As one of the most common minerals in crustal rocks, quartz has been widely used as an indicator for shock metamorphism. Shocked quartz is found in the Chicxulub impact crater, an impact crater that has been linked to the Cretaceous-Tertiary extinction ~66 million years ago. The microstructural deformation features found in the shocked quartz do not form randomly, and their orientation provides a better understanding of the impact cratering process. At present, there are no studies of EBSD data analysis of shocked quartz from Chicxulub. We investigated six thin sections from two samples from the M0077A borehole in the lower peak ring of the Chicxulub impact crater, using the Scanning Electron Microscopy (SEM)-EBSD technique. Both samples consist of shocked granite, with a significant amount of quartz.  Therefore, this study investigates the crystallographic preferred orientation (CPO) of shocked quartz and predicts the seismic velocities and anisotropy, based on the EBSD data. We carried out the analysis of EBSD data by using the MATLAB-based MTEX toolbox that can perform CPO analysis from pole figure plots and the prediction of seismic properties of minerals based on the Voigt-Reuss-Hill effective medium method. Although acquiring the EBSD data from these samples is challenging, leading to the lack of data measured, we found out that the prediction of P wave seismic velocity is in good agreement with other recent studies conducted in the same area. The range of predicted P wave velocities is 5.5-6.5 km/s with anisotropy of 8-15%. The actual observed laboratory measurements and in-situ seismic measurements are considerably smaller than this velocity range because our calculations do not incorporate pores or take microcracks into account.  A likely explanation for the large variability of anisotropy in shocked quartz is the relatively few mapped grains with EBSD, which would influence the CPO and lead to high predicted seismic anisotropy. Considering a greaternumber of grains in the CPO analysis, the CPO is reduced, and seismic anisotropy becomes smaller.

L’objectif de ce travail est d’étudier les couplages entre les propriétés hygroélastiques des papierset leur microstructure. L’exploitation d’images de papiers modèles acquises par microtomographieà rayons X a permis de caractériser de manière inédite l’évolution des propriétésmicrostructurales de ces matériaux en fonction de leurs conditions d’élaboration ainsique lors d’essais où ils ont été placés sous atmosphère à humidité relative contrôlée.Ces résultats constituent un apport nouveau pour la connaissance de la nature statistique desdescripteurs des propriétés des fibres (dimensions et orientation) et de leurs contacts (surface,degré de liaison), de l’architecture des réseaux fibreux que forment les papiers (nombrede contacts entre fibre) et pour la taille des volumes élémentaires représentatifs des propriétésmicrostructurales et élastiques de ces milieux. Sur la base de ces informations, différentsmodèles, plus oumoins raffinés, ont été élaborés dans le cadre de la théorie de l’homogénéisationdes structures périodiques discrètes, pour décrire les propriétésmécaniques des papiers.Cette approche apporte un éclairage nouveau sur le rôle des liaisons entre fibres sur leur comportement mécanique. / The objective of this work is to study the coupling between the hygroelastic properties ofpapers and their microstructure. The use of images of models acquired by X-ray microtomographypapers allowed the characterization in an unprecedentedmanner of the evolutionofmicrostructural properties of thesematerials according to their production conditions andduring tests where they were placed in atmosphere at controlled relative humidity. These resultsprovide a new contribution to the knowledge of the statistical nature of the descriptorsof fibre properties (size and orientation) and their contacts (surface, bonding degree ratio), ofthe architecture of fibrous networks that papers constitute (number of fibre-to-fibre bonds)as well as of the size of the representative elementary volumes of microstructural and elasticproperties. Based on this information, various models, more or less sophisticated, were developedin the framework of the theory of homogenisation of discrete periodic structures todescribe the mechanical properties of paper. This approach sheds new light on the role offibre-to-fibre bonds on themechanical behaviour of thesematerials.

