Ce travail a pour objectif d’évaluer le comportement à l’usure de pièces en CoCrMo utilisé dans l’orthopédie. Le procédé de nanocristallisation superficielle SMAT (Surface Mechanical Attrition Treatment) couplé à un polissage biomédical a été mis en œuvre dans cette étude pour améliorer les propriétés mécaniques, tribocorrosives d’un alliage CoCrMo. Dans un premier temps, une optimisation des paramètres SMAT sur un alliage CoCrMo a été réalisée. Différentes techniques de finition de surface ont ensuite été étudiées afin d’obtenir un état de surface acceptable pour des implants orthopédiques. Des techniques de caractérisation microstructurale ont alors été mises en œuvre sur des échantillons SMATés et polis : microscopie électronique à balayage et transmission (MEB ; MET), diffraction des électrons rétrodiffusés (EBSD), diffraction de kikuchi en transmission (TKD) et diffraction des rayons X (DRX). Les résultats obtenus ont montré que le traitement SMAT peut créer un raffinement des grains en surface de l’alliage CoCrMo avec notamment la présence de nano-grains en extrême surface. Des mesures d’indentation ainsi que des essais par la méthode du trou incrémental ont été effectués. Une augmentation de plus de 30% de la dureté a ainsi été observée après SMAT ainsi que la génération de contraintes résiduelles superficielles de compression. Les propriétés tribocorrosives de l’alliage CoCrMo ont également été étudiées par des essais d’usure par pion disque, scratch tests et des essais électrochimiques avant et après SMAT. / This aims of this work is to evaluate the wear behavior of CoCrMo parts used in orthopedics. The Surface Mechanical Attrition Treatment (SMAT) method coupled with biomedical polishing has been used in this study to improve the mechanical and tribocorrosive properties of a CoCrMo alloy. In a first step, an optimization of the SMAT parameters on a CoCrMo alloy was carried out. Different surface finishing techniques were then studied to obtain an acceptable surface finish for orthopedic implants. Microstructural characterization techniques were then applied on SMATed and polished samples: scanning and transmission electron microscopy (SEM, MET), backscattered electron diffraction (EBSD), transmission kikuchi diffraction (TKD), and ray diffraction X (XRD). The results obtained showed that the SMAT treatment can create a refinement of the surface grains of the CoCrMo alloy with the presence of nano-grains in the extreme surface. Indentation measurements as well as incremental hole tests were performed. An increase of more than 30% of the hardness was observed after SMAT as well as the generation of residual surface compressive stresses. The tribocorrosive properties of the CoCrMo alloy were also studied by disk wear tests, scratch tests, and electrochemical tests before and after SMAT.

This dissertation is to obtain an overall understanding of the crack path selection in adhesively bonded joints. Using Dow Chemical epoxy resin DER 331® with various levels of rubber concentration as an adhesive, and aluminum 6061-T6 alloy with different surface pretreatments as the adherends, both symmetric and asymmetric double cantilever beam (DCB) specimens are prepared and tested under mixed mode fracture conditions in this study. Post-failure analyses conducted on the failure surfaces indicate that the failure tends to be more interfacial as the mode II component in the fracture increases whereas more advanced surface preparation techniques can prevent failure at the interface. Through mechanically stretching the DCB specimens uniaxially until the adherends are plastically deformed, various levels of T-stress are achieved in the specimens. Test results of the specimens with various T-stresses demonstrate that the directional stability of cracks in adhesive bonds depends on the T-stress level. Cracks tend to be directionally stable when the T-stress is compressive whereas directionally unstable when the T-stress is tensile. However, the direction of crack propagation is mostly stabilized when more than 3% mode II fracture component is present in the loading regardless of the T-stress levels in the specimens. Since the fracture sequences in adhesive bonds are closely related to the energy balance in the system, an energy balance model is developed to predict the directional stability of cracks and the results are consistent with the experimental observations. Using the finite element method, the T-stress is shown to be closely related to the specimen geometry, indicating a specimen geometry dependence of the directional stability of cracks. This prediction is verified through testing DCB specimens with various adherend and adhesives thicknesses. By testing the specimens under both quasi-static and low-speed impact conditions, and using a high-speed camera to monitor the fracture sequence, the influences of the debond rate on the locus of failure and the directional stability of cracks are investigated. Post-failure analyses suggest that the failure tends to be more interfacial when the debond rate is low and tends to be more cohesive when the debond rate is high. However, this rate dependence of the locus of failure is greatly reduced when more advanced surface preparation techniques are used in preparing the specimens. The post-failure analyses also reveal that cracks tend to be more directionally unstable as the debond rate increases. Finally, employing interface mechanics and extending the criteria for the direction of crack propagation to adhesively bonded joints, the crack trajectories for directionally unstable cracks are predicted and the results are consistent with the overall features of the crack paths observed experimentally. / Ph. D.

