JP7236622B2 - Particles of nanocrystalline alloy. - Google Patents

Description

TECHNICAL FIELD The present invention relates to magnetic core powder suitable for transformers, choke coils, reactors and the like used in switching power supplies and the like, and to magnetic cores and coil parts using the same.

Switching power supplies are used in EV (electric vehicles), HEV (hybrid vehicles), PHEV (plug-in hybrid vehicles), mobile communication devices (mobile phones, smartphones, etc.), personal computers, servers, and various other electronic devices that require power supply. They are used in the power supply circuits of equipment, and along with being smaller and lighter, there is a growing demand for low power consumption from the standpoint of energy conservation.

In addition, along with the high integration of transistors due to the finer wiring of LSIs (Large Scale Integrated Circuits) used in electronic devices, the breakdown voltage of transistors has decreased and the current consumption has increased, resulting in lower operating voltages and higher operating voltages. Electrification is progressing. Along with this, power supply circuits such as DC-DC converters that supply power to LSIs also need to cope with lower operating voltages and larger currents of LSIs. For example, lowering the operating voltage of an LSI narrows the voltage range in which it can operate normally. Therefore, measures to increase the switching frequency of the power supply circuit have been taken.

Fe-based amorphous alloys, nanocrystalline alloys, and pure Fe-based amorphous alloys, nanocrystalline alloys, and pure alloys that operate at high excitation flux densities in the high-frequency range and are suitable for miniaturization are used for the magnetic cores used in coil components for high-frequency and high-current power supply circuits. Powders of metallic soft magnetic materials such as iron, Fe--Si, and Fe--Si--Cr are often used. As the powder of the soft magnetic material, a granular powder obtained by an atomization method is preferably used because the shape anisotropy of the magnetic properties hardly occurs when the magnetic core is formed, and the powder has good fluidity in molding the magnetic core.

Among the metal-based soft magnetic materials, as a soft magnetic material that has a high saturation magnetic flux density, a small coercive force, and is capable of achieving low magnetostriction, it is an Fe-based alloy that contains FeSi crystals with a fine bcc structure in the organization. Nanocrystalline alloys have been known for some time. In general, nanocrystalline alloys have uniform and ultra-fine crystal grains (for example, the grain size is about 10 nm), the main phase is FeSi crystals with a bcc structure, and the amorphous phase remains in the surroundings. (Hitachi Metals Co., Ltd., Finemet (registered trademark) microstructure, [searched on April 18, 2018], Internet <URL: http://www.hitachi-metals.co.jp/product/finemet/fp04 .htm> (Non-Patent Document 1)). For example, Japanese Patent Application Laid-Open No. 2004-349585 (Patent Document 1) discloses obtaining such a nanocrystalline alloy in powder form by a water atomization method. In addition, Japanese Patent Application Laid-Open Nos. 2016-25352 (Patent Document 2) and 2017-110256 (Patent Document 3) disclose that a nanocrystalline alloy powder is produced by a gas atomization method and a high-speed rotating water stream atomization method. there is

JP 2004-349585 A JP 2016-25352 A JP 2017-110256 A

Hitachi Metals, Ltd., Finemet (registered trademark) microstructure, [searched on April 18, 2018], Internet <URL: http://www. hitachi-metals. co. jp/product/finemet/fp04. http>

The magnetic core used for the coil component is required to have an inductance excited by an alternating current superimposed with a direct current, which maintains its initial value up to a high current value and suppresses its decrease, that is, has excellent superimposition characteristics.

Nanocrystalline alloys have a structure in which randomly oriented ferromagnetic phase FeSi crystal grains are dispersed. The crystal magnetic anisotropy becomes a state close to zero, and it is characterized by high sensitivity to external magnetic fields. Magnetic cores using such nanocrystalline alloys have high magnetic 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 in DC superimposition characteristics has been desired. .

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 capable of improving DC superimposition characteristics when used as a magnetic core, and a magnetic core and coil parts using this magnetic core powder. .

