Non-isothermal kinetic analysis of phase transformations in Fe-Co-V-Mo semi-hard magnetic alloy

Abstract

In this study, the non-isothermal kinetics and phase transformations within the Fe-Co-V-Mo alloy were investigated. Four distinct transformations were identified: disorder → order (T1), first-stage polymorphic (T2), order → disorder (T3), and second-stage polymorphic (T4). The activation energy (E) for each transformation was determined using isoconversional methods. Fitting model were employed to calculate the kinetic triplets, confirming that all transformations follow the Avrami model. The Johnson-Mehl-Avrami (JMA) and Šesták-Berggren (SB) models were used to determine other kinetic parameters (n, M, and N). The findings suggest that the growth mechanisms for transformations T3 and T4 are interface-controlled, whereas transformation T2 is diffusion-controlled. Consequently, the A3/2 and A3 mechanisms were identified as predominant mechanisms for transformations T2 and T4, respectively. Additionally, transformation T3 follows the A3 mechanism at heating rates of 10 and 20 K/min, and the A2 mechanism at 30 K/min. Kinetic analysis revealed that the addition of Mo in Fe-Co-V alloys, acting as a ferrite (α) stabilizer, decreases the onset temperatures of transformations T1 and T3. Conversely, it increases those of transformations T2 and T4. Furthermore, Mo influences the reduction of E associated with transformation T3.