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Fe-based nanocrystalline alloy

by:Catech      2023-04-14

Composition: An alloy composed mainly of iron elements, adding a small amount of Nb, Cu, Si, and B elements, and forming an amorphous material through a rapid solidification process. After heat treatment, microcrystals with a diameter of 10-20nm are obtained, which are dispersed on the amorphous matrix, and are called microcrystalline and nanocrystalline materials.

Performance: It has excellent comprehensive magnetic properties, high saturation magnetic induction, high initial magnetic permeability, low Hc, low high frequency loss under high magnetic induction, and higher resistivity than Permalloy. After longitudinal or transverse magnetic field treatment, high Br or low Br value can be obtained. It is the material with the best comprehensive performance on the market at present.

Application: Widely used in high-power switching power supply, inverter power supply, magnetic amplifier, high-frequency transformer, high-frequency converter, high-frequency choke core, current transformer core, leakage protection switch, common mode inductor core.

In recent years, the emergence of iron-based nanocrystalline alloys has added an excellent core material for common-mode inductors. The manufacturing process of the iron-based nanocrystalline alloy is as follows: first, an amorphous alloy thin strip with a thickness of about 20-30 microns is made by rapid solidification technology, and then wound into an iron core to form nanocrystals through further processing. Nanocrystalline alloys offer some unique advantages over ferrites:

High saturation magnetic induction:

The Bs of the iron-based nanocrystalline alloy reaches 1.2T, more than twice that of ferrite. As a common mode inductor core, an important principle is that the core cannot be magnetized to saturation, otherwise the inductance will drop sharply. However, in practical applications, there are many occasions where the interference intensity is relatively large (such as high-power variable frequency motors). If ordinary ferrite is used as a common-mode inductor, the iron core may be saturated, and the performance under large-intensity interference cannot be guaranteed. Noise suppression effect. Due to the high saturation magnetic induction of nanocrystalline alloys, its anti-saturation characteristics are undoubtedly better than those of ferrite, making nanocrystalline alloys very suitable for occasions that resist high current and strong interference.

High initial permeability:

The initial magnetic permeability of nanocrystalline alloy can reach 100,000, which is much higher than that of ferrite. Therefore, the common mode inductor made of nanocrystalline alloy has large impedance and insertion loss under low magnetic field, and has excellent suppression of weak interference effect. This is especially suitable for weak interference common mode filters that require extremely small leakage currents. In some specific occasions (such as medical equipment), the leakage current caused by the equipment through the capacitance to the ground (such as the human body) is easy to form common mode interference, and the equipment itself has extremely strict requirements on this. At this time, the use of high permeability nanocrystalline alloys to fabricate common mode inductors may be an option. In addition, the high magnetic permeability of the nanocrystalline alloy can reduce the number of turns of the coil and reduce the distribution parameters such as parasitic capacitance, thus increasing the resonant peak frequency on the insertion loss spectrum caused by the distribution parameters. At the same time, the high magnetic permeability of the nanocrystalline iron core enables the common mode inductor to have higher inductance and impedance values, or reduce the volume of the iron core under the premise of the same inductance.

Excellent temperature stability:

The Curie temperature of iron-based nanocrystalline alloy is as high as 570oC or more. In the case of large temperature fluctuations, the performance change rate of nanocrystalline alloy is obviously lower than that of ferrite, which has excellent stability, and the change of performance is close to linear. Generally, in the temperature range of -50oC--130oC, the change rate of the main magnetic properties of nanocrystalline alloys is within 10%. In contrast, the Curie temperature of ferrite is generally below 250oC, and the change rate of magnetic properties sometimes reaches more than 90%, and it is nonlinear and difficult to compensate. This temperature stability of nanocrystalline alloys, combined with their unique low loss characteristics, provides device designers with relaxed temperature conditions. Figure 3 shows the temperature characteristics of the saturation magnetic induction of different materials.

Flexible frequency characteristics:

Through different manufacturing processes, nanocrystalline iron cores can obtain different frequency characteristics, and with appropriate coil turns, different impedance characteristics can be obtained to meet the filtering requirements of different bands, and its impedance value is much higher than that of ferrite. It should be pointed out that any filter cannot expect to use one core material to achieve noise suppression in the entire frequency range, but should choose different core materials, sizes and turns according to the filtering frequency band required by the filter. Compared with ferrite, nanocrystalline alloys can more flexibly adjust the process to obtain the required frequency characteristics.

Since the development of iron-based nanocrystalline alloys in the late 1980s, they have been widely used in switching power supply transformers, transformers and other fields. Due to the advantages of high magnetic permeability, high saturation magnetic induction, and flexible and adjustable frequency characteristics of nanocrystalline alloys, they are also receiving more and more attention in the fields of anti-common-mode interference filters. Iron-based nanocrystalline alloy common-mode inductor cores that can be supplied in large quantities already exist abroad. With the gradual deepening of people's understanding of nanocrystalline alloys, it can be expected that the common mode inductors manufactured by them will have a wider application prospect in China.

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