Nos últimos anos a indústria como um todo vem sofrendo grandes transformações em seus processos produtivos e na área da metalurgia do pó, não são diferentes. Processos novos são criados, analisados e testados. Avanços recentes da aplicação de ligas de alumínio na indústria aeroespacial e automotiva se fazem presentes. Vantagens como resistência à corrosão, condutividade térmica e elétrica, fazem das ligas de alumínio uma excelente matéria-prima para uso comercial. Neste trabalho foi realizado um estudo teórico-experimental do processo de metalurgia do pó de amostras sinterizadas pelo processo Convencional e a Plasma. O processamento de materiais em plasma mostra-se uma técnica inovadora na metalurgia do pó. É possível realizar a sinterização e extração de ligantes/lubrificantes, bem como realizar a deposição de camadas metálicas e tratamentos termoquímicos. A escolha da atmosfera de sinterização se torna um papel fundamental, sendo que a quebra da camada de óxido dos pós e consequente contração das amostras é fortemente influenciada pela presença de nitrogênio Foram compactadas e testadas amostras de alumínio com 1%, 2%, 3% 4% e 5% em peso de cobre. A sinterização convencional consiste no uso de equipamentos de aquecimento resistivo e atmosfera controlada. Já a sinterização a plasma foi feita em uma câmara de vácuo onde foi aplicado um potencial elétrico no gás de trabalho. Em ambos os processos a temperatura de trabalho foi de 500°C em atmosfera de nitrogênio com duração de 60min. Após a sinterização as amostras foram caracterizadas quanto a densificação, microdureza, rugosidade, difração de Raios-X, metalografia e compressão. Embora, que a maioria dos resultados encontrados foram melhores na sinterização a plasma comparados com a sinterização convencional, foi evidenciado um aumento significativo nos valores da rugosidade neste processo, a difração de raios-x indicou a formação de fase e a compressão mostrou um comportamento bem superior das amostras sinterizadas a plasma. / In recent years the industry as a whole has undergone major changes in its production processes and in the area of powder metallurgy this is not different. New processes are created, analyzed, and tested. Recent advances in the application of aluminum alloys in the aerospace and automotive industries are present. Advantages such as corrosion resistance, thermal and electrical conductivity, make aluminum alloys an excellent raw material for commercial use. In this work a theoretical-experimental study of the powder metallurgy process of samples sintered by the Conventional and Plasma processes was carried out. The plasma processing of materials is an innovative technique in powder metallurgy. It is possible to perform the sintering and extraction of binders / lubricants, as well as to perform the deposition of metallic layers and thermochemical treatments. The choice of the sintering atmosphere is an important aspect for the oxide layer breaking of the powders and consequently the samples density is strongly influenced by the presence of nitrogen Aluminum samples were compacted and tested with 1, 2, 3, 4 and 5 wt-% of copper. Conventional sintering consists of the use of resistive heating and controlled atmosphere equipment. Plasma sintering was done in a vacuum chamber where an electric potential was applied to the working gas. In both processes the working temperature was 500 ° C in nitrogen atmosphere with a duration of 60min. After sintering, the samples were characterized for densification, microhardness, roughness, X-ray diffraction, metallography and compression. Although, most of the results found were better in plasma sintering compared to conventional sintering, a significant increase in the roughness values was evidenced in this process, the x-ray diffraction indicated phase formation and better properties in compression tests for samples sintered by plasma.

