JP7696771B2 - powder magnetic core - Google Patents

Description

This disclosure relates to powder magnetic cores.

Patent Document 1 discloses a soft magnetic metal powder having particles consisting of a soft magnetic metal portion and a coating portion that covers the soft magnetic metal portion. The coating portion contains an oxide of Si, and has a first coating portion that contains amorphous matter and a second coating portion that contains crystals.

Patent Document 2 and Patent Document 3 describe an insulating coated soft magnetic metal powder using zirconium oxide. Patent Document 4 describes a soft magnetic powder having an oxygen value per unit specific surface area within a specified range. Patent Document 5 describes a dust core using particles in which an insulating coating of metal oxide is formed on the surface of metal magnetic particles.

JP 2020-167384 A Japanese Patent Application Publication No. 10-335128 JP 2019-192868 A JP 2020-186414 A JP 2009-164401 A

In powder magnetic cores, soft magnetic metal particles are coated with an insulating layer to reduce loss, but the components of the insulating layer tend to diffuse into the soft magnetic metal, adversely affecting the properties of the soft magnetic metal particles.
The present disclosure has been made in view of the above-mentioned circumstances, and has an object to reduce loss in a powder magnetic core. The present disclosure can be realized in the following forms.

[1] A dust core comprising an insulating-coated soft magnetic metal powder having soft magnetic metal particles having an average equivalent circular diameter of 10 μm to 100 μm and an insulating layer formed on the surface of the soft magnetic metal particles,
the insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si;
When a cross section of the powder magnetic core is observed in a field of view of 500 μm × 500 μm, the ratio of an area occupied by the insulating layer to an area of 4% or more and 9% or less when the area of the entire powder magnetic core is taken as 100%,
A powder magnetic core, wherein the difference between the thermal expansion coefficient of the soft magnetic metal particles and the thermal expansion coefficient of the insulating layer is 3.0×10 ⁻⁶ /K or less.

This disclosure makes it possible to reduce losses in insulating coated soft magnetic metal powder.

FIG. 2 is a cross-sectional view that typically illustrates a cross section of a powder magnetic core. FIG. 2 is a schematic diagram of a thin sample. 1 is a graph showing a schematic diagram of Zr concentration when the thickness of a diffusion layer is 50 nm or less. 1 is a schematic graph of the Zr concentration when the thickness of the diffusion layer is greater than 50 nm. FIG. 13 is a graph showing the Zr concentration in the powder magnetic core of Example 3.

Here, a preferred example of the present disclosure is given.
[2] A powder magnetic core, wherein the average equivalent circular diameter of particles constituting the insulating layer is 20 nm to 50 nm.

[3] A powder magnetic core in which, among the soft magnetic metal particles, particles having a circle equivalent diameter of 50 μm to 100 μm are designated as specific particles, and when cross sections of 10 or more different specific particles are subjected to crystal orientation analysis and the number of regions separated by an orientation difference of 5° or more is counted for each of the specific particles, the average number of the regions counted for each of the specific particles is 9 or less.

[4] The insulating layer contains an oxide of at least one of Al and Zr,
the half-value width of the strongest peak derived from the insulating layer as measured by XRD is 0.80° or less;
A powder magnetic core, wherein a thickness of a diffusion layer in which at least one of Al and Zr is diffused in a surface layer of the soft magnetic metal particles is 50 nm or less.

The present disclosure is described in detail below. In this specification, when a numerical range is described using "to", it is intended to include the lower limit and the upper limit unless otherwise specified. For example, the description "10 to 20" is intended to include both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Powder magnetic core 10
The powder core 10 is a powder core 10 containing an insulated soft magnetic metal powder 1 having soft magnetic metal particles 2 with an average equivalent circular diameter of 10 μm to 100 μm and an insulating layer 3 formed on the surface of the soft magnetic metal particles 2. The insulating layer 3 contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si. When a cross section of the powder core 10 is observed in a field of view of 500 μm × 500 μm, the insulating layer 3 occupies an area of 4% or more and 9% or less when the area of the entire powder core 10 is taken as 100%. The difference between the thermal expansion coefficient of the soft magnetic metal particles 2 and the thermal expansion coefficient of the insulating layer 3 is 3.0 × 10 ^-6 /K or less.

