The main aim of this project is to model the effects of varied injection parameters on the gas dynamics and droplet dynamics of the HVSFS and SP- HVOFS processes for improving the droplet breakup and evaporation to enhance the nanoparticles heating and deposition efficiency. Thermal spraying processes are widely used to generate thermal-, corrosion-, and wear-resistant layers over the machine parts, to increase the durability of the equipment under severe environmental conditions. The liquid feedstock is used to achieve nanostructured coatings. It is used either in the form of a suspension or a solution precursor. The suspension is a mixture of solid nanoparticles suspended in a liquid medium consisting, for instance, of water, ethanol, or isopropanol. This dispersion mechanism in a liquid carrier provides adequate flowability to the nanoparticles, which cannot be handled by conventional gas- based feeding systems, whereas the solution precursor is mixed at the molecular level; hence, more uniform phase composition and properties are expected in the sprayed coatings as compared to the suspension and conventional powder spraying. Firstly, experiments are conducted to analyse the effects of different precursor concentrations, solvent types and injection nozzles on the size and morphology of synthesized nanoparticles. The results indicate that the particle size increased with increasing precursor concentration due to the variations in the physical properties of the mixture solution. The higher precursor concentrations had an adverse effect on the droplet atomization and evaporation process that led to bigger size particle formation. The use of aqueous solvent has some limits and with higher precursor concentration the surface tension increases that resulted in the reduction of droplets’ disintegration, and thus bigger size precursor droplets generate larger nanoparticles. A mixture of aqueous-organic solvents and pure organic precursors are preferred to improve the process efficiency of the nanoparticles size and morphology. Furthermore, the nanoparticles size can be controlled by using liquid feedstock atomization before injecting into the HVOF torch. A new effervescent injection nozzle is designed and compared to different types of existing injection nozzles, to see the variations in the droplet disintegration, and its effects on the performance of the HVOF torch processes. It is detected that the atomization would result in smaller size particles with homogeneous morphology. In a numerical study, different droplet injection types are analysed to see their effects on the gas and droplet dynamics inside the HVOF torch. The group-type injection (GTI) and effervescent-type atomization (ETI) are used effectively to overcome the heat losses and delays in the droplet evaporation. These approaches reduce the thermal and kinetic energy losses in the suspension-fed-HVOF torch, thereby improving the coating formation. The effects of using multicomponent water-ethanol mixture injection in the HVOF torch are also modelled, and its impact on the droplet breakup and evaporation are studied. The organic solvents have a low heat of vaporization and surface tension, and can effectively be used in the HVOF spraying process over the water-based solvents. Furthermore, nanoparticles are suspended in the liquid feedstock and injected into the HVOF torch. The effect of increasing nanoparticles’ concentration in the feedstock and its consequence on the gas dynamics, droplet breakup and evaporation are analysed. The augmentation in the nanoparticles loading in the suspension droplets can decrease the droplet breakup and evaporation rate because the required heat of vaporization increases significantly. Moreover, the size of injection droplet affects the droplet fragmentation process; bigger sized droplets observed a delay in their evaporation that resulted in coating porosity. The results suggest that smaller droplet sizes are preferred in coating applications involving a higher concentration of nanoparticles with high melting point. Further, the gas flow rates (GFRs) are regulated to control the droplet dispersion, atomization and evaporation inside the solution precursor fed-HVOF torch. The size of the droplet diameter is decreased by an increment in the GFR, as higher combustion rates increase the combustion flame enthalpy and kinetic energy. Moreover, the increase in the oxygen/fuel flow rates dilutes the injected precursor. It reduces ZrO2 concentration in the process and decreases the rate of particle collision; as a result, non-agglomerated nanoparticles can be obtained.

The effect of surface modification and high intensity electric field (uniform and non – uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non – uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high – resolution camera.

