Made available in DSpace on 2017-07-24T19:37:59Z (GMT). No. of bitstreams: 1 Kelly Cristiane Iarosz.pdf: 3162956 bytes, checksum: 71eb827f1ad61f4e7254616273a9a939 (MD5) Previous issue date: 2009-02-17 / Knowing the crystalline structure of a mineral, considering its geographic location and geological formation, is an important step concerning to the increasing of new perspectives of their utilization, due to the fact that every mineral has its own specificities. In this work, three samples from the Amazon region were analyzed by X-Ray Fluorescence (XRF) to determine the elements contained in the samples; Scanning Electronic Microscopy (SEM), microanalysis and map for analysis of superficial aspects, of the difference of the composition and location of elements; X-Ray Diffraction in the continuous scanning way for previous identification of the phases contained and step scanning to make the refinement in the analysis of the data using the Rietveld Method through the DBWS-9807a, so the identified phases were Quartz, Xenotime and Thorite. / Conhecer a estrutura cristalina de um mineral, considerando sua localização geográfica e formação geológica, é um passo importante na potencialização de novas perspectivas na utilização desses, porque cada mineral em particular tem suas especificidades. Neste trabalho, três amostras da região da Amazônia foram analisadas por Fluorescência de Raios X (FRX) para determinação dos elementos presentes; Microscopia Eletrônica de Varredura, microanálises e mapeamento para análises de aspectos superficiais, de diferença de composição e de localização dos elementos; Difração de Raios X no modo de varredura contínua para identificação prévia das fases presentes e varredura passo a passo para realizar o refinamento usando o Método de Rietveld utilizando o Programa DBWS-9807a, sendo as fases identificadas: Quartzo, Xenotima e Torita.

Made available in DSpace on 2017-07-24T19:38:06Z (GMT). No. of bitstreams: 1 Renata Olegario.pdf: 5279781 bytes, checksum: 47c1e5b7166f5caec9a3a371cfe659e3 (MD5) Previous issue date: 2012-03-02 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This study focused on the Cerium oxide (CeO2) based pigmenting systems, doped with Praseodymium oxide (Pr6O11) and hematite (Fe2O3 – iron oxide) synthesized through the solid state reaction (OM – oxide mixture) and the Pechini method. Simultaneously, CeO2-Pr6O11-Fe2O3 ternary system pigments were synthesized through OM, with the addition of mineralizers. The samples synthesized through OM were wet homogeneized, in isopropyl alcohol, in a horizontal ball mill for 18 hours and dried in oven at 110 C, then thermally treated at 1300 ºC for 3 hours. In samples synthesized through the Pechini method, the process started from the synthesis of the polymeric resin, formed by the citric acid reaction, glycol ethyl, water and the desired oxide salts, kept in thermal blanket at 150 C, under constant agitation for 2 hours, following two thermal treatments at 300 C for 2 hours, and then one at 900 C for 3 hours. After the thermal treatment the pigmenting systems were characterized through XRD, UV-Vis reflectance spectroscopy, scanning electronic microscopy, Raman spectroscopy and thermal analysis, determining the phases present, the colorimetric parameters, band gap values, micro-structural agglomerations and thermal and chemical stability to glass enamel. Single phase pigments were obtained in the binary system CeO2-Pr6O11, with addition of up to 10% Pr6O11 synthesized through OM and up to 3% Pr6O11 synthesized through the Pechini method, whereas the binary system CeO2-Fe2O3, presented single phase only in OM synthesis, with concentrations up to 2% of Fe2O3. More intense shades were obtained in pigments with addition of up to 5% mol praseodymium oxide in the CeO2-Pr6O11 system, and with up to 3% mol iron oxide in the CeO2-Fe2O3 system. The ternary system CeO2-Pr6O11-Fe2O3 presented secondary phase PrFeo3, remaining this phase even with the addition of mineralizers. The pigments applied to low temperature frits (LTF) and windscreen glass (WSG) showed chemically and thermally resistant at 800 C, free of surface defects on the ceramic plates, presenting better dispersion and color homogeneity. / A presente pesquisa estudou os sistemas pigmentantes à base de óxido de cério (CeO2) dopados com óxido de praseodímio (Pr6O11) e hematita (Fe2O3 - óxido de ferro), sintetizados pelo método de reação de estado sólido (mistura de óxidos - MO) e pelo método Pechini. Paralelamente foram sintetizados pelo método MO, pigmentos do sistema ternário CeO2-Pr6O11-Fe2O3 com adição de mineralizadores. As amostras sintetizadas por MO foram homogeneizadas a úmido, em