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Porous materials are widely used in various fields requiring thermal insulation properties, such as the aircraft industry, with thermal barrier coatings. In such applications, plasma-sprayed yttria-stabilized zirconia proved to be a highly effective insulating coating. With higher void content, materials such as aluminum silicate are used in space industry (Intermediate eXperimental Vehicle, for instance) due to their low density and thermal conductivity. In this study, several thermal sprayed coatings were evaluated as candidates for low thermal conductivity applications. Porous deposits were produced thanks to the pore former introduction into the plasma plume, and so integrated inside coatings. Two pore formers were used, aromatic polyester and a mineral agent, leading to different microstructures. Porous mullite microstructures, with 80% porosity due to polyester removal by thermal treatment, were carried out, while layered microstructures were obtained with the mineral agent and low enthalpy plasma. Furthermore, thick coatings were sprayed with different plasma spraying configurations. A static spray set-up allowed porous one centimeter thick coating production without any manufacturing defects before and after thermal treatment. This was made possible throughout a deposit temperature control, via a cryogenic carbon dioxide cooling system.

Ceramics coatings produced by atmospheric plasma spraying (APS) on steel alloys parts involve high residual stress level that can affect the coating properties and integrity. Most of the experimental studies were focused on the stress evaluation into APS-produced coatings onto static targets. However, these studies have not been extended to stresses induced on rotating samples. Indeed, the thermal background and the deposition way onto a static target is different from a rotating one, resulting in indifferent coating residual stresses. The aim of this work is to estimate and understand the real-time stress evolution from the sandblasting process to the coating formation while the substrate is fixed at a rotating support thanks to a new system developed in the laboratory. Three different sources of stresses are analyzed in this paper: stresses induced by sandblasting, substrate heating, and splat quenching followed by the cooling down of the coating/substrate composite. Resulting stresses measurements are compared with after test ones made by incremental hole drilling.

International audience; Innovation in thin-film deposition processes, thermal spraying and cladding technologies mostly rely on evolutions of their previous iteration. Along with other examples, five case studies of emerging elaboration processes for metallurgical coatings are described coupled with their applications. In the frame of the lifetime extension of components exposed to aggressive media or their functionalization, this article depicts all the developments of the detailed processes. Physical vapor deposition (PVD) of coatings with exceptional properties is possible thanks to sources generating highly ionized metallic vapors. The control of the average energy per incident species and particularly metallic ions strongly influences the characteristics of the deposited layer obtained, for example, with HiPIMS (High Power Impulse Magnetron Sputtering). While PVD techniques are mainly directive regarding the growth of the coating, chemical vapor deposition (CVD) processes manage to homogeneously coat complex 3D shapes. The use of specific precursors in DLI–MOCVD (Direct Liquid Injection – MetalOrganic CVD), carefully selected from the whole metalorganic chemistry, allows one to efficiently treat heat-sensitive substrates and broadens their application range. The third detailed example of emerging technology is suspension plasma spraying (SPS). Projection of various solutions containing nanoparticles leads to the growth of unusual morphologies and microstructures and to the generation of porous coatings with multi-scaled porosity. On the other hand, cold-spray uses metallic powders with higher granulometry and does not modify them during the deposition process. As a result, high-purity and dense materials are deposited with properties similar to those of wrought materials. Whereas cold-spray is suitable only for ductile metals, laser cladding can be applied to ceramics, polymers and of course metals. Laser cladding is a key technology for advanced metallurgical engineering and alloy development due to its capability for functionally graded materials production and combinatorial synthesis.

This paper is dedicated to numerical simulations of impact and solidification of several ceramic droplets on a solid substrate. This process is usually encountered in ceramic plasma spraying to manufacture thick coatings. The characteristics of the final product are deeply related to the impact conditions of the droplets, since the particles can interact with the substrate or with neighboring droplets and induce a variable porosity. The objective of the numerical simulation is to gain a better understanding of the coating properties during its elaboration. This paper describes the numerical code based on a finite volume discretization, and presents the results of successive droplets impacting, in terms of hydrodynamics, thermal flux and solid fraction evolutions with time for one given configuration.

