Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-01Bitstream added on 2014-06-13T19:48:08Z : No. of bitstreams: 1 ranieri_k_me_guara.pdf: 3916943 bytes, checksum: 88678d123d4709bfb7b9722e94a20ebd (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / Este trabalho apresenta o projeto e a construção de um equipamento para a produção de lingotes de compósitos de matriz metálica, com ligas de baixo ponto de fusão, e material de reforço na forma de pó cerâmico. O equipamento pode operar em temperaturas de até 1000 °C e carga de aproximadamente 800 g de metal. Possui um sistema para agitação do metal fundido e a possibilidade de controle dos principais parâmetros, térmicos e mecânicos, do processo de fundição com agitação mecânica. São descritas as diferentes partes do equipamento, e apresentados resultados utilizando a liga Al7%Si com reforço de alumina, sem recobrimento, e em granulações diferentes. A rota utilizada envolve a fusão do metal, seguida pelo seu resfriamento até temperaturas entre as linhas liquidus e solidus, seguida pela mistura da alumina, por determinado tempo, e o reaquecimento para vazamento. O equipamento mostrou-se eficiente na obtenção de compósitos particulados. Os lingotes obtidos foram analisados por microscopia eletrônica de varredura, EDS e microscopia óptica. / This work presents the project and construction of an equipment for synthesis of particulated metal matrix composite ingots, with low melting point, and ceramic as reinforcement material, using mechanical stir casting. The equipment can operate in temperatures up to 1000° C and loading of about 800g of metal. It has a system to stir the metal with the possibility of controling the main, thermal and mechanical, parameters of the process. Different parts of the equipament are described and results are presented by using the Al 7% Si alloy, with alumina, without recovering, and with different granulation. The process used was melting the metal followed by its cooling up to temperatures between liquidus and solidus lines, followed by the mixing of alumina and the reheating for pouring . The equipment was efficient in the obtainment of particulated metal matrix composite. The ingots obtained were analysed through electronic microscopy, EDS and optical microscopy.

Compósitos de matriz metálica (CMM) reforçados com dois tipos de particulado cerâmico foram produzidos por meio do processo ARB (Accumulative Roll Bonding) a fim de estudar os efeitos destes no que diz respeito às propriedades mecânicas e microestruturais. ARB é um processo de deformação plástica severa aplicada originalmente a uma pilha de lâminas metálicas, a qual é laminada, seccionada em duas metades, as quais são empilhadas e novamente laminadas, e assim por diante, desenvolvido com o propósito de reduzir o tamanho de grão e aumentar a resistência mecânica do produto final. O processo é econômico e capaz de produzir de folhas ultrafinas a placas espessas, sem que haja restrição de quantidade. Confeccionou-se CMM de alumínio reforçados com partículas de carbeto de silício (Al+SiCp) e alumina (e Al+Al2O3p) com granulometria média de 40µm, as quais foram caracterizadas microestruturalmente e ensaiadas em tração até a falha, cuja análise foi conduzida via microscopia eletrônica de varredura. Ambas as amostras obtiveram ganho em sua resistência mecânica, comparadas ao alumínio monolítico (sem adição de partículas de reforço) e alumínio recozido. Foram ensaiados em tração corpos de prova com e sem presença de entalhe, sendo que as peças entalhadas apresentaram comportamento esperado de aumento de resistência mecânica e baixo alongamento e fratura de aspecto frágil. De acordo com análise feita por fratografia houve boa ancoragem e dispersão das partículas de reforço na matriz. / Metal matrix composite (CMM) reinforced with two types of ceramic particles have been produced through the process ARB (Accumulative Roll Bonding) in order to study their effect as regards the mechanical and microstructural properties. ARB is a severe plastic deformation process originally applied to a stack of metal sheets, which is laminated, sectioned into two halves, which are stacked and rolled again, and so on, developed with the purpose of reducing the grain size and increase the mechanical strength of the final product. The process is economical and capable of producing ultrafine sheets to thicker plates without much restriction. Were fabricated CMM of the aluminum reinforced with particles of silicon carbide (Al + SiCp) and alumina (and Al + Al2O3p) with an average particle size of 40μm, which are characterized microstructurally and tested in tension until failure, whose analysis was conducted via scanning electron microscopy. Both samples were successful in its mechanical strength compared to the monolithic aluminum (without addition of reinforcing particles) and annealed aluminum. They were tested for tensile specimens with and without the presence of notch, and the carved pieces showed strength-enhancing behavior and low elongation and frail fracture. According to analysis by fractography was good anchoring and reinforcement particles dispersed in the matrix.

