Dissertations / Theses on the topic 'X-Ray Micro-diffraction'

Microscopic beams of penetrating synchrotron radiation provide a unique tool for the analysis of material structure and deformation. This thesis describes my contributions to the development of new synchrotron X-ray micro-beam diffraction experimental techniques and data interpretation, and the use of experimental results for the validation of material deformation models. To study deeply buried material volumes in thick samples, the micro-beam Laue technique was extended to higher photon energies. Through-thickness resolution was achieved either by a wire scanning approach similar to Differential Aperture X-ray Microscopy (DAXM), or by applying tomographic reconstruction principles to grain-specific Laue pattern intensity. Both techniques gave promising first results. For reliable micro-beam Laue diffraction measurements of elastic strains in individual grains of a polycrystal, understanding of the error sources is vital. A novel simulation-based error analysis framework allowed the assessment of individual contributions to the total measurement error. This provides a rational basis for the further improvement of experimental setups. For direct comparison of experimental measurements and dislocation dynamics simulations, diffraction post-processing of dislocation models in two and three dimensions was developed. Simulated diffraction patterns of two-dimensional dislocation cell/wall type structures captured correctly some of the features observed experimentally in reciprocal space maps of a large-grained, lightly deformed aluminium alloy sample. Crystal lattice rotations computed from three-dimensional dislocation dynamics simulations of a Frank-Read source showed anisotropic orientation spread similar to that observed in micro-beam Laue experiments. For the experimental study of crystal lattice distortion, a novel technique was proposed that combines micro-beam Laue diffraction with scanning white-beam topography. Diffraction topography allows the study of lattice rotation at scales smaller than the scanning beam size. The new technique makes it possible to apply classical topography methods to deformed samples.

Ce manuscrit a pour sujet principal la diffraction par rayons X des matériaux ondes de densité de charges (ODC). Nous avons étudié le cristal quasi-1D NbSe3 ainsi que le quasi-2D TbTe3. Plusieurs grands instruments ont été utilisés pour cette étude, le synchrotron ESRF de Grenoble sur la ligne ID01 ainsi que le laser à électron libre LCLS à Stanford. Premièrement, grâce à la cohérence du faisceau X à LCLS, nous avons pu observer une perte de cohérence transverse dans NbSe3 lors de l’application d’un courant électrique au-dessus d’un certain seuil ainsi qu’une compression longitudinale de l’ODC. Ensuite, à l’ESRF, nous avons utilisé un faisceau X focalisé au micromètre par une Fresnel zone plate pour scanner l’ODC localement par diffraction sur NbSe3 puis ensuite sur TbTe3. Lorsqu’un courant est appliqué sur l’échantillon, nous avons observé une déformation transverse indiquant que l’ODC est bloquée au niveau de la surface de l’échantillon dans NbSe3. Dans le cas de TbTe3, l’ODC tourne sous courant présentant un cycle d’hystérésis lorsque le courant passe continument de positif à négatif. Nous avons aussi pu constater dans plusieurs régions, toujours pour TbTe3, la création de défauts d’irradiation localisés induisant une compression-dilatation de l’ODC. Dans une dernière partie théorique, nous montrons comment la théorie du transport électrique de l’ODC par un train de solitons portants chacun une charge ainsi que la prise en compte du blocage de l’ODC sur la surface de l’échantillon que nous avons vu expérimentalement permet de comprendre plusieurs mesures de résistivité en fonction des dimensions de l’échantillon trouvées dans la littérature. Nous présentons ensuite plusieurs idées pour expliquer du blocage de l’ODC sur les surfaces au niveau microscopique et proposons l’hypothèse d’une ODC commensurable en surface (et incommensurable dans le volume)
The main subject of this manuscript is the X-ray diffraction of charge density wave (CDW) materials. We studied the quasi-1D NbSe3 crystal and the quasi-2D TbTe3. Several large instruments facilities were used for this study, the ESRF synchrotron in Grenoble on the ID01 line and the LCLS free electron laser in Stanford. First, thanks to the coherence of the X-beam at LCLS, we were able to observe a loss of transverse coherence in NbSe3 when applying an electrical current above a certain threshold as well as a longitudinal compression of the CDW. Then, at the ESRF, we used an X-ray beam focused on the micrometer scale by a Fresnel zone plate to scan the CDW locally by diffraction on NbSe3 and on TbTe3. When a current is applied to the sample, we observed