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The presented diploma thesis deals with the issue of wire electrical discharge machining of SiSiC ceramics. The first part explains the principles of electrical discharge machining, describes the WEDM technology and presents the properties of the advanced ceramics. The second part consists of a detailed analysis of the cutting process of eighteen samples obtained with systematically changing process parameters. Based on the obtained results from EDX analysis, SEM electron microscopy and topography there was performed an analysis of the influence of process parameters on the cutting speed, surface roughness, kerf width and number of wire breaks with usage of the selected brass cutting wire. From the evaluated results it was possible to select a combination of parameters that ensured a stable machining process.

High capacitance devices were developed using rapid electrophoretic deposition (EPD) of barium titanate (BaTiO3) on ultrasonically etched nickel (Ni) substrates. The microstructural and electrical properties of films with varying thicknesses, sintering temperatures and substrate etching times were investigated to study their effect on the capacitance. Although increasing the capacitance was the primary goal, decreasing manufacturing costs and reducing environmental impact was also considered. After confirming the tetragonality and particle size of a 0.2 µm hydrothermal powder, it was dispersed in an aqueous-organic mixture of ethanol, acetone and water. A zeta potential of 50 mV was observed at the EPD pH level (6.8). Flocculation or coagulation was not likely in this situation. Therefore, mixing water with an organic solution was an effective method for reducing environmental impact while maintaining deposition quality. The presence of BaCO3 in the films was proven using X-ray diffraction. Other impurities such as TiO2 and NiO were not detected. A significant variation in the average grain size was not observed for films with different thicknesses whereas films sintered at different temperatures displayed greater variation. A bimodal pore size distribution in the samples suggested that the powder was agglomerated after deposition due to a high deposition voltage (20 V). Rapid deposition times of 2 to 8 seconds offered a potential for cost reduction compared to longer deposition times implemented in industry. Therefore the increased porosity was accepted. The dielectric constant of the films increased from 2900 to 6730 as the thickness increased from 17.75 µm to 47.5 µm. The dissipation factor decreased from 0.27 to 0.06 with increasing thickness. This behavior was attributed to a low dielectric constant interfacial layer and a higher dielectric leakage current at smaller thicknesses. The dielectric constant increased from 1700 to 6350 and the dissipation factor decreased from 0.23 to 0.04 as the sintering temperature increased from 1150°C to 1300°C. This was attributed to an increase in tetragonality with grain size and a decrease in porosity with sintering temperature. Finally, etching a substrate for 60 seconds increased its capacitance by 27.47% and using ultrasonic agitation further increased the capacitance by 8.75%. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-10-12 00:54:53.915

O estudo trata da medição da força de usinagem a verde de corpos de provas cerâmicos e sua correlação com as propriedades mecânicas após a sinterização. A usinagem a verde é empregada em compactos brutos para conferir formatos sem extremo compromisso com precisão dimensional ou para obter uma pré-forma antes da usinagem de acabamento após sinterização; é extensivamente empregada na usinagem de cerâmicas avançadas. Durante o processo de usinagem a verde os esforços de corte determinam a introdução de defeitos críticos na superfície e são geralmente estes defeitos que governam as propriedades mecânicas das cerâmicas após a sinterização. O trabalho objetiva a elaboração e montagem de um sistema de aquisição de dados das forças de usinagem, e procura identificar o limite de agressividade de corte na manutenção da integridade do corpo de prova com produção econômica. As medidas de torque de usinagem e velocidade periférica do rebolo podem representar um modelo para predizer a associação das forças de usinagem. Corpos de prova cilíndricos foram conformados a 100 e 200 MPa, tratados termicamente após a prensagem e usinados com diferentes parâmetros de corte, sinterizados e ensaiados quanto à resistência mecânica através de compressão e flexão a quatro pontos. Os resultados mostraram a importância do tratamento térmico antes da usinagem acima da temperatura de transição vítrea do ligante para peças prensadas a 100 e 200 MPa. Peças prensadas a 200 MPa e tratadas termicamente foram usinadas sem danos a taxas de remoção de 10.000 \'MM POT.3\'/min com potencia consumida de 1700 W. Com o emprego de um cabeçote com mancais aerostáticos de alta potência e baixo ruído não se detectou a introdução progressiva de defeitos críticos na superfície devido à ação do rebolo, porém se identificou um limite de velocidade de 400 mm/min em função da profundidade de corte que excedeu a resistência mecânica dos corpos de prova comprimidos a 100 MPa, levando a ruptura. A correlação entre potência consumida e taxa de remoção, forneceu informações muito importantes para o projeto de uma máquina de usinagem á verde de produtos cerâmicos em alumina. / The present study deals with the measurement forces of green machining ceramics and their correlation with the mechanical properties after sintering. The green machining is employed in crude compacts either to check raw formats without compromising the extreme dimensional accuracy or to obtain a preform prior to finish machining after sintering, extensively used in the machining of advanced ceramics. During the process of the green machining, cutting forces determine the introduction of the critical defects in the surface, which generally govern the mechanical properties after the sintering of ceramics. The study aims at the development and installation of a system of machining forces data acquisition and also the identification of the limit of cutting aggression to maintain the integrity of the ceramics with economic production. The torque measurements of machining and grinding wheel peripheral speed can represent a model to predict the association of the machining forces. Cylindrical bodies were conformed at 100 and 200 MPa, heat-treated after pressing and machined with different cutting parameters, sintered and tested concerning strength by compression and bending at four points. The results showed the importance of the heat treatment before machining above the glass transition temperature of the binder for the parts pressed at 100 and 200 MPa. Parts pressed at 200 MPa and heat-treated were machined without damage at 10.000 \'MM POT.3\'/min removal rates with power consumption of 1700 W. With the use of a spindle with aerostatic bearings for high power and low noise the gradual introduction of critical defects into the surface was not detected due to the action of the wheel. However a speed limit was identified in function of the depth of the cut, which exceeded the strength of the ceramics compressed at 100 MPa, leading to rupture. The correlation between power consumption and rate of removal provided very important information for the design of a green machining of ceramic products in alumina.