Particle-reinforced MMCs (pMMC) such as aluminum alloys reinforced with ceramic silicon carbide particles (AlSiC) require special cutting tools due to the high hardness and abrasive properties of the ceramic particles. Diamond coated cutting tools are ideal for machining this type of pMMC. Previous research studies focus on the machinability of pMMCs with low ceramic content. The aim of this research is to determine the optimal cutting parameters for machining AlSiC material containing high silicon carbide particle reinforcement (>25%). The optimal cutting parameters are determined by investigating the relationship between cutting forces, tool wear, burr formation, surface roughness, and material removal rate (MRR). Experimental milling tests are conducted using CVD diamond coated end mills and non-diamond tungsten carbide end mills. It was found that low tool rotation speeds, feed rates and depths of cut are necessary to achieve smoother surface finishes of R a < 1 μm. A high MRR to low tool wear and surface roughness ratio was obtainable at a tool rotation speed of 6500 r/min, feed rate of 762 mm/min and depth of cut of 3 mm. Results showed that a smooth surface roughness of the workpiece material was achieved with non-diamond tungsten carbide end mills, however, this was at the expense of extreme tool wear and high burr formation. The use of coolant caused a 50% increase in tool wear compared to the dry-cutting experiments which had lower cutting tool forces.

The ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen ionimplanted standard. Aluminum nitride and amorphous nitrogen-rich dispersoids were found in the nanocrystalline aluminum grain boundaries. Nitrogen concentration increased as a function of cryomilling time up to 72hours. A greater nitrogen concentration resulted in an enhanced thermal stability of the nanocrystalline aluminum phase and a resultant increase in hardness. The distribution of the nitrogen-rich dispersoids may be estimated considering their size and the concentration of nitrogen in the composite. Contributions to strength and ductility from the Orowan relation can be more accurately modeled with the quantified nitrogen concentration.

The development of metals that can overcome the strength-ductility-weight trade-off has been an ongoing challenge in engineering for many decades. A promising option for making such materials are Metal matrix composites (MMCs). MMCs contain dispersions of reinforcement in the form of fibers, particles, or platelets that significantly improve their thermal, electrical, or mechanical performance. This dissertation focuses on reinforcement with two-dimensional (2D) materials due to their unprecedented mechanical properties. For instance, compared to steel, the most well-studied 2D material, graphene, is nearly forty times stronger (130 GPa) and five times stiffer (1 TPa). Examples of reinforcement by graphene have achieved increases in strength of 60% due to load transfer at the metal/graphene interface and dislocation blocking by the graphene. However, the superior mechanical properties of graphene are not fully transferred to the matrix in conventional MMCs, a phenomenon known as the "valley of death." In an effort to develop key insight into how the relationships between composite design, processing, structure, properties, and mechanics can be used to more effectively transfer the intrinsic mechanical properties of reinforcements to bulk composite materials, nanolayered composite systems made of Ni, Cu, and NiTi reinforced with graphene or 2D hexagonal boron nitride h-BN is studied using experimental techniques and molecular dynamics (MD) simulations. / Doctor of Philosophy / The design of new metals with concurrently improved strength and ductility has been an enduring goal in engineering for many decades. The utilization of components made with these new materials would reduce the weight of structures without sacrificing their performance. Such materials have the potential to revolutionize many industries, from electronics to aerospace. Traditional methods of improving the properties of metals by thermomechanical processing have approached a point where only minor performance improvements can be achieved. The development of Metal matrix composites (MMCs) is among the best approaches to achieving the strength-ductility goal. Metal matrix composites are a class of materials containing reinforcements of dissimilar materials that significantly improve their thermal conductivity, electrical conductivity, or mechanical performance. Reinforcements are typically in the form of dispersed fibers, particles, or platelets. The ideal reinforcement materials have superior mechanical properties compared to the metal matrix, a high surface area, and a strong interfacial bond with the matrix. Two-dimensional (2D) materials (materials made up of a single to a few layers of ordered atoms) are attractive for reinforcement in composite materials because they possess unprecedented intrinsic properties. The most well-studied 2D material, graphene, is made of a single layer of carbon atoms arranged in a hexagonal honeycomb pattern. It is nearly forty times stronger (130 GPa) and five times stiffer (1 TPa) than steel. Examples of graphene reinforcing have shown increases in strength of 60% due to load transfer at the metal/graphene interface and dislocation blocking by the graphene. Despite their exceptional mechanical properties, the superior mechanical properties of graphene are not fully transferred to the matrix when incorporated into conventional metal matrix composites. This phenomenon, known as the "valley of death," refers to the loss of mechanical performance at different length scales. One cause of this phenomenon is the difficulty of evenly dispersing the reinforcements in the matrix using traditional fabrication techniques. Another is the presence of dislocations in the metal matrix, which cause very large local lattice strains in the graphene. This atomistic-scale deformation at the interface between the metal and the graphene can significantly weaken it, leading to failure at low strains before reaching its intrinsic failure stress and strain. This dissertation aims to provide insight into how the relationships between composites' design, processing, structure, properties, and mechanics can be used to transfer intrinsic mechanical properties of reinforcements to bulk composite materials more effectively. For this, nanolayered composite systems of Ni and Cu reinforced with graphene or 2D h-BN were studied using experimental techniques and molecular dynamics (MD) simulations to elucidate the underlying mechanisms behind the composites' material structure and mechanical behavior. Additionally, we explore the incorporation of graphene in a metallic matrix that does not deform through dislocations (or shear bands), such as the shape memory alloy nickel-titanium ( Nitinol or NiTi), to avoid low strain failure of the metal/graphene interface. This theoretical strengthening mechanism is investigated by designing and fabricating NiTi/graphene composites.

