Complex primary crystallization kinetics of amorphous Finemet alloy

Abstract

The complex primary crystallization kinetics of the amorphous Finemet soft magnetic alloys has been analyzed by non-isothermal DSC measurements. The local activation energies Ec(α) were determined by an isoconversional method without assuming the kinetic model function and its average value was about 383kJ/mol. The nucleation activation energy En and growth activation energy Eg were 425 and 333kJ/mol, respectively. And the apparent local activation energies Ec can be expressed by En and Eg as follows: Ec=aEn+bEg. The local Avrami exponents lies between 1 and 2 in a wide range of 0.2<α<0.9, and it indicates that dominating crystallization mechanism in the non-isothermal primary crystallization of amorphous Finemet alloy is one dimensional growth at a near-zero nucleation rate for surface crystallization. The significant variation of local Avrami exponent and local activation energy for primary crystallization with crystallized volume fraction demonstrates that the primary crystallization kinetics of amorphous Finemet alloy varies at different stages. In addition, the variable local activation energies Ec(α) and local Avrami exponents n(α) are applicable and correct in describing the primary crystallization process of the amorphous Finemet alloy according to the theoretical DSC curve simulation.