Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-to-weight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides and oxides, as well as solid lubrication to mitigate wear. In this study, Ti-TiC (14, 24 and 35 vol% TiC) composite coatings were deposited on mild steel substrates using cold spray with comparisons made to baseline cold-sprayed Ti. The dry sliding friction and wear behavior were studied from 25°C to 575°C and during thermal cycling in this temperature range. While the room temperature friction coefficient of all the coatings remained relatively constant at ~0.5, the wear rate continually decreased from ~1x10-3 to ~2x10-5 mm3/N-m with increasing the TiC loading. Raman spectroscopy measurements determined that the same TiO2 tribochemical phases (rutile and anatase) were present on the room temperature sliding wear surfaces, thus responsible for similar friction coefficients. With increasing sliding temperatures to 575°C, the Ti-35%TiC composite coating exhibited the best overall tribological behavior, i.e., the friction coefficient decreased to ~0.3 along with a negative wear rate of -6.6x10-5 mm3/N-m (material gain on the wear track was recorded due to oxidation and transfer from the counterface). These friction and wear reductions were determined to be due to the formation of stable, low interfacial shear strength oxide glaze layers on the wear surfaces, composed of TiO2, WO3, and CoWO4 (transfer from WC-Co counterface). In addition, self-adaptive friction behavior was observed during thermal cycling as a result of the microstructural and tribochemical differences in the tribolayers.

The majority of the structural weight of many common commercial aircrafts is composed of high strength aluminum alloys. The properties of high performance aluminum alloys such as a high strength to weight ratio (specific strength), ease of recycling, crash energy absorption capacity, and corrosion resistance make them ideal for use in the aerospace field. As a result of the high performance nature of the parts and specific properties of the materials, manufacturing requires intricate casting, precision machining, and specific heat treatments – which results in expensive components. As a result of its excellent corrosion resistance properties, pure aluminum coatings are commonly used in the aerospace field for corrosion protection of steel, aluminum alloy components, and titanium alloy components. The common method to deposit these coatings is called ion vapour deposition (IVD). These IVD aluminum coatings provide the coating adhesion, coverage, thickness, and corrosion resistance required to protect the part. The present study was motivated by the potential use of the cold gas dynamic spray (CGDS) process to repair a) damaged aluminum alloy aerospace parts and b) damaged pure aluminum IVD coatings. The primary research objective was to successfully produce these repairs using commercially available aluminum alloy feedstock powders deposited with commercially available CGDS equipment. This work was treated as prequalification work for The Boeing Company to commercialize this process and therefore the repairs aim to meet the same standards (military and industrial) required of the original aluminum alloy parts and IVD aluminum coatings. The use of CGDS was shown in this research to be a very promising as a process for the restoration of aluminum alloy aerospace components. The adhesion strength of the repaired aluminum components was found to be well above the accepted range for thermally sprayed repairs according to industrial standards. The repairs were subjected to a highly corrosive environment and showed only minor pitting. These sites could be reduced in the future with improved machining techniques and attention to surface detail prior to exposure to the salt fog. The only requirement that the repaired components did not meet was for the wear properties of the anodized layer, measured thought Taber abrasion testing. The results of this test, at times, approached the desired values, and it is believed that, in the future, the quality and consistency of the coatings could be improved and the test would meet industrial standards. The results of this research show that the use of CGDS as a process for the restoration of damaged aluminum IVD coatings is possible and is a promising alternative to conventional methods. The CGDS coatings were scrutinized to the same level as required of IVD coatings when they replaced toxic cadmium coatings in the late 1980s. The coating adhesion, demonstrated through glass bead abrasion and strip rupture testing, was shown to meet the current industrial standards. The corrosion testing of the repairs resulted in no visible red rust of the steel components, even when the steel was exposed.

