Stability of lamellar structures in CoCrFeNiNbx eutectic high entropy alloys at elevated temperatures

• The lamellar structures are stable below 750 °C but coarsened rapidly at 900 °C.
• Alloys with lamellar structures have the best mechanical properties.
• The EHEAs with decayed lamellar structures maintain good strength and ductility.

Eutectic high entropy alloys (EHEAs) are promising candidates for high temperature materials. The stability of eutectic structures of EHEAs at elevated temperatures is in need of examination before pursuing their high temperature applications. In this paper, the stability of eutectic structures in CoCrFeNiNbx EHEAs were characterized and examined. It is found that, the lamellar structures of the EHEAs are stable when the annealing temperature is lower than 750 °C but spheroidization of the lamellar structures occurs when the temperature goes up to 900 °C. The lamellar structures exhibit excellent mechanical properties. Although the mechanical properties decreases as the lamellar structures decay after annealing at 900 °C, the EHEAs of CoCrFeNiNbx maintain good mechanical properties. The evolution of lamellar structures over time at 750 °C was also reported. The application of classical lamellar instability theory in HEAs was discussed.

The typical microstructures of annealed CoCrFeNiNb0.65 EHEA; (a) lamellar structures, (b) decayed lamellar structures, (c) spherical lamellar structures and (d) their corresponding mechanical properties. Although the mechanical properties decreases as the lamellar structures decay after annealing, the EHEAs of CoCrFeNiNbx maintain good mechanical properties.Figure optionsDownload as PowerPoint slide