a transverse deformation indicating that the CDW is pinned on the sample surface in NbSe3. In the case of TbTe3, the CDW rotates under current showing a hysteresis cycle when one is continuously changing from positive to negative current. We have also observed in several regions, in TbTe3, the creation of localized irradiation defects inducing a compression-dilation of the CDW. In a last theoretical part, we show how the theory of electric transport in the CDW state by a train of charged solitons, as well as taking into account the CDW pinning on the surface of the sample that we have seen experimentally, allows us to understand several resistivity measurements, found in the literature, made on samples with different dimensions. Finally, we present several ideas for an explanation of the CDW pinning at the surfaces on a microscopic level and propose the hypothesis of a commensurate CDW on the surface (and incommensurate in volume)

Dans le but d'étudier le comportement mécanique du combustible nucléaire dans un scénario de stockage direct à long terme, des polycristaux d'UO2 sont implantés en ions Hélium dans une fine couche surfacique (environ 1 µm), induisant des déformations. Ces déformations sont mesurées, à l'échelle des grains, par micro-diffraction des rayons X, en utilisant un rayonnement synchrotron (ESRF). Des méthodes d'analyse d'images sont développées pour traiter automatiquement le grand nombre de clichés de diffraction. Le développement d'outils statistiques permet de détecter des clichés problématiques et d'améliorer la précision de l'analyse. Pour des faibles profondeurs d'implantation, l'interaction mécanique entre les grains peut être négligée. Les résultats expérimentaux peuvent être approchés par un modèle mécanique simple. À plus grandes profondeurs, les résultats expérimentaux montrent une plus grande interaction mécanique aux joints de grain qui peut être modélisée par éléments finis. Des outils de géostatistique ont été utilisés pour quantifier ces interactions. Le gonflement et les constantes élastiques de la couche implantée peuvent être ajustés à travers les déformations mesurées sur un grand nombre de grains d'orientations différentes. Ces études permettent de déterminer le gonflement du combustible nucléaire en conditions d'irradiation, ainsi que les modifications de ses propriétés élastiques
In order to study the mechanical behavior of nuclear fuel during direct long term storage, UO2 polycrystals were implanted with Helium ions at a thin surface layer (1 µm approximately), which leads to stress and strain fields in the layer. Strains were measured, at the grains scale, by X-ray micro-diffraction, using synchrotron radiation (ESRF). Image analysis methods were developed for an automatic analysis of the large number of diffraction patterns. Applying statistical tools to Laue patterns allows an automatic detection of low quality images, and enhances the measurement precision. At low layer thickness, the mechanical interaction between grains can be neglected. At higher thickness, experimental results showed a higher mechanical interaction near grain boundaries that can be modeled using finite elements method. Geostatistical tools were used to quantify these interactions. The swelling and the elastic constants in the implanted layer can be estimated through the measured strains on a large number of grains with different orientations. This work allows the determination of the swelling of nuclear fuel in irradiation conditions, as well as the modification of its elastic properties

En instal·lacions de radiació sincrotró, es necessiten detectors amb una bona resolució espacial i un alt ritme de contes local per tal de dur a terme experiments de difracció de raigs x en l'escala temporal del mil·lisegon. Els detectors de gas de micro-fabricació (MPGD) poden satisfer aquests requeriments gràcies a l'alta densitat d'elèctrodes que presenten. No obstant aquest tipus de detectors presenten dos grans problemes: descàrregues elèctriques destructives i un deteriorament continu durant el seu us continuat.
En aquest treball presentem una nova estructura de MPGD: el Micro Reading Mesh Chamber (MRMC). És un MPGD amb un estadi d'amplificació. El detector està dividit en dues regions: la regió de deriva i la regió de multiplicació. Aquestes estan separades per una malla formada per elèctrodes de lectura. El pla de l'ànode té una capa de material resistiu a la seva superfície.
El disseny del MRMC redueix els problemes que els actuals MPGD presenten. Entre d'altres avantatges, el posicionament dels elèctrodes de lectura a la malla incrementa la sensibilitat dels càtodes a la senyal. Això permet una reducció de la intensitat del camp elèctric de multiplicació. En conseqüència, la càrrega del detector i la probabilitat de descàrregues destructives es redueix.
