Microstructure, soft magnetic properties and applications of amorphous Fe-Co-Si-BMo-P alloy Mariusz Hasiak, Marcel Miglierini, Mirosław Łukiewski, Amadeusz Łaszcz, and Marek Bujdoš Citation: AIP Advances 8, 056116 (2018); View online: https://doi.org/10.1063/1.5007781 View Table of Contents: http://aip.scitation.org/toc/adv/8/5 Published by the American Institute of Physics
AIP ADVANCES 8, 056116 (2018)
Microstructure, soft magnetic properties and applications of amorphous Fe-Co-Si-B-Mo-P alloy Mariusz Hasiak,1,a Marcel Miglierini,2,3 Mirosław Łukiewski,4 Amadeusz Łaszcz,1 and Marek Bujdoˇs5 1 Wrocław
University of Science and Technology, Department of Mechanics and Materials Science Engineering, Smoluchowskiego 25, 50 370 Wrocław, Poland 2 Slovak University of Technology in Bratislava, Institute of Nuclear and Physical Engineering, Ilkoviˇcova 3, 812 19 Bratislava, Slovakia 3 Czech Technical University in Prague, Department of Nuclear Reactors, V Holeˇ soviˇck´ach 2, 180 00 Prague, Czech Republic 4 TRAFECO—Transformers and Inductive Components, Dolna 4, 42 283 Boron´ ow, Poland 5 Comenius University in Bratislava, Institute of Laboratory Research on Geomaterials, Ilkoviˇcova 6, 842 15 Bratislava, Slovakia (Presented 7 November 2017; received 2 October 2017; accepted 17 November 2017; published online 3 January 2018)
DC thermomagnetic properties of Fe51 Co12 Si16 B8 Mo5 P8 amorphous alloy in the asquenched and after annealing below crystallization temperature are investigated. They are related to deviations in the microstructure as revealed by M¨ossbauer spectrometry. Study of AC magnetic properties, i.e. hysteresis loops, relative permeability and core losses versus maximum induction was aimed at obtaining optimal initial parameters for simulation process of a resonant transformer for a rail power supply converter. The results obtained from numerical analyses including core losses, winding losses, core mass, and dimensions were compared with the same parameters calculated for Fe-Si alloy and ferrite. Moreover, Steinmetz coefficients were also calculated for the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 amorphous alloy. © 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.5007781
I. INTRODUCTION
Fe-based amorphous and nanocrystalline alloys has been intensively studied in the last 30 years.1 These alloys, when produced in a form of thin ribbons by rapid quenching, show excellent soft magnetic properties.2 The high initial magnetic permeability, low coercivity, low core losses, and high saturation induction make them ideal for electrical industry, e.g. as cores in transformers and magnetic chokes. A new group of soft magnetic materials with high saturation magnetic flux density of about 1.8 T called NANOMET proposed by Makino3,4 is a suitable candidate for energy saving. Addition of Co into similar alloys5 can improve such magnetic parameters as Curie temperature, coercive field, saturation magnetization, etc. This challenge has motivated us to design a metallic glass which is based upon the NANOMET composition but contains also other elements like Co and Mo, namely Fe51 Co12 Si16 B8 Mo5 P8 . To understand the relationship between microstructure and magnetic properties of this alloy, we have employed combination of M¨ossbauer spectrometry and magnetic measurements. Consequently, this work aims at characterization of this novel type of amorphous alloy and assesses its application potential. To reach this goal, DC and AC magnetic properties are investigated. In addition, design and production process of a transformer core prepared from this material and intended for railway applications working in a rail vehicle power converter is also presented. a
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II. EXPERIMENTAL PROCEDURE
Amorphous Fe51 Co12 Si16 B8 Mo5 P8 (at. %) alloy was produced in a form of 6 mm wide and about 0.02 mm thick ribbon using rapid solidification on a cooper quenching wheel. Its exact chemical composition was determined by ICP-MS (Mass Spectrometry with Inductively Coupled Plasma) and AAS (Atomic Absorption Spectrometry) used for the determination of the contents of B, P and Fe, Co, Si, and Mo, respectively. The amorphicity of the as-quenched material was verified by X-ray diffractometer equipped with CoKα radiation. M¨ossbauer spectra were recorded in transmission geometry using a constant acceleration driver equipped with a 57 Co(Rh) radioactive source. DC thermomagnetic characteristic were measured with the help of VersaLab vibrating sample magnetometer (Quantum Design) in the temperature range 50 – 400 K. Moreover, temperature dependence of magnetization in field cooled (FC) mode was recorded in maximum external magnetic field of 10 mT. AC magnetic properties were studied by a hysteresisgraph (AMH-50K-S, Laboratorio ElletroFisico Engineering) using a single strip test fixture (ST-100) for frequencies up to 400 Hz. The evaluation of magnetic characteristics allows us to choose optimal parameters for simulation of transformer parameters. Using the obtained results such as maximum induction and core losses, basic parameters for resonant transformer were calculated by RALE distribution and power transformer design software.
