Near stoichiometric compositions of Ba3+3xB1+yNb20g (B=Co or Zn) perovskites were studied by microstructure analysis and optical techniques. Materials considered in the present research belong to the family of perovskites exhibiting disorder-1:2 order phase transitions that are important for microwave applications. It was found that deviation from stoichiometry involving cation deficiencies on Ba-or B-positions facilitates formation of an ordered structure for small values of cation deficiencies. Excessive deviation from the nominal values as well as introduction of extra cations destabilizes the perovskite structure leading to the precipitation of secondary phases. Formation of a Ba-deficient Bs6BNb9030 (B = Co or Zn) phase influences the grain growth rate through reduction in the surface energy of grains. In combination with large strain in precursor materials caused by applied pressure during fabrication and high sintering temperature this results in increased porosity and lower density. Appearance of Raman active modes in the considered Ba3+3xBl+yNbz0g materials was attributed to the formation of a 1:2 cation ordered structure. It was shown that microwave losses are influenced by the degree of 1:2 cation ordering that depends on the formation of secondary phases as well as a densification process. The appearance of an "extra" peak in Raman spectra was attributed to the formation of 1:1 cation order described based on the "space-charge" model. Changes in the position of the mode, attributed to "breathing-type" vibrations of oxygen anions from materials having "partially" ordered 1:1 structure to those having 1:2 ordered structure, indicate formation of more rigid oxygen octahedra associated with lower microwave losses. Structural distortion caused by 1:2 cation ordering results in changes in the mutual orientation of transition metal-ligand molecular orbitals and the appearance of two emission bands signifying formation of two different Nb06 octahedra. The first octahedron, present in the 1:2 ordered structure, gives origin to the lower energy photoluminescence band, while the second one, forming a disordered cubic structure, produces an emission peak at higher energies with the variation in the position of the maximum depending on the type of cation on the B-site. Changes in the maximum position of the high-energy peak were attributed to different structure distortions caused by off-center motion of Nb^5+ and stabilization by neighboring B06 octahedra. The stabilization power of B06 octahedra depends on the covalency of B-0 bonds and is larger for cobalt containing perovskites. / Thesis / Doctor of Philosophy (PhD)

The following report conducted by the theoretical research and experimental study in the University of Halmstad. The focus of the project is experimental investigation on weld characteristics for shield metal arc welding with SS304 & SS409. Welding is a joining process of similar metals but nowadays it is also joined dissimilar metals by the application of heat. The different types of welding process are available in industry. Welding can be done with or without the application of pressure and filler materials in shielded metal arc welding (SMAW), an arc between a covered electrode and a weld pool is used to accomplish a weld. As the welder steadily feeds the covered electrode into the weld pool, the decomposition of the covering evolves into gases that shield the pool. Austenitic stainless steel and Martensitic chrome alloys is widely used materials in the current industrial area including higher and lower temperature applications such as storage tanks, pressure cups, furnace equipment’s etc. This paper concentrated to the investigate the dissimilar material joining by using shield metal arc welding and study the welding characteristics and do the mechanical tests. The aim of this study performance of steel and maximum hardness of welded material, microstructure of steel on next phase of project. The results will be used to character of dissimilar material performance.