O processo industrial não-contínuo de zincagem por imersão a quente (ZIQ) pode ocasionar a contaminação superficial do aço-carbono zincado por imersão a quente (AZIQ) com resíduos de cloreto. Estes resíduos, se não forem efetivamente eliminados, podem influenciar negativamente no desempenho dos esquemas de pintura dos sistemas dúplex (zincagem mais pintura). Sabe-se que no processo de ZIQ, a cromatização é amplamente utilizada, entretanto, o efeito que este pós-tratamento exerce no desempenho dos esquemas de pintura ainda não é bem estabelecido. Neste contexto, este trabalho teve como objetivos: I - verificar o grau de contaminação no AZIQ com sal de cloreto devido ao próprio processo de ZIQ; II - verificar os efeitos da contaminação com sal de cloreto e da cromatização do processo ZIQ no desempenho de tintas aplicadas sobre o AZIQ; e III – determinar pré-tratamentos para pintura adequados para o bom desempenho das tintas aplicadas sobre o AZIQ. A metodologia adotada para alcançar o objetivo I envolveu a zincagem de chapas de aço-carbono em diferentes prestadores de serviço de ZIQ, em diferentes condições. Estas chapas zincadas foram analisadas por microanálise química qualitativa por espectrometria de dispersão de energia (EDS) em microscópio eletrônico de varredura (MEV) e pela determinação dos teores de cloreto superficiais, por método de extração com água em ebulição. A partir dos resultados obtidos para se alcançar o objetivo I, foi possível definir as condições no processo de ZIQ que potencialmente causam maior contaminação da superfície do AZIQ com sal de cloreto. Assim, para se alcançar os objetivos II e III, chapas de aço-carbono foram zincadas naquelas condições de máxima contaminação com sal de cloreto e parte delas foi submetida ao pós-tratamento de cromatização. Em seguida, uma grande parte destas chapas zincadas (cromatizadas ou não) foi submetida aos pré-tratamentos para pintura de desengraxe com solvente orgânico, de hidrojateamento a alta pressão, de jateamento abrasivo ligeiro e de ação mecânica com esponja abrasiva e água quente. Finalmente, as chapas zincadas, incluindo as não submetidas aos pré-tratamentos, foram pintadas com uma demão de tinta de aderência mais uma demão de tinta de acabamento. As chapas zincadas e pintadas foram submetidas a ensaios acelerados (imersão em água destilada e exposição em câmara de umidade saturada) e não-acelerados de corrosão (exposição em estação de corrosão atmosférica) e avaliadas por meio dos ensaios tradicionais de acompanhamento de desempenho (grau de empolamento e ensaios de aderência de tinta) e eletroquímicos (medida de potencial de circuito aberto, curva de polarização e espectroscopia de impedância eletroquímica – E.I.E.). Algumas chapas zincadas, antes da pintura, foram submetidas aos ensaios de caracterização física (exame microestrutural e morfológico em MEV e rugosidade superficial), química microanálise por EDS, difração de raios X e teor de cloreto superficial pelo método de extração com água em ebulição) e eletroquímica. Os resultados obtidos, neste estudo, permitiram verificar que a aplicação adicional de sal cloreto de amônio sólido durante o processo de ZIQ tende a aumentar o grau de contaminação superficial do AZIQ com cloreto e, as etapas de resfriamento e/ou de cromatização do processo também contribuem para esta contaminação. No geral, o desempenho do AZIQ cromatizado teve desempenho inferior em relação ao não-cromatizados. O hidrojateamento a alta pressão e a lavagem com água e ação mecânica foram os prétratamentos que proporcionaram os melhores desempenhos dos esquemas de pintura. / The batch galvanizing process (BGP) can lead to surface contamination of hot-dip galvanized steel (HDGS) with chloride residues. If these residues are not effectively eliminated, they can influence negatively on the performance of duplex systems (galvanizing plus painting). It is known that the chromate quenching is widely used in the BGP, however the effect of this post-treatment on the performance of duplex systems is not well established yet. In this sense, this work aimed: I – to verify the contamination degree of HDGS with chloride salt due to the BGP itself; II – to verify the effects of the chloride salt contamination and chromate quenching on the performance of paints applied on HDGS; and III – to determine the suitable surface preparation for painting in order for obtaining a good paint performance applied on HDGS. The adopted methodology to achieve goal I involved the galvanizing of steel plates in different service renderings with BGP, in different conditions. These HDGS plates were submitted to the qualitative energy dispersive microanalyses (EDS) in scanning electron microscopy (SEM) and to the determination of superficial chloride contents by the boiling water extraction method. From the