Thesis (M.A.)-- Guo li Zheng zhi da xue. / Cover title. Mimeo, copy. Includes bibliography.

L’amélioration des procédés de fabrication de matériaux de contacts électriques à base d’argent nécessite de mieux comprendre et maîtriser les mécanismes mis en jeu lors du frittage. Ce travail a pour objectif d’identifier et d’expliquer l’influence des paramètres d’élaboration des composites Ag-C-Ni et Ag-WC sur les mécanismes de frittage et les propriétés finales dans le cas d’un frittage conventionnel et par induction.La démarche expérimentale adoptée a consisté à réaliser en parallèle des essais de frittage conventionnel dans un dilatomètre permettant le suivi en continu de la déformation et dans un dispositif de chauffage par induction permettant d’obtenir des vitesses de chauffage élevées. Un intérêt particulier a d’abord été porté à l’influence de la poudre d’argent (morphologie et taux d’impuretés) afin d’identifier les mécanismes de densification de l’argent pur, avant d’étudier l’influence des poudres de renfort (nature, teneur et taille) sur le frittage des composites.L’analyse des résultats de ces essais de frittage a permis de montrer que des phénomènes de gonflement et de densification sont en compétition lors du chauffage. Nous avons déterminé, d’une part, que le gonflement pendant le frittage est le résultat d’un fluage local sous l’effet de la pression à l’intérieur de la porosité fermée, d’autre part, que celui-ci est influencé par la présence et la nature des renforts qui modifient la morphologie et la répartition de la porosité. Quant à la densification elle est induite par les mécanismes classiques de frittage.Enfin nous avons montré que le chauffage rapide par induction, en ne laissant pas assez de temps aux mécanismes de diffusion à longue distance, permet de favoriser les mécanismes de diffusion à courte distance comme la soudure des particules au détriment des mécanismes de densification liés à une diffusion à longue distance. Dans le cas de l’argent et des composites Ag-C-Ni, le frittage par induction permet donc d’atteindre une bonne consolidation avec un gonflement moindre qu’en frittage conventionnel, et d’obtenir ainsi de meilleures propriétés. / Improving the manufacturing of the silver-based electrical contacts requires a better understanding and control of specific mechanisms involved during sintering. This work aims at identifying and explaining the effect of composition and process parameters on sintering mechanisms and final properties of Ag-C-Ni and Ag-WC composites in conventional and induction sintering.Sintering experiments have been carried out in a conventional way in a dilatometer allowing for a continuous monitoring of deformation and in an induction heating device allowing for high heating rates. In a first step, we focused on silver powder parameters (morphology and impurity content) to identify the densification mechanisms involved during pure silver sintering. We then studied the effect of reinforcement powders (nature, amount and size) on the sintering of composites.The results of these experiments showed that swelling and densification phenomena are competing during heating. We have determined, on one hand, that the swelling observed during heating originates from the local creep induced by the pressure inside the closed porosity and, on the other hand, that this swelling is influenced by the presence and the nature of the reinforcements, which modify the morphology and distribution of pores. Meanwhile densification is induced by classical sintering mechanisms.Finally we have shown that fast induction heating does not allow enough time for long-distance diffusion mechanisms and thus favors short-distance diffusion mechanisms, in particular interparticle bonding, in comparison with densification and swelling mechanisms, which are associated to long-distance diffusion. In the case of pure silver and Ag-C-Ni composites, induction sintering therefore enables good consolidation with less swelling than conventional sintering, resulting in better final properties.