In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as sintering aids. SiC batches between 0.25-4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0-2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (~95.5-96.5%) and a fine, equiaxed microstructure (d50 = 2.525 µm). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These parts exhibited higher density and finer microstructure than a commercially-available sintered SiC from Saint-Gobain (Hexoloy Enhanced, 3.153 g/cm3 and d50 = 4.837 µm). Due to the optimized microstructure, Verco SiC parts exhibited the highest Vickers (2628.30 ± 44.13 kg/mm2) and Knoop (2098.50 ± 24.8 kg/mm2) hardness values of any SiC ceramic, and values equal to those of the "gold standard" hot-pressed boron carbide (PAD-B4C). While the fracture toughness of hot-pressed SiC materials (~4.5 MPa m1/2) are almost double that of Verco SiC (2.4 MPa m1/2), Verco SiC is a better performing ballistic product, implying that the higher hardness of the theoretically-dense, clean-grain boundary, fine-grained SiC is the defining mechanical property for optimization of ballistic behavior.

O estudo trata da medição da força de usinagem a verde de corpos de provas cerâmicos e sua correlação com as propriedades mecânicas após a sinterização. A usinagem a verde é empregada em compactos brutos para conferir formatos sem extremo compromisso com precisão dimensional ou para obter uma pré-forma antes da usinagem de acabamento após sinterização; é extensivamente empregada na usinagem de cerâmicas avançadas. Durante o processo de usinagem a verde os esforços de corte determinam a introdução de defeitos críticos na superfície e são geralmente estes defeitos que governam as propriedades mecânicas das cerâmicas após a sinterização. O trabalho objetiva a elaboração e montagem de um sistema de aquisição de dados das forças de usinagem, e procura identificar o limite de agressividade de corte na manutenção da integridade do corpo de prova com produção econômica. As medidas de torque de usinagem e velocidade periférica do rebolo podem representar um modelo para predizer a associação das forças de usinagem. Corpos de prova cilíndricos foram conformados a 100 e 200 MPa, tratados termicamente após a prensagem e usinados com diferentes parâmetros de corte, sinterizados e ensaiados quanto à resistência mecânica através de compressão e flexão a quatro pontos. Os resultados mostraram a importância do tratamento térmico antes da usinagem acima da temperatura de transição vítrea do ligante para peças prensadas a 100 e 200 MPa. Peças prensadas a 200 MPa e tratadas termicamente foram usinadas sem danos a taxas de remoção de 10.000 \'MM POT.3\'/min com potencia consumida de 1700 W. Com o emprego de um cabeçote com mancais aerostáticos de alta potência e baixo ruído não se detectou a introdução progressiva de defeitos críticos na superfície devido à ação do rebolo, porém se identificou um limite de velocidade de 400 mm/min em função da profundidade de corte que excedeu a resistência mecânica dos corpos de prova comprimidos a 100 MPa, levando a ruptura. A correlação entre potência consumida e taxa de remoção, forneceu informações muito importantes para o projeto de uma máquina de usinagem á verde de produtos cerâmicos em alumina. / The present study deals with the measurement forces of green machining ceramics and their correlation with the mechanical properties after sintering. The green machining is employed in crude compacts either to check raw formats without compromising the extreme dimensional accuracy or to obtain a preform prior to finish machining after sintering, extensively used in the machining of advanced ceramics. During the process of the green machining, cutting forces determine the introduction of the critical defects in the surface, which generally govern the mechanical properties after the sintering of ceramics. The study aims at the development and installation of a system of machining forces data acquisition and also the identification of the limit of cutting aggression to maintain the integrity of the ceramics with economic production. The torque measurements of machining and grinding wheel peripheral speed can represent a model to predict the association of the machining forces. Cylindrical bodies were conformed at 100 and 200 MPa, heat-treated after pressing and machined with different cutting parameters, sintered and tested concerning strength by compression and bending at four points. The results showed the importance of the heat treatment before machining above the glass transition temperature of the binder for the parts pressed at 100 and 200 MPa. Parts pressed at 200 MPa and heat-treated were machined without damage at 10.000 \'MM POT.3\'/min removal rates with power consumption of 1700 W. With the use of a spindle with aerostatic bearings for high power and low noise the gradual introduction of critical defects into the surface was not detected due to the action of the wheel. However a speed limit was identified in function of the depth of the cut, which exceeded the strength of the ceramics compressed at 100 MPa, leading to rupture. The correlation between power consumption and rate of removal provided very important information for the design of a green machining of ceramic products in alumina.

