Dual solidification mechanisms of liquid ternary Fe-Cu-Sn alloy

Liquid ternary Fe _47.5Cu _47.5Sn ₅ alloy displayed dual solidification mechanisms when it was undercooled by up to 329 K (0.19T _L). Below a critical undercooling of about 196 K, it solidified just like a normal peritectic alloy, even though metastable phase separation occurred to a microscopic extent. Once bulk undercooling exceeds 196 K, macroscopic segregation played a dominant role in solidification. In both cases, the solidification process was always characterized by two successive peritectic transformations: firstly primary γFe dendrites reacted with liquid phase to form (Cu) phase, and subsequently the (Cu) phase reacted with residual liquid phase to yield βCu _5.6Sn intermetallic compound. The primary γFe dendrites achieved a maximum growth velocity of 400 mm/s and experienced a growth kinetics transition as a result of macrosegregation. Since the (Cu) phase was both the product phase of the first peritectic transformation and also the reactant phase for the second peritectic transformation, it appeared as two layers in solidification microstructures due to the microsegregation of Sn solute. The boundary continuity between the macroscopically separated Fe-rich and Cu-rich zones was enhanced with the increase of undercooling.