WO2019208768A1

WO2019208768A1 - Powder for magnetic cores, magnetic core using same, and coil component

Info

Publication number: WO2019208768A1
Application number: PCT/JP2019/017934
Authority: WO
Inventors: 加藤　哲朗; 千綿　伸彦; 元基太田
Original assignee: 日立金属株式会社
Priority date: 2018-04-27
Filing date: 2019-04-26
Publication date: 2019-10-31
Also published as: CN112105472A; JPWO2019208768A1; JP6673536B1; JP7236622B2; CN112105472B; JP2020111830A

Abstract

A powder for magnetic cores, which contains particles of a first Fe-based alloy having a region in which nano-sized FeSi crystals form a columnar texture and particles of a soft magnetic material composed of a metal texture different from that of the particles of the first Fe-based alloy. The columnar texture is composed of multiple linear FeSi crystals that are arranged along in almost one direction and an amorphous phase that is present between the linear FeSi crystals, and is a striped texture in which the linear FeSi crystals are persent in parallel with each other.

Description

Magnetic core powder, magnetic core and coil parts using the same

The present invention relates to a magnetic core powder suitable for a transformer, a choke coil, a reactor, etc., used for a switching power supply or the like, and a magnetic core and a coil component using the same.

Switching power supplies are EVs (electric vehicles), HEVs (hybrid vehicles), PHEVs (plug-in hybrid vehicles), mobile communication devices (cell phones, smartphones, etc.), personal computers, servers, etc. It is used in the power supply circuit of equipment, and it has been required to be low in power consumption from the viewpoint of energy saving along with reduction in size and weight.

In addition, with the high integration of transistors due to the fine wiring of LSIs (Large Scale Integrated Circuits) used in electronic equipment, the breakdown voltage of transistors decreases and the current consumption increases, resulting in lower and higher operating voltages. Current is progressing. Along with this, power supply circuits such as a DC-DC converter that supplies power to the LSI also need to cope with lowering the operating voltage and higher current of the LSI. For example, the normal operating voltage range is narrowed by lowering the operating voltage of the LSI, so if the supply voltage fluctuation (ripple) from the power supply circuit exceeds or falls below the LSI power supply voltage range, Therefore, measures to increase the switching frequency of the power supply circuit have been taken.

Fe-based amorphous alloys, nanocrystalline alloys, pure alloys that operate at high excitation magnetic flux density in the high-frequency region and are suitable for miniaturization as the magnetic cores used in coil parts respond to higher frequency and higher current in power supply circuits In many cases, powders of metallic soft magnetic materials such as iron, Fe-Si, and Fe-Si-Cr are employed. As the powder of the soft magnetic material, a granular powder obtained by an atomizing method, which hardly causes shape anisotropy of magnetic characteristics when formed into a magnetic core and has good flowability of the powder in forming the magnetic core, is preferably used.

Among the above-mentioned metallic soft magnetic materials, Fe-based alloys are used as soft magnetic materials with high saturation magnetic flux density, low coercive force, and low magnetostriction. Conventionally, a nanocrystalline alloy is known. In general, a nanocrystalline alloy has uniform and ultrafine crystal grains (for example, a particle size of about 10 nm), and the main phase is a bcc structure FeSi crystal with an amorphous phase remaining around it. (Hitachi Metals Co., Ltd., Finemet (registered trademark) microstructure, [Search April 18, 2018], Internet <URL: http://www.hitachi-metals.co.jp/product/finemet/fp04 .htm>). For example, Japanese Patent Application Laid-Open No. 2004-349585 discloses that such a nanocrystalline alloy is obtained as a powder by a water atomization method. JP-A-2016-25352 and JP-A-2017-110256 disclose that a nanocrystalline alloy powder is produced by a gas atomizing method and a high-speed rotating water atomizing method.

The magnetic core used for the coil component is required to maintain the initial value of the inductance of the magnetic core excited by the alternating current superimposed with the direct current up to a high current value and suppress the decrease thereof, that is, to have excellent superposition characteristics.

A nanocrystalline alloy has a structure in which grains of FeSi crystals in a randomly oriented ferromagnetic phase are dispersed, and the crystal grain size is smaller than the magnetic correlation length (approximately the domain wall width, several tens of nanometers), and apparently The crystal magnetic anisotropy is in a state close to zero and has a characteristic of high sensitivity to an external magnetic field. A magnetic core using such a nanocrystalline alloy has high permeability and can reduce loss, but on the other hand, the maximum current value that can be used as a coil component is small, and improvement of the DC superposition characteristics has been demanded. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic core powder that can improve the DC superposition characteristics when used as a magnetic core, and a magnetic core and a coil component using the magnetic core powder.

One aspect of the present invention is a soft magnetic material comprising a first Fe-based alloy particle having a region in which a nano-sized FeSi crystal forms a columnar structure, and a metal structure different from the first Fe-based alloy particle And a magnetic core powder.

In the magnetic core powder, the first Fe-based alloy particles preferably include a plurality of regions in which the extension direction of the FeSi crystal is different in a region having a columnar structure.

The magnetic core powder preferably further includes particles of a second Fe-based alloy having a region in which nano-sized FeSi crystals form a granular structure.

In the X-ray diffraction spectrum measured using the Kα characteristic X-ray of Cu in the magnetic core powder, the bcc near 2θ = 56.5 ° with respect to the peak intensity P1 of the diffraction peak of the bcc structure FeSi crystal near 2θ = 45 ° The peak intensity ratio (P2 / P1) of the peak intensity P2 of the diffraction peak of the Fe ₂ B crystal having the structure is preferably 0.05 or less.

In the powder for magnetic core, the coercive force at an applied magnetic field of 40 μkA / m is preferably 350 μA / m or less.

