Phase selection and microstructure evolution of undercooled Fe-Cu peritectic alloy

Fe-Cu peritectic alloy was melted and superheated within a special boronsilicate glass, then undercooled in argon atmosphere. Undercoolings up to 277 K were attained and the hypercooling limit of the alloy was determined to be 395 K. The microstructures of the alloy were characterized by a supersaturated Fe matrix plus a small amount of Cu phase distributed as tiny particles. δFe phase was the actual nucleating phase in the small undercooling regime below 125 K. But γFe phase might be able to nucleate directly from the liquid alloy at still larger undercoolings. Solute trapping effect was found in this alloy system. It was also found that the recalescence temperature decreased and the recalescence rate increased with undercooling. A maximum dendrite growth velocity of 50 m·s^-1 was detected experimentally, which corresponded more probably to γFe dendrite growth. Theoretical calculations based on the LKT/BCT dendritic growth model indicate that for δFe phase there is a transition from solute diffusion controlled growth to thermal diffusion controlled growth, whereas γFe dendrite is predicted to experience a transition from thermal diffusion controlled growth to interface kinetics controlled growth.