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Cipitria, Amaia. "Sintering of plasma-sprayed thermal barrier coatings." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612066.
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Peng, Hong. "Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties." Doctoral thesis, Stockholms universitet, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129.
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Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.
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Peng, Hong. "Spark plasma sintering of Si₃N₄-based ceramics : sintering mechanism - tailoring microstructure - evaluating properties /." Stockholm : Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129.
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Luke, Matthew Thomas. "Microstructural evolution of nickel during spark plasma sintering." [Boise, Idaho] : Boise State University, 2010. http://scholarworks.boisestate.edu/td/81/.
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Park, Jin-Goo 1961. "Microwave induced plasma sintering of nuclear waste calcines." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276916.
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The microwave induced plasma was used to sinter synthetic Idaho Chemical Processing Plant (ICPP) alumina and zirconia based high level nuclear waste calcines in a nitrogen atmosphere. The sintering behavior of these nuclear waste calcines was observed with identification of the phases formed. A sintered density of higher than 3.20 g/cm3 was obtained within 10 minutes of plasma sintering of pure calcines. The addition of frit in pure calcines to form glass-ceramics resulted in a decrease of density to less than 2.0 g/cm3. This was attributed to the reaction between frit and volatile substances in both zirconia based and alumina based calcines. The removal of volatile substances before sintering increased the sintered density of calcines. The lower sintered density was obtained for the more volatile samples. The phases formed in the plasma sintering of calcines were identified as a function of temperature and amount of frit.
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Salem, Raphael Euclides Prestes. "Desenvolvimento de ZrO2/Al2O3 e ZrO2/Al2O3-NbC usando sinterização convencional e não convencional." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/74/74133/tde-26022018-094441/.
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Os compósitos cerâmicos de alto desempenho têm sido objeto de frequentes estudos nas últimas décadas, visando à melhora das propriedades mecânicas e ao aumento da sua gama de aplicações em produtos tecnológicos. Este trabalho consistiu em estudar a preparação, a sinterização convencional e não convencional e as propriedades mecânicas e tribológicas resultantes de dois sistemas compósitos: t-ZrO2/Al2O3 e t-ZrO2/Al2O3-NbC. No sistema t-ZrO2/Al2O3 foram estudadas as composições de 0, 5 e 15% em volume de Al2O3 usando pós comerciais. No sistema t-ZrO2/Al2O3-NbC, foi usado um pó nanocristalino de Al2O3-NbC, obtido por moagem reativa de alta energia e adicionado na proporção de 5% em volume à matriz de t-ZrO2. Os pós foram prensados uniaxial e isostaticamente e sinterizados em forno convencional e pelas técnicas de flash sintering (FS) (t-ZrO2/Al2O3) e spark plasma sintering (SPS) (t-ZrO2/Al2O3-NbC). Os compósitos t-ZrO2/Al2O3 sinterizados convencionalmente e t-ZrO2/Al2O3-NbC sinterizados convencionalmente e por SPS foram caracterizados por medidas de densidade aparente, dilatometria, microscopia eletrônica de varredura (MEV), e medidas de propriedades mecânicas: dureza, módulo de Young e tenacidade à fratura. Os compósitos t-ZrO2/Al2O3 sinterizados por FS foram caracterizados por medidas de densidade aparente, dilatometria in situ e MEV. Os nanocompósitos de t-ZrO2/Al2O3-NbC foram também caracterizados quanto à resistência ao desgaste pelo método esfera-no-disco, utilizando esferas de Al2O3 e WC-6%Co como contramateriais. Os resultados mostraram que a moagem reativa de alta energia foi completa e efetiva na obtenção de pós nanométricos de Al2O3-NbC, com tamanhos de cristalito de 9,1 nm para Al2O3 e 9,7 nm para o NbC. A desaglomeração posterior à moagem de alta energia foi eficaz na redução do tamanho de aglomerados. Os compósitos t-ZrO2/Al2O3 e t-ZrO2/Al2O3-NbC sinterizados convencionalmente e ZrO2/Al2O3-NbC sinterizados por SPS mostraram alta densificação (>97% DT e boas propriedades mecânicas. Os nanocompósitos de t-ZrO2/Al2O3 sinterizados por FS apresentaram uma densificação ultrarrápida (< 1 min) com retração linear superior às amostras sinterizadas em forno convencional, ocorrente a temperaturas inferiores a 1000°C, com densidades relativas superiores a 90% DT em algumas composições. Os nanocompósitos de t-ZrO2/Al2O3-NbC apresentaram propriedades competitivas entre os compósitos sinterizados convencionalmente e por SPS, com dureza e tenacidade à fratura superiores às da t-ZrO2 monolítica. A resistência ao desgaste desses nanocompósitos sinterizados convencionalmente, no entanto, foi notadamente superior à dos sinterizados por SPS. A oxidação do NbC nos compósitos sinterizados convencionalmente influiu negativamente nas propriedades, levando à sugestão de uma \"janela\" de temperaturas em que a sinterização do nanocompósito de t-ZrO2/Al2O3-NbC seja interessante sem a degradação das propriedades mecânicas. Os resultados permitiram concluir que os materiais estudados apresentam potencial para aplicações industriais que requerem cerâmicas de alto desempenho mecânico e de resistência ao desgaste.<br>High performance ceramic composites have been the subject of frequent studies in recent decades, aiming at improving mechanical properties and increasing their range of applications in technological products. This work consisted in studying the preparation, the conventional and non-conventional sintering and the mechanical properties resulting from two t-ZrO2 matrix composites: the t-ZrO2/Al2O3 system and the t-ZrO2/Al2O3-NbC system. In the t-ZrO2/Al2O3 system, the compositions of 0, 5 and 15% by volume of Al2O3 using commercial powders were studied, while in the t-ZrO2/Al2O3-NbC system, an Al2O3-NbC nanocrystalline powder obtained by high energy reactive milling, deagglomerated, leached in HCl and added in the proportion of 5% by volume to the t-ZrO2 matrix. The obtained powders were uniaxially and isostatically pressed and sintered in conventional furnace and using flash sintering (t-ZrO2/Al2O3) and spark plasma sintering (SPS) (t-ZrO2/Al2O3-NbC). Conventionally sintered t-ZrO2/Al2O3 and conventionally sintered t-ZrO2/Al2O3-NbC composites were characterized by measurements of apparent density, dilatometry, SEM, and mechanical properties: hardness, Young\'s modulus and fracture toughness. The t-ZrO2/Al2O3 composites sintered by FS were characterized by measurements of apparent density, in situ dilatometry and SEM. t-ZrO2/Al2O3-NbC nanocomposites were also characterized for wear strength by the ball-in-disc method, using Al2O3 and WC-6%Co beads as countermaterials. The results showed that the high energy reactive milling was complete and effective in obtaining nanometric powders of Al2O3-NbC, with crystallite sizes equal to 9.1 and 9.7 nm, for Al2O3 and NbC, respectively. The deagglomeration after high energy reactive milling was effective in reducing the size of agglomerates. Conventionally sintered t-ZrO2/Al2O3 and t-ZrO2/Al2O3-NbC composites and SPS-sintered t-ZrO2/Al2O3-NbC showed high densification (> 97% TD), good dispersion of the inclusions in the matrix and good mechanical properties. The t-ZrO2/Al2O3 nanocomposites sintered by FS presented an ultrafast densification (<1 min) with linear shrinkage superior to the sintered samples in conventional furnace, occurring at temperatures lower than 1000°C, with relative densities higher than 90% TD in some compositions. The t-ZrO2/Al2O3-NbC nanocomposites presented competitive properties between conventionally sintered and SPS-sintered composites with higher hardness and fracture toughness than monolithic t-ZrO2. The wear resistance of these conventionally sintered nanocomposites, however, was markedly higher than those of SPS-sintered ones. The oxidation of NbC in the composites sintered conventionally influenced negatively the properties, leading to the suggestion of a \"window\" of temperatures in which the sintering of the t-ZrO2/Al2O3-NbC nanocomposite is interesting without the degradation of the mechanical properties. The results allowed concluding that the studied materials present potential for industrial applications that require high mechanical performance and wear resistance ceramics.
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Eriksson, Mirva. "Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2 composites." Licentiate thesis, Stockholms universitet, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-26122.
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Titanium has been used as a model substance to study how it behaves in a SPS apparatus when heating rate and/or pressure were varied during the sintering and deformation process. The sintering and deformation of Ti in SPS were compared with that occurring in the conventional hot pressing (HP) in order to reveal if there are any positive effects added by the use of SPS. The ductility of Ti was explored in order to understand the sintering and deformation of (Ti) x (TiB2)1-x composites with x = 0.05, 0.1, and 0.2, respectively, expressed in mol ratio. The temperature difference (DT) between the monitored and the temperature that the samples are exposed to was evaluated. It was noticed that Ti can be sintered at relatively low temperatures. High heating rate implied that the onset temperatures of the sintering and deformation processes decreased. Increasing pressure did not affect the onset temperature but revealed that the deformation of Ti is different if the experiments are conducted within the stability region of the a -phase region of Ti or if the deformation takes place in a temperature region that covers both a-and b-phase areas, i. e. the use of high pressures implied a one step deformation process while the use of low implied that the main part of the deformation took place in the b-phase region. (Ti) x (TiB2)1-x composites were prepared to full densities at 1500 °C using a holding time of 3 min and pressure of 50 MPa. During the SPS sintering the composite with x= 0.2 revealed the presence of TiB due to the reaction Ti + TiB 2 -> 2TiB while the composites with low x values did not show any formation of TiB. The formation of TiB impaired the mechanical properties. The deformation of composites was very difficult. Their deformability increased with increasing x and temperature as well as pressure. During the deformations of pre-sintered samples TiB was formed in all of the composites.
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Barančíková, Miriama. "Vysoce porézní keramické materiály připravené metodou Spark Plasma Sintering." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442603.
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Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
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Prasad, R. Anil. "Spark plasma sintering of cerium dioxide and its composites." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62930.
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Cerium dioxide (CeO₂) is an important electroceramic material with a wide array of applications
in the fuel cell industry. Recently, cerium dioxide was also found to have similar thermophysical
properties as common nuclear fuel materials such as uranium dioxide, thorium
dioxide and plutonium dioxide. Thus, it can be used as a surrogate material for simulating
the processing of nuclear fuel materials, without the risks associated with radioactivity. However,
similar to other ceramic materials, processing of cerium dioxide is challenging, due to
its high melting point and low ductility. Consequently, powder metallurgy techniques are
widely employed to overcome the limitations of ceramic processing. In this thesis, studies on
the processing of cerium dioxide and its composites using a novel sintering technique called
Spark Plasma Sintering (SPS) were carried out. The effect of SPS process parameters on the
physical and chemical changes of cerium dioxide were investigated.
The results indicate that an optimal combination of sintering temperature, pressure and
time are required in order to fabricate high integrity CeO₂ coupons. Challenges associated
with chemical expansion and stoichiometric instabilities were observed and related to SPS
processing conditions, as well as the electric current inherent to the SPS fabrication process.<br>Applied Science, Faculty of<br>Engineering, School of (Okanagan)<br>Graduate
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Knittel, Susan Means 1961. "Sintering of aluminum-nitride in a microwave induced plasma." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276877.
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The sintering of aluminum nitride in a microwave induced plasma was investigated. The plasma furnace consisted of a quartz tube inserted into a waveguide connected to a 2450 MHz microwave generator. After evacuating the tube to about 1.33 mbar, nitrogen gas was introduced, generating a steady plasma. Processing parameters such as gas pressure, power level, and time were optimized to yield maximum densification of aluminum nitride. Sintering of pure and doped AlN compacts was performed in the nitrogen plasma at temperatures up to 2000 S C. Undoped specimens reached densities of only 81% theoretical, while densities in excess of 95% theoretical were achieved for yttria doped specimens in less than 15 minutes. Microstructural investigations revealed a smaller grain size in the plasma sintered specimens (about 2μ) than are present in conventionally sintered AlN (about 8μ).
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Klevetová, Tereza. "Vliv plazmové aktivace keramických částic na technologii přípravy a vlastnosti pokročilých keramických materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400853.
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This thesis is focused on the study of the influence of plasma activation of powder ceramic materials on sintered microstructure. In this experiment Diffuse Coplanar Surface Barrier Discharge (DSCBD) device was used for plasma treatment and two materials were chosen to be investigated – Al2O3 (TAI) and ZrO2 doped with 3 mol % Y2O3 (TZ). Two methods of powders dispergation in suspension were used – ultrasound and ball milling. The effect of using of DCSBD on alumina and zirconia powders was investigated by mercury intrusion porosimetry, dilatometry and by evaluation of final relative densities and grain sizes. Generally, was investigated that plasma surface activation of ceramic particles has measurable influence on the final microstructure. In comparison with the non-plasma treated alumina powders, plasma activated powders disperged with ultrasound and ball milling achieved lower values of grain size at comparable relative densities. In case of zirconia powders was observed that plasma treated powders achieve higher relative densities, if ultrasound was used. On the other hand, plasma treated zirconia powders disperged with ball milling achieve lower relative densities compared with non-plasma treated zirconia powders. Final sintering trajectory of plasma treated TZ powders disperged with ultrasound is comparable to the sintering trajectory of non-plasma treated zirconia powders disperged with ball milling and vice versa. Plasma surface treatment is the way of more ecological friendly preparation of suspension and its stabilization than the conventional stabilization methods using chemical additives.
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Manière, Charles. "Spark plasma sintering : couplage entre les approches : modélisation, instrumentation et matériaux." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30219/document.