De nouveaux alliages Zn-TR1-5 %mass.(TR = Ce, La et Mischmetal : Ce 75%/La25%) ont été synthétisés par fusion sous atmosphère contrôlée et coulés sous forme de plaques. Dans ces nouveaux matériaux, les terre rare sont localisées exclusivement dans des phases intermétalliques dispersées de manière homogène dans la matrice de zinc : Zn11Ce, Zn13La ou Zn11Ce1-xLax and Zn13CeyLa1-y. Le comportement électrochimique de ces nouveaux alliages a été étudié dans un milieu corrosif de référence simulant les conditions atmosphériques. En parallèle, les phases intermétalliques pures Zn11Ce and Zn13La ont été synthétisées et leur influence électrochimique a été évaluée par voltamétrie et couplage galvanique. Les résultats montrent que les deux phases intermétalliques sont des sites cathodiques préférentiels de la réduction du dioxygène et induisent une inhibition cathodique de la corrosion des alliages Zn-TR par rapport au zinc pur. Ce phénomène est plus marqué dans le cas des alliages au lanthane. Dans le cas spécifique des alliages au cérium, une inhibition anodique a également été observée et corrélée avec une modification chimique des produits de corrosion (composés majoritairement d'hydrozincite). En fait, une faible quantitéhomogène de cérium a pu être mise en évidence dans la couche de corrosion par spectrométrie dispersive en longueur d'onde. D'après les résultats d'expériences de précipitation contrôlée de sels de cérium et zinc en milieu carbonaté, la présence de cérium dans la couche de corrosion et son caractère protecteur pourraient être attribués à la formation d'un composé mixte double lamellaire zinc-cérium. L'addition de moins de 2%mass. de cérium ou lanthane permet d'améliorer la résistance à la corrosion du zinc. Cependant, lorsque la teneur en terre-rare augmente, l'effet de couplage galvanique devient plus important et rend les alliages moins résistants que le zinc pur / New Zn-RE1-5 wt.% alloys (RE=Ce, La and Mischmetal: Ce 75%/ La 25%) were synthesized by melting under controlled atmosphere and cast in plates. In these materials, rare earth metal are exclusively present in intermetallic phases homogeneously dispersed in the zinc matrix: Zn11Ce, Zn13La or Zn11Ce1-xLax and Zn13CeyLa1-y. The electrochemical behavior of these new alloys was investigated in a reference corrosivemedium. In parallel, the pure intermetallic phases Zn11Ce and Zn13La were synthesized and their electrochemical influence was studied by voltametry and galvanic coupling. Results show that both intermetallic phases act as preferential cathodic sites of dioxygen reduction and induce a cathodic inhibition of the corrosion of the Zn-RE alloys by comparison with pure zinc. This phenomenon is much more significant in the case of lanthanum containing alloys. In the specific case of cerium addition to zinc, an anodic inhibition was also observed and correlated with a chemical modification of the corrosion products (mainly made of hydrozincite). Actually, low quantities of cerium (less than 1 at.%) have been detected homogeneously in the corrosion layer by wave-length dispersive spectrometry. From results of controlled precipitation experiments of cerium and zinc salts performed in carbonated medium, the presence of cerium in the corrosionlayer and its protective character could be attributed to the formation of a mixed double lamellar zinc-cerium product. Therefore, addition to zinc of less than 2 wt.% of cerium or lanthanum allow to improve the corrosion resistance of zinc. However, by increasing the rare earth content in the alloys, the galvanic coupling phenomenon becomes more important and makes the alloys less resistant than pure zinc

Ce travail porte sur la compréhension de l’impact de la microstructure sur les performances des Cellules à Oxyde Solide (SOC), avec une illustration sur l’électrode à oxygène en LSCF-CGO. Une approche couplant de la modélisation géométrique et électrochimique a été adoptée pour cet effet. Le modèle des champs aléatoires plurigaussiens et un autre basé sur des empilements de sphères ont été développés et adaptés pour les microstructures des SOCs. Ces modèles 3D de géométrie stochastique ont été ensuite validés sur différentes électrodes reconstruites par nano-holotomographie aux rayons X au synchrotron ou par tomographie avec un microscope électronique à balayage couplé à une sonde ionique focalisée. Ensuite, des corrélations semi-analytiques ont été proposées et validées sur une large base de microstructures synthétiques. Ces relations permettent de relier les paramètres ‘primaires’ de l’électrode (la composition, la porosité et les diamètres des phases) aux paramètres qui pilotent les réactions électrochimiques (la densité de points triples, les surfaces spécifiques interphases) et sont particulièrement pertinents pour les équipes de mise-en-forme des électrodes qui ont plus de contrôle sur ce premier ensemble de paramètres. Concernant la partie portant sur l’électrochimie, des tests sur une cellule symétrique en LSCF-CGO ont permis de valider un modèle déjà développé au sein du laboratoire, et qui permet de simuler la réponse électrochimique d’une électrode à oxygène à partir des données thermodynamiques et de microstructure. Finalement, le couplage des deux modèles validés a permis d’étudier l’impact de la composition des électrodes, leur porosité ou encore taille des grains sur leurs performances. Ces résultats pourront guider les équipes de mise-en-forme des électrodes vers des électrodes plus optimisées. / This work aims at better understanding the impact of Solid Oxide Cells (SOC) microstructure on their performance, with an illustration on an LSCF-CGO electrode. A coupled 3D stochastic geometrical and electrochemical modeling approach has been adopted. In this frame, a plurigaussian random field model and an in-house sphere packing algorithm have been adapted to simulate the microstructure of SOCs. The geometrical models have been validated on different electrodes reconstructed by synchrotron X-ray nano-holotomography or focused ion-beam tomography. Afterwards, semi-analytical microstructural correlations have been proposed and validated on a large dataset of representative synthetic microstructures. These relationships allow establishing the link between the electrode ‘basic’ parameters (composition, porosity and grain size), to the ‘key’ electrochemical parameters (Triple Phase Boundary length density and Specific surface areas), and are particularly useful for cell manufacturers who can easily control the first set of parameters. Concerning the electrochemical part, a reference symmetrical cell made of LSCF-CGO has been tested in a three-electrode setup. This enabled the validation of an oxygen electrode model that links the electrode morphological parameters to its polarization resistance, taking into account the thermodynamic data. Finally, the coupling of the validated models has enabled the investigation of the impact of electrode composition, porosity and grain size on the cell electrochemical performance, and thus providing useful insights to cell manufacturers.