(1) Soft magnetic metal particles 2
The soft magnetic metal particles 2 are not particularly limited as long as they are soft magnetic metal particles, and can be widely used. As the soft magnetic metal particles 2, soft magnetic pure iron particles and iron-based alloy particles can be widely used. As the iron-based alloy, Fe-Si alloy, Fe-Si-Cr alloy, Fe-Si-Al alloy (Sendust), Ni-Fe alloy (Permalloy), Ni-Fe-Mo alloy (Supermalloy), Fe-based amorphous alloy, Fe-Co alloy, etc. can be suitably used. Among these, Fe-Si alloy, Fe-Si-Cr alloy, Fe-Si-Al alloy (Sendust), Ni-Fe alloy (Permalloy), and Ni-Fe-Mo alloy (Supermalloy) are preferable in terms of magnetic permeability, coercive force, and frequency characteristics.
When an Fe--Si alloy is used, an alloy having a composition of, for example, 0.1 mass % to 10 mass % Si, the balance being Fe and unavoidable impurities, can be used.
When using an Fe-Si-Cr alloy, for example, an alloy having a composition of Si: 0.1 mass % to 10 mass %, Cr: 10 mass % to 20 mass %, the balance: Fe and unavoidable impurities can be used.
The average equivalent circular diameter of the soft magnetic metal particles 2 is 10 μm or more and 100 μm or less, preferably 25 μm or more and 100 μm or less, and more preferably 50 μm or more and 100 μm or less. The average equivalent circular diameter of the soft magnetic metal particles 2 can be appropriately changed depending on the frequency band to be used. In particular, when assuming use in a high frequency band exceeding 100 kHz, it is more preferable that the average equivalent circular diameter is 10 μm or more and 25 μm or less.
The average equivalent circle diameter of the soft magnetic metal particles 2 can be obtained by observing the cross section of the powder core 10 (see FIG. 1). Specifically, the average equivalent circle diameter is calculated from the particle area of the cross section of the powder core 10 observed by FE-SEM. More specifically, the average equivalent circle diameter is obtained as follows. Focus is placed on a plurality of soft magnetic metal particles 2 that can be observed without chipping in a predetermined observation field (e.g., 200 μm×200 μm). The diameter (equivalent circle diameter) of an ideal circle (true circle) having an area equal to the area (projected area) of each particle image of the soft magnetic metal particles 2 is calculated as the equivalent circle diameter of each particle. The average equivalent circle diameter is then obtained by arithmetically averaging the equivalent circle diameters of each particle. The equivalent circle diameter of each particle and the average equivalent circle diameter can be obtained using general image analysis software.

(2) Insulating layer 3
As described above, the insulating layer 3 contains an oxide of at least one element (hereinafter also referred to as a specific element) selected from the group consisting of Al, Zr, and Si.
Examples of oxides of Al (aluminum) include γ-Al ₂ O ₃ and α-Al ₂ O ₃ .
Examples of oxides of Zr (zirconium) include monoclinic ZrO2, tetragonal ZrO2, and cubic ZrO2.
Examples of oxides of Si (silicon) include quartz and cristobalite.
The oxide may be a composite oxide containing a specific element or a mixture of the above oxides. Examples of such composite oxides include MgO-Al2O3 composite oxide, Y2O3-ZrO2 composite oxide, CaO-ZrO2 composite oxide, etc. Examples of such mixtures include ZrO2 _{- SiO2} mixtures, _Al2O3 - _SiO2 mixtures, _ZrO2 - _Al2O3 mixtures, _{Al2O3 - SiO2 - MgO} mixtures, etc.
When a ZrO ₂ —SiO ₂ mixture is used, for example, a mixture of SiO ₂ : 1 mass % to 45 mass %, the balance: ZrO ₂ and unavoidable impurities can be used.
When an Al ₂ O ₃ —SiO ₂ mixture is used, for example, a mixture of SiO ₂ : 1 mass % to 45 mass %, the balance: Al ₂ O ₃ and unavoidable impurities can be used.
When a ZrO ₂ -Al ₂ O ₃ mixture is used, for example, a mixture of Al ₂ O ₃ : 1 mass % to 30 mass %, the balance: ZrO ₂ and unavoidable impurities can be used.
When an Al ₂ O ₃ —SiO ₂ —MgO mixture is used, for example, a mixture of SiO ₂ : 1 mass % to 45 mass %, MgO: 1 mass % to 10 mass %, and the balance: Al ₂ O ₃ and unavoidable impurities can be used.
The composition of the insulating layer 3 can be analyzed by EPMA (Electron Probe Micro Analyser).

(3) Requirements for the Proportion of the Area Occupied by the Insulating Layer 3 When the cross section of the powder core 10 is observed in a field of view of 500 μm × 500 μm, the proportion of the area occupied by the insulating layer 3 in the powder core 10 is 4% or more and 9% or less when the area of the entire powder core 10 is taken as 100%. The proportion of the area occupied by the insulating layer 3 is more preferably 5% or more and 7% or less. As long as the proportion of the area occupied by the insulating layer 3 is within a predetermined range, the balance between hysteresis loss and eddy current loss is good. In other words, if the proportion of the area occupied by the insulating layer 3 is too high, the hysteresis loss will be large, and if it is too low, the eddy current loss will be large.
The proportion of the area occupied by the insulating layer 3 can be calculated by image analysis of a cross section processed by a CP (cross section polisher) by observing with an EPMA. Note that the area occupied by the insulating layer 3 does not include the area of the pores 6. In Fig. 1, among the pores 6, the pores 6 existing between the soft magnetic metal particles 2 and the insulating layer 3 are distinguished as pores 6A.
The proportion of the area occupied by the insulating layer 3 can be controlled by adjusting the mixing ratio of the raw material of the soft magnetic metal particles 2 and the raw material of the insulating layer 3 .

