MCrAlY coatings are commonly applied as the bond coat in TBCs used in modern gas turbines. Cold spray (or CS), characterized by low process temperature and high particle impact velocity, has been demonstrated as a promising alternative to thermal spray processes, such as air plasma spray (APS) and high velocity oxygen fuel (HVOF), for manufacturing MCrAlY coatings. The general objective of the thesis research is to characterize CS deposition on a single-crystal nickel-base superalloy and to develop low-cost/high-performance NiCoCrAlTaY coatings using the CS technique. Several individual studies were carried out with each having a specific focus towards achieving the general research objective. CS deposition of NiCoCrAlTaY coatings using nitrogen was first examined to verify the feasibility of replacing the expensive helium gas typically used as the CS process gas. Several materials were used as the substrates, and the effects of substrate materials and surface preparation on coating microstructure and properties were investigated. Recycling of non-deposited powder particles was then explored to reduce the costs associated with the feedstock powder. A cost model that includes the economics of powder recycling was developed for the CS process, showing that the use of nitrogen and powder recycling could potentially be cost-effective for CS deposition of MCrAlY coatings. A CS process that can produce in-situ nanocrystalline NiCoCrAlTaY coatings was proposed to develop coatings with enhanced oxidation performance. This CS approach utilizes conventional commercial powders instead of pre-milled nanocrystalline powders. Detailed characterization using the scanning electron microscope (SEM), scanning transmission electron microscope (STEM), and X-ray diffraction (XRD) was carried out to investigate the microstructure of the resulting CS NiCoCrAlTaY coatings, single-crystal substrate, and their interface. Isothermal oxidation performance of the CS NiCoCrAlTaY coatings was evaluated at 1100°C for 1h to 500h. Results revealed that the nanostructure promoted the α-Al2O3 scale formation and sustained α-Al2O3 scale growth, suggesting good isothermal oxidation performance. Finally, the effects of different processing sequences on CS NiCoCrAlTaY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically, CS deposition of NiCoCrAlTaY coatings was carried out on single-crystal superalloy substrates that underwent various degrees of full heat treatments prior to being coated. The remaining superalloy heat treatments required were then performed on the coated samples after the CS deposition. The microstructures of the superalloy substrates and CS NiCoCrAlTaY coatings were characterized after each heat treatment. Isothermal oxidation performance of the coated samples following different sequences was evaluated at 1100°C for 2 hours. The results suggested a promising processing sequence that could potentially further improve the oxidation performance of CS NiCoCrAlTaY coatings.

Les pales de turbine Haute Pression des turbines d'hélicoptères sont soumises à des sollicitations cycliques, thermiques et mécaniques, complexes. L'objectif de ce travail est de caractériser l'influence du cyclage thermique sur le comportement et l'endommagement en fluage de systèmes MCrAlY/superalliage à base de nickel et d'étudier les interactions entre le substrat et le revêtement à haute température. Dans un premier temps, des essais de vieillissement et de fluage isothermes ont été menés afin d'évaluer les dégradations environnementales et mécaniques de systèmes superalliage monocristallin CMSX-4/revêtement NiCoCrAlYTa, déposé selon différents procédés (codéposition électrolytique, projection HVOF). Ces essais de vieillissement isotherme et l'analyse microstructurale qui a été réalisée ont notamment permis d'évaluer le pouvoir protecteur des revêtements entre 950 et 1150°C. Des diagrammes d’occurrence de phases représentatifs de l'état de dégradation de ces revêtements ont été construits et ont montré une équivalence des deux procédés vis-à-vis de la protection du superalliage. Les essais de fluage isotherme ont ensuite confirmé cette équivalence et ont constitué une référence pour les essais de fluage cyclés thermiquement. La comparaison des essais de vieillissement et fluage isothermes a également montré que l’épaisseur de la zone d’interdiffusion entre le superalliage et le revêtement était indépendante de l’application d’une contrainte. Dans un second temps, une étude approfondie de l'influence du cyclage thermique sur le comportement en fluage à 1150°C des superalliages a été menée tout d'abord sur le superalliage MC2, pour évaluer l'effet des paramètres qui caractérisent les cycles thermiques (durée du palier à haute température, vitesses de refroidissement, effet de la température basse du cycle). L'effet du cyclage sur la vitesse de déformation et sur la durée de vie à rupture a été confirmé, et le rôle de la répétition des cycles thermiques sur l'accélération prématurée de l'endommagement de la structure du substrat et la déformation accrue a été mis en évidence. Enfin, le comportement en fluage cyclé thermiquement du système CMSX-4/NiCoCrAlYTa déposé par codéposition électrolytique a été caractérisé aux températures 1050 et 1150°C. Pour ces différentes conditions, particulièrement à 1150°C, il a de nouveau été montré sur ce matériau