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.

No description available.

[pt] Esta dissertação pretendeu compreender de que forma a sociedade civil participou na formulação de estratégias e de controle da execução da política de Assistência Social na cidade do Rio de Janeiro. Sobretudo, compreender as formas e os mecanismos pelos quais os conselheiros eleitos, representantes da sociedade civil para a gestão 2013-2015, inscreveram seus projetos políticos no seio do aparelho de Estado através da representação das suas entidades, entendidas neste estudo como aparelhos privados de hegemonia. Neste contexto, buscou-se: a) identificar quais temas e situações foram analisados na gestão 2013- 2015 do CMAS/RJ; b) conhecer as formas e os mecanismos pelos quais os conselheiros civis inscreveram seus projetos através da representação das suas entidades; c) entender como os consensos foram construídos e d) até que ponto os projetos dos conselheiros civis estavam alinhados com as diretrizes do Sistema Único de Assistência Social (SUAS). Para o desenvolvimento do estudo foram utilizados conceitos gramscianos, tais como sociedade civil, intelectuais orgânicos, entre outros Os procedimentos metodológicos adotados incluíram, além da realização da pesquisa bibliográfica que forneceu informações aproximativas sobre o recorte da temática em questão, a análise documental, realizada a partir dos documentos coletados no campo, isto é, de 41 atas, 175 resoluções e 4 relatórios elaborados na gestão analisada, os quais foram posteriormente examinados a partir do seu conteúdo temático. Também foram realizadas 12 entrevistas semiestruturadas, as quais permitiram um contato mais íntimo com os sujeitos da pesquisa. Essa etapa proporcionou uma melhor compreensão não só sobre o material coletado, mas, em especial, sobre a reconstituição da criação do CMAS/RJ, pois alguns desses entrevistados já estavam nesse espaço há bastante tempo. Os dados obtidos e as análises empreendidas levam à constatação de que o CMAS/RJ se encontra numa posição periférica em relação aos processos que envolvem decisões propositivas para a política de assistência social em decorrência do caráter extremamente autorreferenciado e cartorial. Pode-se também identificar uma tendência conscienciosa e colaborativa entre os conselheiros titulares e suplentes civis e governamentais, além de identificada uma dinâmica boca-a-boca para a reprodução e perpetuação do establishment realizada pelos conselheiros que, em sua grande maioria, mais de 90 por cento, são assistentes socais. O que está em disputa na agenda do Conselho é a interdependência entre o público e o privado na prestação dos serviços socioassistenciais. Dessa maneira, o estudo revela o quanto a Política Nacional de Assistência Social (PNAS) não rompeu e nem superou a relação público-privado, mas a resinificou na história da assistência social no Brasil. O grande desafio esteve em pensar o CMAS/RJ tendo em conta suas tensões, contradições, limites e possibilidades sem, contudo, reiterar um discurso fatalista que configura este local como o da barganha, da cooptação e da luta por interesses corporativos ou tomando como o único espaço possível para a materialização da democracia e de exclusivo meio para avaliação e proposição das políticas de assistência social no município. / [en] It was intended to understand how civil society participated in the formulation of strategies and control of the implementation of Social Assistance policy in the municipality of Rio de Janeiro and, above all, to understand the forms and mechanisms by which elected councilors, representatives of civil society in the 2013-2015 administration inscribed their political projects within the State apparatus through the representation of their entities, understood in this study as private hegemony devices. In this context, we was sought to: a) identify which themes and situations were analyzed in the 2013-2015 administration of the CMAS / RJ; b) know the forms and the mechanisms by which the civil councilors inscribed their projects through the representation of their entities; c) to understand how consensus was built; and d) to know the extent to which the civil counselors projects were aligned with the guidelines of the Single Social Assistance System (SUAS). For the development of the study Gramscian concepts such as civil society, organic intellectuals, among others, were used besides the accomplishment of bibliographical research that provided approximate information on the cut of the subject in question. The research also had documentary analysis collected in the field, that is, of 41 minutes, 175 resolutions and 4 reports elaborated in the analyzed management, which were later examined from the thematic content. There were also 12 semi-structured interviews, which allowed a more intimate contact with the research subjects. This step provided a better understanding not only of the material collected, but especially about the reconstitution of the creation of CMAS/RJ, since some of those interviewees had been in this space for a long time. The data obtained and the analyzes undertaken lead to the realization that the CMAS/RJ is in a peripheral position in relation to the processes involving propositive decisions for social assistance policy due to the extremely self-referential and cartorial character. It is also possible to identify a conscientious and collaborative trend among the civil and government board members and deputies, as well as to identify a dynamic word of mouth for the reproduction and perpetuation of the establishment by the councilors, who more of 90 percent, are social workers. What is in dispute on the Council s agenda is the interdependence between the public and the private in the provision of social assistance services. In this way, the study reveals how the National Social Assistance Policy (PNAS) did not break and did not overcome the public-private relationship, but it has resignified it in the history of social assistance in Brazil. The main challenge was to think about CMAS/RJ, taking into account its tensions, contradictions, limits and possibilities, without reiterating a fatalistic discourse that configures this place as that of bargaining, cooptation and the struggle for corporate interests or taking as the the only possible space for the materialization of democracy and the exclusive means for evaluating and proposing social assistance policies in the municipality.