Plasma spraying is used to manufacture thermal barriers composed of a bond coat and a thin ceramic layer on a metallic part. Following the process conditions and material structure, the ceramic layer is a porous medium. The coupling between morphology and properties of ceramics provides high insulation with a thin layer. Due to the small time and space scales (ranges of μs and μm for ceramic droplet spreading and solidification), it is difficult to experimentally measure all the parameters governing the deposition. This work has focused on the plasma flow interaction with a moving substrate in order to quantify the heat transferred to the substrate and to estimate the flow structure in the impingement zone of ceramic particles for different stand-off distances. Previous studies have addressed the plasma torch flow by numerical simulation considering the experimentally measured arc tension time evolution as a boundary condition. This simulation provides unsteady temperature and velocity profiles at the torch exit which have been used as unsteady boundary conditions for the Large Eddy Simulation turbulence modeling. The CFD code takes into account the fluid compressibility, heat transfers with the substrate, turbulent flow, unsteady flow exhausted from the torch, ambient air engulfment in the plasma and solid target motion through penalty methods.

International audience; A novel plasma-spray process, featuring simultaneous injections of dry powders and multiple liquid streams, was employed to produce composite coatings where sub-micrometric particles of Al2O3 and hexagonal BN (h-BN) are dispersed within a NiCrAlY metal matrix. Various coatings, containing up to ≈10 wt% Al2O3 and ≈9 wt% h-BN, were obtained. A co-deposition effect was noted whereby a higher h-BN feed also increases Al2O3 incorporation in the coating, even under a constant flow rate of Al2O3 suspension.Although the microhardness (≈600 HV0.3) seemed rather insensitive to the composition of the coatings, their sliding wear resistance (tested under ball-on-disk configuration against corundum spheres at various temperatures) improved with increasing contents of Al2O3 and h-BN. The improvement was more significant at room temperature, but some beneficial effect also emerged when testing at 400 °C and 700 °C. Al2O3 and h-BN indeed promote the formation and enhance the mechanical stability of an oxide-based tribofilm, protecting the coating surface from direct contact with the counterbody. Specific tribofilm formation mechanisms however vary with temperature. Overall, coatings containing ≥5 wt% of Al2O3 and h-BN keep a reasonably stable wear rate (

The present article describes experimental results of liquid injection in a thermal plasma jet by particle-tracking velocimetry (PTV). This technique delivers an in-situ real-time analysis of the liquid breakup and measures the velocities and the trajectories of the particles. The observations were done within the 10 mm surrounding the injection location where the plasma brightness is considerable. First, a validation of the proposed investigation method was carried out in a slower plasma jet. Subsequently, PTV measurements within faster plasma jets, resulting in a set of trajectories, were compared with trajectories achieved through optical diagnostics based on a simple shadow-graph technique proposed by Damiani et al. [Injection d’un liquide au sein d’un jet plasma thermique: optimisation de la trajectoire des particules, Proceedings of Congres Francophone de Techniques Laser, CFTL 2010, Vandoeuvre les nancy, France, 2010 (in French)]. These trajectories indicated that a higher plasma flow rate was required to spray all droplet sizes in the axis of the flow, thereby enabling an optimal spraying (then coating) application for producing nanostructured thin layers. This study showed that the liquid injection parameters are of main importance to obtain optimal injection and plasma parameters to achieve the required coating properties.

International audience; In order to characterize the adhesion of nanostructured plasma-sprayed Y2O3-ZrO2 coatings presenting some geometrical specificities, it is here suggested to apply the Vickers Indentation Cracking (VIC) technique, which is capable of initiating a crack at the interface by performing the indentation test close to the interface within the substrate. This method renders it possible to overcome the difficulties concerning the characterization of the adhesion of nanostructured Y2O3-ZrO2 (YSZ) coatings. It was suggested to calculate an adhesive stress parameter by employing two physical parameters, i.e., the critical load to initiate the crack and the indentation distance measured between the interface and the indent center. In addition, for the case of brittle coatings, the crack was found to deviate from the interface toward the coating. Under such conditions and on the basis of the critical point (given by the two parameters: load and indentation distance), a stress parameter representative of the cohesive properties of the coating was defined according to the crack deviation conditions.

