Solidification kinetics and microstructure evolution of undercooled phase separated Fe-Cu melts

Electromagnetic levitation experiments were conducted in order to elucidate the effects of melt undercooling and alloy composition on the metastable phase separation and rapid solidification of Fe-Cu alloys. In-situ observations of the solidification kinetics and microstructure investigations of as-solidified samples have been accomplished. The theoretical analysis shows that the liquid-phase nucleation rate exceeds the solid-phase nucleation rate if the temperature falls below the metastable liquid binodal line. The photodiode signals of the recalescence processes exhibit temperature fluctuations which are ascribed to spatially inhomogeneous phase-separated samples. There is a transition from dendritic to phase-separated microstructures if the undercooling exceeds a critical level. Microstructure investigations give evidence of primary Fe-rich phase solidification in highly undercooled Fe-30 to 90 wt.% Cu alloy melts, because of its higher thermodynamic driving force. Substrate quenching (instead of gas cooling) affected the solidification of residual Cu-rich melt only near the chill surface.