La thèse est inscrite au sein du projet ASTRID, qui est un démonstrateur technologique pour les réacteurs de quatrième génération (Gen-IV). Le premier matériau choisi pour constituer les gaines de cœur est un acier inoxydable austénitique stabilisé au titane (type 15Cr-15Ni Ti). L’écrouissage à froid des gaines permet la précipitation de nano-carbures de titane en service sur les dislocations, retardant ainsi les phénomènes de restauration par effet d’épinglage. En conditions accidentelles (T > 650°C), et plus particulièrement dans le cas d’une perte de réfrigérant primaire, le comportement en fluage de ces gaines est très mal connu. L’objectif des travaux de thèse est donc de déterminer les mécanismes de déformation et de rupture en fluage, entre 650°C et 950°C, de cet acier à l’état non irradié.Dans un premier temps, les microstructures d’échantillons après différents recuits ont été comparées afin d’étudier l’influence de la température sur les évolutions métallurgiques. L’étude de la précipitation et des cinétiques de restauration et de recristallisation, ont permis de dresser les évolutions microstructurales sans charge appliquée.En plus d’étudier le comportement en fluage uniaxial de l’acier à haute température, les caractérisations des éprouvettes après essais ont permis de déterminer les évolutions microstructurales au cours et après essais de fluage (contributions simultanées de la température et de la contrainte). La comparaison avec les microstructures obtenues après recuits a mis en évidence une accélération de la cinétique de recristallisation sous charge, rendant l’effet de la contrainte sur ces évolutions non négligeable.Après fluage sous air aux plus basses températures (650°C et 750°C), les fractographies présentent une rupture globalement transgranulaire avec certaines zones intergranulaires. Après fluage sous vide secondaire à plus hautes températures (850°C et 950°C), un fort amincissement des éprouvettes et une striction quasiment complète dans l’épaisseur ont été observés. Ce fort amincissement se traduit par un alignement de cupules, caractéristique de ruptures 100% ductiles à très haute température. / The ASTRID project aims at designing a fast-reactor prototype for the 4th generation of nuclear power plants. The material to be used for fuel cladding is a cold-worked austenitic stainless steel stabilized with titanium (15Cr-15Ni Ti type) and optimized in minor elements. This material was developed to limit recovery and irradiation-induced swelling and to improve microstructural stability and mechanical properties in normal operating conditions. In case of incidental situations (irradiation temperature > 650°C), the cladding might rapidly reach higher temperatures up to 950°C where its stability could be affected. The present work aims at improving knowledge and understanding of the microstructural evolution and creep behaviour of this steel at these temperatures (650°C-950°C).Microstructural characterizations of thermally-aged samples have been performed in order to study the effect of temperature on metallurgical evolutions (precipitation, recovery and recrystallization). A phenomenological model including recovery and recrystallization processes was set up to reproduce hardness measurements versus ageing time and temperatures.Isothermal creep tests up to 950°C under a wide range of stress levels allowed investigation of viscoplastic flow, microstructural evolution under stress and damage/failure processes. In order to evaluate the effect of high-temperature loading, microstructural characteristics of stress-free thermally-aged samples were compared with post-mortem examinations of creep specimens.At 650°C and 750°C the value of stress exponent is higher than 7. The main deformation mechanism during creep test is power-low creep, which is consistent with the results found in the literature.Beyond 850°C, the increase in dislocation mobility promotes recovery and recrystallization processes. As a consequence, a competition between work hardening due to viscoplastic deformation and softening due to dynamic recovery takes place. At 950°C, viscoplastic flow is strongly affected by recrystallization during creep test, especially in the tertiary stage. The comparison between microstructures of crept specimens and stress-free, thermally-aged samples leads to the conclusion that the recrystallization kinetics is accelerated by application of a mechanical loading.As for the fracture behaviour, creep tests under air environment at lower temperatures (650°C-750°C), led to predominating ductile fracture but some intergranular zones were observed on fracture surfaces. Creep tests under high vacuum at higher temperatures (850°C-950°C) lead to a high fracture elongation with a reduction of area up to 100%.

