Combustion gas turbine components designed for application in power generation equipment are subject to periodic replacement as a result of cracking, damage, and mechanical property degeneration that render them unsafe for continued operation. In view of the significant costs associated with inspecting, servicing, and replacing damaged components, there has been much interest in developing models that not only predict service life, but also estimate the evolved state of the material. This thesis explains manifestations of microstructural damage mechanisms that facilitate fatigue crack nucleation in directionally-solidified (DS) Ni-base superalloy components exposed to elevated temperatures and high stresses. In this study, models were developed and validated for damage and life prediction using DS GTD-111 as the subject material. This material has a chemical composition and grain structure designed to withstand creep damage occurring in blades of gas-powered turbines. The service conditions in these components, which generally exceed 600C, facilitate the onset of one or more damage mechanisms related to fatigue, creep, or environment. The study was divided into an empirical phase, which consisted of experimentally simulating service conditions in fatigue specimens, and a modeling phase, which entailed numerically simulating the stress-strain response of the material. Tests have been carried out to simulate a variety of thermal, mechanical, and environmental operating conditions endured by longitudinally (L) and transversely (T) oriented DS GTD-111. In some cases, tests in extreme environments/temperatures were needed to isolate one or at most two of the mechanisms causing damage. Microstructural examinations were carried out via microscopy. A continuum crystal plasticity model was used to simulate the material behavior in the L and T orientations. The constitutive model was implemented in ABAQUS and a parameter estimation scheme was developed to obtain the material constants. A physically-based model was developed for correlating crack initiation life based on the experimental life data. Assuming a unique relationship between the damage fraction and cycle fraction with respect to cycles to crack initiation for each damage mode, total crack initiation life has been represented in terms of the individual damage components observed at the end state of crack initiation.

The A-cluster active site in acetyl coA synthase exploits a Ni(CGC)2- metallopeptide as a bidentate ligand to chelate the catalytically active square-planar nickel center used to produce acetyl coA. As Nature utilizes polypeptides to isolate and stabilize the active sites, we have set out to immobilize biomimetic complexes to polyethylene-glycol (PEG) rich polystyrene polymer beads (TentaGel). The PEG rich resin-beads serve to imitate the peptidic superstructure of enzyme active sites as well as to protect the resin-bound models from O2 decomposition. As a model of the NiN2S2 ligand observed in the A-cluster of acetyl coA synthase, the CGC tripeptide was constructed on resins using Merrifield solid phase peptide synthesis and then metallated with NiII to produce bright orange beads. Derivatization with M(CO)x (M = Rh, W) provided qualitative identification of Ο-Ni(CGC)M(CO)x n- via ATR-FTIR. Additionally, Neutron Activation Analysis (NAA) and UV-vis studies have determined the concentration of Ni and CGC, and qualitatively identify Ο-Ni(CGC)2-. Furthermore, infrared studies and NAA experiments have been used to identify and quantify Ο- Ni(CGC)Rh(CO)2 1-. The S-based reactivity of Ni(ema)2-, a good model of Ni(CGC)2-, toward oxygenation and alkylation has been pursued and compared to neutral NiN2S2 complexes. The spectroscopic, electrochemical and structural effects of these modifications will be discussed and supported using DFT computations and electrostatic potential maps of the resulting Ni(ema)*O2 2- and Ni(ema)*(CH2)3 complexes. Having firmly established the synthesis, characterization and reactivity of NiN2S2 2- systems in solution and resin-bound, CuIIN2S2 analogues were explored. The synthesis and identification of solution complexes, Cu(ema)2-, Cu(emi)2-, and Cu(CGC)2- via UV-Vis, EPR, and –ESI-MS will be discussed in addition to their S-based reactivity with Rh(CO)2 + . Furthermore, the resin-bound Cu(CGC)2- complex has been produced and characterized by EPR and its Rh(CO)2 adduct identified by ATR-FTIR and compared to the analogous NiN2S2 2- systems. As the active site of [FeFe] Hydrogenase utilizes a unique peptide-bound propane dithiolate bridge to support the FeFe organometallic unit, [FeFe]Hydrogenase models have been covalently anchored to the resin-beads via similar carboxylic acid functionalities. The characterization (ATR-FTIR, EPR, Neutron Activation Analysis), stability and reactivity of the immobilized models complexes are discussed as well as work toward establishing the microenvironment of resin-bound complexes.