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Le "Spark Plasma Sintering" est un procédé innovant qui permet de densifier, assembler, forger... tous types de matériaux avec des cinétiques très rapides. Cependant, il nécessite des améliorations pour le contrôle des températures, l'homogénéité microstructurale pour des pièces de formes complexes... et de productivité industrielle. Pour résoudre ces problèmes, un modèle électro-thermo-mécanique-microstructural est identifié : i) pour la partie Thermo-Electrique une instrumentation fine a permis par une approche inverse d'évaluer les résistances de contacts, ii) par essais in-situ de fluage et de compression pour la partie mécanique-microstructurale. Il a permis de trouver des solutions pertinentes pour élaborer des pièces - de microstructure homogène - simultanément en grand nombre (modification du passage du courant électrique) - de formes complexes (intervention de pièces sacrificielles)<br>The "Spark Plasma Sintering" process allows very high consolidation kinetics (densification, assembly, forging) of materials (powder, porous, nanostructured). However, some difficulties remains on this innovative process, particularly in terms of temperature control, microstructural homogeneity especially for complex shapes ... and industrial productivity. To solve these problems, an electro-thermo-mechanical-microstructural model is identified: i) using a thin instrumentation of the machine for the Thermo-Electric part including a reverse approach to evaluate the contact resistances, ii) by in situ creep and compression tests for mechanical microstructural-part. The resulting model has helped to find solutions for microstructural homogenization of the parts, for simultaneously densify of large numbers of parts (modifying the flow of electric current) and/or complex shapes (intervention sacrificial parts)
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Lallemant, Lucile. "Obtention d'alumines α dopées polycristallines transparentes par Spark Plasma Sintering". Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00808873.
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L'élaboration de céramiques polycristallines transparentes constitue un défi technologique important. Les matériaux transparents actuellement utilisés (verres ou monocristaux) possèdent des propriétés mécaniques (dureté, résistance à l'usure) et physico-chimiques (résistance à la corrosion) moins intéressantes que celles des céramiques polycristallines. Par ailleurs, le coût de production de ces dernières est inférieur à celui des monocristaux. Les deux principaux paramètres à contrôler afin d'augmenter les propriétés optiques de l'alumine alpha polycristalline sont sa porosité, comme pour tout matériau transparent, et sa taille de grains, du fait de sa biréfringence. Aussi on cherchera à obtenir après frittage un matériau possédant une très faible porosité (inférieure à 0,05%) avec une distribution fine en taille de pores centrée sur des porosités nanométriques, et une taille de grains très fine (plus grand que 0,5 µm). Actuellement, cette microstructure particulière est obtenue en ~ 15 heures en combinant un frittage naturel suivi d'un traitement par Hot Isostatic Pressing (HIP). La technique de Spark Plasma Sintering (SPS) utilisée dans cette étude permet d'obtenir des céramiques denses possédant une microstructure fine en des temps plus courts. Premièrement, un protocole d'élaboration d'une alumine pure transparente a été mis au point. Il repose sur la préparation de crus à microstructure contrôlée avant l'étape de frittage. Principalement, ils doivent présenter une distribution fine en taille de pores avec un empilement particulaire macroscopique homogène dépourvu d'agglomérats. Le cycle de frittage SPS a également été optimisé afin d'obtenir les meilleures transmissions optiques possibles. Ensuite, un protocole de dopage par des inhibiteurs de croissance de grains a été optimisé. La nature du sel dopant influe au second ordre sur les propriétés optiques des échantillons par rapport à une calcination préalable au frittage. La nature et/ou la quantité de dopant induisent un décalage plus ou moins important de la densification vers les hautes températures. Le cycle de frittage SPS doit donc être adapté en conséquence. Le taux de dopant doit être optimisé afin d'obtenir une microstructure fine après frittage sans présence de particules de seconde phase. Différents dopants ont été comparés (magnésium Mg, lanthane La et zirconium Zr) et l'échantillon possédant les meilleures propriétés optiques a été obtenu grâce à un dopage à 200 cat ppm de lanthane. Des optimisations au niveau de la morphologie des poudres (plus fines et plus sphériques) et de la préparation des suspensions d'alumine alpha dopées au lanthane (lavage par centrifugation) ont permis d'obtenir l'un des meilleurs échantillons d'alumine transparente reporté dans la littérature. Il possède une transmission optique de 68% et une taille de grains de l'ordre de 300 nm. Ses propriétés mécaniques (dureté, résistance à l'abrasion) sont supérieures à celles d'un monocristal de saphir.
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Aman, Yann. "Spark plasma sintering mechanisms of alpha-alumina (α-Al2O3) nanopowders". Lyon, INSA, 2010. http://www.theses.fr/2010ISAL0128.
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The technological interests that present the nanostructured materials allowed the emergence during these last years of the Spark Plasma Sintering “SPS” process. At the origin of this process, it was supposed by its inventors that the application of pulsed D. C. Currents can generate a plasma discharge between the particles of powdered material, thus enhancing the creation of necks at low temperatures. This was supposed to accelerate the matter diffusion and densification at low sintering temperatures, which could prevent from grain growth. This assumption of the existence of plasma or another specific SPS effect has never been verified, although the possibilities offered by the SPS are proven. The objective of this thesis was to study the SPS sintering mechanisms of α-alumina nanopowders. Polycrystalline α-alumina is a ceramic material, which has been widely studied in traditional sintering, and which has excellent mechanical and optical properties when the density of sintered material is close to its theoretical value with submicron grain size in the sintered bulk. In this thesis work, an applied approach is first developed. Thanks to powerful statistical tools, the influence of the combination of a large number of parameters SPS (rate of heating, temperature, duration of stage) as well as the green state processing on the evolution of the density and the grain size during SPS sintering, and its consequences on the optical properties, have been characterized. This allowed the obtention of highly translucent polycrystalline α-alumina. In the second time, from the fundamental point of view, the objective was to elucidate the physico-chemical mechanisms that govern the densification and grain growth kinetics. It was shown by microstructural analyzes that the sintering paths are influenced by the heating rates, and that the densification at low temperature is governed by fast mechanisms of diffusion such as grain boundaries diffusion<br>L‘intérêt technologique que présentent les matériaux nanostructurés a permis l‘émergence au cours de ces dernières années du procédé de frittage flash « SPS » (Spark Plasma Sintering). A l‘origine de ce procédé, il a été supposé par ses inventeurs que l‘application d‘un courant pulsé puisse générer une décharge plasma entre les particules du matériau pulvérulent, favorisant ainsi la création de ponts à des températures faibles et accélérant les phénomènes de diffusion de matière à l‘origine de la densification à basse température. Cette hypothèse de l‘existence de plasma ou de quelconque autre effet SPS n‘a jamais été vérifiée, bien que les possibilités offertes par le SPS soient avérées. L‘objectif de cette thèse a été d‘étudier les mécanismes de frittage SPS de nanopoudres d‘alumine alpha. L‘alumine polycristalline alpha, matériau céramique modèle largement étudié dans le frittage traditionnel, possède d‘excellentes propriétés mécaniques et optiques quand la densité du matériau fritté est proche de sa valeur théorique, et que la taille de grain est submicronique. Dans un premier temps, du point de vue appliqué, cette étude a permis de caractériser, grâce à des outils statistiques puissants, l‘influence de la combinaison d‘un grand nombre de paramètres SPS (taux de chauffage, température, durée de palier) ainsi que de la mise en forme du compact cru sur l‘évolution de la densité et de la taille de grains au cours du frittage, et ses conséquences sur les propriétés optiques. Ceci a permis l‘obtention d‘alumine polycristalline de translucidité élevée. Dans un second temps, du point de vue fondamental, l‘objectif a été d‘élucider les mécanismes physico-chimiques intervenant sur les cinétiques de densification et grossissement de grain. Il a ainsi été démontré, grâce à des analyses microstructurales par microscopie électronique, que les chemins de frittage sont influencés par la vitesse de chauffage, et que la densification à basse température est guidée par des mécanismes rapides de diffusion aux joints de grains. Tandis qu‘à haute température, la densification semble contrôlée par des mécanismes lents de diffusion tels que la diffusion en volume et le glissement au joint de grain. Des analyses dilatométriques ont permis de mettre en évidence l‘influence de la nature des pulses de courant sur le développement microstructural au cours du frittage. Des analyses spectroscopiques de temps de vie de positrons ont permis de caractériser la concentration en défauts ponctuels en fonction du taux de chauffage. Enfin, l‘effet du courant pulsé sur le mécanisme de création des ponts au stade initial du frittage SPS a pu être caractérisé
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Lallemant, Lucile. "Obtention d’alumines α dopées polycristallines transparentes par Spark Plasma Sintering". Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0082/document.
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L'élaboration de céramiques polycristallines transparentes constitue un défi technologique important. Les matériaux transparents actuellement utilisés (verres ou monocristaux) possèdent des propriétés mécaniques (dureté, résistance à l'usure) et physico-chimiques (résistance à la corrosion) moins intéressantes que celles des céramiques polycristallines. Par ailleurs, le coût de production de ces dernières est inférieur à celui des monocristaux. Les deux principaux paramètres à contrôler afin d'augmenter les propriétés optiques de l'alumine alpha polycristalline sont sa porosité, comme pour tout matériau transparent, et sa taille de grains, du fait de sa biréfringence. Aussi on cherchera à obtenir après frittage un matériau possédant une très faible porosité (inférieure à 0,05%) avec une distribution fine en taille de pores centrée sur des porosités nanométriques, et une taille de grains très fine (plus grand que 0,5 µm). Actuellement, cette microstructure particulière est obtenue en ~ 15 heures en combinant un frittage naturel suivi d'un traitement par Hot Isostatic Pressing (HIP). La technique de Spark Plasma Sintering (SPS) utilisée dans cette étude permet d’obtenir des céramiques denses possédant une microstructure fine en des temps plus courts. Premièrement, un protocole d'élaboration d'une alumine pure transparente a été mis au point. Il repose sur la préparation de crus à microstructure contrôlée avant l'étape de frittage. Principalement, ils doivent présenter une distribution fine en taille de pores avec un empilement particulaire macroscopique homogène dépourvu d'agglomérats. Le cycle de frittage SPS a également été optimisé afin d'obtenir les meilleures transmissions optiques possibles. Ensuite, un protocole de dopage par des inhibiteurs de croissance de grains a été optimisé. La nature du sel dopant influe au second ordre sur les propriétés optiques des échantillons par rapport à une calcination préalable au frittage. La nature et/ou la quantité de dopant induisent un décalage plus ou moins important de la densification vers les hautes températures. Le cycle de frittage SPS doit donc être adapté en conséquence. Le taux de dopant doit être optimisé afin d'obtenir une microstructure fine après frittage sans présence de particules de seconde phase. Différents dopants ont été comparés (magnésium Mg, lanthane La et zirconium Zr) et l'échantillon possédant les meilleures propriétés optiques a été obtenu grâce à un dopage à 200 cat ppm de lanthane. Des optimisations au niveau de la morphologie des poudres (plus fines et plus sphériques) et de la préparation des suspensions d'alumine alpha dopées au lanthane (lavage par centrifugation) ont permis d'obtenir l'un des meilleurs échantillons d'alumine transparente reporté dans la littérature. Il possède une transmission optique de 68% et une taille de grains de l'ordre de 300 nm. Ses propriétés mécaniques (dureté, résistance à l'abrasion) sont supérieures à celles d'un monocristal de saphir<br>Obtaining transparent polycrystalline ceramics became an important technological challenge over the last decade. Their high mechanical (hardness, wear resistance) and physico-chemical (corrosion resistance) properties combined with a high transparency and a reasonable price could lead them to replace glasses or monocrystals as sapphire in optical applications. The main parameters to control in order to obtain highly transparent polycrystalline alpha-alumina (PCA) are the porosity size and amount as for the other transparent materials. However, as PCA is a birefringent material, the grain size also needs to be controlled. That’s why PCA should possess after sintering grains as small as possible (bigger than 0.5 µm) and a porosity closed to 0.00% with nanometric pores. This particular microstructure is usually obtained in ~ 15 hours by combining natural sintering in air with a post Hot Isostatic Pressing (HIP) treatment. In our study, the Spark Plasma Sintering (SPS) technique was used as it enables to obtain fully dense ceramics in shorter times while limiting the grain growth. First, a protocol to obtain a pure transparent PCA was established. It consists on preparing green bodies with a controlled particle’s packing before sintering. Mainly, the particle’s packing has to be macroscopically homogeneous and without agglomerates. Moreover, the pore size distribution should be the narrowest. The SPS sintering cycle was also optimised to obtain the highest optical transmission. Then, a doping protocol with grain growth inhibitors was optimised. The nature of the doping salt has a secondary effect on optical properties compared to a thermal treatment applied before sintering. Depending on the doping agent nature and/or amount, the densification temperature changes. The SPS sintering cycle has thus to be adapted. The doping agent amount has to be optimised to obtain a fine microstructure after sintering without second phase particles. Different doping agents have been compared (magnesium Mg, lanthanum La and zirconium Zr). The sample having the highest optical properties was doped with 200 cat ppm of lanthanum. Finally, an optimisation of the powder’s morphology (finer and more spherical) was performed. Moreover, the lanthanum doped alpha-alumina slurry’s preparation was optimized using centrifugation. All these processes have enabled us to obtain one of the most transparent PCA sample ever reported in the literature. It possesses an optical transmission of 68% and a grain size around 300 nm. Its mechanical properties (hardness, wear resistance) are higher than the ones of a sapphire monocrystal
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Schnittker, Kimberlin, and Kimberlin Schnittker. "Processing of Silicon Nitride Ceramics Produced by Spark Plasma Sintering." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625918.