O aumento no consumo energético mundial e a perspectiva de esgotamento das reservas de combustíveis fósseis têm estimulado o desenvolvimento de tecnologias e materiais para aplicações nos futuros reatores de fusão nuclear e reatores de fissão a nêutrons rápidos. O foco deste trabalho é avaliar a estabilidade microestrutural de um material tecnologicamente promissor por meio de diferentes técnicas de caracterização. O material estudado, o aço ODS-EUROFER, é um aço ferrítico-martensítico de atividade reduzida de composição 9%Cr-1%W (em massa) endurecido pela dispersão de 0,3% (em massa) de óxido de ítrio. Amostras foram laminadas até 80% de redução e submetidas a tratamentos isotérmicos em 800 °C por até 6 meses (4320 h) de duração para se investigar a ocorrência de fenômenos tais como recuperação, recristalização, crescimento de grão, precipitação e engrossamento de Ostwald. Outro conjunto de amostras foi recozido por 1 hora em temperaturas entre 900 e 1300 °C para se estudar a transformação martensítica neste material. Diversas técnicas de caracterização microestrutural complementares entre si (MEV, MET, DRX, EBSD, APT, ensaios de microdureza Vickers, dilatometria, DTA e magnetização) foram empregadas. Os resultados obtidos indicam que a dispersão de partículas nanométricas de Y2O3 confere uma grande resistência à recristalização primária, favorecendo a recuperação estática como principal mecanismo de amolecimento durante o recozimento prolongado deste aço. De modo similar, o crescimento de grão foi suprimido no campo austenítico em temperaturas tão altas quanto 1200 °C. / The rise in the world energy consumption and the possibility of depletion of the fossil fuel reserves have stimulated the development of new technologies and new materials for applications in the future nuclear fusion reactors and in the fast breeder fission reactors. The aim of this study is to evaluate the microstructural stability of a technologically promising material by using different characterization techniques. The investigated material, the ODS-EUROFER steel, is 9Cr-1W (%wt) reduced-activation ferritic-martensitic steel reinforced with a dispersion of 0.3%wt of yttrium oxide nanoparticles. Samples were cold rolled to 80% thickness reduction and subjected to isothermal annealing at 800 °C for up to 6 months (4,320 h) to investigate the occurrence of phenomena such as recovery, recrystallization, grain growth, precipitation, and Ostwald ripening. Another set of samples was annealed for 1 hour at temperatures between 900 and 1300 °C to study the martensitic transformation in this steel. Several complementary microstructural characterization techniques were employed (SEM, TEM, XRD, EBSD, APT, Vickers hardness, dilatometry, DTA and magnectic measurements). The results suggest that the dispersion of nanoscaled particles of Y2O3 provides a high resistance to discontinous recrystallization and favors static recovery as the main softening mechanism during long-term annealing in this steel. Similarly, grain growth was suppressed even in temperatures as high as 1200 °C in the austenitic field.

Nos últimos anos, devido ao elevado preço do níquel, uma nova série de aços inoxidáveis austeníticos com um menor teor de níquel foi criada. A essa nova série foi dado o nome de série 200. Dentre os aços dessa classe, o AISI 201 tem sido utilizado em aplicações onde a elevada resistência à corrosão não é tão necessária. Neste trabalho de Mestrado investigou-se a formação e a reversão da martensita induzida por deformação em um aço inoxidável austenítico AISI 201 laminado a frio em 20, 40 e 60% de redução em espessura. Das chapas laminadas foram retiradas amostras que foram recozidas em várias temperaturas (200-800oC) por 1 hora. Amostras do material laminado em 60% de redução em espessura também foram recozidas por várias temperaturas (200-800oC) e por vários tempos (5-180min). Com isso, avaliou-se a evolução microestrutural do material durante a laminação frio e durante o recozimento por meio de medidas de microdureza Vickers, microscopias óptica, eletrônica de varredura e eletrônica de transmissão, difração de elétrons retroespalhados, difração de raios X e medidas de magnetização. Além disso, foram realizados cálculos termodinâmicos para a previsão da formação de fases nesse material. Constatou-se que o material de partida não era completamente austenítico, possuindo uma pequena fração de ferrita ? residual em sua microestrutura. Com relação às medidas de magnetização, observou-se que a fração de fase ferromagnética (martensita) aumenta com o aumento da deformação, aumentando a magnetização de saturação (Ms) do material. Para pequenas deformações (20% de redução em espessura) houve a ocorrência de um pico no valor de campo coercivo do material (Hc). Com o aumento da deformação (40 e 60%) os valores de Hc diminuíram. Com relação à reversão da martensita induzida por deformação durante os recozimentos, observou-se que ela ocorre na faixa de temperatura de 500-700oC para o material laminado em 60% de redução em espessura. O comportamento do material nesse estudo corrobora o que tem sido reportado na literatura para os aços da série 300. Entretanto, pouco