Les contacts électriques, utilisés dans les contacteurs et les disjoncteurs, sont des composants fortement sollicités dont le comportement influence la durée de vie des appareils. Les pastilles de contacts électriques, en matériaux composites à matrice d'argent, sont actuellement élaborées par des opérations classiques de métallurgie des poudres avant d'être assemblées par soudage sur des supports contacts. Un procédé envisagé pour le remplacement de la méthode classique d'élaboration est celui de la projection dynamique par gaz froid communément appelé cold spray. Dans ce procédé, des particules de poudre sont accélérées au moyen d'une tuyère de Laval avant d'aller s'écraser sur un substrat en formant un dépôt par empilement. L'objectif de ce travail est de démontrer le potentiel de ce procédé pour la réalisation de contacts électriques. La démarche retenue s'appuie sur le triplet élaboration, caractérisation et simulation numérique. La souplesse du procédé cold spray a rendu possible l'élaboration d'une large gamme de microstructures composites en ayant optimisé au préalable la projection de la matrice d'argent. La caractérisation de ces microstructures a été menée à différentes échelles, notamment fine pour quantifier la porosité par microtomographie et très fine pour élucider les mécanismes interfaciaux d'adhésion et de déformation survenant lors de l'impact par microscopie électronique en transmission. Ces investigations poussées sont nécessaires pour comprendre le comportement de la matrice d'argent dans un premier temps. Les dépôts composites font l'objet d'études complémentaires, les données disponibles dans la bibliographie étant rares. D'un point de vue plus macroscopique, les microstructures ont été éprouvées par des moyens d'essais classiques ou développés pour les besoins de cette étude en s'appuyant notamment sur les effets engendrés par une impulsion laser. Parallèlement, des calculs par éléments finis ont permis de mieux comprendre les phénomènes induits par un tir laser et donc, par extension, par un arc électrique. Pour compléter cette démarche, une simulation numérique originale basée sur un modèle d'empilement faisant appel à la morphologie mathématique propose de relier microstructure réelle et microstructure simulée, le but étant de prévoir la morphologie d'une microstructure uniquement à partir de la caractérisation de quelques particules. L'ensemble des résultats obtenus a permis d'identifier les facteurs dont dépendent les propriétés d'un dépôt (granulométrie des poudres, taille de grains,...) et ainsi de choisir des microstructures en vue de la réalisation de contacts électriques. L'endurance de prototypes de contacts fabriqués par cold spray a été déterminée sur banc d'essais de contacteurs industriels. Elle a été montrée comme largement compétitive avec celle des contacts industriels actuels réalisés par métallurgie des poudres classiques.

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.

The objective of this study is to investigate the feasibility of depositing 1.5 mm thick titanium coatings, as a repair method for aerospace Ti-6Al-4V substrates, using two new commercially available processes: Low Pressure Cold Spray (LPCS) and Pulsed Gas Dynamic Spray (PGDS). The coatings produced were examined and characterized by their porosity level, microhardness, adhesion strength, particle flattening ratio, wipe tests, fracture surface type and wear tests. Phases and chemical composition were determined using X-Ray diffraction analysis and energy dispersive spectroscopy, respectively. It was found that both spraying processes are capable of producing dense, hard and oxide-free coatings using specific parameters. Finally, as a first step towards repair implementation of these processes, damages were simulated on Ti-6Al-4V samples, which were successfully repaired with low porosity and high hardness levels. The feasibility of repairs was confirmed, the next step will consist in qualification testing to assess coating performances under real life application.

abstract: Nanomaterials exhibit unique properties that are substantially different from their bulk counterparts. These unique properties have gained recognition and application for various fields and products including sensors, displays, photovoltaics, and energy storage devices. Aerosol Deposition (AD) is a relatively new method for depositing nanomaterials. AD utilizes a nozzle to accelerate the nanomaterial into a deposition chamber under near-vacuum conditions towards a substrate with which the nanomaterial collides and adheres. Traditional methods for designing nozzles at atmospheric conditions are not well suited for nozzle design for AD methods. Computational Fluid Dynamics (CFD) software, ANSYS Fluent, is utilized to simulate two-phase flows consisting of a carrier gas (Helium) and silicon nanoparticles. The Cunningham Correction Factor is used to account for non-continuous effects at the relatively low pressures utilized in AD. The nozzle, referred to herein as a boundary layer compensation (BLC) nozzle, comprises an area-ratio which is larger than traditionally designed nozzles to compensate for the thick boundary layer which forms within the viscosity-affected carrier gas flow. As a result, nanoparticles impact the substrate at velocities up to 300 times faster than the baseline nozzle. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2017

