Growth kinetics of L12 phase in a Nb-containing high entropy alloy: A Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis

This work focusses on the growth behavior of dominant secondary phases, particularly L1 2, in Nb-containing high entropy alloys designed for potential high temperature applications. A non equiatomic Al 0.5 Cr 0.9 FeNi 2.5 Nb 0.2 HEA was synthesized via vacuum arc melting, and homogenized, and subjected to direct aging at 700 °C, 750 °C and 800 °C. The growth kinetics of the L1 2 precipitate was studied using a hardness-based Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. Microstructural analysis revealed face centered cubic (FCC) matrix with nanoscale L1 2 ordered precipitates and nominal Laves and B2 phases present at grain boundaries. Peak aging was observed at 8 h for 700 °C, 4 h for 750 °C, and 3 h for 800 °C. The JMAK kinetics model shows low Avrami exponents (n ≈ 0.43–0.45) and an activation energy of 158.55 ± 25.16 kJ/mol, indicating early solute depletion, soft impingement effects, and sluggish diffusion behavior of Nb. The results of the work shed light on kinetics of L1 2 precipitates in Nb-containing HEAs, which might be utilized to tune mechanical properties in comparable systems. The findings contribute to design of high entropy alloys for high temperature applications. • Growth Kinetics of L1 2 precipitating phase in Nb based HEA was investigated. • Hardness based Johnson-Mehl-Avrami-Kolmogorov model utilized for the analysis. • The JMAK model yielded low Avrami exponent (n) values between 0.43 and 0.45. • Activation Energy (Q) found to be around 158.55 kJ/mol indicates solute depletion and soft impingement effects.