Made available in DSpace on 2016-12-08T17:19:24Z (GMT). No. of bitstreams: 1 Claudinei Franco.pdf: 6129117 bytes, checksum: 6059aaddb2af97db39be8b6299acf549 (MD5) Previous issue date: 2014-10-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The interest for improvements in tribological properties of materials, more specifically in steels with low and medium carbon content are of great importance for mechanical components life time. In this work, thermochemical treatments were carried out on ABNT 1020 and ABNT 1045 steels, in order to compare and evaluate the tribological behavior and also the phases and layers formed, to the different types of treatments which are: boronizing, nitriding and multi component boronizing (also known as duplex treatment). The specific objectives were to plan the different ways of treatment; evaluate and compare the effect of the substrate according to the microstructure, support and interface of the layers formed through the treatments; characterize the wear mechanisms for the different treatments and compare the results of both materials. The thermochemical treatments were carried out, using as basis previous works performed by the powder metallurgy research group. Boronizing and nitriding treatments were carried out by solid means, multi component boronizing treatment was performed in two ways: in the first one, boronizing was followed by nitriding (BN) and the in the second one, nitriding was followed by boronizing (NB). These duplex treatments were performed with the same conditions of time and temperature used for nitriding and boronizing treatments. Pin-on-disk sliding wear tests were performed using WC-Co (hard metal) balls as counter body. Through the test it was possible to evaluate the tribological behaviour. Friction coefficient, volume of removed material and wear mechanisms were determined. The microhardness of the formed layers was measured at the surface and on the cross section of the specimens. X-ray diffraction was used to confirm the formed compounds on nitriding, boronizing and boron-nitriding (duplex) treatments. The results showed an increase in the hardness of the surface layer and a reduction in the amount of removed material (volume) in all thermochemical treatments comparing with the condition of non-treated samples. Regarding the tribological behavior, by evaluating the thermochemically treated samples, the nitrided samples of ABNT 1020 presented the highest amount of removed material (0,078 mm3) and its hardness was 436 HV0.05. The boronized ABNT 1020 steel presented the lower amount of removed material (0,013 mm3). The boronized ABNT 1045 steel reached the highest mean hardness on the surface (1750 HV0.05) and the NB duplex treatment in this material provided the highest hardness of the formed layer, about 2270 HV0.05. / O interesse por melhorias nas propriedades tribológicas de materiais, mais específico em aços com baixo e médio teor de carbono são de grande importância para a vida útil de componentes mecânicos. Neste trabalho foram realizados diversos tratamentos termoquímicos em aços ABNT 1020 e ABNT 1045, com o objetivo de comparar e avaliar o comportamento tribológico e também as fases e camadas formadas, para as diferentes formas de tratamentos que são: boretação, nitretação e boretação multicomponente (também conhecido como tratamento duplex). Os objetivos específicos foram: planejar as formas de tratamentos; avaliar e comparar o efeito do substrato relacionado à microestrutura, ao suporte e interface das camadas formadas nos tratamentos realizados; caracterizar os mecanismos e formas de desgastes para os diversos tratamentos e comparar entre os dois materiais. Os tratamentos termoquímicos foram realizados, utilizando como base trabalhos anteriores que foram realizados no grupo de pesquisa de metalurgia do pó. Os tratamentos de boretação e nitretação foram realizados por via sólida, o tratamento de boretação multicomponente foi realizado de duas formas: na primeira foi realizada a boretação seguido de nitretação (BN) e a segunda foi a nitretação seguido de boretação (NB), nos tratamentos duplex utilizaram-se os mesmos parâmetros de boretação e nitretação. Foram realizados ensaios de desgaste por deslizamento do tipo pino sobre disco, com esferas de WC-Co (metal duro) como contra corpo. Foram avaliados: o coeficiente de atrito, o volume de material removido e os mecanismos de desgaste. A dureza da camada formada foi avaliada por microdureza na superfície e na seção transversal. Difratometria de raios-X foi utilizada para a comprovação da formação das camadas de nitretos, boretos e boro-nitretos (duplex). Os resultados mostraram melhoras principalmente na dureza da camada superficial e redução no volume de material removido, em todos os tratamentos termoquímicos, quando comparado com amostras sem tratamento. Em relação ao comportamento tribológico, avaliando as amostras tratadas termoquimicamente, as amostras nitretadas do aço ABNT 1020 foram as que apresentaram os piores resultados com volume de material removido de 0,078 mm3 e dureza de 436 HV0,05. Já a boretação no aço ABNT 1020 foi o tratamento que apresentou o melhor desempenho em volume de material removido com 0,013 mm3. O aço ABNT 1045 com tratamento de boretação apresentou a maior dureza média na superfície, com 1750 HV0,05 e o tratamento duplex NB neste mesmo material proporcionou a maior dureza na seção transversal, resultante da camada formada de nitretos-boro com 2270 HV0,05.