obtained results, the conditions in the BGP that potentially lead to greater surface contamination of HDGS with chloride salt were determined. Thus, to achieve goals II and III, steel plates were galvanized under the maximum chloride salt contamination condition and part of them were submitted to chromate quenching. After that, a great part of these HDGS plates (chromated or non chromated quenching) was submitted to the surface preparations for painting through organic solvent cleaning, high pressure hydroblasting, sweep blasting and handled scrub cleaning with an abrasive sponge and hot distilled water. Finally, the HDGS plates, including those not submitted to the surface preparations for painting, were painted with one coat of primer plus one coat of finishing paint. The HDGS painted plates were submitted to accelerated (distilled water immersion and humidity chamber exposure) and non accelerated (atmospheric exposure) corrosion tests and their performance were verified by means of traditional tests (degree of blistering and paint adhesion) and electrochemical measurements (open circuit potential, polarization curve and electrochemical impedance spectroscopy – E.I.S.). Before painting, some HDGS plates were submitted to tests for physical (microstructural and morphological analyses in MEV and surface roughness), chemical (EDS, X-ray diffraction and superficial chloride contents by the boiling water extraction method) and electrochemical characterization. The obtained results allowed verifying that the additional application of solid ammonium chloride salt during the BGP tends to increase the degree of superficial chloride contamination of the HDGS and, the water and/or chromate quenching also contribute for this contamination. In general, the chromated HDGS presented worst performances. The high pressure hydroblasting and the handled scrub cleaning with an abrasive sponge and hot distilled water were the surface preparations for painting that provided the best performances of paint systems.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O estudo de processos de limpeza por plasma surgiu como uma alternativa e também como uma etapa adicional em processos de limpeza de superfícies que visam a completa remoção de sujidades e contaminantes orgânicos em praticamente todos os tipos de materiais. Sendo as principais vantagens da técnica o fato de ser um tratamento realizado à seco, em temperaturas baixas, que possui pouco consumo de insumos e baixa produção de resíduos prejudiciais ao meio ambiente. Entretanto, uma das dificuldades do processo relaciona a relação complexa que existe entre todas as espécies formadas em um ambiente de plasma e a interação das mesmas com moléculas orgânicas. O presente estudo relaciona como diferentes compostos como hexatriacontano, ácido esteárico, ácido adípico e ácido aminoundecanóico, que representam parte das estruturas presentes nos contaminantes em superfícies, sofrem degradação em ambientes de plasma de Ar e Ar+O2. Para isso foi utilizado um reator de plasma sem eletrodos, com fonte de rádio frequência e descarga do tipo acoplada indutivamente, com a amostra posicionada na região da descarga e com a utilização de atmosferas não oxidantes (Ar) e oxidantes (Ar+10%O2). As análises foram realizadas tanto sobre os produtos voláteis gerados, através das técnicas de especrometria de massa do gás residual e espectroscopia de emisssão ótica, quanto sobre os residuos pós tratamento por espectroscopia de infravermelho e espectrometria de massa de alta resolução. Os resultados mostram que em atmosferas de Ar ocorre a produção de pequenos fragmentos voláteis obtidos através de cisão das ligações C-C ao mesmo tempo em que no material residual, são formados pequenos oligômeros de fragmentos unidos através de radicais. Com a adição de oxigênio na atmosfera observou-se um incremento significativo da produção de H2, H2O, CO, CO2 e fragmentos das moléculas ao mesmo tempo em que ocorre uma considerável oxidação de todos os compostos. Observou-se ainda que a formação de fase líquida altera considerávelmente o processo reacional das moléculas tratadas, levando a um período de alta produção de H2 e H2O junto com uma redução da produção de CO2. / The study of plasma cleaning processes has emerged as an alternative and as an additional step in surface cleaning processes that aim at the complete removal of soils and organic contaminants in virtually all types of materials. The main advantages of this technique are the fact that it is a dry treatment, in low temperatures, that has low consumption of inputs and environmentally harmful waste. However, one of the difficulties of the process relates the complex relationship that exists between all species formed in a plasma environment and the interaction of them with organic molecules. The present study reports