Crystallization kinetics of Co40Fe22Ta8B30 glassy alloy with high thermal stability and soft magnetic properties

• Crystallization kinetics of Co40Fe22Ta8B30 glassy ribbon was studied.
• The ribbon indicates a long incubation time prior to crystallization.
• Co40Fe22Ta8B30 glassy ribbon shows a high activation energy of crystallization.
• Crystallization is governed by three-dimensional diffusion-controlled growth.
• Crystallization enhances the saturation magnetization and coercivity of the ribbons.

In this paper, the thermal stability, the crystallization kinetics and magnetic properties of the melt-spun Co40Fe22Ta8B30 glassy alloy were investigated. The results show that the present alloy has a wide supercooled liquid region of 74 K and a high incubation time prior to crystallization upon isothermal annealing above the glass transition temperature compared to the well-known Co43Fe20Ta5.5B31.5 glassy alloy. The crystallization kinetics was systematically investigated by the Kissinger, Ozawa and isoconversional approaches under the isochronal condition, and Johnson–Mehl–Avrami (JMA) model under the isothermal situation, respectively. It was found that the Co40Fe22Ta8B30 metallic glass indicated an apparent activation energy of 520 ± 5 kJ/mol corresponding to the first crystallization event, which is higher than many other Fe-based and Co-based glassy alloys. The Avrami exponent calculated based on the JMA approach lies in the range of 2.13–1.58 for different isothermal annealing temperatures, revealing that the crystallization is governed by the three-dimensional diffusion-controlled growth with a decreasing nucleation rate. In addition, Co40Fe22Ta8B30 metallic glass exhibits good soft magnetic properties, i.e. a very low coercivity of 0.8 A/m and a magnetization of 42 Am2/kg. The influence of the devitrification on the evolution of the coercivity, magnetization and thermomagnetic behavior of Co40Fe22Ta8B30 glassy alloy was investigated.