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Lately, we have witnessed a growing concern about determining energy consumption and pollutant emissions. Large part of the energy spent is directly related to the friction and wear. Likewise, there a growing demand for production of mechanical systems of high efficiency. To develop systems that are more economical, noiseless and not harmful to the environment, there is a limit imposed by materials and conventional surface treatment. Thus, critical tribological contacts and possible new materials have been intensively investigated. Solid lubrication and solid lubricants are emerging as a promising alternative to control friction and wear in mechanical systems modern. The use of multifunctional coatings have been studied and used in modern mechanical systems, so that the final properties depend on the system composed of substrate - coating - environment. This study aims to optimize the thickness of multifunctional coatings with potential for use in mechanical systems of high efficiency, particularly on soft substrates. The aim is an optimization using the principles of contact mechanics, together with strength criteria to analyse stress and strain. Efficient techniques to characterize the coatings, and powerful simulation tools in the stress analysis of multifunctional coatings were used. The results showed that the thickness of the coating plays an important role on coating properties. / Ultimamente, tem-se presenciado uma preocupação cada vez mais determinante quanto ao consumo energético e emissões de poluentes. Grande parte da energia gasta está relacionada diretamente com o atrito e o desgaste. Há igualmente uma demanda crescente por produção de sistemas mecânicos de alta eficiência, mas, também, para desenvolver sistemas cada vez mais econômicos, silenciosos e não prejudiciais ao meio ambiente, havendo um limite imposto por materiais e tratamento de superfícies convencionais. Assim, a tribologia de contatos críticos e possíveis novos materiais estão sendo amplamente pesquisados. A lubrificação sólida e lubrificantes sólidos estão aparecendo como uma alternativa promissora para controlar o atrito e o desgaste nos sistemas mecânicos modernos. A utilização de revestimentos multifuncionais tem sido estudada e aplicada nos sistemas mecânicos modernos, de modo que as propriedades finais resultantes sejam dependentes do sistema substrato-revestimento-ambiente. O presente trabalho busca a otimização de tribo revestimentos multifuncionais com potencial para a aplicação em sistemas mecânicos de alta eficiência, particularmente sobre substratos macios. Busca-se essa otimização por meio da análise de tensões e deformações, as quais são compreendidas através do princípio da mecânica do contato, juntamente com os critérios de resistência. Usam-se técnicas de caracterização de revestimentos amplamente usadas e eficientes, como também ferramentas de simulação poderosas na análise de tensões de revestimentos multifuncionais. Os resultados demonstram que a espessura do revestimento tem um papel importante na origem das propriedades do revestimento. / Doutor em Engenharia Mecânica

Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

Dès les débuts de la conquête spatiale, la tribologie spatiale est considérée comme une discipline à part entière car il s’agit de lubrifier un mécanisme non seulement dans le vide spatial, mais aussi lors des opérations au sol, et ceci dans différents environnements (vide simulé, air sec et humide, azote sec). Un lubrifiant spatial, fluide ou solide, doit donc relever le défi de procurer le comportement tribologique désiré dans ces environnements successifs, mais doit aussi résister aux sollicitations dynamiques induites par le lancement. Dans l’espace, le mécanisme doit y être autonome sans maintenance et sa lubrification doit être maintenue pendant au moins 15 ans (800 millions de cycles pour un roulement) tout en conservant fiabilité et précision de positionnement (µrad). Malgré ces enjeux, la maîtrise tribologique spatiale se limite à de l’empirisme et du conservatisme de solutions techniques, notamment lors de l’emploi des matériaux sources de lubrifiants solides qui font l’objet de cette étude. Dans