A comparative study of macrosegregation evolution kinetics for undercooled CuFe immiscible alloy during slow cooling and rapid cooling processes

The macrosegregation evolution kinetics of undercooled CuFe immiscible alloy during slow cooling and rapid cooling processes were investigated by laser heating and glass fluxing techniques. The critical undercooling for the occurrence of metastable phase separation (MPS) was determined as 41 K. As the undercooling rised, MPS always occurred even if the undercooling rised to the largest value of 482 K (0.28 T) and the nucleation temperature of primary phase was below the peritectic temperature for the first time. Meanwhile, both the phase separation time and the volume fraction of Fe-rich zone gradually increased under the two conditions. However, the phase separation time and the volume fraction of Fe-rich zone under the laser heating condition were much smaller than that under the glass fluxing state. At slight undercoolings, MPS preferentially happened at the bottom region of laser-heated sample and glass-fluxed sample, and the microstructure in other regions appeared as well-defined αFe dendrites in the (Cu) matrix phase. In highly undercooled state, macrosegregation morphologies composed of floating Fe-rich zones and sinking Cu-rich zones were preserved. The critical undercooling for the macrosegregation formation of glass-fluxed sample was relatively larger. Moreover, the Fe-rich zone completely floated to the top of glass-fluxed sample while that located in the middle region of laser-heated sample. The higher the bulk undercooling, the lower the lattice constant of (Cu) phase and the greater the lattice constant of αFe phase. The calculations and analyses of temperature field and fluid dynamics demonstrated that the difference of heat transfer mechanisms between laser-heated sample and glass-fluxed sample was responsible for the distinctions of macrosegregation evolution kinetics in the two experiments. Graphical abstract: (Figure presented.).