A study on synthesis, crystallization, and magnetic behavior of nanocrystalline Fe-based metallic glasses

Abstract

In the present work, structure of the as-cast melt-spun ribbons, nonisothermal crystallization kinetics, and the effect of heat treatment on the magnetic properties have been studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have revealed the presence of amorphous and partly crystalline structures in the as-cast Fe₆₇Co₁₈Si₁B₁₄ and Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass ribbons, respectively. The crystalline phase present in the as-cast Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass was identified as α -Fe. Direct transformation from liquid to α -Fe has been analyzed from a thermodynamic and kinetics point of view. The differential scanning calorimetry (DSC) studies have shown two-stage crystallization behavior. The primary and secondary crystallization phases were identified as bcc-Fe(Co) and bct-(Fe,Co)₃(Si,B), respectively. Kissinger and Gao et al. methods were employed for nonisothermal crystallization kinetic studies. The activation-energy values obtained by the two models were in good agreement. The nucleation and growth morphologies of crystalline phases have been explained on the basis of the Avrami exponent, which were found to be consistent with the observed microstructures. The magnetic properties of as-cast amorphous ribbons showed low coercivity, and this has been attributed to averaging of magnetocrystalline anisotropy over grains coupled within an exchange length, i.e., based on a random anisotropy model. The influence of microstructure on magnetic properties was studied by crystallizing the amorphous phase at 400°C for 3 hours. The saturation magnetization and coercivity had increased after crystallization for both alloys.