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Acta Metall Sin  2017, Vol. 53 Issue (7): 833-841    DOI: 10.11900/0412.1961.2016.00546
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Dual-Cluster Characteristic and Composition Optimization of Finemet Soft Magnetic Nanocrystalline Alloys
Yaoxiang GENG1(),Xin LIN2,Jianbing QIANG3,Yingmin WANG3,Chuang DONG3
1 School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
2 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
3 Key Lab of Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024, China
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Abstract  

The development of nanocrystalline Fe-Si-B-Nb-Cu alloys, commercially known as Finemet, has established a new approach to obtain soft-magnetic materials with high magnetic flux density. The material consists of α-Fe(Si) nanocrystals embedded in an amorphous matrix, which is made by means of partial crystallization. The composition and local structure of the precursor amorphous alloys are crucial for the formation of the unique nanocrystalline structure. The present study is devoted to understanding the composition characteristics and developing new compositions of Finemet alloys. Using the “cluster-plus-glue-atom” model and noticing the crystallization characteristic of Finemet alloy, a “dual-cluster” amorphous structure model is proposed. In this model, the precursor amorphous structure of Finemet alloy is considered to contain a mixture of the [(Si, B)-B2(Fe, Nb)8]Fe cluster derived from the Fe-B-Si-Nb bulk glassy alloys, and the [Si-Fe14](Cu1/13Si12/13)3 cluster from Fe3Si phase. A series of new Finemet nanocrystalline alloy compositions are designed by mixing [(Si, B)-B2(Fe, Nb)8]Fe and [Si-Fe14](Cu1/13Si12/13)3 cluster formulas with a ratio of 1∶1. Thermal analysis results show that [(Si0.8B0.2)-B2Fe7.2Nb0.8]Fe+[Si-Fe14](Cu1/13Si12/13)3 (alloy composition: Fe74B7.33Si15.23Nb2.67Cu0.77) amorphous alloy exhibits a maximal temperature interval of about 192 K between the first and second crystallization peaks. Magnetic measurement results show that the Fe74B7.33Si15.23Nb2.67Cu0.77 nanocrystalline alloy exhibits optimal soft magnetic properties with a saturation magnetization Bs about 1.26 T, a coercive force Hc about 0.5 A/m and an effective permeability μe about 8.5×105 at 1 kHz after isothermal annealing at 813 K for 60 min. The soft magnetic properties of the new composition nanocrystalline alloys are better than that of the typical Finemet nanocrystalline alloy (Fe73.5Si13.5B9Cu1Nb3).

Key words:  Finemet nanocrystalline alloy      “dual-cluster” model      composition design      soft magnetic property     
Received:  05 December 2016     
Fund: Supported by National Natural Science Foundation of China (Nos.51671045 and 51601073), International Magnetic Confined Fusion Energy Development (Nos.2013GB107003 and 2015GB105003), Fundamental Research Funds for the Central Universities (No.DUT16ZD209) and Fund of the State Key Laboratory of Solidification Processing in NWPU (No.SKLSP201607)

Cite this article: 

Yaoxiang GENG,Xin LIN,Jianbing QIANG,Yingmin WANG,Chuang DONG. Dual-Cluster Characteristic and Composition Optimization of Finemet Soft Magnetic Nanocrystalline Alloys. Acta Metall Sin, 2017, 53(7): 833-841.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2016.00546     OR     https://www.ams.org.cn/EN/Y2017/V53/I7/833