álcool isopropílico, em um moinho de bolas horizontal por 18 horas e secas em estufa a 110 C, e tratadas termicamente a 1300 C por 3 horas. Nas amostras sintetizadas pelo método Pechini partiu-se da síntese da resina polimérica, formada pela reação de ácido cítrico, etileno glicol, água e os sais contendo os íons metálicos dos óxidos pretendidos, mantida em manta térmica a 150 C, sob agitação constante, por 2 horas, sendo tratadas termicamente duas vezes a 300 C por 2 horas, e, na sequência, a 900 C por 3 horas. Após tratamento térmico os sistemas pigmentantes foram caracterizados por difração de raios X, espectroscopia de reflectância na região do UV-Vis, microscopia eletrônica de varredura, espectroscopia Raman e análise térmica, sendo determinadas as fases presentes, os parâmetros colorimétricos, valores de band gap, aglomerações micro estruturais e a estabilidade térmica e química frente à esmaltação vítrea. Pigmentos de fase única foram obtidos no sistema binário CeO2-Pr6O11, com adição de até 10% de Pr6O11 sintetizado por MO e com até 3% de Pr6O11 sintetizado por Pechini; já no sistema binário CeO2-Fe2O3, fase única somente em sínteses por MO, com concentrações até 2% de Fe2O3. Tonalidades mais intensas foram obtidas nos pigmentos com adição de até 5% mol de óxido de praseodímio no sistema CeO2-Pr6O11, e com adição de até 3% mol de óxido de ferro no sistema CeO2-Fe2O3. O sistema ternário CeO2-Pr6O11-Fe2O3 apresentou fase secundária PrFeO3, persistindo esta fase mesmo com adição de mineralizadores. Os pigmentos aplicados em frita de baixa temperatura (FBT) e vidro de pára-brisa (VPB) se mostraram resistentes química e termicamente a 800 ºC, sem presença de defeitos superficiais nas placas cerâmicas, apresentando melhor dispersão e homogeneidade da cor.

Made available in DSpace on 2017-07-24T19:38:15Z (GMT). No. of bitstreams: 1 Joao Francisco Rigoni.pdf: 4975524 bytes, checksum: 965890549173b9947b3268dc0bc5fe6b (MD5) Previous issue date: 2014-08-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The current technological development in the communication, has carrieb, data processing, integration of devices and entertainment, is only possible due to the advances integrated and continuos of the research on new materials to be applied in the technological industry,lighter, cheaper with better incomes. In the work it was become fulfilled synthesis and of the Titanate od calcium and has covered – pure CCTO and its doped version with different ratios of Nb+5 , by means of the method of reaction for solid state. This materials has shown interesting and pertinent physical properties to the current industry technological, as material mainly dielectric. The characterization of material obtained was made through the techniques of diffraction of X-rays (XRD), structural analysis for the Method of Rietveld, morphological and compositional characterization using scanning electron microscopy (SEM), dispersive spectroscopy X-ray (EDX), in addition to the characterization by Raman spectroscopy, and determination of the “band gap” by diffuse reflectance. The gotten, pure and doped samples had been identified as being the material of interest, proven through the described instrumental techniques previously. The gotten Values of “band gap” better present small variation, being able to be studied with use of others techniques. / O desenvolvimento tecnológico atual, na comunicação, transporte, processamento de dados, integração de aparelhos e entretenimento, só é possível graças aos avanços integrados e contínuos das pesquisas sobre novos materiais a serem aplicados na indústria tecnológica, mais leves mais baratos com melhores rendimentos. Neste trabalho realizou-se a síntese e do Titanato de cálcio e cobre – CCTO puro e sua versão dopada com diferentes proporções de Nb+5 , Poe meio do método de reação por estado sólido (RES). Esse material tem exibido propriedades físicas interessantes e pertinentes à indústria tecnológica atual, principalmente como material dielétrico. A caracterização do material obtido foi realizada através das técnicas de difração de raios X (DRX), análise estrutural pelo Método Rietveld, caracterização morfológica e composicional usando microscopia de varredura eletrônica (MEV) e espectroscopia dispersiva de raios X (EDS), bem como a caracterização por espectroscopia de RAMAN e determinação de “banb gap” por reflectância difusa. As amostras obtidas, puras e dopadas foram identificadas como sendo o material de interesse, comprovado através das técnicas instrumentais descritas anteriormente. Os Valores de “band gap” obtidos apresentam pequena variação, podendo ser melhor estudadas com uso de outras técnicas.

