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

Fe-Cu peritectic alloy was melted and superheated within a special boronsil icate glass, then undercooled in argon atmosphere. Undercoolings up to 277 K were attained and the hypercooling limit ol the alloy was determined to b e 395 K. The microstructures of the alloy were characterized by a supersatu rated alpha Fe matrix plus a snail amount of Cu phase distributed as tiny p articles. delta Fe phase was the actual nucleating phase in the small under cooling regime below 125 K. But gamma Fe phase might be able to nucleate di rectly from the liquid alloy at still larger undercoolings. Solute trapping effect was found in this alloy system. It was also found that the recalesc ence temperature decreased and the recalescence rate increased with underco oling, A maximum dendrite growth velocity of 50 m.s(-1) was detected experi mentally, which corresponded more probably to gamma Fe dendrite growth. The oretical calculations based on the LKT/BCT dendritic growth model indicate that for delta Fe phase there is a transition from solute diffusion control led growth to thermal diffusion controlled growth, whereas gamma Fe dendrit e is predicted to experience a transition from thermal diffusion controlled growth to interface kinetics controlled growth.