The purpose of this diploma thesis is to get a better understanding of cold kinetic deposition (cold spray), principles of functioning of this method followed by an evaluation of advantages and disadvantages of cold spray and its comparison to conventional thermal methods and a simple summary of the practical use of cold spray with respect to different materials. Next there is a summary of the properties and uses of frequently applied metals in electrical engineering, aluminium and copper, description of metal corrosion and an understanding of the diagnostic method of acoustic emission. In the practical part, a sample with copper cold spray coating on aluminium substrate was created. Following, this sample was split for corrosion tests, where the split samples were exposed to a corrosive environment for different times of exposure. The extent of corrosion degradation of the samples was evaluated by acoustic emission and metallographic analysis for corrosion-loaded samples for 100, 200 and 300 hours. In the end, an illustrative design of the application of the cold spray technology was created.

This diploma thesis deals with the determination of the Young’s modulus of coatings using the impulse excitation technique (IET). The theoretical part of the thesis describes Cold and Thermal Spray technology, theoretical foundations of the impulse excitation technique and models of composite materials. The experimental part of the thesis deals with the determination of the tensile modulus of copper coating created by Cold Spray technology. The impulse excitation technique has been used to measure fifteen samples with coating thickness ranging approximately from 0,4 to 2 mm. Results from this measurement were evaluated using five composite models to establish the Young’s modulus of the applied coating. The best results were achieved by using the composite model based on rule of mixtures (ROM).

The prediction of material behavior and its microstructural evolution during high velocity impacts has been investigated for decades. The application of this topic can be observed in various engineering applications such as the cold spray process. Cold spray (CS) is an additive manufacturing method in which solid particles are accelerated using a low temperature supersonic inert gas flow, prior to their impact onto a substrate and adhesion/consolidation. In this process, unlike other thermal spray processes, the particles are kept well below their melting point prior to impact. This allows the CS process to be used for the manufacturing of high quality, specialized products at a low energy input. In CS, the deformation and bonding processes happen in a very short time (less than 100 ns). With the current technology, in-situ investigation is almost impossible. In this situation, numerical modeling methods are the best alternative to study the deposition process. There are several factors influencing the particle deposition, such as particle/substrate material properties, particle size, material temperature, particle velocity and so on, but it has been shown that the particle impact velocity has the major role during the deposition process. In fact, despite the type of bonding, i.e., mechanical or chemical, particle is sticking to the substrate after experiencing severe plastic deformation that occurs upon the impact at high velocities. Therefore, in order to develop the understating of the CS process, investigating the deformation behavior of material during high velocity impacts, and also bonding mechanisms involved during particle deposition must be investigated. III Although numerous studies have been done to explore the mechanisms occurring during particle deposition, the details of this process are still unclear. Therefore, the purpose of this research is to study the fundamental aspects of material behavior during the deformation and deposition processes with the aim of improving the understating of the CS process. Two different numerical approaches will be used to achieve the objective of the study, i.e., Finite Element Method (FEM) and Molecular Dynamics (MD) method. FEM will be used to study the metallic bonding occurring between the particle and the substrate. A physically based model to predict this phenomenon will be implemented into ABAQUS/Explicit FEM software. MD simulations will be performed to investigate the microstructure evolution during high velocity impacts. In order to characterize the deformation behavior of materials at a fundamental level, analysis will be focused on the basic mechanisms of plasticity and hardening in metals, i.e., the multiplication, glide and locking of dislocations, and also solid-state amorphization that happens at high strain rate deformations.

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Cold Spray Additive Manufacturing is a technology capable of mass manufacturing components with complicated geometry and coating substrates in hard-to-reach areas. In addition, cold spray also has the ability of conducting a green manufacturing process, with zero waste of renewable feed material, and zero gas and chemical emission. This paper investigates solely cold spray as an additive manufacturing technology with cork as the natural material. CFD results were used to predict the physical behavior of air and the cork particles. After unsuccessful coatings, final results showed that when moisture is added, cork is successfully cold sprayed, and agglomeration is experienced. Following these results, high speed camera and Hopkinson bar tests concluded that pressure is the only significant parameter that drastically effects the disposition quality of the cork coating. This is the first reported result of cork powder being cold sprayed, in addition to groundbreaking results of successfully coating an Aluminum substrate without a binder. Key words: cork, powder, additive manufacturing, natural materials, cold spray, binder, deposition efficiency, coating, high speed camera, Hopkinson bar.

