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(13.5)B(9) ribbons to the nanocrystalline structure has been studied. A differential scanning calorimeter ill the continuous-heating and isothermal measuring regimes and a thermobalance with a permanent magnet have 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 signal in the isothermal regime is monotonically decreasing with a temperature-dependent amplitude, the total transformation enthalpy being slightly changed. Both as-quenched and nanocrystalline samples exhibit two magnetic transformations namely the glass-like and the nanophase-like transformations, the mutual proportion between them being changed a with the proceeding transformation. All the observed phenomena are interpreted bq the grain growth mechanism of the coarsening of the already existing fine-crystalline structure to the nanocrystalline structure. The experimental results can be interpreted also by the Johnson-Mehl-Avrami nucleation-and-growth crystallization mechanism with an abnormal exponent n approximate to 0.9.