Electron micro-probe analysis (EPMA) to show the presence of oxides at the interface. The presence of oxides changes the bond energy as compared to a pure tantalum bond, ultimately affecting the local modulus mapped using AFM. The effect of oxides on the local modulus at the coating-substrate interface is theoretically discussed.

La réparation des composants en alliages légers est un processus clés dans le domaine de l’aéronautique. Ces alliages sont abondamment utilisés dans les constructions aéronautiques notamment pour des composants à forte valeur ajoutée. Leur utilisation combinée à une optimisation de la conception des pièces permet de disposer de produits satisfaisants aux exigences de masse, de coût et de performances. Cependant l’utilisation de ces pièces est limitée dans le temps car divers endommagements peuvent survenir aussi bien lors de leurs manipulations que lors de leurs utilisations en service. Des solutions de retouches existent mais ne permettent pas toujours de redonner leur intégrité aux zones affectées. Ces limitations sont à l’origine d’un fort taux de rebut parmi les pièces à forte valeur ajoutée.Les multiples avantages du procédé Cold Spray en font un candidat idéal pour la projection de revêtements adaptés aux composants en alliages légers mis en oeuvre en aéronautique, que ce soit dans une logique de protection, de retouche ou de réparation. Il s’agit de reconstruire la pièce par un revêtement aux caractéristiques les plus proches possibles de celles du matériau de base. Ce travail de thèse consiste à optimiser l’ensemble des paramètres du procédé de projection dynamique à froid (Cold Spray) pour plusieurs couples substrat-revêtement combinant différents alliages d'aluminium, de magnésium et des composites à matrice métallique à base aluminium.La première étape a consisté à optimiser les paramètres principaux du procédé Cold Spray afin de s’affranchir du phénomène de colmatage pouvant intervenir au sein de la section divergente de la buse de projection. Ce phénomène a pour effet de diminuer la vitesse des particules, les revêtements obtenus devenant alors assez poreux. Une étude s’est ensuite focalisée sur l’optimisation de l’adhérence des couples substrats-revêtements. Il a été démontré le rôle primordial de la préparation de surface dans l’adhérence des revêtements où l’ancrage mécanique apparaît prépondérant. Enfin, une étude originale a été conduite pour mettre au point une méthodologie pour recharger localement une zone défectueuse sans avoir à recouvrir toute la surface du substrat. Une programmation hors ligne du robot a été employée afin de recouvrir deux types de défaut pré-usinés sur des blocs d’alliage d'aluminium. Les résultats sont satisfaisants avec des gains en temps de projection et des dépôts sans défaut après usinage. / The repair of light alloy parts is a major issue in aeronautics. Aluminum alloy and magnesium alloy are widely used in aircraft parts, especially for high value-added components. Their use combined to optimizing design allows to have satisfactory products meeting mass, cost and performance requirements. However, like any other life-limited components, various damages can occur not only during handling procedure but also while operating. Rectification solutions exist but do not always comply with requirements. These limitations entail high scrap rates among high value-added parts.The various advantages of the cold spray process make it an ideal candidate for suitable coatings for light alloy aircraft components as protective, retouching or repair methods. The aim is to rebuild the damaged part by a coating whose characteristics are closest to those of primary materials. This thesis proposes to optimize different cold spray parameters for several substrate-coating pairs combining different aluminum alloys, magnesium alloys and aluminum alloy-based metal matrix composites.The first step was to optimize the main parameters of cold spray process to prevent clogging phenomenon that may occur in the expansion part of the nozzle. It decreases particle kinetics and promotes porous coating. Then, adhesion optimization of substrate-coating couples was investigated. The substrate surface preparation is a key factor on coating adhesion, where the mechanical anchoring appears essential. Finally, an innovative study was conducted to develop a method to cover locally surface defects. Offline programming trajectories were used to fill up two kinds of pre-machined defaults on aluminum alloy blocks. Results are in good agreement with spray time savings and defect free coatings after machining.

