Studies on Kinetics of BCC to FCC Phase Transformation in AlCoCrFeNi Equiatomic High Entropy Alloy

Kinetics of face-centered cubic (FCC) phase evolution in equiatomic AlCoCrFeNi alloy has been studied in this work, measuring the phase fraction from X-ray diffraction (XRD). As-cast alloy showed a body-centered cubic (BCC)+B2 structure. Heat treatments performed at different temperatures showed the formation up-to 30 to 35 pct FCC phase between 1073 K and 1373 K. A systematic decrease in hardness from 540 to 390 HV10 with increase in temperature suggested an increase in the FCC volume fraction. Kinetics of FCC evolution were analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and Arrhenius law to calculate the activation energy for the phase transformation. Furthermore, a time-temperature-transformation diagram was constructed from the isothermal transformation studies. Detailed microstructural investigation suggests faster kinetics of FCC phase formation near dendritic boundaries compared to interdendritic regions. The Kurdjumov-Sachs orientation relationship between FCC and BCC phases suggested a coherent interface between these phases. Results of the present study pave the way to decide on heat treatment practices in AlCoCrFeNi alloy.

Automated summary

This study investigates the kinetics of FCC phase evolution in equiatomic AlCoCrFeNi alloy, revealing the impact of temperature on phase transformation and hardness. A time-temperature-transformation diagram was constructed to demonstrate the differences in FCC phase formation rates in different regions. The results provide valuable insights for determining heat treatment practices in the alloy.