Submitted by Eunice Novais (enovais@uepg.br) on 2018-09-03T21:43:50Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Maicon_Crivoi.pdf: 5082056 bytes, checksum: cf064a8b661e7eb5e1be0dca41eab5f1 (MD5) / Made available in DSpace on 2018-09-03T21:43:50Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Maicon_Crivoi.pdf: 5082056 bytes, checksum: cf064a8b661e7eb5e1be0dca41eab5f1 (MD5) Previous issue date: 2018-02-23 / Dois aços inoxidáveis (AISI430 ferrítico e AISI316L austenítico) foram analisados por testes de tração uniaxial às temperaturas ambiente e criogênica, com taxas de deformação controladas para ambos os metais. Utilizou-se o equipamento Synchrotron Gleeble®, capaz de realizar medições de difração de raios X in situ, controlando a temperatura da amostra, a condição de tensão / tração, bem como a atmosfera da câmara e permitindo também a injeção de nitrogênio líquido diretamente sobre a amostra com excelente versatilidade e reprodutibilidade. Os testes foram realizados em um sistema de simulação termomecânica avançado, XTMS, localizado Centro Nacional de Pesquisa em Energia e Materiais - CNPEM - Campinas, SP, Brasil. A caracterização foi realizada por meio de imagens MEV e XRD in situ. As fotomicrografias e os resultados dos ensaios de tração mostram que o aço AISI 430 apresenta uma fratura dúctil à temperatura ambiente e fratura frágil a temperatura criogênica com aumento da resistência. Os resultados do aço AISI 316L evidenciam que o material tem uma fratura dúctil em ambas as condições. Para este mesmo metal, o alongamento a ambas as temperaturas foi praticamente o mesmo, mas a resistência à tração no ambiente criogênico foi muito maior. Este comportamento pode estar associado ao efeito TRIP, o que está de acordo com os dados XRD, uma vez que os picos de martensita α' induzida por deformação são evidenciados. / Two stainless steels (AISI430 ferritic and AISI316L austenitic) were analyzed by uniaxial tensile tests at room and cryogenic temperatures, with controlled strain rates for both metals. The Gleeble® Synchrotron system was used; it is capable to perform X-ray diffraction measurements in situ, controlling the sample temperature, controlling the stress / strain condition, as well as the chamber atmosphere, and also allowing the injection of liquid nitrogen directly into the sample with excellent versatility and reproducibility. The tests were performed in an advanced thermo mechanical simulation system, XTMS, located in the National Center for Research in Energy and Materials - CNPEM - Campinas, SP, Brazil. The characterization was performed by means of SEM images and in situ XRD. The photomicrographs and the results of the tensile tests show that AISI 430 steel presents a ductile fracture at room temperature and fragile fracture at cryogenic temperature with resistance increasing. The results of the AISI 316 L steel show that the material has a ductile fracture in both conditions. For this same metal, the elongation at both temperatures was practically the same, but the tensile strength in the cryogenic environment was much higher. This behavior may be associated with the TRIP effect, which agrees with the XRD data, since peaks of α’ strain induced martensite are evidenced.

