Microstructure of undercooled Pb–Sn alloys

Melt undercooling opens new solidification pathways for new non-equilibrium phases and non-conventional microstructures. Several techniques have been developed in order to reduce nucleation sites and to produce high undercoolings for metals and alloys including the fluxing technique. In this study, the fluxing technique was applied to hypoeutectic, eutectic and hypereutectic Pb–Sn alloys. For hypereutectic alloy, a morphological change occurs with increasing undercooling and is accompanied by a refinement of the primary dendrites βSn phase. For alloys studied, the eutectic has exhibited anomalous morphology with increasing undercooling, ΔTe. The results indicated that the critical undercooling, ΔTe∗ that causes a transition from lamellar eutectic to anomalous eutectic in the Pb–Sn alloys is around 6 K.