One aspect of the present invention is a soft magnetic material comprising particles of a first Fe-based alloy having a region in which nano-sized FeSi crystals form a columnar structure, and a metal structure different from that of the particles of the first Fe-based alloy. and particles for a magnetic core.

In the magnetic core powder, the particles of the first Fe-based alloy preferably have a plurality of regions in which FeSi crystals extend in different directions in the region forming the columnar structure.

It is preferable that the magnetic core powder further includes particles of a second Fe-based alloy having a region in which nano-sized FeSi crystals form a granular structure.

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

The magnetic core powder preferably has a coercive force of 350 A/m or less in an applied magnetic field of 40 kA/m.

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 Cre} 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 aspect of the present invention is a magnetic core formed by binding the magnetic core powder with a binder.

Yet another aspect of the 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, it is possible to provide a magnetic core and a coil component using this magnetic core powder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining the structure of particles contained in a magnetic core powder according to an example of the present invention; 2 is a schematic diagram for explaining the structure of linear FeSi crystals in the structure of FIG. 1. FIG. 1 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 powder (No.*3) of a reference example. 1 is a graph showing X-ray diffraction spectra of magnetic core powders (Nos. 1 and 2) according to one example of the present invention and magnetic core powder (No.*3) of a reference example. 1 is a TEM photograph of a particle cross section of a powder for a magnetic core (No. 1) of the present invention with a particle size corresponding to d90. FIG. 10 is a TEM photograph of another view of the particle cross section of the magnetic core powder (No. 1) of the present invention with a particle size corresponding to d90. 1 is a Si (silicon) elemental composition mapping photograph of a particle cross section of a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention. 1 is a B (boron) elemental composition mapping photograph of a particle cross section of a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention. 1 is a Cu (copper) elemental composition mapping photograph of a particle cross section of a particle size corresponding to d90 of the magnetic core powder (No. 1) of the present invention.

Hereinafter, a magnetic core powder, a magnetic core using the same, and a coil component according to an embodiment of the present invention will be specifically described. However, the present invention is not limited to these. It should be noted that, in some or all of the drawings, parts that are not necessary for explanation are omitted, and some parts are enlarged or reduced in order to facilitate explanation. In addition, unless otherwise specified, the dimensions, shapes, relative positional relationships, etc. of constituent members shown in the description are not limited to them. Furthermore, in the description, the same names and symbols indicate the same or homogeneous members, and detailed description may be omitted even if they are illustrated.

[1] Magnetic core powder The present invention has been made in the course of the inventors' intensive research on nanocrystalline soft magnetic materials, finding a nanocrystalline alloy having a novel crystallographic structure, and studying how to utilize its characteristics. It is. To facilitate understanding of the invention, a nanocrystalline alloy having a novel crystallographic structure will be described in detail.

(1) Microstructure Conventional nanocrystalline alloys are obtained by crystallization from an amorphous phase starting from Cu clusters (Cu-rich regions), and have an average crystal grain size of, for example, 30 nm or less, and random FeSi crystal grains of the ferromagnetic phase oriented in the direction are dispersed in the amorphous phase. In other words, in conventional nanocrystalline alloys, nano-sized FeSi crystals form a granular structure. Grain growth of FeSi crystals occurs in an arbitrary direction, resulting in random precipitation, and does not result in a regular precipitation form. Nanocrystals (nano-sized crystals) generally refer to those having an average crystal grain size of 100 nm or less.

On the other hand, in the nanocrystalline alloy with 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 are present at intervals in the amorphous phase. 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 crystals 200 exist in parallel lines to form a striped structure, and the amorphous phase 250 is formed between the linear FeSi crystals 200. It has become.

FIG. 2 is a schematic diagram for explaining the structure of linear FeSi crystals 200 observed in the structure of FIG. The linear FeSi crystal 200 has a columnar structure and a beaded shape with many constrictions. The portion between the constrictions has a substantially elliptical spherical shape, and a plurality of substantially elliptical spherical portions are connected to form a columnar shape. The nearly ellipsoidal spherical portion has a nano-size with a minor axis of about 10 nm to 20 nm and a major axis of about 20 nm to 40 nm. Although the length of the linear FeSi crystal 200 varies, it is, for example, 200 nm or more, and the length is considered to fluctuate under the influence of the stress distribution within the alloy structure. Hereinafter, this new structure will be referred to as columnar structure, and the conventional structure will be referred to as granular structure.