Aluminum and aluminum-alumina powder mixtures were used to produce pyramidal fin arrays on aluminum substrates using cold spray as an additive manufacturing process. Using aluminum-alumina mixtures instead of pure aluminum powder could be seen as a cost-effective measure, preventing nozzle clogging. The fin geometries that were produced were observed using a 3D digital microscope to determine the flow passages width and fins geometric details. Heat transfer and pressure tests were carried out using different ranges of appropriate Reynolds numbers for the sought commercial application to compare each fin array and determine the effect of alumina content. It was found that the presence of alumina reduces the fins’ performance when compared to pure aluminum but that they still outperform traditional fins. Numerical simulations were performed and were used to explain the obtained experimental results. The numerical model opens up new avenues in predicting different parameters such as pressure and substrate temperature.

Abstract The cold spray process is an additive manufacturing technology primarily suited for ductile metals, and mainly utilized in coating surfaces, manufacturing of freeform parts and repair of damaged components. The process involves acceleration of solid micro-particles in a supersonic gas flow and coating build-up by bonding upon high velocity impact onto a substrate. Coating deposition relies on the kinetic energy of the particles. The main objective of this study was to investigate the mechanics of polymer cold spray process and deformation behavior of polymers to improve technological implementation of the process. A finite element model was created to simulate metal particle impact for copper and aluminum. These results were compared to the numerical and experimental results found in the literature to validate the model. This model was then extended to cover a wide range of impact conditions, in order to reveal the governing mechanisms of particle impact and rebound during cold spray. A systematic analysis of a single high-density polyethylene particle impacting on a semi-infinite high density polyethylene substrate was carried out for initial velocities ranging between 150m/s and 250m/s by using the finite element analysis software ABAQUS. A series of numerical simulations were performed to study the effect of a number of key parameters on the particle impact dynamics. These key parameters include: particle impact velocity, particle temperature, particle diameter, and particle density, composition of the polyethylene particle, surface composition and the thickness of a polyethylene film on a hard metal substrate. The effect of these parameter variations were quantified by tracking the particle temperature, deformation, plastic strain and rebound kinetic energy. The variation of these parameters helped define a window of deposition where the particle is mostly likely to adhere to the substrate.

Strengthening, resistant and shielding properties, to name a few, can be achieved by implementing a surface material coating onto an engineering component. Various elements of these compounded parts can augment the functionality of the part, such as, increased life time and more interactive surfaces. Tungsten has proven to be a challenge to plate with other metals, but if done correctly, the results can allow for the cold spray of tungsten. Cold spraying tungsten particles alone provides a challenge because the powder is too hard and instead of adhering, it erodes the surface it is attempting to plate. Coating tungsten in a softer metal, like copper, will allow for the particles to adhere to the surface and create a strengthened and radiation shielded component. It also yields a better surface to electroplate onto in the future, as tungsten itself is hard to plate onto, so the copper layer provides the ability to easily plate other metals. The purpose of this thesis project is to encapsulate tungsten powder within copper, then scale up the process to produce bulk amounts of the material in a batch process. The particles will be encased using an electroplating method, that has been vi turned into a semi-autonomous process for the ease of producing bulk powder. While electroless deposition has previously shown positive results for attaining a uniform coating, making it a semi-batch process for bulk material would have an extreme cost in comparison to electrolytic deposition. The tungsten particles have been successfully enclosed in copper by electrolytic deposition in this set of experimentation using an HF electro-etch pretreatment and ultrasonic agitation during electroplating. Further experimentation will include improved methods of stirring and transferring powder, as the transfer takes too long between the etch and the onset of plating and the stirring method is bulky and reduces the area that can be efficiently plated on.

This master’s thesis deals with origin, structure and mechanical properties of architectured material. The theoretical part deals with composits and theory of architectured materials. Further, the cold spray technology is described and it is used to create the network of grooves in the architectured material. In the experimantal part the influence of groof geometry and profil on the mechanical properties of the resulting architectured material is researched. Microstructure and hardness of the samples were also examined.