As ligas de Al-Si são amplamente utilizadas na indústria, recentes avanços possibilitaram a produção de ligas de alumínio com ótimas propriedades podendo-se destacar o seu baixo peso, excelente resistência à abrasão e à corrosão, e baixo coeficiente de expansão térmica em relação ao aço. O objetivo deste trabalho foi avaliar o comportamento da mistura de pós elementares de Cu, Si, Mg, Ni, Fe a uma base de alumínio, sinterizado individualmente em atmosfera controlada com gás argônio e nitrogênio pelo processo de sinterização convencional em forno resistivo. Após realização de análise o composto que forneceu o melhor desempenho foi submetido a um comparativo com amostras sinterizadas via plasma. Os resultados encontrados foram confrontados com os resultados da liga de EN AC- 48000 (AlSi12CuNiMg) fundida, a fim de avaliar os aspectos mecânicos e físicos do composto intermetálico. O desenvolvimento do trabalho se deu a partir do pó de alumínio com pureza de 99,7%, ao qual foi incorporado o percentual dos demais elementos, com base na composição da liga comercial EN AC-48000 (Si12%; Fe0,45%; Cu1,08%; Mg1,08%; Ni1,14%). Após a sinterização as amostras foram caracterizadas quanto a densificação, microdureza e rugosidade superficial, além disso, uma análise metalográfica foi realizada por microscopia óptica, bem como foi feita uma por difração de raios-X para a verificação da formação de novas fases. A densificação das amostras sinterizadas pelo processo convencional com atmosfera controlada por nitrogênio foi superior as produzidas com atmosfera de argônio, ficando também superior ao processo assistido por plasma com nitrogênio. Pelo processo convencional de sinterização a microdureza apresentada pelas amostras obtidas por atmosfera de nitrogênio foi na média superior a encontrada nas amostras produzidas com atmosfera de argônio, já a microdureza apresentada pelas amostras assistida por plasma com atmosfera controlada por nitrogênio, atingiram resultados abaixo da sinterização convencional. Durante o processo de sinterização a plasma, as amostras acabaram sofrendo uma reação abaixo da temperatura de sinterização desejada (510 °C), ocasionando microfusão na superfície da amostra, e logo em seguida deformações. Estas reações tiveram influência direta nos resultados encontrados nas amostras produzidas via sinterização a plasma, desta forma a temperatura teve que ser reduzida. / Al-Si alloys are being used in industry to replace steel and cast iron in high-tech sectors. Recent advances have allowed the production of aluminum alloys with excellent properties, highlighting their low weight compared to steel, excellent resistance to abrasion and corrosion, high resistance at high temperatures and low coefficient of thermal expansion. The objective of this work is to evaluate the behavior of the Cu, Si, Mg, Ni and Fe elemental powder mixtures with an aluminum base, individually sintered in a controlled atmosphere with argon and nitrogen using the conventional sintering process in a resistance furnace. After this process, the best performing compound was submitted to a comparison with plasma sintered samples. The results were compared with those for the EN AC- 48000 (AlSi12CuNiMg) molten alloy, to evaluate the mechanical and physical aspects of the intermetallic compound. The development of the work was based on the 99.7% aluminum powder donated by Alcoa with the addition of other elements from the commercial alloy composition EN AC-48000 (Si12%; Fe0,45%; Cu1,08%, Mg1,08%, Ni1,14%). After sintering, the samples were carachterized by surface roughness, densification, microhardness, optical microscopy and X-ray diffraction analysis. The densification of the sintered samples by the conventional process with the controlled atmosphere by nitrogen gave higher densification values than for samples produced with the argon atmosphere or by the plasma assisted process using nitrogen. By the conventional sintering process, the samples processed in nitrogen atmosphere presented higher hardness values than those produced with argon atmosphere, and also higher than those plasma assisted sintered with nitrogen atmosphere. During the plasma sintering process, the samples underwent a reaction below the desired sintering temperature (510 °C), causing microfusion on the sample surface, and deformations. These reactions had a direct influence on the results found in the samples produced by plasma sintering, therefore the temperature for the plasma process had to be reduced.

