Spinodally decomposed patterns in rapidly quenched Co–Cu melts

The Co–Cu system is analyzed in the region of the metastable miscibility gap with separation of the undercooled melt into the Co-rich and Cu-rich liquids. Phase separation of undercooled and quenched samples of the Co50Cu50 melt are investigated experimentally using an electromagnetic levitation technique, quenching on a Pb-solder-coated copper chill substrate and splat-quenching methods. It is found that quenching of the liquid samples with cooling rate ≳106Ks-1 leads to a freezing of splats having the microstructure of spinodally decomposed liquids. The composition of the Co-rich phase measured by transmission electron microscopy is Co71.7Cu28.3 and that of the Cu-rich phase is Co26.8Cu73.2. These compositions are inside the spinodal region and close to the calculated spinodal boundary in the phase diagram of the Co–Cu system at temperatures below T ≈ 1450 K. Experimental results are compared with predictions of computational modeling using a model of fast spinodal decomposition.