Rapid Growth Of Pb-Sb-Sn And Pb-Sn-Zn Ternary Eutectics Under Substantial Undercooling Conditions

Rapid crystal growth in Pb-Sb-Sn, Pb-Sn-Zn ternary eutectic alloys and other Pb-Sb-Sn alloys with relevant compositions under highly undercooling conditions has been investigated systematically. The main results are obtained as follows.Rapid solidification of undercooled Pb-12%Sb-4%Sn ternary eutectic alloy has been investigated. The maximum undercooling of the samples is up to 65K(0.13T_E). X-ray diffraction analysis reveals that the solidified microstructure is composed of (Pb) and (Sb) solid solution phases as well as SbSn intermetallic compound phase. The microstructual morphology is characterized by regular three-phase lamellar eutectic at low undercooling. With the increase of undercooling, the microstructure is refined and its interlamellar spacing of ternary eutectic becomes samller and smaller. In addition, the primary faceted phase (Sb) preferentially nucleates and grows from the highly undercooled alloy melt. The nucleation rates of ternary eutectic phases have been calculated as a function of undercooling. The results indicate that (Sb) solid solution phase is the leading phase during competitive nucleation. It is predicted that both (Sb) and SbSn phase grow in faceted manner. Moreover, the preferential growth orientation of the primary phase (Sb) is the <100> direction.Rapid solidified microstructure and relationships between the microstructure evolution and undercooling in Pb-15%Sb-10%Sn and Pb-8%Sb-4%Sn ternary alloys have been analyzed in details. For Pb-15%Sb-10%Sn ternary alloy, it is found that primary SbSn phase, SbSn+(Pb) pseudobinary eutectics and SbSn+(Pb)+(Sb) ternary eutectics coexist in the samples at different undercoolings. The primary SbSn dendrites with faceted character grow from undercooled melt. Whereas, the eutectic microstructure is regular two-phase or three-phase lamellar eutectic. The conspicuous refinement of the grains of primary SbSn dendrite and lamellar eutectic is caused by increase of undercooling. The growth velocity of SbSn primary phase was calculated as a function of undercooling in Pb-15%Sb-10%Sn alloy in order to reveal growth...