In this work, the numerical simulation of the interaction between a liquid jet and a plasma flow is investigated for understanding and predicting the physical parameters involved in the liquid plasma spraying process. This process is used for the production of high performance coatings to obtain thinner deposits (

Plasma spraying using liquid feedstock allows realizing thin coatings (< 100 μm). In this process, the plasma jet fluctuations play an important role in the behavior of the liquid fragmentation and then in the final deposit characteristics. In this study, numerical simulations of two different plasma jets (argon or argon hydrogen mixture) issuing into air are investigated. The computations are based on a compressible model and a Large Eddy Simulation (LES) modeling for the turbulence. The aim of this work is to analyze the unsteady effects of the plasma jet regarding those of turbulence. In particular, the characterization of the turbulent zone inside the plasma jet is provided. A turbulence analysis is carried out in order to estimate the levels of turbulence and modeling effects.

This paper proposes an original route for modeling the time-dependent behavior of a plasma jet issued from a DC plasma-spraying torch operating with various kinds of gas mixtures. The hydrodynamic interactions between this jet and a liquid jet for suspension plasma-spraying or a classical particle injection for the deposition of coatings are studied. In a first step, the classical plasma spraying process was explored using the FLUENT CFD code. Zirconia particles, defined as Lagrangian particles, were injected in an Ar/H2 flow and their positions, kinetic and thermal states were compared with experimental results. The trend and intensity of the values demonstrated a rather good agreement. In a second step, the suspension plasma spraying was investigated with the AQUILON CFD to simulate interactions between the plasma and aqueous jets. An Ar/H2 plasma flow was simulated with the Large Eddy Scale turbulence model assumption, in which a liquid jet had been introduced. The behavior observed during the first stage of the interactions between the two fluids corresponded to expectations.

A numerical simulation of the interaction between a plasma flow and a liquid jet was investigated, leading to the proposal of a compressible model, based on augmented Lagrangian, Large Eddy Simulation (LES) turbulence modeling and Volume of Fluid (VOF) approaches, capable of managing incompressible two-phase flows as well as turbulent compressible motions. The VOF method utilized volume markers to advect the local concentration of gas and liquid in a Eulerian manner. The numerical model was validated on single-phase plasma configurations as well as two-phase cross flow liquid jet interactions. Finally, an example of the first simulations of the interactions between a liquid jet and a plasma is presented. However improvements should be realized as to increase the speed of the VOF-SM algorithm or add specific subgrid models related to jet fragmentation and phase change.

Due to the importance of the thermal and kinetic particle states at impact when generating a coating, numerical simulations of particle treatment in a plasma flow are continuously carried out in order to predict the particle behavior. The first goal is to correctly reproduce the plasma outflow in which the particles are introduced. This has been explored with a simplified model, the so-called heating volume model, to simulate industrial runs. Zirconia particles have been introduced in the simulated plasma flow and their melting state, velocity and trajectory have been compared with experimental measurements from specific in-flight-particle-capture and DPV 2000 devices. These comparisons highlight weak delays that depend on the particle size. This could be due, partially, to the particle heating assumptions (heat conduction within the particle) and to a poor knowledge of the thermal conductivity of liquid zirconia.

