This diploma thesis deals with the analysis of mechanical properties of bimetallic materials with clad layer of Inconel. In the theoretical part of the work there is an analysis of the investigated bimetallic material. The following is a description of mechanical tests and methods for evaluating the integrity of the surface, which were used to determine the properties of bimetallic material. The experimental part focuses on individual tests of mechanical properties of the material. For each test, the procedure for the production of test specimens, a description of the test equipment, the performance of the tests, the evaluation of the data obtained and finally, the evaluation of the results obtained are given.

The thesis aim is an evaluation of achieved results coming from the analysis of pipe bend 180° for the critical bending / bend 1D and supercritical bending / bend 0,7D. The theoretical part is focused on material property of a bimetallic pipe and on methods applied to work out the analysis. The definition of critical points at a considered segment and possible defects arisen while bending is embodied in the thesis. The practical part of the thesis is based on presenting dimensional and proportional analysis based on using optical microscopes and 3D scanner GOM ATOS. The material analysis was aimed at macrostructure as well as microstructure of the bimetallic pipe material, at chemical composition and at the hardness when low-loaded. The analysis achieved results are assessed at the end of the thesis.

This thesis is concerned to the study of behaviour of fibre composites with ceramics matrix. The composite consists of pyrolysed polysiloxane matrix reinforced by ceramic fibre Nextel 720. Main aim of this work is optimisation of fibre matrix interface through the selection of suitable precursor of the matrix with respect to temperature stability, sufficient strength and reasonable fracture toughness. Samples of matrices were exposed to the long term heat treatment in the range 1100 – 1500 °C. The mechanical properties as hardness and indentation elastic modulus were determined after heat treatment. Selected precursors of matrices were used for composite fabrication. Elastic modulus and fracture toughness at room and elevated temperatures were studied. Discussion is dedicated to the description of changes in mechanical properties with respect to chemical processes taking place during high temperature exposition. Further, reasons of fracture behaviour of composite materials are discussed, and finally, gained knowledge and outlined possibilities of subsequent development are summarised.

Acoustics is the study of all sound waves, with ultrasound classified as those frequencies above 20,000 Hz. Currently, ultrasound is being used in many industries for a variety of purposes such as ultrasonic imaging, ultrasonic assisted friction stir welding, and ultrasonic spot welding. Despite these uses, the effects of ultrasound on phase stability and resultant mechanical properties has been minimally analyzed. Here we study the impact waves play in ultrasonic welding and design an apparatus to maximize waves entering aluminum alloy samples. Aluminum 2139 and 7050 are used because they are precipitation strengthened by metastable phases so temperature change, and the corresponding phase stability, can greatly impact their strength. Results suggest that the ultrasonic welder primarily imposes a localized temperature spike due to friction, averaging over 200°C in a few seconds, which generally lowers the Vickers hardness due to coarsening or even dissolution of strengthening precipitates. Conversely, the new design increases the Vickers hardness by up to 30% over the initial hardness of approximately 63HV for aluminum 2139 and 83HV for aluminum 7050, respectively, while only increasing the temperature by an average of approximately 10°C. This new design was unable to achieve peak hardness, but the strengthening it achieved in two minutes was equivalent to one month of natural aging. If this system was able to be fine-tuned, it could serve as a quick strengthening process for recently weakened aluminum alloys, such as after friction stir welding.

No description available.