Sintering is a one of the key step in a processing of bulk ceramic materials. New sintering methods were invented in the last years. These new sintering methods, according to their authors, can be used for obtaining finer final microstructure of ceramics only by modifying the heating schedule. This work is focused on an influence of the Two Step Sintering method on the final microstructure for oxide ceramics. Obtained experimental results have shown that the effectivity of the Two Step Sintering method is rising with crystallographic symmetry of used material. Thesis is also focused on a high-temperature dilatometry and concept of the Master Sintering Curve. This concept was used for calculation of the activation energy of sintering and finding different sintering mechanisms acting in the intermediate and final stage of sintering. Activation energy of sintering was compared with activation energy of grain growth with target to find the kinetic window. Kinetic window can allow a sintering without a grain growth. Master Sintering Curve method was also used in a pressure assisted unconventional sintering technique Spark Plasma Sintering. Master Sintering Curve applied to a Spark Plasma Sintering technique reveals and quantified different sintering mechanisms acting in Spark Plasma Sintering. These findings led to preparation of transparent tetragonal ZrO2.

The doctoral thesis is orientated to preparation of advanced ceramic materials by electrophoretic deposition (EPD). The vertical mode of EPD in constant current regime was used in this study. The morphology of prepared materials (image structural analysis), physical properties (EPD yields, relative density, roughness of deposit surface) and mechanical properties (hardness, fracture toughness, elastic module) were characterized on the prepared deposits from alumina (Al2O3), zirconia (ZrO2) or their composites. It was found that the surface charge of alumina or zirconia particles was opposite (inversion charge) in stabilized isopropanolic dispersions than in case of water dispersions. The model of alumina or zirconia particles “inverse” stabilization was proposed. This type of EPD was further studied in presence of different acidic stabilizers. The obtained results from the experimental work (-potential and electric conductivity of dispersions, EPD yields, relative density of deposits, roughness of deposit surface etc.) showed the monochloracetic acid as the optimal type of acidic stabilizer. The kinetic of EPD process from dispersions containing isopropanol, monochloracetic acid and Al2O3 or ZrO2 particles and its influence on the final properties of prepared deposits was studied. The new method of kinetic measurement was developed. Due to good knowledge of EPD kinetic the ceramic laminates (Al2O3/ZrO2) with optimized layer thickness were prepared. The internal stresses and their influence on crack trajectory in ceramic laminates contained 100-150 strongly bonded layers were studied. It was found that the dominant role of crack deflection played the internal compressive stresses, i.e. with increasing of amount of internal compressive stresses the crack deflection was also increased. This work brought a new knowledge in the area of non-aqueous ceramic dispersion stabilization and preparation of heterostructured ceramic materials.