Compared to traditional thermal spray, cold spray as a new emerging surface treatment eliminates or substantially reduces phase transformation of deposited material and reduces coating porosity. Therefore, the appearance of this new type of surface treatment and additive manufacturing process has attracted considerable attention from researchers. In this research, three-dimensional modeling of Al6061-T6 particle impact and cohesion process was simulated by utilizing commercial finite element analysis (FEA) software ABAQUS/Explicit. To guarantee that a stable bonding phenomenon can be realized in the scope of physical validity, a built-in cohesive contact behavior model was implemented in the simulation to understand the bonding phenomenon. A non-planar surface was introduced to replace the usual planar impacted surface to mimic micron-scale curvature of the sprayed target in the real condition. Simulation models of spraying particles impact on positions with spray angle corresponding to 90°, 80°, 70° were created to investigate the effect generated by the curvature for the residual stress after bonding. Curvature function was exploited to describe the non-planar surface wavy condition derived from optimized impacting angle for achieving bonding phenomenon. This numerical simulation work can provide further insights for the residual stress evolution status in the condition of realized cohesion between impactor and non-planar surface after a kinetic peening process. Beneficial suggestions toward cold spray technology utilization in additive manufacturing areas are concluded from the results of the numerical simulation.

This investigation aims to understand and improve the deposition quality and rates of cold spray for additive manufacturing in a way that is economically sound and without the detrimental temperature effects seen in traditional metallic additive manufacturing processes. It focuses on materials that are desired by the additive manufacturing community and built upon the current knowledge in cold spray. This thesis is presented as a collection of published, or soon to be published, manuscripts accompanied by an introduction, literature review, and conclusion. The effect of a non-spherical particle morphology was the first objective investigated. Titanium has been shown repeatedly to require pure helium at very high temperatures and pressures to get dense coatings, however, the unique coral-like morphology resulting from the Armstrong Process was revealed as a key to successful deposition with nitrogen. Using low pressure cold spray, under conditions that would be considered mild, a deposition efficiency of 100% and a porosity of nearly 0% was achieved. This is a promising approach for cold spray as a method for additive manufacturing of titanium parts. The low powder cost and the advantages of additive manufacturing could allow for a substantial cost savings in titanium part production when compared to traditional manufacturing methods. With these cost saving advantages, additive manufacturing of titanium using Armstrong process powder and CS could lead to a paradigm shift of titanium production, allowing titanium to enter markets that under traditional methods would be far too expensive. Unfortunately, this unique powder morphology was not available in other materials. To address the low deposition efficiency of the other metals of interest, such as aluminum and stainless steel, the concept of mixing the propellant gas was introduced in the second objective. Considering the relative costs of gases, powder, electricity, and labour, the second paper focuses on the concept of optimizing the amount of helium to produce the minimum component cost. It was found that for the specific stainless steel and aluminum alloy powders discussed, costs could be reduced by 44% and 59%, respectively, using the gas mixing system. However, no cost saving was found for the most inexpensive of the powders, pure aluminum. For gas mixing to be effective, the cost of helium must be offset by the cost of the powders. Therefore, low-cost powders, such as pure aluminum, results in pure nitrogen as the least expensive option. This however doesn’t address the low deposition efficiency that is preventing its adoption in cold spray additive manufacturing. The third objective addresses just this, an improvement in deposition efficiency without the introduction of expensive helium. In this study, aluminum particles were preheated using a novel particle preheater that does not clog. This resulted in a deposition efficiency increase of 260% with a minimal increase in electrical costs. These three objectives, while studied and published separately, all relate to the purpose of this work to improve the process economics without detrimental temperature effects. These findings have been (or will be) published in international peer reviewed journals to add to the collective knowledge.