Les otolithes, croissances aragonitiques de l'oreille interne des poissons téléostéens, peuvent être utilisés comme traceurs des variations de l’environnement rencontrées par un individu au cours de sa vie. Un ensemble d’otolithes de Sciaenidae et d’Ariidae archéologiques et modernes a été étudié dans le but d'améliorer les méthodes de reconstruction paléo-environnementale utilisant les otolithes et les autres biominéraux carbonatés stratifiés. L'incorporation du strontium, l'élément lié à l'environnement le plus facilement accessible, a été étudiée par analyses ponctuelles et par cartographie de spectroscopie d'absorption des rayons X (XAS). Une approche multivariée de cartographie rapide de l'environnement chimique a été mise en place pour déterminer le mode d’incorporation du Sr sur une superficie de 0,25 mm² avec une résolution micrométrique. Ces résultats démontrent pour la première fois avec une résolution latérale micrométrique sur des distances millimétriques que le Sr se substitue aléatoirement au calcium dans le réseau de l'aragonite, indépendamment de la concentration en Sr, de l’âge de l’individu ou de la période géologique. D’autre part, des cartes élémentaires sur des zones atteignant 2,6 mm² ont été collectées à des résolutions latérales micrométriques avec plusieurs techniques d'émission de rayons X (émissions provoquées par les particules des rayons X (PIXE) et fluorescence des rayons X par rayonnement synchrotron (SR-µXRF)). Ces cartes permettent l'examen détaillé de l'histoire de la vie d'un individu et de la taphonomie de l'échantillon avec une haute résolution temporelle, tout en identifiant les défauts ou les éléments abiogéniques. Enfin, la diffraction des rayons X par rayonnement synchrotron (SR-XRD) a été utilisée pour cartographier la texture cristalline sur des sections complètes d'otolithes afin d’approfondir notre connaissance de la structure interne et de la croissance des otolithes. Ces développements fournissent des outils précieux pour de futures études des biominéraux, mais plus généralement pour les sciences des matériaux. La sélection et la mise en œuvre de ces méthodes ont été réalisées dans le but d’exploiter au maximum leur fort potentiel pour l'étude des biocarbonates stratifiés, tout en tenant compte des approches existantes et en cherchant à en améliorer certains aspects tels que la profondeur d'information, la résolution latérale, la sensibilité, et les dégâts d’irradiation provoqués par les faisceau. Ce travail démontre la stabilité et l'homogénéité de l'incorporation du Sr par substitution aléatoire au Ca dans l’aragonite biogénique des otolithes modernes et archéologiques. Des cartes multi-élémentaires ont été collectées à l'aide de la SR-µXRF dans un temps raisonnable de quelques heures, et permettent de distinguer une contamination ou des défauts dans l'échantillon, mais également de corréler les cartes obtenues à des observations microscopiques des sections pour fournir une résolution temporelle. Les orientations préférentielles des cristallites composant les sections d'otolithes ont été analysées par la méthode d’acquisition rapide « flyscan », permettant de réduire le temps de mesure à quelques minutes au lieu des quelques heures nécessaires auparavant. / Otoliths, aragonitic growths in the inner ear of teleost fishes, can be used as proxies for the water conditions experienced by an individual over its lifetime. A set of archaeological Sciaenidae and Ariidae otoliths and modern counterparts was studied with the objective of improving palaeoenvironmental reconstruction methodologies using otoliths and other incremental carbonate biominerals. The incorporation of strontium, the most accessible environment-related element, was studied by X-ray absorption spectroscopy (XAS) point analyses and mapping. A fast multivariate chemical environment mapping approach was implemented to determine the mode of Sr incorporation over an area of 0.25 mm² with micrometric resolution. XAS results demonstrate for the first time with a micrometric lateral resolution over millimetric distances that strontium randomly substitutes for calcium in the aragonite lattice, independent of strontium concentration, or individual or geological age. Elemental maps on areas up to 2.6 mm² were produced with micrometric lateral resolution X-ray emission techniques (Particle-induced X-ray emission (PIXE) and synchrotron X-ray fluorescence (SR-µXRF)). These maps permit the detailed examination of an individual’s life history and sample taphonomy with a high temporal resolution while also identifying defects or abiogenic elements. Synchrotron X-ray diffraction (SR-XRD) was used to map the crystal texture on complete otolith sections and may deepen understanding of otolith internal structure and growth processes, as well as providing a valuable tool for future studies of biominerals and advanced materials. The selection and implementation of methods were carried out with a view to maximise the potential contribution to the study of stratified biocarbonates, considering and seeking to complement existing approaches in aspects including information depth, lateral resolution, sensitivity, and beam damage. This work demonstrates the stability and homogeneity of Sr incorporation by random substitution for Ca in biogenic aragonite in both modern and archaeological otoliths. Multielemental maps were collected using SR-µXRF in a reasonable time scale of a few to several hours, with the ability to distinguish contamination and defects in the sample, as well as to correlate the maps to microscopic observations of the sections to provide temporal resolution. The preferential orientations of crystallites composing the otolith sections were analysed using the rapid acquisition ‘flyscan’ method, which reduces measurement time to minutes rather than hours.

