Solidification structure evolution in undercooled Fe_82.5Ni_17.5 melts

Fe_82.5Ni_17.5 alloys were undercooled by means of molten glass fluxing and cycling superheating methods. The maximum undercooling of 330 K was achieved. In combination of the theoretical calculations and experimental observations, the solidification behavior and structure formation mechanisms were systematically investigated. If the bulk undercooling ΔT < 63 K, the coarsening dendritic structures result. When AT is in the range of 63 K < ΔT < 158 K, influenced by the serious remelting, which is produced by recalescence, the primary dendrite is remelted into refined spherical crystals. As ΔT increases to the range of 158 K < δT < 203 K, due to the remelting effect decrease to a low level, the as-solidified structure evolve into dendritic structure. While δ T > 203 K, the grain refinement is caused by the stress originating from the rapid solidification contraction.