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Orientador: Carlos Kiyan / Banca: Aélcio Zangrandi / Banca: Carlos de Moura Neto / Resumo: 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. / Abstract: 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. / Mestre

Rapid modern technological changes and improvements bring great motivations in advanced material designs and fabrications. In this context, metal matrix composites, as an emerging material category, have undergone great developments over the past 50 years. Their primary applications, such as automotive, aerospace and military industries, require materials with increasingly strict specifications, especially high stiffness, lightweight and superior strength. For these advanced applications, carbon fiber reinforced aluminum matrix composites have proven their enormous potential where outstanding machinability, engineering reliability and economy efficiency are vital priorities. To contribute in the understanding and development of carbon fiber reinforced aluminum matrix composites, this study focuses on composite fabrication, mechanical testing and physical property modelling. The composites are fabricated by squeeze casting. Plain weave carbon fiber (AS4 Hexcel) is used as reinforcement, while aluminum alloy 6061 is used as matrix. The improvement of the squeeze casting fabrication process is focused on reducing leakage while combining thermal expansion pressure with post-processing pressing. Three different fiber volume fractions are investigated to achieve optimum mechanical properties. Piston-on-ring (POR) bend tests are used to measure the biaxial flexural stiffness and fracture strength on disc samples. The stress-strain curves and fracture surfaces reveal the effect of fiber-matrix interface bonding on composite bend behaviour. The composites achieved up to 11.6%, 248.3% and 90.1% increase in flexural modulus, strain hardening modulus and yield strength as compared with the unreinforced aluminum alloy control group, respectively. Analytical modelling and finite element modelling are used to comparatively characterise and verify the composite effective flexural modulus and strength. Specifically, they allowed iii evaluating how far the experimental results deviate from idealized assumptions of the models, which provides an insight into the composite sample quality, particularly at fiber-matrix interfaces. Overall, the models agree well with experimental results in identifying an improvement in flexural modulus up to a carbon fiber volume fraction of 4.81vol%. However, beyond a fiber content of 3.74vol%, there is risk of deterioration of mechanical properties, particularly the strength. This is because higher carbon fiber volume fractions restrict the infiltration and wetting of carbon fibre by the liquid, potentially leading to poor fiber-matrix interface bonding. It is shown that higher thermal expansion pressures and subsequent post-processing pressing can overcome this challenge at higher carbon fiber volume contents by reducing fiber-aluminum contact angle, improving infiltration, reducing defects such as porosity, and overall improving fiber-matrix bonding.

This research is a systematic study exploring a new fabrication methodology for long-fiber-reinforced metal matrix composites (MMCs) using a novel additive manufacturing technology. The research is devoted to the manufacture of long-fiber-reinforced MMC structures using the Ultrasonic Consolidation (UC) process. The main objectives of this research are to investigate the bond formation mechanisms and fiber embedment mechanisms during UC, and further to study the effects of processing parameters on bond formation and fiber embedment, and the resultant macroscopic mechanical properties of UC-made MMC structures. From a fundamental research point of view, bond formation mechanisms and fiber embedment mechanisms have been clarified by the current research based on various experimental observations. It has been found that atomic bonding across nascent metal is the dominant bond formation mechanism during the UC process, whereas the embedded fiber are mechanically entrapped within matrix materials due to significant plastic deformation of the matrix material during embedment. From a manufacturing process point of view, the effects of processing parameters on bond formation and fiber embedment during the UC process have been studied and optimum levels of parameters have been identified for manufacture of MMC structures. An energy-based model has been developed as a first step toward analytically understanding the effects of processing parameters on the quality of ultrasonically consolidated structures. From a material applications point of view, the mechanical properties of ultrasonically consolidated structures with and without the presence of fibers have been characterized. The effects on mechanical properties of UC-made structures due to the presence of embedded fibers have been discussed.

The present work aims to develop Aluminium metal matrix composites by incorporating of reinforcements such that combination of best properties could be achieved. The metal base was selected was Aluminium 6082 and it is reinforced with varying volume percentage of Alumina oxide and Fly ash. These AMC were developed by using stir casting technique, in which predetermined reinforcement is added to the molten matrix is stirred well to obtain desired castings. These castings were studied for behaviour and subjected to mechanical testing to study the effects of various reinforcements. The Rockwell hardness and tensile tests revealed that composite with 7.5 % Al2O3 5% Fly ash shows highest hardness value of 69 HRB and 100.370 N/mm2, which is better than base alloy as well as impact is more without reinforcement ratio shows highest impact strength value 9 joules. Highly reinforced composites show higher variations due to the agglomeration of particles.