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The Garson Ni-Cu-PGE deposit is located on the South Range of the 1850 Ma Sudbury structure along the contact between the Sudbury Igneous Complex (SIC) and the underlying metasedimentary and metavolcanic rocks of the Paleoproterozoic Huronian Supergroup. It comprises four ore bodies that are hosted by E-W-trending shear zones that dip steeply to the south. The shear zones formed as south-directed D1 thrusts in response to flexural-slip during regional buckling of the SIC. They imbricated the ore zones, the SIC norite, the underlying Huronian rocks and they emplaced slivers of Huronian rocks and anatectic breccia into the overlying Main Mass norite. Coexisting garnet-amphibole pairs yielded syn-D1 amphibolite facies metamorphic temperatures ranging from ~550°C to 590°C. The shear zones were coeval with the moderately southdipping South Range and Thayer Lindsley shear zones, which formed to accommodate the strain in the hinge zone as the SIC tightened with progressive D1 shortening. The SE limb of the SIC was overturned together with the D1 thrusts, which were then reactivated as steeply south-dipping reverse shear zones during syn-D2 greenschist metamorphism. Syn-D2 metamorphic titanite yield a U-Pb age of ca. 1849 ± 6 Ma, suggesting that D1 and D2 are part of a single progressive deformation event that occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to the colinear L1 and L2 stretching mineral lineations. Ore types consist mainly of pyrrhotite-pentlandite-chalcopyrite breccia ores, but also include pyrrhotite-pentlandite-chalcopyrite disseminated sulfide mineralization in norite, and syn-D2 quartz-calcite-chalcopyrite-pyrrhotite-pentlandite iv veins. In the breccia ores, matrix sulfides surround silicate rock fragments that have a strong shape-preferred orientation defining a pervasive foliation. The fragments are highly stretched parallel to the mineral lineations in wall rocks, suggesting that the ore bodies are zones of high strain. Pyrrhotite and chalcopyrite occur in piercement structures, in boudin necks between fragments, in fractures in wall rocks and in fold hinges, suggesting that the sulfides were mobilized by ductile plastic flow. Despite evidence of high strain in the ore zones, the sulfide matrix in D1 and D2 breccia ores show little evidence of strain as they consist predominantly of polygonal pyrrhotite aggregates, suggesting that they recrystallized during, or immediately after D1 and D2. However, rare elongate pyrrhotite grains aligned parallel to S2 are locally preserved only in D2 breccia ores. Exsolution of pentlandite loops along grain boundaries of elongate pyrrhotite formed S2-parallel pentlandite-rich layers in D2 breccia ores, whereas the pentlandite loops are multi-oriented in D1 contact breccia as they were exsolved along grain boundaries polygonal pyrrhotite. Because exsolution of pentlandite post-date D1 and D2, and that individual pentlandite grains neither have a shape-preferred orientation nor show evidence for cataclastic flow, the sulfides reverted to, and were mobilized as a homogeneous metamorphic monosulfide solid solution (mss) during D1 and possibly D2. This is in agreement with predictions from phase equilibria as the average Garson composition plots within the mss field in Fe-Ni-S ternary diagram at temperatures above ~400°C. Disseminated and breccia ores at Garson have similar mantle-normalized multi-element chalcophile patterns as undeformed contact-type disseminated and massive ore, v respectively, at the well known Creighton mine in the South Range. This suggests that the Garson ores are magmatic in origin and that their compositions were not significantly altered by hydrothermal fluids and deformation. The lack of variations in Ni tenors between the disseminated and breccias ores suggest that the R-factor was not the process controlling metal tenors because the disseminated sulfides do not consistently have higher metal tenors than the breccia ore. The breccia ores are enriched in Rh-Ru-Ir and are depleted in Cu-Pd-Pt-Au, in contrast to footwall-type ore at the nearby Garson Ramp mine which is enriched in the same metals. When Ni100, Rh100, Ir100, Pt100 and Pd100 are plotted against Cu100, the breccia and footwall-type ore analyses plot along model mss fractionation and sulfide melt model curves, suggesting that these two ore types are related by mss fractionation. In summary, the Garson breccia ores are mss cumulates that settled quickly at the base of the SIC via a gravity filtration process, and were mobilized as a metamorphic mss by ductile plastic flow during D1 and D2. Despite minor local hydrothermal mobilization of some metals, the study confirms findings from other studies that highly deformed Ni-Cu- PGE deposits, such as the Garson deposit, can provide important information on the genesis of the deposits.