International audience; In nuclear plants, the replacement of hardfacing Stellite, a cobalt-based alloy, on parts of the piping system in connection with the reactor has been investigated since the late 60’s. Various Fe-based or Ni-based alloys, Co-free or with a low content of Co, have been developed but with mechanical properties generally lower than that of Stellites. The 4th generation nuclear plants impose additional or more stringent requirements for hardfacing materials. Plasma-transferred arc (PTA) coatings of cobalt-free nickel-based alloys with the addition of sub-micrometric or micrometric alumina particles are thought to be a potential solution for tribological applications in the primary system of sodium-cooled fast reactors. In this study, PTA coatings of nickel-based alloys reinforced with alumina particles were deposited on 316L stainless steel substrates. Under the conditions of this study, the addition of alumina particles resulted in a refinement of coating microstructure and the improvement of their resistance to abrasive wear. However, it does not bring about any change in coating micro-hardness.

The behavior of plasma flow, generated by a D.C. plasma spraying gun, is simulated in a time-dependent 3 D. design. The high-temperature and high-velocity plasma plume is generated by a simple model based on Joule effect. The criterion of validation is the thermal efficiency while the only adjustment parameter is the length of the plasma column inside the anode. The transient plasma flow issuing in air atmosphere is reproduced. The plasma behavior is quite similar to that observed by fast-image video. Moreover, the centerline plasma plume properties are in agreement with experiment measurements, especially close to the torch exit and downstream the laminar-to-turbulent transition.

International audience; Plasma-spraying processing provides material with typical and complex microstructure. For simulating the mechanical, electrical, optical… properties of such materials, it is necessary to determine the numerical representation of the microstructure. Some techniques, like micro-tomography, give directly an image of the porosity. Although such methods are convenient, they don't allow modifications of the obtained structure, especially in order to observe the influence of the porosity parameters on the material properties. This work investigates the microstructure of Atmospheric Plasma Spraying (APS) and Suspension Plasma Spraying (SPS) coatings thanks to several analysis techniques such as Scanning Electron Microscopy, image analysis, Hg porosimetry or Ultra Small Angle X-ray Scattering (USAXS). From the obtained different results, a flexible 3D representation of each coating is computed.

International audience; Keywords: suspension plasma spraying droplet computational fluid dynamics heat and mass transfer In suspension plasma spraying, nano-sized particles are injected via a liquid or a solvent into a plasma jet. Due to shear by the plasma jet, the liquid is fragmented into small droplets flying into the gas flow. The present work has focused on a single droplet evaporating into the plasma environment, and considers, on the one hand, the physical analysis of the phenomena and, on the other hand, the characterization of the solvent's thermal and motion characteristics of evaporation by means of direct numerical simulation of a multiphase flow. Specific parameters such as the evaporation time of the droplet have been estimated. In addition, a validation study has been proposed by comparing numerical simulation and physical analysis. The direct numerical simulation of multiphase flow was based on a compressible 1-fluid model, modified for handling phase change. The employed numerical methods included the volume of fluid (VOF) approach for interface tracking and finite volumes on structured grids.

International audience; Keywords: Multi-phase flow VOF Eulerian/Lagrangian approach Heat transfer Phase change Thermal contact resistance Spreading and plasma spray a b s t r a c t The direct numerical simulation of the impact and solidification of a tin droplet on a solid substrate is investigated by means of a volume of fluid sub-mesh method Vincent et al. (2010), which is extended for the first time to the solving of the energy equation with phase change. In addition, viscous penalty methods are proposed to treat the solidifying part of the droplet as it spreads onto the target substrate. The presence of a thermal contact resistance is also tackled within the proposed model. The numerical modeling is validated against various typical configurations of phase change with interface that provide analytical solutions. Among them, we can cite the contact of two materials with a thermal contact resistance or the Stefan problem for the propagation of a solidification front. The last part of the article is devoted to the numerical simulation of the impact of a tin droplet on a flat substrate. The simulations are compared to experiments of Aziz and Chandra (2000) and a study on the value of the thermal contact resistance is proposed.