Avanços recentes no processo de Metalurgia do Pó possibilitaram a produção de ligas de alumínio com ótimas propriedades e capazes de serem aplicadas nas indústrias automotiva e aeroespacial. Dentre as principais vantagens destas ligas, estão, a baixa relação peso/resistência, a alta condutividade térmica e elétrica, e a alta resistência à corrosão sob vários ambientes. Este trabalho teve como objetivo o estudo de um processo alternativo de sinterização do alumínio baseado na aplicação de plasma produzido por descarga incandescente anômala. Pó de alumínio comercial foram misturadas com 1% em peso de estearato de zinco (como lubrificante) e então compactadas sob pressão de 600 Mpa. A dimensões das amostras compactadas (verdes) ficaram em aproximadamente 13mm de altura e 10mm de diâmetro e massa controlada em torno de 3,5g. A fim de analisar as diferenças das amostras antes e após o processo de sinterização, foram calculadas as densificações para cada corpo de prova produzido. Posteriormente, as amostras verdes compactadas passaram pelo processo de sinterização a plasma e convencional, ambas com temperatura (500ºC) e atmosfera definidas. A sinterização convencional foi realizada utilizando duas atmosferas, argônio puro e nitrogênio puro, e o processo a plasma empregou, além de argônio e nitrogênio, o gás hidrogênio. Após a sinterização as amostras foram caracterizadas quanto a densificação, dureza, composição química e rugosidade superficial, além disso, uma análise metalográfica foi realizada por Microscopia Eletrônica de Varredura (com EDS). Embora todas as atmosferas foram efetivas na sinterização a plasma, o nitrogênio foi capaz de produzir a menor redução de densificação nas amostras, bem como a maior dureza e a menor rugosidade, dentre as amostras tratadas a plasma. A utilização do plasma também gerou uma melhor extração do lubrificante, porém com um aumento significativo da rugosidade com relação ao processo convencional devido à ação do sputtering gerado pelo bombardeamento iônico. / The recent advances in Powder Metallurgy make possible the production of Aluminum alloys with great properties and applicable in the automotive and aerospace industries. Among the main advantages of these alloys, the low weight to strength rate, high thermal and electrical conductivity, and the high corrosion resistance under several environments can be pointed out. This work had as aim the investigation of an alternative sintering process for Aluminum based on plasma glow discharge. Aluminum commercial powder was mixed with 1 weight-% of Zinc Stearate (as lubricant) and then compacted under 600 MPa pressure. The dimension of the as compacted (green) samples were about 13mm of height and 10mm of diameter and the mass around 3.5g. In order to analyze the differences of samples before and after e sintering process, the densification was calculated for each sample individually. After that, the green samples were sintered by plasma and in a conventional resistive furnace with protected atmosphere, using predefined temperature (500ºC) and gas atmospheres. The conventional sintering was carried out using two different atmospheres pure Argon and pure Nitrogen, and in the plasma sintering, besides Argon and Nitrogen, Hydrogen was used. After sintering the samples were investigated for densification, hardness, chemical composition and roughness, besides that metallography analysis by Electronic Microscopy with EDS were performed. Although all atmospheres were effective in the plasma sintering, the Nitrogen was able to produce the lowest reduction in density, the highest hardness and the lowest roughness, among all tested plasma conditions. The use of plasma also was responsible for an more efficient extraction of the lubricant, however with a significant increase of the roughness in relation to the conventional process, which was attributed to the sputtering effect by ion bombardment.

Nos últimos anos a indústria como um todo vem sofrendo grandes transformações em seus processos produtivos e na área da metalurgia do pó, não são diferentes. Processos novos são criados, analisados e testados. Avanços recentes da aplicação de ligas de alumínio na indústria aeroespacial e automotiva se fazem presentes. Vantagens como resistência à corrosão, condutividade térmica e elétrica, fazem das ligas de alumínio uma excelente matéria-prima para uso comercial. Neste trabalho foi realizado um estudo teórico-experimental do processo de metalurgia do pó de amostras sinterizadas pelo processo Convencional e a Plasma. O processamento de materiais em plasma mostra-se uma técnica inovadora na metalurgia do pó. É possível realizar a sinterização e extração de ligantes/lubrificantes, bem como realizar a deposição de camadas metálicas e tratamentos termoquímicos. A escolha da atmosfera de sinterização se torna um papel fundamental, sendo que a quebra da camada de óxido dos pós e consequente contração das amostras é fortemente influenciada pela presença de nitrogênio Foram compactadas e testadas amostras de alumínio com 1%, 2%, 3% 4% e 5% em peso de cobre. A sinterização convencional consiste no uso de equipamentos de aquecimento resistivo e atmosfera controlada. Já a sinterização a plasma foi feita em uma câmara de vácuo onde foi aplicado um potencial elétrico no gás de trabalho. Em ambos os processos a temperatura de trabalho foi de 500°C em atmosfera de nitrogênio com duração de 60min. Após a sinterização as amostras foram caracterizadas quanto a densificação, microdureza, rugosidade, difração de Raios-X, metalografia e compressão. Embora, que a maioria dos resultados encontrados foram melhores na sinterização a plasma comparados com a sinterização convencional, foi evidenciado um aumento significativo nos valores da rugosidade neste processo, a difração de raios-x indicou a formação de fase e a compressão mostrou um comportamento bem superior das amostras sinterizadas a plasma. / In recent years the industry as a whole has undergone major changes in its production processes and in the area of powder metallurgy this is not different. New processes are created, analyzed, and tested. Recent advances in the application of aluminum alloys in the aerospace and automotive industries are present. Advantages such as corrosion resistance, thermal and electrical conductivity, make aluminum alloys an excellent raw material for commercial use. In this work a theoretical-experimental study of the powder metallurgy process of samples sintered by the Conventional and Plasma processes was carried out. The plasma processing of materials is an innovative technique in powder metallurgy. It is possible to perform the sintering and extraction of binders / lubricants, as well as to perform the deposition of metallic layers and thermochemical treatments. The choice of the sintering atmosphere is an important aspect for the oxide layer breaking of the powders and consequently the samples density is strongly influenced by the presence of nitrogen Aluminum samples were compacted and tested with 1, 2, 3, 4 and 5 wt-% of copper. Conventional sintering consists of the use of resistive heating and controlled atmosphere equipment. Plasma sintering was done in a vacuum chamber where an electric potential was applied to the working gas. In both processes the working temperature was 500 ° C in nitrogen atmosphere with a duration of 60min. After sintering, the samples were characterized for densification, microhardness, roughness, X-ray diffraction, metallography and compression. Although, most of the results found were better in plasma sintering compared to conventional sintering, a significant increase in the roughness values was evidenced in this process, the x-ray diffraction indicated phase formation and better properties in compression tests for samples sintered by plasma.

