Investigation of glass forming ability, crystallization behavior, and soft magnetic properties of Fe–B–P–C–Cu alloy ribbons
Introduction
With the world running out of energy, energy conservation and emission reduction are becoming the most pressing issues. Fe-based nanocrystalline alloys have received a lot of attention as a key functional material in energy consumption because of their excellent comprehensive soft magnetic properties like low coercivity (Hc), high electrical resistivity (ρ), high effective magnetic permeability (μe), and relatively high saturation magnetic flux density (Bs) [[1], [2], [3]]. Despite the development of four Fe-based nanocrystalline alloy systems in the last 30 years, including Fe–Si–B–Cu–Nb (FINEMET) [2], Fe–Zr–B–Cu (NANOPERM) [4], (Fe, Co)–Zr–B–Cu (HITPERM) [5] and Fe–Si–B–P–Cu (NANOMET) [6], only Fe73.5Si13.5B9Cu1Nb3 (FINEMET) has been widely used in power and electronic. However, the low Bs (1.24T) of Fe73.5Si13.5B9Cu1Nb3 alloy prevent it from meeting the miniaturization of power and electronic transformers. Although they have a relatively high Bs of 1.5–1.8 T, the addition of easily oxidized Zr elements in NANOPERM and HITPERM alloys makes them impossible to produce in the atmosphere. According to Makino's findings [[7], [8], [9], [10]], NANOMET alloys not only have high Bs above 1.80 T but also have good formability in the atmosphere and a low cost. It has a promising industrial application. However, as research progressed, researchers discovered that some key issues, such as low glass-forming ability (GFA) [7], high heating rate (300–400 K/min) [9], and short optimum annealing time [10], needed to be addressed for industrial application. Many studies are currently being conducted on how to improve the GFA of NANOMET alloys. It has been discovered that the addition of pretransition metal elements (Nb, Mo, Hf et al.) improves the GFA of NANOMET alloys but increases the cost of the alloys [[11], [12], [13], [14]]. However, there are few reports on how to reduce the sensitivity of soft magnetic properties to heating rate and dwell time. Low cost, a wide crystallization heat treatment window, and excellent soft magnetic properties are the most competitive features of products in terms of industrialization. As a result, developing a type of nanocrystalline soft magnetic alloy with low cost, high GFA, and a wide crystallization heat treatment window to obtain excellent soft magnetic properties has become a research hotspot.
According to our previous research findings [15,16], the optimum crystallization annealing time of the Fe–B–P–C–Cu alloys can be extended to 60 min when the P content reaches 6 at. %, but the alloys’ GFA is only about 23 μm. As a result, optimizing the GFA of the Fe–B–P–C–Cu alloys without shortening the optimal stabilization annealing time has become a critical problem in promoting their industrial application. Previous research by the authors discovered that increasing the P content in the Fe–B–P–C–Cu alloys can promote the rapid nucleation of α-Fe grains during the crystallization annealing process [15]. Based on this result, we designed Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, 1.0 at. %) alloys. High Cu content in Fe-based nanocrystalline alloys is well known to promote the rapid nucleation of α-Fe grains, but it can also decrease GFA because Fe and Cu have a positive mix enthalpy of +13 kJ/mol [17,18]. To balance the relationship between GFA, heat treatment window, and soft magnetic properties, we investigated the effect of Cu content on GFA, crystallization behavior, heat treatment process window, and soft magnetic properties of Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, 1.0 at. %) alloys. This work has implications for the design of Fe–B–P–C–Cu nanocrystalline alloys, processing technologies, and industrial applications.
Section snippets
Experimental procedure
Master alloy ingots with nominal compositions of Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, 1.0 at. % in atomic percent, denoted as Cu-1.0, Cu-0.8, Cu-0.6, Cu-0.4 and Cu-0, respectively, in the following context) were prepared by arc melting the mixtures of Fe (99.99 mass%), C (99.99 mass%), pre-alloyed Fe–B (B: 19.35 wt. %), pre-alloyed Fe–P (P: 17.94 wt. %) and Cu (99.98 mass%) in Ar atmosphere. The ingots were re-melted at least four times to ensure the homogeneity of composition. Ribbon
Glass forming ability and thermal stability
The XRD patterns of melt-spun Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, 1.0 at. %) alloy ribbons at different cooling rates are shown in Fig. 1. When the linear velocity of the copper wheel is 40 m/s and the thickness is 20 μm, the XRD spectra for these five alloys show only one typical broad halo peak appears near 2θ = 44.5°. It indicates that the alloys are of fully amorphous structure on the XRD scale and a high GFA. As shown in Fig. 1 (b) and Fig. 1 (c), as the linear velocity of the copper
Conclusion
In this paper, we systematically investigated the influence of Cu content on GFA, thermal stability, crystalline behavior, soft magnetic properties, and sensitivity of soft magnetic properties to Ta and annealing time in high P content Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, 1.0 at. %) alloys. The GFA of alloys is observed to increase when the Cu concentration decreases. However, the analysis of thermophysical parameters indicates that when the Cu content is less than 0.6 at. %, the Tx1
Author contributions statement
Yuluo Li proposed the idea, designed the investigation procedures and wrote the manuscript.
Ningning Shen contributed to the experiments including XRD and soft magnetic properties.
Li Chen and Kuang Lv contributed to the tests of DSC and TEM.
Xidong Hui supported theoretical instruction and manuscript modification. All the authors contributed to the discussion of this work.
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.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant Nos. 52001024 and 51771020); the National Key Research and Development Program of China (2016YFB0300502).
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