S'han realitzat diverses simulacions per tal d'avaluar i optimitzar el rendiment del detector. Degut al gran nombre de paràmetres que poden ser escollits i del gran nombre de característiques que en depenen, s'ha realitzat un treball de simulació i optimització global. En primer lloc, s'ha dissenyat un programa basat en tècniques Monte-Carlo per tal de simular el procés de detecció i poder així avaluar la resolució espacial en funció dels diferents paràmetres del detector. En segon lloc, s'han realitzat una sèrie de simulacions que involucren la simulació del moviment en tres dimensions de les càrregues i la seva multiplicació dins l'estructura de detecció. Aquests estudis inclouen la estimació de la transparència de la malla, l'estudi de les línies i els temps de deriva dels ions, i la simulació del procés d'allau. Part d'aquestes simulacions han estat verificades experimentalment. Finalment, les capacitancies entre els elèctrodes i l'ànode i entre elèctrodes s'ha simulat per tal d'avaluar el soroll electrònic i els efectes de "crosstalk".
S'ha construït i provat un prototip. Els tests realitzats mostren una bona concordança amb les simulacions del guany. Així doncs, queda demostrat que el MRMC pot arribar a ritmes de contatge local >1.25·105Hz/mm2. No obstant, s'observen guspires en el detector degut a la presència de material dielèctric a la superfície dels càtodes. Degut a la superfície resistiva i la robustesa de l'estructura, el detector ha resistit les descàrregues sense rebre ningun dany. En conseqüència, per tal de que el MRMC esdevingui un detector útil, s'han de millorar tant el procediment de construcció, com les tècniques de neteja.
En conclusió, es necessita més treball experimental per tal d'obtenir un detector lliure de descàrregues completament funcional pel qual les simulacions prediuen un alt ritme de comptes local (>1.25·105Hz/mm2) i una bona resolució espacial (>250?m).
At synchrotron radiation facilities, detectors with high spatial resolution and high local count rate are needed in order to perform x-ray diffraction/scattering on time resolved experiments on the sub-millisecond time scale. Micro Pattern Gas Detectors (MPGD) could provide good spatial resolutions and high count rate thanks to their small cells of amplification region. Despite their promising performance, two major problems have arisen: rare but damaging discharges and, slow but continuous deterioration (aging) during sustained irradiation
Here we present a new MPGD structure: the Micro Reading Mesh Chamber (MRMC). It is a one stage amplification MPGD. It is divided in two regions: the drift/conversion region and the multiplication region. They are separated by a mesh formed by thick (25?m) pick-up strips. The anode plane has a resistive layer on it.
The design of the MRMC reduces the problems that the present MPGD show. Among other advantages, placing the pick-up strips at the mesh, instead of at another readout plane, increases the signal sensitivity of the cathodes. It allows a decrease of the gain through a reduction of the multiplication field. Therefore, it reduces the charging up and the probability of voltage and rate-induced dielectric breakdown.
Different simulations have been carried out to evaluate and optimize the performance of the detector. Due to the large number of detector parameters that can be chosen, and the features that depend on them, a global simulation was done. Firstly, a Monte-Carlo based program that reproduces the detection in the chamber has been developed in order to simulate the spatial resolution as a function of different parameters of the detector. Secondly, a set of studies that involve the simulation of the three dimensional movement of the charges in the chamber and its multiplication have been carried out. These models include the estimation of the mesh transparency, the study of the ion drift paths and times, and the simulation of the avalanche process. Part of these simulations has been cross-checked experimentally. Finally, the capacitances between the strips and the anode, and between strips has been simulated in order to evaluate the electronic noise and the crosstalk effects.
After the simulation work, a prototype was built and tested. The tests show good agreement between the simulated and the experimental gain. This agreement on the space charge calculations demonstrates that the MRMC can deliver local count rates >1.25·105Hz/mm2. Moreover, due to the resistive layer and the strength of the structure, the detector survived without noticeable damage. However, the detector suffers from discharges because of dielectric deposits on the cathode surface. Therefore, to turn this device into a detector for routine use, it will be necessary to both improve the construction process of the mesh structure and to develop an exhaustive cleaning procedure.
