JP2019014960A - Soft magnetic alloy powder and method for producing the same, and, dust core using the same - Google Patents

Abstract

To provide soft magnetic alloy powder which has high saturation magnetic flux density and obtains excellent soft magnetic characteristics, and a dust core using the same.SOLUTION: The soft magnetic alloy powder is used which includes an amorphous phase and an αFe crystal phase residing in the amorphous phase, and in which a mode of volume distribution of a crystallite of the αFe crystal phase is 1 nm or more and 15 nm or less and a half width of the volume distribution of the crystallite of the αFe crystal phase is 3 nm or more and 50 nm or less. A method for producing soft magnetic alloy powder is used that comprises: a pulverizing step of pulverizing an alloy composition having an amorphous phase into a powder; and a heat treatment step of heat treating the powder to precipitate an αFe crystal phase so that the αFe crystal phase has a mode of volume distribution of a crystallite of 1 nm or more and 15 nm or less and has a half width of 3 nm or more and 50 nm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a soft magnetic alloy powder, a method for producing the same, and a dust core using the same. In particular, the present invention relates to a soft magnetic alloy powder used for an inductor such as a choke coil, a reactor, and a transformer, a manufacturing method thereof, and a dust core using the soft magnetic alloy powder.

  In recent years, the electrification of vehicles such as hybrid vehicles (HEV), plug-in hybrid automatics (PHEV), and electric vehicles (EV) is rapidly progressing, and the system is required to be smaller and lighter in order to further improve fuel efficiency. Yes. Driven by the electrification market, miniaturization and weight reduction are required for various electronic components, and soft magnetic alloy powders used in choke coils, reactors, transformers, etc. and dust cores using the same On the other hand, higher performance is required.

  In the soft magnetic alloy powder and the dust core using the soft magnetic alloy powder, in order to reduce the size and weight, the material is required to be excellent in high saturation magnetic flux density and small in core loss. Further, the soft magnetic alloy powder and the dust core using the soft magnetic alloy powder are also required to have excellent direct current superposition characteristics.

  Among these, a nanocrystalline soft magnetic alloy in which a fine αFe crystal phase is precipitated in an amorphous phase is an excellent soft magnetic material capable of achieving both high saturation magnetic flux density and low core loss.

  For example, Patent Document 1 discloses a method for producing a Fe-based nanocrystalline soft magnetic alloy powder composed of nanoscale crystal grains with a high saturation magnetic flux density, and a nanocrystalline soft magnetic alloy powder and a magnetic component exhibiting excellent magnetic properties. Have been described.

Japanese Patent No. 5445888

  FIG. 2 shows a schematic diagram of the microstructure inside the soft magnetic alloy powder described in Patent Document 1. As shown in FIG. In the nano soft magnetic alloy powder, the αFe crystal phase 1 having an average particle diameter of 60 nm or less is dispersed in the amorphous phase 2 by 30% or more by volume fraction.

  However, this includes fine crystal grains having a size of several nanometers or less and insufficient crystallization, and enlarged crystal grains of several tens of nanometers or more. In this case, the magnetic anisotropy of the nano soft magnetic alloy powder increases, and the coercive force of the nano soft magnetic alloy powder increases. Furthermore, the core loss of the dust core using the same also increases.

  The present invention solves the above-mentioned conventional problems, and provides a crystalline soft magnetic alloy powder having a high saturation magnetic flux density and excellent soft magnetic properties, a method for producing the same, and a dust core using the crystalline soft magnetic alloy powder. For the purpose.

  In order to achieve the above object, an amorphous phase and an αFe crystal phase located in the amorphous phase, and a mode of volume distribution of crystallites of the αFe crystal phase is 1 nm or more and 15 nm or less, A soft magnetic alloy powder having a full width at half maximum of the crystallite volume distribution of the αFe crystal phase of 3 nm to 50 nm is used.

  In addition, a pulverizing step of powdering an alloy composition having an amorphous phase, and heat-treating the powder to precipitate an αFe crystal phase, and a mode value of a volume distribution of crystallites of the αFe crystal phase is 1 nm or more and 15 nm In the following, a method of producing a soft magnetic alloy powder is used, which includes a heat treatment step in which the half width of the volume distribution of the crystallites of the αFe crystal phase is 3 nm or more and 50 nm or less.