No presente trabalho quatro ligas Al-Si hipereutéticas, três das quais foram produzidas por conformação por \"spray\" e a outra por fundição, foram caracterizadas quanto a textura, dureza, microestrutura e resistência à corrosão em meio de condensado sintético automotivo (CSA). Duas das ligas conformadas por \"spray\" foram retiradas de camisas de cilindro e a outra de um pré-formado obtido em laboratório. A conformação por \"spray\" envolve a atomização de uma liga e a deposição de gotículas em um substrato, antes mesmo que todas se encontrem no estado sólido. Este processo permite a obtenção de materiais que se caracterizam por uma microestrutura livre de macrossegregações e bastante refinada, implicando melhor trabalhabilidade a quente. A caracterização da microestrutura das quatro ligas hipereutéticas revelou a presença de porosidades na liga obtida em laboratório, e microestrutura com distribuição homogênea de precipitados primários nas três ligas conformadas por \"spray\". A microestrutura de uma das ligas apresentou-se muito diferenciada, com a presença de eutético, sugerindo que esta foi fabricada por fundição. Nas camisas de cilindro foram feitas medidas de rugosidade, e em todas as ligas foram realizados ensaios de microdureza. A liga conformada por \"spray\" e obtida em laboratório foi laminada a quente e a frio. Foram realizados também estudos de textura, para tentar estabelecer uma correlação entre todas as ligas quanto ao processo de fabricação. A avaliação da textura indicou que a presença de fases de silício primário, finamente distribuídas impedem o aparecimento de texturas típicas de deformação de ligas de alumínio, mesmo após severas deformações, como as necessárias para a transformação de pré-formados em tubos que originam as camisas de cilindro. As medidas de rugosidade indicaram características próprias do acabamento superficial usado para a produção das camisas, por brunimento ou por ataque químico. Os ensaios de microdureza apresentaram variações de acordo com as rotas de fabricação sendo que a liga eutética apresentou os maiores valores de microdureza em comparação às ligas conformadas por \"spray\". Todas as ligas foram avaliadas quanto a resistência à corrosão por ensaios de espectroscopia de impedância eletroquímica em dois meios, CSA com pH 3,3 e CSA com pH 11. As quatro ligas hipereutéticas estudadas apresentaram mecanismo de corrosão similar em condensado sintético automotivo (CSA) pH 3,3. Em todas ocorreu o ataque intenso da matriz de alumínio e as partículas de silício primário atuaram como regiões catódicas. A liga 2 apresentou maior resistência à corrosão entre todas as ligas ensaiadas, tanto em CSA pH 3,3 como em pH 11. Neste último meio, uma camada de produtos de corrosão formou-se sobre todas as ligas, e os resultados indicaram mecanismos diferentes para o ataque da matriz de Al e para o crescimento da camada depositada na superfície das ligas estudadas. O ataque da matriz da liga 2 neste meio foi aparentemente mais lento do que sobre as demais ligas, com a formação de uma camada mais compacta de produtos de corrosão, estabelecendo um controle por difusão dos processos interfaciais para maiores períodos de ensaio. A camada formada sobre as demais ligas neste meio apresentou-se mais defeituosa, e nestas ocorreu também menor controle da velocidade das reações interfaciais por processos difusionais. / In the present study four hypereutectic Al-Si alloys, three produced by spray forming and one by casting, were characterized for microhardness, roughness, microstructure, texture and corrosion resistance in a synthetic automotive condensed solution (SACS). Two of the spray formed alloys tested were obtained from cylinder liners and the other was laboratory made. Spray forming involves alloy atomization and droplets deposition on a substrate, previous to the solidification of all of the droplets. This process favours the production of materials with a fine microstructure free of macrosegregation that is related to improved hot workability. The microstructure characterization of the four alloys revealed the presence of porosities in the laboratory made alloy. All the three alloys produced by spray forming showed a homogeneous distribution of primary precipitates. The microstructure of one of the alloys showed eutectic microstructure, indicating that this alloy was fabricated by casting. In the cylinder liners, the surface roughness was measured and the microhardness of all the alloys was also evaluated. Furthermore, the laboratory made alloy was hot and cold rolled. Texture determinations were carried out to investigate the correlation between the alloy type and their fabrication process. The texture investigation indicated that the fine distribution of primary silicon phase in the alloy hindered the development of texture typical of aluminium alloys deformation, even after severe mechanical work, such as those used in the conversion of pre-formed in cylinder liners. The surface roughness results indicated typical characteristics of the surface finishing used, honing or chemical etching. The microhardness results were dependent on the fabrication process used, with higher microhardness associated to the eutectic alloy comparatively to the spray formed ones. All hypereutectic alloys were tested for corrosion resistance using electrochemical impedance spectroscopy in two electrolytes, SACS with pH 3.3 and SACS with pH 11. The four tested alloys showed similar corrosion mechanisms in the acid electrolyte (SACS pH 3.3). The intense attack of the aluminium matrix occurred in ali tested alloys and the primary silicon phase was unattacked and appeared as emerging from the surface after corrosion immersion test. The primary silicon particles acted as cathodic sites. The alloy 2 showed the highest corrosion resistance among the tested alloys in both electrolytes, SACS pH 3.3 and SACS pH 11. In this last medium, a layer of corrosion products formed on all the alloys, and the results indicated different mechanisms for the aluminium matrix corrosive attack and growth of the deposited layer on the alloys surface. The kinetics of aluminium matrix attack was apparently slower in the alloy 2 than for the other alloys, resulting in the formation of a more compact layer of corrosion products, leading to diffusion controlled interfacial processes for longer test periods. The layer of corrosion products on the other three alloys (1, 3, and 4) had more defects and for these alloys diffusional controlled interfacial processes were not as significant as for alloy 2.