L’eau supercritique peut être utilisée comme caloporteur à haute pression pour améliorer le rendement des centrales électriques. Pour un concept de réacteur nucléaire, la durée de vie des matériaux est un paramètre important en termes de sécurité. Par conséquent, les critères de sélection des matériaux pour un concept de réacteur à l’eau supercritique concernent les propriétés mécaniques à haute température pour une bonne tenue au fluage et à l’irradiation mais également une résistance à la corrosion généralisée et à la corrosion sous contrainte. Ce travail à pour objectif d’améliorer la compréhension des mécanismes de corrosion en eau supercritique à 600°C et 25 MPa pour des alliages c.f.c contenant du fer, du nickel et du chrome. Des essais de corrosion ont été réalisés sur des autoclaves échantillons d’alliages 316L et 690 en prenant en compte l’état de surface. Les couches d’oxydes formées ont été décrites en termes de morphologie, de composition et de structure, après caractérisations par microscopie électronique à balayage, par spectroscopie à décharge luminescente et par diffraction des rayons X. Si un comportement de type gazeux de l’eau supercritique est attendu dans les conditions d’essai, les résultats montrent une dissolution significative de certains éléments de l’alliage. Par conséquent, la corrosion en eau supercritique peut être considérée comme similaire à la corrosion aqueuse avec un effet de la température qui peut influencer la diffusion en phase solide par exemple. Pour l’alliage 690, la couche d’oxyde protectrice formée sur une surface polie est composée de chromine et surmontée d’un chromite ou d’un spinelle mixte de nickel et de fer. La double couche d’oxyde formée sur une surface de même finition pour l’alliage 316L semble moins protectrice. La couche externe de magnétite est poreuse et la couche interne riche en chrome est non homogène. Pour chaque alliage, l’étude des mécanismes de diffusion, grâce à des expériences utilisant des marqueurs ou des traceurs, révèle une croissance de la couche d’oxyde contrôlée par un processus anionique. Cependant, l’état de surface influence fortement les mécanismes de formation des couches d’oxyde. La comparaison des résultats sur l’acier suggère qu’il y a une concurrence entre l’oxydation du fer et celle du chrome. Une quantité suffisante de chrome est nécessaire pour former une fine couche d’oxyde protectrice. Les surfaces très déformées ou à microstructure à grains très fins conduisent à des fines couches d’oxyde de chrome, grâce à une forte densité de site de germination ou grâce aux courts-circuits de diffusion du chrome. L’état de surface est donc déterminant pour l’acier mais le même paramètre engendre des effets différents pour l’alliage à base de nickel. Les surfaces usinées deviennent sensibles à une oxydation interne du chrome, même si une fine couche d’oxyde continue et riche en chrome et manganèse se forme. Ce phénomène suggère une diffusion accélérée concurrentielle entre l’oxygène et le chrome. Pour conclure, ce travail propose un mécanisme de croissance de la couche d’oxyde dans chaque cas et discute des conditions favorables à la formation d’une couche d’oxyde protectrice riche en chrome dans l’optique d’une application au réacteur à eau supercritique. / Supercritical water can be use as a high pressure coolant in order to improve the thermodynamic efficiency of power plants. For nuclear concept, lifetime is an important safety parameter for materials. Thus materials selection criteria concern high temperature yield stress, creep resistance, resistance to irradiation embrittlement and also to both uniform corrosion and stress corrosion cracking.This study aims for supplying a new insight on uniform corrosion mechanism of Fe-Ni-Cr f.c.c. alloys in deaerated supercritical water at 600°C and 25MPa. Corrosion tests were performed on 316L and 690 alloys as sample autoclaves taking into account the effect of surface finishes. Morphologies, compositions and crystallographic structure of the oxides were determined using FEG scanning electron microscopy, glow discharge spectroscopy and X-ray diffraction. If supercritical water is expected to have a gas-like behaviour in the test conditions, the results show a significant dissolution of the alloy species. Thus the corrosion in supercritical water can be considered similar to corrosion in under-critical water assuming the higher temperature and its effect on the solid state diffusion. For alloy 690, the protective oxide layer formed on polished surface consists of a chromia film topped with an iron and nickel mixed chromite or spinel. The double oxide layer formed on 316L steel seems less protective with an outer porous layer of magnetite and an inhomogeneous Cr-rich inner layer. For each alloy, the study of the inner protective scale growth mechanisms by marker or tracer experiments reveals that diffusion in the oxide scale is governed by an anionic process. However, surface finishes impact deeply the growth mechanisms. Comparisons between the results for the steel suggest that there is a competition between the oxidation of iron and chromium in supercritical water. Sufficient available chromium is required in order to form a thin oxide layer. Highly deformed or ultra fine microstructure surfaces lead to thin chromium rich oxide layers thanks to either diffusion short circuiting or increasing Cr oxide nucleation site. The nature of the surface is a determining factor in the steel instance. The same parameter breeds different effects for the Ni-based alloy. Machined surfaces lead to internal oxidation on alloy 690 even if a thin Cr and Mn rich oxide scale is formed. Competitive diffusion of oxygen and Cr species through the diffusion short circuit paths of the alloy is suggested. This work proposes oxide growth mechanisms for each case. Finally the conditions leading to the formation of chromium-rich protective oxide films in supercritical water are discussed.