In conclusion, more experimental work is necessary to obtain a spark protected functional detector for which the simulations predict a high local count rate (>1.25·105Hz/mm2) and a good spatial resolution).

Les comportements mécaniques des films minces polycristallins sont encore mal compris à l'échelle sub-micronique. En particulier des hétérogénéités locales de déformation importantes sont attendues, mais elles restent difficile à quantifier expérimentalement. Les nouvelles possibilités offertes par les micro-faisceaux synchrotron de rayons X ont donc été utilisées dans ce travail pour éclairer cette problèmatique. Une réflexion de Bragg provenant d'un grain unique sub-micronique a été acquise avec une très bonne résolution dans l'espace réciproque en trois dimensions lors d'un cycle thermique. Les propriétés de cohérence du faisceau ont été utilisées pour reconstruire à trois dimensions une composante du champ de déplacement intra-grain avec une résolution d'une vingtaine de nanomètres dans les trois directions. Cette technique est basée sur des algorithmes de reconstruction de phase qui néanmoins connaissent des stagnations dans le cas des échantillons fortement déformés. Une méthodologie basée sur la connaissance de la forme du grain a donc été développée pour contourner ces difficultés. Des analyses complémentaires de diffraction X de laboratoire et de microdiffraction monochromatique ont également mis en évidence des hétérogénéités importantes de déformation entre les différents grains.

The viscoelastic behavior of concrete, nearly completely attributable to changes in properties in the cement paste, is an ongoing area of research with the objective of avoiding unpredictable response and potentially failure of concrete structures. This research explores the elastic and viscoelastic response in cement paste beams using relaxation testing, with and without strain reversals in the load history. It was seen that strain reversal imparts significant changes in mechanical response, retarding load relaxation. Companion beams were tested for chemical composition at varying depths in the beam section and the results were compared to those of control specimens not subject to stress. Results indicate significant variations in composition implying that stress accelerates the hydration process. The reasons behind the acceleration are discussed and incorporated into a preliminary solidification-dissolution model for beam relaxation. The model, though in need of improvement through further research, shows promise in potentially predicting relaxation in cement paste and by extension, in concrete structures.
Ph. D.

Les traitements thermomécaniques permettent une mise en forme temporaire et aisée de la chevelure, propriétés recherchées par les utilisateurs. Cependant, les effets obtenus ne sont pas toujours à la hauteur des attentes, notamment en raison d’une mauvaise tenue de la forme dans le temps et de possibles endommagements de la chevelure. Dans le but d’améliorer les appareils de coiffage existants, nous souhaitons comprendre les effets de ces traitements sur le cheveu, pour ensuite déterminer les conditions permettant d’atteindre la meilleure rémanence de la forme tout en minimisant la dégradation du cheveu. Pour ce faire, nous nous appuyons sur des expériences de traction, microdiffraction X et spectroscopie infrarouge. Tout d’abord, nous avons étudié l’organisation structurale de cheveux naturels. Nous avons mis en évidence une distribution de structure cœur – peau avec un cœur de structure régulière d’autant plus excentré que la courbure est marquée. Ensuite, nous avons dégagé les principaux paramètres sur. lesquels jouer lors de la mise en forme: température du mandrin, contrainte et durée d’application. Les effets de ces paramètres sur le comportement mécanique et la nanostructure du cheveu ont été évalués. Il ressort de notre étude que la contrainte de mise en forme est déterminante : nous avons défini la gamme de contraintes permettant de préserver la structure et les propriétés mécaniques du cheveu et celle occasionnant la dégradation du cheveu, voire une restructuration en feuillets bêta. Nous avons également évalué l’efficacité des différentes conditions de traitement à produire une forme durable dans le temps. En complément, nous nous sommes intéressés au mécanisme structural survenant lors de l’étirement de cheveux natifs ou préalablement traités, en couplant étirement continu d’un cheveu et analyse par microdiffraction X. Ainsi nous avons réussi à suivre l’évolution sous étirement d’une structure de cheveu transformée en feuillets bêta. Les résultats originaux obtenus au cours de ce travail, qui établissent un lien entre les mécanismes moléculaires et le comportement macroscopique du cheveu, permettent d’envisager le développement de nouveaux traitements thermomécaniques à l’échelle industrielle