In the magnetic core powder, the particles of the first Fe-based alloy have an alloy composition: Fe _100-abcdefgh Cu _a Si _b B _c M _d Cr _e Sn _f Ag _g C _h (where a, b, c, d , E, f, g and h represent atomic%, 0.8 ≦ a ≦ 2.0, 2.0 ≦ b ≦ 12.0, 11.0 ≦ c ≦ 17.0, 0 ≦ d ≦ 1.0, 0 ≦ e ≦ 2.0, 0 ≦ f ≦ 1.5, (0 ≦ g ≦ 0.2, 0 ≦ h ≦ 0.4, and M is one or more elements selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta, and Mo.) It is preferable to have.

Another embodiment of the present invention is a magnetic core formed by combining the magnetic core powder with a binder.

Still another aspect of the present invention is a coil component including the magnetic core and the coil.

The magnetic core powder of the present invention can improve DC superposition characteristics when used as a magnetic core. Moreover, the magnetic core and coil components using this magnetic core powder can be provided.

It is a schematic diagram for demonstrating the structure | tissue structure of the particle | grains contained in the powder for magnetic cores based on one Example of this invention. FIG. 2 is a schematic diagram for explaining the structure of a linear FeSi crystal in the structure of FIG. 2 is a graph showing the particle size distribution of magnetic core powders (Nos. 1 and 2) according to one example of the present invention and magnetic core powders (No. * 3) of reference examples. 2 is a graph showing X-ray diffraction spectra of a magnetic core powder (No. 1 and 2) according to an example of the present invention and a magnetic core powder (No. * 3) of a reference example. 3 is a TEM photograph of a cross section of a particle having a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention. 4 is a TEM photograph of another visual field in which a cross section of a particle having a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention is observed. 2 is a Si (silicon) element composition mapping photograph of a cross section of a particle having a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention. 3 is a B (boron) element composition mapping photograph of a cross section of a particle having a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention. 4 is a Cu (copper) element composition mapping photograph of a particle cross section having a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention.

Hereinafter, the magnetic core powder according to one embodiment of the present invention, the magnetic core using the same, and the coil component will be described in detail. However, the present invention is not limited to these. Note that in some or all of the drawings, portions that are not necessary for the description are omitted, and some portions are illustrated in an enlarged or reduced manner for ease of description. Further, the dimensions and shapes shown in the description, the relative positional relationships of the constituent members, and the like are not limited to these unless otherwise specified. Further, in the description, the same name and reference numeral indicate the same or the same members, and the detailed description may be omitted even if illustrated.

[1] Powders for magnetic cores The present invention has been conducted in the study of finding a nanocrystalline alloy having a novel crystal structure and utilizing its characteristics, while the inventors have conducted intensive research on nanocrystalline soft magnetic materials. Is. In order to facilitate understanding of the invention, a nanocrystalline alloy having a novel crystal structure will be described in detail.

(1) Microstructure Conventional nanocrystalline alloys are obtained by crystallizing from an amorphous phase starting from a Cu cluster (Cu-rich region). It has a structure in which grains of FeSi crystal in a ferromagnetic phase oriented in a dispersed manner are dispersed in an amorphous phase. That is, in the conventional nanocrystal alloy, nano-sized FeSi crystals have a granular structure. The grain growth of FeSi crystal occurs in an arbitrary direction, resulting in random precipitation, and does not form a regular precipitation form. Nanocrystals (nanosize crystals) generally mean those having an average crystal grain size of 100 nm or less.

On the other hand, in the nanocrystalline alloy having a novel structure, nano-sized FeSi crystals form a columnar structure. This columnar structure is a structure in which a plurality of linear FeSi crystals arranged substantially along one direction exist in the amorphous phase with a gap. FIG. 1 is a schematic diagram for explaining a state in which nano-sized FeSi crystals form a columnar structure. In the nanocrystalline alloy 100 having this columnar structure, the linear FeSi crystal 200 has a striped structure that appears in parallel lines, and an amorphous phase 250 exists between the linear FeSi crystals 200. It has become.

FIG. 2 is a schematic diagram for explaining the structure of the linear FeSi crystal 200 observed in the structure of FIG. The linear FeSi crystal 200 has a bead shape with a columnar structure and a large number of constrictions. The portion between the constrictions is substantially oval spherical, and a plurality of substantially oval spherical portions are connected to form a columnar shape. The minor axis of the substantially oval spherical part is about 10 nm to 20 nm, and the major axis is a nano size of 20 nm to 40 nm. Although the length of the linear FeSi crystal 200 is various, it is, for example, 200 nm or more, and the length is considered to vary under the influence of the stress distribution in the alloy structure. Hereinafter, this new structure may be referred to as a columnar structure, and the conventional structure may be referred to as a granular structure.

As described above, in the conventional nanocrystal structure having a grain structure FeSi crystal, the apparent crystal magnetic anisotropy is in a state close to zero, and the nanocrystal having such a crystal structure is highly sensitive to an external magnetic field. A magnetic core using an alloy is characterized by high permeability and low loss.

On the other hand, in the columnar structure which is a novel structure, the FeSi crystal is a long columnar structure whose length in the extension direction is longer than the width. The structure having a columnar FeSi crystal exhibits a larger magnetic anisotropy than the conventional structure having a FeSi crystal having a granular structure, and increases the coercive force, decreases the permeability, and reduces the loss. A problem is expected in which the desired soft magnetic characteristics cannot be obtained due to an increase. For these problems, the present inventors make the alloy structure have a plurality of regions in which the extension direction of the FeSi crystal is different, that is, the extension direction of the FeSi crystal is aligned in each region. Although there is regularity, the extension direction of the FeSi crystal is different for each region, the linear FeSi crystal is discontinuous between adjacent regions, and it has a crystal structure that has no regularity in the whole alloy I found that it can be improved.

