A comparative study of dendritic growth within undercooled liquid pure Fe and Fe50Cu50 alloy

The dendritic growth characteristics within undercooled liquid pure Fe and binary Fe50Cu50 alloy were investigated by glass fluxing and electromagnetic levitation methods. The growth velocity of pure Fe dendrite increases with undercooling, which reaches 69 ms(-1) at the maximum undercooling of 280 K (0.15 T-m). The microstructure appears as well-defined dendrites under slight undercooling, while it is characterized by a network of grain boundaries without discernible dendrites under substantial undercooling. A glass fluxing method was used to study the dendritic growth within the undercooled liquid Fe50Cu50 alloy. The maximum undercooling achieved was 261 K (0.15T(L)), and the corresponding growth velocity was 15 ms-1. A critical undercooling for metastable liquid phase separation of 7 K was determined. At larger undercoolings, the sample separates into an Fe-rich zone and a Cu-rich zone. The microstructure of the Fe-rich zone displays well-branched dendrites in the condition of slight undercooling, whereas it transforms into monotectic solidification structures in the highly undercooled regime. Slender dendrites and spheres are characteristics of the structural morphology of the Cu-rich zone at all of the undercoolings. Energy-dispersive spectroscopy analysis shows that the average compositions of phaseseparated zones have a large deviation from the original alloy composition, and conspicuous solute trapping has taken place. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.