Thermomechanical hair styling is preferred by users for easy and temporary reshaping of hair. However, the result is not always up to expectations, particularly due to poor shape stability over time and possible hair damage. In this work, we aim to improve hairstyling devices. To this end, we need to understand the effects of such treatments on hair in order to determine conditions which allow the best shape holding while minimizing hair damage. To achieve this, we use tensile testing, X-ray diffraction and infrared spectroscopy experiments. First, we studied the structural organization of natural hair. We highlighted a “core-skin” distribution of structures with a regular core which is all the more off-centered as curvature is high. Subsequently, we identified the main parameters of thermomechanical reshaping: temperature, stress and application time. Then, we evaluated the effects of these parameters on mechanical behavior and hair nanostructure. Our study shows that applied stress is a key factor: we defined stresses range allowing preservation of hair structure and its mechanical properties and the one leading to degradation or even driving to beta-sheets transition. Efficiency of the different treatment conditions in producing long-lasting shape over time was then evaluated. In addition, we analyzed the structural mechanisms that occur during stretching for native and pretreated hair: we used X-ray microdiffraction coupled with continuous stretching of hair. Consequently, we were able to monitor a beta sheet structure in hair during stretching. The original results obtained during this work, bridging internal molecular mechanisms and macroscopic behavior of hair, will allow to develop new thermomechanical treatments at industrial scale

L'introduction d'une contrainte mécanique dans le canal de MOSFETs sur SOI est indispensable pour les noeuds technologiques sub-22 nm. Son efficacité dépend de la géométrie et des règles de dessin du dispositif. L'impact des étapes du procédé de fabrication des transistors (gravure des zones actives, formation de la grille métallique, implantation des Source/Drain (S/D)) sur la contrainte du silicium contraint sur isolant (sSOI) a été mesuré par diffraction des rayons X en incidence rasante (GIXRD). Parallèlement, le gain en performances de MOSFETs sur sSOI a été quantifié par rapport au SOI (100% de gain en mobilité pour des nMOS longs et larges (L=W=10 μm), 35% de gain en courant de drain à saturation (IDsat) pour des nMOS courts et étroits (L=25 nm, W=77 nm)). Des structures contraintes innovantes ont aussi été étudiées. Un gain en IDsat de 37% (18%) pour des pMOS sur SOI (sSOI) avec des S/D en SiGe est démontré par rapport au sSOI avec des S/D en Si, pour une longueur de grille de 60 nm et des films de 15 nm d'épaisseur. Des mesures GIXRD, couplées à des simulations mécaniques, ont permis d'étudier et d'optimiser des structures originales avec transfert de contrainte d'une couche enterrée précontrainte (en SiGe ou en nitrure) vers le canal.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:06/58686-1

Cutting tools are subject to extreme environment during processing, with hightemperatures and pressures. CVD coatings are used to increase lifetime andperformance of the WC/Co composite. Residual stresses in the coatings areinteresting as they may be destructive or constructive for the material duringoperation. Blasting is used to change the as-deposited tensile stress to compressive.The usefulness of X-ray diffraction (XRD) and nanobeam diffraction (NBD) forcharacterization of strains in the different coating layers has been investigated. XRDwith different anode materials has been used to determine the macrostress in thelayers and an attempt was done to calculate the average microstrain and crystallitesize. NBD was used to study the microstrain within single grains of the differentmaterials. A specimen preparation method has been developed for the studiedsamples using the FIB.The XRD analysis shows that the measurement condition is of great importanceduring stress measurements. The macrostress of the different samples show that theZrCN type coating is less stressed than the TiCN type coating after deposition. It isalso shown that the ZrCN type coating is less affected by the blasting. Determinationof microstrain and crystallite size from XRD needs further development.The NBD is a good method to evaluate microstrain within single grains, or betweengrains oriented in the same zone axis. The analyses show more strain within thegrains after blasting. The measurements indicate more strain variation in the Al2O3layer in the TiCN system compared to the ZrCN system.

