<div>Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) provide thermal and environmental protection to superalloy components operating within the combustor and high pressure sections of a gas turbine. However, calcium-magnesium-aluminum silicate (CMAS) deposits originated from particulate matter ingested through the air intake degrade YSZ TBCs, ultimately decreasing the overall efficiency of the engines. With the introduction of biofuels into gas turbines, a new list of impurities with no precedent in jet engines may interact with TBCs, arising the possibility to form CMAS deposits without flying in a particular environment and to exacerbate CMAS negative effect through the addition of other contaminants.</div><div><br></div><div>In this work, a cyclic thermal gradient rig was developed to test TBCs in similar conditions as in a gas turbine. The heat flux and non-contact surface temperature measurements were validated with a thermal transient model. The effect of biofuel impurities on YSZ TBCs was evaluated by spraying the coatings with impurity cocktails, solutions containing the impurities of interest, and subsequently testing their lifetimes in the ablation rig.</div><div><br></div><div>Detailed microstructure analysis revealed that APS and EB-PVD TBCs fail in different ways when exposed to equal concentrations of CMAS. When contaminating APS TBCs with varying combinations of CMAS constituents (e.g., S, C-S, C-A, C-A-S, C-M-S, and C-M-A-S), it was possible to identify that coatings delaminated at different rates depending on the combination of CMAS constituents. Finally, the effect of CMAS in combination with contaminants exclusive of biofuels was analyzed on YSZ TBCs. X-ray diffraction (XRD) analysis and micrographs revealed that glass modifiers (e.g., K₂O and ZnO) accelerated the degradation of YSZ TBCs.</div>

In metal cutting applications, development of coatings to reduce friction between tool and chip and also enhance wear resistance of the tool is an important objective. The effectiveness of such coatings is ultimately evaluated through metal cutting trials; however, bench-scale tests can play a role in predicting some aspects of a candidate coating’s performance. This dissertation further develops the concept of an on-axis rotation pin-on-disc tribometer for the evaluation of friction coefficient between tool and work material pairs under temperature and stress conditions similar to those experienced between tool and chip in metal cutting. Firstly, the characteristics of the imprint formed by the spherical-tipped pin in the disc during tribometer tests are studied. Specific focus is given to the growth of the imprint during the rotating stage of the test; the severity of pile-up of work material around the periphery of the imprint; different zones of contact at the imprint surface; and evidence of (or lack thereof) of bulk shear in the surrounding work material below the surface of the disc. The importance of estimating the actual temperature at the pin-disc interface (inaccessible for direct measurement) is also raised. Evidence is presented that suggests the pin-disc interface is higher for tests involving coatings with higher electrical resistivity, despite exhibiting similar temperatures 2 mm above the interface (accessible for direct measurement). A numerical model is developed in an effort to estimate the pin-disc interface during stationary specimen tests for specific pin and disc materials under controlled conditions. An empirical relationship is also established to express the variation of electrical resistivity with temperature for cemented tungsten carbide (6% cobalt content). Finally, coefficient of friction results for coated and uncoated cemented carbide pins in contact with AISI 1045 steel discs are related to short duration turning trials involving the same material pairs. Coatings exhibiting low friction coefficient result in appreciably lower cutting forces, reduced built-up edge intensity and more tightly curled chips. The possibility that the low thermal conductivity of such coatings could be producing similar effects by forcing more heat into the chips is also explored. / Dissertation / Doctor of Philosophy (PhD) / This dissertation further develops the concept of a pin-on-disc apparatus for evaluating the friction coefficient between materials under temperature and stress conditions similar to those experienced in metal cutting. Firstly, characteristics of the imprint formed by the pin in the disc during tests with the apparatus are studied. Specific focus is given to the growth of the imprint during the rotating stage of the test and different zones of contact at the imprint surface. Secondly, the importance of estimating the actual temperature at the pin-disc interface, inaccessible for direct measurement, is raised and a numerical model developed to aid in its estimation. Finally, coefficient of friction results generated on the apparatus are correlated to the magnitude of forces measured and other observations made during metal cutting trials involving the same material pairs.

