THE KINETICS OF AMORPHOUS-NANOCRYSTALLINE TRANSFORMATION FOR A FINEMET ALLOY

The kinetics of the nanocrystalline structure formation from its amorp hous precursor was investigated for a Finemet alloy with the compositi on Fe73.5Nb3Cu1Si13.5B9. The time- and temperature-dependent transform ation was followed in parallel by differential scanning calorimetry (D SC), thermoelectric power (TEP) and Vickers microhardness (HV) measure ments on ribbon samples 10 mm wide. After annealing the samples in a t in bath at 500, 525, 550 and 575-degrees-C for different annealing tim es between 5 s and 2 h, the TEP and HV data were measured at room temp erature. Using the conventional Johnson-Mehl-Avrami method, for the ap parent activation energy we deduced values from 3.58 to 3.93 eV from t he TEP data and values from 3.84 to 4.08 eV from the HV data which agr ee well with the value we obtained from DSC measurements using the Kis singer method (4.1 +/- 0.4 eV). Our DSC measurements on partially crys tallized samples revealed a third intermediate exothermal peak beside the well-known two peaks. This was attributed to the segregation of a silicide compound out of the alpha-Fe(Si) solid solution.