Kinetics of the discontinuous precipitation of a liquid phase in Cu-In alloys

The morphology and growth kinetics of the discontinuous precipitation of liquid and depleted solid phases from a supersaturated solid solution has been studied. The transformation was carried out in the two-phase (liquid + solid alpha) field in the temperature range 996-1050 K in two Cu-In alloys containing 8.9 and 9.5 at.% In. A lamellar structure consisting, of alternate lamellae of alpha and liquid phases has been observed to grow from the grain boundaries of the supersaturated alpha solid solution. The nucleation of the liquid droplets occurred at the grain boundary and a thin layer of liquid formed between the droplets. The liquid film started migrating resulting in the development of a lamellar structure. In both alloys the growth rate increased with increasing temperature of transformation but the interlamellar spacing decreased with increasing transformation temperature. The growth kinetics was analyzed using the models of Cahn and Petermann and Hornbogen and from a mass balance using Fick's first law. From the diffusivity and activation energy values it can be concluded that the growth of the cellular structure occurs by solute transport through the liquid film.