Non isothermal precipitation in an alloy of Cu-10 %Ni-3 %Al

Using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), the precipitation process for nickel and aluminum atoms was studied based on a solid solution of Cu-Ni-Al. The analysis of the calorimetric curves reveals the presence of two exothermal reactions (stages 1 and 2), that are interpreted as the formation of two types of precipitates. The first stage includes the formation of the β equilibrium phase (NiAl), while stage 2 includes the formation of the γ' precipitate with a stoichiometric composition of Ni3Al. Also, the curves shift at lower temperatures with the decrease in lineal heating velocity. The activation energies of the reactions were evaluated using the modified Kissinger method. The kinetic parameters were calculated using the Johnson- Mehl-Avrami formula. The n values obtained (≅ 1.5) indicate a particle nucleation process based on pre-existing nuclei. The analysis of the TEM micrographs and of the electron diffractions confirmed that the two types of precipitates correspond to the NiAl and Ni3Al phases. The volumetric fractions of the particles were obtained with the calorimetric curves and the TEM micrographs (CW)