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Four silicon nitride powder blends vary in starting powder characteristics, glass chemistry, and phase composition. This work focuses on how these properties influence densification behavior, microstructural development, and the resulting mechanical performance of dense ceramics. Previous work completed on alpha-rich, low oxide containing (8 wt%), and fine silicon nitride powder (GS-44) showed high hardness equiaxed with grained ceramic. GS-44 served as an excellent precursor for the matrix phase material in graphene reinforced composites, which resulted in 235% increase in toughness and high hardness retention [1] with the addition of 1.5 vol% graphene. As the GS-44 powder is no longer in production, investigative work into other commercial powders and customization of powder blends was initiated. Commercial blends were selected based on availability, high alpha content, fine particle size, and additive chemistry (Al2O3, MgO, and Y2O3). The objective was to understand which powder characteristics led to a ceramic design that contained high hardness, strength, and toughness properties in order to increase the use of silicon nitride in extreme temperature environments. One such example is aerospace and structural applications that require a high-performance material that is lightweight and good thermal stability.
Strong covalent bonding in silicon nitride make densification of powders extremely difficult; thereby, sintering additives are necessary to promote liquid phase sintering processes. Compaction of ceramic powders was carried out using a spark plasma sintering (SPS) furnace by utilizing a pulsed direct current through a conductive graphite die that encapsulates the sample powder. SPS was preferred over other conventional sintering methods owing to its high heating rate and short dwell times at the sintering target temperature. Thus, SPS provides superior control for tailoring the final silicon nitride properties by producing a hard alpha-phase and tough beta-phase microstructures.
The custom blend developed had an appreciable amount of media wear included during the milling process that increased the additive content. Development of the custom blend was used to understand the effect of a larger additive content. Commercial GS-44 blend was used as the control to track the effect of adjusting specific surface area and oxide content in silicon nitride powder systems (HCS-M, C-R3, and UA-SN). The mechanical results for the four matrix systems, showed that toughness increased with grain coarsening and minimization of alumina content in beta silicon nitride. Based on these findings it is important to determine tradeoffs (i.e. balance of high hardness, toughness, and strength) to engineer an optimal ceramic that can be used for structural and aerospace applications.
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Nieto, Andy. "Graphene NanoPlatelets Reinforced Tantalum Carbide consolidated by Spark Plasma Sintering." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/840.
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Hypersonic aerospace vehicles are severely limited by the lack of adequate high temperature materials that can withstand the harsh hypersonic environment. Tantalum carbide (TaC), with a melting point of 3880°C, is an ultrahigh temperature ceramic (UHTC) with potential applications such as scramjet engines, leading edges, and zero erosion nozzles. However, consolidation of TaC to a dense structure and its low fracture toughness are major challenges that make it currently unviable for hypersonic applications. In this study, Graphene NanoPlatelets (GNP) reinforced TaC composites are synthesized by spark plasma sintering (SPS) at extreme conditions of 1850˚C and 80-100 MPa. The addition of GNP improves densification and enhances fracture toughness of TaC by up to ~100% through mechanisms such as GNP bending, sliding, pull-out, grain wrapping, crack bridging, and crack deflection. Also, TaC-GNP composites display improved oxidation behavior over TaC when exposed to a high temperature plasma flow exceeding 2500 ˚C.
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Guyon, Julien. "Évolution des microstructures et mécanismes de densification d'un alliage TiAl lors du frittage par Spark Plasma Sintering." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0244/document.
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Ce travail porte sur l'évolution microstructurale d'un alliage TiAl lors du frittage par un procédé appelé Spark Plasma Sintering (SPS). Les poudres initiales, élaborées par atomisation, sont constituées principalement d'une phase métastable. Les transformations qui accompagnent le retour à l'équilibre de cette dernière durant un chauffage sont finement caractérisées par MEB, MET et EBSD. Ces transformations seront ensuite utilisées comme marqueur thermique lors de la densification SPS afin de mieux estimer les amplitudes des gradients thermiques et mécaniques du procédé de frittage. Les mécanismes de densification responsables de la formation des cous sont discutés, ainsi que les origines des hétérogénéités microstructurales des échantillons complètement densifiés. Un comparatif des mécanismes de densification et des microstructures finales entre une poudre broyée et une poudre non broyée est dressé. Enfin, l'influence de l'application d'une contrainte dynamique pendant la compaction au moyen d'un dispositif original est présentée<br>This work focuses on the microstructure evolution of a TiAl alloy during sintering by a process called Spark Plasma Sintering (SPS). The initial powders, elaborated by atomization, consist primarily of a metastable phase. The transformations of the return to equilibrium of the latter during heating are finely characterized using SEM, TEM and EBSD. These phase transformations are then used as a thermal indicator during the SPS densification to estimate the thermal and mechanical gradients. The densification mechanisms responsible for the neck formation and the origins of the microstructure heterogeneities of fully densified samples are discussed. A comparison between the densification mechanisms and the final microstructures of a milled powder and a no milled powder is showed. Finally, the effect of the application of a dynamic stress during the compaction using an original process is presented
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Peng, Hong. "Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties." Doctoral thesis, Stockholm University, Department of Physical, Inorganic and Structural Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129.
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<p>Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si<sub>3</sub>N<sub>4</sub>-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology.</p><p> The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RE<sub>x</sub>Si<sub>12-(3x+n)</sub>Al<sub>3x+n</sub>O<sub>n</sub>N<sub>16-n</sub> while keeping the cation ratios of RE, Si and Al constant. </p><p>Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si<sub>3</sub>N<sub>4</sub>-based ceramics, have been precisely followed and separately investigated in the SPS process.</p><p>The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a <i>dynamic ripening</i> mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. </p><p>The obtained sialon ceramics with fine-grained microstructure show formidably improved <i>superplasticity</i> in the presence of an electric field. The compressive strain rate reaches the order of 10<sup>-2</sup> s<sup>-1</sup> at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming. </p>
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Mani, Mahesh Kumar. "Development of Fe-50Co alloy and its composites by spark plasma sintering." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/60869/.
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Composite strengthening was attempted to improve the mechanical strength and toughness of the brittle near equiatomic Fe-Co alloy. The matrix alloy chosen for this research falls in the Fe-(30-50) Co group, which are known for their highest saturation induction (B-sat) and Curie temperature among the commercial soft magnetic alloys. The reinforcements, which exhibited a wide range of aspect ratios, included SiC particulates, SiC whiskers and carbon nanotubes (CNTs). In order to minimize the interfacial reaction between the reinforcements and the Fe-50Co alloy (matrix) and to realise higher compact density, spark plasma sintering (SPS) was selected for rapid compaction of materials. Reinforcements were coated using electroless deposition with Ni-P, copper and cobalt to modify the interfacial chemistry and thickness, and hence the final properties of the composites. A comprehensive study on the sintering variables found, within the range of examination and under constant heating and cooling rates, the optimum maximum temperature, soaking time and mechanical pressure of 900oC, 2-5 minutes and 80 MPa to rapidly consolidate the Fe- 50Co alloy to near-theoretical density. The volume fraction and size of the ordered regions in the monolithic alloy and hence the magnetic properties, were sensitive to the heating rate, cooling rate, temperature at which the mechanical pressure was applied and removed and post heat treatments. The influence of reinforcement coatings on the wetting characteristics, and in turn the properties, was compared using SiC particulate Fe-50Co composites. The introduction of bare and coarse (20 μm) SiC particulates negatively affected both magnetic and mechanical properties. Electroless Co coating of particulates improved both the flexural properties and magnetic characteristics such as permeability and coercivity by promoting the formation of narrower interfaces and better bonding. The addition of bare and coated whiskers in Fe-Co alloys enhanced densification and grain growth of the matrix. Copper coating over whiskers was found to be not helpful in realising uniform dispersion, whereas Co and Ni-P coating aided to achieve uniform dispersion of whiskers in the matrix. The amorphous Ni-P coating on whiskers was nanocrystallised during the rapid sintering process and resulted in a material with highly improved mechanical strength and ductility in comparison to the monolithic and other whisker reinforced composite materials. A novel attempt to prepare bulk Fe based alloy composites reinforced with CNTs was also undertaken. Both soft magnetic and mechanical property enhancements were observed in composites with lower vol% of CNTs (i.e. < 1.5%, in the range of examination up to 10%) due to the improvement of compact density by CNTs. An increase in the CNT vol% produced a negative effect on saturation induction and mechanical properties due to the agglomeration of CNTs and reduction in compact density. SPS helped to retain the structural integrity of CNTs during processing. Electroless Ni-P coating over the CNTs helped to reduce the structural damage of CNTs during processing and to improve the mechanical strength and ductility at a marginal cost of saturation induction, in comparison to the monolithic compacts and bare CNT reinforced composites. To date accurate temperature assessment of the compact in the SPS die has been difficult due to the remote position of the pyrometer within the body of the die. It has been found that the ferromagnetic Curie transition can be successfully employed to calibrate SPS pyrometer during processing.
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Dupuis, Sébastien. "Etude de la solution solide Ba1-xSrxTiO3-δ : synthèses et caractérisations structurales et microstructurales des nanopoudres et des nanocéramiques obtenues par frittage spark plasma sintering : influence de la composition et de la source en titane sur les propriétés électriques colossales". Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30390.
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Depuis le début du XXIème siècle, les systèmes électroniques embarqués sont utilisés quotidiennement. Cette avancée technologique a été rendue possible grâce au développement de condensateurs plus petits, légers et performants. Afin de concevoir de nouvelles applications (récupérateurs d'énergie, actionneurs électriques...) et d'améliorer celles existantes, il est nécessaire d'accroître les rendements énergétiques de ces composants. Le développement de condensateurs céramiques à base d'oxyde de structure pérovskite possédant un couple permittivité élevée/perte faible, tente de relever ce challenge technologique. Dans ce contexte, la synthèse de nanoparticules de Ba1-xSrxTiO3 (0 < = x < = 1) par chimie "douce", a été étudié. Deux sources de titane (TiOCl2 et TiCl3) ont été utilisées et les études structurales et microstructurales ont été réalisées sur les différents oxydes obtenus. Les céramiques nanostructurées densifiées ont été élaborées par frittage SPS, technique permettant de limiter la croissance granulaire. Pour obtenir un comportement capacitif, ces différentes céramiques ont subi un traitement thermique en atmosphère oxydante et les propriétés électriques, fonction de la composition et du précurseur, sont comprises entre 10 3 [10 puissance 3] et 8.10 5 [8.10 puissance 5] pour les permittivités, associées à des pertes inférieures à 5%. Les mesures en spectroscopie d'impédance en fonction de la température nous ont permis d'appliquer certains modèles physiques comme, Debye, UDR, THP et IBLC à nos systèmes, afin de relier les propriétés électriques à la composition. Nous avons pu montrer qu'il existe une relation entre pouvoir capacitif et taux de strontium. Une diminution de la polarisation par sauts d'électrons a été associée à une dégradation de la polarisation interfaciale entre les grains et les joints de grains lorsque la teneur en strontium augmente. Cela conduit également à un changement de mécanisme de conduction par sauts d'électrons. Nous avons pu montrer que les distances de ces sauts, fixes et confinées entre plus proches voisins (modèle NNH) pour les céramiques riches en strontium, sont délocalisées et s'étendent sur des distances de 3 à 4 nm (modèle VRH), pour les céramiques riches en baryum. La substitution Ba-Sr s'avère donc être un levier expérimental efficace dans le contrôle des propriétés électriques de matériaux à permittivité colossale<br>Since the beginning of the 21st century, embedded electronic systems are daily used. This technological advance has been made possible by the development of lighter, smaller and more efficient capacitors. To design new applications (energy recovery system, electric actuators...) and to improve existing ones, it is necessary to increase the energy efficiency of these components. The development of ceramic capacitors with perovskite structure showing high permittivity and low losses, attempts to meet this technological challenge. In this context, the synthesis of Ba1-xSrxTiO3 (0 < = x < = 1) nanoparticles by soft-chemistry has been studied. Two titanium precursors (TiOCl2 and TiCl3) have been used and the structural and microstructural studies were conducted on each oxide. The nanostructured ceramics have been elaborated by SPS in order to limit the grain growth. To access a capacitive behavior, these different ceramics have undergone a heat treatment in an oxidizing atmosphere and the electrical properties, depending on the composition and on the precursor, are between 10 3 [10 to the power 3] and 8.10 5 [8.10 to the power 5] for permittivities, associated with losses lower than 5 %. The spectroscopic measurements as a function of temperature have allowed the use of various physical models, such as Debye, UDR, THP and IBLC, to link electrical properties and composition. We have shown that a relationship exists between the capacitive power and the strontium content. A decrease of the electron hopping polarization has been associated with the degradation of the interfaciale polarization between grains and grain boundaries when the strontium content increases. This also leads to a change of the electron hopping conduction mechanism. We have shown that the distances of these jumps, are fixed and confined between nearest neighbors (NNH model) for Sr-rich ceramics, while they are delocalized and extended over a distance of 3 to 4 nm (VRH model) for Ba-rich ceramics. Therefore, the Ba-Sr substitution is an effective experimental lever to control the electrical properties of colossal permittivity materials
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Eriksson, Mirva. "Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2 composites." Licentiate thesis, Stockholm University, Department of Physical, Inorganic and Structural Chemistry, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-26122.
