Calorimetric development and study of precipitation processes in Cu-Co-Si alloys

Using differential scanning calorimetry (DSC) the precipitation processes of supersaturated solid solutions of three Cu-Co-Si alloys, with a constant cobalt composition, were studied. Thermograms, and previous studies, reveal that the decomposition begins with cobalt precipitation. Clustering of cobalt initiates the silicon precipitation, finally Co2Si stoichiometric particles are formed. Volume fractions are determined by the amount of cobalt present in these alloys. It is infered that surplus silicon atoms retained in the solution increase the reaction rate. Kinetic parameters were calculated by a method based in the Mehl-johnson-Avrami (MJA) formalism. The lower activation energy obtained, associated with cobalt clustering is attributed to the contribution of quenched-in vacancies.