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The potential to produce coatings with enhanced properties has made high power impulse magnetron sputtering (HiPIMS) an area of great interest within the surface engineering community in recent years. Many papers and conference presentations are coming from the academic community but, at present, industry is slow to take up the technology due to known or perceived processing issues (low deposition rates, power supply instabilities, difficulties with reactive process control, etc.). Also, as yet, few applications have emerged to convince industry that this technology merits the significant investment required to move from lab-scale to production-scale processing. During this thesis a thin (>1 μm) aluminium doped zinc oxide film with a resistivity of 3.38.10-3 Ωcm has been achieved, without annealing of the coating, with low absorption of k - 3.4.10-3. A relationship between peak power and deposition rate has been explored in order to provide further understanding of the coatings produced by HiPIMS. These coatings have simultaneously been deposited onto 12 μm PET without damage to the substrate during static deposition under stable plasma conditions during coating runs of over 15 minutes. Further investigation showed that this resistivity relates to enlarged grain growth in the film and that enlarged grains may also be grown for thin films of an industrially relevant thickness, 100 nm. Further structural modifications have also been made in terms of microstructure of the films and surface roughness, when compared to films prepared by conventional methods such as direct current magnetron sputtering. Further insight into the HiPIMS process has been gained through a study of optical emission spectroscopy and hysteresis for the HiPIMS plasma and, whilst complete understanding of the process has not been attained, the complications and need for multi-parameter analysis have been put forward to aid further research in the field. To increase the understanding gained during this work, titania coatings have also been made as this material proved easy to use during experiments (the reactive zinc oxide process was prone to significant electrical arcing). This also provided a second material for use as comparison. Aluminium doped zinc oxide coatings were also produced by atomic layer deposition, again as a point of comparison to HiPIMS between two very different techniques. This thesis provides additional insight into the process control of commercially useful aluminium doped zinc oxide films to aid with the development of the process for the industrial scale. It also demonstrates that such films can be grown to an industrially relevant scale with the option to deposit these films on thin polymeric web without damage to the substrate. In this manner, the potential of the process is demonstrated although further optimisation would be required for production of the material. The commercial promise of the process is shown; an important factor for the future of HiPIMS technology.

The research described with in this thesis, investigated three surface engineering coatings created by three differing technologies; selectively plated nickel sulfamate, ferritic and austenitic nitrocarburizing and atmospheric plasma sprayed titanium aluminide nano-coating. The microstructures, phase and chemical compositions, mechanical properties and corrosion resistance of the three coatings were studied. An important and innovative outcome of this research was the investigation into how heat treatment influenced the structure and properties of the coatings. The influence of processing parameters was also investigated with in this research, with coatings created using varying parameters so that their effect could be measured. Key and new results relating to the as-coated and heated samples were derived by this work, with trends identified by changing the processing parameters identified

The wetting phenomena related to superhydrophobic and superhydrophilic surfaces have been investigated over the past decade with attention on the micro and nano-scaled structures. Particularly, nanoparticles have been applied to create the structures and change surface wettability. In the present PhD work, it is aimed to produce extremely wettable and non- wettable surfaces out of Si02 nanoparticles and study the characteristics with respect to wetting and surface structures. The nanoparticles are presented and prepared in various solutions, which will be then deposited for the creation of micro and nano-scaled structures. Since the sizes of the individual nanoparticles are extremely small and different, the formed structures and therefore the wettability will be influenced accordingly. Various concentrations of nanoparticles in the solutions are set. The experiments are performed to characterise the wettability of the formed surfaces. The static contact angles are measured, while it is also needed to measure the advancing and receding contact angles for some cases, especially on the superhydrophobic surfaces. The structures of the surfaces are observed using Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). It is noticed that the wettability of the formed surfaces is related to the concentration of nanoparticles, and the size can also make a difference in surface structures. The investigation further explores a variety of experimental conditions where the prepared solutions are promptly evaporated. This significantly changes the surface wettability and leads to very distinctive surface structures. The experimental work demonstrates that the surface structures and roughness play an important role in prompting the wettability of a solid surface. The distribution and assembling of Si02 nanoparticles on surfaces are connected to the processing conditions. Under these circumstances, the uniformity and consistency of the formed surface structures in micro and nano-scale are closely related to the size of nanoparticles. Thus, the use of Si02 nanoparticles for the creation of surface structures and the exhibited characteristics are reflected through the investigations and discussions in this PhD thesis. It sets up a platform to compare and examine the suitability of the theories for wetting phenomena on the formed surfaces, and provides good references for future work on the features of functional surfaces based on various nanoparticles.