Sacrificial metallic coatings have been used in the past, for protecting steel in industrial and urban developments. It has been suggested that thermally sprayed aluminium coatings, immersed in marine environments, are also capable of protecting steel by providing galvanic protection. Researchers have also speculated that the growth of inert oxide products, on top of the coating as well as inside pores and cracks, could enhance even further its protective “shielding” properties. In addition, the self-healing abilities of the coatings, in case of mechanically induce damage, are still a matter of debate. This research project takes a critical look at these assumptions, focusing on the electrochemical response of aluminium metal sprayed (AMS) coatings immersed in 0.6 M NaCl and 0.6 M Na2SO4 solutions, in order to investigate how the presence of chlorides can alter the corrosion behaviour of these coatings. For such, a thin aluminium protective coating was deposited over two different panels (aluminium 1050 and low carbon steel), by the steel making company Fairfield-Mabey, using electric arc thermal spraying (TS). Subsequently, the coated panels were sectioned into smaller specimens, and with the aid of a SEM/EDS, and XRD, observations and analysis were conducted in their surfaces and cross sections, in order to determine the morphology, quality of deposition, and chemical composition of the coatings. Internal porosity/oxide growth after immersion, was studied using 3-D X-ray tomography scanning. Furthermore, the electrochemical behaviour of the coatings (intact and scribed) was also investigated, initially by analyzing the evolution of the open circuit potential in time, when immersed in chloride rich and chloride free environments. Additionally, the anodic polarization behaviour of the substrate and coatings were simultaneously analyzed, by connecting a zero resistance ammeter (ZRA) with the W.E. terminal of a potentiostat. To conclude, EIS and Rp vs. time plots were made in order to corroborate the data obtained from other tests. Results show that although the coating can generate superficial and internal corrosion products, these oxides are not isolating in nature nor will enhance its protective properties. On the other hand, the corrosion potential behaviour of the coatings revealed that AMS coatings have a more active than the substrate; regardless of the environment in which they were immersed or their substrate. Nevertheless, it was also observed that AMS coatings deposited onto steel will corrode faster than their substrates, and for that matter capable of offering corrosion protection, exclusively if chlorides are present in the solution.

La production de poly(chlorure de vinyle) (PVC) sous forme de suspension chez INEOS ChlorVinyls est réalisée en réacteur fermé agité, dont les parois sont en émail ou en acier inoxydable. Il se forme en cours de polymérisation un dépôt de PVC (croûte) sur les parois du réacteur qui génère de nombreux inconvénients. Afin de limiter cet encroûtement, INEOS ChlorVinyls et l’ensemble des producteurs de PVC appliquent à chaque batch (par exemple pour INEOS ChlorVinyls 50 fois par jour pour ses 22 réacteurs) un revêtement organique. L’application systématique du revêtement et la formation de croûtes ont des conséquences économiques non négligeables (arrêts de production, coût de main d’œuvre et matière, coût de traitement des déchets, qualité du PVC contaminé par le revêtement…).La compréhension du phénomène d’encroûtement en vue de développer un revêtement permanent devient donc nécessaire pour améliorer la qualité des produits, diminuer les coûts et dégager un avantage concurrentiel favorable à INEOS vis-à-vis de ses concurrents. Le sujet de thèse a été divisé en deux parties bien distinctes avec premièrement l’étude du mécanisme d’encroûtement et la mise en place d’un scénario permettant d’expliquer de manière physique et chimique la formation de la croûte sur les parois du réacteur. Une seconde partie a été dédiée au développement d’un revêtement polymère avec la sélection d’un système résistant au milieu réactionnel de polymérisation en suspension du chlorure de vinyle puis à l’optimisation de l’adhésion du revêtement polymère sur acier inoxydable afin d’obtenir des performances maximales et durables. / The suspension synthesis of PolyVinyl Chloride (S-PVC) at the INEOS ChlorVinyls facility in Mazingarbe (FRANCE) is realized thanks to a closed-reactor technology with reactor walls made of stainless steel or enamel. One of the major problems during the production of PVC by suspension polymerization is the formation of a deposit (called crust or scale) on the reactor walls. The formation of scale leads to numerous sorts of drawbacks like a decrease of the reactors’ productivity, the need to clean the reactors after each batch, the exposure of the operators to VinylChloride Monomer (VCM) which is classified CMR, some quality issues… At the moment, a coating is applied before each batch (50 times per day for the 22 reactors at Mazingarbe) in order to lower the amount of scale formed during the S-PVC batch. The application of the coating added to the formation of scale leads to important extra costs. The comprehension of the scale formation mechanism with the aim of then developing a durable protective coating becomes a priority in order to increase the final product quality, lower the costs and gain a competitive advantage for INEOS ChlorVinyls. The Ph.D. subject was divided into two parts with the first year dedicated to the comprehension of the scale formation mechanism and the establishment of a complete scenario explaining the formation of scale from a chemical and physical point of view. The second part of this project was dedicated to the development of a polymer coating with the selection of an adapted polymer candidate and then the optimization of its adhesion onto stainless steel in order to obtain the optimal performances and the durability of the coating.