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<p>Titanium has been used as a model substance to study how it behaves in a SPS apparatus when heating rate and/or pressure were varied during the sintering and deformation process. The sintering and deformation of Ti in SPS were compared with that occurring in the conventional hot pressing (HP) in order to reveal if there are any positive effects added by the use of SPS. The ductility of Ti was explored in order to understand the sintering and deformation of (Ti) x (TiB2)1-x composites with x = 0.05, 0.1, and 0.2, respectively, expressed in mol ratio. The temperature difference (DT) between the monitored and the temperature that the samples are exposed to was evaluated.</p><p><p>It was noticed that Ti can be sintered at relatively low temperatures. High heating rate implied that the onset temperatures of the sintering and deformation processes decreased. Increasing pressure did not affect the onset temperature but revealed that the deformation of Ti is different if the experiments are conducted within the stability region of the a -phase region of Ti or if the deformation takes place in a temperature region that covers both a-and b-phase areas, i. e. the use of high pressures implied a one step deformation process while the use of low implied that the main part of the deformation took place in the b-phase region.</p></p><p>(Ti) x (TiB2)1-x composites were prepared to full densities at 1500 °C using a holding time of 3 min and pressure of 50 MPa. During the SPS sintering the composite with x= 0.2 revealed the presence of TiB due to the reaction Ti + TiB 2 -> 2TiB while the composites with low x values did not show any formation of TiB. The formation of TiB impaired the mechanical properties. The deformation of composites was very difficult. Their deformability increased with increasing x and temperature as well as pressure. During the deformations of pre-sintered samples TiB was formed in all of the composites.</p>
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Rudolf, Christopher Charles. "Microstructure and Mechanical Properties of Nanofiller Reinforced Tantalum-Niobium Carbide Formed by Spark Plasma Sintering." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2596.
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Ultra high temperature ceramics (UHTC) are candidate materials for high temperature applications such as leading edges for hypersonic flight vehicles, thermal protection systems for spacecraft, and rocket nozzle throat inserts due to their extremely high melting points. Tantalum and Niobium Carbide (TaC and NbC), with melting points of 3950°C and 3600°C, respectively, have high resistivity to chemical attack, making them ideal candidates for the harsh environments UHTCs are to be used in. The major setbacks to the implementation of UHTC materials for these applications are the difficulty in consolidating to full density as well as their low fracture toughness. In this study, small amounts of sintering additive were used to enhance the densification and Graphene Nanoplatelets (GNP) were dispersed in the ceramic composites to enhance the fracture toughness. While the mechanisms of toughening of GNP addition to ceramics have been previously documented, this study focused on the anisotropy of the mechanisms. Spark plasma sintering was used to consolidate both bulk GNP pellets and near full relative density TaC-NbC ceramic composites with the addition of both sintering aid and GNP and resulted in an aligned GNP orientation perpendicular to the SPS pressing axis that allowed the anisotropy to be studied. In situ high load indentation was performed that allowed real time viewing of the deformation mechanisms for enhanced analysis. The total energy dissipation when indenting the bulk GNP pellet in the in-plane GNP direction was found to be 270% greater than in the out-of-plane orientation due to the resulting deformation mechanisms that occurred. In GNP reinforced TaC-NbC composites, the projected residual damaged area as a result of indentation was 89% greater when indenting on the surface of the sintered compact (out-of-plane GNP orientation) than when indenting in the orthogonal direction (in-plane GNP orientation) which is further evidence to the anisotropy of the GNP reinforcement.
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Trapp, Johannes. "Mikroskopische Aspekte beim feldaktivierten Sintern metallischer Systeme." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-224118.
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1. Beim feldaktivierten Sintern im Temperaturbereich von 500 bis 1000 °C fließen elektrische Ströme mit einer Dichte von 1 bis 3 A/mm².
2. Daraus folgt für die größten verwendeten Pulverteilchen mit einem Radius von 50 µm ein Strom je Teilchenkontakt von 10 bis 50 mA.
3. Die durch das Aufbringen des prozesstechnisch notwendigen Pressdruckes gebildeten relativen Kontaktradien (Kontaktradius geteilt durch Teilchenradius) haben eine Größe von 0,05 bis 0,3.
4. Die Einengung der Strompfade im Kontakt der Pulverteilchen erhöht, zusammen mit dem elektrischen Widerstand der Oxidschicht auf den Pulverteilchen, den elektrischen Widerstand des Pulverpresslings.
5. Der Stromfluss durch die Teilchenkontakte führt mit dem zusätzlichen elektrischen Widerstand dieser Teilchenkontakte zu einer lokalen Temperaturerhöhung (Übertemperatur) von 10-4 bis 1 Kelvin für Kupfer- respektive Stahlpulver.
6. Der zusätzliche elektrische Widerstand der Oxidschicht kann die Übertemperatur beim Kupferpulver auf bis zu 1 mK erhöhen.
7. Mit abnehmendem Teilchenradius sinkt die Übertemperatur quadratisch.
8. Das Wachstum der Teilchenkontakte im Verlauf der Verdichtung führt zu einer kontinuierlichen Verringerung der Übertemperatur.
9. Das Auftreten von schmelzflüssiger Phase, von Metalldampf oder von Plasma wird in den untersuchten metallischen Systemen ausgeschlossen.
10. Auch Elektromigration, Thermomigration oder andere Wirkungen des elektrischen Stromes spielen keine Rolle für die Verdichtung beim feldaktivierten Sintern.
11. Die Verwendung von gepulstem anstelle von kontinuierlichem Gleichstrom beeinflusst die Verdichtung der untersuchten Werkstoffe nicht.
12. Die Verdichtung vom Pulver zum kompakten Werkstoff findet für Pulverteilchen mit einem Radius größer als R = 10 µm über plastische Verformung durch verschiedene Formen des Kriechens statt.
13. Die Verformung ist im Anfangsstadium auf den Kontaktbereich begrenzt.
14. Bei Pulverteilen mit Teilchenradien unter R = 10 µm findet die Verdichtung zunächst als Folge von Leerstellenströmen in die Kontaktkorngrenze statt (Sintern).
15. Durch die schnelle Verdichtung bei niedriger homologer Temperatur werden Kornwachstum und Rekristallisation verringert.
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Mouawad, Bassem. "Assemblages innovants en électronique de puissance utilisant la technique de " Spark Plasma Sintering "." Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00943438.
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L'augmentation des températures de fonctionnement est une des évolutions actuelles de l'électronique de puissance. Ce fonctionnement entraine d'une part des changements de la structure des modules de puissance notamment des structures " 3D " pour assurer un refroidissement double face des composants de puissance, et d'autre part l'utilisation de matériaux qui permettent de réduire des contraintes thermomécaniques, liées à la différence de coefficient de dilatation des matériaux, lors d'une montée en température. Le travail réalisé au cours de cette thèse consiste à développer une nouvelle structure " 3D " basée sur une technique de contact par des micropoteaux en cuivre, élaborés par électrodéposition et ensuite assemblés à un substrat céramique métallisé (notamment, un DBC : Direct Bonding Copper). Pour réaliser ce contact, une technique de frittage par SPS (Spark Plasma Sintering) est utilisée. Nous étudions dans un premier temps le collage direct de cuivre sur des massifs, puis effectuons dans un deuxième temps le collage de cuivre entre les micropoteaux et le DBC. Cette technique SPS est aussi utilisée pour la réalisation d'un nouveau substrat céramique métallisé basé sur des matériaux avec des coefficients de dilatation thermique accordés, pour les applications à haute température.
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Carneiro, Marcelo Bertolete. "Fabricação de ferramentas de corte em gradação funcional por Spark Plasma Sintering (SPS)." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-14122014-155118/.
Full textAbstract:
O objetivo do trabalho foi fabricar ferramentas de corte para usinagem a partir de materiais em gradação funcional (Functionally Graded Materials FGM), fazendo uso da técnica de sinterização por plasma pulsado (Spark Plasma Sintering SPS), a qual permite taxa de aquecimento e resfriamento maior do que as técnicas tradicionais, menor temperatura e tempo de operação, melhor controle energético e alta repetibilidade. Os materiais utilizados foram pós cerâmicos a base de alumina (Al2O3-ZrO2 e Al2O3-TiC) e metal duro (WC-Co), de modo que dois insertos foram desenvolvidos, um de cerâmica branca (Al2O3-ZrO2) em gradação com metal duro e outro de cerâmica mista (Al2O3-TiC) em gradação com metal duro. A metodologia experimental levou em conta a aplicação de um modelo termomecânico para estimar a tensão residual térmica ao longo da espessura da ferramenta, estudo da influência dos parâmetros de sinterização por SPS (Temperatura e Pressão) sobre a qualidade do sinterizado (caracterização da propriedade física, densidade), com base nesses dados foi escolhida a melhor condição de operação para fabricar corpos de prova (CPs) para os ensaios mecânicos de resistência à flexão, dureza e tenacidade à fratura, além de insertos em FGM para os ensaios de usinagem em ferro fundido cinzento fazendo uso da operação de torneamento. Os resultados mostraram que o parâmetro de máquina que mais influenciou a densidade foi a Temperatura, os FGMs de AlTiC e AlZr obtiveram um aumento de 126 e 73% na resistência à flexão em relação às suas respectivas cerâmicas homogêneas, seguindo a sequência dos materiais, a dureza foi avaliada em 13,8 e 15,8 GPa, enquanto a tenacidade à fratura em 4,91 e 5,04 MPa.m1/2. Quanto aos ensaios de usinagem, as ferramentas de FGM AlZr apresentaram menor desgaste do que as de FGM AlTiC, as forças de corte foram influenciadas pelas variáveis Avanço e Velocidade de corte, finalmente, o Avanço foi a variável que mais influenciou os resultados de rugosidade.<br>The aim was fabricating cutting tools from functionally graded materials (FGM) by spark plasma sintering method (SPS), which allow heating and cooling rates higher than traditional methods, lower temperature and shorter time sintering, better energy control and high reproducibility. The materials used were ceramic powders based on alumina (Al2O3-ZrO2 and Al2O3-TiC) and cemented carbide (WC-Co), so that two inserts were developed, one of white ceramic (Al2O3-ZrO2) graded with cemented carbide and the other of mixed ceramic (Al2O3- TiC) graded with cemented carbide. The experimental methodology was developed from thermo-mechanical model application to estimate thermal residual stress along with tool thickness, study into the influence of SPS sintering parameters (Temperature and Pressure) over sintered quality (physical properties characterization, density), on the basis of these data, the best operating condition was chosen to fabricate workpieces for mechanical tests of flexural strength, hardness and fracture toughness, besides FGM inserts to machining tests in grey cast iron using turning operation. The results showed the machine parameter that mostly influenced density was Temperature; the AlTiC and AlZr FGMs got an increase of 126 and 73% in flexural strength in relation to their homogeneous ceramics. Following the materials sequence, the hardness was evaluated at 13.8 and 15.8 GPa, whereas the fracture toughness was 4.91 and 5.04 MPa.m1/2. For the machining tests, FGM AlZr cutting tools showed lower wear than FGM AlTiC ones; the cutting forces were influenced by Feed Rate and Cutting Speed. Finally, the Feed Rate was the variable that mostly influenced the roughness results.
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Middleton, Stoney Alexander. "Effects of Spark Plasma Sintering on Binary Diffusion of Beta Phase Ti-Nb." Thesis, University of California, Irvine, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10827930.
Full textAbstract:
<p> Interest in titanium for mass-scale applications has driven an exploration for rapid, cost-effective consolidation of titanium powders. The effects of electric current and pressure on binary diffusion in beta phase titanium niobium are studied to enhance understanding of Spark Plasma Sintering (SPS), an advanced powder consolidation technology. Binary diffusion couples were annealed in the SPS system, as well as a custom-fabricated load-free furnace, for one hour to elucidate the influences of pressure and current at 1000, 1100, and 1150 °C. The results show Ti-Nb interdiffusion coefficient dependence on composition, temperature, current, and pressure. Compared to published results, the activation energy for low concentration Nb, 10-22 at%, has shown to be reduced in the SPS by an average 38kJ/mol at 15MPa and 70kJ/mol at 80MPa. The effect on activation energy of direct current without pressure, at a similar current density as the SPS, shows an average decrease of 105kJ/mol. The possible mechanisms for these changes are discussed, and concepts for subsequent studies are provided.</p><p>
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Rua, taborda Maria. "Printed ceramic Piezoelectric MEMS for Energy Harvesting : towards Spark Plasma Sintering of multilayers." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0246.