The tribological properties of cold sprayed Ni-WC metal matrix composite (MMC) coatings were investigated under dry sliding conditions from room temperature (RT) up to 400°C, and during thermal cycling to explore their temperature adaptive friction and wear behavior. Characterization of worn surfaces was conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy to determine the chemical and microstructural evolution during friction testing. Data provided insights into tribo-oxide formation mechanisms controlling friction and wear. It was determined that the steady-state coefficient of friction (CoF) decreased from 0.41 at RT to 0.32 at 400˚C, while the wear rate increased from 0.5×10-4 mm3/N·m at RT to 3.7×10-4 mm3/N·m at 400˚C. The friction reduction is attributed primarily to the tribochemical formation of lubricious NiO on both the wear track and transfer film adhered to the counterface. The increase in wear is attributed to a combination of thermal softening of the coating and a change in the wear mechanism from adhesive to more abrasive. In addition, the coating exhibited low friction behavior during thermal cycling by restoring the lubricious NiO phase inside the wear track at high temperature intervals. Therefore, cold sprayed Ni-WC coatings are potential candidates for elevated temperature and thermally self-adaptive sliding wear applications.

No description available.

Este trabalho versa sobre a inspeção fratográfica por Microscopia Eletrônica de Varredura (MEV) e a análise micro-química por Energia Dispersiva de Raios-X de superfícies de fratura de um compósito particulado de matriz metálica (CMM = liga AA356 + SiC) manufaturado por compofundição e submetido a diferentes classes de ensaios mecânicos, a saber, impacto Charpy, flexão quase-estática e fadiga fletiva. A fratografia por MEV em modo de imageamento por elétrons secundários se mostrou uma poderosa ferramenta na análise dos aspectos topográficos de CMM particulados fraturados, que se relaciona diretamente ao aporte de energia (ou ao nível de tensão desenvolvido) para a criação da superfície de fratura, independentemente do tipo de solicitação mecânica aplicada. Mecanismos de tenacificação em CMM, tais como descolamento, trincamento e arrancamento de partículas de SiC da matriz metálica AA356 foram prontamente identificados e documentados por esta modalidade MEV, e correlacionados ao desempenho mecânico dos materiais investigados. Aglomeração de partículas de SiC, assim como a presença de poros e/ou vazios se revelaram freqüentemente como variáveis determinantes do desempenho mecânico do CMM em ensaios dinâmicos, quase-estáticos e cíclicos. MEV em modo de imageamento por elétrons retro-espalhados se mostrou extremamente útil na identificação de partículas de SiC aflorando em superfícies de fratura do CMM quando o emprego de elétrons secundários não foi bem sucedido na tarefa. Micro-análise química por EDS permitiu o mapeamento dos elementos Fe e Cr, além de Mn, e possibilitou classificá-los como formadores de precipitados potencialmente fragilizantes do CMM. Esta técnica também assegurou a identificação de reticulados ricos em Si ao redor dos glóbulos de fase pró-eutética (alfa), os quais (reticulados) são altamente favorecedores de fraturas intergranulares. / This work focuses on the fractographic inspection by Scanning Electron Microscopy (SEM) and micro-chemical analysis by Energy Dispersive X-Ray Spectroscopy (EDS) of fractured surfaces of a compocast particulate metal matrix composite (MMC = AA356 alloy + SiC) subjected to different classes of mechanical testing, namely, Charpy impact, quasi-static flexure and flexural fatigue. SEM fractography in secondary electron imaging mode has shown to be a powerful tool in analyzing topographic aspects of fractured particulate MMC, which are straightforwardly related to the energy apportion (or the developed stress level) to the fracture surface creation, regardless the applied mechanical loading type. Toughening mechanisms for MMC, such as SiC particle debonding, cracking and pulling-out from the metallic matrix AA356 alloy were promptly identified and documented through this SEM modality, and correlated to the mechanical performance of investigated materials. SiC particle clusters as well as pore and/or void presence were very often discovered as the main controlling variables of mechanical performance of MMC during dynamic, quasi-static and cyclic testing. SEM fractography in backscatted electron imaging mode has shown to be extremely useful on the identification of SiC particles emerging from fractured surfaces of MMC when secondary electron mode did not succeed in this task. EDS micro-chemical analysis allowed to map Fe and Cr, besides Mn, and permitted to classify them as potentially MMC-embrittling precipitated forming elements. This technique also assured the identification of Si-rich reticulated structure around pro-eutectic phase globules, which (reticulated structure) highly favors intergranular fracture.