  As described above, according to the means disclosed in the present embodiment, a nanocrystalline soft magnetic alloy powder capable of reducing the coercive force of the soft magnetic alloy powder, obtaining a high saturation magnetic flux density and excellent soft magnetic properties, and The powder magnetic core using can be provided.

The figure which shows the volume distribution of the crystallite of the soft-magnetic alloy powder manufactured by this Embodiment Schematic diagram of the microstructure inside the soft magnetic alloy powder described in Patent Document 1.

<Manufacture of soft magnetic alloy powder>
First, the manufacturing method of the soft magnetic alloy powder of this Embodiment is demonstrated.

  (1) An alloy composition in which fine crystals of the αFe crystal phase are precipitated is melted by high-frequency heating or the like, and an amorphous phase ribbon or flake is produced by a liquid quenching method. As a liquid quenching method for producing a thin ribbon of an amorphous phase, a single roll type amorphous production apparatus or a twin roll type amorphous production apparatus used for production of an Fe-based amorphous ribbon can be used.

  (2) Next, the ribbon or slice is pulverized into powder. A general crusher can be used for crushing the ribbon or flakes. For example, a ball mill, a stamp mill, a planetary mill, a cyclone mill, a jet mill, a rotary mill, etc. can be used. Moreover, the soft magnetic alloy powder which has a desired particle size distribution is obtained by classifying the powder obtained by grinding | pulverizing using a sieve.

  (3) Next, the pulverized powder of the ribbon or flake is heat-treated to precipitate the αFe crystal phase. As the heat treatment apparatus, for example, a hot stove, a hot press, a lamp, a sheath metal heater, a ceramic heater, a rotary kiln, or the like can be used. In particular, it is preferable to perform heat treatment by sandwiching the powder with a hot press. The temperature of the powder itself can be accurately controlled.

  By making the temperature of the powder uniform during the heat treatment, it is possible to prevent the formation of fine crystal grains insufficiently crystallized below several nanometers and enlarged crystal grains above several tens of nanometers. Grains can be precipitated. Simply placing it in a container and in a furnace results in a non-uniform powder temperature. If the temperature of the powder is not uniform, the degree of crystallization varies from place to place, resulting in inhomogeneous crystals.

  As a result, a crystalline soft magnetic alloy powder having a high saturation magnetic flux density and excellent soft magnetic properties can be obtained.

<Production of dust core>
(1) The powder magnetic core in the present embodiment is prepared by mixing the soft magnetic alloy powder and a binder having good insulation and high heat resistance such as phenol resin and silicone resin to produce granulated powder. To do.

  (2) Next, the granulated powder is filled into a highly heat-resistant mold having a desired shape, and pressure-molded to obtain a green compact.

  (3) Thereafter, by performing heat treatment at a temperature at which the binder is heat-cured and the α crystal phase is not precipitated, a powder magnetic core having a high saturation magnetic flux density and excellent soft magnetic properties can be obtained.

(Evaluation method)
<Volume distribution of crystallites>
As for the volume distribution of crystallites in the soft magnetic alloy powder, first, an X-ray diffraction profile of a powder sample obtained by an X-ray diffractometer (XRD) is obtained. Next, the profile shape is expressed using a volume load distribution function, and the volume ratio of the crystallite is obtained by calculating the volume ratio with respect to the diameter.

<Crystallinity>
The crystallinity indicating the proportion of the αFe crystal phase in the soft magnetic alloy powder can be obtained from an X-ray diffraction pattern of a powder sample obtained by an X-ray diffractometer (XRD). The diffraction pattern of the αFe crystal phase is separated from the broad diffraction pattern unique to the amorphous phase. Next, after obtaining the respective diffraction intensities, the crystallinity can be obtained by calculating the ratio of the diffraction intensity of the αFe crystal phase to the total diffraction intensity.

  The X-ray diffractometer (XRD) used was RINT-Ultima (manufactured by Rigaku Corporation), the irradiation X-ray was Cu-Kα, the optical system was a concentrated beam system, and the detector was a goniometer type.

(Examples and comparative examples)
A Fe-based amorphous alloy ribbon of Fe73.5-Cu1-Nb3-Si13.5-B9 (atomic%) produced by a quenching single roll method is pulverized using a rotary mill to obtain a soft magnetic alloy powder in an amorphous phase. It was. The pulverization was performed for 3 minutes after the coarse pulverization for 20 minutes.