(4) Requirement for difference between thermal expansion coefficient of soft magnetic metal particle 2 and thermal expansion coefficient of insulating layer 3 In the powder magnetic core 10, the difference between the thermal expansion coefficient of the soft magnetic metal particle 2 and the thermal expansion coefficient of the insulating layer 3 is 3.0×10 ⁻⁶ /K or less. The difference between the thermal expansion coefficient of the soft magnetic metal particle 2 and the thermal expansion coefficient of the insulating layer 3 is more preferably 2.8×10 ⁻⁶ /K or less, and even more preferably 2.5×10 ⁻⁶ /K or less. If the difference between the thermal expansion coefficient of the soft magnetic metal particle 2 and the thermal expansion coefficient of the insulating layer 3 is a predetermined value or less, the performance degradation after a thermal cycle assuming an actual use environment can be reduced. Note that the difference between the thermal expansion coefficient of the soft magnetic metal particle 2 and the thermal expansion coefficient of the insulating layer 3 is expressed as an absolute value and is 0 or more.

The difference between the thermal expansion coefficient of the soft magnetic metal particles 2 and the thermal expansion coefficient of the insulating layer 3 can be found as follows: The soft magnetic metal particles 2 are press molded without being coated with an insulating layer to prepare a single sample of the soft magnetic metal particles 2. If single powder of the soft magnetic metal particles 2 is not available, the composition of the single soft magnetic metal is found from a sample of the insulating-coated soft magnetic metal powder 1, and a single sample of this composition is prepared.
The soft magnetic metal particles 2 are coated with the insulating layer 3 and press-molded to prepare the powder core 10 .
The thermal expansion amounts of a single sample of the soft magnetic metal particles 2 and the powder core 10 are measured in the range of 25° C. to 100° C. in accordance with JIS R 1618. The thermal expansion amount measured for the single sample is designated A, and the thermal expansion amount measured for the powder core 10 is designated B.
The rate of change in A relative to temperature change in the range of 25° C. to 100° C. is calculated as the thermal expansion coefficient of the soft magnetic metal particles 2 .
The value obtained by the following formula (1) is regarded as the amount of thermal expansion C of the insulating layer 3.
C=B-A...(1)
The rate of change in C relative to temperature changes in the range of 25° C. to 100° C. is calculated as the thermal expansion coefficient of the insulating layer 3.
From the calculated thermal expansion coefficients of the soft magnetic metal particles 2 and the insulating layer 3, the difference between the thermal expansion coefficients of the soft magnetic metal particles 2 and the insulating layer 3 is determined.
The thermal expansion coefficients of the soft magnetic metal particles 2 and the insulating layer 3 can be controlled by appropriately designing the combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3 .

The combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3 is not particularly limited.
From the viewpoint of reducing the difference in thermal expansion coefficient, the preferred combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3 is as follows: In addition to the above, the combination of the composition of the soft magnetic metal particles and the composition of the insulating layer described in the examples can also be used.
A combination of the soft magnetic metal particles 2 being Fe-3.0% by mass Si and the insulating layer 3 being _{ZrO2. A} combination of the soft magnetic metal particles 2 being Fe-6.5% by mass Si and the insulating layer 3 being _Al2O3-20 % by mass _SiO2-5 % by mass MgO. A combination of the soft magnetic metal particles 2 being pure iron (100% Fe) and the insulating layer 3 being _ZrO2.

(5) Presumed Reason for Suppression of Loss in Powder Core 10 The present inventors conducted extensive research to suppress the loss (iron loss) in the powder core 10. As a result, they found that the powder core 10 obtained by adjusting the blending and composition of the soft magnetic metal particles 2 and the insulating layer 3 has the desired effect when the following requirements are satisfied. That is, they unexpectedly discovered that the loss in the powder core 10 can be suppressed when the ratio of the area occupied by the insulating layer 3 is 4% or more and 9% or less, and the difference between the thermal expansion coefficient of the soft magnetic metal particles 2 and the thermal expansion coefficient of the insulating layer 3 is 3.0×10 ⁻⁶ /K or less. The present invention was made based on this knowledge. In addition, when the above requirements are satisfied, the effect of reducing the performance degradation after a thermal cycle assuming an actual usage environment is also achieved.