The plasma-forming gas composition is one of the parameters of a plasma spray process which can be adjusted by the operator to obtain deposits with the required properties. The gas composition affects the heat and momentum transfer to the particles injected in the flow, but also the working and stability of the plasma gun. This paper presents an investigation of the effect of gas composition and flow rate, and arc current on arc instabilities. The study was carried out for various ternary gas mixtures of argon, helium and hydrogen. The movement of the arc root attachment spot on the anode wall was characterized from the time-evolution of arc voltage and the fluctuations of the plasma jet from the velocity fluctuations. The experiments were carried out with a new and a worn anode. The characteristic frequency of arc fluctuations was correlated in terms of the primary parameters of the spray process and gas mixture properties.

The C.E.A. (the French Atomic Energy Agency) has developed the A.T.C. plasma spray process (Atmosphere-and Temperature-Controlled process): a classical inert plasma spraying system is coupled with a cryogenic cooling of the substrate by liquefied gas atomization. This process alternately supplies positive and negative heat fluxes to the substrate. In order to quantify these fluxes, and to better control the process, a heat flux measurement system has been developed: under industrial conditions, several multi-layer sensors measure the flux received by the substrate. This paper presents the diagnostic apparatus and the first results measured in A.T.C. plasma spraying conditions. These results were obtained in dynamic operating conditions.

In plasma spraying, the properties of the plasma-forming gas largely control the characteristics of the plasma jet and the momentum, heat, and mass transfers to the particles injected in the flow. The objective of this work was to investigate the effect of gas composition on the static and dynamic behaviors of the plasma jet. The latter behaviors were investigated from measurements of arc voltage and plasma jet velocity. Ternary gas mixtures of argon, helium, and hydrogen were used. The results were expressed as correlations between arc voltage and flow velocity, and the operating parameters of the gun for a specific nozzle diameter.

International audience; Nanostructured yttria-stabilized zirconia coatings for applications in high-temperature environments can be deposited by suspension plasma spraying (SPS) techniques. The present research has been conducted in order to study the sliding wear response of a SPS ZrO2–8% mol. Y2O3 coating (75 μm in thickness) deposited onto a Haynes 230 substrate, using pin-on-disc tests. Some of the coated samples were subsequently heat-treated for 1 h at 300 and 600 °C. Samples characterization prior and after the wear tests was carried out by SEM, EDS, XRD and optical profilometry techniques. Instrumented indentation was employed to determine elastic modulus and hardness. The results have shown that the as-sprayed and heat-treated samples experienced severe wear (10−13 m3/Nm) and the worst wear performance corresponded to the sample heat treated at 600 °C. Such a behavior could be related to both the structural changes that took place during heat treatment and the nature and level of the residual stresses in the coatings. In general, the morphologies of the wear tracks observed by SEM have shown a smoothing of the surface, brittle fracture, smearing and grain pull-out.

This paper describes an investigation of the suspension plasma spraying process by modelling on small scales. The interactions between a continuous jet of pure water and an Ar/H2 plasma jet were simulated using only NAVIER STOKES and heat equations. The behaviour of such fluids in interaction was analysed during the penetration of the liquid into the gas flow. The film of the interactions shows a complex breakup with a significant variation in WEBER number.

article i nfo Available online 19 November 2012 This paper deals with the modeling of different plasma flows interacting with a liquid jet of pure water. Using only fluid mechanic equations, the goal was to simulate and to understand the first moments of these interac- tions during suspension plasma spraying of nanomaterials. The obtained simulations were then validated by comparing the results with breakup mechanisms described for the same Weber number in a plasma cross- flow with constant temperature. The global model was applied to various suspension plasma spraying condi- tions: two plasma gas mixtures (Ar/H2 and Ar/He) and two types of liquid injections (train of droplets or contin- uous jet). These simulations demonstrated different trajectories of the liquid and, consequently, different modes of breakup. Droplet size distributions were also calculated in the global modeling field.

International audience; Materials which exhibit high specific heat and melting enthalpy combined with a low density, like boron carbide B4C, are difficult to melt by plasma spraying under standard spray conditions. Moreover, the injection of this low-density powder in the plasma jet is critical, especially when fine particles are used. The optimization of the plasma-forming gas composition may make the penetration of the particles in the gas flow easier, and improve their melting state. This paper presents an investigation of the effect of the composition of ternary gas mixtures of argon, helium and hydrogen on B4C particles heating and acceleration. The particle injection and the resulting spray pattern in the jet were controlled by using a 1D imaging technique. The particle velocity distribution was measured with a laser Doppler anemometer and the particle overall temperature with a high-speed pyrometer.