Next, the pulverized powder was heat-treated to precipitate an αFe crystal phase. In addition to Examples 1 to 4, the heat treatment was performed in six ways, Comparative Example 1 and Comparative Example 2, for comparison.
<Heat treatment>
Example 1 was heated with a hot press at 550 ° C. for 20 seconds.

  In Example 2, after heating in a hot air oven at 390 ° C. for 12 hours, it was heated in a hot press at 550 ° C. for 7 minutes.

  In Example 3, the hot pressing was performed at 550 ° C. for 20 seconds.

  Example 4 was heated with a hot press at 550 ° C. for 20 seconds.

  Comparative Example 1 was heated in a hot stove at 530 ° C. for 10 minutes.

  In Comparative Example 2, after heating at 550 ° C. for 20 seconds with a hot press, it was remelted with thermal plasma.

  FIG. 1 shows the result of calculating the frequency distribution of crystallite size for each obtained nanocrystalline soft magnetic alloy powder using an X-ray diffractometer (XRD). From the frequency distribution of FIG. 1, the mode value and the half-value width of the frequency distribution of each crystallite size were calculated. The mode is the crystallite size at the maximum frequency. Further, the crystallinity was calculated by the above-described crystallinity calculation method.

  Moreover, the silicone resin was mixed as a binder, granulated, and granulated powder was produced. Next, the granulated powder was put into a mold and subjected to pressure molding to produce a green compact. The silicone resin was about 3% by weight of the soft magnetic alloy powder.

For each obtained green compact, the core loss at a frequency of 1 MHz and a magnetic flux density of 25 mT was measured using a BH analyzer. The pass / fail criterion for core loss was 1300 kW / m ³ or less. The reason is that the target is to be equal to or less than the core loss of a general metal material.

Table 1 shows the mode, volume at half maximum, crystallinity, and core loss of the crystallite size volume distributions of Examples 1 to 4, Comparative Example 1, and Comparative Example 2. The core loss of Comparative Example 2 is estimated to be 4000 kW / m ³ or more because the coercive force of the soft magnetic powder is about four times that of Example 1 and the core loss is too large to be measured beyond the apparatus limit. .

<Mode and half width of crystal size volume distribution, crystallinity>
The results of Table 1 show that the core loss increases if the mode and half-value width of the crystallite volume distribution is too small or too large, and the crystallite volume distribution is optimal for reducing the core loss. It can be seen that there is a volume distribution of crystallite size. It can also be seen that the higher the crystallinity, the smaller the core loss.
<Mode and half width of volume distribution>
Therefore, the mode of the volume distribution of the crystallites is preferably 1 nm or more and 15 nm or less, and the half width of the volume distribution of the crystallite size is 3 nm or more and 50 nm or less.

  Further, the mode value of the volume part of the crystallite is preferably 6 nm or more and 15 nm or less.

  The mode value of the crystallite volume distribution is preferably 8 nm or more and 15 nm or less, and the half width of the crystallite size volume distribution is preferably 10 nm or more and 20 nm or less.

Further, the mode of the volume distribution of the crystallites is preferably 8 nm or more and 11 nm or less, and the half width of the volume distribution of the crystallites of the αFe crystal phase is preferably 10 nm or more and 15 nm or less.
<Crystallinity>
In addition, when the degree of crystallinity is higher than 55%, a dust core having a smaller core loss can be obtained.
The crystallinity is preferably 70% or more. Furthermore, the crystallinity is preferably 80% or more.

Compared to Example 1, Example 2 increases the thickness of the oxide film formed around the powder by increasing the heat treatment time, thereby improving the pressure resistance of the dust core.

  In Example 2, the volume distribution of the crystal size is slightly larger than that in Example 1, but the core loss is smaller than that of Comparative Example 1 and can satisfy the pass / fail criteria. Therefore, it is considered that excellent magnetic characteristics are obtained with improved reliability.

  Comparative Example 1 has a small crystallite of several nanometers or less, includes many fine particles that are insufficiently crystallized, and has a low crystallinity. Comparative Example 2 includes a large number of enlarged crystal grains of several tens of nm or more and has a low crystallinity.

  Therefore, in both Comparative Example 1 and Comparative Example 2, the magnetic anisotropy of the nano soft magnetic alloy powder increases, and the coercive force of the nano soft magnetic alloy powder increases. Furthermore, the core loss of the dust core using the same also increases.

