Advanced isoconversional kinetics of nanocrystallization in Fe73.5Si13.5B9Nb3Cu1 alloy

Nanocrystallization kinetics of amorphous Finemet alloy was studied using Vyazovkin advanced isoconversional method under non-isothermal condition. Well known Kissinger model-fitting method and four isoconversional methods of Kissinger–Akahira–Sunose (KSA), Flynn–Wall–Ozawa (FWO), Tang, and Starink were also used for the determination of activation energy. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) patterns were used for thermal and structural analyses, respectively. According to Vyazovkin and other isoconversional methods, the mean value of variable activation energy, as a function of conversion, was obtained as 350 kJ mol−1. While, according to Kissinger method, the constant value of activation energy was obtained as 270 ± 10 kJ mol−1 for the same experiments, which shows inaccuracy of this method. The mean value of kinetic exponent 〈n〉 was 1.44 ± 0.05 by considering instantaneous nucleation condition (n = m), which is consistent with one-dimensional growth mechanism. Kinetics and mechanistic predictions were also performed using numerical reconstruction of the experimental kinetic function. Comparison of the numerically reconstructed model with theoretical ones showed that no single model could perfectly fit the numerical values of kinetic function and the mechanism of transformation changes with conversion progress. Nevertheless it could be seen that nanocrystallization almost follows the one-dimensional diffusion mechanism.