Crystallization kinetics of melt-spun Co43Fe20Ta5.5B31.5 amorphous alloy

The crystallization kinetics of Co43Fe20Ta5.5B31.5 amorphous alloy was investigated by differential scanning calorimetry in the mode of continuous heating and isothermal annealing. It is found that, in the case of continuous heating, all the DSC traces have a single exothermic peak and exhibit an extended supercooled liquid region ΔTx before the onset of crystallization, and both the glass transition temperature Tg and the crystallization peak temperature Tp display a strong dependence on the heating rate. The crystallization activation energy was determined by the Kissinger method, which yields Ec = 452.16 kJ/mol. On the other hand, the isothermal kinetics was modeled by the Johnson-Mehl-Avrami equation, the Avrami exponents were calculated to be in the range of 2.51-4.8 for different isothermal temperatures. This implies that the crystallization of Co43Fe20Ta5.5B31.5 amorphous alloy is governed by either diffusion- or interface-controlled three-dimensional growth, depending on the annealing temperature. On the basis of the Arrhenius relation, the activation energy in the isothermal process was calculated to be Ec = 609.6 kJ/mol. Finally, details of the nucleation and growth behaviors during the isothermal crystallization are discussed in terms of local Avrami exponent and local activation energy.