The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
As cerÃmicas atualmente oferecem significantes vantagens por apresentarem baixo custo de produÃÃo para dispositivos eletrÃnicos que operam em radiofrequÃncia (RF) e micro-ondas, alÃm de serem materiais de baixo peso, estÃveis com a temperatura e extremamente passÃveis de miniaturizaÃÃo (compactaÃÃo). As cerÃmicas magnÃticas possuem tambÃm menores perdas dielÃtricas e sÃo preferidas em muitas das aplicaÃÃes tecnolÃgicas atuais. Este trabalho foi dividido em duas etapas. A primeira consistiu em obter as matrizes cerÃmicas Ba2Co2Fe12O22 e CaTiO3 atravÃs da sÃntese de estado sÃlido com moagem mecÃnica de alta energia e a segunda consistiu em estudar as propriedades estruturais, dielÃtricas e magnÃticas de um sÃrie de compÃsitos cerÃmicos formado por essas matrizes. A difraÃÃo de raios-X (DRX) foi essencial na caracterizaÃÃo estrutural dos compÃsitos desejados. A morfologia das amostras foi estudada pela microscopia eletrÃnica de varredura (MEV). Experimentos foram realizados para avaliar o desempenho dielÃtrico e magnÃtico na faixa de radiofrequÃncia (RF) e micro-ondas para posterior anÃlise de uma aplicaÃÃo tecnolÃgica cabÃvel. Os experimentos realizados indicaram que à possÃvel obter compÃsitos cerÃmicos com altos valores de permissividade dielÃtrica e baixas perdas dielÃtricas, resultando em compactaÃÃo e eficiÃncia para dispositivos a serem projetados. Os compÃsitos avaliados nesse trabalho comportaram-se adequadamente como antenas ressoadoras dielÃtricas em micro-ondas, tornando-os importantes no desenvolvimento de antenas de banda larga de quarta geraÃÃo (4G) para telefones celulares, ou aplicaÃÃo em dispositivos de antenas omnidirecionais de baixo ganho e outros produtos para redes sem fio.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Revestimentos de zinco obtidos por imersão a quente têm sido amplamente utilizados em estruturas expostas em solos, águas naturais e atmosfericamente, devido a excelente resistência em meios de baixa agressividade. Nessas aplicações, as arestas de corte ficam expostas e estão mais susceptíveis à corrosão. Objetivando relacionar a microestrutura dos revestimentos com técnicas de microssondas eletroquímicas, para melhor entender os processos corrosivos de aços galvanizados, buscou-se uma nova metodologia para ampliar as fases e obter uma estrutura em camadas. Para a caracterização da morfologia dos revestimentos obtidos pelo processo de galvanização por imersão a quente (galvanized, galvannealed e galvalume) utilizou-se microscopia óptica e eletrônica de varredura com microanálise. Para verificar e analisar os mecanismos de corrosão das fases presentes nos revestimentos de zinco de forma localizada empregou-se a técnica de varredura por eletrodo vibratório (SVET) e microcélula capilar (MEC), e de forma complementar, para identificar os produtos de corrosão formados utilizou-se micro difração de raios X (μ-DRX). Os resultados demonstraram que a metodologia empregada neste estudo é adequada para avaliar as fases de forma individual ou conectadas galvanicamente, e assim identificar as fases mais ativas durante os processos corrosivos. Os resultados obtidos por microcélula complementam os mapeamentos de densidade de corrente obtidos por eletrodo vibratório, mostrando que os intermetálicos permanecem estáveis após os ensaios e a região mais ativa é o revestimento não intemperizado (polido) próximo à interface aço/revestimento. O revestimento que apresentou melhor resistência à corrosão em soluções contendo cloreto foi o Zn55Al. O espectro μ-XRD para o revestimento galvanized, indica a presença das fases zincita e Fe-α sobre o aço IF (interstitial free), mostrando que sob condições de OCP a superfície de aço IF foi protegida pelo revestimento apesar da sua grande área. Esta precipitação pode ainda proteger áreas de aço expostas aonde o revestimento foi danificado por arranhões ou na aresta de corte.
