Effects of copper content and liquid separation on the microstructure formation of Co–Cu immiscible alloys

Abstract

Abstract Applying a melt-fluxing method combined with cyclical superheating, rapid solidification of undercooled Co70Cu30, Co50Cu50 and Co30Cu70 melts was performed to investigate the effects of alloy composition and immiscibility on the resultant non-equilibrium solidification microstructure. As for the samples without liquid separation, grain refinement of primary α-Co dendrite occurs clearly with increases in both copper content and initial undercooling. In contrast, the influence of alloy composition on microstructure evolution is weakened due to the occurrence of liquid separation at larger undercooling, where slight variations in the solute concentration and micro-hardness for Co-rich phase are obtained. After a quantitative thermodynamic calculation, the process of liquid separation is described, which gives an excellent explanation for the observed experimental results.