Macroscopic liquid phase separation of Fe-Sn immiscible alloy investigated by both experiment and simulation

The macroscopic phase separation of undercooled liquid Fe₅₀ Sn₅₀ immiscible alloy was investigated by both drop tube experiment and the modified Model H. Core-shell structures with two, three, and five layers were formed during experiment. The concentric shells comprised of Fe-rich phase and Sn-rich phase distribute periodically in the solidified droplet, and the Sn-rich phase is always located at the sample surface owing to its smaller surface tension. The simulated results of modified Model H reproduce core-shell structures with the same layers, which justifies the prediction of this model. If the fluidity parameter C_f and solute concentration φ satisfy the physical conditions of both C_f <1 and 0<φ<0.45 or C_f ≥ 1, the phase separation morphology exhibits the double-layer core-shell structure, whereas the multilayer core-shell structure is expected to form under the conditions of both C_f <1 and 0.45≤φ<0.5. The forming ability of core-shell structure for various immiscible alloys can be predicted accordingly.