Resumo: Este projeto de pesquisa teve como objetivo estudar toda evolução que governa o crescimento, distribuição e classificação dos pites em aços inoxidáveis austeníticos ABNT 304 e 310S obtidos no estado como recebido e tratados, submetidos a diferentes tempos de exposição em névoa salina. A originalidade deste trabalho baseou-se no desenvolvimento de uma técnica para caracterização morfológica e da corrosão localizada associando com os aspectos de descrição de formas, tamanho, parâmetros específicos e populacionais. O aço inoxidável 304 apresentou morfologia irregulares > região de transição A> cônicos >hemisféricos > região de transição B, sendo que irregulares e região de transição A em maiores quantidades no sistema. Na liga tratada a cada tempo de exposição, a quantidade de pites é da mesma ordem, ou seja, região de transição A, irregulares, cônicos, hemisféricos, região de transição B, sendo que os pites na região de transição A e irregulares estão presentes em maior quantidades no sistema. O aço inoxidável 310S, como recebido, exibiu a seguinte morfologia: pites hemisféricos > região de transição A > região de transição B > irregulares > cônicos, sendo que os pites estão presentes em maiores quantidades em: hemisféricos e região de transição A. A quantidade de pites na liga tratada a cada tempo de exposição é da mesma ordem: região de transição B > hemisféricos > região de transição A > cônicos >irregulares. O aço inoxidável 304 apresentou maior resistência à corrosão por pite do que o aço inoxidável 310S, e também diferenças na distribuição, classificação e mediana dos tamanhos dos pites, conforme os resultados obtidos na avaliação estatística da superfície e perfis dos mesmos. / Abstract: This research project has had as objective to study all evolution that governs the growth, distribution and classification of pits in ABNT 304 and 310S austenitic stainless steels obtained in the state as receveid and treated, submitted to different times of exposition in saline mist. The originality of this work has been based on the development of a technique for morphologic characterization and of located corrosion associating with the shape description, size specific and population parameters. The 304 stainless steel has presented the following morphology: irregular > transition region A > conic > hemispherical > transition region B, in which irregular and transition region A > are in larger amounts in the system. In the treated alloy at each exposition time, the pits amount is at the same order, in other words, transition region A, irregular, conic, hemispherical, transition region B, in which the pits in the transtion region A and irregular are present in larger amounts in the system. The 310S stainless steel, as receveid, has exhibited the following morphology: hemispherical pits > transition region A > transtion region B > irregular > conic, in which the pits are present in large amounts in: hemispherical pits and transition region A. The pits amount in the treated alloy at each time of exposition has the same order: transition region B > hemispherical > transition region A > conic> irregular. The 304 stainless steel has presented pit corrosion resistance larger than the 310S stainless steel, and also differences in the distribution, classification and pits sizes medium, according to the results obtained in the statistical evaluation of their surface and profiles. / Orientador: Eduardo Norberto Codaro / Coorientador: Luis Rogério de Oliveira Hein / Banca: Roberto Zenhei Nakazato / Banca: Hamilton de Felipe / Banca: Gilberto Luis Jardim Pinto da Silva / Banca: Koshun Iha / Doutor

La mise en forme par ice-templating est un procédé d’élaboration permettant via la congélation d’une suspension, d’obtenir des matériaux poreux à porosité contrôlée. L’analyse des mécanismes régissant la congélation de suspensions concentrées en particules et leurs conséquences sur les microstructures poreuses, est très peu développée dans la littérature du point de vue de l’influence de la composition de la suspension, en termes de nature et quantité d’additifs. Les objectifs de ces travaux de thèse sont d’observer et caractériser in situ et ex situ la formation des structures par ice-templating. Il s’agit également d’établir les liens entre la composition des suspensions, le procédé et la morphologie poreuse obtenue pour les structures congelées et frittées qui en découlent. L’évolution de l’avancée du front de congélation d’un panel de suspensions d’alumine aux propriétés caractérisées a été observée par radiographie X et la microstructure des échantillons congelés et frittés a été caractérisée par tomographie X ou par MEB. Nous avons ainsi pu caractériser les différentes étapes de la congélation par ice templating, les microstructures congelées associées, l’influence de la composition de la suspension ainsi que les mécanismes générateurs de défauts. La force ionique générée par la quantité de dispersant, la présence ou non de liant et la vitesse de refroidissement des suspensions sont trois paramètres ayant des conséquences critiques sur la microstructure et sur l’orientation ou la désorientation des cristaux. Nos résultats apportent un éclairage inédit sur les mécanismes de congélation des sols étudiés en géophysique et notamment la formation de glace lenticulaire. / Ice-templating is a processing route used to obtain porous material with a controlled porosity by freezing a suspension. Researches focused on this subject so far revealed a lack of information about mechanisms controlling the freezing of suspensions with a high solid loading and their consequences over porous microstructures, depending on the composition of the suspension in terms of additives nature and quantity. The objectives of this work are to observe and characterize in and ex situ the formation of structures by ice-templating and to establish the relationships between the composition of suspensions, process and porous morphology of frozen and sintered bodies. The advancement of the freezing front of a panel of alumina suspensions, with characterized properties was investigated by X-ray radiography and the microstructures of frozen or sintered samples were characterized by X-ray tomography and SEM. We have defined the different stages of the freezing by ice-templating, the associated frozen and sintered microstructures, the influence of the composition of the suspension and the mechanisms responsible for defects creation. The ionic strength generated by the dispersant quantity, the addition or not of a binder and the cooling rate of suspension are three parameters with critical consequences on microstructures, orientation and disorientation of ice crystals. Our results shed a new light on the freezing mechanisms of soils in geophysics and more particularly the ice lenses formation.