Hot-dip zinc coatings have been widely used in structures exposed to soils, natural water and atmosphere due to their excellent resistance in low aggressive media. In such applications, the cutting edges are exposed and more susceptible to corrosion. In order to correlate the microstructure of the coating with electrochemical microprobe techniques, a new methodology was developed to amplify the size of the phases and to obtain a layered structure. Optical microscopy and scanning electron microscopy were used to characterize the morphology of the coatings obtained by the hot dip galvanization process (galvanized, galvannealed e galvalume). Scanning vibrating electrode technique (SVET) and capillary microcell (MEC) were used to identify and study the corrosion mechanisms of the phases present in zinc coatings. The corrosion products were identified by X-ray micro-diffraction (μ-XRD). The results demonstrated that the methodology employed in this study is adequate to evaluate the phases individually or galvanically connected, thus identifying the most active phases during the corrosive processes. The results obtained by microcell complement the current density mappings obtained by vibrating electrode, showing that the intermetallics remain stable after the analysis and the most active region is the not wedered coating near the steel/coating interface. The coating that showed the best corrosion resistance in solutions containing chloride was the Zn55Al. The μ-XRD spectrum for the galvanized coating indicates the presence of zincite and Fe-α on the IF steel (interstitial free), showing that under OCP conditions the IF steel surface was protected by the coating despite its large area. This precipitation can further protect exposed steel areas where the coating has been damaged by scratches or at the cutting edge.

Les travaux de recherche discutés dans ce manuscrit concernent la conception des générateurs de puissance électrique pour l'aéronautique. L’augmentation de la puissance massique de ces équipements passe par une augmentation des vitesses de rotation, donc une augmentation des contraintes. Un premier point est de s'assurer de la bonne tenue mécanique des matériaux. Un deuxième point est de pouvoir prendre en compte les modifications du comportement magnétique (et donc in fine du couple) lorsqu'ils sont soumis à un état de contraintes multiaxial. L’étude présentée vise en particulier à illustrer l’influence d'états de contraintes biaxiaux sur le comportement magnétique des matériaux constitutifs du rotor. Le défi repose sur la mise en place de méthodes de caractérisation du comportement magnéto-mécanique dissipatif uniaxial et multiaxial des nuances développées par Aperam et utilisées par Thales Avionics pour leurs applications aéronautiques (en FeCo-2V et Fe-3%Si à grains non orientés). Des essais non conventionnels seront effectués sur des échantillons en forme de croix de manière à s'approcher des contraintes réellement subies par le rotor. Les essais sont effectués sur la machine d'essai triaxiale Astrée du LMT-Cachan. L'état de contraintes est estimé par corrélation d'images et par diffraction des rayons X. Des mesures magnétiques anhystérétiques et de pertes d'énergie sous contraintes sont reportées. D'autre part, un modèle multi-échelle multiaxial, décrivant le comportement d’un VER à partir de l'équilibre énergétique à l'échelle microscopique sera présenté. L’approche est fondée sur la comparaison des énergies libres de chaque domaine. Une comparaison probabiliste est faite pour déterminer les variables internes que sont les fractions volumiques des domaines. Différentes stratégies envisageables pour modéliser la dissipation statique seront discutées. Puis nous présentons l’approche magnéto-élastique que nous avons retenue visant à une meilleure considération de l’effet de la contrainte sur le comportement des matériaux ferromagnétiques
The research presented in this thesis is motivated by the design of rotors for high speed rotating machines. The increased power density of these devices requires a higher rotation speed, leading to higher levels of centrifugal forces and stress in the rotor. A first point is to ensure good mechanical strength of the materials. A second point is to take into account changes in the magnetic behavior (and ultimately torque) when they are subjected to a multiaxial stress state. The present study aims at exploring the influence of biaxial stress states on the magnetic behavior of the materials of the rotor. The challenge lies in the development of methods for the characterization of the magneto-mechanical dissipative uniaxial and multiaxial behavior of metal sheets developed by Aperam Alloy and used by Thales Avionics for their aeronautical applications (in FeCo-2V and non-oriented Fe-3%Si). Non conventional experiments are performed on cross-shaped samples in order to apply biaxial stress representative of the loadings experienced by rotors of rotating machines. These experiments are performed on a multiaxial testing machine, Astrée. Stress level is estimated thanks to digital image correlation and X-ray diffraction Both anhysteretic and dissipative magnetic responses to magneto-mechanical loadings have been recorded. On the other hand, a multi-scale multiaxial model describing the behavior of a RVE from the energy balance at the microscopic scale is presented. The approach is based on a comparison of the free energy of each domain. A probabilistic comparison is made to determine the volume fraction of domains used as internal variables. Different strategies for modeling the static dissipation are discussed. Then we present the chosen magneto-elastic approach, improving the description of the effect of stress on ferromagnetic materials behavior