les faits, seules des recommandations d’utilisation existent sans pouvoir prédire le comportement tribologique des solutions. Cette prédiction nécessite la reconstitution de « la vie des contacts ». Cette dernière nécessite l’évaluation des débits de 1ers et 3ème corps. Ces débits dépendent d’un couplage multi-échelles et multi-physique « forcé » par les sollicitations tribologiques. Pour décrypter ces débits, une démarche expérimentale qui couple des mesures mécano-chimiques en temps réel et des analyses post-essai a été développée (forces, analyse de gaz, visualisation électronique et photonique). La simultanéité des mesures permet d’étudier le couplage entre les phénomènes mécaniques (créations de particules de 3ème corps, déformations plastiques des 1er corps) et physicochimiques (adsorption/désorption, modifications chimiques des 1ers et 3ème corps). La démarche est appliquée à l’étude de deux triplets tribologiques ayant respectivement des 1ers corps en MoS2 et MoS2+Ti dont les comportements tribologiques sous vide et sous air humide sont antagonistes. L’utilisation de leur antagonisme permet de mieux comprendre la réponse des 1er et 3ème corps aux sollicitations tribologiques. La reconstitution de la vie de ces triplets a montré : (1) le rôle bénéfique de la structure colonnaire dans l’obtention d’un facteur de frottement faible et d’une longue durée de vie, non parce qu’elle est intrinsèquement colonnaire mais parce qu’elle localise la production de 3ème corps; (2) le rôle bénéfique des contaminations internes et externes aux 1ers et 3ème corps qui délocalisent l’accommodation du volume du 3ème corps vers les complexes de surface, ce qui explique par exemple que l’environnement N2 sec ne puisse, même pour des raisons économiques, simuler l’ultravide. In fine, ces travaux permettent de spécifier une démarche de conception de « triplets tribologiques » qui sera généralisée ultérieurement grâce à la tribologie numérique / From the very beginning of space exploration, “space tribology” became a specific field of competences in its own right because it implies lubricating a mechanism not only in the vacuum of space but also in several environments (simulated vacuum, dry and humid air, dry N2 environment, etc.) on Earth. Consequently, a lubricant, fluid or solid, must provide the desired tribological behaviour in all those successive environments, but it must also resist to the dynamic loading induced by the launch operations. Once in space, a space mechanism must be autonomous, with no possible maintenance, and its lubrication must be sustained during 15 to 30 years (i.e. up to 800 millions cycles for a ball bearing) in space while sustaining high reliability and great precision (to within a few µrad). Despite those stakes, the mastery of space tribology is limited to empiricism and conservatism of technical solutions, especially when solid lubricants, whose are studied in this study, are used. In facts, only directions for use exist without allowing predicting the tribological behaviour of the solutions. That prediction requires the reconstitution of “the contacts’ life”. The latter requires evaluating the 1st and 3rd bodies flows. Those flows depend on a multiscale and multiphysical coupling effect “forced” by the tribological stresses. To decrypt those flows, an experimental procedure which couples both real time and post-mortem mechano-chemical measurements (friction forces, gas analysis, photonic and electronic visualization,) has thus been developed. The simultaneity in the measure allows studying the relationship between mechanical (3rd body particles creation, plastic deformations of 1st bodies, etc.) and physicochemical (adsorption/desorption, chemical changes of 1st and 3rd bodies, etc.) phenomena. The procedure is applied to two tribological triplets respectively containing 1st bodies comprised of MoS2 and MoS2+Ti coatings whose tribological behaviours in vacuum and humid air are antagonistic. Such antagonism allows better understanding the responses of the 1st and 3rd bodies to the tribological stresses. The reconstruction of the contact life of those triplets allowed showing, among others: (1) the beneficial role of coating columnar structure in the obtaining of both a low friction coefficient and a long wear life. This is not because it is columnar but because such a structure localizes the 3rd body creation; (2) the beneficial role of contaminations, which is either internal or external to the 1st and 3rd bodies, by delocalizing the accommodation from the 3rd body volume to the surface complexes, which explains, for example, that dry N2 environment can not, even for financial reasons, mimic ultrahigh vacuum. In fine, the study allows specifying a procedure for designing “tribological triplets” which will be generalized at a latter stage thanks to the numerical tribology.