how different compounds such as hexatriacontane, stearic acid, adipic acid and aminoundecanoic acid, which represent part of the structures present in the contaminants on surfaces, suffer degradation in plasma environments of Ar and Ar + O2. For this, an electroless plasma reactor was used, with a radio frequency source and inductively coupled discharge, with sample positioned in discharge region and with the use of non-oxidizing atmospheres (Ar) and oxidants (Ar + 10% O2). The analyzes were performed on both the volatile products generated by mass spectrometry of the residual gas and optical emission spectroscopy, as well as on the residues after treatment by infrared spectroscopy and high resolution mass spectrometry. The results show that in atmospheres of Ar occurs the production of small volatile fragments obtained by scission of the C-C bonds while at the same time in the residual material, small oligomers of fragments joined by radicals are formed. With the addition of oxygen to the atmosphere, a significant increase in the production of H2, H2O, CO, CO2 and fragments of the molecules was observed at the same time as a considerable oxidation of all the compounds occurs. It was further observed that the formation of the liquid phase considerably altered the reaction process of the treated molecules, leading to a period of high production of H2 and H2O together with a reduction of CO2 production.

Ce travail est centré sur l'étude du décollement de couches minces adhérentes à base cimentaire sur un substrat en béton sous chargement mécanique. Comme matériaux de réparation, des mortiers renforcés par des fibres et/ou incorporant des granulats en caoutchouc sont utilisés. Dans ces conditions, l'étude de la durabilité des réparations implique nécessairement celle de la dégradation de la résistance sous chargement de fatigue. Dans ce contexte, des essais de fatigue par traction, contrôlés par l'ouverture de la fissure (CMOD) sont effectués sur des échantillons composites afin d'établir la loi de dégradation de la résistance du mortier renforcé par des fibres et / incorporant des granulats en caoutchouc. Les résultats montrent que, pour une ouverture de fissure maximale donnée, la résistance résiduelle diminue avec le nombre de cycles et ce quelle que soit la nature du composite. La dégradation maximale de la résistance résiduelle se produit dans le cas du mortier non fibré. Pour des grandes ouvertures de fissure, un renfort par des fibres permet de limiter cette dégradation sous un chargement de fatigue. Dans le cas du mortier incorporant des granulats en caoutchouc, la dégradation de la résistance résiduelle est limitée pour les petites ouvertures de fissure. Une association granulats caoutchouc-renforcement par des fibres permet de limiter les dégâts sur une large étendue d'ouvertures de fissure. Cette solution confère au composite un intérêt pour une application durable dans le cas des réparations minces adhérentes à base cimentaire. En tenant compte des principales pathologies rencontrées dans cette application tels que la fissuration de la couche de réparation suivie par le décollement de l'interface, différentes techniques de préparation de la surface du support ont été évaluées. Parmi celles-ci, un traitement de la surface par sablage, facile à mettre en œuvre dans les conditions réelles, a été utilisé. Pour évaluer la performance structurale, des poutres composites constituées d'un rechargement mince sur des substrats dont la surface a été préalablement traitée par sablage ont été soumises à des essais de flexion trois points (monotone et fatigue). Pour le suivi de l'évolution de la fissuration dans le rechargement et du décollement à l'interface, la technique de corrélation d'image 3D est employée. Il en résulte que l'incorporation des granulats caoutchouc dans le matériau de réparation est efficace pour contrôler la fissuration, et par conséquent pour retarder l'initiation du décollement. De plus, le renforcement du matériau de réparation par des fibres est également efficace pour limiter la propagation du décollement en contrôlant l'ouverture de la fissure. Ainsi, l'utilisation simultanée des granulats caoutchouc et des fibres dans le matériau de réparation par couches minces à base cimentaire peut être une solution appropriée pour retarder l'initiation du décollement et également pour limiter sa propagation, autrement dit pour la durabilité de l'application. Les granulats en caoutchouc utilisés étant obtenus par broyage de pneus usagés non réutilisables, cette approche apporte une valeur ajoutée en valorisant un sous produit industriel et en contribuant à la sauvegarde d'un environnement sain. / This work is devoted to the study of the debonding of thin bonded cement-based overlays from the concrete substrate under mechanical loading. As repair