Crystal growth and its morphology in the mushy zone

In the solidification of multicomponent alloys, a mushy zone appears between the solid and liquid regions and promotes stable solidification by accepting the rejected solute regionally. In this study, the link between heat transfer and microstructures of the mushy zone has been studied experimentally and theoretically. First, the crystal morphology of the mushy zone at a microscale was observed by using succinonitrile–acetone solution and Bi–Sn alloys melts. It was found that the mushy zone consists of a leading front, in which the microstructures originate, and a growing region, where solidification proceeds with the fattening of the crystals. Next, the mechanism of dendritic sidebranch evolution was studied, taking into account the interfacial instability. To summarize these results, a macro–microscopic model is presented, and the change of crystal morphology at the microscale level was analyzed in relation to cooling rate, initial concentration, and distance from a cold wall.