III. RESULTS AND DISCUSSION
Ribbon of the Fe51 Co12 Si16 B8 Mo5 P8 alloy in the as-quenched state was fully amorphous6,7 and only a broad halo characteristic for disordered structures was observed in an X-ray diffraction pattern. The primary crystallization temperature (Tx1 ) for the investigated material equals to 839 K.7 The heat treatment of the investigated sample up to 673 K, i.e. below Tx1 leads only to structural relaxation of the sample and slight improvement of its soft magnetic properties. This behavior is clearly visible in Fig. 1 as an increase of Curie point from 400 K (as-quenched sample) to 411 K (sample annealed at 673 K for 1 h) with the increase the of annealing temperature.7 Changes of the saturation magnetization with annealing of the ribbon at different temperatures imply that segregation of some atoms in the investigated material takes place and magnetically distinct regions are formed inside the amorphous matrix. On the other hand, the temperature of annealing is not high enough to create some crystalline structures. These findings are supported by Fig. 2a where broad M¨ossbauer spectra indicate full amorphicity of the samples. They were refined by distributions of hyperfine magnetic fields P(B) that are plotted in the insets. P(B) of the as-quenched sample in Fig. 2a shows a bell-shaped curve. On the other hand, clear bi-modal behavior of the P(B) distribution corresponding to the sample annealed at 673 K is seen in Fig. 2b. Here, structural rearrangement in the amorphous matrix takes place. This is illustrated by a separation of P(B) into two peaks which clearly demonstrate presence of low- and high-fields.
FIG. 1. Field cooled (FC) magnetization versus temperature for the Fe51 Co12 Si16 B8 Mo5 P8 alloy in the as-quenched state (a) and after annealing for 1 h at 473 K (b), 573 K (c) and 673 K (d).
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FIG. 2. Room temperature M¨ossbauer spectra and corresponding distributions of hyperfine magnetic fields P(B) (insets) of the Fe51 Co12 Si16 B8 Mo5 P8 alloy in the as-quenched state (a) and after annealing at 673 K (b).
They represent magnetically distinct regions inside the amorphous structure. Average value of P(B) distribution increases from (10.9±0.2) T in the as-quenched state to (11.6±0.2) T after annealing at 673 K. Appearance of two distinct maxima in P(B) implies that regions in the amorphous structure exist which have different local atomic arrangement. More detail M¨ossbauer effect study of this metallic glass in the as-quenched state and after annealing up to the crystallization can be found elsewhere.7 Figure 3 shows DC and AC hysteresis loops recorded for the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 alloy. They were traced at different temperatures (Fig. 3a) and different frequencies (Fig. 3b). The investigated sample shows typical ferromagnetic behavior. With increasing the temperature of measurement up to 400 K, paramagnetic behavior occurs in Fig. 3a as close-to-linear dependence of M(T). As for AC hysteresis loops, their shapes in Fig. 3b are almost the same and only coercivity varies with the frequency. The investigated material in the as-quenched state shows extremely low coercivity, which is less than 10 A/m for all analyzed frequencies. Hysteresis loops measured from the annealed samples whose magnetizations are shown in Fig. 1 are almost identical with those of the as-quenched alloy. Minor deviations were unveiled only after annealing at higher temperature of 773 K.6 The AC core losses of the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 ribbon for various frequencies are displayed in Fig. 4a. With increasing frequency of measurement, an increase of core losses is observed. This is related to eddy currents which play dominant role at higher frequencies. Figure 4b shows core losses for the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 alloy versus AC magnetic field. It is seen that above magnetic field of 1 kA/m core losses rapidly increase with frequency of measurement. On the other hand, the observed core losses are much lower than those for typical crystalline Fe-Si materials.
FIG. 3. DC (a) and AC (b) hysteresis loops for the Fe51 Co12 Si16 B8 Mo5 P8 alloy in the as-quenched state measured at the indicated temperatures and frequencies, respectively.
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FIG. 4. AC core losses versus maximum induction for the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 alloy recorded at room temperature at frequency f = 100, 200, 300 and 400 Hz (a) and relation between core losses and AC magnetic field measured at various frequencies (b).
