Preparation and Characterization of the Soft Magnetic FeCo-based Amorphous Alloy with Enhanced Magnetic Properties and T
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Preparation and Characterization of the Soft Magnetic FeCo-based Amorphous Alloy with Enhanced Magnetic Properties and Thermal Stability MARTIN HOLLMARK, VICTOR TKATCH, SERGEY KHARTSEV, ALEX GRISHIN Department of Condensed Matter Physics, Royal Institute of Technology, S-100 44 Stockholm, Sweden ABSTRACT A glassy structure was formed in the Fe40Co40P14B6 alloy by melt-spinning technique. The as-quenched 2-8 mm wide and 15-30 µm thick ribbons exhibit good soft magnetic properties: the saturation magnetization of 1.45 T, the coercive force of 4 A/m and maximum differential permeability at 60 Hz of about 90000. The FeCo-based glass crystallizes via eutectic reaction into a mixture of an austenite and a b.c. tetragonal Fe3P-like phase similar to that of the well-known Fe40Ni40P14B6 metallic glass, but at temperatures about 60 K higher than the latter. The evaluation of the thermodynamic and kinetic parameters of crystallization process brought us to the conclusion that the improved thermal stability of the Fe40Co40P14B6 glass is caused by the enhanced interfacial nucleus-glass energy.
INTRODUCTION There are continuous demands on soft magnetic materials for various applications in electrotechnique, inductive devices, and sensors. Metallic alloys with glassy and nanocrystalline metastable structures play an increasing role among the soft magnets because of their favorable physical properties [1]. The key soft magnetic properties: the saturation magnetization Bs and Curie temperature Tc, are the functions of alloy composition and structure. It is known that the highest values of Bs, both in crystalline and amorphous alloys, have been achieved in the Fe-Co alloys [2,3]. Therefore the FeCo-based alloys with amorphous and nanocrystalline structure have attracted increasing attention over the past few years [4,5]. In this paper we report on how the replacement of Ni by Co affects the soft magnetic properties and thermal stability of one of the most thoroughly investigated metallic glasses, Fe40Ni40P14B6 [6].
EXPERIMENTAL Rapidly quenched ribbons, 2-8 mm wide and 15-30 µm thick, have been prepared by a single roller melt spinning process using high-purity RF-melted master alloy ingots with nominal composition of Fe40Co40P14B6. The melting temperature Tm of the alloy was estimated to be 1253 K. 5-10 g charges of the master alloy were melted by a RF induction heater and ejected by argon gas from a quartz nozzle mounted at 0.15 mm above a rotating copper wheel. For comparison, ribbons of the Fe40Ni40P14B6 alloy were prepared under the same processing conditions. The ribbons were isochronally annealed during 1800 s in a flowing Ar-gas at the temperature 670 K. The structure of the as-cast and annealed specimens was examined using a Siemens D5000 x-ray L7.2.1
diffractometer at CuKα radiation. Thermal stability and crystallization kinetics of the melt-spun ribbons were studied by a differential scanning calorimeter Perkin Elmer DSC7 under continuous heating with rates of 5, 10, 20 and 40 K/min. The saturation magnetization Bs was
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