Also, if the FeSi crystal has a columnar structure, the magnetic moment tends to be oriented in the direction of elongation, and the structure is nano-ordered, leaving high sensitivity to a magnetic field. When the process of rotating the magnetic moment of Fe in the direction of the easy axis of magnetization is illustrated using a spring connected to the easy axis of magnetization, the magnetic field in the direction of elongation is a balance between the orientation of the linear FeSi crystal and the sensitivity to the magnetic field. The magnetic moment rotates to be parallel to the magnetic field with respect to the perpendicular magnetic field, but the rotation is limited by the spring, and when the magnetic field is removed, the magnetic moment quickly moves in the direction of the easy axis. It seems to be suitable. According to the characteristics that the response of the magnetic moment to the magnetic field is linear and the sensitivity to the magnetic field continues to a high magnetic field, the magnetic core using the nanocrystalline alloy having the columnar structure FeSi crystal has a large saturation magnetization due to the FeSi crystal. It is considered that a high incremental permeability μΔ can be maintained up to a large current (high magnetic field).

(2) Powder for magnetic core Based on such knowledge, the present inventors have further studied, nanocrystalline alloy powder having a novel columnar structure, and nanocrystalline alloy further having a conventional granular structure By using mixed powders with other powders and / or powders of other soft magnetic materials, each magnetic characteristic can be used and complemented, and when used as a magnetic core, increase in core loss and decrease in magnetic permeability It was found that a magnetic core powder with improved superposition characteristics can be obtained while suppressing.

The mechanism of the appearance of the columnar structure in the nanocrystalline alloy is not clear, but the FeSi crystal in the columnar structure precipitates the FeSi crystal starting from the Cu cluster from the amorphous phase in the same way as the FeSi crystal in the conventional granular structure. (Crystallized). In previous studies, the conventional FeSi crystal with a granular structure is formed from an amorphous phase by heat treatment, but the FeSi crystal with a columnar structure is formed in the cooling process in which the molten metal is cooled and alloyed. This is different from conventional nanocrystal structure formation.

In the formation of the columnar structure, the cooling rate at the time of alloy preparation and the distribution of the cooling rate in the alloy (rate gradient between the surface part of the alloy particle and the central part) are important and vary depending on the alloy composition. In order to achieve this, for example, the molten metal can be cooled at a rate of about 10 ³ ° C / second or more, and (sub-μm) ³ to (several μm) ³ in volume units in the course of cooling. It is required to produce regions with different stress distributions inside the alloy. In particular, it is considered that the cooling rate near 500 ° C. in the cooling process of the molten metal has an effect.

In the production of a nanocrystalline alloy powder having a columnar-structured FeSi crystal, the production method and conditions are not limited as long as the above-described requirements can be satisfied. For example, the conventional method used to produce nanocrystalline alloy powders with FeSi crystals of granular structure, such as gas atomization method, water atomization method, high-speed rotating water atomization method, etc., which uses water and gas as a means for grinding molten metal Alternatively, it may be pulverized by an atomizing method such as a high-speed combustion flame atomizing method in which a flame is injected as a flame jet at a supersonic speed or a speed close to the sonic speed.

According to the study by the present inventors, it has been found that the high-speed combustion flame atomization method is particularly suitable for producing nanocrystalline alloy particles having a columnar structure. Although the high-speed combustion flame atomization method is not as common as other atomization methods, it is described in, for example, JP-A-2014-136807. In the high-speed combustion flame atomizing method, the molten metal is powdered by a high-speed combustion flame by a high-speed combustor, and is cooled by a rapid cooling mechanism having a plurality of cooling nozzles capable of injecting a cooling medium such as liquid nitrogen and liquefied carbon dioxide.

It is known that the particles obtained by the atomization method are nearly spherical, and the cooling rate greatly depends on the particle size. When molten metal pulverized in a liquid or gas (for example, water, He or water vapor) having a higher heat exchange efficiency than the atmosphere passes at high speed, the surface is cooled at a high cooling rate. When heat is efficiently removed from the surface, the inside is also cooled according to heat conduction, but the cooling rate varies, and a volume difference occurs between the surface layer portion that hardens first and the central portion that hardens later. As the alloy particles obtained have a relatively large diameter, the variation in cooling rate becomes more prominent.

According to the above-described high-speed combustion flame atomization method, in the initial stage of the cooling process, the crushed molten metal is rapidly cooled to become an alloy in a supercooled glass state, and cooling is performed for self-relaxation of strain due to volume difference. In the particles of the process, regions having different stress distributions in volume units having a size of (sub-μm) ³ to (several μm) ³ are generated. And each area | region is considered to be in the state which received the stress mutually by the restraining force from the surrounding area | region. In addition, when the crystal phase and the amorphous phase are separated during the cooling process, the precipitation of FeSi crystal starting from the Cu cluster starts from the amorphous phase in the state where the stress is applied. Due to the effect of creep behavior accompanied by atomic movement of the mass phase, the edge of the FeSi crystal caused the next crystal grain formation, the crystal grain growth progressed in the stress direction, and the lattice was continuously connected at the atomic level. It is thought that crystal grain growth occurs in a bead shape.

Further, according to the study by the present inventors, it has been found that the columnar structure particles and the granular structure particles can be simultaneously produced by the high-speed combustion flame atomization method. In the high-speed combustion flame atomization method, the particle size is typically 10 μm or less, and the same composition has been observed to tend to have a higher cooling rate than the ribbon produced by the single roll method. When the cooling rate during pulverization is high, the cooling rate distribution in the grains is suppressed, and the strain and pressure distributions are also reduced. Therefore, the structure of the resulting particles becomes a substantially amorphous phase and FeSi with a columnar structure. Crystals are difficult to obtain. When it is heat-treated like a conventional nanocrystalline alloy, its structure becomes a granular structure of FeSi crystals as in the conventional case.