Large Igneous Provinces (LIPs) form during short-lived pulses of extensive magmatic activity. LIPs are known for their ability to affect global climate as well as for their Ni-Cu-PGE ore potential. A key factor that controls the intensity of the climate impact of a LIP and its ore potential is the assimilation of volatile-rich sedimentary host rocks. Magmas of the High Arctic Large Igneous Province (HALIP), exposed in the Arctic, intruded volatile-rich black shales, carbonates and evaporites in the Canadian Arctic Islands, offering a great opportunity for studying magma-sediment interaction. The purpose of this study is to test whether assimilation of sedimentary sulphide can promote sulphide immiscibility in magma and thus aid formation of Ni-Cu-PGE ore bodies. This is done by analysing sulphur isotopes in pyrite grains hosted in a HALIP dolerite sill, which was emplaced into black shale, by using Secondary Ion Mass Spectrometry (SIMS). Four dolerite samples are analysed; two coming from the lower contact margin of the sill, one from 60 cm into the sill and one sample from a basaltic vein at the upper contact margin of the sill. A total of 14 pyrite grains (n = 246 individual SIMS spot analyses) were analysed for their sulphur isotope ratios. The results of the SIMS analyses show that all analysed sulphides have highly negative δ34S values ranging from -19.5 to -5.7‰ (average δ34S = -8.2 ± 0.83‰, 2SD), which therefore differ largely from that of the primitive mantle (0 ± 1.8‰). In order to put our four analysed dolerite samples into a broader context, δ34S data of our sulphides are compared with whole-rock δ34S and δ18O data from Hare Fiord shale and dolerite samples. The δ34S values of the sulphide samples from the sill typically trend toward the negative sulphur isotope composition of the sulphides in the surrounding shale, and the shale surrounding the sill experiences a loss of 32S near the contact of the sill. This indicates that sedimentary light sulphur (32S) has been locally incorporated into the sill by the surrounding shale, resulting in negative δ34S values in the magmatic sulphides. Since sulphide immiscibility in the Hare Fiord sill was triggered by assimilation of sulphur from host rock shale, the igneous rocks of the HALIP may be prospective for Ni-Cu-PGE mineralization, though more studies are needed. Furthermore, our results suggest that incorporation of crustal sulphur increased the volatile budget of HALIP magmas, which therefore could have contributed to a deterioration of the environmental conditions during the emplacement of the HALIP. / Stora magmatiska provinser (på engelska Large Igneous Provinces, LIPs) är vulkaniska event då enorma mängder magma avsätts över en väldigt stor yta under ett, i ett geologiskt perspektiv, kort tidsspann. Dessa stora vulkaniska utbrott har väckt stort intresse då de är samtida med flera av de största massutdöendena i jordens historia, men också för att en viss typ av sulfidmalm rik på nickel, koppar och platinametaller (Ni-Cu-PGE malmer) ofta förekommer i provinsernas magmagångar och magmakammare. En viktig faktor som till stor del avgör en magmatisk provins påverkan på klimatet och potentiella malmförekomster är inkorporering av sedimentära bergarter till magman som, när de hettas upp, kan frigöra gaser rika på svavel och kol. I Kanadas arktiska öar trängde magma tillhörande den högarktiska magmatiska provinsen (HALIP) in i svart skiffer, karbonater och evaporiter, som är sedimentära bergarter rika på flyktiga ämnen. Denna magmatiska provins erbjuder därför stora möjligheter till att studera interaktionen mellan magma och sedimentära bergarter. Syftet med denna studie är att testa om inkorporering av sedimentärt svavel kan främja bildandet av sulfidsmälta i magma och därigenom bidra till bildandet av sulfidmalmer. Detta görs genom att analysera svavelisotoper i sulfidmineral i prover från en magmagång, som trängde in i en skifferformation, tillhörande den högarktiska magmatiska provinsen i norra Kanada. Genom att analysera svavelisotopkvoten (δ34S) i sulfidmineral kan man få information om huruvida svavlet i mineralen är av sedimentärt ursprung (där skiffer generellt har negativa δ34S värden) eller om svavlet har δ34S värden liknande de från manteln (som har δ34S värden runt 0‰), vilket i så fall skulle innebära att magman inte har inkorporerat sedimentärt svavel. Genom att använda masspektrometri av typen SIMS analyseras totalt 14 sulfidmineralkorn (n = 246 individuella SIMS punkter) för deras svavelisotopkvoter. Resultatet av studien visar att alla analyserade sulfidmineral har mycket negativa δ34S värden mellan -19.5 och -5.7‰ (med ett δ34S medelvärde på -8.2 ± 0.83‰, två standardavvikelser). Genom att jämföra våra