(6) Requirement for the average equivalent circle diameter of particles constituting the insulating layer 3 When the insulating layer 3 is observed with a TEM (transmission electron microscope), particles constituting the insulating layer 3 are confirmed. At least a part of these particles is formed by crystals of the above-mentioned oxide.
There is no particular limitation on the average equivalent circular diameter of the particles constituting the insulating layer 3. The average equivalent circular diameter of the particles constituting the insulating layer 3 is preferably 20 nm to 50 nm, more preferably 25 nm to 45 nm, and even more preferably 28 nm to 42 nm. Within such a range, the adhesion with the soft magnetic metal particles 2 is improved, and the resistance of the grain boundaries reduces eddy current loss, thereby reducing loss.
The average equivalent circle diameter of the particles constituting the insulating layer 3 can be obtained by observing the cross section of the powder core 10. Specifically, the equivalent circle diameter is calculated from the particle area observed by TEM on the cross section of the powder core 10, and is defined as the average equivalent circle diameter. More specifically, the average equivalent circle diameter is obtained as follows. Focus is placed on a plurality of particles that can be observed without missing particles in five 300 nm x 300 nm square observation fields. The diameter (equivalent circle diameter) of an ideal circle (true circle) having an area equal to the area (projected area) of each particle image is calculated as the equivalent circle diameter of each particle. The average equivalent circle diameter is then obtained by arithmetically averaging the equivalent circle diameters of each particle. The equivalent circle diameter of each particle and the average equivalent circle diameter can be obtained using general image analysis software.

(7) Requirements for Crystal Orientation In the insulating coated soft magnetic metal powder 1, when specific particles are those of the soft magnetic metal particles 2 having a circle equivalent diameter of 50 μm to 100 μm, and cross sections of 10 or more different specific particles are subjected to crystal orientation analysis to measure the number of regions separated by an orientation difference of 5° or more for each specific particle, it is preferable that the average number of regions measured for each specific particle is 9 or less. The average number of regions measured for each specific particle is preferably 8 or less, and more preferably 7 or less.
The average number of regions measured by the specific particles can be an index representing the degree of crystal division in the soft magnetic metal particles. If the average number of regions measured by the specific particles is equal to or less than a predetermined value, the increase in hysteresis loss is suppressed, and the loss is reduced accordingly. Note that the lower limit of the average number of regions measured by the specific particles may be 1 or more, and is usually 2 or more.
The number of regions in a specific particle can be determined by electron backscatter diffraction (EBSD) measurement. The EBSD measurement is performed, for example, under the following conditions.
Acceleration voltage: 10.00 kV
Sample tilt (degrees): 70.00°
Acquisition speed: 109.15Hz
Based on the crystal orientation map obtained by EBSD measurement, measurement points with an orientation difference of 5° or more between adjacent measurement points are defined as grain boundaries, and the number of regions surrounded by grain boundaries is counted. However, among the regions surrounded by grain boundaries, regions with an equivalent circle diameter of 3 μm or less are excluded from the count. The reason for excluding regions with an equivalent circle diameter of 3 μm or less is to eliminate errors in EBSD measurement due to noise, etc.

(8) Requirement for Half Width of Strongest Peak Originating from Insulating Layer 3 The insulating coated soft magnetic metal powder 1 preferably has a half width of the strongest peak originating from the insulating layer 3 measured by XRD of 0.80° or less.
The half width of the strongest peak derived from the insulating layer 3 being equal to or less than a predetermined value can be an indicator of high crystallinity of the oxide contained in the insulating layer 3. The half width of the strongest peak may be equal to or less than 0.72°, or may be equal to or less than 0.66°. The lower limit of the half width of the strongest peak is not particularly limited, but is usually equal to or more than 0.40°.
The half-value width of the strongest peak derived from the insulating layer 3 can be controlled by adjusting the composition of the insulating layer 3 and the heat treatment conditions in the manufacturing method described later.

The half-value width of the strongest peak derived from the insulating layer 3 can be determined by XRD measurement of the dust core 10 containing the insulating-coated soft magnetic metal powder 1. The XRD measurement is performed, for example, under the following conditions.
Equipment: Rigaku SmartLab
・X-ray: CuKα1
Tube voltage: 40 kV
・Tube current: 30mA
Scanning speed: 5°/min
・Sampling width: 0.02°
Measurement range (2θ): 10° to 80°
Entrance slit: 1/2°
・Receiving slit 1: 15.000 mm
・Receiving slit 2: 20.000 mm
In the diffraction pattern of the powder magnetic core 10 obtained by the XRD measurement, peaks originating from the soft magnetic metal particles 2, the measurement cell, etc. are removed, and only peaks originating from the insulating layer 3 are obtained. When there is one peak originating from the insulating layer 3, that peak is identified as the strongest peak. When there are multiple peaks originating from the insulating layer 3, the peak with the highest intensity among the multiple peaks is identified as the strongest peak. For example, when two types of peaks, monoclinic ZrO ₂ and tetragonal ZrO _2, are detected in an insulating layer 3 containing ZrO ₂ , only the peak with the higher intensity (e.g., tetragonal ZrO ₂ ) is identified as the strongest peak.