Spark plasma sintering (SPS), also known as direct current sintering (DCS) is an advanced sintering technique that and uses a continuous pulsed direct current to rapidly process materials through Joule heating and offers significant advantages and versatility over conventional sintering methods. The technique features in energy saving owing to high heating rates and is very suitable for consolidation as well as diffusion bonding of electrical conductive advanced ceramic materials such as ultra high temperature ceramics (UHTCs). However, cooling rate in SPS also plays an important role as it directly influences the generation of residual stress especially for specimens consist of dissimilar phases such as composites and laminates primarily due to CTE mismatch. Therefore, in order to produce high quality materials, a zirconium diboride with addition of silicon carbide (ZrB2-SiC) ultra high temperature ceramic composite is selected to investigate the effect of cooling rate in SPS on microstructure and mechanical properties. After being densified at the target temperature, ZrB2-25vol%SiC specimens are cooled from 1800°C using controlled cooling rates of 10 °C/minute to ~225.5 °C/minute (free cooling). A time dependent finite element analysis (FEA) model is used to simulate the temperature gradients across the specimens at dwell times and during the cooling processes. The residual stress within the specimens are experimentally verified using X-ray diffraction (XRD) and Raman spectrometry, and found maximum residual stress within the specimen cooled at 225.5 °C/minute. Peak Hardness and moderate elastic modulus is found for specimen sintered at 1800 °C and cooled at 100 °C/minute, which make this temperature and cooling rate appropriate conditions for future fabrication of UHTCs with similar thermal and electrical properties. These materials are of great interest for their excellent high-temperature capabilities, wear and corrosion resistance, and are regarded as material candidates for engineering applications in extreme environments. Therefore, development of an effective joining technique is important since near-net shape fabrication is challenging, and joints formed by brazing or conventional solid-state diffusion bonding limit the mechanical strength and high temperature applications of the base materials. Using SPS we have rapidly and successfully joined ZrB2 to hafnium diboride (HfB2) at 1750 and 1800 °C within a minute through electric current assisted solid-state diffusion bonding. The electric current enables localized Joule heating as well as plastic deformation of the mating surface asperities, and enhances the elemental interdiffusion process at the HfB2/ZrB2 interfaces owing to electromigration, which leads to the formation of ZrxHf1-xB2 solid solution. A series of characterization and analytical techniques including scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (S/TEM) are employed to study the microstructure and chemical composition at of the HfB2/ZrB2 interfaces. Apart from enhanced diffusion as a result of electromigration, the applied electric current can also be use to promote plastic deformation in ZrB2, which does not go through gross plastic deformation due to its extremely high melting point and brittle nature even when elevated temperature and pressure are applied. Through “electroplastic effect” (an effect based on electromigration) the mobility and multiplication of the existing dislocations in ZrB2 is enhanced, and a “metal-like” primary recrystallization phenomenon in the ZrB2 is observed meaning the material has experienced a sufficient amount of plastic deformation and reached the critical dislocation density and configuration for nucleation of “strain-free” grains. The average grain size of the recrystallized grain is only ½ of its original value. These findings suggest great potentials in microstructural tailoring and grain refinement of conductive advanced ceramics using SPS, and provide promising ideas for future fabrications and applications.