The durability of Thermal Barrier Coatings (TBCs) used on the turbine blades of aircraft and power generation engines has been known to be affected by sand particle ingression comprised of Calcium-Magnesium-Alumina-Silicate (CMAS). Previous studies have shown that these effects present themselves through variations in the thermomechanical and thermochemical properties of the coating. This study investigated the impact of CMAS ingression on the Yttria Stabilized Zirconia Topcoat (YSZ) and Thermally Grown Oxide (TGO) strain in sprayed Thermal Barrier Coating (TBC) samples of varying porosity with and without CMAS ingression. In-Situ Synchrotron X-ray Diffraction measurements were taken on the sample under thermal loading conditions from which the YSZ and TGO peaks were identified and biaxial strain calculations were determined at high temperature. Quantitative strain results are presented for the YSZ and TGO during a thermal cycle. In-plane strain results for YSZ near the TGO interface for a complete thermal cycle are presented, for a 6% porous superdense sample with CMAS infiltration. The outcomes from this study can be used to understand the role of CMAS on the strain tolerance of the TBC coating. It is well known that under engine operational conditions the development of the TGO layer, with large critical stresses, has been linked to failure of the coating. The growth of the TGO manifests as undulations in a series of peaks and troughs. Understanding the mechanics of the oxide layer at these locations provides significant information with respect to the failure mechanisms of the TBC coating. This study investigated the stress at the peak and trough of a TGO undulation for a cycled Dense Vertically Cracked (DVC) plasma sprayed TBC sample through photo-luminescence (PL) spectroscopy. High resolution nanoscale stress maps were taken nondestructively in the undulation of the TGO. Preliminary results from first line mapping of TGO peak and trough scan, at a resolution of 200 nm, have shown a non-uniform TGO stress variation. The results obtained from this study can be used to understand the stress variation in the peak and trough of a DVC sample's TGO undulation and how it contributes to the life of the TBC coating.

Les alliages métalliques complexes sont des matériaux qui présentent un ordre à longue distance caractérisé par de grandes mailles comprenant plusieurs centaines d’atomes disposés en clusters. Une propriété caractéristique des CMAs est une conductivité thermique de réseau, dû aux phonons, très faible (~1.3 W/m.K), ce qui donne un intérêt pour leur utilisation comme thermoélectriques. Malgré de récentes avancées sur les connaissances de leurs structures, la nature des modes de vibrations des phonons dans ces réseaux restent une question ouverte : quel est le rôle des clusters ? Est-ce qu’il y a des modes critiques ? Pour répondre à cette problématique, mon projet de thèse a eu pour objectif de comprendre la nature des modes de vibrations à l’échelle atomique et la relation avec la conductivité thermique de réseau sur deux systèmes : la phase o-Al13Co4 qui est un approximant de la phase décagonale AlNiCo et le clathrate Ba8Ge40.3Au5.25, présentant des propriétés thermoélectriques. Mes investigations combinent des expériences de diffusion inélastiques des neutrons et des rayons-X et des simulations à l’échelle atomique.Une analyse détaillée des résultats expérimentaux obtenus par diffusion inélastique sur monocristaux pour les branches acoustiques a permis de mettre en évidence, pour la première fois, un temps de vie fini des phonons acoustiques lorsqu’ils interagissent avec les modes de basses énergies liés aux atomes dans les clusters. Pour les deux systèmes étudiés, nous observons que la branche acoustique n’est plus linéaire et le temps de vie des phonons acoustiques est réduit à quelques picosecondes. Ce faible temps de vie dépend peu de la température comme la conductivité thermique. Les simulations à l’échelle atomique, en utilisant des calculs DFT et des potentiels de pairs oscillants pour des simulations de dynamique moléculaire, ont permis de montrer que ce temps de vie est un effet anharmonique lié au désordre de structure. Les simulations confirment la faible dépendance en température de ce temps de vie. Dans o-Al13Co4, nous avons calculé la conductivité thermique avec la dynamique moléculaire et la méthode de Green-Kubo. Pour Ba8Ge40.3Au5.25 nous avons appliqué un modèle phénoménologique pour l’estimer en utilisant les résultats INS. En conclusion nous démontrons les effets de la complexité structurale sur la conductivité thermique en lien avec la dynamique de réseau. / Complex metallic alloys are long range ordered materials, characterized by large cells, comprising several hundreds of atoms and cluster building blocks. A key property of CMAs is the low lattice thermal conductivity (1.3 W/m. K), which suggests a potential application for CMAs for thermoelectricity. Despite recent advances structure determination, the nature of the phonons modes remains an open question: do the clusters playing a role? Are there critical modes? To tackle this problem, my PhD project aims to understand the vibrational modes at atomic scale and the relation to lattice thermal conductivity in o-Al13Co4 which is an approximant of the quasicrystal, decagonal phase AlNiCo and the clathrate Ba8Ge40.3Au5.25. In this worked we have used Inelastic Neutron and X-ray Scattering experiments and atomic scale simulations, based on density functional theory and empirical pair potentials.A detailed analysis of the results of inelastic scattering experiments on monocrystals for the acoustic branches have shown, for the first time, a finite lifetime for acoustic phonons when they interact with the low-lying dispersion-less excitations due to atoms in the cluster. In both systems, we observe that when an acoustic branch flattens near the zone boundary, the phonon lifetime is a few picoseconds. The phonon lifetime is approximately independent of temperature like the lattice thermal conductivity. Lattice and molecular dynamics simulations with DFT and empirical, oscillating pair potentials show that the finite phonon lifetime is an anharmonic effect, due to structural disorder, explaining the weak temperature of the phonon lifetime. For o-Al13Co4, we have calculated the thermal conductivity with the Green-Kubo method based on equilibrium MD simulations. For Ba8Ge40.3Au5.25 we have developed a phenomenological model based on individual phonon modes. In conclusion, we have demonstrated how structural complexity affects thermal conductivity through the lattice dynamics.