Pd3Si nucleation in undercooled Pd-Cu-Si melts

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Abstract
The undercooling behaviour of the easy glass former Pd77.5Cu6Si16.5 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.