δ34S värden med δ34S och δ18O värden för andra prover från både magmagången och den omgivande skiffern kunde vi se att δ34S värdena för sulfidmineralen i de yttre delarna av magmagången har liknande negativa värden som den omgivande skiffern, och att δ34S värdena för skiffern närmast magmagången är mer positiva. Detta tyder på att sedimentärt svavel i kontakten mellan magmagången och skiffern har blivit inkorporerat i magman från den omgivande skiffern. Våra resultat tyder därför på att sulfidmineralen i våra prover från magmagången bildades genom assimilering av svavel från den omgivande skiffern. Detta innebär i sin tur att den kanadensiska högarktiska magma provinsen potentiellt kan vara en källa för sulfidmalm, även om ytterligare studier behövs. Dessutom visar våra resultat att inkorporering av sedimentärt svavel förmodligen ökade de vulkaniska gaserna i magman, vilket kan ha bidragit till klimatförändringar relaterade till den vulkaniska aktiviteten av den högarktiska magmatiska provinsen.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-20T14:23:35Z No. of bitstreams: 1 GLERYSTON THIAGO GOMES DA SILVA - DISSERTAÇÃO (PPGEM) 2017.pdf: 4116473 bytes, checksum: 5df445f57ab1b4d9326f681288378141 (MD5) / Made available in DSpace on 2018-08-20T14:23:35Z (GMT). No. of bitstreams: 1 GLERYSTON THIAGO GOMES DA SILVA - DISSERTAÇÃO (PPGEM) 2017.pdf: 4116473 bytes, checksum: 5df445f57ab1b4d9326f681288378141 (MD5) Previous issue date: 2017-05-03 / Capes / O presente trabalho avalia a adesão entre fios e fitas de uma liga com memória de forma (LMF) de Ni-Ti e uma borracha de silicone, para o desenvolvimento de estruturas flexíveis. A avaliação da adesão foi realizada através de ensaios de extração (Pull Out). Para realização dos ensaios, foram produzidos seis tipos de corpos de prova (CPs) em que os fios e as fitas foram embebidos em uma matriz de borracha de silicone. Primeiramente, as fitas foram obtidas laminando a frio fios de Ni-Ti superelástico. Após a laminação as fitas foram submetidas a tratamento térmico em temperaturas e tempos diferentes, a fim de obter dois tipos de fitas: uma com característica de superelasticidade (SE) e outra com o efeito memória de forma (EMF). Um promotor de adesão Dow Corning 1200 Primer foi aplicado nas superfícies dos fios e das fitas para aumento da adesão. Os fios e as fitas de Ni-Ti e a borracha de silicone foram individualmente caracterizados por Calorimetria Exploratória Diferencial (DSC), Análise Dinâmico-Mecânica (DMA) e tração uniaxial, analisando o comportamento do fator de amortecimento, módulo de elasticidade, tensões de transformação e temperaturas de transformação de fase. O ensaio de carregamento – descarregamento em tração na borracha de silicone também foi realizado para analisar a presença do efeito Mullins. Para verificação qualitativa do aumento da rugosidade e da adesão geradas pelo processo de laminação e pela aplicação do primer, respectivamente, foram realizadas imagens por Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Energia Dispersiva (EDS) nos fios e nas fitas de Ni-Ti antes e após o ensaio de extração (Pull Out). A partir dos resultados obtidos, observa-se que o fio superelástico e as fitas de Ni-Ti laminadas e tratadas termicamente sem aplicação do primer não apresentam adesão suficiente para o desenvolvimento de estruturas flexíveis compostas por borracha de silicone e elementos atuadores como fios e fitas de Ni-Ti, sendo necessária a aplicação de um promotor de adesão (primer) nas superfícies das LMF. / The present work evaluates the adhesion between Ni-Ti Shape Memory Alloy (SMA) wires and ribbons embedded into a silicone rubber, for the development of flexible structures. Adhesion evaluation was performed through pullout tests. To perform the tests, six types of specimens were produced, in which the wires and ribbons were embedded in a silicone rubber matrix. Firstly, the ribbons were obtained by cold rolling of a superelastic Ni-Ti wire. After the cold rolling, the ribbons were subjected to heat treatment at different temperatures and times in order to obtain two types materials: one with Superelasticity (SE) property and other with Shape Memory Effect (SME). A Dow Corning 1200 Primer adhesion promoter was applied to the surfaces of the wires and ribbons to improve adhesion. Ni-Ti wire and ribbons and silicone rubber were characterized by Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA) and uniaxial tensile tests, to obtain loss factor behavior, elastic modulus, tensile stress transformations and phase transformation temperatures. Analysis of tensile loading - unloading test on silicone rubber was also performed to evaluate the presence of the Mullins effect. For the qualitative verification of the roughness and adhesion improvement, generated by the cold rolling process and the application of the primer, respectively, images of Scanning Electron Microscopy (SEM) and Dispersive Energy Spectroscopy (EDS) in the Ni- Ti wire and ribbons were performed before and after the pullout tests. The obtained results indicate that the Ni-Ti superelastic wires and heat treated cold rolled ribbons without primer do not present sufficient adhesion for the development of silicone rubber flexible structures with embedded Ni-Ti wires and ribbons, requiring the application of an adhesion promoter (primer) on the surfaces of the SMA.