Full textAbstract:
Une application émergente pour les MEMS (Micro-Electromechanical Systems) piézoélectriques concerne la récupération d’énergie mécanique vibratoire. Leur fabrication en couches épaisses sérigraphiées est une approche bas coût attractive. En effet, les couches épaisses, sont une alternative intéressante aux couches minces pour maximiser le couplage électromécanique. De plus, le remplacement des substrats passifs silicium par des substrats métalliques plus flexibles est aussi recherché pour améliorer les performances. Les couches épaisses piézoélectriques imprimées présentent cependant une porosité résiduelle néfaste pour les propriétés piézoélectriques. L'objectif de cette thèse est de développer un récupérateur d'énergie mécanique résonant pour l’alimentation des systèmes autonomes. Le récupérateur d’énergie consiste en une structure multicouche formée de Pb(ZrTi)O3 (PZT) comme matériau piézoélectrique actif, situé entre deux électrodes d’or. L’ensemble est sérigraphié sur un substrat en acier inoxydable (SS). L’implémentation d’une géométrie innovante a aussi conduit à une optimisation de la fréquence de résonance de la structure et de la densité de puissance. Enfin, pour améliorer la densification des couches de PZT, la technique de frittage avancé SPS (Spark Plasma Sintering) associée à la technique de sérigraphie a été explorée.Au cours de ce travail de thèse, le récupérateur d’énergie a été réalisé par sérigraphie de toutes les couches en incorporant une étape de pressage des échantillons avant le co-frittage conventionnel réalisé à 900 °C. Le procédé de fabrication a été optimisé avec notamment une résolution des problèmes d’adhésion des couches et de déformation de la structure. Une géométrie de type zig-zag modifié a été développée. Plus spécifiquement, ce récupérateur d’énergie MEMS dédié à des technologies de réseau électrique intelligent (Smart Grids), fonctionne sur la base d’un couplage des effets piézoélectrique et électromagnétique, avec l’intégration d’un aimant et l’interaction d’un champ électromagnétique autour d’un fil porteur de courant alternatif (AC). Une fréquence de résonance de 60Hz a été obtenue avec une puissance de sortie de 9 µW pour un courant de 7 A. La densité de puissance normalisée est nettement améliorée comparée à la littérature. Une électronique associée à ce dispositif a aussi contribué à mettre en valeur les potentialités de ce microsystème. Bien que la performance du récupérateur d’énergie ait été prouvée, la structure présente une densification de la couche active de PZT limitée (densité ≈82%). La deuxième partie de cette thèse a porté sur une amélioration de la densification du PZT en utilisant le procédé SPS. Une optimisation des différents paramètres SPS (température, pression, durée et vitesse de chauffe) a d'abord été menée pour la densification des poudres de PZT. Les conditions SPS optimales ont été déterminées et des céramiques de densités proches de 98% ont été obtenues à des températures aussi basses que 850 °C. Les propriétés électromécaniques proches de celles de céramiques commerciales de PZT attestent de l’efficacité du SPS. Les poudres de PZT ont pu être densifiées sans ajout d’aide au frittage et l’utilisation originale d’une couche protectrice pour protéger le PZT de toute réduction chimique a permis d’éviter un traitement thermique post-SPS. Ces paramètres ont ensuite été transférés sur des structures simples de multicouches Au/PZT/Au/SS. Les principaux verrous identifiés sont la porosité de la couche active PZT, les problèmes d’interfaces conduisant à des interdiffusions entre les couches, les problèmes de délamination ou de courbures. Les différents essais ont conduit à la conception d’un moule SPS en graphite spécifiquement modifié et optimisé pour la densification de ce type de structures multicouches. L’efficacité du SPS en termes de réduction des températures et de rapidité du cycle de frittage s’avère prometteur pour le développement de MEMS imprimés<br>An emerging application for piezoelectric MEMS (Micro-Electromechanical Systems) concerns the harvesting of mechanical vibratory energy. The fabrication of these piezoelectric MEMS in thick screen printed layers is an attractive low-cost approach. For MEMS energy harvesting applications, thick layers (1-100µm) are an attractive alternative to thin layers to maximize electromechanical coupling. Furthermore, the replacement of MEMS passive silicon substrates with more flexible metal substrates is also expected to improve performance. However, printed piezoelectric thick films maintain a residual porosity that is detrimental to the piezoelectric properties. The objective of this thesis is to develop a resonant mechanical energy harvester (frequency <100Hz) for the supply of autonomous systems. The printed device consists of a multilayer structure formed of Pb(ZrTiO3) as the active piezoelectric material sandwiched between two gold electrodes. The multilayer structure is screen printed on stainless steel (SS) substrate. The implementation of an innovative geometry led to an optimization of the structure resonance frequency and the power density. Finally, to improve the densification of PZT layers, the SPS (Spark Plasma Sintering) sintering technique combined with the screen printing technique was explored. During this thesis work, the energy harvesting device was fabricated by screen printing of all the layers. The manufacturing process was optimized, in particular, by solving problems of layer adhesion and structural deformation. Additionally, a modified zig-zag geometry was developed in collaboration with the University of Waterloo in Canada (UW). More specifically, this specific MEMS system is dedicated to smart grid technologies and operates based on a coupling of piezoelectric and electromagnetic effects. A frequency of 60Hz was obtained with an output power of 9 µW (load resistance 1 MΩ) for a current of 7A and 6.5mm wire-magnet distance. Compared to other piezoelectromagnetic devices in the MEMS-based literature, the normalized power density was significantly improved. Electronics associated with this device has also helped to highlight the potential of this microsystem. Although the performance of the EH was proven, the structure has limited the densification of the active layer of PZT (density ∽82%). Thus, to improve the performance of the device, the second part of this thesis focused on improving the densification of PZT using the SPS process. Optimization of the various SPS parameters (temperature, pressure, duration, and heating rate) was first carried out for the densification of PZT powders. Optimal SPS conditions were determined, and ceramics with densities close to 98% were obtained at temperatures as low as 850°C. The electromechanical properties close to those of PZT's commercial ceramics attest to the effectiveness of SPS. PZT powders could be densified without the addition of sintering aids, and the original use of a protective layer to protect the PZT from chemical reduction has allowed avoiding post-SPS heat treatment. These parameters were then transferred to simple Au/PZT/Au/SS multilayer structures. The main locks identified are the porosity of the active PZT layer, interface problems leading to interdiffusion between layers, delamination, or curvature problems. The various tests led to the design of a graphite SPS mold specially modified and optimized for the densification of this complex multilayer structure. Thanks to significant advantages in reducing sintering temperatures and sintering cycle, SPS is a promising process for the development of printed MEMS
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Sébileau, Jean-Charles. "Elaboration d'assemblages multicouches polymère/métal par frittage "Spark Plasma Sintering" pour des applications d'allègement de structure." Thesis, Mulhouse, 2018. http://www.theses.fr/2018MULH1038/document.
Full textAbstract:
Les assemblages multicouches polymère-métal, combinant la faible densité du polymère à la résistance du métal, se présentent comme une solution à fort potentiel pour répondre aux problématiques d’allégement de structure dans le secteur des transports. Plus particulièrement, ces travaux s’intéressent à l’élaboration de multicouches basés sur l’utilisation de polymères thermoplastiques thermostables associés à un alliage d’aluminium via un procédé de la métallurgie des poudres appelé « Spark Plasma Sintering » (SPS). Dans un premier temps, la mise en forme par SPS du polymère seul a été étudiée. Les influences des paramètres SPS tels que la température, la pression appliquée et le temps de maintien sur les caractéristiques structurales et les propriétés mécaniques du polyétheréthercétone (PEEK) ont été déterminées au moyen d’un plan d’expérience. Cette étude a permis de proposer des mécanismes de frittage et de mettre en évidence le rôle complexe joué par la pression sur la structure cristalline. Ensuite, le développement des assemblages, sans colle, d’un polyimide ou PEEK associé avec l’aluminium a été considéré. Une approche expérimentale a été mise en place, dans le but d’améliorer l’adhésion entre les deux matériaux. Des traitements de surface appliqués à l’aluminium visant à augmenter l’ancrage mécanique et la compatibilité chimique ont été testés. Le renforcement du polymère afin de limiter sa dilatation thermique a également été abordé. Les contributions de chacun des facteurs sont discutées sur la base de mesures d’adhérence et de caractérisations microstructurales. Cette stratégie a permis d’obtenir des multicouches avec une forte résistance à l’interface<br>Polymer/metal multilayer assemblies, combining the low density of the polymer with the strength of the metal, are considered to be of great interest for high-demand engineering applications, especially in the transportation industries where the lightweighting issues are predominant. Keeping this in mind, the present study deals with the development of this kind of assembly, using thermostable thermoplastic polymers associated with an aluminum alloy by means of a powder metallurgy process: the “Spark Plasma Sintering” (SPS) technology. As the first part of this work, the sintering of the polymer was considered. The effects of SPS parameters such as temperature, pressure, and dwell time on mechanical properties of a PolyEtherEtherKetone (PEEK) were investigated thanks to a design of experiment. This study allowed to determine the mechanisms of polymer’s consolidation and the intricate role of pressure on the PEEK crystallinity was examined with particular attention. Then, the development of the assembly, without adhesive part, composed of both polymer (polyimide or PEEK) and aluminum alloy was considered. An approach was set up to improve the compliance between these dissimilar materials comprising: surface treatments on aluminum in order to enhance their mechanical anchoring and their chemical compatibility, as well as polymer reinforcement with the aim of reducing its thermal expansion. The efficiency of each solution is discussed based on microstructural and mechanical characterizations. This approach enabled to process multilayer assemblies with a significant strength at the interface
30
Billard, Romain. "Mise au point d’un composite à fibre oxyde et matrice d’aluminosilicate de baryum modifiée." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0291/document.
Full textAbstract:
L’intérêt de ces travaux est de proposer un nouveau composite BaAl2Si2O8 (BAS) renforcé par des fibres d’alumine ayant des propriétés physiques similaires tout en étant plus réfractaire que les composites SiO2 / SiO2. La forme cristalline hexagonale du BAS est la forme stable à haute température. Cependant, elle est métastable en dessous de 1590 °C et il est donc nécessaire de la stabiliser pour éviter les transformations cristallines. La stabilisation de la forme hexagonale par substitution atomique, notamment par du rubidium à hauteur de 5 % atomique a été la solution retenue. Concernant le composite à matrice BAS, le choix de fibres d’alumine est motivée par la compatibilité physico-chimique BAS / alumine. Diverses voies d’élaboration de la matrice BAS et du composite BAS / alumine ont été explorées. La voie d’élaboration par « reactive spark plasma sintering » (R-SPS) apporte un gain important en termes de réduction du temps d’élaboration et de rendement. Ce gain de temps évite donc l’exposition du BAS aux hautes températures et le risque de transformation de la phase hexagonale en monoclinique. Cependant la mise en forme par SPS de matériaux oxydes, dont le BAS, est confrontée à l’existence de gradients thermiques importants au sein de l’échantillon. C’est pourquoi, la mise en oeuvre d’un moule chauffant est développée comme une alternative au SPS. Ce système, en cours d’évaluation, devrait permettre l’utilisation de cycles thermiques équivalents à ceux du SPS, tout en limitant fortement les gradients thermiques<br>The main purpose of the present work is to propose a new BaAl2Si2O8 (BAS) composite reinforced with alumina fibers exhibiting similar physical properties but a higher refractoriness than SiO2 / SiO2 composites. The hexagonal crystal form of BAS is the stable one at high temperatures. However, it is metastable below 1590 °C and it is therefore necessary to stabilize it in order to prevent crystalline transformations. The stabilization of the hexagonal form by atomic substitution, including rubidium at 5 atomic % has been chosen. Regarding the matrix BAS composite, the alumina fibers selection has been justified by their low physical and chemical reactivity with this material. Several elaboration methods of the BAS matrix and of the BAS / alumina composite have been investigated. The development by "reactive spark plasma sintering" (R-SPS) brings an important benefit in terms of reduced elaboration time and yield. This saving time thus limits the BAS exposure to high temperatures and the risk of transformation into monoclinic. Nevertheless, the SPS shaping of oxide materials, including the BAS, is confronted with the presence of important thermal gradient within the sample. This is why shaping in a heating mold is currently in progress, as an alternative to the SPS. This system should allow the use the same thermal cycles as for SPS, but with lower thermal gradient
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Wang, Steven Yuan Jun. "Thermal conductivity and sintering characteristics of plasma sprayed dysprosia-yttria-zirconia thermal barrier coatings." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/7379.
Full textAbstract:
Yttria-stabilized zirconia has long been the favoured refractory material for demanding
applications such as thermal barrier coatings on turbine components. Its low thermal
conductivity, relatively high thermal expansion coefficient, and good fracture toughness are most
useful parameters when acute thermal cycles are considered. In recent years however, the
demand for higher turbine operating temperatures has led to novel and innovative research in
improving the thermal conductivity and sintering resistance of thermal barrier coatings. Rareearth
doped zirconia, rare-earth zirconates, and lanthanum hexa-aluminate have all been
proposed as candidate materials for the next generation of thermal barrier coatings. Drawn from
research conducted during 2003-2005, this study focuses on dysprosia as a ternary dopant to
yttria-stabilized zirconia, examining the relationship of dopant content with overall thermal
conductivity and sintering behaviour under cyclic thermal loading between room temperature
and 1100°C. Air plasma spray deposition technique was employed for coatings deposition.
Based on existing published works, this study is prefaced with four hypotheses: 1. increasing
levels of dysprosia would likely result in lower overall thermal conductivity; 2. best
improvement occurs at about 10 mol% total dopant (Dy + Y); 3. addition of dysprosia is also
likely to increase sintering resistance during thermal cycling, since Dy cation radius is larger
than Zr; 4. higher dopant concentrations, between 10 mol% and 50 mol%, should increasingly
lead to shorter coating life under thermal cycling. As-sprayed coating heat capacity, thermal
diffusivity, and porosity were measured by differential scanning calorimetry, laser flash method,
and image analyses, respectively. Post-cycle coating porosity levels were compared against data
for as-sprayed coatings. A theoretical model for estimating the thermal conductivity of plasma
sprayed zirconia coatings was derived and constructed from previous works by other researchers.
Experimental data and theoretical model presented in this study offer positive confirmations for
the hypotheses, with the exceptions that the greatest reduction in thermal conductivity was seen
at 15 mol% total dopant and that increased levels of dysprosia did not result in continued
reductions in thermal conductivity. Literature data suggests long range ordering of oxygen
vacancies could be a contributing factor in this trend.
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Buchheim, Cláudia Sofia de Andrade Redondo Murilhas. "Mechanical behaviour of AISiC nano composites produced by Ball Milling and Spark Plasma Sintering." Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11645.
Full textAbstract:
Doutoramento em Engenharia Mecânica<br>Neste trabalho foram produzidos nanocompósitos
de AlSiC
misturando alumínio puro com
nano partículas de SiC com diâmetro de 45 – 55 nm, usando, de forma sequencial, a técnica da
metalurgia do pó e a compactação por “ Spark Plasma Sintering”. O compósito obtido
apresentava grãos com 100 nm de diâmetro, encontrandose
as partículas de SiC localizadas,
principalmente, nas fronteiras de grão. O nanocompósito
sob a forma de provetes cilíndricos foi
submetido a testes de compressão uniaxial e a testes de nanoindentação
para analisar a
influência das nanopartículas de SiC, da fração volúmica de ácido esteárico e do tempo de
moagem, nas propriedades mecânicas do material. Para efeitos de comparação, utilizouse
o
comportamento mecânico do Al puro processado em condições similares e da liga de alumínio
AA1050O.
