L'objectif de ces travaux a été d'estimer les propriétés thermomécanique des revêtements abradables. Lesmatériaux abradables sont des structures fortement hétérogènes et le but a été de considérer leurs microstructuresdétaillées. L'intérêt de ces travaux a été de passer outre la difficulté de leur dimensionnement lors de l'élaborationdes couches. Trois revêtements abradables ayant différentes natures et différentes microstructures ont étéétudiées, la complexité de leur microstructure était différente les unes des autres. Leurs propriétés ont étédéterminées par une méthode de modélisation 2D appliquée directement pixel par pixel pour prendre enconsidération la microstructure détaillée. Afin de valider la méthode de modélisation, les résultats calculés ont étécouplés et comparés à des valeurs expérimentales. Deux méthodes de modélisations ont été appliquées : uneméthode conventionnelle; avec une image des revêtements représentant les détails de la microstructure aussi bienque la microstructure dans sa globalité ainsi qu'une méthode de modélisation 2-échelles, avec une première échellereprésentant les détails de la microstructure de la matrice et une seconde échelle représentant le revêtement globalet notamment la distribution des plus gros pores.Une des conclusions principales de ces travaux est la suivante : Si la complexité du matériau augmente, le nombred'échelle nécessaire pour décrire la microstructure réelle augmente. La méthode de modélisation 2 échelles a étévalidée à travers la comparaison entre les valeurs calculées et les résultats expérimentaux. Ces travaux ont aidé àobtenir un outil pour sélectionner digitalement les microstructures les plus prometteuses pour les applicationsd'abradabilité. Ceci permet de réduite le nombre de tests expérimentaux à effectuer. Ces tests expérimentaux sontplus longs à mettre en oeuvre et coutent plus cher. C'est un outil support quant au développement des structuresabradables. / The objective of this work was to estimate apparent thermomechanical properties of abradable coating. Abradablematerials are strongly heterogeneous structures and the aim was to consider their detailed microstructure. Theinterest of this work is to overstep one difficulty when manufacturing abradable coating which is their dimensioning.Three abradable coatings having different nature and different microstructures have been studied. Theirmicrostructure complexity was different one from each other. Their properties were determined by a 2D modelingmethod which was applied directly pixel by pixel to take account of all the microstructural details. To validate themodeling method, the results calculated were coupled and compared to experimental ones. Two modeling methodhave been applied, a conventional one, with coating image representing coating microstructural details as well asthe global coating microstructural distribution and a 2-scale modeling method, with one scale representing themicrostructural details of the matrix and a second on representing the global coating coarse pores distribution. Onemain conclusion of this work is the following one: If the material complexity increases, the number of scalemandatory to describe the real microstructure increases. The 2-scales modeling method has been validated throughcomparison of the calculated values with those obtained experimentally. This work helps to provide a tool for digitallyselect the most promising abradable layers with the effect of reducing the number of experimental tests, which arelonger and more expensive to implement. It is a tool for decision support in the abradable coating development.