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-10-09T13:19:28Z No. of bitstreams: 1 JOSÉ JOELSON DE MELO SANTIAGO - DISSERTAÇÃO (PPGEM) 2018.pdf: 5893476 bytes, checksum: 9fec0f8b27ff639270bebb4444b2285c (MD5) / Made available in DSpace on 2018-10-09T13:19:28Z (GMT). No. of bitstreams: 1 JOSÉ JOELSON DE MELO SANTIAGO - DISSERTAÇÃO (PPGEM) 2018.pdf: 5893476 bytes, checksum: 9fec0f8b27ff639270bebb4444b2285c (MD5) Previous issue date: 2018-08-30 / Em muitas situações de projeto em sistemas mecânicos deseja-se rigidez e ao mesmo tempo uma certa flexibilidade. Nesses casos, as molas são elementos interessantes, por isso esses componentes foram bastante estudados. Em paralelo, visando ampliar as possibilidades, novos materiais têm se desenvolvido, a exemplo de materiais funcionais, como é o caso das ligas com memória de forma (LMF). As molas helicoidais fabricadas a partir de LMF são componentes promissores para aplicações como atuadores/sensores, pela capacidade de recuperar grandes deformações elásticas e pseudo-plásticas. Atualmente esses componentes são obtidos em sua maioria através da conformação de fios, a frio ou a quente, e tem aplicação consolidada no campo biomédico, porém no campo industrial as aplicações comerciais ainda são limitadas. Neste cenário, utilizar a fundição de precisão para este tipo de componente pode ampliar as possibilidades e aumentar as aplicações em diversos setores. Por outro lado, é de amplo interesse entender a relação entre as propriedades mecânicas e as configurações geométricas destes elementos. Neste contexto, o principal objetivo deste trabalho é a caracterização térmica e mecânica de molas helicoidais de LMF Ni-Ti (MLMFNiTi) com diferentes configurações, produzidas pelo processo de fundição de precisão, empregando a fusão por indução com injeção por centrifugação (FIC) em moldes cerâmicos. Os resultados obtidos mostraram que as molas produzidas apresentaram transformação de fase característica dos fenômenos de superelasticidade (SE). Por meio dos ensaios mecânicos constatou-se que as molas suportaram, no geral, deformações de até 70%. Os parâmetros dimensionais influenciaram o comportamento mecânico para o qual o aumento do passo e do diâmetro do fio fizeram aumentar a força aplicada para submeter as molas as mesmas deformações. Dessa forma, as molas produzidas apresentam características funcionais adequadas para potencializar aplicações industriais a partir de LMF Ni-Ti. / In many situations of design in mechanical systems one wants rigidity and at the same time a certain flexibility. In these cases, the springs are interesting elements, so these components were well studied. In parallel, in order to expand possibilities, new materials have been developed, such as functional materials, such as shape memory alloys (LMF). Helical springs made from LMF are promising components for applications such as actuators / sensors, for the ability to recover large elastic and pseudo-plastic deformations. Currently, these components are mostly obtained through wire forming, either cold or hot, and have consolidated application in the biomedical field, but in the industrial field commercial applications are still limited. In this scenario, using precision casting for this type of component can expand the possibilities and increase the applications in several sectors. On the other hand, it is of broad interest to understand the relation between the mechanical properties and the geometric configurations of these elements. In this context, the main objective of this work is the thermal and mechanical characterization of LMF Ni-Ti helical springs (MLMFNiTi) with different configurations, produced by the invesment casting process, using induction fusion with centrifugal injection (FIC) in ceramic molds. The obtained results showed that the produced springs presented phase transformation characteristic of the phenomena of superelasticity (SE). Through the mechanical tests it was found that the springs generally supported deformations of up to 70%. The dimensional parameters influenced the mechanical behavior for which the step increase, and the wire diameter increased the applied force to subject the springs to the same deformations. Thus, the springs produced have functional characteristics suitable to enhance industrial applications from LMF Ni-Ti.