>Magister Scientiae - MSc / To study nuclear reactions and nuclear structures, target materials are bombarded with high-energy particles. The target material can either be in a form of a metal film or gas. A target material designed to study certain nuclear reactions or to produce nuclei to study their structure should yield as minimum as possible of competing reactions under ion bombardment. This requires a chemically and isotopically pure target material prepared as a self supporting thin film, or as alternative, prepared on a thin career foil. Additional requirement for lifetime measurement experiments are homogeneity and precise thickness of the target material. Some of the data obtained from the stopping power experiment where targets of 114Cd were used for lifetime measurement are presented. Moreover, a nuclear target should influence the spectroscopic resolution as little as possible. Thus, film thickness must be adjusted to the respective reaction under study while observing the optimum thickness homogeneity.

Les verres métalliques massifs à base de zirconium, développés depuis la fin des années 80, présentent des propriétés mécaniques très intéressantes. Ils peuvent être envisagés pour de multiples applications y compris à des températures élevées et il est donc intéressant d’étudier leur résistance à l’oxydation dans de telles conditions. L’objectif fondamental de cette étude consiste à mieux comprendre le rôle de divers paramètre thermodynamiques et chimiques sur le comportement à l’oxydation des verres métalliques à base de zirconium à des températures intermédiaires sous air sec, à déterminer les contraintes résiduelles au sein de la couche d’oxyde formée, en comparaison avec des alliages amorphe cristallisés après un traitement de recuit. La cinétique d’oxydation de ces verres et la structure cristalline de la couche d’oxyde ZrO2 dépend de la température et de la durée d’oxydation : pour des durées courtes d’oxydation et pour une température légèrement inférieure à Tg, la cinétique d’évolution est parabolique alors que si l’échantillon est oxydé à T > Tg, la loi cinétique peut être décomposée en deux parties. Les mêmes alliages cristallisés après un traitement de recuit, s’oxydent selon une loi parabolique quelque soit la température. Pour des durées d’oxydation longues à une température proche de Tg, les lois cinétiques deviennent plus complexes et la cristallisation du verre métallique pouvant avoir lieu au cours des essais d’oxydation. De même la structure cristalline des couches d’oxyde dépend de la température d’oxydation. Ainsi, pour T < Tg, la couche d’oxyde des alliages amorphes est uniquement constituée de la zircone tétragonale alors que pour ces mêmes alliages portés à une température T > Tg et pour les alliages cristallisés, on observe de la zircone monoclinique. Les mécanismes d’oxydation dépendent de la température d’oxydation. Pour les températures où les alliages restent vitreux, la formation de l’oxyde est due à la fois à la diffusion des ions d’oxygène vers l’intérieur mais également à la diffusion des ions de zirconium vers l’extérieur de la couche. En revanche, pour les alliages en cours de cristallisation, la diffusion des ions de zirconium est progressivement freinée jusqu’à devenue nulle lorsque la cristallisation est totale, l’oxydation étant alors uniquement contrôlée par la diffusion interne des ions d’oxygène.Les contraintes résiduelles correspondantes au sein de couches d’oxyde sont de compression, aussi bien pour les alliages amorphes que pour les alliages cristallisés, et qu’elles augmentent linéairement avec l’épaisseur de la couche. Les contraintes de croissance lors de l’oxydation et résiduelle après l’oxydation sont fortement influencées par le changement de phase de la zircone. / The Zr-based bulk metallic glasses, developed since the late 1980s, have very interesting mechanical properties, which can be considered for many applications including working under oxidizing atmosphere conditions at high temperatures. It is therefore interesting to study their oxidation resistance and to characterize the oxide scale formed on alloys’ surface. The fundamental objective of this thesis is to enhance the understanding of the role of various thermodynamic and chemistry parameters on the oxidation behaviour of the Zr-based bulk metallic glasses at high temperature under dry air, to determine the residual stresses in the oxide layer, in comparison with their crystalline alloys with the same chemical composition after an annealing treatment. The oxidation kinetics of these glasses and the crystalline structure of oxide scale ZrO2 depend on the temperature and the oxidation duration: for short periods of oxidation or at a temperature below Tg, the kinetics follows a parabolic law, whereas, if the sample is oxidized at T > Tg, the kinetics can be divided into two parts. The crystalline counterparts are oxidized by a parabolic rule whatever the