Engineered components can gain desirable properties when coated with surface materials. Wear-resistant coatings can improve the performance of contacting surfaces and allow for an extended life of the parts. Hard chromium has been the plating material of choice for certain wear and corrosion- resistant coatings because of its desirable combination of chemical resistance, adhesion, and mechanical properties. However, hexavalent chromium, a component of the process for applying hard chromium coatings, has been recognized by the EPA as having hazardous health and environmental impacts. Existing and planned environmental regulations restricts the use of process chemicals containing hexavalent chromium ions. This substantiates a need to develop an environmental friendly process for alternative coatings. Praxair has reported that Cr-Ni-C particles have a better corrosion resistance than current chromium carbide and nickel chromium powders. Today, Cr-Ni-C provides great qualities for flame spray and does not contain the toxic compounds used to deposit hard chromium, but is not compatible with application by cold spray. The purpose of this thesis project is to compare two processes for plating metal powder, chromium nickel carbide (Cr-Ni-C, CRC-410-1 from Praxair), with nickel. The particles were encapsulated using three different methods: one electroplating method previously used on particles, and two electroless plating processes using different solutions. The Cr-Ni-C particles were successfully encapsulated with Ni by one of the electroless deposition methods. The electrolytic deposition experiments did not yield the uniformity of coating without agglomeration that is being attained in industrial practice today. Further research on this method is recommended, due to the material operational cost in an industrial setting that is projected to be over 200 times cheaper than electroless deposition method. In the meantime, it should be possible to produce enough coated powder by electroless deposition to validate the utility of this coated powder in depositing wear- and corrosion-resistant coatings of Cr-Ni-C by cold spray.

Le principe de la projection dynamique par gaz froid ou « cold spray » repose sur la projection de particules de poudres convoyées par un gaz à des vitesses supersoniques vers un substrat. La déformation des particules à l’impact avec ce dernier permet la construction d’un dépôt. Ce procédé permet de conserver la microstructure des particules de poudre et de produire des dépôts peu poreux. Cette dernière caractéristique est essentielle dans le cadre d’applications anticorrosion. L’ambition de la thèse est de comprendre le rôle de la microstructure sur les mécanismes de corrosion marine d’un dépôt à base d’aluminium élaboré par cold spray. Pour atteindre cet objectif sont projetées des poudres à base d’aluminium (aluminium pur, alliages d’aluminium et mélanges avec ajout d’alumine) sur un substrat en acier. Les microstructures des dépôts sont étudiées jusqu’à l’échelle nanométrique (MET). L’adhérence des dépôts est mesurée par l’essai de plot collé. A partir des microstructures sont proposés plusieurs mécanismes de formation de la porosité dans un dépôt cold spray à différentes échelles. Une étude numérique par éléments finis complète cette analyse microstructurale. Grâce aux mesures de la vitesse (DPV-2000) et de la température (caméra thermique) d’impact des particules, les paramètres de nouveaux modèles matériau sont optimisés pour simuler le comportement de l’aluminium et de l’alumine à l’impact. De plus, plusieurs essais de corrosion marine (immersion et brouillard salin) sont conduits. L’étude des microstructures corrodées permettent d’établir différents mécanismes de corrosion du dépôt cold spray. Un lien entre la porosité du dépôt et son comportement en corrosion est notamment montré. Enfin, une première approche du transfert de technologie du procédé à l’échelle industrielle est décrite. / Cold spray process is based on spraying particles carried by a gas at a supersonic speed onto a substrate. Particle deformation during impact with the substrate creates a coating. This spraying process can retain particle microstructure and produce very dense coating. This property is crucial for anticorrosion applications. The aim of this work is to understand the effect of cold spray aluminum coating microstructure on marine corrosion mechanisms. To achieve this goal, several aluminum powders (including pure aluminum, aluminum alloys and mixtures with alumina) are sprayed onto a steel substrate. Coating microstructure is studied down to a nanoscale (TEM). The coating-substrate bond strength is determined using pull-off testing. From a thorough microstructure study, various mechanisms are proposed to explain multiscale porosity formation in coatings. A numerical study using finite elements modeling complements this microstructure analysis. From particle speed (DPV-2000) and temperature (thermal camera) measurements during impact, new material models are optimized to model aluminum and alumina behavior at particle impact. Moreover, corrosion tests are conducted (including immersion and salt spray tests). The study of corroded coating microstructures is used to identify corrosion mechanisms which occur in the coating. A relationship between coating porosity and its corrosion behavior is particularly brought into light. Finally, a first approach to a technological transfer of this process to an industrial application is proposed.