When the particle size exceeds 10 μm, typically about 20 μm, the difference in cooling rate between the inside and outside increases, and strain resulting from the time difference in volume change during cooling accumulates. However, a FeSi crystal having a columnar structure is likely to precipitate from the relatively slow inside.

Based on such knowledge, a nanocrystalline alloy having columnar FeSi crystals, even if it is a powder containing particles having a particle size of 10 to 20 μm, even if it is a powder obtained by a single atomization treatment, is used. It is possible to obtain a powder containing the powder and a powder of a nanocrystalline alloy having FeSi crystals with a granular structure. Moreover, if it is classified, it is possible to vary the ratio of the nanocrystalline alloy powder having a columnar structure and the nanocrystalline alloy powder having a granular structure.

The nanocrystalline alloy having a columnar-structured FeSi crystal may partially contain a crystal phase other than the FeSi crystal as long as the magnetic core powder satisfies the required magnetic properties. Examples of the crystal phase other than the FeSi crystal include an Fe ₂ B crystal that has a high magnetocrystalline anisotropy and is considered to be a phase that deteriorates soft magnetic properties. For example, if the peak intensity ratio (P2 / P1) of the peak intensity P2 of the diffraction peak of the bcc structure Fe ₂ B crystal with respect to the peak intensity P1 of the diffraction peak of the bcc structure FeSi crystal described later is defined, the peak intensity ratio (P2 / P1) is preferably 0.05 or less. In order to obtain a crystalline magnetic core powder with excellent magnetic properties, the peak intensity ratio (P2 / P1) is preferably 0.03 or less, and the peak intensity P2 is substantially 0 (zero) below the measured noise level. Is desirable.

The powder for magnetic core of the present invention may be prepared by mixing a nanocrystalline alloy powder having a granular structure and / or a powder of another soft magnetic material prepared in advance with a nanocrystalline alloy powder having a columnar structure, and may be crystallized. A powder obtained by mixing a powder that later becomes a nanocrystalline alloy having a granular structure and a nanocrystalline alloy powder having a columnar structure may be heat-treated for crystallization. Here, the heat treatment for crystallization is performed to obtain a nanocrystalline alloy having a granular structure.

(3) Heat treatment When heat treating a powder that becomes a nanocrystalline alloy with a grain structure after crystallization and a powder of a nanocrystalline alloy with a columnar structure, the furnace used for the heat treatment can control the temperature to around 600 ° C. Any heating furnace can be used without any particular problem. For example, a batch type electric furnace or a mesh belt type continuous electric furnace can be used. In order to prevent oxidation, it is preferable that the atmosphere can be adjusted.

The heat treatment conditions in such a heat treatment may be an appropriate setting that does not increase the crystal phase that deteriorates the soft magnetic properties, such as Fe ₂ B crystals other than FeSi crystals, in the nanocrystalline alloy having a columnar structure. The heat treatment temperature can be appropriately set based on the crystallization start temperature of the nanocrystalline alloy that becomes a granular structure. The crystallization start temperature is determined by thermal analysis of the powder at a temperature increase rate of 600 ° C / hr in a temperature range from room temperature (RT) to 600 ° C using a differential scanning calorimeter (DSC). Can be measured. The heat treatment temperature is 350 to 450 ° C., preferably 390 to 430 ° C., although it depends on the crystallization temperature of the nanocrystalline alloy that forms the granular structure. The heat treatment temperature is the maximum temperature reached after the temperature rise, and is also the holding temperature when the temperature is held for a predetermined time.

The heat treatment time is preferably 1 to 3 hours, preferably 1 to 300 seconds for a continuous furnace, and 300 to 2 hours (7200 seconds) for a batch furnace. The heat treatment time is a time that is maintained at the heat treatment temperature.

Average heating rate (average heating rate until reaching the target heat treatment temperature) in the temperature range of 300 ° C or higher in heat treatment is 0.001 to 1000 ° C / second, preferably 0.5 to 500 ° C / second in a continuous furnace In the case of a batch furnace, it is desirable to be in the range of 0.006 to 0.08 ° C./sec. When the rate of temperature rise is in the above range, excessive temperature rise due to self-heating caused by crystallization of the alloy is prevented, and overshooting with respect to the heat treatment temperature setting is suppressed, and the magnetic properties of the resulting powder are reduced. It is possible to prevent deterioration of characteristics.

(4) Alloy composition The composition of the nanocrystalline alloy may be any as long as it can form a columnar structure of FeSi crystals and contains Si, B, and Cu. Although the alloy composition suitable for obtaining the columnar structure | tissue nanocrystal alloy by the atomizing method is illustrated below, it is not limited to it. The particle size distribution of the magnetic core powder obtained by the atomization method may be an alloy composition in which particles having a large particle diameter become FeSi crystals having a columnar structure and particles having a small particle diameter become FeSi crystals having a granular structure.

The composition of the nanocrystalline alloy is Fe _100-abcdefgh Cu _a Si _b B _c M _d Cr _e Sn _f Ag _g _Ch (where a, b, c, d, e, f, g and h represent atomic%) 0.8 ≦ a ≦ 2.0, 2.0 ≦ b ≦ 12.0, 11.0 ≦ c ≦ 17.0, 0 ≦ d ≦ 1.0, 0 ≦ e ≦ 2.0, 0 ≦ f ≦ 1.5, 0 ≦ g ≦ 0.2, and 0 ≦ h ≦ 0.4 And M is preferably one or more elements selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta, and Mo.

