Influence of copper addition and heat treatment parameters on nanocrystallization process of Fe-Co-Mo-B-Si amorphous ribbons with high saturation magnetization about 1.6 T

Adrian Radoń,Rafał Babilas,Patryk Włodarczyk,Przemysław Zackiewicz,Dariusz Łukowiec,Marcin Polak,Mariola Kądziołka-Gaweł,Aleksandra Kolano-Burian,Łukasz Hawełek

doi:10.1016/j.jmmm.2019.165951

Abstract

In this paper the influence of copper addition on the formation of the amorphous phase and the nanocrystallization process of Fe79.8−xCo2CuxMo0.2Si4B14 (x = 0, 0.25, 0.5, 0.75, 1, 1.5, 2) ribbons was described. The formation of crystalline phases was described using differential scanning calorimetry, X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy. It was confirmed that the addition of copper decreases the glass forming ability, while facilitating the process of nanocrystallization. The analysis of the Avrami exponent allowed to state, that for fully amorphous alloys the crystallization of the α-Fe phase is associated with diffusion-controlled growth with decreasing nucleation rate and the Fe2B phase with interface controlled growth with increasing nucleation rate. Additionally, with increasing copper addition onset temperature of crystallization of α-Fe phase shifts to lower values, whereas for second, Fe2B phase, these changes are not so visible. Optimization of the annealing process of toroidal cores made from amorphous ribbons with different copper content allowed to obtain nanocrystalline, soft magnetic materials characterized by low coercivity ~9 A/m and high saturation induction of about 1.6 T. Analysis of transmission electron microscope images and electron diffraction confirmed that high magnetic parameters are related to the coexistence of the amorphous and nanocrystalline phases, which was confirmed also by Mössbauer spectroscopy.

Highlights

The Fe-based amorphous and nanocrystalline alloys can be used in the various forms as magnetic cores and sensors, which is related to their high magnetic permeability (μ), low coercivity (Hc) and low power losses (Ps) [1,2,3]
That the amorphous ribbons can be prepared from alloys with Cu addition below 2 at. % and flexible ribbons from alloys with Cu addition below 1 at.%
The double stage crystallization of amorphous samples studied by differential scanning calorimetry (DSC) technique and X-ray diffraction method is associated with diffusion controlled growth with decreasing nucleation rate of α-Fe phase and interface controlled growth with increasing nucleation rate of Fe2B phase

Summary

Introduction

The Fe-based amorphous and nanocrystalline alloys can be used in the various forms as magnetic cores and sensors, which is related to their high magnetic permeability (μ), low coercivity (Hc) and low power losses (Ps) [1,2,3]. The nanocrystallization process of amorphous alloys allows obtaining materials with lower coercivity and higher saturation magnetization than amorphous precursors [4] These magnetic parameters can be modified by changing the heat treatment parameters such as temperatures, time and heating rate [5,6]. The optimal parameters of annealing of amorphous alloys can be determined on the basis of differential scanning calorimetry (DSC) curves through determination of onset temperatures of the first peak crystallization. This peak is associated with crystallization of α-Fe phase, whereas second peak with crystallization of for example Fe2B phase. Fe atoms form nucleus and crystallize into α-Fe phase on the Cu clusters-amorphous phase boundary [17]

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