Microstructure evolution of undercooled Fe–Co–Cu alloys

Rapid solidification of undercooled Fe–Co–Cu alloys was investigated by means of fluxing purification and cyclic superheating technique. A transition in microstructure from dendrites to phase-separation occurred above a phase-separation undercooling ΔTsep. When ΔT<ΔTsep, dendrite was observed, the trunks were rich in Fe and Co, while Cu was rich at inter-dendrites. However, the phase-separated microstructure was obtained once ΔT>ΔTsep, with a large sphere of L1 phase located almost at the center of the sample and enwrapped by L2 phase. ΔTsep was 222, 88 and 45 K for Fe50Co30Cu20, Fe25Co25Cu50 and Fe15Co15Cu70 alloys in this work, respectively. It was investigated that L1 phase solidified before L2 phase after liquid separation and followed different ways.