Le squat est un défaut de fatigue de contact apparaissant à la surface du rail et dont le mécanisme d’amorçage est mal compris. Afin de pallier ce manque, une analyse tribologique locale de la bande de roulement du rail est mise en oeuvre à proximité d’un squat naissant. Cette caractérisation révèle une anisotropie importante des couches superficielles du rail associée aux développements de Transformations Tribologiques Superficielles. Ces résultats témoignent de conditions de contact roue/rail particulières dans la zone d’étude, notamment d’un niveau d’efforts de cisaillement inhabituel pour une voie en alignement. Dans le but de valider ces observations, plusieurs essais sont effectués. D’une part les conditions de contact roue/rail dans une zone de squats sont mesurées à partir d’un train instrumenté. D’autre part, la réponse tribologique de l’acier à rail à ces conditions de contact est étudiée à travers le suivi régulier d’une zone d’essais soumise à la circulation ferroviaire. Ces essais permettent d’identifier un déséquilibre important des efforts de traction sur les bogies moteurs et des glissements locaux élevés de la roue sur le rail. Différents mécanismes d’amorçage thermo-mécaniques sont alors proposés au sein d’un schéma global de la réponse tribologique de l’acier à rail. / Squats have recently become recognised as one of the major rolling contact fatigue defects in modern railway networks for which there is currently no solution other than preventive grinding operations or costly rail renewal. To better understand the entire damage mechanism of squat, A tribological and metallurgical analysis of the rolling band and the near surface layer was performed close to an incipient squat. This characterization show a significant anisotropy of the rail surface layer associated with developments of Tribological Transformation of Surface. These results reflect some specific wheel/rail contact conditions in this squat area, including an unusual level of shear forces in a straight track. In order to validate this observations, two tests were performed. On the one hand, the contact conditions in a squat area were measured from an instrumented train. On the other hand, the tribological response of the rail steel was studied through regular monitoring of a test site subjected to railway traffic. These tests allow to identify a high imbalance of the traction forces and the presence of local slips at the wheel/rail interface. Several thermomechanical initiation mechanism of squats are then given in a overall diagram of the tribological response of rail steels.

Les matériaux énergétiques sont, par définition, des matériaux susceptibles de dégager un volume important de gaz, en se décomposant via les phénomènes suivants : combustion, déflagration ou détonation. Ils sont notamment utilisés dans les secteurs industriels de l’automobile (déploiement d’airbag), du militaire (propulsion de missiles tactiques et stratégiques, munitions) et du spatial (boosters de lanceurs spatiaux type Ariane 5). La maîtrise de leur fabrication nécessite que soient vérifiées certaines contraintes spécifiques rencontrées lors de leur mise en œuvre dans un malaxeur bivis. En effet, ce procédé de malaxage en continu induit de fortes évolutions de gradients de pression et de cisaillement au sein du matériau énergétique (entrefers réduits...) qui peuvent initier les constituants fluides et solides. Par conséquent, dans un souci de parfaite maîtrise des risques industriels, les conditions tribologiques menant à l’initiation d’un matériau énergétique, ici le propergol, lors de sa fabrication, doivent être étudiées. Malheureusement, à cause de la confidentialité industrielle liée à ce secteur d’activité, la bibliographie de la tribologie des propergols est limitée. Il apparait toutefois que peu d’études portent effectivement sur le comportement tribologique du troisième corps, c’est à dire le propergol. Ce dernier étant hétérogène (mélange de constituants fluides et de solides), il est donc nécessaire d’appréhender les écoulements internes qui l’animent sous sollicitations tribologiques. Ainsi, pour reproduire les sollicitations mécaniques