tem sido publicado com relação às propriedades magnéticas do aço inoxidável austenítico AISI 201, principalmente com relação ao campo coercivo. Neste trabalho também foram realizadas medidas de magnetização durante o recozimento das amostras (condição in situ). Os parâmetros obtidos desses experimentos in situ foram comparados com aqueles obtidos para as amostras recozidas isotermicamente. / In the last years, since nickel price increased, another series of austenitic stainless steel with less amount of nickel has emerged: the series 200. The AISI 201 stainless steel has been used where intermediated corrosion resistance is needed. In this work, the formation of strain-induced martensite and its reversion in an AISI 201 austenitic stainless steel were studied. The material was characterized in terms of microstructure and then cold rolled up to 20, 40 and 60% of thickness reduction. For all degree of reduction, samples were annealed at several temperatures (200-800oC) for 1 hour. Additional samples taken from the 60% cold-rolled material were also annealed at several temperatures (200-800oC) for several times (5-180minutes). The microstructural evolution during cold rolling and annealing was evaluated using microhardness Vikers testing, light optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, X-Ray diffraction and magnetization measurements. Phase predictions were also performed using software Thermo-calc©. It was observed that the as-received material was not fully austenitic. It has a small fraction of ?-ferrite within its matrix. The amount of ferromagnetic phase (martensite) increases with increasing deformation. For small deformation (20%), there is a peak in the coercive field of the material (Hc). As deformation increases, Hc values decrease. It was also observed that the martensite reversion takes place at 500-700oC. The behavior of the material is in accordance with what has been reported in the literature for the 300 series. However, only few works have been reported concerning AISI 201 stainless steel and its magnetic properties. In this work, magnetic measurements were also carried out during annealing (in situ condition). The obtained parameters from the in situ magnetic measurements were compared to those ones obtained from the isothermally annealed samples.

Made available in DSpace on 2017-07-21T20:43:46Z (GMT). No. of bitstreams: 1 Jean Cleber Bertoni.pdf: 7862049 bytes, checksum: 4c77f7ebc3fc211aac8ad8a7de58ccad (MD5) Previous issue date: 2015-01-30 / There are currently extensive research on aluminum alloys, mainly due to its wide application in the automotive and aerospace industries, due to the following characteristics, among them, low density, high thermal conductivity and high corrosion resistance at room temperature. Al-Fe alloys have a high degree of microstructural change due to changes in their properties when appropriate techniques are applied. The Al-Fe alloy was studied in the composition of 1.5% Fe by weight, which was subjected to the treatment laser surface remelting in order to enhance its surface characteristics. The characterization of these alloys in order to determine the variation of the chemical composition at different depths was performed by Grazzing incidence x-ray diffraction (GIXRD). In this technique, the angle of incidence of the X-ray beam was fixed and the detector moved in 2θ, it is possible to obtain the XRD patterns at different depths by varying the angle of incidence. In this work, the characterizations the micro and nano structural sample of alloy Al-1.5wt.%Fe treated by laser surface remelting (LSR) were performed, on the treated surface, as well as the transverse section, this study was performed at treated samples surface and at the isolated weld fillet on samples, where were applied laser beam speeds of 20, 40 and 60 mm / s. In this study we used different characterization techniques, such as, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, together with atomic force microscopy, and the Vickers hardness. Also in this work the technique of GIXRD was used to obtain depth profiles of near the surface chemical composition of the alloy. The analysis was performed in the micrometer range varying the angle of incidence between 0.5° to 6° in steps of 0.5° and analysis with incident angles 3° and 6° in steps of 0.02° for each 10 sec. As a result by examining the microstructure was characterized melted zone, the heat affected zone and the substrate, a particular features were found for each velocity of the laser beam, generally the treated area showed a more homogenous microstructure consisting of grains smaller feature, with low roughness and high hardness. The heat affected zone was more notorious the morphology of grains elongated feature in the treated and untreated interface for low laser beam scanning velocities. By means of the technique of X-ray diffraction various metastable phases were found, such as aluminum oxide, nitrides, etc., with different intensities of peaks as a consequence of the variation of angle of incidence. / Atualmente há uma ampla investigação sobre ligas de alumínio, principalmente devido a sua larga aplicação