Cu is an element that refines the alloy structure after crystallization and contributes to the formation of columnar FeSi crystals. It is also an element that contributes to the formation of a granular structure. The Cu content is preferably 0.8% or more and 2.0% or less in atomic%. If the Cu content is low, the effect of addition cannot be obtained, while if it is high, the saturation magnetic flux density decreases. When Cu is excessive, crystallization in the cooling process proceeds too much, so the residual amorphous phase that has the effect of suppressing crystal grain growth is deficient, and Fe ₂ B has high crystal grain coarsening and high magnetic anisotropy. Precipitation is likely to occur, and soft magnetic properties may be deteriorated. In the atomization cooling process, the Cu content is more preferably 1.0% or more, further preferably 1.1% or more, and most preferably 1.2% or more so as to provide a sufficient number density of Cu clusters. Further, the Cu content is more preferably 1.8% or less, and further preferably 1.5% or less.

Si dissolves in Fe, which is the main component of FeSi crystals, and contributes to the reduction of magnetostriction and magnetic anisotropy. The Si content is preferably 2.0% or more and 12.0% or less in atomic%. In addition, it is known to have an effect of promoting the amorphization of the nanocrystalline alloy, and in the cooling process, it has an effect of enhancing the amorphous forming ability by being present together with B. Moreover, it has the effect of suppressing coarse crystal grain precipitation in the cooling process. If the Si content is low, the effect of addition cannot be obtained. On the other hand, if the Si content is too high, the saturation magnetic flux density decreases. On the other hand, since the ordered arrangement of Fe ₃ Si tends to occur, the lower limit of the Si content is more preferably 3.0%. In order to obtain a high saturation magnetic flux density, the Si content is more preferably 10.0% or less, further preferably 8.0% or less, and most preferably 5.0% or less.

B is known to have the effect of promoting the amorphization of the alloy during rapid cooling. The B content is preferably 11.0% or more and 17.0% or less in atomic%. If the B content is low, an extremely high cooling rate is required for the formation of the amorphous phase, and relatively coarse crystal grains on the order of micrometers are likely to precipitate, and good soft magnetic properties may not be obtained. . In addition, if the B content is large, the volume fraction of the residual amorphous phase in the structure after crystallization increases, leading to a decrease in magnetic properties such as saturation magnetization. Since the Fe content can be increased as the total content of Si and B decreases, the total content of Si and B is preferably 20.0% or less, and 19.0% or less in order to obtain a high saturation magnetic flux density. More preferably, it is 18.0% or less.

M is one or more elements selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta and Mo. When heat treating a powder that becomes a nanocrystalline alloy of a granular structure after crystallization and a powder of a nanocrystalline alloy of a columnar structure, it is not essential for obtaining a FeSi crystal having a columnar structure or a granular structure. It is effective for uniformizing the grain size of FeSi crystals with a granular structure, and the content of M element is preferably 1.0% or less (including 0) in atomic%, and 0.8% or less (including 0). More preferably, it is 0.5% or less (including 0).

Cr is preferably 2.0% or less (including 0) in atomic%. Although not essential for obtaining a columnar-structured FeSi crystal, it is an effective element for improving the corrosion resistance of a nanocrystalline alloy. When producing the powder by the atomization method, the Cr content is preferably 0.1% or more, and more preferably 0.3% or more, in order to obtain the effect of preventing the inside from being oxidized. On the other hand, since it behaves antiferromagnetically as a single substance and weakens the ferromagnetism of Fe by being mixed with Fe atoms, leading to a decrease in saturation magnetic flux density, the upper limit of Cr content is more preferably 1.5%. 1.1% is most preferred.

Sn is preferably 1.5% or less (including 0) in atomic percent. Although it is not essential for obtaining a FeSi crystal having a columnar structure, it is an effective element for assisting Cu cluster formation. When added in a small amount, Sn atoms first gather during the crystallization process, and Cu atoms that are diffusing gather around it to lower the potential energy and form clusters. Considering the effect of being an auxiliary agent for forming Cu clusters, it is preferable that the upper limit of the Sn content does not exceed the Cu content. Further, since it is a nonmagnetic element, the Sn content is more preferably 0.5% or less (including 0). The lower limit of the Sn content is more preferably 0.01%, and most preferably 0.05%.

Ag is not essential for obtaining FeSi crystals with a columnar structure, but Ag is separated from the molten metal and precipitated from the initial solidification stage of the nanocrystalline alloy after atomization, so that it becomes the nucleus of Cu clusters in the early stage of heat treatment. Function. A preferable content of Ag is 0.2% or less (including 0) in atomic%.

C is not essential for obtaining FeSi crystals having a columnar structure, but C acts to stabilize the viscosity of the molten metal, and its preferred content is 0.4% or less (including 0) in atomic%.

In addition, S, O, N, etc. may be included as inevitable impurities contained in the nanocrystalline alloy. The contents of inevitable impurities are preferably such that S is 200 ppm or less, O is 5000 ppm or less, and N is 1000 ppm or less.

Fe is a main element constituting a nanocrystalline alloy and affects magnetic properties such as saturation magnetization. Although depending on the balance with other non-ferrous metals, it is preferable to contain 77.0% or more of Fe in atomic%, whereby a nanocrystalline alloy having a large saturation magnetization can be obtained. The Fe content is more preferably 77.5% or more, further preferably 78.0% or more, and most preferably 79.0% or more.

In addition, although the composition suitable for obtaining the nanocrystal alloy which has FeSi crystal of columnar structure was shown above, the conventional nanocrystal alloy which has FeSi crystal of granular structure with the alloy composition can also be obtained.