élémentaires (compression et cisaillement) appliquées par les deux premiers corps que sont les vis et le fourreau, et subies par le troisième corps lors du malaxage, il a été choisi d’utiliser une approche couplée expérimentale et numérique. Cette dernière s’organise autour de l’instrumentation d’un dispositif de sécurité permettant la sollicitation par frottement du propergol et de la modélisation par éléments discrets du triplet tribologique (parois supérieure et inférieure des premiers corps, et troisième corps). Il est ainsi apparu un comportement tribologique caractéristique du troisième corps : des ségrégations entre les constituants mènent à un arrangement selon trois couches superposées dans l’épaisseur du troisième corps. Ces ségrégations sont issues de la mise en place de débits internes, spécifiques à chaque nature et géométrie de constituants. Ces débits sélectionnent les constituants présents dans l’aire de contact et favorisent l’existence de conditions tribologiques favorables à l’initiation du troisième corps (assèchement de l’épaisseur, localisation des efforts appliqués au troisième corps ...). L’ensemble de ces débits permet de reconstituer un circuit tribologique d’initiation d’un propergol et ainsi d’envisager des solutions techniques permettant d’endiguer la mise en place des conditions défavorables à la fabrication en sécurité d’un propergol dans un malaxeur bivis. / By definition, energetic materials can deliver a huge amount of gas and cause different kinds of phenomena, such as: burning, deflagration or detonation. These materials are mainly used in the automotive industry (airbag deployment), military devices (missiles, ammunition) and space launchers (Ariane 5 boosters and pyrotechnic devices). The manufacturing process, although well controlled by the historical “batch” process, presents several challenges when it is transferred to the continuous mixing process, using a twin-screw mixer device. Indeed, this last device induces extreme evolutions of pressure gradients and shearing gradients (reduced air-gap...). Plus, the energetic material is composed of fluid components and different diameters of solid components that can ignite by shearing. Consequently, tribological conditions leading to the ignition of an energetic material, a solid propellant, are studied during its manufacturing in a twin-screw mixer. Unfortunately, because of the industrial confidentiality on solid propellants, the bibliography on the solid propellants tribology is limited. However it appears that too few studies have effectively dealt with the tribological behaviour of this third body. By nature, this last is a composite material; therefore it is necessary to understand internal flows that evolve from tribological stresses. Thus, a coupled approach experimental and numerical is chosen in order to reproduce the mechanical elementary stresses applied by the two first bodies (top of screw thread and bore of the barrel element), and undergone by the third body during its manufacturing in a twin-screw mixer (compression and shearing). This approach consists of the instrumentation of a security test that shears the solid propellant and a discrete element simulation of the tribological triplet (inferior and superior first bodies, and the third body). The distinctive tribological behaviour of this third body appears obvious: different types of component segregations lead to a three superposed layer arrangement of the solid propellant thickness. These segregations come from the creation of internal component flows, specific to the nature and the geometry of the third body components. These flows select the components that remain within the contact area and also establish the tribological conditions that favour the third body ignition (gradient of mobility between solid components, draining of the third body thickness, localization of the efforts applied to the third body…). Ultimately, this study rebuilds the ignition tribological circuit(s) of a solid propellant and offers technical solutions to prevent the materialisation of unfavourable conditions to a safe solid propellant manufacturing in a twin-screw mixer.

