Phase relations in the Co–CoAl–C system involving E21 type Co3AlCx phase

Abstract Solid–liquid phase equilibria have been studied in a part of the Co-rich corner of the Co–CoAl–C alloy system where the ternary Co 3 AlC x carbide is a significant component in the microstructure of alloys on solidification. fcc-Co can coexist with Co 3 AlC x , graphite, and β-CoAl. They form inter alia two ternary eutectics and an invariant fcc-Co–Co 3 AlC x eutectic reaction between them. The eutectic reaction was utilized to grow directionally solidified (DS) ingots that exhibit aligned regular lamellar Co–Co 3 AlC x microstructures. Melt equilibria were established via differential thermal analysis (DTA) and light microscopy. A DTA signal observed in the solid-state with the DS microstructure and alloy composition was associated to X-ray diffraction, dilatometry and transmission electron microscopy work and attributed to the action of a second order reaction.