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.

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.

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.

<p>Nano-powders of BaTiO₃, SrTiO₃, Ba_0.6Sr_0.4TiO₃, a mixture of the composition (BaTiO₃)_0.6(SrTiO₃)_0.4 with particle sizes in the range of 60 to 80 nm, and Bi₄Ti₃O₁₂ with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO₃)_0.6(SrTiO₃)_0.4 mixture is 125 ^oC, ~75 ^oC for Bi₄Ti₃O₁₂, ~25^oC for BaTiO₃ and SrTiO₃, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba_0.6Sr_0.4TiO₃. During the densification of the (BaTiO₃)_0.6(SrTiO₃)_0.4 mixture the reaction 0.6BaTiO₃+0.4SrTiO₃ → Ba_0.6Sr_0.4TiO₃ takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures.</p><p>The dielectric properties of selected samples of (Ba, Sr)TiO₃ ceramics have been studied. The results are correlated with the microstructural features of these samples, <i>e.g.</i> to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region.</p><p>The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi₄Ti₃O₁₂ (BIT) and CaBi₂Nb₂O₉ (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism.</p><p>A new processing strategy for obtaining highly textured ceramics is described. It is based on a<i> directional dynamic ripening mechanism</i> <i>induced by superplastic deformation</i>. The new strategy makes it possible to produce a <i>textured</i> microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties.</p><p>The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi₄Ti₃O₁₂ ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi₄Ti₃O₁₂ ceramics. Textured CaBi₂Nb₂O₉ ceramics exhibited a very high Curie temperature, <i>d</i><i>33</i>-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.</p>

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.

Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3, a mixture of the composition (BaTiO3)0.6(SrTiO3)0.4 with particle sizes in the range of 60 to 80 nm, and Bi4Ti3O12 with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO3)0.6(SrTiO3)0.4 mixture is 125 oC, ~75 oC for Bi4Ti3O12, ~25oC for BaTiO3 and SrTiO3, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba0.6Sr0.4TiO3. During the densification of the (BaTiO3)0.6(SrTiO3)0.4 mixture the reaction 0.6BaTiO3+0.4SrTiO3 → Ba0.6Sr0.4TiO3 takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures. The dielectric properties of selected samples of (Ba, Sr)TiO3 ceramics have been studied. The results are correlated with the microstructural features of these samples, e.g. to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region. The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi4Ti3O12 (BIT) and CaBi2Nb2O9 (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism. A new processing strategy for obtaining highly textured ceramics is described. It is based on a directional dynamic ripening mechanism induced by superplastic deformation. The new strategy makes it possible to produce a textured microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties. The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi4Ti3O12 ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi4Ti3O12 ceramics. Textured CaBi2Nb2O9 ceramics exhibited a very high Curie temperature, d33-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.

The unique features of the Spark plasma sintering (SPS) were used to investigate the sintering and deformation behaviour of titanium and titanium–titanium diboride composites, and to control the sintering and grain growth of ferroelectric Na0.5K0.5NbO3 (NKN) and of hydroxyapatite (HAp). In the SPS the samples experience a temperature different from that recorded by the thermocouple (pyrometer) used and this temperature difference has been estimated for Ti and NKN.   Sintering and deformation of titanium was investigated. Increasing heating rate and/or pressure shifted the sintering to lower temperatures, and the sintering and deformation rates changed when the α→β phase transition temperature was passed. Fully dense Ti/TiB2 composites were prepared. The Ti/TiB2 composites could be deformed at high temperatures, but the hardness decreased due to the formation of TiB.    The kinetic windows within which it is possible to obtain fully dense NKN and HAp ceramics and simultaneously avoid grain growth are defined. Materials have a threshold temperature above which rapid and abnormal grain growth takes place. The abnormal grain growth of NKN is due to a small shift in the stoichiometry, which in turn impairs the ferroelectric properties. Fully transparent HAp nanoceramics was prepared, and between 900 and 1050 oC elongated grains are formed, while above 1050 oC abnormal grain growth takes place.NKN samples containing grains of the sizes 0.35–0.6 µm yielded optimum ferroelectric properties, i.e. a high remanent polarization (Pr = 30 µC/cm2) and high piezoelectric constant (d33= 160 pC/N). The ferroelectric domain structure was studied, and all grains exhibited a multi-domain type of structure. / At the time of doctoral defense the following articles were unpublished and had a status as follows: Article 4: Manuscript; Article 5 : Manuscript

Currently, there is a high demand for lightweight aerospace materials, driven by the desire to provide enhanced fuel efficiency by reducing vehicular weight. Aluminum alloys are attractive due to their excellent mechanical properties and high strength to weight ratios. Powder metallurgy (PM), which converts metal powder into a high performance product, presents an alternative to traditional forming techniques, which are often unable to provide adequate dimensional tolerances. The challenge is to determine if aluminum PM alloys and technologies can be successfully employed within aerospace applications. This research focuses on the PM processing technologies (die compaction, cold isostatic pressing (CIP), and spark plasma sintering (SPS)) of two alloys, PM2024 and PM7075. Processing parameters were assessed using attributes such as density, hardness, and tensile properties. Both powders showed comparable densities and tensile properties to their wrought equivalents. Ultimately, the groundwork was laid for future research into these alloys and their processing methods.

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.