Cintiladores inorgânicos com tempo de decaimento de luminescência rápido, densidade alta e boa produção de luz têm sido objeto de estudos para aplicações em física nuclear, física de energias altas, tomografia nuclear e outros campos da ciência e da engenharia. Cristais de cintilação baseados em iodeto de césio (Csl) são materiais que apresentam higroscopia relativamente baixa, número atômico alto, fácil manuseio e custo baixo, características que favorecem o seu uso como detectores de radiação. Neste trabalho descreve-se a obtenção de cristais Csl puro, Csl:Br e Csl:Pb, utilizando-se a técnica de Bridgman. A concentração do elemento dopante bromo (Br) foi estudada no intervalo de 1,5x10-1 M a 10-2 M e o elemento chumbo (Pb) no intervalo de 10-2 M a 5x10-4 M. Para avaliar os cintiladores desenvolvidos foram efetuadas medidas sistemáticas de emissão de luminescência e tempo de decaimento de luminescência para a radiação gama, ensaios de transmitância óptica, ensaios de microdureza Vickers, determinações da distribuição dos dopantes ao longo dos cristais crescidos e análise da resposta dos cristais à radiação gama no intervalo de energia de 350 keV a 1330 keV e partículas alfa provenientes de fonte de 241Am com energia de 5,54 MeV. Os resultados obtidos de tempo de decaimento de luminescência para os cristais CsI:Br e CsI:Pb, no intervalo de 13 ns a 19 ns, mostraram-se promissores para medidas de alta energia. O estudo de microdureza mostrou um aumento significativo em função da concentração dos elementos dopantes, quando comparado ao cristal Csl puro, melhorando desta forma a resistência mecânica dos cristais crescidos. A validade de utilização desses cristais como sensores de radiação para medidas de radiação gama e partículas alfa, pode ser demonstrada pelos resultados da resposta à radiação. / Inorganic scintillators with fast luminescence decay time, high density and high light output have been the object of studies for application in nuclear physics, high energy physics, nuclear tomography and other fields of science and engineering. Scintillation crystals based on cesium iodide (CsI) are matters with relatively low higroscopy, high atomic number, easy handling and low cost, characteristics that favor their use as radiation detectors. In this work, the growth of pure CsI crystals, CsI:Br and CsI:Pb, using the Bridgman technique, is described. The concentration of the bromine doping element (Br) was studied in the range of 1,5x10-1 M to 10-2 M and the lead (Pb) in the range of 10-2 M to 5x10-4 M. To evaluate the scintillators developed, systematic measurements were carried out for luminescence emission and luminescence decay time for gamma radiation, optical transmittance assays, Vickers micro-hardness assays, determination of the doping elements distribution along the grown crystals and analysis of crystals response to the gamma radiation in the energy range of 350 keV to 1330 keV and alpha particles from a 241Am source, with energy of 5.54 MeV. It was obtained 13 ns to 19 ns for luminescence decay time for CsI:Br and CsI:Pb crystals. These results were very promising. The results obtained for micro-hardness showed a significant increase in function of the doping elements concentration, when compared to the pure CsI crystal, increasing consequently the mechanical resistance of the grown crystals. The validity of using these crystals as radiation sensors may be seen from the results of their response to gamma radiation and alpha particles.