Silver is a precious metal that has traditionally been used for jewellery and money. It also possesses desirable properties such as being corrosion resistant and having good electrical conductivity, resulting in its use for industrial applications. Furthermore, it is also recognised for its tribological properties in non-cost prohibitive applications. Silver can be used as a surface coating and can be deposited using an electroplating process. The utilisation of silver as a surface coating is advantageous and sustainable, as the substrate material properties are enhanced while usage of silver is kept to a minimum. On the other hand, electroplating has been used for over a century. It is a process which is able to produce a layer of uniform and dense coating that adheres well to the substrate metal, thus modifying the properties of the substrate. It benefits from being relatively low cost and is scalable. Silver is electroplated onto stainless steel threaded compression fittings to prevent galling. Traditional silver electroplating, which contains the use of cyanide as a complexing agent in the electroplating bath, is still in use within industry, even to this day. Cyanide, in its various forms can be poisonous, toxic and even lethal, which presents a risk during the silver electroplating process. Furthermore, the toxic wastes created during the cyanide silver electroplating process are detrimental to the environment. The aim of this work is to develop a self-lubricating non-cyanide silver PTFE composite coating suitable for use in threaded compression fittings of the ferruled type. The composite can be considered self-lubricating when a concentration of 8% or more by volume of the self-lubricating PTFE substance is incorporated. My original contribution to knowledge is firstly the successful development and characterisation of a self-lubricating non-cynanide Ag-PTFE coating on stainless steel without a strike resulting in improved CoF of 0.06 from the CoF of 0.6 based on an unlubricated surface. Secondly is the application of a non-cyanide Ag-PTFE MMC for threaded compression fittings. Thirdly is the characterisation of the make-up process of threaded compression fittings through the proposed use of the torque-angle slope in assessing coating performance for threaded compression fittings during make-up. Conclusions that can be drawn for the work are that the performance non-cyanide Ag-PTFE coating exceeded the performance of the pure Ag coating made using the same non-cyanide process. Moreover, the performance of the Ag-PTFE coating shows promising results when compared to the performance of the commercial silver cyanide coating. As a viable replacement to the current silver cyanide process, the self-lubricating non-cyanide Ag-PTFE coating, will improve the working conditions and have a positive contribution to the environment. Moreover, a thinner coating with has the potential to reduce raw material usage and electroplating waste disposal costs.

Ce travail a permis de mettre en évidence l’impact du procédé SMAT (Surface Mechanical Attrition Treatment) sur la résistance à l’oxydation des aciers de type AISI 316L. Cette étude a permis de comparer la composition et la morphologie des couches d’oxydes, la cinétique d'oxydation, les mécanismes de croissance et les contraintes résiduelles sur les surfaces des pièces traitées et oxydées à différentes températures. Ces observations ont montré l’existence d’un effet bénéfique du SMAT sur la résistance à l’oxydation de l’acier 316L pour des hautes températures. En effet, la cinétique d’oxydation des échantillons traités semble être reliée à une croissance préférentielle de chromine dès 700°C. Ceci nous a amenés à conclure que le procédé SMAT utilisé sur le 316L inverse la phase d’oxyde majoritaire, en inhibant la croissance de l’hématite et en favorisant celle de la chromine. Un scénario d’oxydation pour l’acier brut et Smaté a ainsi été proposé et le rôle de la densité des joints de grains introduits par le traitement a été explicité. Pendant ce travail, il a également été proposé un chaînage numérique complet qui prendrait en compte les paramètres du procédé et les propriétés mécaniques du matériau, afin de prévoir les caractéristiques de la nanostructure générée suite au traitement SMAT, en lien possible avec son influence sur l’oxydation à hautes températures / This work aims at highlighting the impact of the SMA process (Surface Mechanical Attrition Treatment) on the oxidation resistance of steels of type AISI 316L. This study compares the composition and morphology of the oxide layers, the oxidation kinetics, the growth mechanisms and the residual stresses on the surface of treated and oxidized samples at different temperatures. These observations show a beneficial effect of the SMA process on the oxidation resistance of the 316L steel for high temperatures. Indeed, the oxidation kinetics of the treated samples is shown to be related to a preferential growth of chromia starting at 700°C. This led us to conclude that the SMAT used on the 316L reverses the main oxide phase, inhibiting the growth of the hematite and promoting the chromia. An oxidation scenario for untreated and SMATed steel samples is proposed, demonstrating the role of the density of the grain boundaries introduced by the mechanical treatment. During this work, a comprehensive numerical chaining process is proposed. It takes into account the process parameters and mechanical properties of the material, in order to predict the characteristics of the nanostructure generated by SMAT, that could influence the oxidation of this stainless steel at high temperatures