High strength boron steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength boron steels are usually formed by press hardening at elevated temperatures with a view to facilitate forming and simultaneous hardening by quenching of complex shaped parts.The high strength steel sheets are used with an Al–Si coating with a view e.g. to prevent scaling of components during hot-metal forming. The Al-Si coated high strength steel can lead to problems with galling (i.e. material transfer from the coated sheet to the tool surface) which have a negative influence on the quality of the produced parts as well as the process economy. The available results in the open literature pertaining to high temperature galling are very scarce. With this in view, the friction and wear behaviours of different tool steel coatings and different roughness lay directions sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature reciprocating friction and wear tester at temperature of 900 °C.The results have shown that parallel sliding with respect to the surface roughness lay reduces the severity of galling compared to perpendicular sliding. None of the coatings included in this study have shown beneficial effects in view of galling. The DLC coating experienced less galling compared to the AlCrN and TiAlN. Post polishing of the coated tool steel has resulted in more severe material transfer with higher and more unstable friction. / <p>Validerat; 20111022 (anonymous)</p>

Hard coatings deposited by physical vapour deposition (PVD) are commonly used to improve the scratch resistance and hardness of objects made of softer materials such as steel, and they can also be used as decorative coatings since they exhibit a wide range of different colours. In this research, stainless steel tableware utensils were coated with multilayer Ti/TiCN thin films to give the tableware a wear-resistant decorative finish. A cathodic arc PVD system was used to deposit the coatings since it has the potential to produce very dense coatings with excellent adhesion and wear-resistance properties in relatively short deposition times. Several system parameters were varied between deposition cycles to create a large set of samples which included: changing the amount of flatware present inside of the chamber during deposition, changing the size of the flatware used, changing the mounting location of the flatware inside of the chamber, and changing the depletion level of the titanium cathode targets used to deposit titanium. It was found that changing these variables had an effect on the deposition rate of the coating and thus had an effect on the thickness of the titanium interlayer, which was found to be an important factor in achieving good adhesion of the TiCN layer. The optimal titanium interlayer thickness was found to be in the range of approximately 120 to 230 nm. / Thesis / Master of Applied Science (MASc)

Friction in machining is a complex phenomenon that can directly affect cutting productivity and product quality. Currently, different coatings are developed for machining applications which can increase tool life in the machining processes. Since performing a real machining test to quantify the friction is expensive and time-consuming, developing a bench scale testing method to simulate the friction in machining can reduce the cost and help researchers and industries select a suitable coating for their specific applications. The goal of this work was to study the adhesion between the tool and workpiece material under machining conditions by simulating them using a heavy-load high-temperature tribometer. A high normal load was applied to plastically deform the workpiece material. The contact zone was then heated up using a resistance heating method. The normal load should be in the range that can generate a plastic flow on the surface of the workpiece material prior to seizure. Three groups of in-house coatings were tested to study the effects of coating deposition parameters on the coefficient of friction. The results of these tests showed that the coating with the lowest bias voltage and highest Nitrogen pressure had the best tribological performance. As a next step, three different commercial coatings were selected. Super duplex stainless steel was chosen as the workpiece material and the tribometer tests were performed. To validate the tribometer results real machining tests and tool wear analysis were performed. AlTiNOS+ WC/C was observed to be a lubricious coating which reduced the cutting force and coefficient of friction during the running-in stage. However, the low hardness of the coating provided little abrasion resistance and was removed after the first pass. AlTiNOS+ TiB2 demonstrated a good combination of hardness and lubricity associated with improved coating tribological performance as well as wear resistance. / Thesis / Master of Applied Science (MASc)