Examples of the crystal phase exhibiting the strongest peak derived from the insulating layer 3 include crystal phases selected from the group consisting of monoclinic ZrO ₂ , tetragonal ZrO ₂ , cubic ZrO ₂ , γ-Al ₂ O ₃ , and SiO ₂ (quartz). Examples of the strongest peaks in these crystal phases are as follows. Among these, the strongest peak is preferably the peak of any one of monoclinic ZrO ₂ , tetragonal ZrO ₂ , cubic ZrO ₂ , or γ-Al ₂ O ₃ .
Monoclinic _ZrO2
PDF card number: 01-080-0966
Strongest peak (hkl): (-1, 1, 1)
d value of strongest peak: 3.15
Tetragonal _ZrO2
PDF card number: 01-073-1441
Strongest peak (hkl): (0,1,1)
d value of strongest peak: 3.00
・Cubic ZrO2
PDF card number: 01-080-4012
Strongest peak (hkl): (1,1,1)
d value of strongest peak: 2.97
γ _{- Al2O3}
PDF card number: 00-010-0173
Strongest peak (hkl): (4, 4, 0)
d value of strongest peak: 1.40
・SiO ₂ (quartz)
PDF card number: 00-033-1161
Strongest peak (hkl): (1,0,1)
d value of strongest peak: 3.34

(9) Requirements for the Thickness of Diffusion Layers 5A, 5B When the insulating layer 3 contains an oxide of at least one of Al and Zr, it is preferable that the thickness of the diffusion layers 5A, 5B in which at least one of Al and Zr is diffused in the surface layer of the soft magnetic metal particles 2 is 50 nm or less.
The diffusion layers 5A, 5B can be generated by diffusing at least one of the elements Al and Zr into the soft magnetic metal particles 2 by heat treatment or the like. That is, the diffusion layers 5A, 5B can be generated in the areas where the soft magnetic metal particles 2 and the insulating layer 3 are in close contact with each other. The diffusion layers 5A, 5B may be formed on the entire surface layer of the soft magnetic metal particles 2, or may be formed partially on the surface layer of the soft magnetic metal particles 2. The diffusion layers 5A, 5B may not be formed (have a thickness of 0 nm).
The thickness of the diffusion layers 5A and 5B can be controlled by adjusting the rate of temperature rise within a predetermined temperature range in the manufacturing method described below.

Whether the thickness of the diffusion layers 5A, 5B is 50 nm or less is determined by TEM-EDS (energy dispersive X-ray spectrometry) measurement of the powder core 10. Specifically, the powder core 10 is processed by a FIB (focused ion beam) device into a thin sample 11 having a thickness of 100 nm, and the TEM-EDS measurement is performed.
The TEM-EDS measurement is performed under conditions equivalent to a predetermined resolution (for example, Φ10 nm). An example of such measurement conditions is a beam diameter of Φ0.24 nm, an acceleration voltage of 200 keV, and an irradiation current of 30 μA.

The thin sample 11 will be described. As shown in FIG. 2, the thin sample 11 is processed so that the cross section of the insulating layer 3 appears on the FIB observation surface S1 and the TEM observation surface S2. The TEM observation surface S2 of the thin sample 11 is the XY surface, and the FIB observation surface S1 is the XZ surface. The boundary between the insulating layer 3 and the soft magnetic metal particles 2A and 2B appears on the FIB observation surface S1. The inclination of both boundary lines is 100 nm vertically (Z-axis direction) and 10 nm horizontally (X-axis direction) or less. In FIG. 2, the inclination of the boundary line on the right side is within a predetermined range, but the inclination of the boundary line on the left side is also within a predetermined range. The TEM-EDS observation is performed at a position 600 nm from the FIB observation surface S1 on the TEM observation surface S2. In this way, it is possible to suppress the detection of the insulating layer 3 components present inside the thin sample 11 as the diffusion layers 5A and 5B due to the inclination of the insulating layer 3 with respect to the Z axis. Note that the diffusion layers 5A and 5B are not shown in FIG. 2.