materials, fiber-reinforced and rubbberized cement-based mortars are used. Under these conditions, assessment of durability of the repairs necessarily involves the study of the degradation of the bridging strength under fatigue loading. In this context, tensile fatigue tests controlled by crack mouth opening displacement (CMOD) are conducted on composite specimens in order to establish the degradation law of fiber-reinforced and/or rubberized mortar. The bridging strength decreases with the number of fatigue cycles for the same maximum crack width, whatever the nature of the composite. The maximum cyclic bridging strength degradation occurs in plain mortar. The cyclic bridging strength degradation for large pre-cracked widths is limited for mortar reinforced with metallic fibers. In case of rubberized mortar, cyclic bridging strength degradation is limited at less pre-cracked width values. A combine use of rubber aggregates and fibers in mortar appeared to be a suitable solution to limit the cyclic bridging strength degradation for a wide range of pre-cracked widths. It confers to the composite an interest for durable application such as cement-based thin bonded overlays. Taking into account the main cause of distress in thin bonded cement-based applications i.e. cracking and interface debonding, different surface preparation techniques were evaluated in this research. Among them, the sandblasting one is usually implemented in actual conditions. In order to investigate the structural performance, composite beams consisting of a thin repair layer on top of sandblasted substrates are subjected to three point bending tests (monotonic and fatigue). For monitoring the evolution of cracking in the repair layer and of debonding at interface, digital 3D image correlation technique is used. It emerges as a conclusion that the rubber aggregates incorporation in repair material is helpful to control micro-cracking, which results in the delay of the debonding initiation. Moreover, a fiber-reinforcement of repair material is also helpful to limit the interface debonding propagation by restraining opening of the crack. So, the dual-use of rubber aggregates and fibers in the repair material of thin bonded cement-based overlays can be a suitable solution to delay the debonding initiation and also to limit the interface debonding propagation. This shows that the synergetic effect provided by the combine use of rubber aggregates and fibers remains valid under fatigue loading also. The used rubber aggregates are obtained by grinding end-of-life tyres. In such conditions, the approach brings an added value, the recycling of this industrial by-product being also a contribution to the maintenance of a clean environment. Incidentally, this approach also helps towards the development of a circular economy.

O processo industrial não-contínuo de zincagem por imersão a quente (ZIQ) pode ocasionar a contaminação superficial do aço-carbono zincado por imersão a quente (AZIQ) com resíduos de cloreto. Estes resíduos, se não forem efetivamente eliminados, podem influenciar negativamente no desempenho dos esquemas de pintura dos sistemas dúplex (zincagem mais pintura). Sabe-se que no processo de ZIQ, a cromatização é amplamente utilizada, entretanto, o efeito que este pós-tratamento exerce no desempenho dos esquemas de pintura ainda não é bem estabelecido. Neste contexto, este trabalho teve como objetivos: I - verificar o grau de contaminação no AZIQ com sal de cloreto devido ao próprio processo de ZIQ; II - verificar os efeitos da contaminação com sal de cloreto e da cromatização do processo ZIQ no desempenho de tintas aplicadas sobre o AZIQ; e III – determinar pré-tratamentos para pintura adequados para o bom desempenho das tintas aplicadas sobre o AZIQ. A metodologia adotada para alcançar o objetivo I envolveu a zincagem de chapas de aço-carbono em diferentes prestadores de serviço de ZIQ, em diferentes condições. Estas chapas zincadas foram analisadas por microanálise química qualitativa por espectrometria de dispersão de energia (EDS) em microscópio eletrônico de varredura (MEV) e pela determinação dos teores de cloreto superficiais, por método de extração com água em ebulição. A partir dos resultados obtidos para se alcançar o objetivo I, foi possível definir as condições no processo de ZIQ que potencialmente causam maior contaminação da superfície do AZIQ com sal de cloreto. Assim, para se alcançar os objetivos II e III, chapas de aço-carbono foram zincadas naquelas condições de máxima contaminação com sal de cloreto e parte delas foi submetida ao pós-tratamento de cromatização. Em seguida, uma grande parte destas chapas zincadas (cromatizadas ou não) foi submetida aos pré-tratamentos para pintura de desengraxe com solvente orgânico, de hidrojateamento a alta pressão, de jateamento abrasivo