na indústria automotiva e aeroespacial, devido as seguintes características, entre elas, a baixa densidade, alta condutividade térmica e elevada resistência à corrosão a temperatura ambiente. Ligas de Al-Fe possuem um alto grau de modificação microestrutural, devido a mudanças em suas propriedades quando técnicas adequadas forem aplicadas. A liga Al-Fe foi estudada na composição de 1,5% de Fe em peso, a qual foi submetida ao tratamento de refusão superficial a laser de modo a aprimorar suas características superficiais. A caracterização dessas ligas com a finalidade de determinar à variação de composição química em diferentes profundidades foi realizado mediante a difração de raios X com ângulo de incidência rasante (DRXIR). Nesta técnica, o ângulo de incidência do feixe de raios X foi fixado e o detector moveu-se em 2θ, sendo possível obter os difratogramas em diferentes profundidades com a variação do ângulo de incidência. Neste trabalho, as caracterizações a nível micro e nano estrutural das amostras da liga Al-1,5%Fe tratadas por refusão superficial a laser (RSL) foram realizadas, tanto na superfície tratada e bem como na parte transversal, este estudo foi realizado nas amostras tratadas em toda a superfície, quanto nas amostras com trilhas isoladas que foram aplicadas as velocidades de feixe laser de 20, 40 e 60 mm/s. Para isso foram utilizados diferentes técnicas de caracterização, tais como, microscópio ótico, microscópio eletrônico de varredura, espectroscopia por energia dispersiva, acompanhada da microscopia de força atômica, bem como da microdureza Vickers. Também neste trabalho a técnica de DRXIR foi utilizada para obtenção de perfis de profundidade da composição química próxima à superfície da liga. A análise foi realizada em escala micrométrica por meio da variação do ângulo de incidência entre 0,5° a 6° com passos de 0,5°, bem como as análises com ângulos incidentes de 3º e 6º com passos de 0,02º a cada 10 s. Como resultado mediante o estudo microestrutural foram caracterizados a zona fundida, a zona afetada termicamente e o substrato, sendo encontradas características particulares para cada velocidade do feixe de laser, de modo geral a zona tratada mostrou ter uma característica microestrutural mais homogênea formada por grãos menores, com baixa rugosidade e de alta dureza. A zona afetada termicamente mostrou ser mais notória a morfologia de grãos com característica alongada na interface tratada e não tratada para baixas velocidades de varredura do feixe laser. Por meio da técnica de difração de raios X diferentes fases metaestáveis foram encontradas, tais como, óxido de alumínio, nitretos, etc, com diferentes intensidades de picos como consequência da variação do ângulo de incidência.

Materiais odontológicos inovadores que apresentem propriedades antimicrobianas são altamente desejáveis na cavidade oral. O objetivo deste estudo foi avaliar a atividade antimicrobiana do vanadato de prata nanoestruturado (&beta;-AgVO3) incorporado em duas resinas acrílicas frente a Candida albicans, Streptococcus mutans, Staphylococcus aureus e Pseudomonas aeruginosa, além de examinar as propriedades mecânicas e o padrão de incorporação do nanomaterial nas resinas. O nanomaterial foi caracterizado por difração de raios X (DRX), espectroscopia no infravermelho por transformada de Fourier (FTIV), análise elementar por energia dispersiva (EDS) e microscopia eletrônica de varredura (MEV). As propriedades antimicrobianas das resinas acrílicas incorporadas com diferentes porcentagens de &beta;-AgVO3 foram investigadas pelo método de redução do XTT, unidades formadoras de colônias (UFC) e microscopia confocal à laser e o comportamento mecânico por meio de ensaios de dureza e rugosidade superficial, resistência à flexão, à compressão e ao impacto. O padrão de incorporação do &beta;-AgVO3 nas resinas foi analisado por microscopia eletrônica de varredura (MEV) e análise elementar por energia dispersiva (EDS). Os dados foram analisados por ANOVA, Tukey e pelo teste Generalized Linear Models (&alpha;=0,05). Para ambas as resinas, em relação ao grupo controle, a incorporação de 5% e 10% de &beta;-AgVO3 reduziram significantemente a atividade metabólica de C. albicans e P. aeruginosa (p<0,05), enquanto que para S. mutans houve redução significante apenas com a incorporação de 10% (p<0,05). Não houve diferença na atividade metabólica pelo método do XTT frente a S. aureus (p> 0,05). Para ambas as resinas, observou-se uma redução significativa no número de UFC/mL de C. albicans para o grupo incorporado com 10% de &beta;-AgVO3 e de S. mutans para os grupos com 2,5%, 5% e 10% do nanomaterial (p<0,05). Para S. aureus e P. aeruginosa, houve redução significante com a incorporação de 5% e 10% (p<0,05). A dureza superficial da resina termopolimerizável permaneceu inalterada pela incorporação do nanomaterial (p>0,05) e da autopolimerizável aumentou com 0,5% (p<0,05). Concentrações maiores que 1% promoveram redução na resistência flexural das resinas (p<0,05) enquanto que a rugosidade superficial permaneceu inalterada (p>0,05). A resistência à compressão da resina autopolimerizável permaneceu inalterada (p>0,05) e da termopolimerizável