A tensão limite de elasticidade do nanocompósito
com 1% Vol./Vol. de SiC é dez
vezes superior à do AA1050. O refinamento de grão à escala nano constitui o principal
mecanismo de aumento de resistência mecânica. Na realidade, o Al nanocristalino sem reforço
de partículas de SiC, apresenta uma tensão limite de elasticidade sete vezes superior à da liga
AA1050O.
A adição de 0,5 % Vol./Vol. e de 1 % Vol./Vol. de SiC conduzem, respetivamente, ao
aumento da tensão limite de elasticidade em 47 % e 50%. O aumento do tempo de moagem e a
adição de ácido esteárico ao pó durante a moagem conduzem apenas a um pequeno aumento
da tensão de escoamento. A dureza do material medida através de testes de nanoindentação
confirmaram os dados anteriores. A estabilidade das microestruturas do alumínio puro e do
nanocompósito AlSiC,
foi testada através de recozimento de restauração realizado às
temperaturas de 150 °C e 250 °C durante 2 horas. Aparentemente, o tratamento térmico não
influenciou as propriedades mecânicas dos materiais, excepto do nanocompósito com 1 %
Vol./Vol. de SiC restaurado à temperatura de 250 °C, para o qual se observou uma redução da
tensão limite de elasticidade na ordem dos 13 %. No alumínio nanocristalino, a tensão de
escoamento é controlada pelo efeito de HallPetch.
As partículas de SiC, são segregadas pelas
fronteiras do grão e não contribuem para o aumento de resistência mecânica segundo o
mecanismo de Orowan. Alternativamente, as nanopartículas
de SiC constituem um reforço das
fronteiras do grão, impedindo o seu escorregamento e estabilizando a nanoestrutura. Deste
modo, as propriedades mecânicas do alumínio nanocristalino e do nanocompósito de AlSiC
poderão estar relacionadas com a facilidade ou dificuldade do escorregamento das fronteiras de
grão, embora não seja apresentada prova explícita deste mecanismo à temperatura ambiente.<br>AlSiC nano composites were prepared by mixing pure Al and 50 nm diameter SiC nanoparticles
using a powder metallurgy technique, followed by compression and spark plasma sintering. The
final composites had grains of approximately 100 nm dimensions, with SiC particles located
mostly at grain boundaries. The samples were tested in uniaxial compression and by
nanoindentation in order to establish the effect of the SiC and stearic acid volume fraction, and
the milling time on the mechanical properties. The results are compared with those obtained for
pure Al processed under similar conditions and for AA1050 aluminum. The yield stress of the
nano composite with 1 Vol. % SiC is more than ten times larger than that of AA1050. The largest
increase is due to grain size reduction; nanocrystalline Al without SiC and processed by the
same method has a yield stress 7 times larger than AA1050. Adding 0.5 Vol. % SiC increases
the yield stress by an additional 47 %, while the addition of 1 Vol. % SiC leads to 50 % increase
relative to the nanocrystalline Al without SiC. Increasing the milling time and adding stearic acid
to the powder during milling lead to relatively small increases of the flow stress. The hardness
measured in nanoindentation experiments confirms these trends, although the numerical values
of the gains are different. The stability of the microstructure was tested by annealing samples to
150 oC and 250 oC for 2 h, in separate experiments. The heat treatment had no effect on the
mechanical properties of all samples, except when treating the material with 1 Vol. % SiC at
250 oC, which led to a reduction of the yield stress by 13 %. In nanocrystalline Al, the flow stress
is controlled by the HallPetch
effect. As observed in this work, the added SiC particles
segregate at grain boundaries and do not contribute to strengthening through the Orowan
mechanism, rather pin the grain boundaries helping to stabilize the nanostructure of the material.
Grain boundary sliding is expected to be important in both nanocrystalline Al and AlSiC,
although we do not present explicit proof for the operation of this mechanism at room
temperature.
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Madec, Clémentine. "Elaboration de matériaux à gradient de fonction céramique / métal par SPS pour la protection balistique." Thesis, Dijon, 2016. http://www.theses.fr/2016DIJOS057/document.
Full textAbstract:
Les propriétés idéales d’un matériau de blindage sont la combinaison d’une extrême dureté pour casserles noyaux des projectiles et d’une grande ductilité pour résister à l’impact et arrêter les fragments du projectile. Or cettecombinaison de propriétés est incompatible avec un matériau unique. Pour pallier ce problème, les concepteurs de blindageassocient un matériau dur (céramique) à un matériau ductile (métal). Une autre solution serait de réaliser un matériauprésentant un gradient de propriétés mécaniques : dans le cas présent, d’une très grande dureté de la face avant à une grandeductilité de la face arrière. Les technologies non conventionnelles de frittage telles que le Spark Plasma Sintering (SPS)permettent d’assembler ou de fritter/assembler des matériaux aux caractéristiques aussi différentes et complémentaires. Ils’agit donc d’étudier les conditions d’assemblage ou de cofrittage de tels matériaux (dans le cas présent, Al2O3 et Ti) ainsique l’influence de la microstructure résultante de l’ensemble sur sa performance balistique.La première partie de ce travail a porté sur la caractérisation de l’alumine et du titane. Cinq poudres d’alumines ontété étudiées d’un point de vue comportement au frittage. Trois d’entre elles sont retenues en raison de leurs microstructuresintéressantes, proches en termes de densité et de taille de grains. Ces alumines ont été caractérisées mécaniquement (dureté,ténacité, résistance à la rupture) et balistiquement pour n’en garder qu’une dans la deuxième partie du travail. Le titane, frittédans les mêmes conditions que l’alumine, a montré qu’il n’avait malheureusement pas les propriétés attendues (absence deductilité).La seconde partie du travail a montré que l’obtention de MGFs sains à partir de Al2O3 et Ti uniquement est délicate,que ce soit avec un intercalaire sous forme de monocouche ou de multicouche. La forte affinité du titane avec l’oxygène(formation d’oxyde ou en insertion) et le carbone (formant des carbures), ainsi que sa réactivité avec l’alumine (produisantdes intermétalliques) rend le MGF fragile et incapable d’accommoder les contraintes résiduelles d’élaboration. L’insertiond’une faible proportion de nickel (plus ductile et moins réactif vis-à-vis de l’oxygène que le titane) dans les composites apermis d’obtenir des MGFs sains, dont le comportement balistique a pu être évalué<br>The objective is to improve ballistic performance of armors. A perfect armor combines ductility to resistto the impact and high hardness to stop projectile’s fragments. However, such an association of properties is inconsistent witha single material. The solution is to perform a functionally graded material (FGM) with a ductile metal at the back side of thesample and a hard ceramic on the top side. Non-conventional technologies like Spark Plasma Sintering allow joining orsintering all types of materials with different and additional properties. Furthermore, with this technique, high heating ratescan be achieved, limiting grain growth and resulting in a fine microstructure. The goal is to study joining conditions or cosinteringof such materials (in this case, Al2O3 and Ti), as well as the resulting microstructure on the ballistic efficiency.The first part of the study focused on the characterization of alumina and titanium. Five powders of alumina werestudied from a sintering point of view. Three of which were selected because of their interesting microstructures, close indensities and grain sizes. These ceramics have been characterized mechanically (hardness, toughness and strength) andballistically. One of them is adopted to realize FGM. Titanium, sintered with the same conditions, unfortunately, doesn’t haveexpected properties (absence of ductility).The second part of the work showed that the preparation of FGM without cracks from Al2O3 and Ti only ischallenging, with an interlayer with one or more layers. The strong affinity of Ti with oxygen (formation of oxides orinsertion) with C (forming carbides) and its reactivity with alumina (forming intermetallics) make the FGM brittle and enablethe release of residual stresses during the process. By adding a low amount of nickel (more ductile and less reactive withoxygen and titanium) in composites, FGMs almost without cracks were obtained. The latter were evaluated ballistically
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Denoix, Arthur. "Étude et synthèse par chimie douce de nanoparticules de β-Zn4Sb3 pour la réalisation de composants thermoélectriques par des solutions d’impression". Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20192/document.
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L'utilisation de la thermoélectricité passe par une amélioration du rendement du module thermoélectrique à travers l'optimisation de ses dimensions et l'augmentation du facteur de mérite des matériaux thermoélectriques, mais aussi par une réduction des coûts de synthèse et de mise en forme. Dans le cadre de cette thèse nous nous sommes intéressés à la synthèse de β–Zn4Sb3 nanométrique par une méthode de chimie douce à faible dépense énergétique. Nous avons étudié la mise en forme de ce matériau par des technologies d'impression qui permettent d'atteindre les dimensions optimales et présentent un coût réduit. β-Zn4Sb3 est obtenu en deux étapes : une synthèse à reflux suivie d'un traitement thermique à 400°C sous vide secondaire. La composition chimique (DRX, affinement Rietveld), la morphologie (MEB, TEM) et la stabilité en température (spectroscopie Raman) de la poudre sont étudiées. β-Zn4Sb3 ainsi obtenu est densifié par SPS et ses propriétés thermoélectriques sont mesurées montrant une augmentation du facteur de mérite pour des températures inférieures à 100°C. Au dessus de cette température, la présence de porosité et de zinc augmente la résistivité électrique et la conductivité thermique et les échantillons ont un facteur de mérite de 0,6 à 400°C. Enfin, la poudre est mise en forme par sérigraphie et atomisation sur substrat en verre et en Kapton. Le β-Zn4Sb3 montre une forte résistivité électrique juste après impression mais l'application de traitement mécanique et thermique permet de la diminuer. Le facteur de mérite estimé des dépôts est de 0,06 à 400°C. Cependant le faible coût de mise en forme et la possibilité d'automatisation rendent ces techniques viables<br>Use of thermoelectricy involves an increase of the module efficiency. In this purpose we need to optimize the dimension of the module and to increase the figure of merit of thermoelectric materials. But we also need to reduce the synthesis and shaping cost. Within the framework of this thesis, we focused on the synthesis of β-Zn4Sb3 nanoparticles by a low energy technique: wet chemistry. We also studied the shaping of this material by printing technologies. These cost-effective technologies allow reaching optimized dimensions. β-Zn4Sb3 is synthesized in two steps: a reflux synthesis flowed by a thermal treatment at 400 °C under vacuum. Chemical composition (XRD, Rietveld refinement), morphology (SEM, TEM) and thermal stability of the powder are studied. The as product β-Zn4Sb3 is densified by SPS and we measured its properties. They show an increase of the figure of merit for temperatures below 100 °C. However above this temperature the presence of zinc and porosity increase electric resistivity and thermal conductivity, leading to a figure of merit of 0.6 at 400 °C. Finally the powder is shaped by two printing technologies: screenprinting and atomization on glass and Kapton substrate. Just after printing the samples show a high electrical resistivity but a decrease is observed after mechanical and thermal treatment. The estimate figure of merit of printing β-Zn4Sb3 is 0.06 at 400 °C. However the printing techniques are cost-effective and allow mass production, which make them still interesting
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Wollf, Cyprien. "Modélisation du processus thermo-électro-mécanique de frittage flash." Thesis, Metz, 2011. http://www.theses.fr/2011METZ018S/document.
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Le « Frittage Flash » ou « Spark Plasma Sintering (SPS) » est utilisé pour consolider des poudres en des temps relativement courts (quelques minutes). Ce procédé utilise un haut courant continu pulsé (quelques kA), traversant les parties conductrices du système et générant une montée rapide en température induite principalement par effet Joule. L’application d’un chargement mécanique, via des pistons, et d’une rapide montée en température permet d’obtenir une pièce dense sans grossissement excessif des grains. L’objectif de ce travail a été de proposer une simulation numérique thermo-électro-mécanique du procédé « Frittage Flash » sur ABAQUS, afin de suivre in situ les évolutions de température, de porosité et des contraintes difficilement accessibles expérimentalement. Dans ce travail, un modèle de comportement des corps poreux est proposé. Cette approche est basée sur les modèles micromécaniques de la littérature et modifiés de manière heuristique pour reproduire la densification réelle du matériau pour des porosités comprises entre 0 et 50%. Les simulations thermo-électro-mécanique incluant ce modèle, intègrent la dépendance en porosité et température des paramètres matériaux. Quatre cycles d’élaboration de poudre de nickel ont été réalisés avec différentes histoires de température. Les évolutions de la température et de la porosité calculées ont été confrontées avec des résultats expérimentaux. Des analyses post mortem sur des échantillons densifiés confortent la distribution de la température obtenue par le calcul. Ce travail ouvre de nombreuses perspectives, notamment, la possibilité d’optimiser le procédé<br>Nowadays, Spark Plasma Sintering (SPS) is used to consolidate powders in a relative short time (few minutes). This process uses a pulsed high DC electrical current (few kA) which flows through the conductive part of the device and generates large heating rate mainly due to Joule effect. The application of an uniaxial pressure via punches combined with a rapid heating allow the production of near net shape specimen. The thermal electrical mechanical numerical simulation of SPS process is a powerful tool to capture in situ evolutions of temperature, porosity and stresses which are difficult to obtain in experiments. In this work, a new constitutive model is presented for the description of the behavior of porous medium. This model is based on original viscoplastic micromechanical models of the literature and modified in a heuristic manner to better reproduce the real densification of sintered material for porosity in the range [0;0,5]. The model has been implemented in ABAQUS software. A thermal electrical mechanical simulation of SPS is performed where the dependence of material parameters on temperature and porosity is taken into account. Four processing cycles of nickel have been conducted with different temperature histories. Calculated porosity and temperature evolutions are compared to experimental results. Post-mortem analyses of the material (grain size, yield stress) confirm the temperature distribution obtained by numerical simulations in the sample made of nickel. This simulation is seen to be able to capture experimental trends. The work will permit in a near future the optimization of the sintering conditions to reach prescribed properties
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Guillard, François. "Densification des carbures de silicium et de zirconium par un procédé innovant : le spark plasma sintering." Toulouse 3, 2006. http://www.theses.fr/2006TOU30178.