que les séquences rapides et successives de dissolution - re-précipitation de la phase γ' induisaient une accélération et une généralisation dans le substrat de la déstabilisation de la morphologie en radeaux. Dans une moindre mesure, il a également été montré que le cyclage thermique affecte la zone d'interdiffusion plus en profondeur dans le substrat. / Turbine blades of helicopters are subjected to complex thermal and mechanical cycles. The purpose of this work is to characterize the influence of the thermal cycling on high temperature creep behaviour and damage of MCrAlY coating / single crystal nickel-based superalloys systems, and to study the interactions between the superalloy and the coating. Firstly oxidation and isothermal creep tests have been performed to measure the environmental and mechanical resistance of systems made of CMSX-4 superalloy / NiCoCrAlYTa coating deposited by several processes (Tribomet process and HVOF spraying). Microstructure and chemical composition of both coatings were examined after oxidation and creep testing and quite similar observations were made for both coating processes. The combination of phases and chemical analysis after oxidation testing allowed the establishment of an occurrence diagram of phases for both coating processes, according to temperature and duration of exposure. The obtained diagrams seemed similar for both processes. Finally both processes appeared to be equivalent for the protection of CMSX-4 superalloy in isothermal oxidation and creep conditions. Moreover the growth of the inderdiffusion zone between coating and superalloy is independent of the stress. Secondly the influence of thermal cycling parameters on creep properties of the MC2 single crystal nickel-based superalloy has been studied at 1150°C and 80MPa.We have demonstrated that thermal cycling creep was more damaging than isothermal creep in terms of creep lifetime and rates. Furthermore, the number of low temperature incursions and low cooling and heating rates have severe detrimental effect on creep resistance, whereas the low temperature value of the thermal cycle is not significant. These results specify the role of re-precipitation and dissolution of γ’ particles during thermal cycling creep. Finally the effect of thermal cycling on high temperature creep of thin-walled and coated CMSX-4 single crystal superalloy was evaluated by performing thermal cycling and isothermal creep tests at 1050°C and 1150°C. The deleterious effect of thermal cycling on the creep behavior and lifetime has been confirmed, particularly for the condition at 1150°C and 80 MPa. Furthermore, the number of low temperature incursions has severe detrimental effect on creep resistance on account of the rafted microstructure destabilization induced by these sequences. These results confirm the role of re-precipitation and dissolution of γ’ particles during thermal cycling creep. Thermal cycling infers also on destabilization of subcoating zone in the superalloy but this effect seems to be secondary.

The aim of this research project was to investigate the microstructural changes of MCrAlY coated Ni-based superalloys that are routinely used in industrial gas turbine engines for power generation. One of the main aims of the characterisation was to understand ageing time and temperature effects on the microstructural evolution so that a methodology could be developed where the characterisation of a thermally exposed microstructure can be used to estimate unknown service exposure conditions.

Hot section components in gas turbines can be NiCoCrAlY-coated to provide the component with an Al reservoir that maintains a protective oxide layer on its surface. Over the service life of the component, the coatings degrade by composition and phase changes due to oxidation/hot-corrosion, and multicomponent interdiffusion from and into the superalloy substrate. In this study, the rate of Al interdiffusion into selected Ni-base superalloys using various diffusion couples of two-phase NiCoCrAlY (beta + gamma) and single beta-phase NiAl with the selected alloys is measured. The diffusion couples were examined with an emphasis on the composition-dependence of Al interdiffusion. Microstructural analysis of the NiCoCrAlY vs. superalloys couples is performed to examine the dependence of coatings lifetime on the superalloy composition. The beta-NiAl diffusion couples were analyzed to determine the integrated, apparent and average effective interdiffusion coefficient as a function of superalloy's composition. Concentration profiles were obtained by EPMA of the NiAl vs. superalloy diffusion couples. Findings of this study show that the lifetimes of NiCoCrAlY are heavily dependent on superalloy compositions. The rate of interdiffusion in the diffusion couples is affected by the refractory precipitate phase microstructure structures in the interdiffusion zones as well as by component interactions. The results of the beta-NiAl diffusion couples show that increasing concentrations of Cr, Mo and Ti in the superalloy increase the Al effective interdiffusion coefficient into the superalloy, while increasing concentrations of Al, Ta and W reduce it. Thus NiCoCrAlY-superalloy systems may be designed to produce optimal microstructures in the interdiffusion zone and minimize Al interdiffusion by consideration of these diffusional interactions.

