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Estudo de duas pseudoligas de Nb-Cu obtidas pela rota da metalurgia do p?Melchiors, Gilberto 26 March 2015 (has links)
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Previous issue date: 2015-03-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / As pseudoligas Nb-Cu apresentam-se como potenciais substitutas ?s ligas de um sistema
conhecido e j? aplicado comercialmente, como as de W-Cu, usadas em aplica??es como
dissipadores de calor, contatos el?tricos e bobinas para gera??o de altos campos magn?ticos.
Por tratar-se de um sistema imisc?vel, onde h? insolubilidade m?tua e baixa molhabilidade do
Cu l?quido na superf?cie do Nb, a rota de processamento empregada neste trabalho foi a da
Metalurgia do P?. Duas composi??es de Nb foram utilizadas, com adi??es de 10% e 20% em
peso de Cu, e tempos de 20, 30 e 40 horas, para a moagem de alta energia dos p?s de partida.
A evolu??o da moagem dos p?s ? apresentada atrav?s de diversas t?cnicas de caracteriza??o,
como a particulometria por difra??o a LASER, DRX, MEV, EDS, DSC, dilatometria, MET e
an?lise qu?mica. Ap?s a moagem, partes das cargas de p?s foram submetidas ao tratamento
t?rmico de recozimento. O processo empregado para a consolida??o das amostras foi a
compacta??o a quente, a qual foi aplicada tanto em algumas amostras de p?s mo?dos, quanto
nos p?s recozidos. Tratamentos t?rmicos posteriores foram realizados nas amostras, nas
temperaturas de 1000?C (em fase s?lida) e 1100?C (em fase l?quida do Cu). Todos os
conjuntos de amostras consolidadas e tamb?m os dois conjuntos das tratadas termicamente
foram analisados por DRX, MEV, EDS, densidade e microdureza Vickers. Paralelamente,
outras amostras de p?s de Nb com 10% e 20% em peso de Cu obtidas por simples mistura
mec?nica, foram consolidadas, tratadas termicamente e caracterizadas com as mesmas
t?cnicas aplicadas nas demais, e os resultados foram comparados entre eles. Apesar da
dificuldade de consolida??o e densifica??o das duas pseudoligas do sistema Nb-Cu deste
estudo, na rota que passa pela MAE, foram obtidas amostras com densidades em torno de
90% da densidade te?rica. E, na rota de processamento das amostras que foram apenas
misturadas, os valores chegaram at? 97%. Por isso, nesse trabalho, tamb?m s?o enfatizados os
processos que tornaram poss?veis os resultados encontrados. / The Nb-Cu pseudoalloys present themselves as potential substitutes for the alloys from a well
known system and already commercially applied, as the W-Cu alloys, used in applications
such as heat sinks, electrical contacts and coils for the generation of high magnetic fields.
Because it is an immiscible system, where there is mutual insolubility and low wettability of
the liquid Cu on the Nb surface, the processing route used in this work was the Powder
Metallurgy. Two Nb alloys were used, with additions of 10% and 20% in weight of Cu, and
times of 20, 30 and 40 hours for the high energy milling of the starting powders. The milling
evolution of the powders is presented through the characterization techniques, such as the
LASER diffraction for particle size, XRD, SEM, EDS, DSC, dilatometry, TEM and chemical
analysis. After the milling, portions of the loads were submitted to the annealing heat
treatment. The process used for the samples consolidation was the hot pressing, which has
been applied both on some milled powders samples, as on the annealed powders. Subsequent
heat treatments were performed in the samples at temperatures of 1000?C (solid phase) and
1100?C (in the Cu liquid phase). All sets of consolidated samples, and also the two sets of the
heat treated, were analyzed by XRD, SEM, EDS, density and Vickers microhardness.
Moreover, other Nb powder samples with 10% and 20% in weight of Cu obtained by simple
mechanical mixing, were consolidated, thermally treated and characterized with the same
techniques applied to the others, and the results were compared among themselves. Despite
the difficulty of consolidation and densification of the two pseudoalloys of the Nb-Cu system
of this study, on the route that passes through the HEM, samples were obtained with densities
around 90% of the theoretical density. And, on the processing route of which were only
mixed, the values reached up to 97%. Therefore, in this work are also emphasized the
processes that made possible these results.
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Estudo da s?ntese e sinteriza??o de p?s comp?sitos do sistema Ta-CuSilva J?nior, Jos? Ferreira da 17 March 2008 (has links)
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Previous issue date: 2008-03-17 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical
contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100?C / 60 minutes and with heat rate at 10?C/min and were sintered by plasma furnace with
sintering temperatures at 550, 660 and 800?C without isotherm under hydrogen atmosphere with heat rate at 80?C/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with
shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu
melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores / O comp?sito Ta-Cu alia a alta resist?ncia mec?nica do Ta com a alta condutividade t?rmica e el?trica do Cu. Estas s?o caracter?sticas importantes para contatos el?tricos,
absorvedores de microondas ou dissipadores de calor. Todavia, a baixa molhabilidade do Cu l?quido no Ta s?lido e a m?tua insolubilidade desses elementos tornam dif?cil a densifica??o deste material. A moagem de alta energia (MAE) produz p?s comp?sitos com alta homogeneidade e refina o tamanho de gr?o. Este trabalho faz um estudo sobre p?s comp?sitos Ta-20%Cu preparados por mistura mec?nica e moagem de alta energia com duas condi??es distintas de moagem em um moinho do tipo planet?rio e sua posterior sinteriza??o em um forno a plasma de hidrog?nio e em um forno resistivo sob v?cuo. Amostras cil?ndricas foram
obtidas usando uma press?o de 200 MPa. Elas foram sinterizadas em forno resistivo a 1100?C por 60 minutos sob um v?cuo de 10-4torr com uma taxa de aquecimento de 10?C/min e em um forno a plasma de H2 a 550, 660 e 800?C sem tempo de isoterma de sinteriza??o com uma taxa de aquecimento de 80?C/min. Para caracteriza??o dos p?s produzidos foram realizadas microscopia eletr?nica de varredura (MEV), difra??es de raios x (DRX) e granulometria a
laser. Ap?s a sinteriza??o as amostras foram analisadas atrav?s de MEV, DRX, densidade e perda m?ssica. Os resultados mostram que para condi??o de moagem mais intensa part?culas comp?sitas s?o produzidas com poucas horas de moagem e h? uma amorfiza??o do t?ntalo e
do cobre ap?s 50 horas de moagem. A MAE produz part?culas comp?sitas com uma densidade estrutural maior do que os p?s misturados, se as amostras forem aquecidas acima
do ponto de fus?o do cobre. Ap?s o cobre atingir o ponto de fus?o, o cobre l?quido deixa as part?culas comp?sitas e preenche os poros
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