Composite materials are usually multi-phase materials, made up from two or more phases, which are combined to provide properties that the individual constituents cannot. This technology represents an economical way to improve product performances avoiding the use of expensive materials. Composite materials can be obtained as films by means of the electrolysis of electroplating solutions in which micrometre- or submicrometre-size particles are suspended: variable amounts of these particles become incorporated in the electrochemically produced solid phase, to which they impart enhanced properties. The main aims of the present work contributing to this thesis are the study of different parameters influencing the electroco-deposition process in order to promote and improve the applicability of such a technology in the high speed electroplating industry. Following a comprehensive review on the electroco-deposition of composite coatings, the phenomena have been analysed moving from a microscopic point of view i. e. the role of the metal ions present in the electrolyte and adsorption on the inert particles and their interactions with the growing metal layer, to a macroscopic point of view i. e. the electrolyte agitation, its influence on particle motion and all the issues related to the presence of particles in an electrolyte during electroplating. In particular the inert particle influence in terms of geometry, dimension and chemical nature (spherical polystyrene particles vs. irregular alumina particles with different dimensions), the metal matrix influence (nickel, copper and zinc), the influence of electrolyte agitation (using a Rotating Cylinder Electrode cell system) and the influence of the coating thickness on particle content in the final coating, using different deposition times, have been examined. The importance of the particle shape has been highlighted showing how incorporating irregular geometries gave higher particle incorporation densities than regular geometries. The influence of the substrate finishing in terms of imperfections has been related to the particle incorporation rate showing how small surface imperfections enhanced the incorporation of particles. Different hydrodynamic regimes have been analysed resulting three different regimes being discerned: laminar, transitional and turbulent. The consequence, in terms of particle incorporation levels, has been found showing how the amount of particles in the coating changed from one regime to another. Different rate-determining steps were related to the hydrodynamics: when the regime is laminar, particles were incorporated as agglomerates and the process was under particle transfer control, whilst in the turbulent zone, the rate determining step was the velocity of reduction of the ions adsorbed on the particle surface.

Le passage de la technologie au slurry à celle au fil diamanté sur les machines à fils de découpe des blocs de silicium en wafers est motivé par des enjeux économiques et environnementaux. Depuis peu, cette transition de technologie dans l’industrie photovoltaïque s’est accélérée avec la commercialisation d’une nouvelle génération de machines. Afin de profiter de cette transition et de son avenir prometteur, Thermocompact s’est engagé dans le développement de fils diamantés. Le procédé choisi pour le dépôt des particules et du liant métallique enchâssant les particules à la surface du fil est la voie électrochimique. Les premiers essais de fabrication de fils diamantés ont révélé un manque de maîtrise du procédé d’élaboration et un échec pour atteindre les caractéristiques techniques demandées pour la découpe du silicium. Les travaux de cette thèse se sont donc axés dans un premier temps sur la relation entre le bain électrolytique, les conditions de dépôt et ses propriétés, puis sur le comportement des particules à la fois dans le bain jusqu’à leur incorporation à la surface du fil. L’étude s’est poursuivie sur la relation complexe entre les caractéristiques du fil produit, la matière à découper et la machine de découpe utilisée (design, paramètres utilisés). Ce travail a abouti à produire un fil diamanté de diamètre 70µm conforme aux exigences des usineurs pour la découpe à l’échelle industrielle du silicium monocristallin sur des machines de nouvelle génération. Les résultats de découpe vont permettre désormais de démarcher des clients potentiels dans l’industrie photovoltaïque. / The change of technology from slurry to diamond wires in the wafer slicing machines is motivated by economic and environmental issues. Only recently, this transition of technology in the photovoltaic industry has ramped up with the commercialization of a new generation of wafering machines. So as to take advantage of this situation, Thermocompact has launched the development of diamond wires. The selected process is an electrochemical codeposition of metal and diamond particles embedded on the wire surface.The first tests of diamond wire production have shown a lack of process control and a failure to reach the technical characteristics requested by its use. The studies in this thesis are based on the relationship between the electrolytic bath, the coating conditions and the coating properties, then on the behavior of particles both in the bath and up to their incorporation on the wire surface. The researches continued afterwards on the complex link between the characteristics of diamond wire, the material to slice and the machine used for slicing (design, recipe). This work has succeeded in defining a diamond wire with a diameter of 70µm in compliance with customer requirement for the industrial slicing of single crystalline silicon with the new generation of machines. These results will be now used for prospecting new customers in the photovoltaic industry.

Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

Composite coatings have great potential due to the possibility to combine properties of two different materials in one coating. This way, new surface properties can be tailored and applied to any material's surface. Among different manufacturing routes, electrodeposition has the biggest potential in creating composite metal matrix coatings, especially nanocomposites. Nevertheless, there is a knowledge gap between the deposition of composite coatings in laboratory conditions, described in the literature, and those that are now in place on an industrial level. While micro-composites have been industrialised for about ten years, the production of Ni/SiC nanocomposite coatings by electroplating is still far from an industrial manufacturing floor. This is due to the lack of understanding of the mechanisms of nanoparticles codeposition leading to scattering results. The production of nanocomposite coatings is much more sensitive to the process parameters compared to microcomposite. The correlation between parameters and their influence on the codeposition are still not fully identified and understood. The codeposition models proposed in the literature are only valid in specific conditions, but composite depositions behave differently, or even opposite if some of the variables are modified. The main objective of this work is to identify the particle-current-electrocrystallization interactions in the production of Ni/SiC nanocomposites. A series of experiments are designed to isolate single variables and identify the controlling parameters of these interactions and their impact on the final properties. In this thesis, the effect of current density, type of current and particles size are identified as primary variables controlling the metal crystallisation and coatings properties. Among many parameters, a specific current waveform in pulse reverse mode proved to increase the codeposition rate effectively, doubling the content of nanoparticles compared to other techniques. Ultrasound assistance is also considered as stirring method when particles are suspended in the deposition bath to increase their stability and dispersion. The effect of Ultrasound on the particles codeposition and metal crystallisation is studied and compared to silent condition. Moreover, a surface treatment for the particle has been proven successful in making any particle to behave similarly in the Ni deposition bath. Furthermore, the codeposition rate doubled or tripled compared to untreated ones thanks to this treatment. Both ultrasonic agitation and surface treatment reduce the formation of aggregates, improving the particle dispersion and metal microstructure thus increasing the final hardness. The work proved the synergistic effect between particle and metal microstructure which affected the final properties of the coating. Therefore, when tailoring the composite coating to improve hardness, it is not only the amount of the particles that should be considered but also their influence on the electrocrystallisation process. / Kompositbeläggning har stort potential tack vare möjligheten att kombinera två material i samma ytskikt. På detta sätt kan nya ytegenskaper skräddarsys och appliceras på ett materials yta. Elektrodeposition är den tillverkningsmetod som har störst potential att uppnå kompositbeläggningar, i synnerhet nanokompositer. Ett kunskapsgap existerar mellan elektrodeposition under laboratorieförhållanden, som beskrivet i vetenskaplig litteratur, och hur processen går till i industriell miljö. Medan industriell tillämpning av mikrokompositer pågått ungefär tio år, så har produktion av Ni/SiC nanokompositbeläggningar fortfarande inte nått fabriksgolvet. Detta är en konsekvens av bristande förståelse kring mekanismer för samdeposition av nanopartiklar som leder till varierande resultat. Produktion av nanokompositbeläggningar är mycket mer känslig för processparametrar jämfört med mikrokompositer. Korrelationer mellan parametrar och dess inverkan på samdeposition är fortfarande inte fullt identifierade och förstådda. Modeller för samdeposition som föreslås i vetenskaplig litteratur är endast giltiga under särskilda förhållanden. Kompositdeposition kan uppvisa avvikande eller till och med motsatt beteende om variabler förändras. Huvudmålet med detta arbete är att identifiera interaktioner mellan partikel, ström och elektrokristallisering under tillverkning av Ni/SiC nanokompositer. En serie av experiment är utvecklade för att isolera variabler och identifiera de parametrarna som kontrollerar dessa interaktioner och dess inverkan på ytans egenskaper. I denna avhandling identifieras strömtäthet, typ av ström, och partiklars storlek som primära variabler som kontrollerar metallkristallisering och beläggningens egenskaper. Bland många parametrar, visades en specifik vågform på strömmen i omvänd pulsläge öka samdepositionen effektivt, ledande till en fördubbling av andelen nanopartiklar jämfört med andra tekniker. Ultraljud tillämpades som metod för omrörning av depositionsbadet för förbättrad stabilitet och fördelning. Effekten av ultraljud på samdepositionen av metallkristallisering studeras och jämfört med tyst tillstånd. Dessutom har en ytbehandling för partiklarna visats framgångsrik för att få godtyckliga partiklar att bete sig likt Ni i depositionsbadet. Detta ledde till att samdepositionens takt ökade med en faktor av två till tre jämfört med obehandlade partiklar. Både ultraljud och ytbehandling av partiklarna ledde till minskad aggregation vilket förbättrade fördelningen av partiklar och metallstruktur och därigenom ökad hårdhet. Arbetet bevisar synergieffekten mellan partiklar och metallstruktur vilket påverkar beläggningens slutliga egenskaper. Vid utveckling av nya ytbeläggningar ska därför inte bara mängden partiklar beaktas utan även dess interaktion med elektrokristalliseringsprocessen.

The thesis deals with mechanical properties of thin hard wear-resistant coatings. The work presents a method of dynamic testing of thin hard coatings on a newly constructed prototype of impact wear tester. It provides a comparison with standard methods of layer testing and presents new experimental results of dynamic impact wear test of the coatings. Finally, the thesis covers preparation techniques of thin film systems deposited on various substrates and their characterization using optical and electron microscopy.