reduziu com a incorporação de 0,5% e 10% (p<0,05). As concentrações de 5% e 10% promoveram redução significante na resistência ao impacto das resinas, em relação ao controle (p<0,05). A caracterização das resinas quanto a dispersão da carga utilizada mostrou a presença de domínios de &beta;-AgVO3 ao longo da matriz polimérica seguindo um padrão circular. Conclui-se que o método proposto foi capaz de promover atividade antimicrobiana às resinas acrílicas frente aos micro-organismos avaliados, sendo a mesma dependente da concentração do nanomaterial. Porém, alterações na dispersão do &beta;-AgVO3 na matriz dos polímeros são necessárias para não sacrificar as propriedades mecânicas e para potencializar o efeito antimicrobiano / Innovative dental materials that have antimicrobial properties are highly desirable in the oral cavity. The aim of this study was to evaluate the antimicrobial activity of nanostructured silver vanadate (&beta;-AgVO3) incorporated into two acrylic resins against Candida albicans, Streptococcus mutans, Staphylococcus aureus and Pseudomonas aeruginosa, while examining the mechanical properties and the pattern of nanomaterial incorporation into resins. The nanomaterial was characterized by X-ray diffraction (XRD), infrared spectroscopy Fourier transform (FTIR), elemental analysis by energy dispersive (EDS) and scanning electron microscopy (SEM). The antimicrobial properties of acrylic resins incorporated with different percentages of &beta;-AgVO3 were investigated by the reduction of XTT method, colony forming units (CFU) and confocal laser microscopy and the mechanical behavior through hardness, surface roughness, flexural, compression and impact tests. The pattern of incorporation of &beta;-AgVO3 resins was analyzed by scanning electron microscopy (SEM) and elemental analysis by energy dispersive (EDS). Data were analyzed by ANOVA, Tukey test and the Generalized Linear Models (&alpha; = 0.05). For both resins, compared to the control group, the incorporation of 5% and 10% &beta;-AgVO3 caused a significantly reduced in the metabolic activity of C. albicans and P. aeruginosa (p <0.05), while for S. mutans significant reduction was observed only with the incorporation of 10% (p <0.05). There was no difference in metabolic activity by XTT method against S. aureus (p> 0.05). For both resins, there was a significant reduction in the number of CFU / mL for C. albicans incorporated group with 10% &beta;-AgVO3 and S. mutans in groups with 2.5%, 5% and 10% of nanomaterial (p <0.05). For P. aeruginosa and S. aureus, there was a significant decrease with the incorporation of 5% to 10% (p <0.05). The surface hardness of the heat-cured resin was unchanged by the incorporation of the nanomaterial (p <0.05) and increased self-cured with 0.5% (p <0.05). Concentrations above 1% promote the reduction in flexural strength of the resins (p <0.05) while the surface roughness remained unchanged (P> 0.05). The compressive strength of the self-cured resin remained unchanged (P> 0.05) and heat-cured reduced with the incorporation of 0.5% and 10% (p <0.05). Concentrations of 5% and 10% caused a significant reduction in impact strength of resins, compared to control (p <0.05). The characterization of the resins as the dispersion of the filler used showed the presence of &beta;-AgVO3 domains along the polymer matrix following a circular pattern. It was concluded that the proposed method was able to promote antimicrobial activity to acrylic resins against microorganisms evaluated, with the same concentration dependent of the nanomaterial. However, changes in the &beta;-AgVO3 dispersion in the polymer matrix are necessary to do not sacrifice the mechanical properties and to enhance the antimicrobial effect

Dans le cadre du développement des Réacteurs à Haute Température (RHT), un des systèmes retenus pour la quatrième génération de centrale nucléaire, l’utilisation d’un cycle indirect est envisagée. Ce type d’installation, utilisant de l’hélium comme caloporteur, nécessite un échangeur intermédiaire de chaleur (Intermediate Heat eXchanger, IHX) le plus compact possible entre les circuits primaire et secondaire. Les contraintes imposées par la conception ainsi que les conditions sévères d’utilisation pour ce type d’installation (température maximale 850°C à 950°C, durée de vie 20000 h) ont orienté le choix des matériaux constitutifs de l’IHX vers deux alliages base nickel en solution solide : l’Inconel 617 et le Haynes 230. Le premier matériau a été largement étudié dans les années 1980 lors du projet allemand sur les RHT car possédant de bonnes propriétés mécaniques et en corrosion à haute température mais sa forte teneur en cobalt potentiellement activable est à considérer. Le Haynes 230, plus récent, possède des caractéristiques similaires à celles de l’alliage 617, le cobalt ayant été remplacé par du tungstène. L’objectif de cette thèse est d’étudier le comportement mécanique à haute température de ces deux alliages en relation avec les évolutions de leur microstructure. Les observations microstructurales à l’état de réception révèlent la présence de carbures primaires (M6C), la majorité étant répartie