ligeiro e de ação mecânica com esponja abrasiva e água quente. Finalmente, as chapas zincadas, incluindo as não submetidas aos pré-tratamentos, foram pintadas com uma demão de tinta de aderência mais uma demão de tinta de acabamento. As chapas zincadas e pintadas foram submetidas a ensaios acelerados (imersão em água destilada e exposição em câmara de umidade saturada) e não-acelerados de corrosão (exposição em estação de corrosão atmosférica) e avaliadas por meio dos ensaios tradicionais de acompanhamento de desempenho (grau de empolamento e ensaios de aderência de tinta) e eletroquímicos (medida de potencial de circuito aberto, curva de polarização e espectroscopia de impedância eletroquímica – E.I.E.). Algumas chapas zincadas, antes da pintura, foram submetidas aos ensaios de caracterização física (exame microestrutural e morfológico em MEV e rugosidade superficial), química microanálise por EDS, difração de raios X e teor de cloreto superficial pelo método de extração com água em ebulição) e eletroquímica. Os resultados obtidos, neste estudo, permitiram verificar que a aplicação adicional de sal cloreto de amônio sólido durante o processo de ZIQ tende a aumentar o grau de contaminação superficial do AZIQ com cloreto e, as etapas de resfriamento e/ou de cromatização do processo também contribuem para esta contaminação. No geral, o desempenho do AZIQ cromatizado teve desempenho inferior em relação ao não-cromatizados. O hidrojateamento a alta pressão e a lavagem com água e ação mecânica foram os prétratamentos que proporcionaram os melhores desempenhos dos esquemas de pintura. / The batch galvanizing process (BGP) can lead to surface contamination of hot-dip galvanized steel (HDGS) with chloride residues. If these residues are not effectively eliminated, they can influence negatively on the performance of duplex systems (galvanizing plus painting). It is known that the chromate quenching is widely used in the BGP, however the effect of this post-treatment on the performance of duplex systems is not well established yet. In this sense, this work aimed: I – to verify the contamination degree of HDGS with chloride salt due to the BGP itself; II – to verify the effects of the chloride salt contamination and chromate quenching on the performance of paints applied on HDGS; and III – to determine the suitable surface preparation for painting in order for obtaining a good paint performance applied on HDGS. The adopted methodology to achieve goal I involved the galvanizing of steel plates in different service renderings with BGP, in different conditions. These HDGS plates were submitted to the qualitative energy dispersive microanalyses (EDS) in scanning electron microscopy (SEM) and to the determination of superficial chloride contents by the boiling water extraction method. From the obtained results, the conditions in the BGP that potentially lead to greater surface contamination of HDGS with chloride salt were determined. Thus, to achieve goals II and III, steel plates were galvanized under the maximum chloride salt contamination condition and part of them were submitted to chromate quenching. After that, a great part of these HDGS plates (chromated or non chromated quenching) was submitted to the surface preparations for painting through organic solvent cleaning, high pressure hydroblasting, sweep blasting and handled scrub cleaning with an abrasive sponge and hot distilled water. Finally, the HDGS plates, including those not submitted to the surface preparations for painting, were painted with one coat of primer plus one coat of finishing paint. The HDGS painted plates were submitted to accelerated (distilled water immersion and humidity chamber exposure) and non accelerated (atmospheric exposure) corrosion tests and their performance were verified by means of traditional tests (degree of blistering and paint adhesion) and electrochemical measurements (open circuit potential, polarization curve and electrochemical impedance spectroscopy – E.I.S.). Before painting, some HDGS plates were submitted to tests for physical (microstructural and morphological analyses in MEV and surface roughness), chemical (EDS, X-ray diffraction and superficial chloride contents by the boiling water extraction method) and electrochemical characterization. The obtained results allowed verifying that the additional application of solid ammonium chloride salt during the BGP tends to increase the degree of superficial chloride contamination of the HDGS and, the water and/or chromate quenching also contribute for this contamination. In general, the chromated HDGS presented worst performances. The high pressure hydroblasting and the handled scrub cleaning with an abrasive sponge and hot distilled water were the surface preparations for painting that provided the best performances of paint systems.