When the element contained in the insulating layer 3 is Zr, whether or not the diffusion layers 5A, 5B are 50 nm or less is determined by the following procedure, which will be described below with reference to FIGS.
[1] A TEM observation image is obtained on the TEM observation surface S2, and a line analysis is performed on the measurement line ML that crosses the insulating layer 3 at a position 600 nm from the FIB observation surface S1.
[2] Two lines L1 and L2 perpendicular to the measurement line ML are drawn from the intersection of the measurement line ML and the boundary between the soft magnetic metal particles 2A and 2B and the insulating layer 3. Line L1 is located on the left side of the insulating layer 3, and line L2 is located on the right side of the insulating layer 3.
[3] In the measurement range inside the two lines L1 and L2, the average value of all points of the Zr concentration obtained by the linear analysis is calculated. This average value is defined as the 100% line of the Zr concentration.
[4] Calculate the average value of all points of Zr concentration obtained by linear analysis in the measurement range from 500 nm to the left of line L1 and from 500 nm to the right of line L2. This average value is defined as the base (0%) line of Zr concentration.
[5] Calculate the 10% line of the Zr concentration based on the base (0%) line of the Zr concentration and the 100% line of the Zr concentration. Find points P1 and P2 that are located on the outermost side among the points where the 10% line of the Zr concentration intersects with the Zr concentration graph.
[6] Calculate the distance between point P1 and line L1. From the TEM observation image, determine the angle θ1 (0°<θ1≦90°) between the boundary line between the soft magnetic metal particle 2A and the insulating layer 3 and the measurement line ML. Calculate the thickness T1 of the diffusion layer 5A based on the following formula.
Thickness T1 of the diffusion layer 5A=distance between the point P1 and the line L1×sin θ1
The distance between point P2 and line L2 is calculated. From the TEM observation image, the angle θ2 (0°<θ2≦90°) between the boundary line between the soft magnetic metal particle 2B and the insulating layer 3 and the measurement line ML is obtained. The thickness T2 of the diffusion layer 5B is calculated based on the following formula.
Thickness T2 of the diffusion layer 5B=distance between the point P2 and the line L2×sin θ2
[7] When the thickness T1 of the diffusion layer 5A is 50 nm or less and the thickness T2 of the diffusion layer 5B is 50 nm or less, it is determined that the "thickness of the diffusion layer is 50 nm or less" (see FIG. 3). When at least one of the thickness T1 of the diffusion layer 5A and the thickness T2 of the diffusion layer 5B is greater than 50 nm, it is determined that the "thickness of the diffusion layer is greater than 50 nm" (see FIG. 4).
The thicknesses T1 and T2 of the diffusion layers 5A and 5B may be 0 nm, that is, the diffusion layers 5A and 5B may not be detected.

The insulating coated soft magnetic metal powder 1 may be determined to have a "diffusion layer thickness of 50 nm or less" by line analysis at one location on at least one soft magnetic metal particle 2. It is preferable that the insulating coated soft magnetic metal powder 1 is determined to have a "diffusion layer thickness of 50 nm or less" by line analysis at three different locations on one soft magnetic metal particle 2. It is more preferable that the insulating coated soft magnetic metal powder 1 is determined to have a "diffusion layer thickness of 50 nm or less" by line analysis at multiple thin flake samples 11 obtained from different locations on the powder core 10. The number of multiple thin flake samples 11 is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more.

When the element contained in the insulating layer 3 is Al, the Al concentration can be measured and judged in a similar manner. When the insulating layer 3 contains both Al and Zr, the same procedure can be used to judge Al and Zr and confirm that all elements meet the requirements. Note that even when the insulating film contains oxides of elements other than Al and Zr (e.g., oxides of Si), the thickness of the diffusion layer is defined by the Zr concentration or Al concentration, and the concentrations of elements other than Al and Zr are not taken into consideration.

2. Manufacturing Method of Powder Core 10 There are no particular limitations on the manufacturing method of powder core 10. An example will be described below.
(1) Preparation of Insulated Soft Magnetic Metal Powder 1 A suspension containing soft magnetic metal powder, oxide particles of a specific element, and a small amount of organic components is mixed and dried. The obtained dried powder is heat-treated to obtain the insulated soft magnetic metal powder 1. The conditions of this heat treatment are not particularly limited. For example, the following conditions are preferably adopted as the heat treatment conditions: heat treatment temperature: 600°C to 1200°C, inert atmosphere ( _N2 atmosphere, Ar atmosphere).
(2) Molding (press molding)
The insulating coated soft magnetic metal powder 1 is placed in a die and press molded at a molding pressure of 1.0 to 1.7 GPa to obtain a molded body.
(3) Heat treatment (annealing)
The obtained compact is heat treated (annealed) to obtain the powder magnetic core 10. As the heat treatment conditions, for example, the following conditions are suitably adopted: heat treatment temperature: 600° C. to 1200° C., heating rate at 350° C. to 600° C.: 3° C./min or more, holding time: 10 minutes to 120 minutes, inert atmosphere ( _N2 atmosphere, Ar atmosphere).
The conditions of the heat treatment are appropriately changed depending on the types of soft magnetic metal powder and oxide used.

The present invention will be explained in more detail below with reference to the following examples.

