Comparisons of grain refinement and recalescence behavior during the rapid solidification of undercooled Cu–Co and Cu–Ni alloys

Applying the melt-fluxing method, rapid solidifications of undercooled Cu50Co50 immiscible and Cu70Ni30 solid solution alloys were performed to investigate the grain refinement regularity at moderate undercooling. Due to the essential distinction of physical properties between these alloys, grain refinement phenomenon was detected in Cu50Co50 alloy with a tendency of liquid separation, while dendrite structure appears for Cu70Ni30 alloy. The association of microstructure morphology to non-equilibrium solidification process was constructed with the description of recalescence degree as a function of undercooling. Quantitative thermodynamic calculation for the undercooled liquid of the researched systems was carried out to elucidate the influence of liquid separation on the variation of Gibbs free energy for the subsequent rapid solidification, which gives a better understanding of the as-observed experimental results.