En aéronautique, l’optimisation du fonctionnement des freins de roue nécessite qu’ils aient des comportements tribologiques qui décélèrent progressivement les aéronefs tout en maximisant l’endurance des freins. Ces comportements sont obtenus par le biais d’empilements de disques en composites carbone-carbone situés dans la jante de chaque roue qui, mis en contact par l’action d’une couronne hydraulique, transforment, emmagasinent puis restituent l’énergie de freinage. La jante, la couronne hydraulique (mécanisme), les disques (premiers corps) et le film intercalaire (troisième corps) constituent le triplet tribologique qui gouverne le freinage. Du fait du confinement du "contact" entre les disques d’une part, et entre les disques et la jante d’autre part, la compréhension locale des phénomènes énergétiques (conversions thermo-mécaniques) opérant pendant le freinage, nécessite un découplage des phénomènes tribologiques mis en jeu, en particulier au niveau de la "peau" des premiers corps et du troisième corps (échelle locale). Le découplage, difficile à établir expérimentalement, est réalisé dans cette étude par une modélisation numérique la plus réaliste possible des circuits tribologiques thermo-mécaniques activés (flux de matière et d’énergie). Cette dernière est obtenue en enrichissant la méthode des éléments discrets afin de prendre en compte les arrangements locaux des constituants des premiers et troisième corps. Ces enrichissements sont confrontés numériquement et expérimentalement, à l’aide d’une "boîte granulaire" instrumentée, puis exploités pour analyser les réponses thermo-mécaniques des premiers et troisième corps. Les analyses suggèrent qu’une "dégradation seuil" des premiers corps engendre des arrangements locaux aux comportements thermo-mécaniques singuliers, même si l’énergie globale appliquée (pression × vitesse) est constante. Par exemple, les constituants du troisième corps induisent des phénomènes conservatifs tels que la formation de "rouleaux thermiques" liée à la recirculation locale du troisième corps, et des phénomènes dissipatifs tels que la conduction de la chaleur par le biais des hétérogénéités (paquets de fibres) des premiers corps. Les arrangements locaux, les endommagements, ... peuvent être caractérisés par des mesures numériques de résistance thermique de contact qui résultent de la compétition entre des énergies à l’échelle locale et des énergies à l’échelle globale (mécanisme). Cette résistance permet de distinguer dans les bilans d’énergie thermo-mécaniques, en plus des phénomènes dissipatifs bien connus, les phénomènes conservatifs qui amènent le triplet tribologique vers un équilibre. Dans le cas du freinage, l’équilibre est conditionné par le choix des arrangements qui restreignent l’usure (phénomènes conservatifs), et de ceux qui maximisent l’évacuation de la chaleur hors du contact (phénomènes dissipatifs). / In aeronautics, optimizing the operation of wheel brakes requires tribological behaviors which gradually decelerate aircrafts while maximizing endurance brakes. These behaviors are obtained through stacks of carbon-carbon composite discs located in the rim of each wheel which, brought into contact by action of pistons housing, transform, store and restore the braking energy. Rim, pistons housing (mechanism), discs (first body) and the separating film (third body) constitute the tribological triplet governing braking. Due to confinement of the "contact" firstly between discs, and secondly between discs and rim, the local understanding of energetical phenomena (thermo-mechanical conversions) operating during braking, requires a decoupling of tribological phenomena, especially at the scale of "skins" of the first body and third body (local scale). Such decoupling, experimentally difficult to operate, is performed in this study by a more realistic numerical modeling of activated tribological thermo-mechanical circuits (matter and energy flows). The modeling is obtained by enriching a discrete element method in order to take into account the local arrangements of the first and third body constituents. These enhancements are numerically and experimentally compared, using a "granular box" instrumented and used to analyze thermo-mechanical responses of first and third bodies. Analyzes suggest that a "threshold degradation" of first body generates local arrangements to singular thermo-mechanical behavior, even if the global applied energy (pressure × speed) is constant. For example, constituents of third body induce conservative phenomena such as formation of "heat rollers" linked to local recirculation of third body, and dissipative phenomena such as heat conduction through heterogeneities (fiber bundles) of first body. Local arrangements, damaging, ... can be characterized by numerical measures of thermal contact resistance which result from competition between energies at local scale and energies at global scale (mechanism). This resistance becomes here a probe of local arrangements. It distinguishes in thermo-mechanical energy balances, in addition to well-known dissipative phenomena, the conservative phenomena that lead to the tribological triplet balance. In the case of braking, balance is determined by the choice of arrangements which restrict wear (conservative phenomena), and the ones they maximize evacuation of heat from the contact (dissipative phenomena).

