Kinetics of nanocrystallization in Finemet alloy

In this study, the kinetics of nanocrystallization of amorphous Finemet alloys is investigated under non-isothermal condition. In order to estimate kinetic parameters, differential scanning calorimetric analyses of the amorphous samples were performed at various heating rates. This results show that crystallization of α-Fe phase starts at around 450 ̊C. X-ray diffraction pattern samples confirm these results. According to the XRD results, crystallite size of the sample annealed at 450 ̊C and 550 ̊C were 12 nm and 19 nm, respectively. Variable activation energy of crystallization was calculated, based on differential scanning calorimetric results and according to Vyazovkin advanced isoconversional method. Results show that, the activation energy is variable as a function of transformed fraction and increases from 290 to 390 kJ mol-1. Variation of activation energy confirms the complexity of nanocrystallization process. Numerical reconstruction of the reaction model using experimental data showed that nanocrystallization mechanism could not be described with a single theoretical model. But it is closer to three dimensional phase boundary reaction mechanism. Rrounded and isotropic crystallites observed on the TEM images confirmed these results.