Metal carbides have attracted much attention over the past several years due to their unique qualities. The purpose of this research is to develop a cermet that demonstrates desired properties of nano-size titanium carbide (TiC) and copper-nickel (Cu-Ni) metals. In this study stoichiometric, nano-size TiC was synthesized through a patented carbothermal synthesis process (U.S. Patent No.: 5,417,952). The resulting TiC was sintered with varying copper (12.5-37.5wt %) and nickel (12.5-25wt %) contents. Hardness, fracture toughness, and microscopy studies were performed. Average hardness ranging between 325-1292 HV were found, with copper content showing a strongly negative correlation with hardness. Fracture toughness values were found to be between 4.85-14.36 Mpa*m^.5; TiC content had a nearly linear, negative correlation with fracture toughness. Samples with high copper to nickel ratios showed poor homogeneity and wetting.

Une SOFC peut être alimentée en biogaz sans reformage préliminaire du fait de sa température de fonctionnement élevée. Cependant, la présence de polluants comme le soufre peut empoisonner les électrodes. Cette thèse se concentre sur la compréhension des effets de H2S sur la structure de l'anode et les performances électriques. Spectroscopie Raman, imagerie optique et spectroscopie d'impédance ont été utilisées in situ pour évaluer la cinétique de sulfuration et les modifications morphologiques de Ni et Ni-CGO en présence de H2S à différentes températures. Les performances électriques de Ni-YSZ/YSZ/Pt ont été mesurées à 500°C à l'abandon et sous polarisation (500 mV). Un circuit électrique avec une impédance de concentration du second ordre est proposé. Les caractéristiques de l'anode avec combustibles propre et pollué sont discutées à partir des formes et des décompositions des spectres. Les corrélations entre propriétés électriques et accumulation de sulfure de nickel sont présentées. / A Solid Oxide Fuel Cell (SOFC) can be fed with biogas without a preliminary reforming due to its high operating temperature. However, the biogas contains numerous pollutants like sulfur which poison the electrodes. This thesis focuses on the understanding of the H2S impacts on the anode structure and electrical performances. Raman Spectroscopy, optical imagery and Impedance Spectroscopy have been used in situ to evaluate the sulfidation kinetics and the morphological changes of Ni and Ni-CGO pellets exposed to H2S at various temperatures. The electrical performances of Ni-YSZ/YSZ/Pt cells under open circuit and 500 mV-polarizing conditions at 500°C have been measured. An electrical circuit with a second-order concentration impedance is proposed. The anode behaviors in clean and polluted fuel are discussed based on the evolutions of impedance shapes and on the fitted parameters. Correlations between the electrical properties and the build-up of nickel sulfide are presented.

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-10Bitstream added on 2014-06-13T20:07:39Z : No. of bitstreams: 1 cascadan_d_me_bauru.pdf: 1660084 bytes, checksum: f1924a7f3bbd4a75d15f8d6ec924a8c6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Dentre os materiais avançados que a Ciência e Engenharia de Materiais vêm desenvolvendo estão os biomateriais. Há muito, estes são utilizados para reparar partes do corpo danificadas ou deterioradas, mas em função da enorme complexidade dos tecidos vidos e do organismo como um todo, é comum ocorrerem falhas a curto ou longo prazo. No entando, a demanda por esses materiais tende a aumentar, justificando a importância de mais pesquisas nesta área. Existem muitos dispositivos médicos e odontológicos confeccionados com a liga Ti-Ni em função de suas propriedades de memória de forma, superelasticidade e biocompatibilidade. No entando, o elemento níquel é muito tóxico em níveis elevados. A liga Ti-5Ni é o objeto deste estudo e foi preparada a partir da fusão dos metais precursores, tratada térmica e mecanicamente, além de ser dopada com oxigênio. Em cada condição, foi caracterizada em termos de sua composição química, densidade, difração de raios X e microscopia óptica. Também foram analisadas propriedades como microdureza, módulo de elasticidade e biocompatibilidade. As micrografias mostraram que a microestrutura das amostras são dependentes dos tratamentos térmicos e que propriedades tais como microdureza e módulo de elasticidade sofrem variações de acordo com a microestrutura e quantidade de oxigênio. O refinamento pelo método de Rietveld permitiu averiguar as variações nos parâmetros de rede com a inserção de níquel e oxigênio ao titânio. Foram obtidos resultados satisfatórios nos testes de