1. Preparation of powder magnetic cores (1) Examples 1 to 13
The soft magnetic metal particles (raw powder) used were various particles having the types and average equivalent circular diameters shown in Table 1. In Table 1, each description represents the following particles.
Fe: Pure iron particles Fe-3.5Si: Fe-3.5 mass% Si particles produced by gas atomization method Fe-Ni: Permalloy particles Fe-Si-Cr: Fe-3.5 mass% Si-1.5 mass% Cr particles produced by water atomization method Fe-Si-Al: Sendust particles Fe-Ni-Mo: Supermalloy particles Fe-Si: Fe-5.0 mass% Si particles produced by gas atomization method

Next, the soft magnetic metal particles were mixed with a suspension containing the type of oxide particles described in Table 1, a small amount of organic components, and a solvent, dried, and heat-treated. The concentration of the oxide particles in the suspension was 0.1 to 2 mass% relative to the entire suspension. The amount of the suspension mixed with the soft magnetic metal particles was such that the total amount of oxide particles contained was 6 volume% relative to the soft magnetic metal particles. The heat treatment (first heat treatment) was performed under the conditions of a heat treatment temperature of 600°C to 1200°C in nitrogen. The heat treatment was performed for the purpose of removing the organic components in the insulating layer and promoting the crystallization of the oxide. In this way, the insulating coated soft magnetic metal powders of Examples 1 to 13 were obtained. In addition, in Table 1, each description represents the following oxide particles.
Al: Al ₂ O ₃ particles Si: SiO ₂ particles Zr: ZrO ₂ particles Zr-Si: ZrO ₂ -20% by mass SiO ₂ particles Al-Si: Al ₂ O ₃ -20% by mass SiO ₂ particles Zr-Al: ZrO ₂ -10% by mass Al ₂ O ₃ particles

The obtained insulating coated soft magnetic metal powder was placed in a mold and pressed at a molding pressure of 1.0 to 1.7 GPa to obtain a pressed compact with a diameter of 10 mm. This compact was heat treated (second heat treatment). The heat treatment was performed under the following conditions: heat treatment temperature: 600 to 1200°C, heating rate in the range of 350°C to 600°C: less than 3°C/min, in nitrogen. In this way, the dust cores of Examples 1 to 13 were obtained.

(2) Examples 14 to 20
The heat treatment temperature of the heat treatment (second heat treatment) was 600 to 1200° C., and the heating rate in the range of 350° C. to 600° C. was 3° C./min to 10° C./min. Otherwise, the same procedures as in Examples 1 to 13 were carried out to obtain insulating coated soft magnetic metal powders and dust cores.
The crystallinity of the insulating layer was controlled by performing heat treatment at a higher temperature than in the past. Furthermore, the rate of temperature rise in a specified temperature range was increased to control the rate at which an insulating layer with high crystallinity was obtained. As a result, it was possible to shorten the temperature range required to form an insulating layer with high crystallinity, and it is presumed that this made it possible to suppress the diffusion of at least one of the elements Al and Zr that constitute the insulating layer into the soft magnetic metal particles.

(3) Comparative Examples 1 and 2
For the soft magnetic metal particles (raw material powder), various particles having the types and average equivalent circular diameters shown in Table 1 were used. Otherwise, in the same manner as in Examples 1 to 13, insulating coated soft magnetic metal powders and dust cores were obtained.

(4) Comparative Example 3
A suspension not containing oxide particles of a specific element was used. Otherwise, the same procedures as in Examples 1 to 13 were carried out to obtain insulating coated soft magnetic metal powders and dust cores.

(5) Comparative Examples 4 and 5
The heat treatment temperature in the heat treatment (second heat treatment) was 600 to 1200° C., and the temperature increase rate in the range of 350° C. to 600° C. was 2.5° C./min. Otherwise, the same procedures as in Examples 1 to 13 were carried out to obtain insulating coated soft magnetic metal powders and dust cores.

Table 1 shows the characteristics of the soft magnetic metal particles and the insulating layer of each of the examples and comparative examples.
The "Crystal Orientation" column indicates the average number of regions measured for a particular grain, as measured by the method described in the embodiment.
The column "Half width" indicates the half width of the strongest peak derived from the insulating layer, measured by the method described in the embodiment.
The "Thickness of diffusion layer" column indicates the larger of the "thickness T1 of diffusion layer 5A" and the "thickness T2 of diffusion layer 5B" calculated by the method described in the embodiment. For Example 2 and Comparative Example 3, at least one of the elements Al and Zr was not detected, and therefore "-" is entered. A graph of the Zr concentration and O concentration in the powder magnetic core of Example 3 is shown in FIG. 5.
The column "average equivalent circular diameter" of the insulating layer indicates the average equivalent circular diameter of the particles constituting the insulating layer, measured by the method described in the embodiment.
The "Occupied Area" column indicates the percentage of the area occupied by the insulating layer, measured by the method described in the embodiment.

2. Loss Evaluation Method Using a powder core produced by press-molding only soft magnetic metal particles (median diameter _D50 : 40 μm) without heat treatment after molding (hereinafter referred to as simple metal powder core) as a standard, the hysteresis loss and eddy current loss of the powder cores of each of the Examples and Comparative Examples were determined under the following conditions.
Number of turns: Primary: 20 turns, Secondary: 40 turns Applied magnetic field: 0.1T, Frequency: 30kHz to 50kHz

The evaluation was as follows:
Hysteresis loss D: 95% or more of the hysteresis loss of metal powder cores C: 80% or more and less than 95% of the hysteresis loss of metal powder cores B: 70% or more and less than 80% of the hysteresis loss of metal powder cores A: Less than 70% of the hysteresis loss of metal powder cores Note that "D" is considered to be at the same level as the hysteresis loss of metal powder cores or greater than the hysteresis loss of metal powder cores.

