Phase separation in undercooled Cu–Cr melts

Phase separation in undercooled Cu–25 wt.% Cr melts was investigated using the electromagnetic levitation technique in combination with splat-quenching. The solidification microstructure of the levitated and splat-quenched samples showed many Cr-rich spheres in a Cu-rich matrix in addition to fine Cr-rich dendrites. The Cr-rich dendrites nucleated preferentially on the surface of the Cr-rich spheres, and grew outwards. Such a microstructure shows clear evidence of metastable liquid phase separation in undercooled Cu–Cr melts. In the levitated samples without splat-quenching, however, a dendritic microstructure was observed showing no evidence of liquid phase separation. The results are discussed in terms of a newly established phase diagram based on thermodynamic calculations.