Rapid solidification structure refinement mechanism in highly undercooled Cu based ternary alloys

Applying cycle superheating and molten glass purification technologies, Cu60Ni35Co5 alloys were deeply undercooled to maximum undercoolings of 284 K. The microstructure characteristics and its evolution varying with bulk undercooling during the rapidly solidified process were analyzed. It was found that, after minor addition of element Co, crystal refinement mechanisms of the undercooled Cu60Ni35Co5 system was similar to those of the Cu–Ni sytem. Crystal refined microstructure appearing at the low undercoolings was result of dendrite remelting mechanism; the dominant factor of grain refinement microstructure appearing at high undercooling regime was resultant from the recrystallization process. Driving force of stress induced strain energy for recrystallization could be divided into two parts, one was the thermal stress generated by the solidification latent releasing in the recalescence process, and the other was accumulated stress and plastic strain resultant from interaction between primary dendrite and liquid flow driven by rapid solidification.