1.School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China 2.Shanxi Province Key Laboratory of Magnetic and Electric Functional Materials and Their Applications, Taiyuan University of Science and Technology, Taiyuan 030024, China
Cite this article:
GUO Lu, ZHU Qianke, CHEN Zhe, ZHANG Kewei, JIANG Yong. Non-Isothermal Crystallization Kinetics of Fe76Ga5Ge5B6P7Cu1 Alloy. Acta Metall Sin, 2022, 58(6): 799-806.
Fe-based amorphous and nanocrystalline alloys can be used for technological applications on iron core materials owing to their high permeability, low coercivity, and core loss. However, when compared to Si-steels, their application is limited owing to low saturation magnetization. Thus, the saturation magnetization of Fe-based amorphous and nanocrystalline alloys should be improved, which may reduce the content of metalloid elements, and thus, the amorphous forming ability. Consequently, as-spun Fe-based amorphous and nanocrystalline alloys with high saturation magnetization may be incompletely amorphous. In this case, annealing processes should be modified by investigating crystallization behavior because traditional annealing processes with low heating rates may degrade ferromagnetic exchange and soft magnetic properties owing to grain-size inhomogeneity. Fe76Ga5Ge5B6P7Cu1 ribbons were fabricated using the melt spinning technique, and their crystallization behavior and mechanism were studied. Results showed that two exothermic peaks are present in the DSC curve, which correspond to the precipitation of α-Fe(Ga, Ge) and Fe(B, P) phases. Under nonisothermal conditions, the initial activation energy is greater than the apparent activation energy. According to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, for an incomplete amorphous alloy, the crystallization process combines the growth of pre-existing nucleus and nucleation, whereas the nucleation rate decreases. Moreover, a rapid heating annealing process is conducive to the formation of a uniform and dispersed nanocrystalline structure. It was found that the magnetic properties of the annealed alloy with a heating rate of 100 K/min was better than those with 10 and 50 K/min. Further, the optimal initial permeability was 2.86 × 10-2 H/m, and the coercivity was 1.77 A/m.
Fund: Shanxi Scholarship Council of China(HGKY2019083);Key Research and Development Program of Shanxi Province(201803D421046);Scientific and Technologial Innovation Programs of Higher Education Institutions in Shanxi(2021L293);Reward Fund for Outstanding Doctor in Shanxi(20212045);Doctoral Startup Foundation of Taiyuan University of Science and Technology(20202034)
About author: ZHANG Kewei, professor, Tel: (0351)2161126, E-mail: drzkw@126.comZHU Qianke, Tel: (0351)2161126, E-mail: drzhuqianke@126.com
Fig.1 XRD spectrum (a) and DSC curves (b), evolution of the characteristic crystallization temperatures (Tx1—initial exothermic temperature of the first peak, Tp1—peak temperature of the first peak, Tx2—initial exothermic temperature of the second peak, Tp2—peak temperature of the second peak) with the natural logarithm of the heating rate lnβ (β—heating rate) (c) of as-spun Fe76Ga5Ge5B6P7Cu1 ribbons, XRD spectra of Fe76Ga5Ge5B6P7Cu1 alloys annealed under different temperatures at heating rate of 100 K/min (d)
β / (K·min-1)
Tx1
Tp1
Tx2
Tp2
5
660.65
676.23
793.98
803.09
15
678.44
693.66
809.30
819.64
25
684.49
702.11
816.33
826.43
35
689.04
708.41
820.63
832.22
Table 1 The characteristic crystallization temperatures at different heating rates of as-spun Fe76Ga5Ge5B6-P7Cu1 ribbons
Fig.2 Fitting plots by Kissinger (a) and Ozawa (b) equations in as-spun Fe76Ga5Ge5B6P7Cu1 ribbons (Ex1—initial activation energy of the first peak, Ea1—apparent activation energy of the first peak, Ex2—initial activation energy of the second peak, Ea2—apparent activation energy of the second peak; T—temperature, R—gas constant, Adj.R2—goodness of fit)
Fig.3 Evolutions of crystallization fraction (α) with temperature for the first peak (a) and the second peak (b) at different heating rates
Fig.4 Evolutions of the Avrami exponent (n) as a function of α during crystallization for the first peak (a) and the second peak (b)
β / (K·min-1)
α
n
a
b
p
5
0 ≤ α ≤ 0.4
1.5 < n < 2.5
0 < a < 1
3
0.5
0.4 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
15, 25
0 ≤ α ≤ 0.2
1.5 < n < 2.5
0 < a < 1
3
0.5
0.2 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
35
0 ≤ α ≤ 0.1
1.5 < n < 2.5
0 < a < 1
3
0.5
0.1 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
Table 2 Specific parameters for characterizing the non-isothermal crystallization mechanism of the first peak
β / (K·min-1)
α
n
a
b
p
5
0 ≤ α ≤ 0.8
1.5 < n < 2.5
0 < a < 1
3
0.5
0.8 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
15
0 ≤ α ≤ 0.5
1.5 < n < 2.5
0 < a < 1
3
0.5
0.5 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
25, 35
0 ≤ α ≤ 0.3
1.5 < n < 2.5
0 < a < 1
3
0.5
0.3 < α ≤ 1
n ≤ 1.5
a = 0
3
0.5
Table 3 Specific parameters for characterizing the non-isothermal crystallization mechanism of the second peak
Fig.5 Initial permeability (μi) (a) and coercivity (Hc) (b) versus annealing temperature at different heating rates
Fig.6 TEM images, SAED patterns, and grain size distributions of Fe76Ga5Ge5B6P7Cu1 ribbons annealed at 400oC with heating rate of 10 K/min (a) and 425oC with heating rate of 100 K/min (b), and schematic of the crystallization of Fe76Ga5Ge5B6P7Cu1 alloys (c)
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