Dendritic growth in undercooled Ni-25wt%Pb alloy melts

Undercooled dendritic growth of bulk Ni-25 wt%Pb alloy was investigated. When the alloy was undercooled less than 50 K, the solidification microstructures were composed of common dendrites and interdendritic lead phase. When the undercooling was up to 77 K, rapidly directional "pseudo-couple" microstructure formed. With the undercooling increasing into the range of 132-240 K, uniformly precipitated fine lead particles resulted from primary supersaturated dendrites were observed. When the alloy was undercooled up to 308 K, refined granular grains with homogeneously distributed fine lead particles on it formed. By calculating the thermodynamic parameters based on the BCT model, it was found that the formation of "pseudo-couple" microstructure was owing to the directional growth of primary dendrites. (c) 2005 Elsevier Ltd. All rights reserved.