Made available in DSpace on 2014-06-11T19:34:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Bitstream added on 2014-06-13T20:27:46Z : No. of bitstreams: 1 ribeiro_rb_dr_guara.pdf: 6899626 bytes, checksum: 243c390b34b8f55eaccd7334a877efe4 (MD5) / Este projeto de pesquisa teve como objetivo estudar toda evolução que governa o crescimento, distribuição e classificação dos pites em aços inoxidáveis austeníticos ABNT 304 e 310S obtidos no estado como recebido e tratados, submetidos a diferentes tempos de exposição em névoa salina. A originalidade deste trabalho baseou-se no desenvolvimento de uma técnica para caracterização morfológica e da corrosão localizada associando com os aspectos de descrição de formas, tamanho, parâmetros específicos e populacionais. O aço inoxidável 304 apresentou morfologia irregulares > região de transição A> cônicos >hemisféricos > região de transição B, sendo que irregulares e região de transição A em maiores quantidades no sistema. Na liga tratada a cada tempo de exposição, a quantidade de pites é da mesma ordem, ou seja, região de transição A, irregulares, cônicos, hemisféricos, região de transição B, sendo que os pites na região de transição A e irregulares estão presentes em maior quantidades no sistema. O aço inoxidável 310S, como recebido, exibiu a seguinte morfologia: pites hemisféricos > região de transição A > região de transição B > irregulares > cônicos, sendo que os pites estão presentes em maiores quantidades em: hemisféricos e região de transição A. A quantidade de pites na liga tratada a cada tempo de exposição é da mesma ordem: região de transição B > hemisféricos > região de transição A > cônicos >irregulares. O aço inoxidável 304 apresentou maior resistência à corrosão por pite do que o aço inoxidável 310S, e também diferenças na distribuição, classificação e mediana dos tamanhos dos pites, conforme os resultados obtidos na avaliação estatística da superfície e perfis dos mesmos. / This research project has had as objective to study all evolution that governs the growth, distribution and classification of pits in ABNT 304 and 310S austenitic stainless steels obtained in the state as receveid and treated, submitted to different times of exposition in saline mist. The originality of this work has been based on the development of a technique for morphologic characterization and of located corrosion associating with the shape description, size specific and population parameters. The 304 stainless steel has presented the following morphology: irregular > transition region A > conic > hemispherical > transition region B, in which irregular and transition region A > are in larger amounts in the system. In the treated alloy at each exposition time, the pits amount is at the same order, in other words, transition region A, irregular, conic, hemispherical, transition region B, in which the pits in the transtion region A and irregular are present in larger amounts in the system. The 310S stainless steel, as receveid, has exhibited the following morphology: hemispherical pits > transition region A > transtion region B > irregular > conic, in which the pits are present in large amounts in: hemispherical pits and transition region A. The pits amount in the treated alloy at each time of exposition has the same order: transition region B > hemispherical > transition region A > conic> irregular. The 304 stainless steel has presented pit corrosion resistance larger than the 310S stainless steel, and also differences in the distribution, classification and pits sizes medium, according to the results obtained in the statistical evaluation of their surface and profiles.