biocompatibilidade, concluindo que a liga apresenta bom potenciala como biomaterial / Among the advanced materials that are developing by science and materials and materials engineering are the biomaterials. There are a lot, these are used to repair damaged or deteriored parts of the body, but in the function of the enormous complexity of living tissue and organism as a whole, are common failures in the short or long term. However, the demand for these materials tends to increase, justifying the importance of further research in this area. There are many medical and dental devices made with Ti-Ni alloy due to its properties of shape memory, supereslaticity and biocompatibility. However, the nickel element is very toxic at high levels. Ti-5Ni alloy is the object of this study and was prepared from arc-melting and heat mechanically treated, besides being doped with oxygen. In each condition, it was characterized in terms of its chemical composition, density, x-ray diffraction and optical microscopy. Were also examined properties such as microhardness, elasticity modulus and biocompatibility. The micrographies showed that the microstructure of samples is dependent on the heat treatment and properties such as microhardness and elasticity modulus suffer variations according to the microstructure and oxygen amount. Refinement by Rietveld method allowed investigating changes in lattice parameters with the addition of nickel and oxygen to titanium. Satisfactory results were obtained in biocompatibility tests, concluding that the alloy presents good potential as a biomaterial

Made available in DSpace on 2018-08-01T21:58:45Z (GMT). No. of bitstreams: 1 tese_10233_Thamyres Fernandes Messa Moreira20170116-145305.pdf: 3284740 bytes, checksum: ab4ac23a7af942990086e3906900baec (MD5) Previous issue date: 2016-08-18 / A reciclagem de baterias Ni-Cd exauridas é importante por razões ambientais, cientificas e econômicas podendo ser realizada, principalmente, por processos pirometalurgicos e hidrometalurgicos. Neste trabalho, foram desenvolvidas rotas hidrometalurgicas para a reciclagem dos eletrodos positivos e negativos de baterias Ni-Cd. O eletrodo negativo foi lixiviado com ácido sulfúrico (H2SO4) 0,50 mol L-1 e o eletrodo positivo em ácido cítrico (C6H8O7) 0,50 mol L-1 . O objetivo do trabalho foi a síntese e caracterização de filmes de cádmio metálico, óxido de cádmio e óxido de níquel, cádmio, cobalto e ferro. Os óxidos foram aplicados em processos de fotocatalíticos. Os filmes de cádmio metálico foram formados com auxilio da técnica galvanostática sob as condições: densidade de corrente de -28 mA cm-² e densidade de carga variando em 11,4 C cm-2 e 28,4 C cm-2, densidade de corrente de -56 mA cm-2 e densidade de carga de 11,4 C cm-2 e 28,4 C cm-2. A eficiência máxima de deposição de cádmio alcançou 84,87% e a reação de evolução de hidrogênio no sistema ocorre simultaneamente a redução do cádmio. Realizou-se a síntese do óxido de cádmio (CdO) a partir do tratamento térmico do precursor de carbonato de cádmio (CdCO3). O CdO obtido tem tamanho médio de cristalito de 22,21 nm e foi caracterizado por espectroscopia de Infravermelho (IV-TF), difração de raios X (DRX) e microscopia eletrônica de transmissão (MET). O óxido metálico sintetizado por método sol-gel apresentou composição mista contendo óxido de níquel (NiO), CdO, óxido de cobalto (Co3O4) e óxido de Ferro (Fe2O3) sendo denominado de NiO/CdO/Co3O4/Fe2O3 e caracterizado por IV-TF, DRX, MEV, espectroscopia de raios X por dispersão em energia (EDX), microscopia eletrônica de transmissão (MET) e espectrometria de emissão ótica com plasma indutivamente acoplado (ICP OES). Os óxidos sintetizados foram aplicados no processo de degradação do corante têxtil Preto Reativo V-2B. Os óxidos CdO e NiO/CdO/Co3O4/Fe2O3 apresentaram comportamento catalítico e a eficiência de degradação não depende do pH. A maior eficiência de degradação do corante obtida para o CdO foi de 67,10% e para o NiO/CdO/Co3O4/Fe2O3 de 86,30% após 480 minutos de análise