Super Duplex Stainless Steels (SDSS) are widely used in offshore oil and gas industrial components. They are dual phase materials consisting of ferrite and austenite in similar ratios with high contents of chromium and presence of molybdenum. This combination of microstructure and chemical composition results in enhanced mechanical strength and corrosion resistance. However, this material has poor machinability, exhibiting the following characteristics: (i) tendency to strain-harden; (ii) extreme adhesive behaviour; and (iii) high cutting temperatures. These circumstances not only result in high tool wear rates, but also lead to poor surface integrity due to the work hardening effect, high roughness and tensile residual stress. To minimize these detrimental effects, PVD coating technologies have been widely applied to cutting tools due to their tribological properties exhibited during cutting, which reduce friction and diminish heat. In this work, three different PVD coatings were tested during the turning of super duplex stainless steel of grade UNS S32750. In addition to the tool performance, surface integrity was assessed by surface texture analysis, residual stresses and hardness profile. The electrochemical behaviour of the machined surface was evaluated by potentiodynamic anodic polarization measurements. Stress cracking corrosion (SCC) tests were also performed. Results indicate a relationship between the tool performance and surface electrochemical behaviour, where the tool with best cutting performance, AlTiN, also presented the best electrochemical behaviour. Stress cracking corrosion was found to be associated with residual stresses on the workpiece, among the three tested PVD coated tools the AlCrN/TiSiN showed lowest tensile residual stresses and lowest SCC susceptibility. The surface generated by AlTiN coated tool presented the highest levels of tensile residual stresses, resulting in a higher SCC susceptibility. / Thesis / Master of Applied Science (MASc)

Ce travail de thèse est une contribution au développement d’afficheurs électroluminescents inorganiques utilisant le luminophore CaTiO3 :Pr3+ comme couche active. Il comporte deux volets. Le premier concerne l’étude du dépôt de CaTiO3 :Pr3+ par pulvérisation cathodique à partir d’une cible céramique élaborée au laboratoire et s’est plus particulièrement attaché à l’influence de la pression de dépôt et aux conditions de recuit (température, type de fours) sur les propriétés morphologiques, structurales, optiques et électriques des films. Les films obtenus sont cristallisés en structure orthorhombique, photoluminescents, transparents sur toute la gamme du visible et possèdent des propriétés électriques compatibles avec l’application visée. Des pistes d’optimisation de ces propriétés sont également avancées. Le second volet du travail utilise le modèle de transfert de charge par intervalence (TCIV) développé ces dernières années au laboratoire, pour orienter la recherche d’autres luminophores dopés par des ions Pr3+ utilisables dans des afficheurs électroluminescents. Sur cette base, des titanates de formulations (Ca,Sr)TiO3 :Pr3+, CaTiO3 :Bi3+ ;Pr3+ et Na1/2Ln1/2TiO3 :Pr3+ (Ln = La, Gd, Y, Lu) ont été synthétisés et caractérisés. L’évaluation détaillée du comportement de ces matériaux en photoluminescence a permis de valider le modèle TCIV, d’initier d’autres modèles et de mettre en évidence l’intérêt d’un codopage au bismuth pour accroître l’intensité de fluorescence de l’ion Pr3+ dans la matrice CaTiO3. Le luminophore rouge CaTiO3 :Bi3+ ; Pr3+ apparaît être un candidat intéressant pour des applications en électroluminescence. / This work reports on the pre-development of inorganic electroluminescent devices based on luminescent CaTiO3 :Pr3+ thin films. It includes two parts. The first part is dedicated to the deposition of CaTiO3: Pr3 + films by sputtering of a home-made target and post-treated for their crystallization. Influence of gas pressure during deposition and post-treatment conditions (temperature, oven…) on the morphology, structure, optical and electrical properties of the films was investigated. Finally, the possibility to obtain films crystallized in the orthorhombic phase, photoluminescent, transparent in the whole visible range and with electrical properties needed for the aimed application, was demonstrated. Conditions for further optimization are also given. The second part of the work aims to use the Intervalence Charge Transfer (IVCT) model that has been recently elaborated in the laboratory, as a tool for the design of new Pr3+-doped phosphors that could be integrated in electroluminescent devices. On this basis, the titanates (Ca,Sr)TiO3 :Pr3+, CaTiO3 :Bi3+ ;Pr3+ and Na1/2Ln1/2TiO3 :Pr3+ (Ln = La, Gd, Y, Lu) were prepared and characterized. The detailed analysis of the photoluminescence behaviors confirmed the IVCT model and allowed to propose new models. Further, the role of Bi3+ codopant as a sensitizer of the Pr3+ luminescence in CaTiO3 is demonstrated and interpreted. The red phosphor CaTiO3 :Bi3+ ;Pr3+ appears as a possible interesting candidate for applications in electroluminescence.

