Solidificação de ligas Pb-Sn super-resfriadas.

Abstract

Melt undercooling opens new solidification pathways for nevv nonequilibrium phases and non-conventional microstructures. Several techniques have been developed in order to reduce nucleation sites and to produce high undercoolings for metais and alloys including the fluxing technique. In this work, 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 pSn phase. The eutectic alloys have exhibited anomalous morphology with increasing undercooling, ATe. The results indicated that the criticai undercooling, ATe, that causes a transition from lamellar eutectic to anomalous eutectic in the Pb-Sn alloys is around 6 K. The results of Diferential Calorimetry (DSC) indicated that non-reciprocal nucleation characteristics were also observed for the Pb-Sn.