The numerical simulation of the interaction between a plasma flow and a liquid jet is important for understanding and predicting the physical parameters involved in plasma spraying processes. This work proposes an original model for dealing with three-dimensional and unsteady turbulent interactions between a plasma flow and a liquid water jet. A compressible model, based on augmented Lagrangian, Large Eddy Simulation (LES) turbulence modeling and Volume of Fluid (VOF) approaches, capable of managing incompressible two-phase flows as well as turbulent compressible motions is presented.

International audience; The design concept of the gas-cooled fast reactor which is a 4th generation nuclear reactor, requires protective coatings able to operate at 850 °C and protect the underlying structure in case of sudden increase of the functional temperature up to 1250 °C and depressurization from 0.70 MPa to atmospheric pressure. The parts to be covered are made of 1-mm thick materials resistant to heat and erosion and exhibiting high mechanical properties at high temperatures, such as the Haynes® 230 nickel-based alloy. In this study, the use of suspension plasma spraying to manufacture zirconia coatings is explored. The spraying conditions were optimized for the elaboration of coatings on stainless steel AISI 304L substrates and then adapted for Haynes 230 substrates. A special attention was paid to coating adhesion that was investigated by using a Vickers indentation cracking method.

Ultrafine particles of aluminium nitride (AlN) are produced by a transferred arc plasma on aluminium metal in nitrogen or nitrogen/hydrogen atmospheres. They are collected in a bag filter and on the walls of the reaction chamber. The powder is confirmed to be hexagonal AlN with a few metal aluminium traces. A growth of an aluminium nitride crystal from molten Al under the arc is observed. It is sectioned vertically in halves and examined by light and electron microscopy, and analysed by XRD and electron probe microanalysis. It consists of about equal amounts of Al metal and AlN with an increase in AlN towards the top. This mode of occurrence of the AlN crystallites in the Al matrix shows that it is a good composite. Five different textures, observed in this crystal, suggest a complex history of crystallization.

Ce memoire presente en introduction les proprietes physico-chimiques du nitrure d'aluminium et ses usages. La situation du marche est exposee et la necessite de developper de nouvelles methodes de synthese justifiee. L'auteur a fait une etude bibliographique qui lui permet de presenter l'etat de l'art en matiere de synthese de poudres submicroniques de nitrure d'aluminium en plasma thermique. Dans le premier chapitre, sont presentes les resultats de l'approche thermodynamique du procede de synthese etudie. La nucleation et la croissance des particules au cours du refroidissement de la phase vapeur ont ete modelisees. Le second chapitre decrit le dispositif experimental utilise: un four a plasma ou un arc d'azote est transfere sur un lingot d'aluminium. Ensuite, la methode de diagnostic spectroscopique du plasma d'azote est introduite et discutee. Dans le troisieme chapitre, l'auteur met en evidence les resultats obtenus. Des essais typiques sont decrits; les bilans calorimetriques sont presentes; les distributions spatiales de temperature dans la colonne d'arc et au voisinage de la cathode sont tracees. Le lingot apres traitement est analyse et un mecanisme de synthese est propose. Enfin, la composition chimique des poudres collectees est correlee avec la nature des gaz plasma et du gaz de trempe utilises. L'auteur conclut en presentant un four pre-industriel qui a permis d'obtenir des poudres contenant au moins 99,3% de nitrure d'aluminium et dont la surface specifique est de l'ordre de 10m#2/g