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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les films de nitrures métalliques nanostructurés sont généralement utilisés comme revêtements protecteurs. Ti1-xAlxN (0 ≤ x ≤ 1) peut être considéré comme un système modèle, où TiN (cubique) et AIN (hexagonal) sont partiellement miscibles. L’élaboration par dépôt physique en phase vapeur donne au film une microstructure colonnaire complexe composée de phase métastable pouvant cohabiter avec des précipités localisés aux joints de grains. Une haute dureté et une grande résistance à l’oxydation sont observées pour un maximum d’atomes de Ti substitué par des atomes de Al en réseau cubique. Les conditions de dépôt et la composition jouent un rôle majeur sur la substitution des éléments métalliques (Ti ,Al). Nous avons préparé deux séries de films déposés par pulvérisation cathodique magnétron réactive à partir de cibles TiAl compartimentées et frittées. La micro- et nanostructure des films ont été analysées par Diffraction, Spectroscopie d’Absorption des rayons X et Microscopie Electronique à Transmission. L’usure des revêtements a été étudiée par microtribologie. Nous observons pour les films riches en Ti (x < 0,5) des directions de croissances [200]c et [111]c, caractéristiques d’un réseau cubique. Tandis que, les films riches en Al (x > 0,7) présentent une croissance de domaines bien cristallisés suivant la direction [002]h du réseau hexagonal. De plus, nous avons mis en évidence l’apparition de la transition cubique / hexagonal à des teneurs en Al plus élevée pour les films issus de cible frittée. Ces films montrent une meilleure résistance à la fissuration et à l’usure que ceux déposés à partir de cible compartimentées
Ti1-xAlxN (0 ≤ x ≤ 1) is considered as a model system, where TiN (fcc) and AlN (hcp) do not mix over the whole composition range due to their low miscibility. However, the physical vapour deposition (PVD) allows achieving metastable phases of Ti1-xAlxN, where Al atoms are partially substituting for Ti in fcc lattice. Ti1-xAlxN coatings exhibit high hardness and oxidation resistance for the maximum Al substituted to Ti in fcc lattice (about x=0.6). The proportion of grain boundaries and the limit solubility play a major role on the mechanical properties and resistance to wear of the coatings. Several techniques are employed to investigate two sets of Ti1-xAlxN thin films deposited by magnetron reactive sputtering from two types of metallic targets onto Si (100). Lattice symmetry of crystallised domains and columnar growth structure of the films are characterized by X-ray diffraction (XRD) and electron microscopy (TEM, HRTEM). Several local probes such as X-ray absorption fine structure (XAFS), diffraction anomalous fine structure (DAFS) and Electron Energy Loss Spectroscopies (EELS) which are very sensitive to the symmetry of the atomic sites either octahedral for fcc lattice or tetrahedral for hcp one are carried out. For Ti-rich films (x < 0.5), the competitive growth of cubic domains between [200]c and [111]c is observed. For Al-rich films (x > 0.7) have a domain growth well crystallized in the direction [002]h the hexagonal lattice. In addition, the cubic / hexagonal transition in Al contents higher is observed for films from sintered target. These films show better wear resistance than those deposited from target compartmentalized

Historical painted works of art have a very complex inner structure. The period painting technique led to the execution of a ground layer followed by several layers of underpainting and a top paint layer, over which a layer of glaze has been applied to increase the resistance to external wear. Each of these colour layers is composed of a dye or a pigment (or their mixture) bound by organic binder. Throughout the history, pigments were commonly prepared from minerals, either extracted from natural deposits or created artificially. In these heterogeneous layers containing both inorganic and organic components, undesirable degradation changes either driven by processes taking place directly in the colour layer or influenced by external agents may occur. Mineralogical approach, which focuses primarily on the structure of studied pigments, helps in the clarification of the occurring processes, in the determination of conditions leading to degradation as well as in the identification of original/degradation phases. Furthermore, it can be profitably applied in the micro- analysis of mineral pigments present in tiny micro-samples obtained from works of art, contributes to the artwork's provenance/authorship studies and the determination of regional provenance of the employed mineral pigments. This Ph.D....