The continued focus to include high hydrogen fuels such as Syngas in aircraft operation to reduce emissions and increase engine efficiency has led to an ongoing investigation into bond coat materials capable of withstanding unfavourable oxidation in high temperature humid environments. The increased presence of water in the engine exhaust leads to increased oxygen activity in the hot section of the engine. In this work, four commercially available MCrAlY bond coat materials were oxidized in high temperature environments with various humidities to understand the behaviours of different reactive element inclusions in resisting high temperature oxidation. Oxidation tests were done at 0%, 18%, and 33% water by volume at 1100C in a 1atm environment to simulate conditions expected in engines using high hydrogen fuels. Oxidation was done for 2h and 20h to observe transient oxide formation behaviour. The surfaces and cross sections of the specimens were examined using SEM and EDS analysis, along with XRD analysis. The progression of surface oxides, TGO thickness, and element depletion zones were observed. Two opposing mechanisms are observed: the upward diffusion of metal cations to the free surface and the inward diffusion of oxygen to the alloy. The presence of water is shown to increase internal oxidation of the bond coat alloy and delay the formation of a protective alumina TGO. Tantalum inclusion in the alloy composition is shown to produce the most stable alumina TGO with the least internal oxidation after 20h exposure in 33% H2O (%vol); the most hostile oxidation environment tested.

[EN] The coaxial laser cladding process is an excellent tool to obtain quality coatings, achieving complete melting and deposition of alloys with high melting point on complex 3D surfaces. In this work we have studied the coaxial laser cladding parameters for MCrAlY coatings (where M = Ni, Co, Fe or combinations of these), commonly used as bond coats in thermal barrier systems, among them: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY and CoNiCrAlY; selecting the laser parameters that allow to obtain overlapping coatings with adequate geometrical aspect ratio, minimum dilution, low porosity and good metallurgical bond with the austenitic stainless steel substrate, by using a 2.2 kW Nd:YAG laser equipment and coaxial head with annular nozzle. The laser coatings have been characterized using various microstructural tech-niques, to identify their constituent phases and the type of microstructure obtained with coaxial laser processing. The mechanical properties were determined by three-point bending tests as well as micro hardness and nanoindentation tests. The high temperature oxidation behavior of the laser coatings and austenitic stainless steel substrate were studied through isothermal oxidation tests at 1100 ºC. The morphology and chemical composition of the oxidized surface were evaluated in detail. The oxidation kinetics and the thermal growth oxide scale, thickness, structure and composition of the oxide layers formed according to the oxidation time were also studied. Finally, friction and wear behavior at room temperature and elevated temperature (500 ºC) were studied by dry sliding tribological tests, in order to obtain the friction coefficient and wear resistance of MCrAlY laser cladding coatings and to compare their behavior with the substrate. The experimental results, allowing to analyze the influence of coaxial laser processing on mechanical properties and high temperature behavior of MCrAlY laser coatings, as well as their comparison with the AISI 304 austenitic stainless steel and MCrAlY coatings obtained by thermal spray processes that are currently used in bond coats. The results indicate that the coaxial laser cladding may be a good alternative to thermal spray processes, because microstructural integrity is improved and defects such as porosity and lack of metallurgical bonding were decreased. These facts, along with the enhancement of the oxidation and the wear resistance of MCrAlY alloys at high temperature, make the coaxial laser process potentially useful to obtain MCrAlY bond coats for new generation of thermal barrier systems. / [ES] El proceso de plaqueado láser coaxial es una excelente herramienta para la obtención de recubrimientos de calidad, logrando la completa fusión y deposición de aleaciones con elevado punto de fusión sobre superficies 3D complejas. En este trabajo se han estudiado los parámetros de procesado láser coaxial de superaleaciones MCrAlY (donde M = Ni, Co, Fe o combinaciones entre ellos), comúnmente empleadas como recubrimientos de anclaje en sistemas de barrera térmica, entre ellas: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY y CoNiCrAlY; logrando seleccionar una combinación de parámetros que permiten obtener recubrimientos por solape de cordones con