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

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 Am-2/kg. The influence of the devitrification on the evolution of the coercivity, magnetization and thermomagnetic behavior of Co40Fe22Ta8B30 glassy alloy was investigated. (C) 2014 Elsevier B.V. All rights reserved.