Formation and crystallization behavior of Fe-based amorphous precursors with pre-existing α-Fe nanoparticles—Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

doi:10.1016/j.jmst.2020.05.049

Abstract

Abstract:

Structure, crystallization behavior, and magnetic properties of as-quenched and annealed Fe_81.3Si₄B₁₃Cu_1.7 (Cu1.7) alloy ribbons and effects of Nb alloying have been studied. Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized α-Fe Particles (PN-α-Fe) are coexistence in the melt-spun Cu1.7 amorphous matrix, and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters. Two-step crystallization behavior associated with growth of the PN-α-Fe and subsequent nucleation and growth of newly-formed α-Fe is found in the primary crystallization stage of the Cu1.7 alloy. The number densities of the Cu-clusters and PN-α-Fe in melt-spun Fe_81.3-xSi₄B₁₃Cu_1.7Nb_x alloys are gradually reduced with enriching of Nb, and a fully amorphous structure forms at 4 at.% Nb, although smaller Cu-clusters still exist. After annealing, 2 at.% Nb coarsens the average size (D_α-Fe) of the α-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm, and 4 at.% Nb refines the D_α-Fe to 8.9 nm. The mechanisms of the α-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed, and an annealing-induced α-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-α-Fe and diffusion-suppression effect of Nb atoms has been proposed. A coercivity (H_c) ∝ D_α-Fe³ correlation has been found for the nanocrystalline alloys, and the permeability is inverse with the H_c.

Key words: Fe-based nanocrystalline alloy, Cu-cluster, Pre-existing α-Fe nanoparticle, Crystallization behavior, Soft magnetic property

Yanhui Li, Xingjie Jia, Wei Zhang, Yan Zhang, Guoqiang Xie, Zhiyong Qiu, Junhua Luan, Zengbao Jiao. Formation and crystallization behavior of Fe-based amorphous precursors with pre-existing α-Fe nanoparticles—Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys[J]. J. Mater. Sci. Technol., 2021, 65: 171-181.

Figures/Tables 13

Fig. 1. Bright-field TEM images inset with corresponding SAED patterns and grain size distribution with normal fitting, and HRTEM images of melt-spun Fe81.3Si4B13Cu1.7 (a, b) and Fe81.7Si4B13Cu1.3 (c, d) alloys.

Fig. 2. APT element maps of melt-spun Fe81.7Si4B13Cu1.3 (a) and Fe81.3Si4B13Cu1.7 (b) alloys; highlighting Cu with 7 at.% Cu iso-concentration surface (c), and enlarged portion illustrating Cu and Fe with 7 at% Cu and 85 at.% Fe iso-concentration surfaces (d) of Fe81.3Si4B13Cu1.7 alloy, and concentration depth profiles from selected cylindrical regions c1 (?1.5 nm × 25 nm) (e) and c2 (?1.5 nm × 35 nm) (f) shown in (d), respectively.

Fig. 3. DSC curves of melt-spun Fe81.3Si4B13Cu1.7 (Cu1.7) and Fe81.7Si4B13Cu1.3 (Cu1.3) alloys before and after isochronal annealing at different temperature (a) and the corresponding bright-field TEM images and grain size distributions with normal fitting. (b) Cu1.7, Ta1 = 665 K; (c) Cu1.7, Ta2 = 690 K; (d) Cu1.7, Ta3 = 750 K; (e) Cu1.3, Ta1’ = 710 K; (f) Cu1.3, Ta2’ = 750 K.

Fig. 4. Variation in Hc of Fe81.3Si4B13Cu1.7 and Fe81.7Si4B13Cu1.3 alloys as a function of annealing heating rate.

Fig. 5. Bright-field TEM images inset with corresponding SAED patterns and grain size distribution with normal fitting, and HRTEM images of melt-spun Fe81.3-xSi4B13Cu1.7Nbx alloys. (a, b): x = 2; (c, d): x = 4.

