TRANSFORMATION KINETICS OF THE FE73.5CU1NB3SI13.5B9 RIBBONS TO THE NANOCRYSTALLINE STATE

The transformation kinetics of the as-quenched Fe(73.5)Cu(1)NBb(3)Si(1 3.5)B(9) ribbons to the nanocrystalline structure has been studied. A differential scanning calorimeter ill the continuous-heating and isoth ermal measuring regimes and a thermobalance with a permanent magnet ha ve been used. The main differential scanning calorimetry (DSC) peak in the continuous-heating regime is wide and asymmetrical, having a long high temperature part and a small transformation enthalpy. The DSC si gnal in the isothermal regime is monotonically decreasing with a tempe rature-dependent amplitude, the total transformation enthalpy being sl ightly changed. Both as-quenched and nanocrystalline samples exhibit t wo magnetic transformations namely the glass-like and the nanophase-li ke transformations, the mutual proportion between them being changed a with the proceeding transformation. All the observed phenomena are in terpreted bq the grain growth mechanism of the coarsening of the alrea dy existing fine-crystalline structure to the nanocrystalline structur e. The experimental results can be interpreted also by the Johnson-Meh l-Avrami nucleation-and-growth crystallization mechanism with an abnor mal exponent n approximate to 0.9.