This research focused on a comprehensive microstructural and mechanical property characterisation study of the Ni-Fe-Cr alloys 718 and 945X. The aim of the project was to better understand the relationship between performance and microstructure of existing (Alloy 718) and newly developed (Alloy 945X) high strength nickel alloys focusing on downhole applications. The main difference between the two alloys is that alloy 945X has lower Nb content than alloy 718, which may minimise the tendency to form delta when combined with correct processing. Previous studies have related the hydrogen embrittlement in alloy 718 with the collection of hydrogen by delta phase. Microstructural characterisation of the new alloy 945X after long term isothermal exposure up to 120 hours in the temperature range 650◦C to 900◦C was conducted with scanning electron microscopy (SEM), to generate a time-temperature-transformation (TTT) diagram. The TTT diagram was used as a road map for designing two isothermal heat treatments of alloy 945X on tensile specimens. Then, the effect of hydrogen charging on the tensile properties and microstructure of the 'as-received' and these two variant heat treatments was investigated. Fractographic analysis showed that, in the presence of hydrogen, intergranular fracture occurred for all the heat treatments, regardless the presence of delta phase at grain boundaries. There was no simple correlation between the volume fraction of delta-phase and susceptibility to hydrogen assisted embrittlement. Rather, it was demonstrated that the morphology and distribution of delta-phase along grain boundaries plays a key role and the other precipitate phases also have an influence through their effect on the ease of strain localisation. This study also examined the hydrogen embrittlement sensitivity of nickel alloy 718 given four different heat treatments to obtain various microstructural states. Each heat treatment leads to differences in the precipitate morphologies of γ', γ'' and delta phases. Material characterisation and fractography of the examined heat treatments were performed using a high resolution FEG-SEM. Three specimens of each condition were pre- charged with hydrogen and tensile properties were compared with those of non-charged specimens. It was observed that hydrogen embrittlement was associated with intergranular and transgranular microcrack formation, leading to an intergranular brittle fracture. delta phase may assist the intergranular crack propagation, and this was shown to be particularly true when this phase is coarse enough to produce crack initia- tion, but this is not the only factor determining embrittlement. Other microstructural features play a role, as does the strength of the material. Finally, the evolution of delta-(Ni3Nb) phase in alloy 718 from the early stages of precipitation, with a particular focus on identifying the grain boundary characteristics that favour precipitation of grain boundary delta phase was investigated. Results showed that delta phase was firstly formed on Σ3 boundaries after 5 hours at the examined temperature (800◦C). Increasing ageing time at 800◦C was observed to lead to an increase in size and precipitation of phases γ'-γ''-delta, an increase in fraction of the special CSL boundaries and an evolution in the morphology of twins and the growth of grains.