Les procédés de fabrication additive permettent, à partir d’un fichier de CAO, la fabrication de pièces complexes sans outillage, dans des délais de développement très courts et avec une grande flexibilité. Parmi les procédés de fabrication additive employés avec les polymères, le frittage laser de poudre est le plus utilisé. Ces travaux de thèse sont consacrés à l’étude et la compréhension des mécanismes fondamentaux impliqués lors du procédé de frittage laser de poudres de polyamide 12. Au cours du procédé de frittage laser de nombreux paramètres interviennent. Ainsi l’énergie fournie à la poudre par l’intermédiaire du rayon laser dépend de la puissance de celui-ci, de la vitesse de balayage et de l’espacement entre deux balayages successifs. De plus, le matériau subit un cycle thermique sévère : avant d’être frittée, la poudre est préchauffée. Puis, dans le bac de fabrication, la poudre non frittée ainsi que les pièces séjournent pendant toute la durée de la fabrication à des températures élevées. Cette histoire thermique entraîne un vieillissement et donc une modification des propriétés de la poudre ce qui complique sa réutilisation. L’influence de ces différents paramètres sur la microstructure et les propriétés mécaniques des pièces finales a été mise en évidence. De plus l’utilisation de différentes poudres de polyamide 12 a permis l’identification des paramètres-clés de la matière.Le frittage laser des polymères semi-cristallins est régi par plusieurs mécanismes fondamentaux : la fusion des particules de poudre, l’interdiffusion des chaînes macromoléculaires aux interfaces, la coalescence des particules fondues, la densification et enfin la cristallisation. L’étude et la modélisation de la cristallisation ont été effectuées pour l’un des polyamides 12 employés au cours de cette thèse. De ce traitement théorique ont pu être déduits les temps de maintien du polymère à l’état fondu au cours du procédé. Dans une seconde phase, des analyses rhéologiques menées dans le cadre de la viscoélasticité linéaires des polymères à l’état fondu ont permis de déduire les temps d’interdiffusion des chaînes macromoléculaires. Par ailleurs, le processus de coalescence des particules de poudres à l’état fondu a été suivi expérimentalement et modélisé pour différentes températures. Ces temps ont été confrontés à la durée de maintien du polymère à l’état fondu, confirmant ainsi la bonne consolidation obtenue lors du frittage du polyamide 12. En conclusion, ce travail contribue à la compréhension des différents mécanismes physico-chimiques intervenant au cours du frittage laser : il permet d’expliciter de façon assez approfondie les relations entre les propriétés des poudres, les paramètres du procédé et les propriétés finales des pièces. De nombreuses préconisations relatives à l’optimisation des propriétés des poudres pourront être déduites de ce travail et aideront au développement de nouveaux matériaux adaptés à ce procédé. / Additive processing technologies are aimed at manufacturing parts directly from a computer-aided design (CAD) file, without the need for tooling. Therefore flexibility of production increases and manufacturing of small to mid-size series of very complex or even customized parts becomes possible within reduced development time and expenses. Because of the good mechanical properties obtained in the parts, the most commonly used among additive technologies for polymers is laser sintering (LS). The objective of this work is to contribute to a better understanding of the different physical mechanisms involved during laser sintering of polyamide 12 powders. Many operating variables impact the laser sintering process. Especially, the energy supplied to the powder with the laser beam depends on its power, its displacement velocity and the scan spacing. Moreover, the polymer material undergoes a quite severe thermal treatment : before its sintering, the powder is preheated, then in the build tank the sintered parts and the un-sintered surrounding powder remain until the end of the job at elevated temperatures. This thermal history induces ageing, which modifies some powder features and hinders its future reuse. The influence of the parameters mentioned above on the part microstructure and mechanical properties was investigated. Moreover the use of different polyamide 12 powders enabled to identify the key material characteristics towards the physical processes involved in LS and towards the final properties of parts. The laser sintering of semi-crystalline polymers is governed by several fundamental mechanisms: melting