Presentation Information
[P1-47]Development strategy of Fe-Cr-Co alloy powder for high-performance microwave absorbers and noise suppression sheets
*Saijian Ajia1, Mitsuharu Sato1,2, Hirotaka Asa1,3, Tomoki Ishijima1,4, Yasushi Endo1, Masashi Matsuura1, Satoshi Sugimoto1 (1. Graduate School of Engineering, Tohoku University (Japan), 2. Present: Research Institute for Electromagnetic Materials (Japan), 3. Present: PwC Consulting LLC (Japan), 4. Present: TDK Corporation (Japan))
Keywords:
Fe-Cr-Co,Microwave absorption,Noise suppression,permeability,core-shell
One way to suppress electromagnetic interference is to use microwave absorption materials (MAMs) and noise suppression sheets (NSSs) made from magnetic materials [1]. Although spinodal decomposition material of Fe-Cr-Co alloys have been extensively studied as permanent magnetic materials, there have been no report to date concerning the utilization of Fe-Cr-Co alloy as microwave absorbers. We have proposed Fe-Cr-Co alloy powder as an alternative material for MAMs and NSSs [2-4]. This study outlines the development strategy of Fe-Cr-Co alloy for producing high-performance MAMs and NSSs, ranging from spherical powders to flakes, to core/shell structured flaky Fe-Cr-Co/Co ferrite powders.
Spherical gas-atomized powder (< 45 μm) of Fe-25mass%Cr-12mass%Co-1.5mass%Ti was subjected to a step-aging treatment consisting of heat treatment at 655°C for 80 min, continually at 620℃ for 1 h and 600℃ for 2 h, then subsequently quenched in ice water (denoted as Sphere). The step-aged sample was ball-milled at 200 rpm for 3 h to produce optimal flaky shape powder (Flake). To fabricate the core/shell structured powder, cobalt ferrite was deposited onto flaky Fe-Cr-Co powder (Flake/Co-ferrite) by sputtering. Consequently, Sphere, Flake, and Flake/Co-ferrite were mixed with epoxy resin, respectively, with volume ratio of 56:44 to fabricate resin composite samples for evaluation of their microwave absorption and noise suppression properties. The power dissipated in a magnetic material is due to magnetic loss can be expressed as P = ωμr2H2 [5], H is external magnetic field and ω is angular frequency (ω = 2πf). Herein, the parameter ωμr2 was used to evaluate the noise suppression properties in the frequency range of 0.1–40 GHz.
In our previous study, it is demonstrated that the relative permeability (μr) of the resin composites of spherical Fe-Cr-Co alloy powders can be tuned by step aging at different final aging temperatures, which is contributed by ferromagnetic FeCo-rich (α1) phase particles with single-domain structure induced by spinodally decomposed Fe–Cr–Co alloy powder [2]. However, the value of μr decreased with the decrease of step-aging temperature. To improve the μr, we flattened the spherical powder into flakes, which significantly improved the μr and enhanced the microwave absorption [3] resulting from the microstructural changes in both the powder and α1 phase owing to the excellent ductility of the Fe-Co-Co alloy [6]. Recently, we have successfully fabricated the resin composites of flake/Co-ferrite powders with core/shell structures, aimed at further improving microwave absorption performance [4].
The noise suppression performance using magnetic loss represented by ωμr2 was shown in Fig. 1. Compared with the resin composite of sphere, the resin composite of flake exhibited higher ωμr2 between 0.1-15 GHz, suggesting higher magnetic loss ability in this frequency range. On the other hand, the resin composite of flake/Co-ferrite showed enhanced ωμr2 values at 5-40 GHz. It can be attributed to the combination of microstructural changes in the Fe-Cr-Co flake and the high magnetic anisotropy of the shell of Co-ferrite. This promising finding demonstrates the potential of using Fe-Cr-Co alloy powders for microwave absorption and noise suppression up to 40 GHz.
Acknowledgements
This work was supported by JSPS KAKENHI Grant No. JP19H05620 and the Development of Technical Examination Services Concerning Frequency Crowding program, MIC, Japan.
