Non isothermal calorimetric study of the precipitation processes in a Cu-10% Ni-3% Al alloy

Using differential scanning calorimetry (DSC), the precipitation process of nickel and aluminium atoms from a solid solution of Cu-Ni-Al were studied. Analysis of calorimetric traces displayed shows the presence of two exothermic reactions (stage 1 and 2), which were interpreted as the formation of two types of precipitates. The first stage corresponds to the formation of an equilibrium beta (NiAl) phase, whilst stage 2 corresponds to the formation of gamma' precipitate with Ni3Al stoichiometric composition. it is observed the shift of the traces to lower temperatures while linear heating rate decrease. The activation reaction energies were evaluated from modified Kissinger's method. Kinetic parameters were calculated by means Johnson-Mehl-Avrami formalism. The values obtained for parameter n were indicative of a particle nucleation process from pre-existent nucleus. Microhardness measurements and micrographies obtained by transmission electron microscopy were helpful to confirm the formation and the dissolution of the mentioned phases.