Made available in DSpace on 2016-12-23T14:08:14Z (GMT). No. of bitstreams: 1 Capa, Cap 1 e Cap 2 ate secao 2-2-1-9.pdf: 1005078 bytes, checksum: 68579a03ea37b6d408ea44008ec9ad0f (MD5) Previous issue date: 2010-12-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho tem o objetivo de avaliar uma possível relação entre as propriedades mecânicas calculadas a partir dos dados de micropenetração instrumentada e o comportamento sob desgaste microabrasivo dos compósitos à base de tungstênio (W) infiltrados por latão, usados em coroas diamantadas utilizadas em sondagem mineral. As amostras dos compósitos de tungstênio foram sinterizadas com combinações de diferentes tamanhos de partículas W e adições de ligas à base de outros elementos, além de adições de abrasivos secundários (SiC). Após a preparação metalográfica, as amostras foram analisadas em um micropenetrador instrumentado com um pen etrador do tipo Vickers. As fases foram penetradas com uma carga de 30 mN, exceto o carbeto de silício, com carga de 250 mN. As curvas geradas a cada penetração permitiram calcular a microdureza e o módulo de elasticidade para cada fase. Estes resultados foram comparados com os coeficientes de desgaste microabrasivo dimensionais obtidos em um trabalho anterior, através de ensaios de microabrasão com lamas abrasivas à base de carbeto de silício, sílica e hematita, efetuados com equipamento do tipo Calowear. Foi observada uma diminuição na microdureza conforme o tamanho dos grãos de tungstênio aumenta. Para a lama abrasiva contendo SiC, uma diminuição no coeficiente de desgaste microabrasivo se seguiu à diminuição na microdureza do tungstênio. O oposto foi observado com a lama de SiO2, enquanto, para a lama de Fe2O3, nenhuma correlação clara foi obtida. Também é importante dizer que o efeito da dureza do latão infiltrado (fase aglutinante) tornou-se mais significativa nos ensaios com as pastas de SiO2 e de Fe2O3. Quando as ligas à base de outros elementos são adicionadas, para o abrasivo SiC, o aumento da plasticidade do latão aumenta o desgaste, porque as deformações plásticas são aumentadas, levando em consideração a relação Habr./Hfase muito alta. A plasticidade da fase W parece não interferir no desgaste. Ocorre o contrário para o abrasivo SiO2. Para ambos os abrasivos, o cobre adicionado aumenta a fração volumétrica de fase macia , proporcionando um desgaste ainda maior. Para o abrasivo Fe2O3, o aumento na plasticidade do latão aumenta o coeficiente de desgaste, pois leva a indentações maiores, ou seja, a maiores deformações plásticas. Dependendo do tipo do abrasivo, os mecanismos observados foram riscamento e rolamento de partículas (múltiplas indentações), além da ocorrência de ambos simultaneamente, embora dissociados / This work intends to evaluate a possible relationship between the mechanical properties calculated from instrumented microindentation data and the microabrasive wear behavior of infiltrated tungsten (W) composites used in impregnated diamond bits for rock drilling. Specimens of brass-infiltrated W composites were sintered with combinations of different W particle sizes, and additions of alloys based on other elements, as well as additions of secondary abrasives. After metallographic preparation, the specimens were analyzed in an instrumented microindenter with a Vickers indenter. All phases were indented with a load of 30 mN, except the silicon carbide, with a load of 250 mN. The indentation curves allowed the calculation of microhardness and Young s modulus for each phase. Those results were compared with dimensional microabrasive wear coefficients obtained in a previous work, by testing microabrasion with abrasive slurries based on silicon carbide, silica and hematite, performed with Calower equipment. It was observed a decrease in microhardness as the tungsten grains size increase. For the SiC abrasive slurry, a decrease in microabrasive wear coefficient followed the decrease in tungsten microhardness. The opposite was observed with the SiO2 slurry, whereas, for the Fe2O3 slurry, no clear correlation was obtained. It is also important to say that the effect of infiltrated brass (binder phase) hardness became more significant in the tests with the SiO2 and Fe2O3 slurries. When the alloys based on other elements are added, to the SiC abrasive, the increase of the brass plasticity increases its wear, because the plastic deformations are increased, taking into account the very high Habr./Hphase relation. The plasticity of the W phase seems not to interfere in wear. The opposite is true for the SiO2 abrasive. For both abrasives, the copper added increases the "soft" phase volumetrical fraction, providing an additional wear. For the Fe2O3 abrasive, the increase in the brass plasticity increases the wear coefficient, since it leads to larger indentations, i. e., to larger plastic deformations. Depending on the abrasive type, the observed mechanisms were grooving and particles rolling (multiple indentations), besides the occurrence of both simultaneously, although, dissociated

