Liquid–liquid phase separation in undercooled Co–Cu alloys

Abstract

The liquid–liquid phase separation in undercooled Co–Cu alloy melts has been investigated by differential thermal analysis in combination with glass fluxing technique over a composition range of 16.0–87.2 at.% Cu. The DTA signals, obtained during isochronous cooling, indicate that this separation process is exothermic and proceeds till the rapid solidification of Co-rich liquid phase occurs. The metastable miscibility gap that was determined directly and reproducibly from the onset temperatures of this process is slightly shifted to the Cu-rich side and roughly symmetrical about a Cu concentration of 53 at.%. The measured critical temperature of phase separation is 1547±1.5 K and is about 108 K below the corresponding liquidus temperature. In the present measurements the separated Co-rich liquid always solidified prior to the Cu-rich phase, which crystallized near the peritectic temperature. Lower surface tension and better wetting properties of the Cu-rich liquid phase with glass flux are responsible for the Co-rich phase to be always encased by the Cu-rich phase. In addition, thermodynamic calculations have been accomplished leading to a binodal line, which is in sufficient agreement with the experimental results.