References
[1] S. Sugimoto, et. al., IEEE Trans. Magn., 35 (1999) 3154-3156
[2] S. Ajia, et. al., J. Alloy. Compd., 903 (2022) 163920, 1-9.
[3] S. Ajia, et. al., J. Magn. Magn. Mater., 564 (2022) 170200, 1-11.
[4] M. Sato, et. al., oral presentation, Autumn Meeting of JSPPM (2023) (Paper submitted to The Journal of the JSPM; in Japanese)
[5] C. Poole, et. al., Microwave active circuit analysis and design, in: Academic Press, Oxford, 2015.
[6] S. Jin, et. al., Metall. Mater. Trans. A. 11 (1980) 69-76.
Spherical gas-atomized powder (< 45 μm) of Fe-25mass%Cr-12mass%Co-1.5mass%Ti was subjected to a step-aging treatment consisting of heat treatment at 655°C for 80 min, continually at 620℃ for 1 h and 600℃ for 2 h, then subsequently quenched in ice water (denoted as Sphere). The step-aged sample was ball-milled at 200 rpm for 3 h to produce optimal flaky shape powder (Flake). To fabricate the core/shell structured powder, cobalt ferrite was deposited onto flaky Fe-Cr-Co powder (Flake/Co-ferrite) by sputtering. Consequently, Sphere, Flake, and Flake/Co-ferrite were mixed with epoxy resin, respectively, with volume ratio of 56:44 to fabricate resin composite samples for evaluation of their microwave absorption and noise suppression properties. The power dissipated in a magnetic material is due to magnetic loss can be expressed as P = ωμr2H2 [5], H is external magnetic field and ω is angular frequency (ω = 2πf). Herein, the parameter ωμr2 was used to evaluate the noise suppression properties in the frequency range of 0.1–40 GHz.
In our previous study, it is demonstrated that the relative permeability (μr) of the resin composites of spherical Fe-Cr-Co alloy powders can be tuned by step aging at different final aging temperatures, which is contributed by ferromagnetic FeCo-rich (α1) phase particles with single-domain structure induced by spinodally decomposed Fe–Cr–Co alloy powder [2]. However, the value of μr decreased with the decrease of step-aging temperature. To improve the μr, we flattened the spherical powder into flakes, which significantly improved the μr and enhanced the microwave absorption [3] resulting from the microstructural changes in both the powder and α1 phase owing to the excellent ductility of the Fe-Co-Co alloy [6]. Recently, we have successfully fabricated the resin composites of flake/Co-ferrite powders with core/shell structures, aimed at further improving microwave absorption performance [4].
The noise suppression performance using magnetic loss represented by ωμr2 was shown in Fig. 1. Compared with the resin composite of sphere, the resin composite of flake exhibited higher ωμr2 between 0.1-15 GHz, suggesting higher magnetic loss ability in this frequency range. On the other hand, the resin composite of flake/Co-ferrite showed enhanced ωμr2 values at 5-40 GHz. It can be attributed to the combination of microstructural changes in the Fe-Cr-Co flake and the high magnetic anisotropy of the shell of Co-ferrite. This promising finding demonstrates the potential of using Fe-Cr-Co alloy powders for microwave absorption and noise suppression up to 40 GHz.
Acknowledgements
This work was supported by JSPS KAKENHI Grant No. JP19H05620 and the Development of Technical Examination Services Concerning Frequency Crowding program, MIC, Japan.
References
[1] S. Sugimoto, et. al., IEEE Trans. Magn., 35 (1999) 3154-3156
[2] S. Ajia, et. al., J. Alloy. Compd., 903 (2022) 163920, 1-9.
[3] S. Ajia, et. al., J. Magn. Magn. Mater., 564 (2022) 170200, 1-11.
[4] M. Sato, et. al., oral presentation, Autumn Meeting of JSPPM (2023) (Paper submitted to The Journal of the JSPM; in Japanese)
[5] C. Poole, et. al., Microwave active circuit analysis and design, in: Academic Press, Oxford, 2015.
[6] S. Jin, et. al., Metall. Mater. Trans. A. 11 (1980) 69-76.