[2] Magnetic Core and Coil Parts The magnetic core powder of one embodiment of the present invention is suitable for a dust core or a metal composite. In the dust core, for example, the magnetic core powder is mixed with an insulating material and a binder that functions as a binder. Examples of the binder include, but are not limited to, an epoxy resin, an unsaturated polyester resin, a phenol resin, a xylene resin, a diallyl phthalate resin, a silicone resin, a polyamideimide, a polyimide, and water glass. The mixture of powder for magnetic core and binder is mixed with a lubricant such as zinc stearate if necessary, then filled in a molding die, and with a molding pressure of about 10 MPa to 2 GPa using a hydraulic press molding machine. It can be pressed to form a green compact of a predetermined shape. Next, the green compact after molding is heat-treated at a temperature of 300 ° C. to less than the crystallization temperature for about 1 hour to remove molding distortion and cure the binder to obtain a dust core. The heat treatment atmosphere in this case may be an inert atmosphere or an oxidizing atmosphere. The obtained powder magnetic core may be in an annular shape or an annular shape such as a rectangular frame shape, or may be in the shape of a rod or a plate, and the form may be variously selected according to the purpose. it can.

When used as a metal composite material, the coil may be buried in a mixture containing a magnetic core powder and a binder and integrally molded. For example, if a thermoplastic resin or a thermosetting resin is appropriately selected as the binder, a metal composite core (coil component) in which a coil is easily sealed by a known molding means such as injection molding can be obtained. A mixture containing the magnetic core powder and the binder may be formed into a sheet-like magnetic core by a known sheet forming means such as a doctor blade method. Moreover, you may use the mixture containing the powder for magnetic cores and a binder as an irregular-shaped shielding material.

Further, in the magnetic core powder of one embodiment of the present invention, the Fe-based amorphous alloy, the pure crystalline iron, Fe-Si, and Fe-Si-Cr crystalline materials are added to the nanocrystalline alloy powder in which the FeSi crystal forms a columnar structure. Other soft magnetic powders such as metallic soft magnetic material powders may be added.

In any case, the obtained magnetic core has excellent DC characteristics with improved DC superposition characteristics, and is suitably used for inductors, noise filters, choke coils, transformers, reactors, and the like.

[3] Examples Hereinafter, the powder for a magnetic core according to an embodiment of the present invention, and a magnetic core and a coil component using the powder will be described in detail, but the present invention is not limited to this, and technical It can be appropriately changed within the scope of the idea.

After atomization of Fe, Cu, Si, B, Nb, Cr, Sn, and C, weigh them so that they have the alloy composition of composition A and composition B shown below, put them in an alumina crucible, It was placed in a vacuum chamber and evacuated, and then dissolved by high-frequency induction heating in an inert atmosphere (Ar) under reduced pressure. Thereafter, the molten metal was cooled to produce two kinds of master alloy ingots.

[Alloy composition]
Composition A: Fe _bal. Cu _1.2 Si _4.0 B _15.5 Cr _1.0 Sn _0.2 C _0.2
Composition B: Fe _bal. Cu _1.0 Si _13.5 B _11.0 Nb _3.0 Cr _1.0

Next, the obtained ingot was redissolved, and the molten metal was pulverized by a high-speed combustion flame atomization method. The atomizing device used is capable of injecting a frame jet toward a container for storing molten metal, a pouring nozzle provided at the center of the bottom of the container and communicating with the inside of the container, and toward the molten metal flowing downward from the pouring nozzle. A jet burner (manufactured by Hard Industry Co., Ltd.) and a cooling means for cooling the crushed molten metal are provided. The flame jet is configured to pulverize molten metal to form molten metal powder, and each jet burner is configured to inject a flame as a flame jet at a supersonic speed or a speed close to the sonic speed. The cooling means has a plurality of cooling nozzles configured to be able to inject a cooling medium toward the crushed molten metal. As the cooling medium, water, liquid nitrogen, liquefied carbon dioxide, or the like can be used.

The temperature of the flame jet to be injected was 1300 ° C, and the dripping speed of the molten metal as a raw material was 5 kg / min. Water was used as a cooling medium, and a liquid mist was sprayed from the cooling nozzle. The cooling rate of the molten metal was adjusted from 4.5 liters / min to 7.5 liters / min.

The obtained powders of composition A and composition B were classified with a centrifugal airflow classifier (TC-15 manufactured by Nissin Engineering Co., Ltd.), and two types with different average particle diameters d50 of composition A (the larger d50 was No. .1, the smaller one was No. 2 powder), and one powder of composition B (No. * 3 powder) was obtained. The particle size of the obtained magnetic core powder was measured by the following evaluation method.

[Powder particle size]
From a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution analyzer (Horiba LA-920), the cumulative percentage from the small diameter side is 10% by volume, 50% by volume and D10, d50 and d90 having a particle size of 90% by volume were obtained. Fig. 3 shows the particle size distribution of No. 1 to * 3 powders.

For each obtained powder, saturation magnetization, coercive force, and diffraction spectrum by X-ray diffraction method were measured by the following evaluation methods.

[Saturation magnetization and coercivity]
The sample powder is put in a container, and magnetization measurement is performed with a VSM (Vibrating Sample Magnetometer, VSM-5 manufactured by Toei Industry Co., Ltd.). From the hysteresis loop, the magnetic strength is Hm = 800 kA / m. Saturation magnetization and coercivity under the condition of Hm = 40 kA / m.

[Diffraction spectrum]
Using an X-ray diffractometer (Rigaku RINT-2000, manufactured by Rigaku Corporation), the diffraction peak of the bcc structure FeSi crystal around 2θ = 45 ° (between 44 ° and 46 °) from the diffraction spectrum by the X-ray diffraction method The peak intensity P1 and the peak intensity P2 of the diffraction peak of the bcc structure Fe ₂ B crystal near 2θ = 56.5 ° (between 56 ° and 57 °) were obtained, and the peak intensity ratio (P2 / P1) was calculated. The X-ray diffraction intensity measurement conditions were X-ray Cu-Kα, applied voltage 40 kV, current 100 mA, divergence slit 1 °, scattering slit 1 °, light-receiving slit 0.3 mm, scanning continuously, scanning speed 2 ° / min. The scanning step was 0.02 ° and the scanning range was 20 to 60 °.

