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 undercool ings for metals and alloys including the fluxing technique. In this study: the fluxing technique was applied to hypoeutectic, eutectic and hypereutect ic Pb-Sn alloys. For hypereutectic alloy, a morphological change occurs wit h increasing undercooling and is accompanied by a refinement of the primary dendrites beta Sn phase. For alloys studied, the eutectic has exhibited an omalous morphology with increasing undercooling, DeltaT(e). The results ind icated that the critical undercooling, DeltaT(e)* that causes a transition from lamellar eutectic to anomalous eutectic in the Pb-Sn alloys is around 6 K. (C) 2001 EIsevier Science All rights reserved.