Fig. 6. APT element maps of melt-spun Fe81.3-xSi4B13Cu1.7Nbx alloys with x = 2 (a) and x = 4 (b); highlighting Cu with 7 at.% Cu iso-concentration surface and enlarged portion illustrating Cu (and Fe) element(s) with 7 at% Cu (and 85 at.% Fe) iso-concentration surface(s) of the alloys with x = 2 (c) and x = 4 (d), respectively, and (e) concentration depth profile from selected cylindrical region (?1.5 nm × 25 nm) shown in (d).

Table 1 DCu-cluster, Nd, Cu-cluster, Dα-Fe and Nd, α-Fe of melt-spun Fe81.3-xSi4B13Cu1.7Nbx (x = 0-4) alloys.

Alloy	D_Cu-cluster (nm)	N_{d, Cu-cluster} (m^-3)	D_α-Fe (nm)	N_{d, α-Fe} (m^-3)
x = 0	2.9	5.1 × 10²³	6.2	2.2 × 10²³
x = 2	3.0	3.7 × 10²³	4.3	4.5 × 10²²
x = 4	2.0	2.7 × 10²³	-	-

Fig. 7. DSC curves of melt-spun (a) Fe81.3-xSi4B13Cu1.7Nbx and (b) Fe81.7-ySi4B13Cu1.3Nby (x/y = 0-4) alloys.

Table 2 Tx1, ΔT, Dα-Fe, Nd, α-Fe, Hc, Bs, and μe of Fe81.3-xSi4B13Cu1.7Nbx (Cu1.7Nbx) and Fe81.7-ySi4B13Cu1.3Nby (Cu1.3Nby) nanocrystalline alloys.

Alloys		T_x1 (K)	ΔT (K)	D_α-Fe (nm)	N_{d, α-Fe} (m^-3)	H_c (A/m)	B_s (T)	μ_e (@1 kHz)	μ_e (@100 kHz)
Cu_1.7Nb_x	x = 0	634	170	14.0	2.8 × 10²³	7.1	1.77	16,500	14,800
	x = 1	659	183	18.3*	-	11.9	1.69	-	-
	x = 2	668	202	21.6	5.2 × 10²²	17.0	1.60	3800	3500
	x = 3	724	180	14.9*	-	7.8	1.51	-	-
	x = 4	749	190	8.9	4.1 × 10²³	1.9	1.42	25,000	18,000
Cu_1.3Nb_y	y = 0	699	107	53.3	3.8 × 10²¹	379.3	1.73	1370	1360
	y = 1	707	138	42.7*	-	112.8	1.68	-	-
	y = 2	723	149	39.8	6.5 × 10²¹	90.4	1.57	1550	1450
	y = 3	738	168	16.3*	-	12.1	1.51	-	-
	y = 4	758	188	8.7	3.9 × 10²³	2.4	1.41	18,000	10,000

Fig. 8. Bright-field TEM images inset with corresponding SAED patterns and grain size distributions with normal fitting of Fe81.3-xSi4B13Cu1.7Nbx and Fe81.7-ySi4B13Cu1.3Nby alloys after annealing at Toa for 60 min. (a): x = 0, Toa = 668 K; (b): x = 2, Toa = 743 K; (c): x = 4, Toa = 783 K; (d): y = 0, Toa = 668 K; (e): y = 2, Toa = 763 K; (f): y = 4, Toa = 783 K.

Fig. 9. Variation in Hc of (a) Fe81.3-xSi4B13Cu1.7Nbx and (b) Fe81.7-ySi4B13Cu1.7Nby (x/y = 0-4) alloys as a function of annealing temperature. The results in melt-spun state are shown for comparison.

Fig. 10. Variation in Dα-Fe of Fe81.3-xSi4B13Cu1.7Nbx and Fe81.7-ySi4B13Cu1.3Nby (x/y = 0-4) nanocrystalline alloys as a function of Nb content (a), and schematic of barriers to annealing-induced α-Fe growth in Cu1.7Nbx alloys with different melt-spun structure (b). Black dash curve schematizes Nd, α-Fe in melt-spun state.

Fig. 11. Hc vs. Dα-Fe for Fe-Si-B-Cu-(Nb) nanocrystalline alloys in this work and Ref. [27].

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