SOLIDIFICATION KINETICS AND MICROSTRUCTURE EVOLUTION OF UNDERCOOLED PHASE-SEPARATED FE-CU MELTS

Electromagnetic levitation experiments were conducted in order to eluc idate the effects of melt undercooling and alloy composition on the me tastable phase separation and rapid solidification of Fe-Cu alloys. In -situ observations of the solidification kinetics and microstructure i nvestigations of as-solidified samples have been accomplished. The the oretical analysis shows that the liquid-phase nucleation rate exceeds the solid-phase nucleation rate if the temperature falls below the met astable liquid binodal line. The photodiode signals of the recalescenc e processes exhibit temperature fluctuations which are ascribed to spa tially inhomogeneous phase-separated samples. There is a transition fr om dendritic to phase-separated microstructures if the undercooling ex ceeds a critical level. Microstructure investigations give evidence of primary Fe-rich phase solidification in highly undercooled Fe-30 to 9 0 wt.% Cu alloy melts, because of its higher thermodynamic driving for ce. Substrate quenching (instead of gas cooling) affected the solidifi cation of residual Cu-rich melt only near the chill surface.