  On the other hand, in Examples 1 and 2, the crystallite has a small proportion of several nm or less and several tens of nm or more, and the crystallinity is high, and the magnetic anisotropy of the nano soft magnetic alloy powder is averaged. It is considered that the coercive force of the nano soft magnetic alloy powder is reduced and the magnetic force is reduced. Furthermore, the core loss of the powder magnetic core using it can also be reduced.

<Discussion>
The powder aggregate has low thermal conductivity due to the presence of voids between the powders. For this reason, when heat treatment is performed in a hot stove, heat is not sufficiently transferred to some powders, and the temperature during the heat treatment of the powder does not rise sufficiently.

  On the other hand, since the hot stove does not have an endothermic function, some powders run away due to self-heating due to the αFe crystal phase precipitation, and the temperature during the heat treatment of the powder is too high.

  Therefore, the heat treatment in the hot stove makes the temperature of the powder non-uniform during the heat treatment, resulting in a state where a large number of fine crystal grains of several nm or less and a large number of enlarged crystal grains of several tens of nm are mixed. The coercive force increases.

  On the other hand, the heat treatment in the hot press has high thermal conductivity because the powder is sandwiched between the heating plates and heated from above and below. Further, when the temperature of the powder becomes higher than that of the hot press due to self-heating due to the precipitation of the αFe crystal phase, the heat generation of the powder can be absorbed by the heating plate.

  Therefore, the temperature of all the powders during the heat treatment can be made uniform, and the αFe crystal phase of the optimum size can be precipitated. Therefore, a crystalline soft magnetic alloy powder having a high saturation magnetic flux density and excellent soft magnetic characteristics can be obtained.

(as a whole)
Note that the Fe-based amorphous alloy ribbon is not limited to the ribbon having the composition of the embodiment, but may be any as long as it can precipitate fine crystals of the αFe crystal phase.

  Further, the crystallite size volume distribution and the crystallinity are the same even if they are not the compositions of the examples.

  According to the present embodiment, it is possible to provide a nanocrystalline soft magnetic alloy powder with a high saturation magnetic flux density and excellent soft magnetic characteristics, and a dust core using the nanocrystalline soft magnetic alloy powder.

1 αFe crystal phase 2 Amorphous phase

Claims (12)

An amorphous phase,
An αFe crystal phase located in the amorphous phase;
Have
The mode of volume distribution of crystallites of the αFe crystal phase is 1 nm or more and 15 nm or less,
A soft magnetic alloy powder having a half width of a volume distribution of crystallites of the αFe crystal phase of 3 nm to 50 nm. The soft magnetic alloy powder according to claim 1, wherein a mode value of volume distribution of crystallites of the αFe crystal phase is 6 nm or more and 15 nm or less. The soft magnetic alloy powder according to claim 1, wherein the mode value of the volume distribution of crystallites of the αFe crystal phase is 8 nm or more and 15 nm or less. The soft magnetic alloy powder according to claim 1 or 2, wherein a half width of a volume distribution of crystallites of the αFe crystal phase is 10 nm or more and 20 nm or less. The soft magnetic alloy powder according to any one of claims 1 to 3, wherein a mode value of a volume distribution of crystallites of the αFe crystal phase is 8 nm or more and 11 nm or less. The soft magnetic alloy powder according to any one of claims 1 to 4, wherein a half width of a volume distribution of crystallites of the αFe crystal phase is 10 nm or more and 15 nm or less.   The soft magnetic alloy powder according to claim 1, wherein the crystallinity of the αFe phase is higher than 55%.   The soft magnetic alloy powder according to claim 7, wherein the crystallinity of the αFe phase is 70% or more.   The soft magnetic alloy powder according to claim 7, wherein the crystallinity of the αFe phase is 80% or more.   A dust core comprising the soft magnetic alloy powder according to any one of claims 1 to 9 and a binder. A pulverizing step of powdering an alloy composition having an amorphous phase;
The powder is heat-treated to precipitate an αFe crystal phase, and the mode value of the volume distribution of the crystallite size of the αFe crystal phase is 1 nm or more and 15 nm or less, the half width of the volume distribution of the crystallite size of the αFe crystal phase And a heat treatment step of 3 nm or more and 50 nm or less. The method for producing a soft magnetic alloy powder according to claim 11, wherein in the heat treatment step, the heat treatment is performed by sandwiching the powder with a hot press.

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