Relationships between electrical properties of thermally sprayed titania coatings and their microstructures have been investigated. It is well known that the quality and properties of the plasma-sprayed coatings are strongly dependent on the in-flight particle characteristics, which directly influences the plasma-sprayed coating microstructures. As far as possible, a broad range of microstructures was produced by using various processes of plasma spraying with different powder size ranges and variation of the plasma operating parameters. The two plasma-spraying processes consisted of direct current (DC) and radio frequency (RF) plasma spraying. The major concern of the study was that plasma-sprayed parameters influence also the stoichiometry of the titania coating resulting in a large variation of their electrical properties. It is the reason why coatings with identical stoichiometry were compared. The comparison between RF and DC plasmasprayed titania coatings highlighted that electrical resistivity was directly linked to the quality of the contact between the splats and their density through the titania plasma-sprayed coatings.

Analysis of two different plasma jets and the study of the air entrainment into them are investigated by two different ways, i.e., high-speed visualization or numerical simulation.

This article describes a small-scale modeling investigation of the suspension plasma spraying process. The heat transfer between a droplet of pure water and an Ar/H2 plasma jet was analyzed. The low dwell time of the droplet in the flow before impacting the substrate leads to consider radiation as not the main mechanism while convection and conduction were enhanced as the droplet became deformed.

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In dc plasma spray guns, the properties of the plasma forming gas largely control the characteristics of the plasma jet and the momentum and heat of the particles injected into the flow. This paper examines the effect of Ar-He-H2 mixtures on the dynamic and static behavior of plasma jets expressed in terms of arc voltage and gas velocity. Correlations between these parameters and operating variables (arc current, gas flow rate, volume composition) were established from a dimensional analysis and supported by the calculation of the thermodynamic and transport properties of the gas mixtures used in the study.

Considerable attention is now being focused on porous ceramics in the industrial field as used in a large variety of applications, such as thermal insulation, filter membranes, catalysts, heat exchangers, bioreactors, and refractories. As part of thermal insulating function, this study evaluates the plasma spraying process for the realization of materials that combine high porosity rates, higher than 70%, with good mechanical strength, so these materials could be machined. Operating temperatures around 1 200 °C and mass minimization stresses influence sprayed material choice to aluminum silicates. Considering the expected porosity rates, different pore formers were used in plasma spraying. Depending on the pore former nature, the plasma spraying parameters and the powder morphologies, several organized porous microstructures with a thickness of one millimeter and porosity rates between 70 and 80% were obtained. To satisfy the functional requirements, the 80% microstructure, resulting from the evacuation of aromatic polyester was obtained over one centimeter. This required a thorough study of residual stresses induced during plasma spraying and cooling steps, carried out by the deflection measurement method on standardized specimens. Understanding the mechanism that generated these stresses and minimizing them allowed the spraying of thick, flat and cylindrical microstructures. The thermomechanical behavior associated with such microstructures was analysed with different porous mullite shades. Thermal conductivities of 80 mW.m-1.K-1 were measured at room temperature on amorphous microstructures and then at temperature up to 800 °C on crystallized and amorphous structures. Young modulus, flexural stress and strain at rupture were evaluated by destructive (bending 3 – 4 points) and non-destructive (acoustic wave testing) methods. Finally, empirical relationships describing thermal and mechanical behaviour of free standing mullite microstructures following porosity and heat treatments were presented. In the end, coatings obtained by plasma spraying process have similar thermal and mechanical properties to those traditionally obtained in the literature by more conventional processes, such as gelcasting.; Les céramiques poreuses font l’objet d’une très grande attention dans le domaine de l’industrie car elles sont utilisées pour une grande variété d’applications, telles que l’isolation thermique, les membranes filtrantes, les catalyseurs, les échangeurs thermiques, les bioréacteurs et les réfractaires. Dans le cadre d’une fonction d’isolation thermique, cette étude évalue le procédé de projection plasma pour la réalisation de matériaux associant des taux de porosité élevés, supérieurs à 70 %, à une bonne tenue mécanique, pour que ces matériaux soient usinables. Les températures de fonctionnement, de l’ordre de 1 200 °C, et les contraintes de minimisation de masse orientent le choix des matériaux à projeter vers les aluminosilicates. Considérant les taux de porosité recherchés, différents agents porogènes ont été utilisés en projection plasma. Selon la nature de l’agent, des paramètres de projection et de la morphologie des poudres, différentes microstructures poreuses structurées d’épaisseur un millimètre, dont la porosité varie entre 70 et 80 %, sont obtenues. Pour satisfaire les exigences fonctionnelles, la microstructure à 80 %, issue de l’évacuation d’un polyester aromatique, a été obtenue sur un centimètre. Ceci a nécessité une étude approfondie des contraintes résiduelles induites durant les phases de projection et de refroidissement, réalisée par la méthode de la mesure de la flèche sur des éprouvettes normalisées. La compréhension des mécanismes générant ces contraintes et leur minimisation ont permis l’obtention de microstructures épaisses planes et cylindriques. Le comportement thermomécanique associé à de telles microstructures a été analysé sur différentes nuances poreuses en mullite. Des conductivités thermiques de 80 mW.m-1.K-1 sont mesurées à température ambiante sur des microstructures amorphes puis en température jusqu’à 800 °C sur des structures amorphes et cristallisées. Le module d’Young, la contrainte et la déformation à la rupture sont quantifiées via des méthodes destructives (flexion 3 – 4 points) et non destructives (tests d’ondes acoustiques). Enfin, des relations empiriques décrivant le comportement thermique et mécanique de microstructures autoportées en mullite suivant la porosité et le traitement thermique subi par ces dernières sont présentées. Les revêtements obtenus par projection plasma possèdent des propriétés thermiques et mécaniques analogues à celles classiquement obtenues dans la littérature par des procédés plus conventionnels, type « gelcasting ».