Fig.1  Number of atoms per unit volume ρa distributions around Si and Fe atoms in Fe3Si phase (Fe1 and Fe2 represent different Fe atom positions in Fe3Si phase, r represent cluster radius)
Cluster formula Composition r / nm ρ / (gcm-3) e/u
[Si-Fe14]Fe Fe93.75Si6.25 0.2618 7.43 22.0
[Si-Fe14]Fe3 Fe94.44Si5.56 0.2618 7.45 24.8
[Si-Fe14]Si Fe87.5Si12.5 0.2618 7.30 21.7
[Si-Fe14]Si3 Fe77.78Si22.22 0.2618 7.08 23.9
[Si-Fe14]FeSi2 Fe83.33Si16.67 0.2618 7.20 24.3
[Si-Fe14]Fe2Si Fe88.89Si11.11 0.2618 7.33 24.5
Table 1  Cluster formulas, corresponding chemical compositions, r, densities ρ and valence electron number per unit cluster formula e/u of Fe-Si binary alloys
No. Dual cluster formula Composition
1 [(Si0.95B0.05)-B2Fe7.5Nb0.5]Fe[17]+[Si-Fe14](Cu1/13Si12/13)3 Fe75B6.83Si15.73Nb1.67Cu0.77
2 [(Si0.9B0.1)-B2Fe7.4Nb0.6]Fe[17]+[Si-Fe14] (Cu1/13Si12/13)3 Fe74.67B7Si15.56Nb2Cu0.77
3 [(Si0.85B0.15)-B2Fe7.3Nb0.7]Fe[17]+[Si-Fe14](Cu1/13Si12/13)3 Fe74.33B7.17Si15.40Nb2.33Cu0.77
4 [(Si0.8B0.2)-B2Fe7.2Nb0.8]Fe[17]+[Si-Fe14](Cu1/13Si12/13)3 Fe74B7.33Si15.23Nb2.67Cu0.77
5 [(Si0.75B0.25)-B2Fe7.1Nb0.9]Fe[17]+[Si-Fe14](Cu1/13Si12/13)3 Fe73.67B7.5Si15.06Nb3Cu0.77
6 [(Si0.7B0.3)-B2Fe7Nb]Fe[17]+[Si-Fe14](Cu1/13Si12/13)3 Fe73.33B7.67Si14.90Nb3.33Cu0.77
7 - Fe73.5Si13.5B9Cu1Nb3[2]
Table 2  New compositions after design (Nos.1~6) and typical composition (No.7) of Finemet nanocrystalline alloys
Fig.2  XRD spectra of samples No.1~No.7
Fig.3  DTA curves of samples No.1~No.7 (Tx1—onset crystallization temperature of first crystallization peak, Tp1—first maximum peak temperature, Tx2—onset crystallization temperature of second crystallization peak, Tp2—second maximum peak temperature, Tl—liquid temperature)
No. Tx1 Tp1 Tx2 Tp2 ΔTp Tl
1 768 784 934 954 170 1489
2 776 794 949 970 176 1477
3 787 805 962 982 177 1473
4 788 811 990 1003 192 1472
5 800 823 985 995 172 1461
6 809 833 983 992 159 1440
7 793 813 936 953 140 1440
Table 3  Tx1, Tp1, Tx2, Tp2, ΔTp and Tl of samples No.1~No.7 (K)
Fig.4  XRD spectra of Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous alloys after isothermal annealing at room temperature~793 K (a) and 813~973 K (b) for 60 min
Fig.5  HRTEM image and SAED pattern (inset) of Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous alloy after annealing at 713 K for 60 min
Fig.6  Bright-field TEM image (a) and SAED pattern (b) of Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous alloy after annealing at 873 K for 60 min
Fig.7  Bright-field TEM image and SAED patterns for region I (a) and SAED patterns for region II (b~d) of Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous alloy after annealing at 973 K for 60 min
Fig.8  Changes of grain size D with isothermal temperature for Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 nanocrystalline alloys
Fig.9  Changes of saturation magnetization Bs and coercive force Hc with annealing temperature for No.4 amorphous and nanocrystalline alloys
T / K D / nm Bs / T Hc / (Am-1) μe / 105
713 - 1.30 1.0 5.4
733 - 1.31 1.0 6.0
753 8 1.30 1.1 5.8
773 10 1.25 1.5 6.2
793 13 1.25 1.8 7.0
813 15 1.26 0.5 8.5
833 18 1.26 1.5 6.9
853 18 1.26 2.0 5.3
873 18 1.27 3.5 3.1
893 20 1.25 35 -
933 26 0.76 350 -
973 110 0.67 800 -
Table 4  Changes of D, Bs, Hc and effective permeability μe of Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous alloys at different annealing temperatures T
Fig.10  Changes of μe and Hc with different annealing temperatures for Fe74B7.33Si15.23Nb2.67Cu0.77 No.4 amorphous and nanocrystalline alloys
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