Discontinuous precipitation in a Cu-4-5 at.-%In alloy

The morphology and kinetics of the discontinuous precipitation reaction in a Cu-4.5 at.-%In alloy were studied by means of analytical electron microscopy. A grain boundary movement was experimentally observed before the precipitation reaction at this grain boundary started. Subsequent development of the discontinuous precipitation reaction led to the formation of an alpha/delta(Cu7In3)) lamellar two phase microstructure, where alpha is the In depleted solid solution and delta the precipitate phase. By application of energy dispersive X-ray microanalysis a solute depletion in the a lamellae in the wake of the advancing reaction front was observed. Indium concentration profiles were determined parallel to the moving reaction front for individual a lamellae. These concentration profiles fall into two categories, namely symmetrical and asymmetrical with respect to the central axis of the a lamella, which were attributed to regular morphology and irregular morphology of the discontinuous precipitates, respectively. A local analysis was applied to characterise the kinetics of the discontinuous precipitation reaction. The local grain boundary diffusivity was determined.