Le Cold spray est une technique de réalisation de dépôts épais par projection à haute vitesse de particules. Pour cette technologie, la température du gaz vecteur reste inférieure au point de fusion de poudres projetées. Dans ce cas, les mécanismes d’adhésion sont liés aux hautes déformations plastiques que subissent les particules lors de leur impact avec le substrat. Parmi la grande variété de poudres disponibles, trois compositions ont été retenues pour ce travail. Elles autorisent l’élaboration (i) d’alliage d’aluminium, (ii) d’acier inoxydable et (iii) de magnésium. L’ajout de particules de SiC (en fonction de leur quantité ou taille) aux poudres d’aluminium a également permis de modifier les propriétés mécaniques (telle que la dureté) des couches produites. En formant des couches denses et très peu poreuses, les revêtements cold spray présentent tous les atouts des revêtements anti-corrosion. Ce travail de thèse s’est attaché à comprendre les relations existantes entre les paramètres de projection de poudres (température et pression du gaz vecteur, concentration et tailles des particules de SiC) et la qualité du revêtement obtenu, de définir les interfaces substrat / revêtement en fonction de leur composition chimique et leurs influences sur les propriétés de protection vis-à-vis de la corrosion du substrat. D’un point de vu microstructural, les résultats obtenus montrent que l’augmentation de température du gaz améliore la densité des revêtements. En diminuant le nombre de défauts mais également en optimisant la qualité de l’interface substrat/revêtement, la résistance à la corrosion se trouve également améliorée. Sur la base des différences de potentiel entre le revêtement et le substrat, il est possible de classer la nature des couches selon (i) les revêtements sacrificiels et (ii) les revêtements cathodiques. Quel que soit leur nature, les revêtements obtenus par cold spray présentent tous de bonnes propriétés barrières. Toute fois le mode de dégradation des revêtements sacrificielles a pu être assimilé à de la corrosion intergranulaire en lien avec la morphologie du dépôt mais également la distribution et la taille de particule SiC (cas particulier du revêtement d’aluminium). Si les essais de corrosion longue durée ne permettent pas d’amorcer la corrosion du substrat après dissolution du revêtement (pour les couches sacrifielles), des essais de corrosion galvanique autorisent une discrimination rapide de l’efficacité de la couche barrière. Ces tests électrochimiques sont également l’occasion de discuter des effets de la rupture d’un revêtement sur les cinétiques de corrosion des matériaux qu’ils protègent. L’ensemble des caractérisations métallurgiques ainsi que les tests électrochimiques menés sur les différents assemblages substrat/revêtements indiquent que la technique de cold spray est une méthode de choix pour la protection des matériaux de structures vis-à-vis de la corrosion. / Cold spray is a relatively new coating technology in which coatings are produced by powders projected at high velocity. A significant feature of cold spray is that bonding is generated through severe plastic deformation at temperatures well below melting point of feedstock powders. In the present study, kinds of metallic coatings were produced by cold spray, including aluminum alloy coating, pure magnesium coating, magnesium alloy coating, stainless steel coating and SiC reinforced composite coatings. According to the manner in which the coating protects its substrate against corrosion, these cold sprayed coatings can be divided into two types, i.e. sacrificial anodic coating and noble barrier coating. The objective of this thesis is to verify the feasibility of producing both sacrificial anodic coating and noble barrier coating with high corrosion performance by cold spray, and meanwhile demonstrate the usefulness of electrochemical measurements for the characterization of corrosion protection properties of cold sprayed coatings. Besides material system, process parameters which influence corrosion performance of cold sprayed coatings were studied. Two factors, i.e. process gas temperature and process gas pressure were chosen. Results showed that higher process gas temperature leads to denser aluminum coating. Likely, higher process gas pressure improves denseness and corrosion resistance of stainless steel 316L coating. SiC reinforced aluminum based composite coatings were deposited on aluminum, stainless steel and magnesium substrate. Compared with aluminum coating, the addition of hard ceramic particle affects microstructure of coatings, and improves corrosion resistance by increasing denseness. Ceramic particle fraction and size affect coating microstructure in different ways and also influence corrosion behavior. In view of corrosion process, results indicate that corrosion protection of cold sprayed coating could be divided into two steps. In the first step, substrate is completely shielded by dense coating, no corrosion reaction occurs on substrate. In the second step, two types of coatings show totally different behavior. In the case of sacrificial anodic coating, substrate is under cathodic protection in galvanic couple; hence no corrosion (or weakened corrosion) happens on substrate. In contrast, when the coating is noble than substrate, the protection effect would be immediately interrupted once corrosive electrolyte penetrates through coating to interface. The overall results indicate that cold spray is a highly reliable alternative for production of coatings in anti-corrosion applications. Electrochemical measurements are useful tools for quality evaluation of corrosion behavior of cold sprayed coatings.