of particles, interdiffusion of macromolecular chains at interfaces, coalescence of molten particles, then densification and finally crystallisation. The study and modelling of crystallisation were carried out with one of the PA12 powders used in the first part of this work. From this modelling, the time during which the polymer remains in the molten state during the process was estimated. Next, a rheological analysis made within the framework of linear viscoelasticity of polymer melts allowed to compute the interdiffusion time of the macromolecular chains. Moreover, the coalescence process of molten particles was observed at different temperatures and modeled. The characteristic times thus estimated for these physical processes were opposed to the time during which the polymer remains in the molten state and confirmed the good consolidation obtained by laser sintering of polyamide 12. In conclusion this work contributes to understand the different physico-chemical mechanisms involved during polymer laser sintering by specifying the relations between powder parameters, process variables and final properties of parts. Many recommendations for the optimisation of powder properties can be derived from this work for the purpose of developing new polymeric materials adapted to this process.

No description available.

<p> Laser powder bed fusion (LPBF) is a rapidly emerging manufacturing technology capable of producing complex part geometries through the repeated, precise laser melting of metallic powder layers. At present, the process is primarily employed in high-value-added applications which exist in the aerospace, biomedical, and dental industries. As industrial implementation of LPBF has matured, research has focused on established materials for which there are already large bodies of literature and regulatory approval, such as Inconel 718, Inconel 625, Ti-6Al-4V, and 316 stainless steel. However, the rapid solidification process inherent to LPBF leads to vastly different microstructures with improved strength compared to these traditional materials in cast or wrought forms. In general, the high solidification velocity and thermal gradients result in cellular and dendritic solidification structures with finer grain and precipitate sizes than conventionally processed alloys. These microstructure changes warrant the exploration of new alloy systems and reevaluation of historically cast compositions with optimized microstructures, especially considering the tunability of a digitally controlled fabrication process. This work examines laser powder bed fusion of Mar-M 509, a carbide-strengthened cobalt alloy that is typically investment cast directly into complex-shaped components such as nozzle guide vanes (NGVs). NGVs are stationary components in gas turbine engines for propulsion and energy production which require strength under moderate mechanical loading at high temperatures. Investment cast microstructures have porosity defects in slower-cooled regions due to lack of liquid feed to interdendritic regions. As-printed, the cellular and dendritic Mar-M 509 LPBF microstructures lead to the formation of continuous, fiber-like, eutectic carbide structures in the intercellular and interdendritic regions, which limit macroscopic ductility. Thermo-Calc is used for calculation of phase diagrams (CALPHAD) to estimate the equilibrium transformation temperatures of MC, M23C6, and M7C3-type carbides, which informs design of isothermal heat treatments to engineer microstructures with enhanced ductility over the as-printed or cast versions of Mar-M 509 while maintaining tensile strength. Scanning and transmission electron microscopy reveals the composition and distribution of carbide phases as a function of heat treatment temperature. Lastly, heat treatment recommendations for nozzle guide vanes are made.  </p>

In the constant pursuit of better-performing cemented carbides, recent studies suggest that a combination of better hardness and toughness can be obtained by changing its WC grain size distribution. As the area is still rather unexplored, this  thesis  aims  to  broaden  the  knowledge  and  answer  whether mechanical properties can be changed by changing the WC grain size distribution, in the context of mining drill bit inserts. This was performed by producing four dual grained material as well as four single grained reference materials, for which the carbon content and presence of alloying element were varied. The materials were characterised and compared with regard to magnetic saturation, magnetic coercivity,  hardness,  fracture  toughness,  wear resistance,  energy  needed  to cause  fracture,  as  well  as  detailed microstructural  analysis  obtained  through imaging and electron backscatter diffraction analysis The results showed that mining drill bit inserts with alternative WC grain size distribution  could  successfully  be  produced,  but  that  a  traditional  bimodal distribution  with  two  peaks  could  not  be  obtained.  