Eddy current loss D: 90% or more of the eddy current loss in the elemental metal powder core C: 80% or more but less than 90% of the eddy current loss in the elemental metal powder core B: 60% or more but less than 80% of the eddy current loss in the elemental metal powder core A: Less than 60% of the eddy current loss in the elemental metal powder core "D" is defined as a case in which the eddy current loss in the elemental metal powder core is not clearly improved.

3. Evaluation Results The evaluation results are shown in Table 1.
Examples 1 to 20 satisfy the following requirements (a), (b), (c), and (d).
Requirement (a): The magnetic material is provided with soft magnetic metal particles having an average equivalent circular diameter of 10 μm to 100 μm.
Requirement (b): The insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si.
Requirement (c): The ratio of the area occupied by the insulating layer is 4% or more and 9% or less.
Requirement (d): The difference between the thermal expansion coefficient of the soft magnetic metal particles and the thermal expansion coefficient of the insulating layer is 3.0×10 ⁻⁶ /K or less.

In contrast, Comparative Examples 1 to 5 do not satisfy the following requirements.
Comparative Examples 1 and 2 do not satisfy requirement (a).
Comparative Example 3 does not satisfy requirement (b).
Comparative Examples 4 and 5 do not satisfy the requirements (c) and (d).

In Examples 1 to 20, the hysteresis loss and the overcurrent loss were suppressed in a well-balanced manner compared to Comparative Examples 1 to 5. Furthermore, in Examples 1 to 20, the performance degradation after the thermal cycle was small.
Among Examples 1 to 20, Experimental Examples 6 to 20, which further satisfied the following requirement (e), had smaller hysteresis loss.
Among Examples 1 to 20, Experimental Examples 11 to 20, which further satisfied the following requirement (f), had smaller hysteresis loss and eddy current loss.
Among Examples 1 to 20, Experimental Examples 14 to 20, which further satisfied the following requirement (g), had smaller eddy current loss.
Requirement (e): The average equivalent circular diameter of the particles constituting the insulating layer is 20 nm to 50 nm.
Requirement (f): The average number of regions measured for a specific particle is 9 or less.
Requirement (g): The insulating layer contains an oxide of at least one of Al and Zr, the half-width of the strongest peak derived from the insulating layer measured by XRD is 0.80° or less, and the thickness of the diffusion layer in which at least one of Al and Zr is diffused in the surface layer of the soft magnetic metal particle is 50 nm or less.

4. Effects of the Example The dust core of the example had low hysteresis loss and low eddy current loss.

The present invention is not limited to the embodiments detailed above, and various modifications and variations are possible within the scope of the claims of the present invention.

The powder magnetic core of the present invention is particularly suitable for use in motor cores, transformers, choke coils, noise absorbers, etc.

1... Insulating coated soft magnetic metal powder 2, 2A, 2B... Soft magnetic metal particles 3... Insulating layer 5A, 5B... Diffusion layer 6, 6A... Pore 10... Powder magnetic core

Claims (4)

A powder magnetic core comprising an insulating-coated soft magnetic metal powder having soft magnetic metal particles having an average equivalent circular diameter of 10 μm to 100 μm and an insulating layer formed on the surface of the soft magnetic metal particles,
the insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si;
When a cross section of the powder magnetic core is observed in a field of view of 500 μm × 500 μm, the ratio of an area occupied by the insulating layer to an area of 4% or more and 9% or less when the area of the entire powder magnetic core is taken as 100%,
A powder magnetic core, wherein the difference between the thermal expansion coefficient of the soft magnetic metal particles and the thermal expansion coefficient of the insulating layer is 3.0×10 ⁻⁶ /K or less. The powder magnetic core according to claim 1, wherein the average circular equivalent diameter of the particles constituting the insulating layer is 20 nm to 50 nm. The powder magnetic core according to claim 1 or 2, in which the soft magnetic metal particles are those with a circle equivalent diameter of 50 μm to 100 μm, and when the cross sections of 10 or more different specific particles are subjected to crystal orientation analysis and the number of regions separated by an orientation difference of 5° or more is measured for each of the specific particles, the average number of the regions measured for each of the specific particles is 9 or less. the insulating layer contains an oxide of at least one of Al and Zr;
the half-value width of the strongest peak derived from the insulating layer as measured by XRD is 0.80° or less;
4. The dust core according to claim 1, wherein a thickness of a diffusion layer in which at least one of Al and Zr is diffused in a surface layer of the soft magnetic metal particle is 50 nm or less.

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