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-10-09T13:44:00Z No. of bitstreams: 1 ANTÔNIO ARISTÓFANES DA CRUZ GOMES - DISSERTAÇÃO (PPGEM) 2018.pdf: 3128879 bytes, checksum: 1a0aaa662fd3e47d06a1e3545ab63f87 (MD5) / Made available in DSpace on 2018-10-09T13:44:00Z (GMT). No. of bitstreams: 1 ANTÔNIO ARISTÓFANES DA CRUZ GOMES - DISSERTAÇÃO (PPGEM) 2018.pdf: 3128879 bytes, checksum: 1a0aaa662fd3e47d06a1e3545ab63f87 (MD5) Previous issue date: 2018-08-07 / CNPq / Os procedimentos cirúrgicos de reconstrução crânio facial vêm se desenvolvendo significativamente e grande parte desse progresso se deve às inovações nas técnicas cirúrgicas e ao emprego de novos materiais na fabricação dos dispositivos de fixação. O objetivo principal é tornar os procedimentos mais eficientes e menos invasivos aos pacientes, consequentemente haverá diminuição nos índices de retrabalhos. O emprego de Ligas com Memória de Forma (LMF) pode ser uma alternativa interessante nesses casos, uma vez que esses materiais possuem um comportamento adaptativo, com a capacidade de reagir a estímulos externos de natureza térmica ou mecânica. As LMF da família Ni-Ti lideram o interesse das pesquisas devido ao maior número de aplicações comerciais, principalmente nas áreas médica e odontológica. Essas LMF Ni-Ti, além de serem biocompatíveis possuem também módulo de elasticidade inferior ao de ligas de titânio, como o Ti-Al-V, e dos aços inoxidáveis. Neste contexto, o objetivo deste trabalho é desenvolver um protótipo de placa de fixação óssea, que poderá ser destinada a procedimentos de trauma e reconstrução mandibular, utilizando uma LMF Ni-Ti com características superelásticas. Foi escolhido um elemento de fixação, tipo placa, como modelo para os protótipos e as dimensões foram baseadas em componentes fornecidos comercialmente. Para a fabricação dos dispositivos optou-se pelos processos de fundição de precisão: Plasma Skull Push-Pull (PSPP), e fusão por indução com injeção por centrifugação (FIC), os quais se mostraram bastante eficazes. Foram realizados ensaios de caracterização para determinar as propriedades térmicas e mecânicas do dispositivo fabricado. Os principais resultados foram um componente de rigidez variável com a temperatura, módulo de elasticidade da ordem de 50 GPa na temperatura corpórea e vida em fadiga ente 103 e 106 para amplitudes de deslocamento em flexão entre 0,5 mm e 2,5 mm. Estes resultados de caracterização termomecânica indicam o potencial das LMF Ni-Ti e dos processos de fundição de precisão para a produção de placas de fixação óssea. / Surgical procedures for facial skull reconstruction have been developing significantly and much of this progress is due to innovations in surgical techniques and the use of new materials in the manufacture of fastening devices. The main objective is to make the procedures more efficient and less invasive to the patients, consequently there will be a decrease in the rates of reworking. The use of Shape Memory Alloys (SMA) may be an interesting alternative in these cases, since these materials have an adaptive behavior, with the ability to react to external stimuli of a thermal or mechanical nature. The SMA of the Ni-Ti family lead the research interest due to the greater number of commercial applications, mainly in the medical and dental areas. In addition to being biocompatible, these Ni-Ti SMAs also have lower modulus of elasticity than titanium alloys, such as Ti-Al-V, and stainless steels. In this context, the objective of this work is to develop a prototype bone fixation plate, which can be used for trauma and mandibular reconstruction procedures, using a Ni-Ti SMA with superelastic characteristics. A plate-type fastening element was chosen as the prototype model and the dimensions were based on commercially supplied components. In order to manufacture the devices, it was chosen the precision casting processes: Plasma Skull Push-Pull (PSPP) and induction fusion with centrifugal injection (FCI), which proved to be quite effective. Characterization tests were performed to determine the thermal and mechanical properties of the fabricated device. The main results were a variable stiffness component with temperature, modulus of elasticity of the order of 50 GPa at body temperature and fatigue life between 103 and 106 for flexural displacement amplitudes between 0.5 mm and 2.5 mm. These thermomechanical characterization results indicate the potential of Ni-Ti SMA and precision casting processes for the production of bone fixation plates.

