Formation of single-phase supersaturated solid solution upon solidification of highly undercooled Fe–Cu immiscible system

Applying glass fluxing combined with cyclic superheating and rapid quenching after recalescence, the solidification of undercooled immiscible Fe–Cu alloy melts was studied. Subjected to low undercooling, a coarse dendritic pattern results, where both Cu precipitation and dot substructure can be observed. For sufficiently high undercooling, a typical granular structure forms, where the dot substructure still exists because of the effect of post-recalescence. Only if both sufficiently high undercooling and rapid quenching immediately after recalescence are satisfied, a single-phase supersaturated solid solution can be obtained, where the Cu precipitation and the dot substructure are suppressed. Therefore, the formation of single-phase supersaturated solid solution can be attributed to a combination of an absolute solute trapping occurring upon rapid recalescence and a selection of rapid quenching point after recalescence, which suppresses the dot substructure through δ/γ massive transformation. This has been qualitatively interpreted using an extended steady-state dendritic growth model and the classical solid-state transformation kinetics, e.g., temperature–time–transformation (TTT) diagram.