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La recherche de matériaux adaptés à une utilisation dans les réacteurs nucléaires de IVème génération nécessite la recherche de nouvelles voies pour la densification de matériaux tests. Parmi ceux-ci, deux carbures présentent des propriétés, thermiques, mécaniques et de transparence aux neutrons en accord avec le cahier des charges de réacteur du futur, le carbure de silicium et le carbure de zirconium. Les difficultés de les fritter, même à haute température, restent leur principal inconvénient. Le système SPS est une méthode récente de frittage de matériaux, aussi bien métalliques que céramiques ou composites. Ce procédé a été utilisé afin de densifier SiC et ZrC au plus près de leurs densités théoriques. Une base de compréhension des mécanismes de densification par SPS et la réalisation d’échantillons composites a été élaborée. Le mémoire de thèse rapporte ces résultats originaux sur les céramiques SiC et ZrC obtenues à partir de poudres pures sans le moindre additif<br>Materials research for suitable utilization in IVth generation nuclear plants needs new ways to densify testing components. Two carbides, silicon and zirconium carbide seems to be the most suitable choice due to their mechanical, thermal and neutron-transparency properties against next nuclear plant specifications. Nevertheless one main difficulty remains, which is densifying them even at high temperature. Spark Plasma Sintering a new metal-, ceramic- and composite-sintering process has been used to densify both SiC and ZrC. Understanding bases of mass transport mechanisms in SPS have been studied. Composites and interfaces have been processed and analyzed. This manuscript reports original results on SiC and ZrC ceramics sintered with commercial powder started, without additives
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Almansoori, Alaa. "Feasibility study of plasma treatment of clays and polymers for nanocomposite manufacture by laser sintering." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22162/.
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Additive Manufacturing (AM) describes a powerful set of techniques which have the potential to become a reliable method for the manufacture of complex and accurate parts. Laser Sintering (LS) is one of the most promising AM techniques, capable of manufacturing 3-dimensional (3D) products from polymer powders. However, some key challenges still limit their widespread applications. The most common key challenges, specifically for the Laser Sintering AM process are limited availability of different materials, inconsistent or poor mechanical properties and surface quality, each of which is currently still restricting the functions of the end-use parts. In some cases, nanoclay reinforcement of polymers has been shown to provide performance benefits, improving part quality, and offering new applications. However, the dispersion of those nano-sized materials still remains a critical issue for the preparation of Laser Sintering nanocomposites. A novel method of using plasma treatment to tackle these challenges was developed in this study. Plasma treatment was used to increase the surface area of nanoclay particles and with the expectation of simultaneous surface functionalisation aiming for increased homogeneity after dry mixing of polymer and nanoclay powders. SEM images of treated composite powders confirmed this expectation as the plasma treatment reduce agglomerations and improved nanoclay dispersion in the powders. To consolidate these powders into parts a novel methodology, i.e. Downward Heat Sintering (DHS) method was initially used as a powerful replication method for the Laser Sintering technique. DHS process was employed with a hot press to process small quantities of PA12 and dry mixed composite powders into tensile test specimens after optimisation attempts based on differential scanning calorimetry (DSC) and hot-stage microscopy (HSM). SEM images of the heat sintered specimens showed clearly the plasma treatment prevented the aggregation of the nanoclay resulting in an improved elastic modulus of treated composite compared with neat PA12 and untreated composites. Moreover, the reduction in elongation at break for the treated composite was less pronounced than untreated composite. Further work resulted in successfully LS parts with different complex and accurate shapes. No significant deterioration in LS processibility was observed and complex LS parts could be produced when including the plasma treated nanoclay. SEM images of the cross-sections of the fabricated parts that the layer by layer structure were successfully consolidated and relatively uniform. In addition, the introduction of the plasma treated nanoclay was found to improve the elastic modulus of the LS composite parts. Most notably however, a substantially improved surface quality in part’s appearance and microstructure was found as a result of incorporating plasma treated nanoclay compared to the nontreated nanoclay. PA12 exposed to Low Pressure Air Plasma Treatment showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from surface functionalisation and materials removal during the plasma exposure. However, it showed poor melt behaviour under heating conditions typical for Laser Sintering. In contrast, brief Plasma Jet treatments demonstrated similar changes in porosity, but crucially, retained the favourable melt characteristics of PA12 powder. To summarise, this is a unique study on the use of plasma treatment and polymer/polymer nanocomposites in LS applications, demonstrating for the first time that plasma treatment has the potential to provide crucial performance benefits for laser sintered nanocomposites.
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Motsi, Glenda Tsholofelo. "Spark plasma sintering de composites base titane renforcés par des carbures pour applications en tribocorrosion." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30309.
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La faible résistance à l'usure du titane et de ses alliages limite leur application dans laquelle l'effet combiné de l'usure et de la corrosion peut être rencontré. À cet égard, l'ajout de phases céramiques sous forme de whiskers (TiB) ou de particules (TiB2 et TiC) dans une matrice à base de titane pour former des composites avancés à matrice de titane (TMC), peut aider à réduire les pertes de matériau et à prolonger la durée de vie. Dans cette étude, les composites de titane à base de TiB2, TiB et TiC ont été produits par Spark Plasma Sintering (SPS) réactif de titane pur commercial (CP-Ti) et de poudres B4C de différentes tailles de particules. On s'est rendu compte qu'à une température de consigne de 800°C, la réaction avait commencé en raison des avantages du courant pulsé dans le SPS. L'analyse SEM / FIB / TEM sur le matériau fritté à 800°C a montré une phase grise continue, constituée d'amas de particules de B4C partiellement réagies ségrégés aux joints des grains de la matrice Ti. À 1100°C, les réactifs ont complètement réagi et se sont transformés en clusters de divers composés riches en B et C (Ti-B et Ti-C). L'homogénéisation de la microstructure a été obtenue à des temps de séjour de 0 à 30 min pour éliminer les amas formés. Le comportement en corrosion et en tribocorrosion du CP-Ti et des TMC a été étudié dans des solutions 3,5% molaire de NaCl. Les résultats ont montré qu'une quantité croissante des phases de renforcement à 5% en poids réduisait la sensibilité à la corrosion et à la tribocorrosion des TMC frittés à 1100°C, car les valeurs de potentiel en circuit ouvert étaient positivement décalées pour Ti5wt% B4C. De graves dommages à la surface avec des rainures profondes dans CP-Ti ont été observés dans les pistes usées indiquant une usure adhésive. Aucun retrait des phases de renforcement TiB et TiC n'a été observé pour Ti5wt% B4C, en raison de la forte force de liaison interfaciale avec la matrice Ti<br>The poor wear resistance of titanium and its alloys limit their application in which the combined effect of wear and corrosion may be encountered. In this regard, addition of ceramic phases in the form of whiskers (TiB) or particles (TiB2 and TiC) in titanium based matrix to form advanced titanium matrix composites (TMCs), can aid reduce material loss and prolong the service life. In this study TiB2, TiB and TiC based titanium composites were produced by reactive Spark Plasma Sintering (SPS) of commercial pure titanium (CP-Ti) and B4C powders of varying particles sizes. It was realized that at 800°C set-point temperature the reaction had initiated due to the benefits of pulsed current in the SPS. SEM/FIB/TEM analysis on the material sintered at 800°C showed a continuous grey phase, constituted of clusters of partially reacted B4C particles segregated at Ti matrix grain boundaries. While at 1100°C, the reactants completely reacted and transformed into clusters of various compounds high in B and C (Ti-B and Ti-C). Microstructure homogenization was achieved at dwell times of 0-30 min to remove the formed clusters. Corrosion and tribocorrosion behaviour of CP-Ti and TMCs was investigated in solutions 3.5% molar of NaCl. The results showed that increasing amount of the reinforcing phases to 5wt% reduced the corrosion and tribocorrosion susceptibility of the TMCs sintered at 1100°C, as the open circuit potential values were positively shifted for Ti5wt%B4C. Severe surface damage with deep grooves in CP-Ti was observed in worn tracks indicating adhesive wear. No pulling out of TiB and TiC reinforcing phases was observed for Ti5wt%B4C, due to the strong interfacial bond strength with the Ti matrix
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Elango, Rakesh. "Thick binder free electrodes for Li-ion battery using Spark Plasma Sintering and templating approach." Thesis, Amiens, 2018. http://www.theses.fr/2018AMIE0047/document.
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La réalisation du stockage d'énergie et le retour de l'approvisionnement en énergie est crucial pour plusieurs applications (VE, téléphones portables, ordinateurs portables). Des électrodes épaisses avec des matériaux inactifs minimisés dans la batterie globale peuvent améliorer la densité d'énergie des batteries lithium-ion. Spark Plasma Sintering est une technique de densification avancée qui a été utilisée pour préparer des électrodes épaisses en quelques minutes. L'approche de modèle est adoptée pour préparer des électrodes poreuses avec des tailles de pores et des morphologies interconnectées bien contrôlées. Ici, des particules de microsize de chlorure de sodium sont utilisées comme agent de gabarit pour créer des pores à l'intérieur des électrodes épaisses. Ces électrodes frittées sans liant sont auto-supportées, ce qui contribue à augmenter la densité énergétique des batteries lithium-ion. Les performances électrochimiques des batteries demi- et pleines révèlent une capacité surfacique spécifique remarquable (20 mA h cm-2), qui est 4 fois supérieure à celle des électrodes de 100 μm présentes dans les batteries Li-ion classiques (5 mAh cm) -2). L'étude morphologique 3D est réalisée par micro-tomodensitométrie pour obtenir des valeurs de tortuosité et des distributions de tailles de pores conduisant à une forte corrélation avec leurs propriétés électrochimiques. Ces résultats démontrent que le couplage entre le procédé de matriçage de sel et le frittage par plasma d'étincelles est également appliqué pour la fabrication d'électrodes épaisses en utilisant d'autres matériaux actifs et que différentes configurations de cellules sont également proposées<br>The achievement of energy storage and return of energy supply is crucial for several applications (EVs, cellphones, laptops). Thick electrodes with minimized inactive materials in the overall battery can improve the energy density of lithium ion batteries. Spark Plasma Sintering is an advanced densification technique has been used to prepare thick electrodes in minutes. The templating approach is adopted for preparing porous electrodes with interconnected well-controlled pore sizes and morphologies. Here, sodium chloride microsize particles are used as a templating agent to create pores inside the thick electrodes. These sintered binder-free electrodes are self-supported that helps to increase the energy density of lithium ion batteries. The electrochemical performances of half and full batteries reveal a remarkable specific areal capacity (20 mA h cm−2), which is 4 times higher than those of 100 μm thick electrodes present in conventional tape-casted Li–ion batteries (5 mA h cm−2). The 3D morphological study is carried out by micro computed tomography to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results demonstrate that the coupling between the salt templating method and the spark plasma sintering is also applied for thick electrodes fabrication using other active materials and also different cell configurations are proposed
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Delobel, Florimond. "Élaboration de carbure de silicium par Spark Plasma Sintering pour des applications en protection balistique." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2018. http://www.theses.fr/2018ENCM0016.
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Le développement de protections balistiques toujours plus légères et performantes reste un sujet de recherche très actif. Malgré de très hautes performances, la difficulté de mise en forme du SiC conduit généralement à l’utilisation d’aides au frittage en quantité importante, favorisant la formation de phases secondaires pouvant fragiliser le matériau. De plus, les hautes températures de mise en forme induisent la présence de phase α, conférant au matériau des propriétés mécaniques anisotropes et inférieures à celles de la phase cubique β.Dans ces travaux de thèse, l’objectif a été d’élaborer un matériau SiC cubique de très haute pureté, avec une densité de 100% et une stœchiométrie Si/C idéale afin d’optimiser les performances de cette céramique. Deux types de précurseurs ont été envisagés : une poudre commerciale et une poudre issue de la conversion d’un précurseur polymère précéramique.Dans un premier temps, une étude paramétrique de frittage par SPS a permis d’atteindre des densités de 95% pour les 2 précurseurs, tout en conservant la phase cubique seule. Ces résultats, bien qu’encourageants mais n’étant pas suffisants pour l’application visée, l’étude s’est tournée vers l’ajout d’aides au frittage. Des densités de 100% ont ainsi été obtenues sur des échantillons préparés à partir de poudre commerciale, même pour de très faibles teneurs en additif. Un second aspect de ces travaux a permis de mettre en évidence une dépendance de la température de transition β -> α du SiC vis-à-vis de la pression de frittage mais également vis-à-vis du type de précurseur, l’utilisation du précurseur polymère étant plus favorable à la stabilité de la structure cubique. Enfin des mesures de dureté ont été réalisées sur les meilleurs échantillons et ont permis de souligner le rôle prépondérant de la densité sur cette propriété<br>The development of light and high performance ballistic protections is currently a sensitive subject of research. Despite promising mechanical characteristics, the complexity of SiC shaping generally leads to the use of high content of sintering aids, favouring secondary phases formation which could weaken the material. Nevertheless, high sintering temperatures induce the presence of the α form of SiC, conferring to the material anisotropical and lower mechanical properties than the one obtained with the cubic β phase.The goal of this PhD work is the development of high purity cubic SiC, with density close to 100% and perfect Si:C stoichiometry to optimize the performances of this ceramic. Two kinds of precursors were considered: a commercial powder and a powder from the conversion of preceramic polymer precursor.Firstly, the parametric study of SPS sintering allowed to reach densities of 95% for both precursors, while conserving only the cubic phase. These encouraging results being not sufficient, this study switched to the use of sintering aids. Densities close to 100% were thus reached on samples sintered with prepared mixtures from commercial powder, even for very low content of additive. The second subject of this thesis highlighted a dependence of the β -> α transition temperature of SiC as a function of sintering pressure, but also according to the kind of precursor. Indeed, the use of polymer precursor is favourable to cubic structure stability. Then, hardness measurements were performed on the most promising samples and allowed to highlight the major role of density on this property
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Lide, Hunter. "Processing-Structure-Property Relationships of Reactive Spark Plasma Sintered Boron Carbide-Titanium Diboride." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538698/.
