Experimental Investigation of the Co-Ge Phase Diagram

The Co-Ge phase diagram has been reinvestigated with 20 decisive alloys over the whole composition range by means of differential scanning calorimeter, x-ray diffraction, optical microscopy and electron probe microanalysis. The liquidus lines in Co-rich and Ge-rich portions have been measured for the first time. The compound Co 3 Ge has been determined to be an ordered fcc-cubic phase and observed to be stable within the temperature range of about 600-750 °C. The previously reported Co 5 Ge 2 and Co 4 Ge phases were not found in the present work, and instead Co 2 Ge was confirmed to be stable at 600 °C. The system contains one congruent melting compound βCo 5 Ge 3 and three incongruent melting phases ε(Co), CoGe and CoGe 2 . Three compounds Co 3 Ge, Co 2 Ge and Co 5 Ge 7 are formed via peritectoid reactions. A revised Co-Ge phase diagram is presented based on the present experimental results and reliable literature data.