Le cold spray, procédé qui consiste en la projection de particules de poudre à haute vitesse sur un substrat solide, permet de réaliser des dépôts denses de tantale sur substrat de cuivre. Tout au long de la projection, les particules restent à l'état solide ce qui prévient toute pollution ou modification chimique indésirable comme l'oxydation. Le risque d'altération de la composition chimique est ainsi reporté sur d'autres étapes telles l'obtention des matériaux ou la conservation des poudres. Le tantale est particulièrement sensible à la présence d'oxygène et peut ainsi voir sa dureté augmenter même pour des très faibles taux. Cette étude s'intéresse donc aux conséquences d'une augmentation du taux d'oxygène dans les particules avant projection sur la qualité (adhérence, cohésion) du dépôt. Pour cela, des particules de poudres ont été enrichies en oxygène puis ont été analysés suivant différentes méthodes (DRX, microsonde de Castaing, MET, XPS, nanoindentation, …) afin de déterminer le type d'oxydation et le comportement mécanique des particules oxydés. Ensuite, la phénoménologie des particules à l'impact a été étudiée via l'observation de particules isolées adhérant au substrat après impact (splats), d'une part, et des dépôts, d'autre part. Les techniques d'analyses et les procédés utilisés pour caractériser leur déformation et leur adhérence sont le MEB, le MET, l'EBSD, un essai de rayure modifié, la structuration laser et un essai d'adhérence et de cohésion par choc laser (LASAT®). Enfin, une simulation numérique de la construction de dépôt a été réalisée selon les lois ensemblistes établies par la morphologie mathématique. L'influence de l'oxydation des poudres est représentée dans ce modèle via l'introduction du rebond des particules. / Cold gas dynamic process, namely Cold Spray, can be used to achieve fully-dense tantalum coatings onto a copper substrate due to spraying of powder particles at a high velocity. During spraying, the particles stay at the solid state, which prevents pollution and detrimental chemical modification such as oxidation. The risk for chemical damage therefore moves to other processing stages, primarily raw material production and powder storage. Tantalum is very sensitive to oxygen (for example, hardness increases even for low oxygen contents). In the present work, the consequences of the particle oxygen degree on coating quality are studied. Oxidized powder particles were analyzed using different methods (XRD, EPMA, TEM, XPS, nanoindentation, …) to characterize oxidation and particle mechanical properties. Particle impact phenomenology is studied from observation of splats, i.e. single deposited particles, and coatings. Analysis techniques and processes to describe splat deformation and adhesion are SEM, TEM, EBSD, modified scratch testing, laser structuring and LAser Shock Adhesion Test (LASAT®). In a final part, numerical simulation of coating build-up was developed using a mathematical morphology approach. Particle oxidation is involved in this simulation through the particle rebound phenomenon.

Le principe du procédé cold spray réside dans la projection de poudres à haute vitesse sur un matériau, le substrat. La formation d'un revêtement plus ou moins dense à sa surface passe par l'adhérence et l'empilement des particules projetées. Un des domaines d'application d'un tel procédé est la réparation de composants métalliques ou composites utilisés dans le secteur aéronautique. Les particules et le substrat adhèrent par différents mécanismes, notamment mécaniques. Les duretés respectives des matériaux et la topographie de surface du substrat influent sur l'intensité de cet ancrage mécanique. Cette étude permet de statuer sur ces deux contributions. Pour cela, des systèmes purement métalliques et composites aux propriétés mécaniques différentes sont choisis. Le dépôt de particules sur des surfaces rugueuses est étudié à travers l'élaboration de revêtements d'aluminium pur sur substrats d'alliage d'aluminium plus durs. Des mécanismes de déformation plastique et d'empilement sont analysés par construction de revêtements d'Al-SiC sur aluminium. L'élaboration de ces revêtements passe par l'optimisation de nombreux paramètres liés au procédé et à la nature des matériaux (température, pression, granulométrie). Les conditions d'impact des particules sont également déterminées par l'emploi de techniques mesurant la vitesse des poudres projetées (DPV 2000), la température du substrat par thermocouples et la température des particules par simulation numérique. L'ancrage mécanique des particules est analysé par observation en coupe de l'interface revêtement-substrat. Le gradient de dureté est également quantifié. Une analyse de la morphologie des surfaces sablées est réalisée afin de corréler la granulométrie des particules aux dimensions de rugosité mesurées. Un modèle d'impact par simulation numérique est mis en place pour étudier les déformations plastiques des interfaces en fonction de la topographie de surface. Enfin, des essais d'adhérence par choc laser (LASAT®) sont entrepris afin d'identifier le rôle de la rugosité d'interface sur les seuils de rupture déterminés numériquement. / The cold spray process is based on high-speed spraying of a powder onto a substrate. The formation of a more or less dense coating depends on sprayed particle adhesion and coating build-up. The repair of metallic or composite aircraft / aerospace components is a recent application of cold spraying. The particle-substrate bond strength is due to various mechanisms, including mechanical anchoring. Substrate material hardness and surface topography governs the degree of mechanical anchoring. This thesis study is centered on the influence of these two contributions. Pure metallic and composite systems with different mechanical properties are selected. Particle deposition onto rough surfaces is investigated through the development of pure aluminium coating of harder aluminum alloy substrates. Plastic deformation and build-up mechanisms are studied for Al-SiC coatings onto ductile substrate. All the coatings resulted from an optimization stage where process parameters and materials properties are considered (gas temperature, gas pressure, particle size). Particle impact conditions are also determined by particle speed experimental measurements (using a DPV 2000 system). Substrate temperatures are determined using thermocouple and particle temperatures are studied by numerical simulation. Mechanical anchoring of particles is investigated by cross-section observation of the coating-substrate interface. Hardness gradient is also quantified. An analysis of sand-blasted surfaces morphology is performed to correlate particle size and roughness parameters. A model of particle impact is established from a finite element analysis of interface plastic deformation as a function of surface topography. Lastly, dynamic adhesion testing using a laser shock (LASAT®) are undertaken to study the potential role of interface roughness on the fracture thresholds in the light of a numerical analysis.