Made available in DSpace on 2018-08-01T21:58:49Z (GMT). No. of bitstreams: 1 tese_12206_Luma Barbosa Magnago.pdf: 1956140 bytes, checksum: 16d722634803eabf0f76fd98302d22f7 (MD5) Previous issue date: 2018-03-16 / Neste trabalho, o método de co-precipitação foi utilizado para a síntese de ferritas não dopadas (Fe2O3/Fe3O4-R) e dopadas com níquel a partir de reagentes comerciais (NiFe2O4-R) e a partir do níquel reciclado de baterias de níquel hidreto-metálico (Ni-MH) exauridas (NiFe2O4-B). A estrutura e composição das ferritas foi confirmada por difratometria de raios X (DRX), espectroscopia dispersiva de raios X (EDX) e espectrometria com plasma indutivamente acoplado (ICP OES). A microscopia eletrônica de varredura (MEV) mostrou que as ferritas são formadas por partículas aglomeradas de diferentes tamanhos e formatos e a microscopia eletrônica de transmissão (MET) revelou partículas esféricas de 50 nm, aproximadamente. Ferritas são materiais multifuncionais que podem ser utilizados como catalisadores e pseudocapacitores. A propriedade catalítica das ferritas foi analisada através da descoloração do corante azul de metileno (AM) pelo processo foto Fenton heterogêneo utilizando radiação solar. O planejamento experimental apontou as ferritas na seguinte ordem referente a eficiência de descoloração do corante: NiFe2O4-B = NiFe2O4-R > Fe2O3/Fe3O4-R. Utilizando a NiFe2O4-B, a solução do AM foi descolorida com mais de 90% de eficiência em 90 minutos. A análise por ICP OES da solução final após descoloração com a NiFe2O4-B indicou uma concentração de (0,00057 ± 0,00067) 𝑚𝑔L-1 de íons de níquel e não detectou-se íons de ferro. As concentrações de íons de níquel e de ferro estão abaixo do recomendado pela resolução 430/2011 do CONAMA para o descarte de efluentes. NiFe2O4-B não transfere íons metálicos presentes em sua composição para a solução. Na solução final também foram identificados os ácidos fórmico, acético e propiônico por cromatografia de íons (CI). A propriedade pseudocapacitiva das ferritas foi analisada por voltametria cíclica (VC) e mostrou que a NiFe2O4-B possui maior eficiência de carga (84,3%) quando comparada com as ferritas NiFe2O4-R (65,5%) e Fe2O3/Fe3O4-R (57%) após 1000 ciclos. A ferrita NiFe2O4-B é um eficiente catalisador na degradação do corante AM e ainda pode ser utilizado como um pseudocapacitor eletroquímico.

Compte tenu de l’évolution des températures d’entrée de turbines, le principal enjeu pour les métallurgistes est d’élaborer des alliages capables de présenter d’excellentes propriétés mécaniques à des températures de plus en plus élevées. Dans ce contexte, connaitre les relations entre les différents paramètres microstructuraux et les propriétés mécaniques à haute température (700°C et plus) est capital.La durabilité en fluage et en fatigue-temps de maintien ainsi que les processus d’endommagement de l’alliage AD730™, un nouveau superalliage pour disques de turbines, ont été analysés. Plusieurs paramètres ont été étudiés, qu’ils soient microstructuraux (joints de grains, taille de grains, taille et distribution des précités γ′), ou expérimentaux (température, environnement, contrainte appliquée, temps de maintien). L’utilisation de monograins de composition chimique identique à l’alliage de l’étude a permis de mettre en évidence le fait qu’une microstructure monogranulaire ne présente pas nécessairement de meilleures propriétés en fluage qu’une microstructure polycristalline. Ceci est attribué au rôle durcissant des joints de grains. Il a de plus été montré qu’à 700°C, la taille et la distribution des précipités γ′ est le paramètre microstructural pilotant les propriétés viscoplastiques à l’ordre 1.En fatigue avec temps de maintien, un comportement original a été observé pour les longs temps de maintien en fonction de la contrainte appliquée. Ce phénomène est attribué à un effet « type Bauschinger » apparaissant lors des phases de décharges. / In view of the turbine entry temperature evolution, the main challenge for metallurgists is to elaborate new alloys able to withstand higher temperatures while keeping great mechanical properties. Therefore, knowing the relationships between microstructural parameters and mechanical properties at high temperatures (700°C and more) is mandatory.The creep and dwell-fatigue durability as well as the damage mechanisms of AD730™, a new nickel base superalloy developed for turbine disks, have been analyzed. Several microstructural parameters were studied (grain boundaries, grain size, size and distribution of γ′ precipitates) as well as experimental parameters (temperature, environment, applied stress or dwell period). By using single crystalline specimens having the same chemical composition of the studied alloy, it has been shown unambiguously that single crystalline microstructures do not necessarily present better creep properties compared to polycristalline ones. This result is supposed to be caused by a grain boundary strengthening mechanism. Moreover, in creep at 700°C, it has been shown that the main viscoplasticity controlling parameters are the size and distribution of γ′ precipitates.An unexpected dwell-fatigue behavior has been observed for long hold times and in a specific applied stress window. This phenomena is attributed to a “Bauschinger type” effect, occurring during unloading phases.