Solidification behaviour of Pb droplets embedded in a Cu matrix

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A hypomonotectic alloy of Cu-5wt%Pb has been manufactured by melt spinning and the resulting microstructure examined by transmission electron microscopy. As-melt spun hypomonotectic Cu-5wt%Pb consists of a homogeneous distribution of faceted 20–100 nm diameter Pb particles embedded in a matrix of Cu, formed during the monotectic solidification reaction. The Pb particles show a cube-cube orientation relationship with the surrounding Cu matrix and a truncated octahedral shape bounded by {111} and {100} facets. The kinetics of Pb particle solidification have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Pb particle solidification is nucleated catalytically by the surrounding Cu matrix, with an undercooling of 0.5 K and a contact angle of 4°. Analysis of the nucleation kinetics of Pb particle solidification seems to indicate a breakdown of the classical spherical cap model of heterogeneous nucleation.