Lamellar microstructure of discontinuous precipitation reaction front in Cu-7.5%In

Abstract

There is an increasing body of evidence for discontinuous precipitation (DP) as a general solid state phase transformation in materials. The understanding of the DP phenomenon, however, requires to establish its energy balance. The lamellar microstructure at the grain boundary reaction front (RF) is of particular interest since it results from the optimization of, at least, chemical, capillary and interfacial energy terms coupled with the boundary mobility at a given undercooling. Our investigation into this field has lead us to the conclusion that an additional term reflecting the residual stresses in the transformed product should be incorporated. In the present paper, microstructural features focused at the lamellar growth front are illustrated and discussed supporting the idea that DP is a non-equilibrium reaction.The alloy used for this study, Cu-7.5at.%In, was prepared at the Max-Planck-Institut, Stuttgart, from high purity components by induction melting under argon atmosphere and chill cast. After homogenization at 600°C/300h samples were directly aged isothermally at different temperatures and quenched. The parent FCC matrix α decomposes into depleted α lamellae and tetragonal Cu3In β lamellar precipitates.