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

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 CoCrFeNiNb_x 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 CoCrFeNiNb_x 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.