L’objectif de ce travail est de qualifier l’utilisation du collage structural en remplacement des solutions d’assemblage conventionnel dans les applications lanceur spatiaux. Si les gains potentiels tant en terme opérationnel qu’en terme de performance ne sont plus à démontrer il reste à mettre en place une démarche de dimensionnement qui garantisse le niveau important de fiabilité requis. Deux adhésifs structuraux de types époxydes ont été étudiés : l’EA9394 et le SW2216. Un travail important d’analyse physico-chimique des surfaces a été mené pour mettre en place un procédé d’assemblage stable et performant. L’analyse mécanique des liaisons collées a montré que l’adhésif subit en situation des sollicitations combinées de traction et de cisaillement. Un dispositif dérivé des essais Arcan à été proposé qui permet d’obtenir la réponse du film de colle sous forme de courbe contrainte déplacement relatif des substrats. La résistance mécanique mesurée au moyen des essais Arcan mais également sur le matériau adhésif montre une forte dispersion liée à un taux de porosité important mais également à une microstructure très hétérogène constituée d’une matrice époxyde et mélangée à des particules d’aluminium (adhésif EA9394). Enfin, le collage a été étudié à une échelle plus macroscopique en tentant de proposer un dimensionnement de liaison pour le lanceur démonstrateur Arcadia. Les lanceurs étant des structures à symétrie de révolution, un modèle semi-analytique de liaison collée axisymétrique a été développé.Ce travail a permis la mise en place d’une démarche d’analyse mettant en avant les analyses à l’échelle du film, de la liaison et de la structure pour mettre en évidence les nombreux phénomènes à l’origine d’une ruine prématurée de la liaison. Cette optimisation multiéchelle doit être conduite pour maximiser la résistance spécifique de la liaison en assurant le niveau de fiabilité requis pour cette application spatiale. / The objective of this study is to qualify the use of structural bonding as a replacement for conventional assembly solutions in space launcher applications. Potential benefits in fabrication and of final performance are already known, but it remains to establish a design approach to guarantee the high level of reliability required. Two epoxy structural adhesives have been studied: EA9394 and SW2216. A study of the physico-chemistry of surfaces has been effected in order to find a stable and strong bonding process. Mechanical analysis of bonded connections revealed that the adhesives could be subjected in use to mixed loadings in tension and shear. A device derived from Arcan tests has been proposed in which it is possible to obtain adhesive layer responses as stress/relative deformation for different substrates. Mechanical strength measured with the Arcan device and also on the bulk adhesive material revealed a high variability coming from a significant porosity fraction but also due to a highly heterogeneous microstructure constituted of epoxy matrix and aluminium particles (EA9394adhesive). Bonding has been studied on a macroscopic scale proposing connection design for the demonstration Arcadia launcher. A rocket being an axially symmetrical structure, a semi-analytical model of axisymmetric bonded connections has been developed. This study resulted in the finalisation of an analysis approach pointing to scale analysis of the adhesive layer, connection and structure in order to emphasise the many phenomena which could cause early bond failure. This multiscale approach should be effected to increase specific assembly strength while assuming the required reliability level for this spatial application.

In this study, the possibility of using low pressure hydrogenated steam to simulate primary water reactor conditions is examined. The oxides formed on Alloy 600 (WF675) between 350 Celsius and 500 Celsius in low pressure hydrogenated steam (with a ratio of oxygen at the Ni/NiO to oxygen in the system of 20) have been characterised using analytical electron microscopy (AEM) and compared to oxide that formed in a high pressure water in a autoclave at 350 Celsius with 30 cc/kg of hydrogen. Preferential oxidation of grain boundaries and bulk internal oxidation were observed on samples prepared by oxide polishing suspension (OPS). Conversely, samples mechanically ground to 600 grit produced a continuous, protective oxide film which suppressed the preferential and internal oxidation. The surface preparation changed the form of the oxides in both steam and autoclave tests. The preferential oxidation rate has been determined to be K_{oxide} = Aexp{-Q/RT}with A = 2.27×10^(−3) m^(2)s^(−1) and Q = 221 kJ.mol^(−1) (activation energy) for WF675 and A = 5.04 × 10^(−7) m^(2)s^(−1) and Q = 171 kJ.mol^(−1) for 15% cold worked WF675. These values are consistent with the activation energy of primary water stress corrosion cracking (PWSCC) initiation. Bulk oxygen diffusivities were calculated from the internal oxidation after 500 h exposures. At 500 Celsius the oxygen diffusivity was determined to be 1.79×10^(−20) m^(2)s^(−1) for WF675 and 1.21×10^(−20) m^(2)s^(−1) for 15% cold worked WF675, the oxygen diffusivity at 400 Celsius in 15% cold worked WF675 was calculated to be 1.49×10^(−22) m^(2)s^(−1).The Cr-depletion associated with preferential oxidation has been assessed by AEM. The Cr-depletion was asymmetric and it could not be accounted for by local variations in the diffusion rate. Chemically induced grain boundary migration is suggested as a possible explanation. Constant load SCC tests conducted in hydrogenated steam at 400 Celsius have shown a similar trend to the classical dependency of PWSCC as a function of potential. The SCC samples were also prepared with two surface finishes, OPS and 600 grit. In all SCC tests, significantly more cracking was observed on the OPS surface and all failures initiated from this surface.