Made available in DSpace on 2015-05-08T14:59:52Z (GMT). No. of bitstreams: 1 parte1.pdf: 2223950 bytes, checksum: 585473348fd57251708f0ba93240c53b (MD5) Previous issue date: 2008-10-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The presented work consists of a study for observation of the martensite kept in the transformation of martensite phase - austenite in a alloy of Ni - Al - V, with memory shape effect, into, a room temperature. We defined that the alloy with composition the 3,5% (in weigh) of nickel, presents better results when happens successive loading and downloading cancel though, 3,0% of deformation into a room temperature, back to austenite phase after retreat the load. Above 3,0% of deformation became evident the appearance of retrain martensite. For her identification it was necessary the development of on equipment to traction, as well as bodies of proofs dimensioned for that. The analyses were done through X rays diffraction of optical microscopy and rehearsal of traction. / O trabalho apresentado consta de um estudo para observação da martensita retida na transformação de fase de martensita austenita em uma liga de Ni Al V, com efeito de memória de forma, a temperatura ambiente. Definimos que a liga com composição 3,5% (em peso) de níquel, apresenta melhor resultado quando submetida a carregamento e descarregamento sucessivos; chegando a 3,0% de deformação a temperatura ambiente, retornando ao estado austenítico depois de retirada a carga. Acima de 3,0% de deformação, evidencia-se o surgimento de martensita retida. Para sua identificação, foi necessária a confecção de um equipamento para tracionar, como também corpos de prova dimensionados para tanto. As observações foram realizadas através de análises de raios X, microscopia ótica e ensaios de tração.

Submitted by Kilvya Braga (kilvyabraga@hotmail.com) on 2018-04-23T13:32:14Z No. of bitstreams: 1 ROANA D'ÁVILA SOUZA MONTEIRO - DISSERTAÇÃO (PPGEM) 2015.pdf: 3977570 bytes, checksum: e1760f7cd8bdc07cce68f5b1aedd33a2 (MD5) / Made available in DSpace on 2018-04-23T13:32:14Z (GMT). No. of bitstreams: 1 ROANA D'ÁVILA SOUZA MONTEIRO - DISSERTAÇÃO (PPGEM) 2015.pdf: 3977570 bytes, checksum: e1760f7cd8bdc07cce68f5b1aedd33a2 (MD5) Previous issue date: 2015-08-31 / Capes / As Ligas com Memória de Forma (LMF) constituem uma classe de materiais metálicos que possuem a capacidade de recuperar uma deformação pseudo plástica, introduzida por aplicação de carga mecânica, e retornar à sua forma original através de um simples aquecimento. O principal interesse nos atuadores de LMF utilizados no formato de molas helicoidais reside no grande deslocamento proporcionado pelo fenômeno de Efeito Memória de Forma (EMF), que permite a realização de trabalho mecânico quando este componente é submetido a diferentes condições de temperatura e cargas mecânica. No caso de elementos de LMF em estado de superelasticidade (SE) na temperatura ambiente, quando a carga mecânica é aplicada e mantida sob o material, a deformação originada pela formação de martensita induzida por tensão poderá também ser revertida por meio de um aquecimento. Nesse caso, tem-se um EMF em um elemento de LMF originalmente superelástico. Nesse contexto, o objetivo deste trabalho é realizar a caracterização eletromecânica de uma mini mola superelástica de LMF NiTi (Nitinol) quando submetida a um carregamento mecânico constante, avaliando a influência da taxa de variação da corrente elétrica e do aumento da carga mecânica nas temperaturas de transformação, além de determinar o comportamento do deslocamento com a variação de resistência elétrica. Para isso, foi desenvolvida uma plataforma experimental capaz de submeter a mini mola a carregamento mecânico constante (peso) e sinais de corrente elétrica variáveis com o tempo. Verificou-se que, para todas as cargas mecânicas e níveis de corrente elétrica, os resultados para a taxa de variação da corrente elétrica mais lenta (6 mA/s) apresentou uma melhor resposta em deslocamento e na variação da resistência elétrica quando comparados com a taxa mais rápida (12 mA/s), embora esta última resulte em um comportamento histerético mais estreito (resistência elétrica versus deslocamento). Também foi observado um aumento das temperaturas de transformação com o aumento da carga mecânica, como esperado pela lei de Clausius-Clayperon para LMF. Finalmente, foi verificada uma relação praticamente linear entre a variação do deslocamento e a variação de resistência elétrica, no aquecimento e no resfriamento. / The Shape Memory Alloys (SMA) are a class of metallic materials that have the