Tantalum carbide (TaC) and hafnium carbide (HfC) possess extremely high melting points, around 3900 oC, which are the highest among the known materials. TaC and HfC exhibit superior oxidation resistance under oxygen deficient and rich environments, respectively. A versatile material can be expected by forming solid solutions of TaC and HfC. However, the synthesis of fully dense solid solution carbide is a challenge due to their intrinsic covalent bonding which makes sintering challenging. The aim of the present work is to synthesize full dense TaC-HfC solid solutions by spark plasma sintering with five compositions: pure HfC, HfC-20 vol.% TaC (T20H80), HfC- 50 vol.% TaC (T50H50), HfC- 80 vol.% TaC (T80H20), and pure TaC. To evaluate the oxidation behavior of the solid solutions carbides in an environment that simulates the various applications, an oxygen rich, plasma assisted flow experiment was developed. While exposed to the plasma flow, samples were exposed to a temperature of approximately 2800 oC with a gas flow speed greater than 300 m/s. Density measurements confirm near full density was achieved for all compositions, with the highest density measured in the HfC-contained samples, all consolidated without sintering aids. Confirmation of solid solution was completed using x-ray diffraction, which had an excellent match with the theoretical values computed using Vegard’s Law, which confirmed the formation of the solid solutions. The solid solution samples showed much improved oxidation resistance compared to the pure carbide samples, and the T50H50 samples exhibited the best oxidation resistance of all samples. The thickness of the oxide scales in T50H50 was reduced more than 90% compared to the pure TaC samples, and more than 85% compared to the pure HfC samples after 5 min oxidation tests. A new Ta2Hf6O17 phase was found to be responsible for the improved oxidation performance. Additionally, the structure of HfO2 scaffold filled with molten Ta2O5 was also beneficial to the oxidation resistance by limiting the availability of oxygen.

The quasicrystals are characterized by unusual rotational symmetries that are not observed in the crystalline materials, which is the cause of their interesting material properties. Because of that a particular attention was paid to quasicrystalline structures in the literature research. The research also contains a description of electron beam technology, spark plasma sintering method and introduction to the problematics of wear. As the default materials for the experimental part were selected Titanium Grade 2 powder and Cristome A5 powder which was partially composed of quasicrystalline phase. The first series of samples was sintered only from powder Cristome A5. The second series was sintered from the mixture of 80 % Titanium Grade 2 powder and 20 % Cristome A5 powder. For the compaction of samples spark plasma sintering technology was selected. Samples were then systematically modified by electron beam and subjected to pin on disc tests. Samples modified at 750 °C had the best wear resistance. Samples modified at 1150 °C contained increased amount of quasicrystalline phase.

The diploma thesis deals with the preparation of the composite material based on the NiSi system using powder metallurgy supplemented by the sintering with the usage of SPS method (spark plasma sintering). Theoretical part contains general information about the mechanical-chemical process and sintering, while materials and methods used for experimental observation are explained in a separate chapter. Experimental part explains the procedure of the experiment and selected parameters of individual processes. In the experiment, two powder mixtures were created in order to form the NiSi phase in the maximum possible amount of powder material. After successfully reaching presence of the NiSi phase in the range of 87 to 89 wt. %, both mixtures were used to produce sintered samples at temperatures from 700 to 900 °C. Experiments showed the best results for sample number 2, which was sintered at 900 °C for 4 minutes. Resulting porosity was 0.9 % and hardness reached a maximum value of 718 HV 1. However, all sintered samples show cracks at room temperature associated with increased brittleness of the material.

Ceramic materials are in general characterized by high hardness, high modulus of elasticity, excellent abrasion resistance, etc. These properties make ceramics among others useful in optically transparent applications. An ideal form of optically transparent ceramic material is monocrystalline. However, the monocrystalline fabrication is expensive and/or time consuming. From this point of view polycrystalline ceramics is preferred. But the polycrystalline transparent ceramics fabrication is fraught with complications such as porosity, inappropriate grain size and insufficient purity. These circumstances could be solved by using sintering additives. This master’s thesis compiles literature research summarizing modern technologies of advanced ceramics sintering and ceramic polycrystalline microstructure dependence on its optical properties. The experimental part of this thesis focuses on the fabrication parameters of polycrystalline advanced ceramics based on Al2O3MgO and evaluation of their optical properties. Polycrystalline magnesium-aluminate spinel with sintering additive contents 0; 0.3 and 0.6 weight % LiOH was fabricated by optimalisation of Spark Plasma Sintering cycle. Fully dense ceramic samples of polycrystalline magnesium-aluminate spinel with favourable optical properties in visible spectrum radiation were achieved. Real In-line Transmission RIT and Total Forward Transmittance TFT were analysed. RIT exceeded 84 % at wavelength of 633 nm and TFT exceeded 83 % at wavelength above 860 nm. The decisive factors in terms of the optical properties of ceramics sintered with sintering additives were the amount of time-spending at high temperatures and the purity of ceramic powders.

Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.