Cintiladores inorgânicos com tempo de decaimento de luminescência rápido, densidade alta e boa produção de luz têm sido objeto de estudos para aplicações em física nuclear, física de energias altas, tomografia nuclear e outros campos da ciência e da engenharia. Cristais de cintilação baseados em iodeto de césio (Csl) são materiais que apresentam higroscopia relativamente baixa, número atômico alto, fácil manuseio e custo baixo, características que favorecem o seu uso como detectores de radiação. Neste trabalho descreve-se a obtenção de cristais Csl puro, Csl:Br e Csl:Pb, utilizando-se a técnica de Bridgman. A concentração do elemento dopante bromo (Br) foi estudada no intervalo de 1,5x10-1 M a 10-2 M e o elemento chumbo (Pb) no intervalo de 10-2 M a 5x10-4 M. Para avaliar os cintiladores desenvolvidos foram efetuadas medidas sistemáticas de emissão de luminescência e tempo de decaimento de luminescência para a radiação gama, ensaios de transmitância óptica, ensaios de microdureza Vickers, determinações da distribuição dos dopantes ao longo dos cristais crescidos e análise da resposta dos cristais à radiação gama no intervalo de energia de 350 keV a 1330 keV e partículas alfa provenientes de fonte de 241Am com energia de 5,54 MeV. Os resultados obtidos de tempo de decaimento de luminescência para os cristais CsI:Br e CsI:Pb, no intervalo de 13 ns a 19 ns, mostraram-se promissores para medidas de alta energia. O estudo de microdureza mostrou um aumento significativo em função da concentração dos elementos dopantes, quando comparado ao cristal Csl puro, melhorando desta forma a resistência mecânica dos cristais crescidos. A validade de utilização desses cristais como sensores de radiação para medidas de radiação gama e partículas alfa, pode ser demonstrada pelos resultados da resposta à radiação. / Inorganic scintillators with fast luminescence decay time, high density and high light output have been the object of studies for application in nuclear physics, high energy physics, nuclear tomography and other fields of science and engineering. Scintillation crystals based on cesium iodide (CsI) are matters with relatively low higroscopy, high atomic number, easy handling and low cost, characteristics that favor their use as radiation detectors. In this work, the growth of pure CsI crystals, CsI:Br and CsI:Pb, using the Bridgman technique, is described. The concentration of the bromine doping element (Br) was studied in the range of 1,5x10-1 M to 10-2 M and the lead (Pb) in the range of 10-2 M to 5x10-4 M. To evaluate the scintillators developed, systematic measurements were carried out for luminescence emission and luminescence decay time for gamma radiation, optical transmittance assays, Vickers micro-hardness assays, determination of the doping elements distribution along the grown crystals and analysis of crystals response to the gamma radiation in the energy range of 350 keV to 1330 keV and alpha particles from a 241Am source, with energy of 5.54 MeV. It was obtained 13 ns to 19 ns for luminescence decay time for CsI:Br and CsI:Pb crystals. These results were very promising. The results obtained for micro-hardness showed a significant increase in function of the doping elements concentration, when compared to the pure CsI crystal, increasing consequently the mechanical resistance of the grown crystals. The validity of using these crystals as radiation sensors may be seen from the results of their response to gamma radiation and alpha particles.

O objetivo desse trabalho foi desenvolver um compósito cerâmico de zircônia-grafeno para aplicação odontológica. Este estudo avaliou o efeito do pó de partida, concentração de grafeno e da temperatura de sinterização sobre as propriedades mecânicas (dureza e tenacidade à fratura) do compósito desenvolvido. Para isto foram sintetizados os pós de Y-TZP a partir de soluções de óxido-cloreto de zircônio e cloreto de ítrio na proporção desejada de 3mol% através da rota de co-precipitação em solução de hidróxido de amônio seguido por uma série de lavagens em água, etanol e butanol com posterior destilação azeotrópica, secagem, moagem e calcinação. O grafeno foi obtido a partir da exfoliação química de grafite pelo método de Hummers [40] modificado por Marcano [39], o que resultou em um gel acastanhado que foi submetido a lavagem por centrifugação, secagem e desaglomeração em almofariz de ágata, resultando, por fim, no óxido de grafeno. Uma segunda etapa foi o processo de redução química com ácido ascórbico para obtenção de óxido de grafeno reduzido, um pó de coloração escura que foi adicionado à Y-TZP para a obtenção do compósito nas diversas concentrações (em mol%) que foram estudadas: (0,01%, 0,05%, 0,10%, 0,50%, 1,00% e 2,00%). Os pós foram caracterizados por termogravimetria, difração de raios X e espectroscopia (FT-IR). Os espécimes foram confeccionados em matriz metálica cilíndrica e sinterizados em forno tubular em atmosfera inerte. Outros