Rapid Annealing Optimizing Magnetic Softness and Thermal Stability of Mn-Substituted Fe-Based Nanocrystalline Alloys

Bojun Zhang,Yu Han,Jiawei Li,Huiyun Xiao,Aina He,Fuyao Yang,Yaqiang Dong

doi:10.3390/met11010020

Abstract

Good high-frequency magnetic softness and thermal stability are very important for the wide application of Fe-based nanocrystalline alloys. The present work reports the influence of Mn-doping and rapid annealing on the magnetic softness, nano-structure, and magnetic-microstructure of Fe76−xSi13B8Nb2Cu1Mnx (x = 0, 1, 2, 3, and 4) alloys. It was found that the Fe74Si13B8Nb2Cu1Mn2 alloy exhibits a superior magnetic softness with the high-saturation magnetic induction of 1.32 T and a large permeability at 100 kHz of over 15,000 at a large annealing-temperature region of 120 °C. The microstructure and magnetic domains characterization indicate that the good magnetic softness and thermal stabilization can be ascribed to the superb nano-structural stability caused by the Mn doping and rapid annealing at elongated temperatures, which can maintain a fine and high number density α-Fe(Si) nano-grains and facilitate the formation of regular and wide domains.

Highlights

Due to high saturation magnetic induction (Bs), large high-frequency permeability (μ), and small high-frequency loss (P), Fe-based nanocrystalline alloys are gradually replacing permalloy and soft-ferrite and are widely applied in filter inductions, high-frequency transformers/inverters, and leakage short-circuit devices, etc. [1,2]
Finemet ® alloys with an excellent comprehensive magnetic softness were first discovered by Yoshizawa et al in 1988 [3], and are still the most widely used nanocrystalline alloys so far
The Tx1 and Tx2 corresponding to the onset temperature for the precipitation of the α-Fe(Si) phase

Summary

Introduction

Due to high saturation magnetic induction (Bs), large high-frequency permeability (μ), and small high-frequency loss (P), Fe-based nanocrystalline alloys are gradually replacing permalloy and soft-ferrite and are widely applied in filter inductions, high-frequency transformers/inverters, and leakage short-circuit devices, etc. [1,2]. Finemet ® alloys (representative composition Fe73.5Si13.5B9Nb3Cu1) with an excellent comprehensive magnetic softness were first discovered by Yoshizawa et al in 1988 [3], and are still the most widely used nanocrystalline alloys so far Their low Bs of around 1.24 T is not conducive to the miniaturization and high power of electromagnetic devices. Many efforts have been devoted to improve the Bs of Fe-based nanocrystalline alloys—e.g., increasing the Fe content [4,5,6], adding Co element to increase the magnetic exchange interaction [7,8,9], decreasing the amount non-magnetic and large-sized elements [10,11], and removing Cu element [12,13] These alloys with high Bs suffer from a low amorphous-forming ability and poor high-frequency magnetic softness, which is unable to meet the requirement for mass production and high-frequency applications. The RA alloy exhibits a high Bs, good high-frequency permeability, and wide annealing-temperature region, making it very suitable for high-power and high-frequency devices

Experimental Procedures

Results and Discussion

Conclusions