Les détecteurs infrarouges InSb sont composés d'un circuit intégré Si et d'une matrice InSb qui sont connectés électriquement et mécaniquement par des billes de soudure en indium, préalablement déposées sur une métallisation. La jonction établie entre ces deux substrats est sollicitée thermomécaniquement à chaque utilisation à la température de l'azote liquide. Cette sollicitation thermomécanique est propice à la fatigue limitant la durée de vie du détecteur. Ce travail de thèse a pour objet l'amélioration des métallurgies de la métallisation et de la soudure au vu de la tenue en cyclage thermique de composants assemblés. L'effet des conditions de dépôt sur la microstructure, les propriétés électrique et de diffusion de la barrière de diffusion est évalué pour les métaux réfractaires suivants : alliage tungstène-titane (WTi) et tantale (Ta). L'élaboration par voie physique conduit à l'apparition inopinée d'une phase métastable néfaste, qui peut cependant être contrôlée par l'intermédiaire d'une sous couche. Un alliage indium-argent (eutectique) est déposé par évaporation qui permet de diminuer la température de fusion, et par conséquent les contraintes résiduelles du composant. L'effet de l'élément d'alliage Ag est évalué au vu de la résistance de contact et de la tenue mécanique de l'assemblage. Les résultats ont montré que la métallurgie est affectée par la méthode de fabrication, qui conditionne la tenue thermomécanique du composant optoélectronique. / InSb based infra-red (IR) detectors are constituted by a Si integrated circuit and an InSb matrix which are electrically and mechanically connected thanks to solder balls in pure indium deposited on underbump metallic layers (UBM). IR detectors are cooled down to liquid nitrogen for each use. This thermomechanical solicitation affects the device reliability. The thesis purpose is to improve the UBM and solder metallurgies taking into account thermal cycling behavior of industrial components. The effect of deposition conditions on the diffusion barrier microstructure, electrical properties and diffusion efficiency is estimated for several refractory metals : tungsten-titanium alloy (WTi) and tantalum (Ta). The physical vapor deposition yield unexpected and harmful metastable phase formation, which can be controlled using a sub-layer. An indium-silver eutectic alloy is deposited by evaporation which allows to reduce the melting temperature and hence residual stresses within the component. The effect of Ag alloying is estimated by both the contact resistance and mechanical shear resistance. Results emphasize that the metallurgy is affected by the deposition technique, which impinges on IR detectors thermomechanical behavior.

The control of interfacial microstructural stability is of utmost importance to the reliability of liquid solder interconnects in high temperature electronic assemblies. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation, which practically renders conventional barrier metallisations inadequate. In this study, electrically conducting, NbOx containing Ni coatings were developed using electrodeposition. Their suitability as a solder diffusion barrier layer was assessed in terms of the electrical conductivity and barrier property. The present work explores a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, compactness and purity, from non-aqueous glycol-based electrolytes consisting of NiCl2 and NbCl5 as metal precursors. The effects of cathodic current density and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. A combined study of Scanning Transmission Electron Microscopy (STEM) and Electrochemical Quartz Crystal Microbalance (EQCM) was conducted to understand the fundamental aspects of this novel electrodeposition process. The composite coatings generally exhibited good electrical conductivity. The reaction behaviour between a liquid 52In-48Sn solder and Ni-NbOx, with Nb contents up to 6 at.%, were studied at 200°C. The results indicate that, Ni-NbOx with sufficient layer thickness and higher Nb content, offered longer service lifetime. Nb enrichment was generally observed at or close to the reaction front after high temperature storage, which suggests evident effectiveness of the enhanced diffusion barrier characteristics.