In a conventional nanocrystalline structure comprising FeSi crystals with a granular structure, as described above, the apparent magnetocrystalline anisotropy is close to zero, and the sensitivity to external magnetic fields is high. Magnetic cores using alloys are characterized by high magnetic permeability and low loss.

On the other hand, in the columnar structure, which is a novel structure, the FeSi crystal has a long columnar structure with a length in the extension direction that is longer than the width. In a structure having FeSi crystals with a columnar structure, a larger magnetic anisotropy is exhibited than in a structure having FeSi crystals with a conventional granular structure, resulting in an increase in coercive force, a decrease in magnetic permeability, and a reduction in loss. It is expected that the magnetic field will increase and the desired soft magnetic properties will not be obtained. In order to solve such a problem, the inventors of the present invention provide the alloy structure with a plurality of regions in which the FeSi crystals have different elongation directions. Although it has regularity, the FeSi crystals have different elongation directions in each region, and the linear FeSi crystals are discontinuous between adjacent regions. I have found that it can be improved.

In addition, when FeSi crystals have a columnar structure, the magnetic moment tends to be oriented in the direction of elongation, and since the structure is nano-order, high sensitivity to magnetic fields remains. If we imagine the process of rotating the magnetic moment of Fe in the direction of the easy axis using a spring connected to the easy axis, we find that the orientation of the linear FeSi crystals and their susceptibility to the magnetic field produce a magnetic field in the direction of elongation. , the magnetic moment rotates parallel to the magnetic field in response to a perpendicular magnetic field, but the rotation is restricted by the spring, and when the magnetic field is removed, it quickly rotates to the easy axis direction. It is thought that it will turn. According to the characteristic that the response of the magnetic moment to the magnetic field is linear and the susceptibility to the magnetic field persists up to a high magnetic field, a magnetic core using a nanocrystalline alloy with FeSi crystals in a columnar texture exhibits a large saturation magnetization due to the FeSi crystals. It is believed that a high incremental magnetic permeability μΔ can be obtained and maintained up to large currents (high magnetic fields).

(2) Powders for magnetic cores Based on these findings, the inventors of the present invention, in the course of further studies, have found powders of nanocrystalline alloys having a novel columnar structure and nanocrystalline alloys having a conventional granular structure. powder and/or mixed powder with powder of other soft magnetic materials, the different magnetic characteristics of each are utilized and complemented, and when used as a magnetic core, increase in core loss and decrease in magnetic permeability It has been found that a magnetic core powder can be obtained that improves the superimposition properties while suppressing the

Although the mechanism of the appearance of the columnar structure in nanocrystalline alloys is not clear, FeSi crystals with a columnar structure precipitate FeSi crystals from the amorphous phase starting from Cu clusters in the same way as FeSi crystals with a conventional granular structure. (Crystallization). In the studies so far, FeSi crystals with a conventional granular structure are formed from the amorphous phase exclusively by heat treatment, but FeSi crystals with a columnar structure are formed in the cooling process in which the molten metal is cooled and alloyed. This is different from conventional nanocrystal structure formation in that respect.

In the formation of a columnar structure, the cooling rate during alloy production and the distribution of the cooling rate within the alloy (velocity gradient between the surface layer and the center of the alloy particle) are important. For example, it is possible to cool the molten metal at a rate of about 10 ³ ° C./sec or more, and in the process of cooling, the volume unit of the size of (sub μm) ³ to (several μm) ³ It is required to create regions with different stress distributions inside the alloy. In particular, it is considered that the cooling rate around 500°C in the cooling process of the molten metal has an effect.