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Ferroelectric and piezoelectric ceramic reinforced metal matrix composites are new materials being explored for vibration damping purposes. The high damping ability of ferroelectric and piezoelectric ceramics such as barium titanate (BaTiO3) and lead zirconate titanate (PZT) is due to the anelastic response of ferroelastic domain walls to applied external stress. In piezoelectric ceramics, vibration energy can also be dissipated through the direct piezoelectric effect if the appropriate electric circuit is connected across the ceramic. In this work we have examined the vibration damping behavior of BaTiO3, nickel-barium titanate (Ni-BaTiO3) composites and nickel-lead zirconate titanate (Ni-PZT) composites. BaTiO3 ceramics were fabricated by a combination of uniaxial pressing and cold isostatic pressing followed by sintering in air. Low frequency (0.1Hz-10Hz) damping capacity of BaTiO3, tanδ has been measured in three-point bend configuration on a dynamic mechanical analyzer. Tanδ has been found to increase with temperature up to the Curie temperature (Tc) of BaTiO3, after which there was a drop in damping capacity values due to the disappearance of ferroelectric domains above Tc. Furthermore within the frequency range tested, tanδ has been found to decrease with increasing vibration frequency. We also observed that tanδ decays with the number of vibration cycles (N). The decrease in tanδ with N, however, is fully recovered if BaTiO3 is heated above the Tc. Ni-BaTiO3 composite composed of a layer of BaTiO3 ceramic sandwiched between two layers of Ni were fabricated using a combination of electroless plating and electroforming. The damping behavior of the composite was analyzed in terms of the damping mechanisms below Tc and the damping mechanisms above Tc of BaTiO3. Below Tc, vibration damping ability of the composite was highly influenced by ferroelastic damping in the BaTiO3 component. Above the Curie temperature, the damping capacity was influence more by the inherent damping mechanisms in the nickel matrix. The damping mechanisms in Ni-PZT composites were evaluated at a low vibration frequency of 1Hz. In these composites we identified ferroelastic domain wall motion as the main damping mechanism active below the Tc of PZT. Using a poled PZT ceramic enhanced the damping capacity of the composite because of favorable ferroelastic domain orientation in the direction of applied stress. Based on our experimental results, we found no evidence of a direct piezoelectric damping mechanism in the Ni-PZT composites. / Ph. D.

A mathematical model has been created based on J.D. Eshelby's equivalent inclusion method that can predict the elastic modulus and damping capability in the form of Joule heat for any piezoelectric ceramic-reinforced metal matrix composite system. Specifically, barium titanate (BaTiO₃), lead titanate (PbTiO₃), and zinc oxide (ZnO) piezoelectric ceramics have been modeled as dispersed particles shaped as spheres, prolate spheroids, and discs within a host of common structural metallic matrices including 304 stainless steel, mild steel, aluminum, brass, copper, lead, magnesium, nickel, Ni-20wt%Cr, tin, titanium, Ti-6Al-4V(at%), and tungsten. Composite systems that were predicted to exhibit the greatest level of damping capacity include copper, aluminum, and magnesium matrices reinforced with PbTiO₃, BaTiO₃, and ZnO, in descending order of damping magnitude. In general, higher-conducting, lower-stiffness metallic matrices coupled with more-piezoelectric, higher-stiffness ceramic reinforcement resulted in the greatest level of predicted damping capability and enhanced composite elastic modulus. Additionally, a Ni-20wt%Cr-30v%BaTiO₃ composite has been created using mechanical alloying processing. Specifically, pure constituent powders were combined stoichiometrically in a SPEX milling vial utilizing a charge ratio of 4:1 and subsequently milled for 24 hours. Separate composite powder samples were then annealed in a hydrogen tube furnace at 400°C, 500°C, and 600°C for one and five hours at each temperature. X-ray diffraction was performed on the as-milled and the annealed powders revealing that each was composed of the starting constituents in the appropriate proportions. Representative powders were mounted and polished using common metallographic procedures and microstructures were examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. All of the powders exhibited a good dispersion of BaTiO₃ particles ranging in diameter from 1μm to about 25nm with no noticeable difference between the as-milled and the annealed powders. / Master of Science

Ferroelectric-reinforced metal matrix composites (FR-MMCs) show promise as high damping materials for structural applications. Most structural materials are valued based on their stiffness and strength; however, stiff materials typically have limited inherent ability to dampen mechanical or acoustic vibrations. The addition of ferroelectric ceramic particles may also augment the strength of the matrix, creating a multifunctional composite. In this work, the damping behavior of FR-MMCs created by the addition of barium titanate (BaTiO3) discontinuous reinforcement in a bearing bronze (Cu-10w%Sn) matrix has been studied. It has been shown that even when combined with other traditional composite mechanisms, added damping ability has been achieved due to the ferroelectric nature of the reinforcement. FR-MMCs currently represent a material system capable of exhibiting increased damping ability, as compared to the structural metal matrix alone. / Master of Science