Effect of Cr Content on Microstructure of Spinodal Decomposition and Properties in FeCrCoSi Permanent Magnet Alloy

doi:10.11900/0412.1961.2021.00094

Acta Metall Sin

2022, Vol. 58

Issue (1): 103-113 DOI: 10.11900/0412.1961.2021.00094

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Effect of Cr Content on Microstructure of Spinodal Decomposition and Properties in FeCrCoSi Permanent Magnet Alloy

XIANG Zhaolong¹^,²^,³, ZHANG Lin¹, XIN Yan³, AN Bailing¹^,²^,³, NIU Rongmei³, LU Jun³, MARDANI Masoud³, HAN Ke³(

), WANG Engang¹(

)

^1. Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China
^2. School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
^3. National High Magnetic Field Laboratory, Florida State University, Tallahassee 32310, USA

Cite this article:

XIANG Zhaolong, ZHANG Lin, XIN Yan, AN Bailing, NIU Rongmei, LU Jun, MARDANI Masoud, HAN Ke, WANG Engang. Effect of Cr Content on Microstructure of Spinodal Decomposition and Properties in FeCrCoSi Permanent Magnet Alloy. Acta Metall Sin, 2022, 58(1): 103-113.

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Abstract

FeCrCo permanent magnet alloys draw wide attention because of their excellent machinability. These alloys can be deformed and extruded into thin wires or sheets for various applications, such as electric motors, telephone receivers, printers, and stereo cartridges. In these alloys, the content and distribution of Cr play an important role in improving their magnetic and hardness properties. To optimize both properties of these alloys, the effect of Cr must be studied. This study describes the effect of Cr content on microstructure, i.e., volume fraction, size, and composition of α ₁ and α ₂ phases in (84 - X)FeXCr15Co1Si (X = 20, 25, 30, 35, mass fraction, %) samples using atomic-resolution STEM. The effect of microstructure parameters on both Vickers hardness and magnetic properties was evaluated. STEM images showed that the average size of the α ₁ phase increased from 26 nm to 55 nm with an increase in Cr content from 20% to 35%. When the content of Cr increased from 20% to 25%, the volume fraction of the α ₁ phase increased by 12%, and when the content of Cr increased beyond 25%, the volume fraction remained the same. EDS results showed that with the increase of Cr content, in the (Fe-Co)-rich α ₁ phase, the content of Fe decreased, whereas the contents of Cr and Co increased. By contrast, in the Cr-rich α ₂ phase, the contents of Fe and Co decreased but the content of Cr increased. After step aging, hardness increased because of spinodal decomposition and continued to increase with an increase in Cr content. Remanence, coercivity, and magnetic energy product reached their maximum values when the content of Cr was at 25% and decreased as the content of Cr increased. The dependence of magnetic properties on the size, volume fraction, composition of α ₁ phase, and difference in composition between α ₁ and α ₂ phases was discussed. The mechanism for hardening was also discussed, which increased with the Cr content.

Key words: FeCrCoSi alloy spinodal decomposition STEM-HAADF magnetic property hardness

Received: 01 March 2021

ZTFLH:

TG132.27

Fund: National Natural Science Foundation of China(51674083);Programme of Introducing Talents of Discipline Innovation to Universities 2.0(BP0719037);National Science Foundation of America(DMR-1157490)

About author: WANG Engang, professor, Tel: (024)83681739, E-mail: egwang@mail.neu.edu.cn

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	Articles by authors
	Zhaolong XIANG
	Lin ZHANG
	Yan XIN
	Bailing AN
	Rongmei NIU
	Jun LU
	Masoud MARDANI
	Ke HAN
	Engang WANG

URL:

https://www.ams.org.cn/EN/10.11900/0412.1961.2021.00094 OR https://www.ams.org.cn/EN/Y2022/V58/I1/103

Fig.1 Schematic of solution treatment, annealing, and step aging of FeCrCoSi samples

Table 1 Description of FeCrCoSi samples with different contents of Cr after different heat treatments

Fig.2 XRD spectra of solution-treated (a) and step-aged (b) FeCrCoSi samples with different contents of Cr

Fig.3 HAADF images (a1-d1) and size distributions of α ₁ phase (a2-d2) of spinodal decomposition after step aging in samples 20Cr-SA (a1, a2), 25Cr-SA (b1, b2), 30Cr-SA (c1, c2), and 35Cr-SA (d1, d2)

Sample	$D α 1$ nm	Magnetic property			Mass fraction / %			$V α 1$
		Br T	H kA·m^-1	BH _max kJ·m^-3	$C α 1$	$C α 2$	ΔC _t	%
		Br T	H kA·m^-1	BH _max kJ·m^-3	$C α 1$	$C α 2$	ΔC _t
20Cr-SA	26 ± 4.1	0.61	10.2	1.67	69.3Fe12.9Cr16.9Co0.9Si	49.6Fe36.5Cr12.0Co1.9Si	49.2	54
25Cr-SA	30 ± 6.0	0.84	41.7	13.69	67.2Fe11.8Cr20.3Co0.7Si	38.5Fe51.9Cr8.1Co1.5Si	81.8	60
30Cr-SA	33 ± 5.7	0.64	35.3	6.92	60.1Fe16.4Cr22.9Co0.6Si	33.6Fe56.2Cr8.1Co2.1Si	82.6	62
35Cr-SA	55 ± 8.9	0.30	14.5	1.11	57.4Fe19.1Cr23.2Co0.3Si	31.3Fe60.7Cr6.8Co1.2Si	85.0	61

Table 2 Parameters of magnetic properties, sizes and volume fractions of α ₁ phase, compositions of α ₁ and α ₂ phases, and total values of absolute composition difference of Fe, Cr, Co, and Si between α ₁ and α ₂ phases of step-aged FeCrCoSi samples with different contents of Cr

Fig.4 HAADF images of spinodal decomposition of sample 35Cr-SA, as viewed along [001] direction (The upper insets show fast Fourier transform (FFT) of Figs.4a, b, and c, respectively. The lower insets show the intensity profile of values taken along the lines AB, CD, and EF, respectively)
(a) α ₁ and α ₂ phases (b) α ₁ phase (c) α ₂ phase

Fig.5 Hysteresis loops of step-aged samples with different contents of Cr (J—magnetic polarization)

Fig.6 Vickers hardnesses of samples with different contents of Cr under different heat treatments

Fig.7 Superimposed EDS maps of Fe, Cr, Co, and Si after step aging in samples 20Cr-SA (a), 25Cr-SA (b), 30Cr-SA (c), and 35Cr-SA (d)

Table 3 Parameters of E, Y, ΔC _Cr, ΔC _Co, and ΔC _Si ofsamples 20Cr-SA-35Cr-SA

Fig.8 Average amplitudes (a) and wavelengths (b) of spinodal decompositions in step-aged samples with different contents of Cr

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