adecuada relación de aspecto, mínima dilución, bajo nivel de porosidad y buena unión metalúrgica con el sustrato de acero inoxidable austenítico, utilizando un equipo láser Nd:YAG de 2.2 kW y un cabezal coaxial. Los recubrimientos láser han sido caracterizados microestructuralmente con diversas técnicas, logrando identificar las fases que los constituyen y el tipo de microestructura obtenida con el procesado láser coaxial. Se han determinado sus propiedades mecánicas a través de ensayos de microdureza, nanoindentación instrumentada y de flexión a tres puntos. Se ha estudiado también el comportamiento de oxidación a alta temperatura de los recubrimientos y del acero inoxidable austenítico mediante ensayos de oxidación isotérmica a 1100 ºC, logrando evaluar en detalle la morfología y composición de la superficie oxidada, la cinética de oxidación, así como la evolución del espesor, estructura y composición de las capas de óxido formadas en función del tiempo de oxidación. Por último, se ha realizado el estudio del comportamiento ante la fricción y el desgaste a temperatura ambiente y a elevada temperatura (500 ºC), mediante ensayos tribológicos de desgaste por deslizamiento en seco, con la finalidad de obtener el coeficiente de rozamiento y evaluar la resistencia al desgaste que presentan los recubrimientos láser MCrAlY y su comparación con el comportamiento que presenta el sustrato. Los resultados de la experimentación han permitido analizar la influencia del procesado láser coaxial en las propiedades mecánicas y el comportamiento a alta temperatura de recubrimientos MCrAlY, y su comparación con el acero inoxidable AISI 304 y recubrimientos similares obtenidos por procesos de proyección térmica y utilizados en la actualidad. Los resultados indican que el plaqueado láser coaxial puede ser una buena alternativa a los procesos de proyección térmica, ya que se mejora la integridad microestructural, se disminuyen los defectos como la porosidad y la falta de unión metalúrgica, mejorando también el comportamiento ante la oxidación y el desgaste a elevadas temperaturas de los recubrimientos de anclaje MCrAlY que pueden ser utilizados en nuevos sistemas de barrera térmica. / [CA] El procés de plaquejat làser coaxial és una excel·lent eina per a l'obtenció de recobriments de qualitat, aconseguint la completa fusió i deposició d'aliatges amb elevat punt de fusió sobre superfícies 3D complexes. En aquest treball s'han estudiat els paràmetres de processament làser coaxial de superaliatges MCrAlY (on M = Ni, Co, Fe o combinacions entre ells), comunament emprades com recobriments d'ancoratge en sistemes de barrera tèrmica, entre elles: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY i CoNiCrAlY; aconseguint seleccionar una combinació de paràmetres que permeten obtenir recobriments per solapament de cordons amb adequada relació d'aspecte, mínima dilució, baix nivell de porositat i bona unió metal·lúrgica amb el substrat d'acer inoxidable austenític, utilitzant un equip làser Nd:YAG de 2.2 kW i un capçal coaxial. Els recobriments làser han estat caracteritzats microestructuralment amb diverses tècniques, aconseguint identificar les fases que els constitueixen i el tipus de microestructura obtinguda amb el processat làser coaxial. S'han determinat les seves propietats mecàniques mitjançant assaigs de microduresa, nanoindentació i de flexió a tres punts. S'ha estudiat també el comportament d'oxidació a alta temperatura dels recobriments i de l'acer inoxidable austenític mitjançant assaigs d'oxidació isotèrmica a 1100 ºC, aconseguint avaluar en detall la morfologia i composició de la superfície rovellada, la cinètica d'oxidació, així com la evolució del gruix, estructura i composició de les capes d'òxid formades en funció del temps d'oxidació. Finalment, s'ha realitzat l'estudi del comportament davant la fricció i el desgast a temperatura ambient i a elevada temperatura (500 ºC), mitjançant assajos tribològics de desgast per lliscament en sec, amb la finalitat d'obtenir el coeficient de fricció i avaluar la resistència al desgast que presenten els recobriments làser MCrAlY i la seva comparació amb el comportament que presenta el substrat. Els resultats de l'experimentació han permès analitzar la influència del processat làser coaxial en les propietats mecàniques i el comportament a alta temperatura de recobriments MCrAlY, i la seva comparació amb l'acer inoxidable AISI 304 i recobriments similars obtinguts per processos de projecció tèrmica, utilitzats actualment. Els resultats indiquen que el plaquejat làser coaxial pot ser una bona alternativa als processos de projecció tèrmica, ja que es millora la integritat microestructural, es disminueixen els defectes com la porositat i la falta d'unió metal·lúrgica, millorant també el comportament davant l'oxidació i el desgast a elevades temperatures dels recobriments d'anclatge MCrAlY que poden ser utilitzats en nous sistemes de barrera tèrmica. / Pereira Falcón, JC. (2015). Desarrollo y caracterización de recubrimientos MCrAlY obtenidos mediante técnicas láser para aplicaciones de barrera térmica en aceros inoxidables [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52946