espécimes foram confeccionados em matriz de grafite de alta densidade e sinterizados por Spark Plasma Sintering (SPS). Todas as amostras foram caracterizadas por meio de ensaios de densidade, dureza Vickers, tenacidade à fratura e microscopia eletrônica de varredura. Os maiores valores de densidade relativa foram observados para as amostras sinterizadas em SPS, sendo que se obteve valor de densidade relativa de 98,7 % para a concentração de 0,50% de grafeno e 98,4% para a Y-TZP pura. Por outro lado, o maior valor encontrado em sinterização em atmosfera a 1400°C sem a presença de H2 para Y-TZP pura foi da ordem de 96,76%. Os valores de dureza foram maiores nas amostras sinterizadas em SPS, no entanto a tenacidade à fratura mostrou não se alterar em função do conteúdo de grafeno. As fotomicrografias de MEV mostraram que houve uma variação de tamanho de grão de acordo com a presença do grafeno e do método de sinterização. De acordo com os resultados obtidos neste trabalho foi possível concluir que o processamento desenvolvido permitiu a criação de um compósito cerâmico zircônia-grafeno que pôde ser caracterizado por diversos métodos analíticos. A densidade teórica do compósito desenvolvido não foi alcançada por meio de nenhum dos métodos de sinterização utilizados (Tubular ou SPS) e nem variando-se a temperatura. Para espécimes sinterizados em atmosfera inerte, a maior temperatura de sinterização (1400°C) e a presença do gás H2 não melhorou a densificação. Além disso, esses espécimes tiveram aumento da dureza com o aumento da concentração de grafeno, entretanto, a sua tenacidade à fratura não foi afetada pelo teor de grafeno. Para espécimes sinterizados por meio de SPS, a temperatura de sinterização de 1350°C resultou em melhores valores de densificação. Além disso, para este tipo de sinterização, tanto a dureza como a tenacidade à fratura foram afetadas pelo teor de grafeno. / The objective of this work was to develop a zirconia-graphene ceramic composite for dental application. The study evaluated the effect of the starting powder effect, graphene concentration and sintering temperature on the mechanical properties of the composite. For this, the Y-TZP powders were synthesized from zirconium chloride and yttrium chloride solutions in the desired ratio of 3 mol% through the co-precipitation route in ammonium hydroxide solution followed by a series of washes in water, ethanol and butanol with subsequent azeotropic distillation, drying, grinding and calcination. Graphene was obtained from the chemical exfoliation of graphite by the method of Humans modified by Marcano, which resulted in a brownish gel that was subjected to washing by centrifugation, drying and deagglomeration in agate mortar, resulting finally in the graphene oxide. A second step was the chemical reduction with ascorbic acid to obtain reduced graphene oxide, a dark-colored powder that was added to the Y-TZP to obtain the composite in the various concentrations (in mol%) that were studied (0, 01%, 0.05%, 0.10%, 0.50%, 1.00% and 2.00%). The powders were characterized by thermogravimetry, X-ray diffraction and spectroscopy (FT-IR). The specimens were made in cylindrical metallic matrix and sintered in a tubular oven. Other samples were made in high density graphite matrix and sintered by Spark Plasma Sintering (SPS). All samples were characterized by means of density tests, Vickers hardness, fracture toughness and scanning electron microscopy. The highest values of relative density were observed for the sintered samples in SPS. A relative density of 98.7% was obtained for the 0.50% concentration of graphene and 98.4% for the pure Y-TZP. On the other hand, the highest value found in tubular sintering at 1400 ° C without the presence of H2 for pure Y-TZP was of the order of 96.76%. The hardness values were higher in the sintered samples in SPS, however the fracture toughness showed not to change as a function of the content of graphene. SEM images showed that there was a variation of grain size according to the presence of graphene and the sintering method. According to the results of this study it was concluded that the process developed allowed the creation of a graphene-zirconia ceramic composite which can be characterized by various analytical methods. The theoretical density of the composite developed was not achieved by any of the sintering methods used (tubular or SPS) nor by varying the temperature. For tubular sintered specimens, the higher sintering temperature (1400 ° C) and the presence of H2 gas did not improve densification. In addition, these specimens had increased hardness with increasing graphene concentration, however, their fracture toughness was not affected by graphene content. For sintered specimens by SPS, the sintering temperature of 1350 ° C resulted in better densification values. In addition, for this type of sintering, both hardness and fracture toughness were affected by the content of graphene