Pd3Si nucleation in undercooled Pd-Cu-Si melts

Abstract

The undercooling behaviour of the easy glass former Pd_77.5Cu₆Si_16.5 has been investigated. Different nucleation processes have been found responsible for the solidification of the undercooled melt. Formation of the intermetallic compound Pd₃Si initiates crystallisation. This kind of heterogeneous nucleation within the volume is analysed on the basis of nucleation theory, allowing a quantitative determination of the transformation kinematics. Heating the melt above the melting temperature of Pd₃Si leads to a pronounced reduction of Pd₃Si nucleation. As a consequence, surface-induced heterogeneous nucleation becomes dominant. Thorough surface cleaning reduces nucleation further, enabling extended degrees of undercooling up to 310 K.