Microstructure and solidification process of Fe-Cu immiscible alloy by using containerless process

Liquid phase separation usually occurs in immiscible alloys under gravity. The drop tube and electromagnetic levitation processes, which are types of containerless processes, enable solidification melt without using a container. This would avoid heterogeneous nucleation induced by the container walls, thus obtaining undercooling conditions. The abovementioned processes have been used to study the undercooling solidification and metastable phase formation of the melt. Metastable miscibility gap is observed in the Fe-Cu binary alloy; however, metastable phase formation in the wide composition range used by the drop tube process has never been reported. In this study, we obtained samples of Fe-Cu binary alloy using a drop tube apparatus with a free fall length of 2.5 m and an electromagnetic levitation apparatus. In addition, we aimed to examine the effectiveness of the containerless process for microstructure formation of the Fe-Cu binary alloy based on undercooling solidification. The results of the SEM and EDS analyses showed that the minor liquid phase, Fe or Cu, finely dispersed in the matrix of the major liquid phase of Fe₇₅Cu₂5 and Fe₂5Cu₇₅ particle samples, and the two or three layer structure of Fe₅₀Cu50 particle samples. In particular, all the samples exhibited a phase separation caused by the metastable miscibility gap and the dendrite growth of Fe phase with the decrease of the cooling rate.