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Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their effects on fracture toughness, hardness and flexural strength are shown. Mechanical testing of Vickers hardness, 3-point bend and Chevron notch was done and the microstructural effects on the resulting mechanical properties are investigated.
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Pille, Annika. "Development of optically transparent alumina and spinel ceramics with fine microstructure." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCD026/document.
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Ce travail de thèse porte sur l’élaboration et l’étude des propriétés physiques de céramiques à base d’alumine optiquement transparentes et luminescentes pour lesquelles des applications sont envisagées dans le domaine des matériaux résistants aux rayonnements ionisants. L’enjeu de ce travail a consisté à obtenir un matériau qui présente simultanément une densité élevée et des tailles de grains à l’échelle nanométrique afin de conférer respectivement à la céramique des propriétés de transparence et une résistance aux radiations ionisantes par la capture et la recombinaison des charges induites au niveau des joints de grains.Des céramiques de composition Al2O3 et MgAl2O4 ont été consolidées par Spark Plasma Sintering (SPS) à partir d’alumines ultra-poreuses (UPA) d’une part, et par frittage réactif d’un mélange de précurseur Al2O3 : MgO dans un ratio 1 : 1 d’autre part. Les UPA ont été élaborés par un procédé original mis en place au LSPM. Elles ont ensuite été imprégnées par une solution de nitrate de magnésium puis calcinée à basse température afin d’obtenir le « Précurseur Nanostructuré » (PN) pour la phase spinelle MgAl2O4. Les PNs synthétisés, tout comme les UPA, ont ensuite été consolidées par SPS. Les paramètres de frittage ont été optimisés de manière à obtenir des céramiques possédant les propriétés microstructurales et physiques visées. L’effet de Ta2O5 comme inhibiteur de croissance des grains a été éprouvé sur la microstructure des céramiques élaborées. Les propriétés de transmittance ainsi que de luminescence, avant et après irradiation, des matériaux les plus prometteurs ont été mesurées et corrélées à leurs caractéristiques structurales<br>This thesis deals with the elaboration and study of the physical properties of optically transparent and luminescent alumina-based ceramics for which applications are foreseen in the field of ionizing radiation resistant materials. The challenge of this work was to obtain a material that simultaneously has a high density and grain size at the nanoscale in order to give the ceramic transparency properties and resistance to ionizing radiation by capturing and recombination of induced charges at the grain boundaries. Ceramics of composition Al2O3 and MgAl2O4 were consolidated by Spark Plasma Sintering (SPS) from ultra-porous aluminas (UPA) on the one hand, and by reactive sintering of a mixture of Al2O3: MgO precursor in a ratio of 1 : 1 on the other hand. The UPAs were developed using an original process implemented at the LSPM. They were then impregnated with a solution of magnesium nitrate and then calcined at low temperature to obtain the "Nanostructured Precursor" (NP) for the spinel phase MgAl2O4. The synthesized NPs, like the UPAs, were then consolidated by SPS. The sintering parameters have been optimized to obtain ceramics with the desired microstructural and physical properties. The effect of Ta2O5 as a grain growth inhibitor has been tested on the microstructure of elaborated ceramics. The transmittance and luminescence properties, before and after irradiation, of the most promising materials were measured and correlated with their structural characteristics
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Rubink, William S. "Processing-Structure-Property Relationships of Spark Plasma Sintered Boron Carbide and Titanium Diboride Ceramic Composites." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157631/.
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The aim of this study was to understand the processing – structure – property relationships in spark plasma sintered (SPS) boron carbide (B4C) and B4C-titanium diboride (TiB2) ceramic composites. SPS allowed for consolidation of both B4C and B4C-TiB2 composites without sintering additives, residual phases, e.g., graphite, and excessive grain growth due to long sintering times. A selection of composite compositions in 20% TiB2 feedstock powder increments from 0% to 100%, was sintered at 1900°C for 25 minutes hold time. A homogeneous B4C-TiB2 composite microstructure was determined with excellent distribution of TiB2 phase, while achieving ~99.5% theoretical density. An optimum B4C-23 vol.% TiB2 composite composition with low density of ~3.0 g/cm3 was determined that exhibited ~30-35% increase in hardness, fracture toughness, and flexural bend strength compared to commercial armor-grade B4C. This is a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B4C matrix in compression and TiB2 phase in tension, and c) TiB2 phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB2 serves as a strengthening and toughening agent, and SPS shows promise for the manufacture of hybrid ceramic composites.
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Lide, Hunter. "Processing-Structure-Property Relationships of Reactive Spark Plasma Sintered Boron Carbide-Titanium Diboride Composites." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538698/.
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Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their effects on fracture toughness, hardness and flexural strength are shown. Mechanical testing of Vickers hardness, 3-point bend and Chevron notch was done and the microstructural effects on the resulting mechanical properties are investigated.
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Kinkenon, Douglas. "Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc407776/.
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Monolithic composites are needed that combine low friction and wear, high mechanical hardness, and high fracture toughness. Thin films and coatings are often unable to meet this engineering challenge as they can delaminate and fracture during operation ceasing to provide beneficial properties during service life. Two material systems were synthesized by spark plasma sintering (SPS) and were studied for their ability to meet these criteria. A dual hybrid composite was fabricated and consisted of a nickel matrix for fracture toughness, TiC for hardness and graphite for solid/self‐lubrication. An in‐situ reaction during processing resulted in the formation of TiC from elemental Ti and C powders. The composition was varied to determine its effects on tribological behavior. Stellite 21, a cobalt‐chrome‐molybdenum alloy, was also produced by SPS. Stellite 21 has low stacking fault energy and a hexagonal phase which forms during sliding that both contribute to low interfacial shear and friction. Samples were investigated by x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDS), and electron back‐scattered diffraction (EBSD). Tribological properties were characterized by pin on disc tribometry and wear rates were determined by profilometry and abrasion testing. Solid/self‐lubrication in the TiC/C/Ni system was investigated by Raman and Auger mapping. A tribofilm, which undergoes a stress‐induced phase transformation from polycrystalline graphite to amorphous carbon, was formed during sliding in the TiC/C/Ni system that is responsible for low friction and wear. TiC additions help to further decrease wear. Stellite 21 was also found to exhibit acceptably low friction and wear properties arising from the presence of Cr23C6 in the matrix and work hardening of the cobalt and chromium during sliding.
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Wagner, Amalia Christina [Verfasser], and Harald [Akademischer Betreuer] Hillebrecht. "Direktsynthese dotierter Silicium-Germanium-Mischkristalle mit dem Spark Plasma Sintering-Verfahren, Nährstabsynthese und Einkristallzüchtung mittels Zonenschmelzen." Freiburg : Universität, 2015. http://d-nb.info/1119899133/34.
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Kanakala, Raghunath. "Spark plasma sintering of a structurally amorphous metal (SAM7) with addition of Y₂O₃ with nanoparticles." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1456485.
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Katz, Aurélien. "Élaboration de céramiques polycristallines transparentes Er ³+ : YAG par Spark Plasma Sintering pour applications laser de puissance." Thesis, Valenciennes, 2016. http://www.theses.fr/2016VALE0007.
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Cette étude s’intéresse à l’amélioration des performances du laser solide Er3+:YAG, dont la longueur d’onde de 1,64 µm est dite « eye-safe ». L’une des solutions est le remplacement des monocristaux actuellement utilisés comme milieu amplificateur par des céramiques polycristallines Er:YAG transparentes, dont les propriétés thermomécaniques remarquables permettent une meilleure cohérence du faisceau de sortie et de ce fait, une augmentation des performances du laser. Cependant, la réunion des différents critères requis pour obtenir la transparence reste un réel challenge dans l’élaboration de ces céramiques. L’utilisation de poudres commerciales issues de deux voies de synthèse différentes a permis de souligner le rôle primordial des caractéristiques physiques de la poudre sur le comportement à la compaction et au frittage, effectué par Spark Plasma Sintering, tandis que la composition phasique et la pureté chimique conditionnent la qualité optique finale. Il ressort également que la coloration de la céramique observée lors du frittage résulte, non pas d’une contamination au carbone, mais de la formation de lacunes d’oxygène. Enfin, l’analyse et la compréhension du mode d’action du LiF utilisé comme aide au frittage ont permis d’établir des mécanismes réactionnels permettant d’optimiser le cycle de frittage. Cette démarche a conduit à l’obtention de céramiques polycristallines transparentes (Ø = 30 mm, e = 3 mm) à qualité optique élevée avec des valeurs de transmission de 80 % à 400 nm et 84 % à 1100 nm. Sur la base de ces résultats et de la simulation numérique, un changement d’échelle des céramiques (Ø = 50 mm, e = 5 mm) a été effectué dans le but de les évaluer en cavité laser<br>This work focus on the improvement of the solid state Er3+:YAG laser performances presenting an "eye-safe" wavelength at 1.64 µm. One way is the replacement of single crystals currently used as gain media by polycrystalline ceramics as they present improved thermo-mechanical properties allowing a longer use of the laser. However, the meeting of different criteria requested to get transparency remains a challenge in the development of these ceramics. The use of commercial powders produced by two different synthesis ways allowed to highlight the essential role of the physico-chemical characteristics of the powder on compaction and sintering behaviors, performed by Spark Plasma Sintering, Phase composition and chemical purity have an influence of the final optical quality. It was also figured out that the gray coloration of the ceramic observed after sintering is caused by the formation of oxygen vacancies, rather than a carbon contamination. Finally, the mode of action of LiF, used as sintering aid to increase optical transmittance, was studied in order to establish reaction mechanisms allowing an optimization of the SPS cycle. This approach helps to reach Er3+:YAG transparent polycrystalline ceramics (Ø = 30 mm, thk = 3 mm) with an optical transmittance of 80 at 400 nm and 84 % at 1100 nm. On the basis of these results and with the help of numerical simulation, an up-scaling of ceramics (Ø = 50 mm, thk = 5 mm) was undertaken in order to evaluate their laser performances through laser cavity tests
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Neff, Paul K., and Paul K. Neff. "Development of an Experimentally Validated Finite Element Model for Spark Plasma Sintering of High Temperature Ceramics." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/620665.
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Spark plasma sintering (SPS) is a powder consolidation technique used to rapidly densify a variety of material systems. SPS is capable of precisely controlling material microstructures and achieving non-equilibrium phases due to rapid heating and cooling rates through the simultaneous application of pressure and direct current. Due to these characteristics, SPS is an ideal processing technique for high temperature ceramics which require processing at temperatures greater than 1500°C. Due to the desirable properties obtained on small diameter materials processed by SPS, larger and more complex geometries are desired while maintaining sample microstructures. In order to accurately scale ceramics produced by SPS, a finite element model must be developed that can be used as a predictive tool. My research focuses on developing a finite element model for the spark plasma sintering furnace at the University of Arizona and validating modeled results using experimentally obtained data. Electrical and thermal conductivity as functions of temperature vary widely among different grades of commercially available electrode grade graphite at constant density. Modeled material properties are optimized in order to calibrate modeled results to experimentally obtained data (i.e. measured current, voltage, and temperature distributions). Sensitivity analysis is performed on the model to better understand model physics and predictions. A calibrated model is presented for 20mm ZrB2 and Si3N4 discs. Sample temperature gradients are experimentally confirmed using grain size and β-Si3N4 phase composition. The model is used to investigate scale up from 20mm to 30mm discs and 30mm rings as well as effects of processing conditions on β-Si3N4 content.
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Shinozaki, Maya. "The effect of sintering and CMAS on the stability of plasma-sprayed zirconia thermal barrier coatings." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244944.
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State of the art thermal barrier coatings (TBCs) for gas turbine applications comprise (7 wt.%) yttria partially stabilized zirconia (7YSZ). 7YSZ offers a range of attractive functional properties – low thermal conductivity, high thermal expansion coefficient and high in-plane strain tolerance. However, as turbine entry temperatures are raised, the performance of 7YSZ coatings will be increasingly affected by sintering and environmental contamination, by calcia-magnesia-alumina-silica (CMAS) deposits. The effect of sintering-induced stiffening on the driving force for spallation of plasma-sprayed (PS) TBCs was investigated. Spallation lifetimes of TBC specimens sprayed onto alumina substrates were measured. A simple fracture mechanics approach was employed in order to deduce a value for the strain energy release rate. The critical strain energy release rate was found to be constant, and if this value had been known beforehand, then the rationale presented here could be used for prediction of coating lifetime. The effect of vermiculite (VM) and volcanic ash (VA) contamination on the sintering-induced spallation lifetime of PS TBCs was also investigated. The presence of both VM and VA was found to accelerate the rise in their Young’s modulus with sintering. Spallation results show that coating lifetime may be significantly reduced, even at relative low addition levels, due to the loss of strain tolerance caused by the penetration of glassy deposits. This result gives a clear insight into the role CMAS plays in destabilizing TBCs. Finally, the adhesion characteristics of ingested volcanic ash were studied using a small jet engine. The effects of engine speed and particle size were investigated. Deposition on turbine surfaces was assessed using a borescope. Deposition mainly occurred on the nozzle guide vane and blade platform. A numerical model was used to predict particle acceleration and heating in flight. It was observed that larger particles are more likely to adhere because they have greater inertia, and thus are more likely to impact surfaces. The temperature of the larger particles at the end of its flight was predicted to be below its softening point. However, since the component surface temperatures are expected to be hotter, adhesion of such particles is probable, by softening/melting straight after impact.