Melting of CuIn solid solutions at small superheating by droplet formation and liquid film migration

Abstract

The melting of homogenized, polycrystalline α-CuIn solid solutions was studied by Differential Thermal Analysis and metallographic methods. At small superheating melt forms by two mechanisms. The formation of homogeneously distributed droplets in the interior of the grains and the subsequent diffusion of the excess indium to these nuclei dominates, if the solid solution is heated up rapidly (≈ 20 K s −1) up to 50 K above its solidus temperature. At small heating rates of ≈ 8.3·10 −1 K s −1, homogenization takes place by the formation of thin liquid films at the grain boundaries and their subsequent migration. The moving liquid films accumulate the excess indium from the dissolved supersaturated solid solution and leave a solid solution of equilibrium concentration in their wake. From the correspondence between the experimental migration velocities and calculated values it is concluded, that coherency strains in the solid adjacent to the liquid film provide the driving force for the second mechanism.