Le couplage des traitements de surface mécaniques et thermochimiques a fait l’objet de nombreuses études ces dernières années. L’objectif d’un tel couplage est l’amélioration des cinétiques de diffusion d’espèces chimiques résultant en une augmentation des profondeurs de diffusion, et/ou une diminution de la température du traitement thermochimique sur les matériaux prétraités mécaniquement. Dans cette thèse, le procédé SMAT (Surface Mechanical Attrition Treatment) de nanocristallisation superficiel par déformation plastique sévère a été combiné avec la nitruration plasma sur un acier inoxydable 316L de qualité médicale. Ce procédé duplex permet une amélioration notable sur la capacité de diffusion de l’azote sous la surface de l’acier SMATé. Une étape intermédiaire entre le SMAT et la nitruration plasma a été proposée ; son rôle significatif pour la diffusion de l’azote a été démontré. Ainsi, la comparaison des résultats obtenus après la nitruration plasma sur les échantillons SMATés avec ceux uniquement nitrurés a permis de constater une augmentation jusqu’à 60% de l’épaisseur des couches nitrurées. Par ailleurs, de nombreux moyens de caractérisation ont été mis en œuvre à travers divers essais mécaniques de fatigue et de tribologie. Un modèle numérique multi-échelle de diffusion a également été développé pour simuler les profils de concentration d’azote après traitement duplex. Les profils de concentration d’azote simulés sont en bon accord avec les résultats expérimentaux / Coupled mechanical and thermochemical surface treatments have been the subject of much research effort in recent years. The goal of such a coupling is to improve diffusion kinetics leading to increased penetration depths, and/or to decrease the treatment temperature for mechanically pretreated materials. In this work, SMAT (Surface Mechanical Attrittion Treatment), used to refine the grain size by severe plastic deformation, is combined with plasma nitriding of a 316L medical-grade stainless steel. This duplex process significantly improves nitrogen diffusion. An intermediate treatment between SMAT and plasma nitriding is also proposed and its significant effect on the nitrogen diffusion is demonstrated. Comparisons between nitrided-only samples and duplex-treated samples have shown up to 60% increase of the nitrided layer thickness. In order to better understand the link between the generated microstructures and the mechanical fatigue and tribological responses, the samples have been characterised by many different techniques. Also, a multiscale numerical model of the diffusion process is proposed in order to simulate the nitrogen concentration profiles after duplex treatment. The simulated and experimental profiles correspond rather well

Le grenaillage est souvent utilisé sur les pieds d’aube de turbine haute pression afin de retarder l’apparition des fissures dans les zones de concentration de contraintes. Ce traitement de surface génère des contraintes résiduelles et de l’écrouissage en surface de la pièce, ce qui influe sur sa durée de vie. L’enjeu de cette thèse est de mettre en place une méthodologie permettant de prendre en compte cet état mécanique initial, ainsi que son évolution en service, dans l’analyse de durée de vie d’une aube élaborée en superalliage monocristallin à base de nickel (AM1). Tout d’abord, cet état mécanique (contraintes résiduelles et écrouissage) est déterminé expérimentalement. Les contraintes résiduelles sont notamment évaluées par diffraction des rayons X en utilisant la méthode d’Ortner. Cet état mécanique est ensuite introduit dans les calculs de structure. Pour cela, on s’inspire de la méthode connue de l’introduction directe du champ d’eigenstrains qui est, ensuite, étendue afin d’introduire également les variables d’écrouissage ainsi que l’état mécanique anisotrope complet dans toute la structure. L’étape suivante a visé à suivre expérimentalement et à modéliser l’évolution de ces quantités sous sollicitations thermique, d’une part et cycliques à température constante (650°C), d’autre part. Enfin, la chaîne complète de calcul de durée de vie de l’AM1 est appliquée afin d’analyser la durée de vie des éprouvettes grenaillées. Les résultats obtenus sont discutés en regard des essais de fatigue effectués sur éprouvettes représentatives / Shot-peening is widely used on roots of high pressure turbine blade to postpone crack initiation in stress concentration area. This pre-stressing introduces compressive residual stress and strain hardening in a surface layer which will influence lifetime. The aim of this thesis is to propose a methodology which allows taking into account the impact of such pre-stressing and their evolution on the fatigue behaviour of a single crystal nickel-based superalloy (AM1) used for high pressure turbine blades. Firstly, the experimental work is devoted to the determination of the initial mechanical state (residual stresses and strain hardening). Residual stresses are namely determined using X-ray diffraction involving the use of a specific method developed by Ortner. This experimental initial mechanical state is then introduced as an input in structure calculation. The well-known method involving the direct introduction of eigenstrain profiles is used and improved to also introduce strain hardening variables and the complete anisotropic mechanical state in all the integration points of the structure. The next step consist in following experimentally and modeling the evolution of these quantities under thermal and mechanical loads under an uniform temperature (650°C). Finally, the complete lifetime assessment is carried out on representative shot-peened samples. Results are discussed with respect to experimental fatigue tests