The  distribution instead became significantly wider as well as skewed towards larger grains for the dual grained materials compared with their references. It was further also confirmed that the alternative dual grain size distribution could be used to improve the mechanical properties of fracture toughness and wear resistance, but only for material that was not alloyed, and the magnitude of the improvement may be considered  to  be  small.  For  the  alloyed  materials,  it  turned  out  to  be more difficult to influence the mechanical properties, as the improving effect of analloying element outweighed the effect of grain size distribution. / I en ständig jakt på hårdmetall med bättre prestanda, så föreslår ny forskning att en bättre kombination av hårdhet och seghet kan erhållas genom att ändra den mikrostrukturiella  WC-kornstorleksfördelning.  Då  det  ännu  är  ett relativt outforskat område, så har denna studie för avsikt att öka kunskapen genom att besvara frågan om de mekaniska egenskaperna kan förändras genom att ändra på materialets kornstorleksfördelning inom applikationsområdet hårdmetall för bergborrning. Detta gjordes genom att producera fyra material med WC pulver av två olika storlekar, samt fyra referensmaterial med en kornstorlek. För dessa varierades parametrarna kolhalt och närvaro av legeringselement. Materialen karakteriserades och jämfördes med avseende på magnetisk mättnad, magnetisk koercivitet, hårdhet,  brottseghet,  slitstyrka,  energi  som  behövs  för  att  orsaka brott, samt  en  detaljerad  mikrostrukturanalys  som  erhölls  genom  avbildning samt elektrondiffraktionsanalys. Resultaten visade att material med alternativ WC-kornstorleksfördelning kunde produceras, men att en fullt bimodal fördelning inte gick att skapa i denna studie. Fördelningen blev istället betydligt bredare samt förskjuten mot större korn för materialen som innhöll WC av två olika storlekar. Det bekräftades också att den alternativa     kornstorleksfördelningen     kunde     förbättra     de     mekaniska egenskaperna för brottseghet och slitstyrka, men endast för de material som inte var legerade och storleken på förbättringen får dessutom anses vara relativt liten. För de legerade materialen visade det sig vara svårare att påverka de mekaniska egenskaperna,  eftersom  den  förbättring  av egenskaper  som  legeringselement tillförde överträffade effekten av kornstorleksfördelning.

The dissertation deals with the image processing in digital holographic microscopy and X-ray computed tomography. The focus of the work lies in the proposal of data processing techniques to meet the needs of the biological experiments. Transmitted light holographic microscopy is particularly used for quantitative phase imaging of transparent microscopic objects such as living cells. The phase images are affected by the phase aberrations that make the analysis particularly difficult. Here, we present a novel algorithm for dynamical processing of living cells phase images in a time-lapse sequence. The algorithm compensates for the deformation of a phase image using weighted least squares surface fitting. Moreover, it identifies and segments the individual cells in the phase image. This property of the algorithm is important for real-time cell quantitative phase imaging and instantaneous control of the course of the experiment. The efficiency of the propounded algorithm is demonstrated on images of rat fibrosarcoma cells using an off-axis holographic microscope. High resolution X-ray computed tomography is increasingly used technique for the study of the small rodent bones micro-structure. In this part of the work, the trabecular and cortical bone morphology is assessed in the distal half of rat femur. We developed new method for mapping the cortical position and dimensions from a central longitudinal axis with one degree angular resolution. This method was used to examine differences between experimental groups. The bone position in tomographic slices is aligned before the mapping using the propound standardization procedure. The activity of remodelling process of the long bone is studied on the system of cortical canals.