Ce travail présente un procédé innovant d’élaboration de revêtements prothétiques phosphocalciques : l’électrodéposition. Il porte sur la synthèse et la caractérisation de phosphates de calcium destinés au recouvrement de prothèses de hanche. Un protocole original a été développé en associant l’électrodéposition en mode courant pulsé à un traitement thermique sous atmosphère contrôlée appelé THUCA. La morphologie, la composition et la structure des revêtements obtenus ont été analysées respectivement par MEB, microanalyse X et diffraction des rayons X. Les résultats ont montré que nous obtenons un implant constitué d’un revêtement biphasique (hydroxyapatite HAP et phosphate tricalcique b-TCP) sur l’alliage de titane TA6V.Les caractérisations mécaniques par indentation, les tests de rayure (scratch test) et d’usure (tribologique) réalisées pour la première fois sur cet implant ont montré que le revêtement possède un excellent aspect cohésif et adhésif avec une excellente résistance à l’usure. Par ailleurs, la bioactivité des revêtements élaborés est évaluée en milieu physiologique en étudiant d’une part leur comportement vis-à-vis de la corrosion, et d’autre part leur comportement en milieu de culture cellulaire. L’ensemble de ces résultats indiquent que l’implant proposé possède de bonnes propriétés faisant de lui un bon candidat en tant qu’implant pour la chirurgie orthopédique.Par ailleurs, ce travail de thèse a été achevé par des études préliminaires concernant une technique complémentaire à l’électrodéposition : l’électrophorèse. Nous avons obtenu pour la première fois un revêtement constitué de nanoparticules d’hydroxyapatite ayant de bonnes propriétés mécaniques. / This work presents an innovative process to develop prosthetic calcium phosphate coatings: electrodeposition. It focuses on the synthesis and characterization of calcium phosphates for the recovery of hip prostheses. Thus, an original protocol was developed, which combines pulsed current electrodeposition to a heat treatment method under controlled atmosphere called THUCA. Morphology, composition and structure of the coatings obtained were analyzed respectively by SEM, X-ray microanalysis and X-ray diffraction. The results showed that we obtain an implant consisting of a two-phases coating (HAP hydroxyapatite and tricalcium phosphate b-TCP) on the titanium alloy TA6V.Mechanical characterizations made by indentation, scratch tests (scratch test) and wear (tribological) for the first time on this implant showed that the coating has a good adhesive and cohesive appearance with improved wear resistance. Moreover, the bioactivity of the developed coatings was evaluated by studying their corrosion behavior in physiological medium and also their behavior in cell culture medium. All these results indicate that the proposed implant has good properties making it a good candidate as an implant for orthopedic surgery.Furthermore, this thesis was completed by preliminary studies of a complementary technique to electrodeposition: electrophoresis. We obtain for the first time a coating consisting of nano-particles of hydroxyapatite having good mechanical properties.

The titanium alloy, Ti-6Al-4V, is vastly studied and used in many applications because it has a transformation microstructure, which can be tailored for apt properties that are consistent up to 500°C. Compared to conventional steels, this alloy favours certain applications due to its high specific strength, hardenability, corrosion resistance, biocompatibility and weldability. Its weldability makes the alloy a good candidate for additive manufacturing (AM). Ti-6Al-4V parts are widely built by the AM process of electron beam melting (EBM). However, heat transfer remains crucial in EBM process. The high intensity localized, moving, electron beam heat source and the rapid self-cooling are critical, especially in thin parts/ sections. When thin sections are built by the EBM process, there will be microstructural variation in their build direction, which can lead to the variation of their mechanical properties. It is necessary to understand the microstructure and mechanical properties of thin sections when they are used as functional parts in various applications in aerospace, automotive, medical, etc. industries. The microstructure, tribological behaviour and mechanical properties of Ti-6Al-4V, as-built EBM thin plates were studied by means of various hardness, scratch and tensile testing. The hardness and scratch tests were performed on the thin plates to correlate the microstructural variation. In-situ micro tensile test was performed inside the scanning electron microscope (SEM), to see the sample’s deformation behaviour. Microstructural characterization revealed equiaxed grains in the transverse section and the longitudinal surface exhibited columnar grains elongated along the build direction. The size of the equiaxed grains are found to vary across the thickness of the plate. The indentation and scratch hardness also vary in correlation with the varying grain size across the plate’s thickness. The micro tensile results reveal that the tensile properties of the thin plate are comparable to that of its bulk Ti-6Al-4V counterpart.

