Microstructural evolution mechanism of rapidly solidified ternary Fe_62.5Cu_27.5Sn₁₀ alloy

Liquid ternary Fe_62.5Cu_27.5Sn₁₀ alloy was rapidly solidified under free fall condition. The results show that the liquid phase separation leads to the formation of two- or three-layer core-shell structures and uniformly dispersed structures. These two types of microstructures are both composed of α-Fe and Cu₃Sn phases. According to the movement characteristics of L₂(Cu-rich) liquid phase, the thermal and solutal Marangoni migrations are the dynamic mechanisms responsible for the development of core-shell structure. The finally solidified microstructure of ternary Fe_62.5Cu_27.5Sn₁₀ alloy depends on the combined effects of cooling rate, undercooling and Marangoni migration. If the droplet diameter is sufficiently small so that its high cooling rate suppresses the liquid phase separation, the solidification microstructure evolves into the equiaxed dendrite morphology. The dendritic microstructure is composed of α-Fe solid solution and Cu₂FeSn intermetallic compound. EDS analysis reveals that α-Fe phase exhibits a remarkable solute trapping effect during containerless rapid solidification.