Estudo do efeito da variação na concentração de Al em ligas do sistema Cu-Al-Mn-Ag
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Data
2016-08-05
Autores
Santos, Camila Maria Andrade dos [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho os efeitos da variação da concentração de Al sobre as transformações de fase e as propriedades mecânicas das ligas Cu-7%Al-10%Mn-3%Ag, Cu-10%Al-10%Mn- 3%Ag e Cu-11%Al-10%Mn-3%Ag foram estudadas utilizando-se metalografia por microscopias óptica (MO), eletrônica de varredura (MEV) e eletrônica de transmissão (MET), calorimetria exploratória diferencial (DSC), difratometria de raios X (DRX), ensaios de tensão-deformação, análise por dispersão de energias de raios X (EDXS), medidas de variação da resistividade elétrica com a temperatura e medidas de variação da microdureza com a temperatura e o tempo de envelhecimento. Os resultados obtidos para as ligas inicialmente submetidas a tratamento térmico de recozimento e inicialmente submetidas a tratamento térmico de têmpera mostraram que o aumento de 7 para 9%Al não modifica o comportamento térmico e a dureza das ligas Cu-7%Al-10%Mn-3%Ag e liga Cu-9%Al- 10%Mn-3%Ag, pois as curvas obtidas apresentaram o mesmo perfil, indicando que elas passam pelas mesmas transições. Porém, o aumento de 9 para 11%Al provoca uma mudança nas transformações pelas quais a liga passa, modificando assim o seu comportamento térmico e os valores da microdureza. Nas ligas inicialmente recozidas foi possível notar a ocorrência da decomposição espinodal em decorrência da retenção das fases 1 e 3 durante o resfriamento lento das amostras. Os resultados obtidos a partir das ligas submetidas a tratamento térmico de envelhecimento mostraram que aumento da dureza durante este processo está principalmente relacionado à precipitação bainítica. A partir das curvas de variação da microdureza com o tempo de envelhecimento foi possível obter os parâmetros cinéticos (n, k e Ea), utilizando-se as equações de Johnson-Mehl-Avrami-Kolmogorov (JMAK) e Arrhenius. Os valores de energia de ativação obtidos mostraram que o aumento na concentração de Al diminui Ea para o processo de precipitação. A diminuição destes valores deve estar associada principalmente à ocorrência da reação de precipitação de uma fase rica em Ag, que deve ocorrer com razoável intensidade na liga com 7%Al e vai diminuindo até não mais ser detectada na liga contendo 11%Al. Os resultados obtidos pelos testes de tensãodeformação indicaram que as ligas com maior teor de Al são mais frágeis.
In this work, the effects of changes in the Al concentration on the phase transformations and the mechanical properties of the Cu-7%Al-10%Mn-3% Ag, Cu-10%Al-10%Mn-3%Ag and Cu-11%Al-10%Mn-3% Ag alloys were studied using metallography by optical microscopy (OM), scanning electron microscopy (SEM) and electronic transmission mycroscopy (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), stress-strain tests, analysis by X-ray energy dispersing (EDXS), measurements of the variation of electrical resistivity with temperature and microhardness changes measurements with temperature and aging time. The results obtained for alloys initially annealed and initially quenched showed that the increase from 7 to 9% Al does not modify the thermal behavior and hardness of the Cu-7%Al- 10%Mn-3%Ag and Cu-9%Al-10%Mn-3%Ag alloys. However, the increase from 9 to 11%Al causes a change on the transformations of the alloys, thereby modifying their thermal behavior and values of microhardness. In the annealed alloys it was possible to notice the occurrence of the spinodal decomposition due to the retention of 1 and 3 phases during the slow cooling of the samples. The results obtained from aged alloys showed that the hardness increasing observed during this process is mainly related to bainitic precipitation. The isothermal ageing kinetics for this precipitation was studied considering four different ageing temperatures and the kinetic parameters n, k and Ea were obtained using the Johnson-MehlAvrami-Kolmogorov (JMAK) and the Arrhenius equations. The results showed that the increase on the Al concentration decreases the activation energy values for the precipitation process. This should be mainly associated with the occurrence of the precipitation reaction of an Ag-rich phase, that should occur with reasonable intensity in the alloy with 7%Al and decreases until it is no longer detectable in the alloy containing 11%Al. The results obtained for stress-strain testing indicated that the increase in the Al content increases the fragility of the alloys.
In this work, the effects of changes in the Al concentration on the phase transformations and the mechanical properties of the Cu-7%Al-10%Mn-3% Ag, Cu-10%Al-10%Mn-3%Ag and Cu-11%Al-10%Mn-3% Ag alloys were studied using metallography by optical microscopy (OM), scanning electron microscopy (SEM) and electronic transmission mycroscopy (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), stress-strain tests, analysis by X-ray energy dispersing (EDXS), measurements of the variation of electrical resistivity with temperature and microhardness changes measurements with temperature and aging time. The results obtained for alloys initially annealed and initially quenched showed that the increase from 7 to 9% Al does not modify the thermal behavior and hardness of the Cu-7%Al- 10%Mn-3%Ag and Cu-9%Al-10%Mn-3%Ag alloys. However, the increase from 9 to 11%Al causes a change on the transformations of the alloys, thereby modifying their thermal behavior and values of microhardness. In the annealed alloys it was possible to notice the occurrence of the spinodal decomposition due to the retention of 1 and 3 phases during the slow cooling of the samples. The results obtained from aged alloys showed that the hardness increasing observed during this process is mainly related to bainitic precipitation. The isothermal ageing kinetics for this precipitation was studied considering four different ageing temperatures and the kinetic parameters n, k and Ea were obtained using the Johnson-MehlAvrami-Kolmogorov (JMAK) and the Arrhenius equations. The results showed that the increase on the Al concentration decreases the activation energy values for the precipitation process. This should be mainly associated with the occurrence of the precipitation reaction of an Ag-rich phase, that should occur with reasonable intensity in the alloy with 7%Al and decreases until it is no longer detectable in the alloy containing 11%Al. The results obtained for stress-strain testing indicated that the increase in the Al content increases the fragility of the alloys.
Descrição
Palavras-chave
Ligas de Cu-Al-Mn-Ag, Transições de fase, Precipitação bainítica, Cinética isotérmica, Cu-Al-Mn-Ag alloys, Phase transitions, Isothermal kinetics, Bainitic precipitation