In the frequency range 100-400 Hz, we have calculated the Steinmetz coefficients K and α according to the formula:8 W = K × f × Bα where: W – core losses, f – frequency, and B – magnetic induction. The obtained K-values of 0.808, 0.818, 0.943, and 1.006 ×10-2 increase with frequency for 100, 200, 300, and 400 Hz, correspondingly. They are much lower than those reported for other Fe-based materials (sheet iron: 10.05, cast iron: 10.23 - 40.2, cast steel: 7.54 - 30.14, hard cast steel: 63 – 70.34, Fe-4.8%Si: 1.91). The calculated α-values are of 3.16, 2.92, 3.31, and 3.42, respectively. The AC magnetic characteristics obtained for the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 alloy, which are presented in Fig. 4, resulted in a choice of the design input data for a two-winding transformer for a rail power supply converter for railway applications. The schematic model and real resonant transformer with core made from the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 alloy is shown in Fig. 5. The initial parameters for the design comprised: input and output voltage of 700 and 350 V, respectively, power of 25 kW, switching frequency of 400 Hz, primary and secondary current of 35.7 a, and 71.4 A, respectively, and overload of 140 A. The insulation test performed under 4 500 V/50 Hz/60 s with air cooling was considered. The same initial parameters were applied in simulations for the Fe-Si sheet ET 150-30S and ferrite 3C90 to allow for mutual comparison of the obtained results. Results obtained from the simulations are listed in Table I. These results were received for a two-winding resonant transformer for railway applications made from the currently investigated amorphous alloy (Fe51 Co12 Si16 B8 Mo5 P8 ) as well as from Fe-Si sheet (ET 150-30S) and ferrite (3C90). As it is seen from this table, the investigated material for the frequency of 400 Hz shows the lowest value of core losses. Moreover, some other parameters like winding losses, core and
FIG. 5. Schematic model (left) and real resonant transformer (right) with core made from the as-quenched Fe51 Co12 Si16 B8 Mo5 P8 amorphous alloy.
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TABLE I. Resonant transformer parameters for f = 400 Hz obtained from the simulation processes. Material Maximum induction (in core) Core losses Winding losses ∆T (in core) ∆T (in winding) Core mass Total mass Core dimensions (L×B×H) [mm]
sheet ET 150-30S
ferrite 3C90
Fe51 Co12 Si16 B8 Mo5 P8
0.45 T 187 W 376 W 57 K 81 K 43 kg 65 kg 210×100×350
0.25 T 115 W 273 W 32 K 75 K 46 kg 77 kg 240×120×420
0.8 T 64 W 206 W 39 K 76 K 24 kg 41 kg 180×100×300
total mass as well as the dimensions are also reduced for the Fe51 Co12 Si16 B8 Mo5 P8 amorphous alloy. IV. CONCLUSION
The DC/AC thermomagnetic characteristics for the amorphous Fe51 Co12 Si16 B8 Mo5 P8 alloy were measured. Changes in the measured magnetic parameters were ascribed to structural modifications that took place on atomic level as derived from M¨ossbauer spectrometry. The simulations suggest that the investigated material shows better soft magnetic properties than classical Fe-Si alloys and/or ferrites, which are used in electrical industry. ACKNOWLEDGMENTS
Financial support of the grants VEGA 1/0182/16 and APVV-16-0079 is acknowledged. 1 Y.
Yoshizawa, S. Oguma, and K. Yamauchi, “New Fe-based soft magnetic alloys composed of ultrafine grain structure,” Journal of Applied Physics 64, 6044 (1988). 2 M. E. McHenry, M. A. Willard, and D. E. Laughlin, “Amorphous and nanocrystalline materials for applications as soft magnets,” Progress Mat. Sci. 44, 291 (1999). 3 A. Makino, “Nanocrystalline soft magnetic Fe-Si B-P-Cu alloys with high B of 1.8-1.9 T contributable to energy saving,” IEEE Transaction on Magnetics 48(4), 1331 (2012). 4 P. Sharma, X. Zhang, Y. Zhang, and A. Makino, “Competition driven nanocrystallization in high B and low core loss s Fe-Si-B-P-Cu soft magnetic alloys,” Scripta Materialia 95, 3 (2015). 5 K. Takenaka, A. D. Setyawan, Y. Zhang, P. Sharma, N. Nishiyama, and A. Makino, “Production of nanocrystalline (Fe, Co)-Si-B-P-Cu alloy with excellent soft magnetic properties for commercial applications,” Mater. Trans. 56, 372 (2015). 6 M. Hasiak, M. Miglierini, N. Amini, and M. Bujdoˇs, “Microstructure and magnetic properties of amorphous Fe51 Co12 Si16 B8 Mo5 P8 alloy,” Nukleonika 62, 85 (2017). 7 N. Amini, M. Miglierini, and M. Hasiak, “Impact of annealing on magnetic and structural features of FeCoSiBMoP metallic glass,” AIP Conference Proceedings 1781, 020001 (2016). 8 C. P. Steinmetz, “On the law of hysteresis,” Proceedings of the IEEE 72(2), 197–221 (1984), (Reprinted from the American Institute of Electrical Engineers Transactions 9 (1892) 3).
