Sb74.7Sn25.3 hyperperitectic alloy was rapidly solidified during containerless processing in a drop tube. The diameters of the droplets vary from 70μm to 1080μm. Theoretical analysis indicates that with the decrease of droplet diameter, the undercooling and cooling rate increase exponentially, the maximum undercooling is 298K(0. 36 Tl ) in this study. The microstructure is composed of primary Sb solid solution phase and SbSn peritectic phase. The Sb phase grows by faceted and non-faceted manners. The morphology of non-faceted primary Sb phase exhibits a transition of "coarse dendrites→broken dendrites" with the increase of the undercooling. It is also found that the length of the primary arm and the secondary arm spacing of Sb dendrite decrease with the reduction of droplet diameter. When the diameters of the droplets are less than 400μm, the change is especially remarkable. All of the change is caused by the increase of latent heat of fusion. In the meantime, solute trapping effect takes place as well, thus the solubility of Sn in primary Sb phase increases linearly with the increase of the undercooling, from 7. 86 at% to 10. 47 at% Sn.%采用落管无容器处理技术研究了Sb747 Sn25.3二元过包晶合金的快速凝固,获得的合金粒子直径D介于70～1080μm之间.理论计算表明,随着粒子直径的减小,过冷度和冷却速率均呈指数关系增大,最大过冷度为298K(0.36TL).研究发现,在自由落体条件下,快速凝固组织由初生Sb固溶体相和包晶SbSn金属间化合物相组成,Sb固溶体相以非小平面和小平面两种生长方式长大.当过冷度增大时,释放的熔化潜热增多,初生相逐渐细化,非小平面初生Sb相由“粗大枝晶”向“碎断枝晶”转变,当D＜400μm时,一次枝晶臂显著变短,二次枝晶间距明显减小；同时发生溶质截留现象,初生Sb固溶体相中溶质Sn的固溶度发生了显著拓展,由ΔT=32K时的7.86％(原子分数,下同)线性增大至ΔT=298K时的10.47％.
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