This work deals with the metal surface wetting problems of molten lead-free solder and monitoring of ongoing processes at the inter-phase interface using the method of evaluation of the height of the molten solder deducted from the video sequences. The work is aimed at evaluating the metal surface wettability, wetting angle determined. Wettability of the metal surface is compared for different types of surface treatments and for different ages of the measured samples. Measurement is performed at the improved workplace, is used to evaluate the newly derived formula for calculating the wetting angle and created program for automatic evaluation of Picture is used to.

Damages of metallic aircraft structures that occur during manufacturing, assembly and in service require local repair. Especially with current service-life extensions of ageing aircraft fleets, the importance of such repair methods is increasing. Typically, the repair of smaller damages on aluminium fuselage or wing skins is done by riveting a patch onto the flawed structure. However, the use of rivets reduces the strength of the structure and promotes fatigue. Joining the patch by adhesive bonding would not only offer more homogenous load distribution and weight savings, but even an increase of structural integrity. Metal adhesive bonding is commonly used in aeronautics, but requires elaborated surface treatments of the adherends, employing hazardous chemicals like chromates, due to the high durability demands. Furthermore, these treatments are usually tank processes that are not suitable for local repairs. Hence, there is a strong need for locally applicable surface preparation methods that allow safe and reliable adhesive bonding of primary aircraft structures. The aim of this thesis is to assess the – still emerging – method of atmospheric pressure plasma deposition of silicon (Si) containing compounds concerning its suitability as surface preparation for adhesive bonding of aluminium aerostructures. Atmospheric plasma deposition is not yet used in the aircraft industry, and the knowledge on functionality of this technology concerning bonding of aluminium parts is limited. Moreover, the durability requirements of the aircraft industry greatly exceed the standards in other industries. Hence, special attention is paid to a thorough analysis of the key characteristics of the deposited coupling films and their effectiveness in terms of adhesion promotion as well as joint durability under particularly hostile conditions. In order to do so, the altering mechanisms of the treated joints and the behaviour of the coupling films during accelerated ageing will be investigated in detail for the first time in this thesis. Furthermore, the influence of the aluminium surface pre-treatment (i.e. topography and oxide properties of the substrate) on the overall joint performance after coupling film deposition is thoroughly examined. Based on these findings, the surface preparation is optimised, and a process is developed to achieve maximal joint performance. As alternative local surface treatments prior to adhesive bonding, solution derived deposition of silane and sol-gel films have already been widely investigated and can be considered as reference, even though these techniques are rarely used in civil aeronautics. The knowledge on their effectiveness and capabilities in corrosive atmosphere is still very limited. Therefore, all analyses of degradation mechanisms are conducted for both plasma deposition and wet-chemical reference treatments to reveal the differences and communalities of the two Si-based coupling films. Physical and chemical analysis of the films, the oxides and the interfaces reveal differing, but interdependent failure mechanisms that are inhibited differently by the individual coupling films. Using the optimum deposition parameters, plasma films of only several nanometres in thickness significantly enlarge the corrosion resistance of bonded joints, reaching almost the level of anodising treatments with several micrometres thick oxides and strongly outperforming solution derived silane treatments. However, plasma film performance is found to be largely dependent on the precursor selection. With plasma deposition of 3-glycidoxypropyltrimethoxysilane, which has not been reported before, highest joint stability is achieved. Moreover, it is discovered that the properties of plasma and solution derived silane based films are complementary. It is shown that an optimised combined plasma and wet-chemical treatment process provides even superior resistance to bondline corrosion than state-of-the-art anodising techniques.