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 Co3Ge has been determined to be an ordered fcc-cubic phase and observed to be stable within the temperature range of about 600-750 A degrees C. The previously reported Co5Ge2 and Co4Ge phases were not found in the present work, and instead Co2Ge was confirmed to be stable at 600 A degrees C. The system contains one congruent melting compound beta Co5Ge3 and three incongruent melting phases epsilon(Co), CoGe and CoGe2. Three compounds Co3Ge, Co2Ge and Co5Ge7 are formed via peritectoid reactions. A revised Co-Ge phase diagram is presented based on the present experimental results and reliable literature data.