This PhD thesis is a contribution to the numerical simulation of the plasma sprayedcoating build-up by APS process (Atmospheric Plasma Spraying). This work focuses onthe build-up of a representative volume of the coat considering a great range of phenomenonappearing in APS process such as gas flow properties, kinetic (multiphase flow,wettability) and thermal (heat transfers, thermal contact resistance, solidification) duringthe impact and steaking of particles. An original numerical method, named VOF-SM(Volume Of Fluid - Sub Mesh) is developped. The simulation of the impact of an unsteadyand turbulent ArH2 plasma flow is carried out in order to define the gas flow closeto the wall and heat transferred to the substrate by the plasma. Specific phenomena of theimpact of particles were incorporated into the CFD code (Thétis) and validated independentlyby caparison with analytical solutions, then together combined by the comparisonto a millimeter size impact experimental data. Finally, a study of successive impacts ofYttria-Stabilized Zirconia particles onto a steel substrate was carried out by thermal andkinetic approach similarities to overcome the difficulty of resolving small scales., Cette thèse apporte une contribution à la simulation numérique de la construction de dépôts dans le cadre de la projection plasma type APS (Atmospheric Plasma Spraying). Ce travail est focalisé sur la construction d’un volume représentatif du revêtement en prenant en compte l’ensemble des phénomènes propres au procédé, tels que la nature de l’écoulement de gaz, la cinétique (multiphasique, mouillabilité) et la thermique (transferts thermiques, résistance thermique de contact, solidification) durant l’impact et l’empilement de particules. Une méthode numérique particulière, appelée VOF-SM (Volume Of Fluid - Sub Mesh), est développée. La simulation de l’impact d’un jet instationnaire et turbulent de plasma ArH2 sur un substrat a été réalisée pour définir la nature de l’écoulementen proche paroi et le transfert thermique entre cet écoulement et le substrat. Les phénomènes propres à l’impact de particules ont été intégrés au code de calcul Thétiset validés indépendamment par comparaison à des solutions analytiques et combinés par comparaison à un cas d’étude expérimentale millimétrique. Enfin, une étude d’impacts successifs de particules de Zircone Yttriée sur un substrat en acier a été menée, par une approche en similitudes thermique et cinétique pour pallier la difficulté de la résolution à petites échelles.