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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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