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Le frittage et le traitement par laser sont des techniques remarquables, couramment utilisées dans de nombreux domaines d’applications du fait des qualités qu’ils confèrent aux surfaces traitées. Ces technologies permettent de substantielles économies d’énergie comparée aux traitements de surfaces conventionnels. Le chauffage est par ailleurs, strictement localisé à la zone choisie. Notre recherche a pour objectif de développer une fine couche de verre de silice à la surface de céramiques poreusescomposites : le diborure de zirconium-carbure de silicium (ZrB2-SiC) et le diborure de titane-carbure de silicium (TiB2-SiC) frittées avec une porosité contrôlée d’environ 30%. La principale application de ces matériaux concerne les piles à combustibles protoniques fonctionnant à basse température (de type LTPCFCs). Les poudres ZrB2-SiC et TiB2-SiC sont soigneusement mélangées et pressées à froid dans un moule à la pression de 40 MPa. Le frittage naturel est conduit dans un four à 1900 et 2100 °C durant 2,5 heures, sous atmosphère contrôlée d’argon. Après polissage, le traitement de surface est effectué par laser verre-ytterbium. Les paramètres du traitement ont été optimisés (puissance et trajet du faisceau laser, temps de traitement, atmosphère) et ont permit d’obtenir une couche superficielle d’un verre à forte conduction protonique, sans affecter la structure et la composition des couches situées au-dessous de la surface. Les échantillons ont été caractérisés en utilisant les méthodes classiques : EDS, XRD, MEB, microscopie optique. Les meilleurs résultats ont été obtenus avec des échantillons de composition 61 mol. % ZrB2-SiC et 61 mol. % TiB2-SiC traités thermiquement a 1900 °C. La porosité obtenue, de l’ordre de 30%, assure une bonne circulation des gaz. La couche de verre produite sur le composite ZrB2-SiC, d’une épaisseur moyenne de 8 μm, est continue et exempte demacro fissuration. Une microfissuration est cependant détectée par MEB aux plus forts grossissements. Les essais ont été conduits à plus haute température de frittage (2100 °C) et avec des compositions différentes dans le but d’améliorer les propriétés du substrat. ZrB2-SiC. A la composition de 80 mol. % ZrB2-SiC les analyses révèlent la présence de cristaux de forme cuboïdale, attribuée à la formation de carbure de bore B4C dont la formation est admise par l’analyse thermodynamique. Les essais sur le composite ZrB2-SiC conduisent à l’apparition de bulles et de défauts dans la couche de verre. Une optimisation des conditions de traitement sera nécessaire pour contrôler ce phénomène. Cette étude démontre qu’il est possible de développer des couches poreuses de matériaux céramiques de type ZrB2-SiC, et de former à leur surface une couche de verre dense et exempte de fissuration par traitement laser. Les propriétés générales de cette couche permettent d’envisager une utilisation comme électrolyte solide dans les piles à combustibles de type LTPCFCs. / Sintering and laser are a remarkable technology with a broad range of applications especially material processing. It offers a wide variety of desired surface properties depending on the type of usage. Sintering allows high reliability and repeatability to the large mass production. Laser benefits in the aspect of energy saving compared to conventional surface heat treatment due to the heating is restricted and localized only to the required area. Therefore, this research aims to develop a silica-glass-layer onto a porous non-oxide, Zirconium Diboride-Silicon Carbide (ZrB2-SiC) and Titanium Diboride-Silicon Carbide (TiB2-SiC) ceramic composites by sintering and laser surface treatment for potential application in the Low-Temperature Protonic Fuel Cells (LTPCFCs). ZrB2-SiC and TiB2-SiC mixed powders at different composition were cold-pressed around 40 MPa under ambient environment. Next, the composites were pressureless sintered at 1900 °C and 2100 °C for 2.5 h dwell time under argon atmosphere, respectively. The pressureless sintering was conducted by Nabertherm furnace and followed by surface treatment via an ytterbium fibre laser (Yb). Anew round spiral laser pattern was inspired, designed and scanned onto the surface of pellets to obtain a smooth glass surface layer that acted as proton-conducting (electrolyte) while preserving the beneath structures of laser-treated pellets that served as an electrode. Characterization techniques such as Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS) and X-ray Diffraction (XRD) were performed accordingly onto the samples. Pressureless sintering of 61 mol.