The results obtained are shown in Table 1. In Table 1, samples with “*” assigned to No. are reference examples.

As a result of confirming the diffraction spectrum by the X-ray diffraction method, the diffraction peak of the bcc structure FeSi crystal and the bcc structure are found in two types of magnetic core powders (No.1 and No.2 powders) with different average particle sizes of the A composition. The diffraction peak of the Fe ₂ B crystal was confirmed, but only one halo pattern was observed for one type of magnetic core powder (No. * 3 powder) of B composition, and the diffraction peak of the FeSi crystal and Fe ₂ B crystal was It was not confirmed. In addition, a TEM observation confirmed a striped structure in which linear FeSi crystals continued at intervals in the two types of powders of A composition. This structure was also observed in the powder after heat treatment described later.

Next, in an electric heat treatment furnace capable of adjusting the atmosphere, three types of No. 1 to * 3 magnetic core powders in 100 g in a SUS container were heat-treated in an N ₂ atmosphere with an oxygen concentration of 0.5% or less. The heat treatment was performed at a rate of 0.006 ° C./second, reaching the holding temperature shown in Table 2, and holding at this holding temperature for 1 hour, and then heating was stopped and the furnace was cooled.

Saturation magnetization, coercive force, and diffraction spectrum by X-ray diffraction method were measured on the No. 1 to * 3 powders after heat treatment by the same evaluation method as described above. The results obtained are shown in Table 2.

In addition, a plurality of particles having a particle size corresponding to d10 and d90 are selected from the No. 1 to * 3 powders after heat treatment, embedded in resin, cut and polished, and then the cross section is subjected to a transmission electron microscope (TEM / EDX: Observation with Transmission (Electron) Microscope / energy (dispersive) (X-ray (spectroscopy)). FIG. 5 is a TEM photograph obtained by observing a cross section of a No. 1 d90-equivalent particle after polishing. FIG. 6 is a TEM photograph of another field of view observed under the same conditions. FIG. 7 is a photograph obtained by observing another field of view of the cross section of the No. 1 d90 equivalent particle and composition mapping with Si (silicon) element, FIG. 8 is a photograph mapping composition with B (boron) element, FIG. 9 is a photograph of composition mapping with Cu (copper) element.

From FIG. 5, a columnar structure (stripe pattern structure) in which the shades appear alternately in parallel lines in the observation field was confirmed. By spot diffraction measurement and composition mapping by TEM, it was determined that a dark portion with a low brightness observed in a linear shape is an FeSi crystal and a light portion with a high brightness is an amorphous phase. In addition, from FIG. 6 in another field of view, a region with a striped pattern, a region where a dark portion with low brightness appears to be a dot-like structure, and the like were observed. In any region, the dark part with low brightness was FeSi crystal, and the light part with high brightness was amorphous phase. Observation in more detail revealed that FeSi crystals were linearly formed in any region and looked like stripes or dots in the direction of appearance on the observation surface. That is, each grain has a region in which the FeSi crystal group extends in different directions, and in each region, the FeSi crystal has a columnar structure in which crystals are precipitated in almost one direction. In this single region, the linear FeSi crystal has a uniform elongation direction, but the FeSi crystal has a different elongation direction in each region, and the linear FeSi crystal becomes discontinuous between adjacent regions. As a whole, the particles had a regular structure.

In element distribution mapping, the brighter the color, the greater the number of target elements. From the results shown in FIGS. 7, 8, and 9 in which Si, B, and Cu are respectively compositionally mapped in the same field of view, the region corresponding to the linear FeSi crystal is enriched with Si and Cu, and the linear FeSi crystal. It is confirmed that B is concentrated in the region corresponding to the amorphous phase. Fe (not shown) was confirmed as a whole, but it was confirmed that the concentration was high in a region where Si and Cu were concentrated.

By spinodal decomposition of the linear FeSi crystal and the amorphous phase, Fe and Si are used to form the FeSi crystal, and B that does not easily enter the crystalline phase is concentrated into the amorphous phase. It is considered that phase separation proceeds so that the concentration becomes relatively high, and a periodic concentration modulation structure appears.

In the No. 2 powder, in the observation of a plurality of particles having a particle size corresponding to d90, a striped columnar structure region similar to the structure observed in FIGS. 5 and 6 was observed. In the powder No. 3, the region of the striped columnar structure was not observed, and the conventional structure was a granular structure in which FeSi crystal grains having a particle diameter of about 30 nm were dispersed in the amorphous phase.

In the observation of a plurality of particles having a particle size corresponding to d10 of No. 1 to * 3 powder after heat treatment, all had a granular structure which is a conventional structure. That is, it can be seen that the magnetic core powders No. 1 and No. 2 are powders in which a nanocrystalline alloy powder having a granular structure and a nanocrystalline alloy powder having a columnar structure are mixed. On the other hand, the No. * 3 powder in the reference example does not have a nanocrystalline alloy powder having a columnar structure, but is a nanocrystalline alloy powder having a conventional granular structure.