Compósitos de matriz metálica combinam diferentes classes de materiais a fim de obter novas propriedades, superiores às dos materiais originais. A adição de partículas cerâmicas (reforço) em ligas de cobre pode melhorar suas propriedades mecânicas sem gerar grande perda na condutividade elétrica. Este trabalho teve como objetivo processar e estudar a microestrutura e propriedades (condutividade elétrica, dureza e fratura) de compósitos à base de cobre reforçados com alumina e céria. As amostras foram processadas pela técnica de metalurgia do pó: pesagem, mistura (sem bolas por 30min a 46 rpm), compactação (uniaxial à frio com pressão de 1080 Mpa por 10s) e sinterização (800°C por 6h sob vácuo de 10-5 torr). As análises de MO, MEV, EDS e DRX (com refinamento Rietveld) indicaram boa coalescência das partículas, formando superfície continua e com baixa porosidade. A alumina formou regiões aglomeradas da ordem de 20 &mu;m, a céria ficou finamente dispersa nos contornos de grão do cobre com algumas regiões aglomeradas, o cromo formou regiões de cerca de 100 &mu;m e não teve distribuição completamente uniforme ao longo da matriz, a prata formou solução sólida com o cobre e, durante o resfriamento lento, formou precipitados menores do que 5 &mu;m uniformemente dispersos no interior dos grãos de cobre. Os compósitos apresentaram condutividade elétrica entre 15 e 40 %IACS, dureza entre 62 e 88 HV5 e as fractografias apresentaram fratura mista e regiões indicando boa adesão matriz-reforço. Em relação ao cobre puro, foi observado efetivo aumento na dureza (cerca de 2x), porém, em todos os compósitos, o acréscimo da fase cerâmica acarretou na diminuição da condutividade elétrica. Os compósitos de Cu-8%(Al2O3, CeO2) foram os que apresentaram melhor equilíbrio entre essas duas propriedades, com condutividade de 40 e 38 %IACS e dureza de 63 e 69 HV5. / Metal matrix composites combine different classes of materials to obtain new properties, superior to those of the original materials. The addition of ceramic particles (reinforcement) in copper alloys could improve their mechanical properties without generating great loss in electrical conductivity. The aim of this work was to process and study the microstructure and properties (electrical conductivity, hardness and fracture) of copper-based composites reinforced with alumina and ceria. The samples were processed by the powder metallurgy technique: weighing, blending (no balls for 30 min at 46 rpm), compaction (cold uniaxial at 1080 MPa for 10s) and sintering (800°C for 6 h under vacuum of 10-5 torr). Analysis of OM, SEM, EDS and XRD (with Rietveld refinement) indicated good coalescence of the particles, forming continuous surface with low porosity. The alumina formed agglomerated regions with approximately 20 &mu;m, the ceria was finely dispersed in the grain boundary of the copper with some agglomerated regions, the chromium formed regions of about 100 &mu;m and have a non-uniform distribution throughout the matrix, the silver formed solid solution with copper and, during slow cooling, formed precipitates smaller than 5 &mu;m, uniformly dispersed inside the copper grains. The composites presented electrical conductivity between 15 and 40 %IACS, hardness between 62 and 88 HV5 and the fractographs presented mixed fracture and regions indicating good matrix-reinforcement adhesion. In relation to pure copper, it was observed an increase in hardness (about 2x), however, in all the composites, the increase of the ceramic content led to a decrease in the electrical conductivity. The Cu-8%(Al2O3, CeO2) composites showed the best balance between these two properties, with conductivity of 40 and 38 %IACS and hardness of 63 and 69 HV5.

