Composition dependence of amorphous forming, crystallization behaviors and magnetic properties in Fe-rich Fe-B-Cu-Hf alloys
Introduction
Fe-based amorphous/nanocrystalline alloys have been played one critical role in both power and electronic fields in the previous three decades. Among them, the “Nanomet” alloys and their derivatives exhibit excellent magnetic properties including rather high saturated magnetic flux density (Bs), high initial permeability (μi) and low coercivity (Hc) [1,2]. As demonstrated that the low load loss of amorphous transformers is only 1/3 - 1/5 of the conventional Si steel transformers, which is promising for decreasing wasteful dissipation of energy in electrical apparatus and minimizing the physical dimensions of components [1,3]. However, there is still a great distance between theory and practice. On one hand, compared with the commercialized Metglas or Finemet ribbons with a width of 5 ~ 213 mm and a thickness of 20 ~ 35 μm, “Nanomet” alloys with high Fe content are limited into thin ribbons with a thickness of less than 20 μm due to poor amorphous forming ability (AFA) [4]. Therefore the higher cooling rate is required to obtain an entire amorphous precursor [5]. One the other hand, the current commercial amorphous/nanocrystalline alloys exhibit lower Bs than Fe-Si steels (Bs: 1.9 - 2.1 T), increasing the cost of materials [6]. Generally, the increase of Fe content helps to increase Bs and thus greatly reduces the physical dimensions of amorphous cores [7]. Therefore, increasing Fe content and adjusting amorphous forming elements simultaneously are effective methods for balancing the high Bs and strong AFA.
In general, AFA of metallic glass-forming liquids is sensitive to the compositions, and could be altered by microalloying [8]. According to the previous reports, the adjustment of metalloid elements of Si [9], B [8],C [4,10,11], P [12,13] and the introduce of ferromagnetic elements of Co [14], [15], [16], Ni [17], [18], [19] have been reported to be effective to overcome the limited AFA of “Nanomet” alloys and increase Bs. For instance, Fe85Si1.4B9Cu0.5P4C0.1 alloy with just 0.1 at.% C addition shows increased AFA, high Bs of about 1.93 T and low Hc of 5.8 A/m [10]. Fe83.3Si4B8P4Cu0.7 alloy with 1.0 at.% P exhibits finer grain size, high Bs of over 1.88 T and high μe of about 25,000 [1]. However, the high Fe content (over 84 at.%) in Fe-based amorphous/nanocrystalline alloys puts forward higher requirements for preparation conditions such as the wheel speed increases to 50 m/s, that for Fe-based amorphous/nanocrystalline alloys with 80 at.% Fe is only about 35 m/s [10,14,20]. The increased Fe content inevitably causes a reduction of metalloid elements content such as Si, B, etc., and seriously affects the ability to form amorphous microstructure. Under these circumstances, establishing a high-efficiency element alloying method via the design and optimization of alloy composition helps to explore amorphous materials and their modification, which contributes to the stronger amorphous forming ability and higher soft magnetic properties. In addition, the effective heat treatment process plays a key role in adjusting the nano-sized α-Fe/amorphous complex structure. The annealing conditions including annealing temperature [21], dwell time [22] and heating rate [23] affect the crystallization rate, the crystalized α-Fe volume fraction, the precipitating of Fe2B, Fe3B, Fe3P, Fe3(B,P)1 and so on [16,24]. Meanwhile, the heat treatment technologies including flash annealing, current annealing and stress-current annealing have also been applied for controlling grain size and inner stress. The nano-sized α-Fe grains with about 12 nm are obtained under a short dwell time, which however resulted in low fractional crystalline volume (25% ~ 30%) [25,26]. Therefore, the simultaneous design of alloy composition and heat treatment contributes to the formation of a fine and uniform nanocrystalline structure of Fe-based amorphous/nanocrystalline alloys.
Through the composition design and the optimization of heat treatment process, the new-developed FeBCuHf and FeSiBPCuHf alloys exhibited high Bs of about 1.91 T and low Hc of about 2.3 A/m, implied a wonderful application prospect [21,[27], [28], [29]]. In this paper, we further investigated the influence of Si or P addition and Si/P ratio together with increasing Fe content on the crystallization behavior, thermal stability and soft magnetic properties of FeBCuHf and FeSiBPCuHf alloys.
Section snippets
Compositions design and samples preparation
The raw materials of Fe (99.8 wt.%), Si (99.8 wt.%), Fe-B (99.5 wt%), Fe-P (99.5 wt.%) and purity metal Hf (99.99 wt.%) were used for preparing the origin ingots by arc melting. The nominal compositions of the alloys were listed in Table 1. The mixing enthalpy (kJ/mol) between B, P, Si, Cu and Fe, Cu and Hf elements was listed in Table 2. All ingots were melted for 4 times in high-purity argon atmosphere in order to ensure the ingredient uniformity. The as-quenched ribbons with a width of 1.0 ~
Effect of P or Si addition on AFA, crystalline behavior and thermal stability of the FeBCuHf ribbons
Fig. 2 shows the XRD patterns and DSC curves of FeBCuHf as-quenched ribbons with 0.5 at.% P or Si addition. Fig. 2(a) and (c) show XRD patterns of P-doped and Si-doped alloys, when x = y = 0.2, only one broad diffraction peak at around 2θ = 45°, indicating the amorphous structure. However, when x = y = 0.4, the diffraction peak of α-Fe at about 2θ = 45° can be detected, revealing these alloy structure changed into a multiple-structure which consists α-Fe and amorphous phases. Fig. 2(b) and (d)
Conclusions
This paper has studied the effect of minor P and/or Si addition in Fe-B-Cu-Hf alloys on AFA, crystallization behaviors, thermal stability and magnetic properties. The results show Si-doped alloys and co-addition of P and Si alloys with high Si/P ratio of 3/1 can still keep a relatively strong AFA and the entire amorphous ribbons are easy to be fabricated as Fe content increase up to 86.4 at.%. The addition of P and/or Si reduces the thermal stability of α-Fe, meanwhile, the co-addition of P and
CRediT authorship contribution statement
Meng Xiao: Investigation, Methodology, Data curation, Formal analysis, Writing - original draft. LiBao Zheng: Formal analysis, Writing - review & editing. Lin Zhou: Data curation, Writing - review & editing. Haoyang Yu: Investigation, Methodology. GuoTai Wang: Data curation, Writing - review & editing. DeChang Zeng: Funding acquisition, Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (Grant No. 51901079), the Fundamental Research Funds for the Central Universities, the Opening Project of National Engineering Research Center for Powder Metallurgy of Titanium & Rare Metals, the Natural Science Foundation of Guangdong Province (No. 2018A030313615, 2018A030310406, 2020A1515010736), the Guangzhou Municipal Science and Technology Program (No. 202007020008), the Zhongshan Municipal Science and Technology
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