In the nanocrystalline alloy particles having a columnar structure, Fe ₂ B crystals are easily formed in the amorphous phase. In addition, since the peak of Fe ₂ B crystal develops more strongly as the proportion of particles containing Fe ₂ B crystal in the powder increases, the relative proportion of the proportion of particles having a columnar structure structure should be evaluated relatively from the peak intensity. Can do. In the diffraction spectrum diagram shown in FIG. 4, the FeSi crystal peak and the Fe ₂ B crystal peak were confirmed in both No. 1 and No. 2 powders of the alloy composition A (after heat treatment). In the alloy composition B No. * 3 powder (after heat treatment), the FeSi crystal peak was confirmed, but the Fe ₂ B crystal peak was not confirmed. The ratio P2 / P1 of the peak intensity P2 of the Fe ₂ B crystal to the peak intensity P1 of the FeSi crystal was smaller in the No. 2 powder having a small particle size distribution as a whole. Also, the coercive force of the No. 2 powder was smaller.

Add 100 parts each of No. 1 to * 3 powder after heat treatment to 5 parts of silicone resin, knead them, fill them into a molding die, and mold them with a hydraulic press molding machine under 400 MPa. An annular magnetic core of φ13.5 mm × φ7.7 mm × t2.0 mm was prepared. The produced magnetic core was evaluated for space factor, core loss, initial permeability, and incremental permeability. The results are shown in Table 3. In Table 3 as well, samples using the magnetic core powder of the reference example are distinguished by adding * to No.

[Space factor (Relative density)]
The annular magnetic core evaluated for magnetic measurement was heat-treated at 250 ° C., and the binder was decomposed to obtain a powder. Calculate the density (kg / m ³ ) by the volume weight method from the weight of the powder and the size and mass of the annular magnetic core, and divide by the true density of the powder of each alloy composition A and B obtained from the gas replacement method. The space factor (relative density) (%) of the magnetic core was calculated.

[Magnetic core loss]
Using an annular magnetic core as an object to be measured, each of the primary side winding and the secondary side winding was wound 18 turns, and the maximum magnetic flux density was 30 mT and the frequency was 2 MHz using BH analyzer SY-8218 manufactured by Iwatatsu Measurement Co., Ltd. Under these conditions, the core loss (kW / m ³ ) was measured at room temperature (25 ° C.).

[Initial permeability μi]
Using an annular magnetic core as the object to be measured, winding the lead wire for 30 turns to form a coil component, and using an LCR meter (Agilent Technology Co., Ltd. 4284A), the inductance was measured at room temperature and at a frequency of 100 kHz. . The value obtained under the condition that the AC magnetic field was 0.4 A / m was defined as the initial permeability μi.
Initial permeability μi ＝ (le × L) / (μ ₀ × Ae × N ² )
(le: magnetic path length, L: sample inductance (H), μ ₀ : vacuum permeability = 4π × 10 ⁻⁷ (H / m), Ae: cross-sectional area of magnetic core, and N: number of turns of coil)

[Incremental permeability μΔ]
LCR meter (Agilent Technology Co., Ltd. 4284A) with a DC magnetic field of 10 kA / m applied with a DC application device (42841A: Hewlett Packard) using the coil components used for initial permeability measurement ), And the inductance L was measured at a frequency of 100 kHz at room temperature (25 ° C.). The result obtained from the obtained inductance by the same calculation formula as the initial permeability μi was defined as the incremental permeability μΔ. The ratio μΔ / μi (%) was calculated from the obtained incremental permeability μΔ and initial permeability μi.

The magnetic cores using the No. 1 and No. 2 magnetic core powders of the present invention had a sufficiently small change in permeability regardless of the current change, and were able to exhibit stable DC superposition characteristics at a substantially constant value. In addition, the magnetic core using the No. 2 magnetic core powder having a small peak intensity ratio P2 / P1 has a small magnetic core loss and a high initial permeability. If the magnetic permeability is low, it is necessary to increase the cross-sectional area of the magnetic core and increase the number of turns of the winding in order to obtain the required inductance, and as a result, the outer shape of the coil component becomes large. Therefore, it can be seen that the No. 2 powder is more advantageous in reducing the size of the coil component.

Claims

A magnetic core comprising a first Fe-based alloy particle having a region in which a nano-sized FeSi crystal forms a columnar structure, and a soft magnetic material particle having a metal structure different from the first Fe-based alloy particle Powder.
In the powder for magnetic core according to claim 1,
The first Fe-based alloy particle is a magnetic core powder having a plurality of regions in which the extension direction of the FeSi crystal is different in the columnar structure.
In the magnetic core powder according to claim 1 or 2,
A magnetic core powder further comprising particles of a second Fe-based alloy having a region in which nano-sized FeSi crystals form a granular structure.
The magnetic core powder according to any one of claims 1 to 3,
In the X-ray diffraction spectrum measured using Cu Kα characteristic X-ray, the peak intensity P1 of the diffraction peak of bcc structure FeSi crystal near 2θ = 45 ° is compared with the peak intensity P1 of bcc structure Fe 2 B crystal near 2θ = 56.5 °. A magnetic core powder having a peak intensity ratio (P2 / P1) of a peak intensity P2 of a diffraction peak of 0.05 or less.
In the magnetic core powder according to any one of claims 1 to 4,
Magnetic core powder having a coercive force of 350 A / m or less at an applied magnetic field of 40 kA / m.
In the magnetic core powder according to any one of claims 1 to 5,
The particles of the first Fe-based alloy are
Alloy composition: Fe 100-abcdefgh Cu a Si b B c M d Cr e Sn f Ag g C h (where a, b, c, d, e, f, g and h represent atomic%, 0.8 ≦ a ≦ 2.0, 2.0 ≦ b ≦ 12.0, 11.0 ≦ c ≦ 17.0, 0 ≦ d ≦ 1.0, 0 ≦ e ≦ 2.0, 0 ≦ f ≦ 1.5, 0 ≦ g ≦ 0.2, and 0 ≦ h ≦ 0.4 , M is one or more elements selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta, and Mo.).
A magnetic core obtained by binding the magnetic core powder according to any one of claims 1 to 6 with a binder.
A coil component comprising the magnetic core according to claim 7 and a coil.