Este trabalho apresenta um módulo sensor de pressão absoluta do duto de admissão (MAP) para aplicações automotivas desenvolvido em substrato cerâmico LTCC. Em um veículo com sistema de injeção eletrônica de combustível, o sensor MAP informa a unidade de controle do motor sobre a pressão no duto de admissão permitindo o cálculo da vazão de ar e o ajuste da injeção de combustível. O sensor desenvolvido possui circuitos eletrônicos para a aquisição de sinais analógicos e digitais, realiza o condicionamento de sinal, a calibração e compensação de temperatura através de processamento digital, que permitem a indicação de pressões de 0 a 100kPa na faixa de temperaturas de -40 a +125ºC. Utilizou-se um elemento sensor de pressão piezorresistivo com membrana micro fabricada em silício e um sensor resistivo de temperatura. São apresentadas: a topologia do circuito, a construção, caracterização e testes. O protótipo apresenta precisão melhor do que 1,5% FE em pressão e 0,5% em temperatura. O teste de diferentes sensores de pressão e diferentes funções de transferência é facilmente realizado através de um circuito versátil que permite a alteração via programa. A montagem em cerâmica LTCC é realizada e é desenvolvida uma técnica de montagem do sensor de pressão MEMS em flip-chip, com excelentes resultados. Finalmente, é apresentado o teste em operação real em um veículo. / This paper presents a manifold absolute pressure (MAP) sensor module developed on LTCC substrate. In electronic fuel injection systems, a MAP sensor measures the vacuum at the engine intake manifold, allowing the electronic control unit to calculate mass flow and control the fuel injection. The sensor developed is composed by electronic circuits for analog signal acquisition and generation, digital signal processing and features software calibration and temperature-compensated pressure indications from 0 to 100kPa in the -40 to +125ºC temperature range. It is presented the assembly of a MEMS silicon pressure sensor and a thermistor on ceramic substrate and also the circuit topology, construction, characterization and tests. The prototype exhibits full scale accuracy better than 1.5% for pressure and 0.5% for temperature measurements. Tests are easily performed with different pressure sensors and different transfer functions due to a versatile circuit which enables software updates. The assembly on LTCC ceramic substrate is performed and an innovative flip-chip assembly technique is developed for MEMS pressure sensors, with excellent results. Finally, it is presented the test on a real vehicle.

Nesta tese foram sintetizadas nove amostras de hidróxido de alumínio, a partir da reação de folhas de alumínio amalgamado em diversos meios reagentes. Esses hidróxidos foram caracterizados por microscopia eletrônica de transmissão, difração eletrônica de varredura e difração de raios-X. A caracterização permitiu descrever a morfologia dos cristais obtidos e identificar rotas novas de preparo de hidróxidos de alumínio. Sendo elas: em meio metanol foi sintetizada gibsita (com alteração em seu hábito cristalino); em meio etanol foram sintetizadas misturas de hidróxidos de alumínio (à concentração de 20% resulta em mistura de cristais de baierita e nordstrandita; à concentração de 50%, mistura de gibsita, baierita e pseudoboemita; quando usando o etanol comercial, apenas a pseusoboemita); foi observado que a elevação da concentração de etanol leva a predominância da síntese de pseudoboemita; em meio álcool isopropílico foi sintetizada uma mistura de baierita e nordstrandita e em meio glicerina sintetizou-se apenas pseudoboemita. Foi desenvolvido um estudo de transformação de fase dos cristais de dois dos hidróxidos produzidos por essas rotas: baierita e nordstrandita. Pelos métodos de difração eletrônica de área selecionada e análise térmica diferencial foi determinada a seguinte sequência de transformações em função da temperatura: alumina-eta alumina-tetaalumina-alfa; as modificações na textura e morfologia foram acompanhadas, ao longo desse processo, pelas microscopias eletrônica de transmissão e varredura. Por microscopia eletrônica de transmissão e suas técnicas associadas, o processo de cristalização da nordstrandita pode ser acompanhado, que permitiu descrever, pela primeira vez, a nucleação e o crescimento desses cristais assim como seus efeitos na morfologia final do cristal. O mecanismo de transformação da pseudoboemita em nordstrandita permitiu mostrar, que o modelo de trasnformação da pseudoboemita pode ser generalizado para as três formas de trihidróxidos de alumínio. / Nine aluminium hydroxides were synthesized from the reaction between amalgameted aluminium foils and different aqueous solutions. The synthetic hydroxides were characterized by transmission electron microscopy, selected area electron diffraction, X-ray microanalysis, scanning electron microscopy and x-ray diffraction. These characterizations identified new routes for producing gibbsite, bayerite, nordstrandite and fibrilar pseudoboehmite and the influence of different aqueous solution in these crystallization. A morphological description of these hydroxides was made. The thermal transformation of bayerite and nordstrandite crystals into transition aluminas was studied by transmission electron microscopy, scanning electron microscopy and selected area diffraction. The nordstrandite crystallization process was followed by electron optical techniques. Original results about nucleation and crystal growth were obtained for nordstrandite. The mechanism of transformation (pseudoboehmite into nordstrandite) was verified, and in general Al(OH) IND 3 comes from the pseudoboehmite.