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    Efeito das adições de gadolínio e manganês no comportamento térmico da liga cu-9%al
    (Universidade Federal de São Paulo (UNIFESP), 2016-03-02) Brazolin, Giovanna Fernandes [UNIFESP]; Silva, Ricardo Alexandre Galdino da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    In this work the effects of the Gd and Mn additions on thermal behavior of the Cu-9%Al alloy were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), X-ray difratometry (XRD) and energy dispersive X-ray spectroscopy (EDX). The results showed that for the as cast Cu-9%Al alloy the dominant phases are stable and that the presence of 3%Gd does not change the phase transformations sequence found in the Cu-9%Al alloy and it does not introduce new thermical events, but increases the decomposition rate of the martensitic ?´ phase during the heating of the Cu-9%Al-3%Gd alloy inicially as cast. The results also show that only a small fraction of Gd added in the Cu-9%Al-3%Gd alloy is dissolved in the metallic matrix, but with de Mn addition the quantity of Gd dissolved is increased. The remain fraction of the Gd atoms undissolved forms precipitates that are distributed on the matrix and presents size lower than 200 nm. The results obtained for the Cu-9%Al alloy inicially annealed indicated that the boundary line of the (?+?1) / (Cu) phases may be shifted to richer Cu field at temperatures above 320 °C. The addition of 3%Gd to the Cu-9%Al alloy decreases the relative fraction of the produced phases on the slow cooling and induces the formation of Gd rich phase. This one is totally dissolved between 500 oC and 600 oC. The addition of 10%Mn to the Cu-9%Al alloy inicially annealed decreases the eutectoid decomposition rate, thus avoinding the presence of the ?2 and ? phase at low temperatures. Because of this, the ?(DO3) and ?(L21) phases produced from ?(A2) phase become stable at low temperatures. On heating of the formed phases at low temperatures, the grains of ? phase are reordered to promote the high temperature phases formation. The presence of Gd in the Cu-9%Al-10%Mn alloy seems not introduce new phase transitions, but the Mn increases the solubility of Gd in Cu, when compared to the Cu-9%Al-3%Gd alloy. In the Cu-9%Al-10%Mn-3%Gd alloy inicially annealed Al rich regions were indentified, suggesting the presence of the ?1 phase or other phases rich in Al. The presence of Gd contributes to the increase of the (?+?1)?(?+?) reaction rate, but the ?1 phase formation on the cooling is controlled by cooling rate. For the samples inicially quenched from high temperatures in water at 0 °C, it is possible to conclude that the Gd addition to the Cu-9%Al alloy increases the ?1 decomposition rate into (?+?1) phases. In the Cu-9%Al-10%Mn alloy the formation of the ?1 phase is delayed, thus preventing the occurrence of the (?+?1)?(?+?) reaction. For the Cu-9%Al-10%Mn-3%Gd alloy inicially quenched was verified a change in the bainitic phaseprecipitation characteristics in the presence of Gd and also that the characteristics of Mn dominate on those verified to the Cu-9%Al-3%Gd alloy.