La résistance à l'écaillage d'un système barrière thermique est fonction de la composition et microstructure des matériaux constituant le système, ainsi que des procédés utilisés pour son élaboration. Cette thèse s'intéresse à l'influence d'une couche de platine déposée à la surface du dépôt NiCoCrAlYTa (sous-couche) sur le comportement en oxydation du système barrière thermique. Une étude approfondie est d'abord menée afin d'identifier les atouts et points faibles en oxydation cyclique d'un système comprenant un revêtement NiCoCrAlYTa. La formation d'une couche d'oxyde composée non exclusivement d'alumine et l'importante rugosité de la sous-couche, favorisant les défauts au sein de la barrière thermique, accélèrent l'écaillage de la barrière thermique. Parallèlement, la présence de carbures de tantale au sein du dépôt ne suffit pas à stopper le titane qui diffuse depuis le superalliage jusqu'à la couche d'oxyde et dégrade le système. Le platine ayant déjà démontré son effet très bénéfique sur les dépôts aluminures de nickel, il apparaît comme prometteur pour améliorer le comportement en oxydation du revêtement NiCoCrAlYTa. L'étude de son influence débute par une analyse fine de deux sous-couches NiCoCrAlYTa modifié platine : la première comprend un revêtement NiCoCrAlYTa obtenu par co-dépôt électrolytique, la seconde un dépôt NiCoCrAlYTa élaboré par projection plasma sous vide. Cette caractérisation, par diffraction des rayons X et microscopie électronique à balayage et en transmission, met en évidence la présence de martensite en surface du revêtement, conséquence de la diminution de l'activité de l'aluminium par le platine. Elle révèle également la forte influence du procédé utilisé pour l'élaboration du dépôt NiCoCrAlYTa sur la microstructure obtenue après le traitement thermique de diffusion. Des essais d'oxydation isotherme et de préoxydation sont ensuite réalisés sur la sous-couche dont le revêtement NiCoCrAlYTa est élaboré par co-dépôt électrolytique. Les couches d'oxydes formées sont analysées par diffraction des rayons X, spectroscopie Raman et fluorescence. Grâce à l'ajout de platine, qui entraîne l'augmentation de la teneur en aluminium dans la zone externe du revêtement, l'oxydation sélective de l'aluminium est favorisée. Cela se traduit par une diminution de la cinétique d'oxydation et une augmentation de la résistance à l'écaillage de la couche d'oxyde. Cependant, les carbures de tantale se décomposent lors du traitement thermique de diffusion puis lors de l'oxydation, laissant le titane libre de diffuser depuis le superalliage jusqu'à l'oxyde. De l'oxyde de titane est en effet détecté par spectroscopie Raman en petite quantité dans de la couche d'oxyde (avec l'AM3 comme substrat). Un autre point important sur la composition du superalliage est la présence d'élément réactif qui permet de diminuer la croissance de la couche d'oxyde. Concernant les essais de préoxydation, les résultats obtenus indiquent la nécessité d'une faible pression partielle d'oxygène afin de promouvoir la formation d'alumine-a. Le platine, quant à lui, ne favorise pas la formation d'alumine de transition. Des essais d'oxydation cyclique sur des systèmes barrière thermique sont ensuite menés. L'effet bénéfique du platine sur l'oxydation sélective de l'aluminium est confirmé, ce qui entraîne une augmentation de la durée de vie en cyclage. Cependant, la décomposition des carbures de tantale est de nouveau observée. Une diffusion très importante de titane depuis le superalliage jusqu'à l'oxyde est ainsi notée pour les systèmes barrière thermique comprenant une sous-couche modifiée platine avec un dépôt NiCoCrAlYTa obtenu par projection plasma sous vide. Dans le cas de système avec une sous-couche modifiée platine comprenant un dépôt NiCoCrAlYTa élaboré par co-dépôt électrolytique, le problème majeur est la présence de pores en surface et d'une certaine porosité à l'intérieur du revêtement. L'oxydation des pores en surface ainsi que le cyclage thermique provoque la pénétration de l'oxyde puis sa propagation catastrophique dans le revêtement. Les résultats obtenus permettent de dégager les points importants de l'élaboration d'un système barrière thermique. Il est alors recommandé que le superalliage contienne un élément réactif mais peu de titane. Le dépôt NiCoCrAlYTa nécessaire à la fabrication de la sous-couche doit être dense et la préparation de surface, avant et après le dépôt de platine, doit permettre d'obtenir une faible rugosité de surface avant le dépôt de la barrière thermique. Enfin, les