Selective laser melting (SLM) is a powder-based additive manufacturing technique consisting of the exact reproduction of a three dimensional computer model (generally a computer-aided design CAD file or a computer tomography CT scan) through an additive layer-by-layer strategy. Because of the high degree of freedom offered by the additive manufacturing, parts having almost any possible geometry can be produced by SLM. More specifically, with this process it is possible to build parts with extremely complex shapes and geometries that would otherwise be difficult or impossible to produce using conventional subtractive manufacturing processes. Another major advantage of SLM compared to conventional techniques is the fast cooling rate during the process. This permits the production of bulk materials with very fine microstructures and improved mechanical properties or even bulk metallic glasses. In addition, this technology gives the opportunity to produce ready-to-use parts with minimized need for post-processing (only surface polishing might be required). Recently, significant research activity has been focused on SLM processing of different metallic materials, including steels, Ti-, Ni- and Al-based alloys. However, most of the research is devoted to the parameters optimization or to feasibility studies on the production of complex structures with no detailed investigations of the structure-property correlation. Accordingly, this thesis focuses on the production and structure-property correlation of Al-12Si samples produced by SLM from gas atomized powders. The microstructure of the as-prepared SLM samples consists of supersaturated primary Al with an extremely fine cellular structure along with the residual free Si situated at the cellular boundaries. This microstructure leads to a remarkable mechanical behavior: the yield and tensile strengths of the SLM samples are respectively four and two times higher than their cast counterparts. However, the ductility is significantly reduced compared with the cast samples. The effect of annealing at different temperatures on the microstructure and resulting mechanical properties of the SLM parts has been systematically studied by analyzing the size, morphology and distribution of the phases. In addition, the mechanical properties of the SLM samples have been modeled using micro- structural features, such as the crystallite and matrix ligament sizes. The results demonstrate that the mechanical behavior of the Al-12Si SLM samples can be tuned within a wide range of strength and ductility through the use of the proper annealing treatment. The Al-Si alloys are generally used as pistons or cylinder liners in automotive applications. This requires good wear resistance and sufficient strength at the operating temperature, which ranges between 373 – 473 K. Accordingly, the tensile properties of the SLM samples were also tested at these temperatures. Changing the hatch style during SLM processing vary the texture in the material. Hence, samples with different hatch styles were produced and the effect of texture on their mechanical behavior was evaluated. The results show that the hatch style strongly influences both the mechanical properties and the texture of the samples; however no direct correlation was observed between texture and mechanical properties. The wear properties of the Al-12Si material was evaluated using pin-on-disc and fretting wear experiments. These experiments show that the as-prepared SLM samples exhibit better wear resistance than their cast counterparts and the SLM heat-treated samples. Finally, the corrosion investigations reveal that the SLM samples have similar corrosion behavior as the cast specimens under acidic conditions. A major drawback for the wide application of SLM as an industrial processing route is the limited size of the products. This is a direct consequence of the limited dimensions of the available building chambers, which allow for the production of samples with volumes of about 0.02 m3. A possible way to overcome this problem would be the use of the welding processes to join the small SLM objects to form parts with no dimensional limitations. In order to verify this possibility, friction welding was employed to join Al-12Si SLM parts. The results indicate that friction welding not only successfully permits the join materials manufactured by SLM, but also helps to significantly improve their ductility. This work clearly demonstrates that SLM can be successfully used for the production of Al-12Si parts with an overall superior performance of the mechanical and physical properties with respect to the conventional cast samples. Moreover, the mechanical properties of the SLM samples can be widely tuned in-situ by employing suitable hatch styles or ex-situ by the proper heat treatment. This might help the development of SLM for the production of innovative high-performance Al-based materials and structures with controlled properties for automotive and aerospace applications.