temperature; for long oxidation duration at a temperature close to Tg, the kinetics becomes more complex because of the crystallisation of the glasses during the oxidation tests. Also the crystalline structure of the oxide layers depends on the oxidation temperature: the oxide layer consists only in tetragonal Zirconia at T < Tg, while monoclinic Zirconia was formed at higher temperature. The mechanism of the formation of the oxide scale is due to both the interior diffusion of Oxygen ions and the external diffusion of Zirconium ions. However the diffusion of Zirconium ions slows gradually during the crystallisation process of the glass matrix. When the crystallisation is completed, the formation of Zirconia is controlled by only the internal diffusion of oxygen ions. The corresponding residual stresses existing in the oxide layer are compressive, both for the metallic glass and counterpart, and they increase linearly with the thickness of the oxide layer. The growth and residual stresses are strongly influenced by the phase transition of Zirconia during oxidation process.

In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content. A list of revisions as requested by the examiners is produced on pages 18 and 19 of the thesis for examination. Abstract: In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content.

During loss-of-coolant accidents (LOCA) and reactivity-initiated accidents (RIA), nuclear fuel rods experience high heating rates that change the microstructure and properties of zirconium cladding materials, which are in forms of stress-relieved, like cold-worked (CW) or recrystallised (RX) microstructure. The present study aimed to determine how different fast heating rates and starting microstructures affect the kinetics of phase transformation, the transformation textures and eventually the mechanical response in the dual-phase region. The LOCA/RIA cycles from heating at 8 to 100C/s to alpha+beta or above beta transus temperature were achieved via resistive heating in an electro-thermal-mechanical tester. Synchrotron X-ray diffraction (SXRD) and electrical resistivity measurements showed that the approach curves of CW Zircaloy-4 shift to higher temperature at faster constant heating rates and change to a new approach curve when changing rates. 2-second holding at two-phase temperature produces identical phase fractions as equilibrium. These observations are consistent with the diffusional character of the phase trans- formation. Heated at 100oCs1, RX samples transform with 2D beta-growth while CW ones show simultaneous beta-nucleation and growth. The difference arises because the fast heating rate helps preserve low-angle grain boundaries (GB) in the CW microstructure up to phase transformation temperature, increasing beta nucleation sites and prevent beta-growth. This gives rise to different textures of RX and CW materials before transformation, producing different textures, which are weak in both cases. However, this difference is enhanced during grain growth and transformation on cooling. Thus, the RX material shows strong final alpha texture with 0002 maxima aligned in TD and tilted 20deg from ND towards TD while the CW reveals an essentially random one. In both RX and CW materials, variant selection does not occur during transformation on heating. During beta-grain growth, although there is variability in beta-textures measured by SXRD and EBSD beta reconstruction, it is clear that variant selection occurs, leading to strengthening of the beta texture. During transformation on cooling, variant selection occurs early in nucleation of the alpha phase from the shared 110 beta GB in the RX condition. The flow stresses of CW Zircaloy-4 in the two-phase regime at a given temperature depend on the heating rates, despite having the same phase fractions. Heated at a slower rate, the material shows an upper yield stress followed by softening behaviour while that heated faster has a smaller yield stress followed by a high work-hardening rate and then stable flowing stresses. The evolution of diffraction elastic strains and intensity suggest the upper yield stress and softening are due to stress-induced transformation of the harder alpha grains into large and isolated softer beta grains. In contrast, the sample heated faster develops an almost continuous film of beta grains along the GB of unrecrystallised alpha-grains which results in early beta-yielding and coherent deformation of the two phases, leading to constant flow stresses. The findings will improve the accuracy of inputs from phase fractions, microstructure and texture of zirconium claddings when modelling LOCA/RIA. A crystal plasticity model should consider the effects of heating rates and cold-work, which are often ignored. The link between deformation, fast heating rates and microstructure evolution might be relevant to other processes like additive layer manufacturing and even forging in the two-phase region.

