Key Takeaways & Executive Findings
- •• Cryogenic treatment at 213 K optimally enhances soft magnetic properties of (Fe0.5Co0.5)75B21Nb4 metallic glasses while maintaining fully amorphous structure. • Appropriate CT and relaxation annealing synergistically increase saturation magnetization and reduce coercivity, with linear correlations to free volume and packing density. • CT promotes uniform nanocrystallization during annealing by lowering nucleation activation energy and increasing growth activation energy. • Corrosion resistance is improved via stabilization of Nb-rich passive film in 3.5wt% NaCl solution, attributed to CT and relaxation annealing.
Abstract
The effect of cryogenic treatment (CT) and relaxation annealing on the average nearest neighboring distance of atom (dm), thermodynamic stability, soft magnetic properties, microhardness (Hv), and corrosion resistance of as-spun (Fe0.5Co0.5)75B21Nb4 metallic glasses (MGs) is studied. On the premise of maintaining a fully amorphous phase, appropriate CT and relaxation annealing are conducive to achieving the synergistic effect of increasing saturation magnetization (Ms) and reducing coercivity (Hc). Shallow CT at 213 K optimally enhances the soft magnetic properties of MGs. Given its low activation energy of nucleation and increased activation energy of growth, appropriate CT is beneficial for achieving uniform annealed nanocrystals in amorphous phases. The correlation between free volumes (FVs) and potential energy suggests that the variation in Hc depends on the expansion and contraction behavior of amorphous phases after different CT processes. The fitting formulas of Hc–dm and Ms–Hv correlations demonstrate that soft magnetic parameters have a solid linear relationship with the contents of FVs and degree of dense random packing. Moreover, pitting resistance is improved by appropriate CT and relaxation annealing. This improvement is characterized by the promotion of the stability of the Nb-rich passive film formed during electrochemical corrosion in 3.5wt% NaCl solution.
1. Introduction
Since they were first discovered in the form of binary Au–Si alloy [1], metallic glasses (MGs) have attracted increasing attention owing to their superior properties over their crystalline counterparts [2–3]. Given their outstanding soft magnetic properties, such as high saturation magnetization (Ms), permeability, and electric resistance, and low coercivity (Hc) and core loss [4–6], Fe-based MGs have been applied as excellent soft magnetic materials in numerous electric and electronic fields [7].
In addition, the saturation magnetizations of Fe-based MGs and their nanocrystalline counterparts have approached those of silicon steels [8]. However, their wide industrial application is hindered by the processing complexity resulting from the high-heating-rate annealing to obtain nanograins and the existence of volatile phosphorus. An uncontrolled high annealing temperature caused the rapid grain growth and precipitation of the second phase, which sharply increased Hc (over 1000 times higher than the Hc of precursor materials) [9–10]. Crystallization-induced boundaries also degrade corrosion resistance performances [11]. Therefore, unremitting efforts are needed to develop novel and simple Fe-based MGs with a fully amorphous phase while achieving high glass-forming ability and excellent magnetic softness.
MGs have been observed to transform into novel metastable states after cryogenic treatment (CT) in liquid nitrogen, leading to irreversible changes in their main physical properties [12]. Combined with essential compositional design, CT enables effective modulation of soft magnetic properties in MGs while maintaining their fully amorphous structural integrity [13–14]. [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 MG with good soft magnetic properties and surprisingly high ductility was obtained through cryogenic thermal cycling (CTC) [15]. Furthermore, in consideration of the urgent requirement to extend the endurance life of magnetic components in various environments effectively, the development of excellent soft magnetic MGs with comprehensive performance, such as high corrosion resistance, has received considerable attention [16–18]. Accordingly, it is necessary to tailor MGs possessing excellent soft magnetic properties and high corrosion resistance.
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Zongqi Xiao, Xingyu Zhou, Xin Zhang, Qikun Huang, Li Cai, Yan Wang (2025). Characterization and properties of soft magnetic (Fe0.5Co0.5)75B21Nb4 metallic glasses subjected to cryogenic treatment and relaxation annealing. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3084-4
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Frequently Asked Questions
What is the effect of cryogenic treatment on the soft magnetic properties of (Fe0.5Co0.5)75B21Nb4 metallic glasses?
Cryogenic treatment at 213 K optimally enhances soft magnetic properties by increasing saturation magnetization and reducing coercivity while maintaining a fully amorphous structure.
How does cryogenic treatment influence the nanocrystallization behavior of metallic glasses?
Appropriate cryogenic treatment lowers the activation energy of nucleation and increases the activation energy of growth, promoting uniform nanocrystal formation during annealing.
What is the relationship between free volume and coercivity in these metallic glasses?
The variation in coercivity depends on the expansion and contraction behavior of amorphous phases, which correlates with free volume content and potential energy changes.
How does cryogenic treatment affect corrosion resistance?
Cryogenic treatment and relaxation annealing improve pitting resistance by promoting the stability of the Nb-rich passive film formed during corrosion in 3.5wt% NaCl solution.
What are the key findings regarding the linear correlations of soft magnetic parameters?
The fitting formulas show that soft magnetic parameters (Hc and Ms) have a solid linear relationship with free volume content and degree of dense random packing.
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