Les systèmes barrières thermiques protégeant les aubes de turbine sont des multicouches constitués d’une couche céramique isolante appliquée sur un superalliage par l’intermédiaire d’une couche de liaison qui, dans les systèmes actuels est à base de NiAl(Pt). Pour en comprendre et décrire le comportement thermomécanique, il est nécessaire de connaître le comportement de chaque couche, en particulier celui de la couche de liaison dont le rôle est critique. Nous avons employé une technique originale, la microindentation instrumentée à chaud (jusqu’à 850°C), pour obtenir des informations sur le comportement mécanique de matériaux de couches de liaison. Il a fallu d’abord fiabiliser le dispositif pour minimiser les effets d’oxydation et caractériser la stabilité thermique pour s’assurer de la validité et la reproductibilité des résultats. Un second volet a consisté à mettre en place une méthode de traitement de données et une méthode d’analyse inverse des résultats associant une approche analytique et une simulation de l’essai par éléments finis. Les essais menés sur des matériaux massifs élaborés sous forme de couples de diffusion pour explorer une large gamme de compositions ont permis de déterminer la loi de comportement élastoviscoplastique du composé NiAl(Pt) sous forme [bêta] et sous forme martensitique. Des propriétés mécaniques ont été également été déterminées sur les composés NiAl(Ru) et NiAl(Zr) envisagés pour des systèmes futurs. L’influence des divers éléments (Al, Pt et Ru) a pu ainsi être mise en évidence. Finalement des essais ont été effectués sur des couches de liaison de barrière thermique et les résultats corrélés à ceux obtenus sur matériaux massifs / Thermal barrier systems, which protect turbine blades, are multilayers constituted of an insulating ceramic layer applied on a metallic bondcoat itself in contact with the superalloy substrate. A widely used bondcoat is composed of a NiAl(Pt) compound. In order to understand and describe the thermomechanical behaviour of such systems, it is required to know the mechanical behaviour of each layer, in particular that of this bondcoat whose role is critical for maintaining the integrity of the systems. In this study, we have employed an original technique – high temperature instrumented microindentation, up to 850°C – to extract information on the mechanical behaviour of bondcoat materials. A preliminary phase consisted in improving the experimental procedure - in particular to minimise oxidation phenomena - and in characterising the thermal stability of the equipment at high temperature to ensure the reliability, validity and reproducibility of the results obtained. We have then developed a systematic data treatment and an inverse problem analysis combining analytical approaches and a FEM simulation of the experiment to extract a mechanical behaviour law of the materials investigated. Tests performed on bulk diffusion couples, selected to explore a wide range of compositions representative of aging bondcoats, permitted to extract an elastic viscoplastic behaviour law of NiAl(Pt), both in the B2 phase and in the martensitic phase. Some mechanical properties could also be determined on NiAl(Ru) and NiAl(Zr) systems. Finally the results of a few tests performed on thermal barrier bondcoats could be correlated with the results obtained on bulk materials