Manufacturing in modern society has taken on a different role than in previous generations. Today’s manufacturing processes involve many different physical phenomenon working in concert to produce the best possible material properties. It is the role of the materials engineer to evaluate, develop, and optimize applications for the successful commercialization of any potential materials. Laser-assisted cold spray (LACS) is a solid state manufacturing process relying on the impact of supersonic particles onto a laser heated surface to create coatings and near net structures. A process such as this that involves thermodynamics, fluid dynamics, heat transfer, diffusion, localized melting, deformation, and recrystallization is the perfect target for developing a data science framework for enabling rapid application development with the purpose of commercializing such a complex technology in a much shorter timescale than was previously possible. A general framework for such an approach will be discussed, followed by the execution of the framework for LACS. Results from the development of such a materials engineering model will be discussed as they relate to the methods used, the effectiveness of the final fitted model, and the application of such a model to solving modern materials engineering challenges.

Additive manufacturing technologies place materials at the direct point of need of the warfighter, enabling the development of optimal, situation-specific means to produce and repair parts of Army and DoD weapons systems. In the case of solid-state AM, a full understanding of the metallic powder is critical with producing ideal consolidated material properties reliably and repeatably. By way of iteratively coupling computational models with supportive experimental testing, one can rapidly archetype differences in processing methods, alloy compositions, and heat treatments for metallic powders that serve as feedstock for these AM technologies. Through the combination of thermodynamic models, advanced characterization, and dynamic nano-indentation, representative correlations are established between microstructural features and mechanical properties, enabling the development of enhanced feedstock materials that can achieve the specific needs of the warfighter efficiently without forfeiting quality. This represents both a holistic and a materials-by-design approach to AM through the deliberate use of computation to drive down the discovery process and allow feedstock powders to be engineered with specific properties dictated by Army requirements for performance. In a case study of Al 6061, unique observations were made through the combination of modeling and experimentation. It was discovered that the precipitation kinetics were greatly accelerated in powders and therefore, typical heat treatment processes used for cast-aluminum alloys were not valid. Due to this shift in precipitation sequences, high-temperature treatment was limited to discourage precipitate and grain coarsening. Additionally, when compared to typical cast Al 6061, the main precipitation hardening phase shifts from Mg2Si to Al4Cu2Mg8Si7, changing how aging mechanisms were accounted for. These conclusions were supported by both the computational models and experimental results. Through the generation of numerous data, the models were calibrated, enabling more efficient and precise development of tailored material characteristics from specific microstructural features to serve as an input in a holistic through-process model for a solid-state AM process and guide future experimentation.

The aerospace industry is constantly looking for methods to reduce the cost of flying their airplanes. These savings can come in many forms, one of them being cost savings attributed to fuel savings by either reducing the weight of the airplane or reducing the drag. Friction stir welding (FSW) was introduced as a means of joining previously unweldable Al 7075, a high-strength aluminum alloy commonly used in aerospace for its high specific strength. This eliminated the need for costly and time consuming rivets to be installed, firstly reducing the production cost of the airplane and secondly reducing the overall weight of the airplane therefore improving fuel consumption. There are many factors at play in the process of producing FSW Al 7075, but the result of this process creates a weld joint that is more susceptible to corrosion than the rest of the panel. For this reason, FSW Al 7075 panel fail prematurely and must be replaced too often. The main goal of this project is, using cold gas dynamic spray, to create a metallic layer on top of an Al 7075 FSW joint to protect it against corrosion. A series of 3 corrosion tests indicated that pure Al, among coatings of pure Al, Al 5038 and Al 7075, offered the best protection against corrosion. Al 5083 would also be a suitable material and should be used in applications where high bond strengths are required. Al 7075, although of the same alloy as the parent material, is not recommended for corrosion protection as it offered little advantage over the parent material. In order to better understand the interaction of creating a coating after a hot welding process, several analyses were performed. These included deposition at multiple substrate temperatures as well as hardness and velocity measurements. Results indicate that some aluminum alloys are very sensitive to temperature, yielding better coatings at high substrate temperatures. Individual particle deposition tests reveal that these improvements do not occur at the substrate-coating interface. Another portion of this project was dedicated to creating tensile specimens composed entirely of pure Al cold sprayed coatings. Several sets of samples were produced. Results indicate that pulling in the direction of nozzle travel direction yields UTS values 50% higher than pulling in the direction perpendicular to the direction of nozzle travel during coating deposition. Results after annealing seem to converge towards the same value. Finally, a new nozzle design was performed which should create a more efficient spraying process, resulting in cost savings for the industry.