ability to recover pseudo plastic deformation introduced by the application of mechanical load, and return to original shape by heating. The main interest in the SMA actuators used in the form of coil springs lies in the large displacement provided by the shape memory effect (SME) phenomenon, which allows performing mechanical work when the component is subjected to varying conditions of temperatures and mechanical loads. In the case of SMA elements in a state of superelasticity (SE) at room temperature, when mechanical load is applied and maintained on the material, the deformation caused by the formation of stress induced martensite can be reversed by heating. In this case, we have a SME in a SMA element originally superelastic. In this context, the objective of this work is to realize the electromechanical characterization of a superelastic mini coil spring of Ni-Ti SMA (Nitinol), when subjected to a constant mechanical loading, evaluating the influence of the electric current rate, the influence of mechanical load on the phase transformation temperatures, and determining the displacement behavior to the variation of electrical resistance. For this, an experimental platform was developed to submit the mini spring under constant load (dead weight) to electric current signals varying with time. It was found that for all mechanical loads and electrical current levels, the results for the slower rate of change electrical current (6 mA/s) showed a better response in displacement and the variation in the electrical resistance when compared to faster rate (12 mA/s), although the faster rate present a narrower hysteretic behavior (electrical resistance vs displacement). There was also verified an increase in phase transformation temperatures with increased mechanical load, as expected by the Clausius-Clayperon law for SMA. Finally, a practically linear relationship was found between the change in displacement with the variation in electrical resistance, during heating and cooling.

Submitted by Kilvya Braga (kilvyabraga@hotmail.com) on 2018-04-23T13:59:14Z No. of bitstreams: 1 SUELENE SILVA ARAÚJO - DISSERTAÇÃO (PPGEM) 2015.pdf: 3709690 bytes, checksum: 1d6f1a6f3675dd7c45fb2cd75c6c92bf (MD5) / Made available in DSpace on 2018-04-23T13:59:14Z (GMT). No. of bitstreams: 1 SUELENE SILVA ARAÚJO - DISSERTAÇÃO (PPGEM) 2015.pdf: 3709690 bytes, checksum: 1d6f1a6f3675dd7c45fb2cd75c6c92bf (MD5) Previous issue date: 2015-08-07 / CNPq / Neste trabalho foi avaliado o comportamento dinâmico e a fadiga termomecânica de fios de uma liga com memória de forma (LMF) CuAlNi submetidos a ensaios cíclicos utilizando um analisador dinâmico mecânico (DMA). Assim, foram realizadas análises para determinar a capacidade de amortecimento e o módulo de elasticidade dos fios e adicionalmente a fadiga estrutural sob controle de deformação em modo de flexão simples alternada, a partir da variação da amplitude de deslocamento, para três temperaturas distintas. O comportamento dinâmico revelou uma considerável capacidade de amortecimento dos fios, principalmente durante a transformação de fase martensitica, apresentando um expressivo pico de absorção de energia. Além disso, o módulo de elasticidade (rigidez) apresentado pelos fios revelou a existência de um importante aumento durante a transformação, diferenciando as duas distintas fases. Notou-se também a partir dos resultados dos ensaios de fadiga que as características funcionais dos fios dependem de forma direta da amplitude de deformação imposta, influenciando nos valores de tensão e no tempo de vida dos fios, revelando que a fadiga pode ser considerada de baixo ciclo. / This study evaluated the dynamic behavior and the thermomechanical fatigue of CuAlNi SMA wires subjected to cyclic tests using a DMA device. Therefore, analyzes were performed to determine the damping capacity and stiffness of SMA wires, in addition to structural fatigue under strain control from the amplitude variation at three different temperatures. The evolution of the wire’s behavior has shown a considerable damping capacity, mainly during the martensitic phase transformation, presenting a significant peak of energy absorption. Moreover, the storage modulus (stiffness), revealed a significant increase during transformation, differentiating the distinct phases. It has been also noted, from the results of fatigue tests, that the functional behavior of the SMA wires depend directly on the amplitude of the imposed strain, influencing on the stress values as well as on the wire’s lifetime, revealing that fatigue can be considered of low cycle type.