Orientador: Paulo Noronha Lisboa-Filho / Banca: Fabio Furlan Ferreira / Banca: Manuel Henrique Lente / Banca: André Maurício Brinatti / Banca: Guinther Kellermann / O Programa de Pós graduação em Ciência e Tecnologia de Materiais, PosMat, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi da UNESP / Resumo: Nesse trabalho foi realizado o processo de síntese, e a caracterização estrutural e magnética de compostos HoMn1-x(Ni, Co)xO3 de estrutura perovskita. As sínteses das amostras foram realizadas por meio do método dos precursores poliméricos modificado. Após a síntese e a remoção do solvente, a resina polimérica formada foi tratada em 350ºC/4h para a remoção dos constituintes orgânicos, seguida de tratamentos térmicos em 500ºC/4h e 900ºC/20h para obtenção da fase cristalina. Para a caracterização estrutural foi utilizada a linha D10B-XPD do Laboratório Naiconal de Luz Síncrotron (LNLS), onde comprimentos de onda de raios X abaixo da borda de absorção do cobalto, do maganês e do níquel, foram utilizados. A formação das fases HoNi0.50Mn0.50O3, HoCo0.50O3 e HoNi0.25Co0.25Mn0.50O3, foram observadas pelas técnica da difração de raios X. Com o método de refinamento Reitveld para a amostra HoNi0.25Co0.25Mn0.50O3, foi determinado que o cobalto e o níquel apresentaram ocupações similares, no topo e na base da cela unitária, enquanto que o manganês ocupou preferencialmente o plano 002. A resposta magnética das amostras foi estudada através de curvas de magnetização em função da temperatura, e do campo magnético aplicado. As curvas ZFC demonstraram uma resposta paramagnética associada ao momento magnético do hólmio, além da coexistência de ferromagnetismo, antiferromagnetismos e ferrimagnetismo, devido às sub-redes formadas pelos metais de transição. As curvas FC evidenciaram o fenômeno da inversão de spin, associado à interação entre as sub-redes formadas pelos metais de transição com a sub-rede formada pela terra-rara, considerando um mecanismo de interação de troca antiferromagnética / Abstract: In this work was accomplished the syntheis process and structural and magnetic characterization of HoMn1-x(NiCo)xO3 compounds of pervskites structure. The sample synthesis were performed through modified polymeric precursos method. After synthesis and solvent removal, the polymer resin formed was treated at 350ºC/4h for organic constituents removal, followed by heating treatment at 500ºC/4h and 900ºC/20h to obtain the crystalline phase. For structural characterization, it was used D10B-XPD beam line of Laboratório Nacional de Luz Síncrotron (LNLS), where X-rays wavelengths below cobalt, manganeses and nickel absorption edge, were used. The formation of HoNi0.50Mn0.50O3, HoCo0.50O3 e HoNi0.25Co0.25Mn0.50O3 phases were observed by X-ray diffraction technique. By Rietveld refinement method for sample HoNi0.25Co0.25Mn0.50O3, it was determined that cobalt and nickel had similar occupations at the top and bottom of unit cell, while the manganeses preferentially occupied plan 002. The magnetic response of samples was studied through magnetization curves according to the temperature function and the applied magnetic field. The ZFC curves showed a paramagnetic response associated to holmium magnetic moment, and ferromagnetism, antiferromagnetism and ferrimagnetism coexistence, due to sublattices formed by transition metals. The FC curves evidenced the spin reversal phenomenon, associated to the interaction between the sublattice formed bu transition metals with sublattices formed by rare-earth, considering a mechanism of antiferromagnetic exchange interaction / Doutor