In the present investigation, the microstructures and morphologies of Y-35wt.% Cu and Y-28wt.% Cu alloys which were processed in a 7-meter drop tube and other two drop tubes of 1.2 and 5 meters, respectively, have been observed. The different sizes of samples for Y-35wt.% Cu alloy were treated both in 1.2 meter and 7 meters high drop tubes. Because of the size differences the amount of undercooling reached are also different. With the increasing amount of undercooling, refined structure was observed and the volume fraction of eutectic was decreased obviously. In addition, since gravity-induced convection disappeared, nearly the same structure was observed for two samples which had small difference in diameters (0.33 mm and 0.34 mm, respectively) but were different in shape, one a column over 2-cetimetre high and the other a sphere. While for Y-28wt.% Cu alloy, as the amount of undercooling increased, hypereutectic with much more fraction of YCu than equilibrium solidification, dispersed eutectic and vague morphology were observed successively.
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