paramètres (température, pression partielle d'oxygène, sablage) lors de la première oxydation du système doivent être contrôlés de manière à favoriser la formation d'alumine-a. / The resistance to spallation of a thermal barrier coating system depends on the composition and the microstructure of the materials constituting the system, as well as on the processes used for its manufacturing. This PhD is interested in the influence of a Pt layer deposited on the surface of the NiCoCrAlYTa coating (bond coating) on the oxidation behavior of the thermal barrier coating system. A thorough study is first carried out in order to define the assets and the weak points under cyclic oxidizing conditions of a system composed of a NiCoCrAlYTa coating. The formation of an oxide layer not only composed of alumina and the great roughness of the bond coating, favoring defects within the thermal barrier, speed up the thermal barrier spallation. At the same time, the presence of tantalum carbides within the coating is not sufficient to prevent titanium from diffusing from the bond coating toward the oxide layer and from degrading the system. Platinum having already demonstrated its beneficial effect on nickel aluminide coatings, it seems promising in order to improve the oxidation resistance of the NiCoCrAlYTa coating. The study of its influence starts by a thorough analyses of two Pt-modified NiCoCrAlYTa bond coatings: the first one is composed of a NiCoCrAlYTa coating made by composite electroplating, the second one is composed of a NiCoCrAlYTa coating manufactured by vacuum plasma spray. This characterization, done using X-ray diffraction and secondary and transmission electron microscopy, highlights the presence of martensite at the coating surface, consequence of the decrease in the aluminium activity by platinum. It also reveals the strong influence of the process used to manufacture the NiCoCrAlYTa coating on the microstructure obtained after diffusion heat treatment. Preoxidation and isothermal oxidation tests are then carried out on the systems for which the NiCoCrAlYTa coating is made by composite electroplating. The oxide layers that formed are analyzed by X-ray diffraction, Raman spectroscopy and fluorescence. With Pt addition, that leads to an increase in the aluminium concentration in the external part of the coating, the selective oxidation of aluminium is favored. This results in a decrease in the oxidation kinetics and an increase in the resistance to spallation of the oxide layer. However, tantalum carbides decompose during the diffusion heat treatment and then during the oxidation, making the titanium free to diffuse from the superalloy toward the oxide. Indeed, titanium oxide is identified in small quantity in the oxide layer by Raman spectroscopy (with AM3 as substrate). Another relevant point on the superalloy composition is the presence of reactive elements that leads to a decrease in the oxide layer growth. Concerning the preoxidation tests, the obtained results indicate the necessity of a low oxygen partial pressure so as to promote the a-alumina formation. As for platinum, it does not favor the formation of transient alumina. Cyclic oxidation tests on thermal barrier coating systems are then carried out. The beneficial effect of platinum on the selective oxidation of aluminum is confirmed, that leads to longer lifetimes under thermal cycling. However, the tantalum carbides decomposition is observed once again. A great titanium diffusion from the superalloy toward the oxide is noticed for the thermal barrier coating systems composed of a platinum modified bond coating with a NiCoCrAlYTa deposit made by vacuum plasma spraying. In the case of systems composed of a Pt modified bond coating with a NiCoCrAlYTa deposit manufactured by composite electroplating, the main issue is the presence of pores at the surface and of a porosity within the coating. The pores oxidation at the surface as well as the thermal cycling result in the oxide penetration and then its disastrous propagation within the coating. The obtained results reveal the relevant points concerning the manufacturing of thermal barrier coating systems. It is recommended to use a reactive element containing superalloy that has very little titanium. The NiCoCrAlYTa coating required for the bond coating manufacturing has to be dense and the surface preparation, before and after the Pt deposit, has to lead to a surface with a low roughness before the deposition of the thermal barrier coating. Finally, the parameters during the first oxidation of the system (temperature, oxygen partial pressure, grit blasting), has to be done in order to favor a-alumina formation.

The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.

The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.

The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.