de manière homogène. Des carbures secondaires M23C6, peu nombreux, sont visibles à l’état de réception pour les deux matériaux. Les vieillissements thermiques imposés aux alliages à 850°C permettent une précipitation importante de carbures M23C6 sur les lignes de glissement et aux joints de grains, la taille de ces carbures augmentant et leur nombre réduisant avec la durée de traitement. A 950°C, l’évolution microstructurale conduit à une précipitation intragranulaire beaucoup plus limitée et à une évolution intergranulaire plus importante. Pour les deux matériaux, les observations de la microstructure et les résultats de dureté montrent que la majorité des évolutions microstructurales se produisent avant 1000 h aux deux températures étudiées. Les caractéristiques mécaniques de ces alliages ont été testées en traction, en fluage et en fatigue et fatigue relaxation. En particulier, les propriétés à 850°C et 950°C ont été étudiées pour différentes charges (en fluage), vitesses de déformation (en traction) et durées de relaxation (fatigue relaxation). Les effets d’un traitement initial ont également été étudiés, tels que l’effet d’un vieillissement thermique testé en fluage et traction et l’effet d’une prédéformation sur le fluage. Il ressort de cette étude que différents mécanismes de déformation sont mis en jeu successivement ou en parallèle au cours des essais réalisés. Ainsi, l’importance de la précipitation des carbures sur les propriétés mécaniques de l’Inconel 617 et du Haynes 230 a pu être démontrée, malgré leur statut d’alliages en solution solide. Par ailleurs, un même mécanisme thermiquement activé opère sur une très large gamme de vitesses de déformation, correspondant aux essais de traction, fluage et relaxation. Cette mise en relation entre microstructure et propriétés mécaniques permet de déterminer les avantages de chaque alliage ainsi que leurs limites d’utilisation dans le cadre de la fabrication d’un échangeur de chaleur de centrale nucléaire. / High Temperature Reactors (HTR), is one of the innovative nuclear reactor designed to be inherently safer than previous generation and to produce minimal waste. The most critical metallic component in that type of reactor is the Intermediate Heat eXchanger (IHX). The constraints imposed by the conception and the severe operational conditions (high temperature of 850°C to 950°C, lifetime of 20,000 h) have guided the IHX material selection toward two solid solution nickel base alloys, the Inconel 617 and the Haynes 230. Inconel 617 is the primary candidate alloy thanks to its good high temperature mechanical and corrosion properties and the large data base developed in previous programs. However, its high cobalt content has to be considered as an issue (nuclear activation). The more recent alloy Haynes 230, in which most of the cobalt has been replaced by tungsten, present characteristics similar to the 617 alloy. The objective of this thesis is to study the high temperature mechanical behaviour of both alloys in relation with their microstructural evolutions. The as received microstructural observations have revealed primary carbides (M6C). Most of this precipitates are evenly distributed in the materials. Few M23C6 secondary carbides are observed in both alloys in the as received state. Thermal ageing treatments at 850°C lead to an important M23C6 precipitation on slip lines and at grain boundaries. The size of this carbides increases and their number decreases with increasing ageing duration. The intragranular precipitation of secondary carbides at 950°C is more limited and the intergranular evolution more important than at 850°C. The microstructural observations and the hardness evolution of both alloys show that the main microstructural evolutions occur before 1,000 h at both studied temperatures. The mechanical properties of the Inconel 617 and the Haynes 230 have been studied using tensile, creep, fatigue and relaxation-fatigue tests. Particularly, the properties at 850°C and 950°C have been evaluated using several stress levels (creep), strain rates (tensile) and relaxation duration (fatigue). The effects of initial treatments have also been studied, i.e.ageing treatments effects on creep and tensile properties and cold-work effects on creep properties. At high temperature, the as received Inconel 617 does not show classical creep behaviour. This study shows the importance of the fast carbides precipitation on their mechanical properties, despite the fact that the Inconel 617 and the Haynes 230 are listed as solid solution alloys. Low cycle fatigue tests with and without holding time have been performed at 850°C under air and under vacuum on both alloys. The results showed that cyclic hardening, cyclic stability and life time are closely related to the duration of the holding time. Furthermore, a single thermally activated mechanism operates over a very wide range of strain rates, corresponding to tensile tests, creep and relaxation. The link between microstructure and mechanical behaviour presented in this thesis helps to determine the advantages as the operation limits of each alloy in order to manufacture a nuclear power plant heat exchanger