L'électrolyse de la vapeur d'eau à haute température et sous pression avec des électrolytes à conduction protonique est un moyen envisagé pour produire massivement de l'hydrogène à un coût compétitif. Pour être fonctionnelle, une cellule d'électrolyse doit être hermétique vis-à-vis de l'extérieur et entre le compartiment anodique (O2 et H2O) et le compartiment cathodique (H2). Ainsi, la réalisation de liaisons céramique-métal est nécessaire, soit pour l'intégration de l'électrolyte (liaison perovskite-métal), soit pour l'intégration d'alimentations électriques (liaison alumine-métal). Compte-tenu des conditions de fonctionnement de la cellule (600°C, 50 bars, vapeur d'eau), seul un procédé de brasage est envisageable pour réaliser des jonctions résistantes mécaniquement et hermétiques. L'expertise des processus de corrosion sous vapeur d'eau a permis de définir la partie métallique et la brasure pour cette application et a montré que des alliages spécifiques étaient requis. L'étude de métallisation des céramiques par PVD pour permettre le mouillage de la brasure au moment du brasage a montré que la présence d'une barrière de diffusion était nécessaire, pour éviter la dissolution du dépôt lors du passage à l'état liquide de la brasure. Après une étude de mouillabilité à chaud de la brasure sélectionnée sur les céramiques métallisées et les substrats métalliques, les liaisons ont été optimisées en appliquant la méthodologie des plans d'expériences sur des éprouvettes normalisées. L'ensemble des résultats a ainsi conduit au développement de liaisons céramique-métal possédant de bonnes propriétés mécaniques (Rm = 60 MPa à 20°C) et hermétiques. / Steam electrolysis at high temperature and under pressure with protonic conduction electrolyte is a way to produce hydrogen massively at low cost. To operate, an electrolysis cell must be hermetic especially between the anodic compartment (O2 and H2O) and the cathodic one (H2). Thus, ceramic to metal assemblies are needed, either to insert the electrolyte (perovskite-metal junction) or to realize power supply (alumina-metal junction).Considering the operating conditions (873°K, 725 PSI, steam), only a brazing process is possible to realize strong and hermetic junctions.The evaluation of corrosion process under steam pressure has enabled to select a metallic component and a brazing alloy for this application, and has shown that specific alloys are needed.The studies of ceramics metallization by PVD to assure the brazing alloy wetting throughout the brazing process have shown that a barrier diffusion was necessary to avoid the dissolution of coatings when the brazing alloy become liquid.After wetting experimentations of the chosen brazing alloy over the metalized ceramics and the metallic substrate, ceramic to metal assemblies have been optimized in applying the experimental design methodology on standard samples (ASTM).The whole results have enabled to develop hermetic ceramic to metal assemblies having good mechanical properties (Rm = 8700 PSI at 300°K).

