Abstract: The homogeneous liquid was separated into two phases, (Fe, Co)-rich L1 and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature T_sep. If the duration from T_sep to T_s1 (solidification temperature of L1 phase), termed the liquid-phase separation interval Δt, exceeded a critical value, an egg-type structure was observed. By utilizing differential thermal analyses (DTA), the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of x_Cu=0.52. Depending on the relative amounts of L1 and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.

Key words: Undercooled Fe-Co-Cu alloys, Egg-type structure, Liquid-phase separation