MICROSTRUCTURE DEVELOPMENT DURING RAPID SOLIDIFICATION OF HIGHLY SUPERSATURATED CU-CO ALLOYS

We report a detailed microstructure analysis of rapidly quenched Cu1-xCox (0.1 less than or equal to x less than or equal to 0.5) alloys. The chemical homogeneity of the alloys was investigated on nanometer scale using a combination of AP/FIM- and TEM-studies. Cu-Co alloys with a Co concentration up to 10 at. % Co can be prepared homogeneously by rapid quenching. For larger Co contents, the microstructure is determined by a competition between polymorphic solidification, nucleation of the Go-rich solid solution from the melt, and spinodal decomposition of the unstable supersaturated solid solution. The microstructures are discussed in terms of the kinetics of the Cu-Co system, provided quantitatively by recent thermodynamic calculations.