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.