Made available in DSpace on 2017-07-21T20:43:49Z (GMT). No. of bitstreams: 1 Pedro Henrique F Oliveira.pdf: 13888256 bytes, checksum: 45c80d3205c28d94e4c7c0eb2987187f (MD5) Previous issue date: 2016-09-23 / The aim of this study was to produce deposit of the alloy AA 6351-T6, filled with alumina particles, on an AA5052-32 alloy substrate using friction-surfacing technology. The depositions were performed with holes in the AA6351-T6 consumable rods, which were filled with particulate alumina (Al2O3). A conventional milling machine, KONE KFE-3 / BR, available by SENAI Ponta Grossa – Paraná, was used to carry out the deposition. The control parameter used for the making the deposits was the rod feed rate being calculated from the relationship between the upward axial displacement in the Z axis (Dz) of the machine table and the total time (t) of deposition. The deposits obtained were evaluated from their physical aspects such as width, thickness and length. In addition, bending tests were conducted for a qualitative assessment of the influence of the alumina particles in the adhesion of the deposit to the substrate and microhardness profiles were obtained to evaluate the influence of the alumina particles produced in the hardness of the deposits. Images of optical microscopy images (OM) and scanning electron microscopy (SEM) were obtained to evaluate the microstructure and morphology of the deposits produced. The volume fraction of alumina particles in the deposits were obtained by digital processing of the images by optical microscopy. EBSD analysis of deposits in specific regions were performed in order to support the microstructural analysis, enabling verify grain size distribution in different regions of deposits showing the existence of substructures indicating the occurrence of dynamic recrystallization phenomenon. The results showed that it was possible to produce deposits with a refined microstructure and with a certain dispersion of alumina particles. Depositions with two holes in the rod produced deposits with higher volume fraction, and this increase in volume fraction was accompanied by higher hardness values. / O presente trabalho buscou depositar a liga AA 6351-T6, preenchida com partículas de alumina (Al2O3), sobre um substrato de liga AA5052-32 através da tecnologia de deposição superficial por atrito (friction surfacing). As deposições foram realizadas com um e dois furos nas hastes de liga AA6351-T6, que foram preenchidos com partículas de alumina. Para a realização das deposições foi utilizada uma fresadora convencional KONE KFE-3/BR disponibilizada pelo SENAI Ponta Grossa – Paraná. O parâmetro de controle utilizado para a confecção dos depósitos foi a taxa de alimentação da haste, sendo calculada a partir da relação entre o deslocamento axial ascendente no eixo Z (Dz) da mesa da máquina com o tempo total (t) de deposição. Os depósitos obtidos após o processamento foram avaliados a partir de seus aspectos físicos tais quais largura, espessura e comprimento. Também foram realizados ensaios de dobramento para uma avaliação qualitativa da influência das partículas de alumina na adesão do depósito no substrato e foram obtidos perfis de microdureza para avaliação da influência das partículas de alumina na dureza dos depósitos produzidos. Foram obtidas imagens de microscopia ótica (MO) e microscopia eletrônica de varredura (MEV) para avaliação da microestrutura e morfologia dos depósitos produzidos. Ainda foi obtida a fração volumétrica das partículas de alumina nos depósitos produzidos através de processamento digital das imagens obtidas por microscopia óptica. Análises de EBSD em regiões específicas dos depósitos foram realizadas com o intuito de reforçar a análise microestrutural possibilitando verificar a distribuição de tamanho de grão em diferentes regiões dos depósitos, mostrando a existência de subestruturas indicando a ocorrência do fenômeno de recristalização dinâmica. Os resultados mostraram que foi possível produzir depósitos com uma microestrutura refinada e com uma certa dispersão de partículas de alumina. As deposições com dois furos na haste produziram depósitos com maior fração volumétrica, sendo que esse aumento da fração volumétrica foi acompanhada pelo aumento dos valores de dureza.