% ZrB2-SiC and 61 mol.% TiB2-SiC pellets at 1900 °C exhibited ca. 29% porosity. The resulting porosity was in the best range of effectiveness for gas diffusion. SEM micrographs revealed the formation of semiglassy layer on the surface of sintered 61 mol.% ZrB2-SiC pellets. The bulk structures remained unaffected and unoxidized. SEM micrographs and EDS patterns displayed thatsilica (SiO2) at a thickness of 8 μm, presence on the surface of ZrB2-SiC structures. It demonstrated that the surface treatment by Yb-fibre laser on sintered ZrB2-SiC ceramic composites at 1900 °C had accomplished. The laser surface treatment was ineffective for TiB2-SiC pellets due to several bubbles formation and crack deflection. Nevertheless, at higher magnification of the SEM for laser-treated ZrB2-SiC ceramic composites, cracks were observed. Therefore, the pressureless sintering at high temperature was conducted to improve the ZrB2-SiC structural properties. Sintering at 2100 °C had demonstrated increment of density and at 80 mol.% ZrB2-SiC sintered pellet unpredictably exhibited the presence of boron carbide (B4C) compounds. SEM micrographs revealed the dark cuboidal shapes and XRD patterns identified as B4C peaks. The reactions of B4C formation were proposed andsupported by thermodynamic analysis. In conclusion, the present research had developed a glassy layer on the surface of ZrB2-SiC ceramic composites which has potential in the application of LTPCFCs. It proved that B4C was possible to be developed by pressureless sintering at 2100 °C and it might assist in developing better morphology for ZrB2-SiC ceramic composites.

Des poudres céramiques multiéléments dans le système Si/C/N peuvent être obtenues avec le procédé de spray pyrolyse. Les paramètres de synthèse et leur influence sur la composition et la morphologie de poudres obtenues a fait l’objet de précédentes études. Toutefois, les mécanismes de décomposition et de recombinaison des espèces dans la zone de réaction restent inconnus. Cette étude vise à approfondir la compréhension du procédé, de la formation de l’aérosol jusqu’aux mécanismes de formation des particules solides. Ainsi, la caractérisation de l’aérosol par ombroscopie laser, couplée à la mise en place d’un modèle numérique du transport et traitement des gouttes du précurseur au sein du dispositif, a permis l’identification de distributions en taille de gouttes de type bimodal jusqu’à leur entrée en zone de réaction. Cette double approche a également permis de vérifier l’effet des phénomènes physiques et hydrodynamiques sur les distributions en taille des gouttelettes lors de leur transport vers la zone réactionnelle. L’introduction d’une distribution bimodale dans le four de pyrolyse permet d’envisager un mécanisme de décomposition du précurseur en deux étapes, lié à la taille des gouttelettes. Cette hypothèse combinée à l’étude de décomposition du précurseur Hexaméthyldisilazane à haute température a permis de proposer des mécanismes de formation de poudres dont la composition chimique varie selon l’atmosphère de synthèse utilisée. / Multielement ceramic powders in the Si/C/N system could be obtained by spray pyrolysis process. Synthesis parameters and their effect on powder chemical composition and morphology have been already studied. Nevertheless, the mechanisms of precursor decomposition and gas phase species recombination that take place in the reaction zone are still unknown. The aim of this study is the comprehension of the process, from the aerosol generation to the solid powders formation mechanisms. The shadowgraphy technique was used to characterize the spray, and coupled with the implementation of a numerical model of droplets transport and treatment through the device allowed to identify bimodal size distributions at the furnace entrance. This double approach let confirm the effect of physical and hydrodynamic phenomenon in drop size evolution. The introduction of a bimodal distribution into the pyrolysis furnace allows to consider a precursor decomposition mechanism in two steps, depending on the drop sizes. This hypothesis combined to the study of precursor decomposition at high temperature led to the proposal of powder formation mechanisms in which their chemical composition varies with the synthesis atmosphere.