Ce travail de thèse a eu comme objectif la mise en place et la validation d’une méthodologie expérimentale pour le suivi de l’évolution in-vitro de substituts osseux à base de phosphates de calcium. Du phosphate dicalcique dihydraté (DCPD, CaHPO4·2H2O) et du phosphate tricalcique bêta (β-TCP, β-Ca3(PO4)2) ont été choisis comme matériaux modèles de deux grandes classes de substituts osseux: les “biosolubles” (sujets à dissolution après implantation) et les “biorésorbables” (sujets à résorption cellulaire après implantation). Pour l’étude des phénomènes de dissolution et de reprécipitation observés lorsque les phosphates de calcium sont plongés en solution, ces matériaux ont été produits sous forme d’échantillons microporeux (60% de porosité pour le DCPD, 75% pour le β-TCP) et soumis à des tests de dissolution in-vitro en conditions statiques ou dynamiques (sans ou avec renouvellement du liquide) dans différentes solutions tamponnées à pH physiologique (TRIS et PBS) et pour des durées s’étalant entre 30 minutes et 2 mois. L’analyse des propriétés physico-chimiques, microstructurales et mécaniques des échantillons avant et après immersion a permis d’évaluer l’influence du type de milieu et des conditions de test choisies sur l’évolution des échantillons. Une attention particulière a été prêtée à la caractérisation mécanique: la technique de micro-indentation instrumentée sphérique a été préférée à autres essais plus conventionnels. Cette technique permet d’évaluer plusieurs paramètres tels que la dureté et le module de Young de façon quasi non-destructive et à une échelle locale. En conséquence, l’utilisation de la micro-indentation s’est avérée d’une grande aide pour le suivi des caractéristiques d’échantillons dégradés qui présentaient un gradient de propriétés entre la surface (où le processus de dégradation commence) et le cœur (sujet à des changements sur plus long terme). La dernière partie de cette étude a été dédiée à l’étude du deuxième phénomène qui entraine la résorption de substituts osseux in-vivo, à savoir la résorption cellulaire. Pour cela des essais cellulaires avec des cellules précurseurs d’ostéoclastes ont été réalisés sur des échantillons denses de β-TCP pur ou dopé avec 5% molaire de magnésium. L’addition de cet élément est censée modifier les propriétés du matériau (notamment sa solubilité) et, par conséquence, modifier le comportement cellulaire. Les résultats des tests ont confirmé la cytocompatibilité des deux types de β-TCP, mais ont également mis en avant une difficulté d’activation des ostéoclastes. Deux des causes possibles seraient liées à la topographie de surface des échantillons et au relargage des ions calcium suite à la dissolution du matériau. / The present Ph.D. thesis work was aimed to establish and assess an experimental methodology to monitor the in-vitro evolution of calcium phosphate (CaP) bone substitutes. Dicalcium phosphate dihydrate and beta-tricalcium phosphate were chosen as model of two main classes of bone substitutes: “biosoluble” ones (which undergo dissolution after implantation) and “bioresorbable” ones (which undergo cellular resorption after implantation). In order to study the dissolution and precipitation phenomena, which take place once CaPs are immersed in solution, these materials were produced in the form of micro-porous samples (60% of porosity for DCPD, 75% for β-TCP) and used for dissolution tests in-vitro in static and dynamic conditions (without or with liquid renewal) in different buffered solutions at physiologic pH (TRIS and PBS) and for periods of time ranging between 30 minutes and 2 months. The analysis of the physico-chemical, microstructural and mechanical properties of the samples before and after immersion allowed to evaluate the influence of the chosen medium and immersion conditions on the evolution of the specimens. Particular attention was paid to the mechanical characterisation: instrumented spherical micro-indentation was preferred to other more conventional tests. This technique enables the evaluation of several parameters such as the hardness and the Young’s modulus in a quasi-non-destructive way and on a local scale. As a consequence, the use of micro-indentation proved to be of great help for monitoring the characteristics of the degraded specimens, which presented a gradient of properties between the surface (where the degradation process starts) and the core (subject to changes on a longer period). The last part of this work was focused on the study of the second main phenomenon, which takes part in the in-vivo resorption of bone substitutes, that is to say the cellular resorption. For this purpose, cellular tests with osteoclast-precursor cells were carried out on dense samples made of pure and magnesium-doped β-TCP (5 mol.% of Mg). The addition of magnesium was aimed to modify the properties of the material and, as a consequence, the cellular behavior. The results confirmed the cytocompatibility of both types of β-TCP, but they also showed a difficult activation of osteoclasts. Two of the possible causes would be linked to the topography of the surface of the specimens and to the release of calcium ions due to the dissolution of the material.