Thermal barrier coatings (TBC) with MCrAlY (M=Co and/or Ni) bond coats have been widely used in hot sections of gas turbines to protect underlying superalloys from high temperatures, oxidation, and hot corrosion. Deposition of MCrAlY bond coats using atmospheric plasma spray (APS), as oppose to conventionally employed vacuum/low-pressure plasma spray and high velocity oxy-fuel deposition, allows greater flexibility in ability to coat economically and rapidly for parts with complex geometry including internal surfaces. There were three objectives of this study. First, relationships between APS spray parameters and coating microstructure was examined to determine optimum spray parameters to deposit APS CoNiCrAlY bond coats. Second, free-standing APS CoNiCrAlY coatings were isothermally oxidized at 1124ºC for various periods to examine the evolving microstructure of internal oxidation. Third, as a function of time of isothermal oxidation (i.e., internal oxidation), thermal conductivity and coefficient of thermal expansion were measured for free-standing APS CoNiCrAlY bond coats. Thirteen CoNiCrAlY coatings were deposited on steel substrates by APS using the F4-MB plasma torch. APS CoNiCrAlY bond coats were produced by incremental variation in the flow rate of primary (argon) gas from 85 to 165 SCFH and the flow rate of secondary (hydrogen) gas from 9 to 29 SCFH. Optimum coating microstructure was produced by simultaneously increasing the flow rate of both primary and secondary gas, so that the particle temperature is high enough for sufficient melting and the particle velocity is rapid enough for minimum in-flight oxidation. Optimum spray parameters found in this study were employed to deposit free-standing APS CoNiCrAlY coatings that were isothermally oxidized at 1124ºC for 1, 6, 50,100, and 300 hours. Extent of internal oxidation was examined by scanning electron microscopy and image analysis. Internal oxidation occurred by a thickening of oxide scales segregated at the splat boundaries oriented parallel to the coating surfaces. Thermal conductivity and coefficient of thermal expansion (CTE) of the free-standing APS CoNiCrAlY coatings were measured as a function of internal oxidation (i.e., time of oxidation or extent of internal oxidation). Thermal conductivity of free-standing APS CoNiCrAlY was found to decrease with increasing internal oxidation from 28 to 25 W/m-K. This decrease is due to an increase in the amount of internal oxides with lower thermal conductivity (e.g., Al2O3). CTE of free-standing APS CoNiCrAlY, measured in temperature range of 100°~500°C, was also found to decrease with increasing internal oxidation. Internal oxides have lower CTE than metallic CoNiCrAlY coatings. These evolving properties of APS CoNiCrAlY should be beneficial to the overall performance of TBCs in gas turbine applications.

Thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application and typically consisting of ceramic top coat and CoNiCrAlY bond coat (BC), both thermally sprayed. Nanostructured CoNiCrAlY bond coatings were deposited onto Ni-based alloy (Inconel 718) by both HVOF and CGDS spraying techniques. Subsequently the deposits were remelted by electron beam up to depth of about 100 m which resulted in removal of defects on the substrate to the bond coat interface. The primary objective of this thesis was to investigation of the influence of parameters used for EB remelting, including multiple remelting on the microstructural changes, phase modification and final state of the coatings. The amount of porosity in the coatings and surface roughness has been evaluated. Scanning electron microscopy and X-Ray diffraction were performed in order to characterize the phase modification before and after the applied treatment. The results indicated that multiple remelting process improved the coating properties in terms of porosity, smooth surface, strength and chemical homogeneity and at last but not least this study demonstrate that low-temperature processing of CoNiCrAlY bond coat represents an interesting and promising alternative for their manufacturing.

The aim of this thesis was to modify microstructure and coating-substrate interface of CoNiCrAlY coatings deposited by HVOF and cold spray on Inconel 718 substrates. Electron beam remelting and annealing in a protective atmosphere were used to modify the coatings. Microstructure, chemical and phase composition were analyzed. The effect of beam current, transversal velocity and beam defocus on remelted depth was evaluated. As-sprayed microstructure and chemical composition of coatings were analyzed and compared with remelted samples. The effect of annealing of the as-sprayed and remelted samples was evaluated. Remelted layers exhibited dendritic structure. Chemical composition changed only after remelting of interface and part of a substrate. When only the coating was remelted, chemical composition remained the same. Phases coarsened after the annealing. Chemical composition changed after annealing due to the diffusion.

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.

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 master thesis is dealing with characterization of the structure and properties of the YSZ thermal barrier coating deposited by water hybrid plasma spray technology on the CoNiCrAlY bond coats modified by using electron beam and vacuum annealing. Deposition of the bond coats was performed via high velocity oxy-fuel technology and cold spray. In case of experimental evaluation, the microstructure and chemical composition of the ceramic top coat deposited with powder and suspension feedstock was analyzed. The same analysis procedure was used also for bond coats after electron beam remelting by using two sets of parameters. Furthermore, the changes in microstructure and chemical composition of the remelted and annealed bond coats was evaluated. Eventually, the micromechanical properties of the top coats and the bond coats were measured. The ceramic top coats deposited with powder feedstock exhibited the structure composed by splats, while the top coats deposited in form of suspension showed fine structure with columnar grains. The dendritic structure was observed on remelted bond coats. The annealing process had an influence on the structure in form of coarsened phases and the chemical composition was changed due to diffusion of the elements.