Neste trabalho foram produzidas camadas de boretos de elevadas durezas e resistências ao desgaste nos aços AISI H13 e AISI D2, por meio de tratamento termo-reativo em banho de bórax com adição de 10% de alumínio. Posteriormente foram realizados tratamentos pela técnica PVD sobre as camadas de boretos. As amostras foram caracterizadas por meio de microscopia óptica, microscopia eletrônica de varredura, ensaios de dureza e ensaios de micro desgaste abrasivo com esfera livre. Para ambos os materiais, os tempos de tratamento de boretação foram de 4 horas, seguido de resfriamento em óleo ou ao ar. As camadas produzidas por boretação no caso do aço AISI H13 apresentaram espessura média de 70 &mu;m e para o aço AISI D2 espessura média de 100 &mu;m. As durezas das camadas de boretos produzidas variaram de 1500 a 1700 HV. Os ensaios de micro desgaste abrasivos com esfera livre foram realizados com uso de solução abrasiva de carboneto de silício. Todas as camadas produzidas apresentaram resistências ao desgaste muito superiores as dos substratos. As amostras com tratamentos duplex boretação-PVD apresentaram os melhores desempenhos ao desgaste, seguidas pelo aço AISI D2 e AISI H13 boretados e por último os aços AISI D2 e AISI H13 temperados e revenidos. / Borides layers with high hardness and wear resistances were produced on AISI H13 and AISI D2 steels by thermo-reactive treatment in borax added with 10% of aluminum. Subsequently, treatments by the PVD technique were performed on the layers of borides. The samples were characterized using Optical Microscopy, Scanning Electron Microscopy, hardness testing and free-ball micro abrasive wear test. For both materials, the boriding treatment times were 4 hours long, followed by cooling in oil or air. In the case of AISI H13, the layers produced by boriding showed an average thickness of 70 &mu;m while AISI D2 steel presented an average thickness of 100 &mu;m. The hardness of the produced boride layers ranged from 1500 to 1700 HV. The micro abrasive wear tests were performed using abrasive solution of silicon carbide. All produced layers showed wear resistance much higher than the substrates. Samples with treatments duplex PVD-boriding presented the best wear performances, followed by AISI D2 and AISI H13 borated steels and finally, AISI D2 and AISI H13 steels quenched and tempered.

La spintronique est un nouveau domaine de recherche qui exploite l'influence de la caractéristique quantique de l’électron (le spin) sur la conduction électrique. Pour réaliser des composants de spintronique innovants, l’obtention des semi-conducteurs ferromagnétiques à température ambiante devenait un challenge international. Dans ce contexte, après les premières prédictions théoriques de la haute température de Curie de Zn1-xCoxO et les rapports contradictoires sur l'état magnétique de ce système, nous nous sommes attaché à étudier le semi-conducteur magnétique dilué Zn1-xCoxO. Une étude ab initio des propriétés structurales, électroniques et magnétiques du Zn1-xCoxO a été effectuée en utilisant la méthode de pseudopotentiels dans le cadre de la théorie de la fonctionnelle de la densité (DFT) avec les deux approximations GGA et GGA+U. En parallèle, des films minces de Zn1-xCoxO ont été synthétisés par co-pulvérisation cathodique magnétron en condition réactive avec différentes conditions d’élaboration. Les propriétés structurales, morphologiques, électriques et magnétiques ont été analysées par différentes techniques de caractérisation et confrontées à celles obtenues par l’étude ab inito. / Spintronic is a new field of research exploiting the effect of the quantum property of the electron (spin) on the electrical conduction. In order to realize innovative spintronic components, ferromagnetic semiconductors obtained at room temperature became an international challenge. In this context and following initial reports of high Curie temperature and contradictory reports on the magnetic states of this system, we investigated the diluted magnetic semiconductor Zn1-xCoxO. An ab initio study of structural, electronic and magnetic properties of Zn1-xCoxO was performed using the pseudopotentials method within the framework of density functional theory (DFT) with both GGA and GGA+U approximations. In parallel, thin films of Zn1-xCoxO were synthesised by reactive magnetron co-sputtering with different deposition conditions. The structural, morphological, electrical and magnetic properties were analyzed by various characterization techniques and compared with those obtained by ab inito study.