Fe-Co-B Soft Magnetic Ribbons: Crystallization Process, Microstructure and Coercivity.

Anna Wojcik,Wojciech Maziarz,Wojciech Maziarz,Maciej Szlezynger,Maciej Szlezynger,Przemyslaw Zackiewicz,Przemyslaw Zackiewicz,Maciej Kowalczyk,Lukasz Hawelek,Aleksandra Kolano-Burian,Aleksandra Kolano-Burian,Patryk Wlodarczyk,Pawel Czaja,Pawel Czaja,Robert Chulist,Robert Chulist

doi:10.3390/ma13071639

Abstract

In this work, a detailed microstructural investigation of as-melt-spun and heat-treated Fe67Co20B13 ribbons was performed. The as-melt-spun ribbon was predominantly amorphous at room temperature. Subsequent heating demonstrated an amorphous to crystalline α-(Fe,Co) phase transition at 403 °C. In situ transmission electron microscopy observations, carried out at the temperature range of 25–500 °C and with the heating rate of 200 °C/min, showed that the first crystallized nuclei appeared at a temperature close to 370 °C. With a further increase of temperature, the volume of α-(Fe,Co) crystallites considerably increased. Moreover, the results showed that a heating rate of 200 °C/min provides for a fine and homogenous microstructure with the α-(Fe,Co) crystallites size three times smaller than when the ribbon is heated at 20 °C/min. The next step of this research concerned the influence of both the annealing time and temperature on the microstructure and coercivity of the ribbons. It was shown that annealing at 485 °C for a shorter time (2 s) led to materials with homogenous distribution of α-(Fe,Co) crystallites with a mean size of 30 nm dispersed in the residual amorphous matrix. This was reflected in the coercivity (20.5 A/m), which significantly depended on the volume fraction of crystallites, their size, and distribution.

Highlights

Among several groups of soft magnetic materials, Fe-based amorphous and nanocrystalline alloys are extremely interesting from both a scientific and an application point of view [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
Based on the in situ Transmission Electron Microscope (TEM) experiments and the nano- and microstructure observations, the following conclusions can be drawn: (i) independently of the heating rate, the crystallization process following conclusions can be drawn: (i) independently of the heating rate, the crystallization process of amorphous Fe67 Co20 B13 melt-spun ribbons is realized by the nucleation and dendritic growth of of amorphous
20B13 melt-spun ribbons is realized by the nucleation and dendritic growth◦of αα-(FeCo) phase, while the first crystallization effects are manifested at a temperature close to 370 C; (FeCo) phase, while the first crystallization effects are manifested at a temperature close to 370 °C; (ii) finer and more homogeneous microstructures are observed in the case of sample heated with the heating rate of 200 °C/min than in the one heated with 20 °C/min; (iii) formation of Fe2B phase at 500

Summary

Introduction

Among several groups of soft magnetic materials, Fe-based amorphous and nanocrystalline alloys are extremely interesting from both a scientific and an application point of view [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] They exhibit optimal soft magnetic properties (e.g., low coercivity (Hc ) and high permeability (μ’)) and are characterized by relatively low magnetic core losses (Ps ) in comparison with other materials. This behavior, explained by Herzer [18] in 1989, is based on a random anisotropy model in which the averaging of magnetocrystalline anisotropy plays a key Materials 2020, 13, 1639; doi:10.3390/ma13071639 www.mdpi.com/journal/materials

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Conclusion