Macroscopic phase separation and primary FeSi compound growth within undercooled ternary Fe-Sn-Si monotectic alloy

Liquid ternary Fe37Sn32Si31 monotectic alloy in bulk form has been undercooled by 305 K (0.18TL) by the glass fluxing method. Macroscopic phase separation took place and led to the formation of a top Fe-rich zone and a bottom Sn-rich zone. The large degree of undercooling was found to facilitate the evolution of macrosegregation. Dendritic growth was the characteristic of the primary FeSi compound in an Fe-rich zone. The growth velocity was up to 0.42 m/s and the dendrite grains were efficiently refined by an increase in the level of undercooling. The solute trapping of Sn atoms could not occur in the FeSi compound within the undercooling range achieved here, resulting in the suppression of the dendritic growth velocity compared with that in binary Fe50Si50 alloy. The interdendritic microstructures mainly consisted of decomposed Fe5Si3 compound plus some -Fe phase.