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

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

Particles obtained by the atomization method are nearly spherical, and it is known that the cooling rate greatly depends on the particle size. When the pulverized molten metal passes through a liquid or gas (for example, water, He or water vapor), which has a higher heat exchange efficiency than air, at a high speed, the surface is cooled at a high cooling rate. When heat is efficiently removed from the surface, the inside is also cooled by heat conduction, but the cooling rate varies, and a volume difference occurs between the surface layer that hardens first and the center that hardens later. The larger the diameter of the obtained alloy particles, the more pronounced the variation in the cooling rate.

According to the high-velocity combustion flame atomization method described above, in the early stages of the cooling process, the pulverized molten metal is quenched into a supercooled glassy state alloy, and due to the self-relaxation of the strain due to the volume difference, cooling In process particles, regions with different stress distribution occur in volume units with a size of (sub-μm) ³ to (several μm) ³ . Each region is considered to be in a state of being mutually stressed by the restraining force from the surrounding regions. Furthermore, when separating into a crystalline phase and an amorphous phase during the cooling process, when FeSi crystals start to precipitate from the amorphous phase in a stress-applied state starting from Cu clusters, this triggers an amorphous phase. Partly due to the effect of creep behavior that accompanies the atomic migration of the solid phase, the edge of the FeSi crystal triggered the formation of the next grain, and the grain growth progressed in the stress direction, and the lattice was continuously connected at the atomic level. It is considered that grain growth occurs in a beaded shape.

Further, according to the studies of the present inventors, it has been found that particles with a columnar structure and particles with a granular structure can be produced simultaneously by the high-speed combustion flame atomizing method. In the fast burning flame atomization method, the particle size is typically less than 10 μm, and a trend towards higher cooling rates than ribbons made by the single roll method of the same composition has been observed. When the cooling rate during pulverization is fast, the cooling rate distribution in the grains is suppressed, and the strain and pressure distributions are also small. Crystals are difficult to obtain. When it is heat-treated like a conventional nanocrystalline alloy, its structure becomes a grain structure of FeSi crystals as before.

When the particle size exceeds 10 μm, typically about 20 μm, the difference in cooling rate between the inside and the outside increases, and strain due to the time difference in volume change during cooling accumulates, further increasing the cooling rate. FeSi crystals with a columnar structure tend to precipitate from the inside where the flow rate is relatively slow.

Based on such findings, it is believed that a powder containing particles with a particle size of at least 10 to 20 μm, even if it is a powder obtained by a single atomization process, can produce a nanocrystalline alloy having FeSi crystals with a columnar structure. It can be a powder comprising a powder and a powder of a nanocrystalline alloy with FeSi crystals in a grain structure. Further, by classifying the particles, it is possible to differentiate the ratio between the nanocrystalline alloy powder having a columnar structure and the nanocrystalline alloy powder having a granular structure.

The nanocrystalline alloy having FeSi crystals with a columnar structure may partially contain crystal phases other than FeSi crystals as long as the magnetic properties required for magnetic core powders are satisfied. Crystal phases other than FeSi crystals are exemplified by Fe ₂ B crystals, which have high magnetocrystalline anisotropy and are considered to deteriorate soft magnetic properties. For example, if defined by the peak intensity ratio (P2/P1) of the peak intensity P2 of the diffraction peak of the Fe ₂ B crystal with the bcc structure to the peak intensity P1 of the diffraction peak of the FeSi crystal with the bcc structure, which will be described later, 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 measurement noise level. is desirable.

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

(3) Heat treatment When heat-treating a powder that is a mixture of a nano-crystalline alloy powder with a granular structure after crystallization and a nano-crystalline alloy powder with a columnar structure, the temperature of the furnace used for heat treatment can be controlled up to around 600°C. Any suitable heating furnace can be used without any particular problems. 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 appropriately set so as not to increase crystal phases that deteriorate soft magnetic properties, such as Fe ₂ B crystals other than FeSi crystals, in the columnar nanocrystalline alloy. The heat treatment temperature can be appropriately set based on the crystallization start temperature of the nanocrystalline alloy that forms the granular structure. The crystallization start temperature is determined by thermal analysis of the powder using a differential scanning calorimeter (DSC) in a temperature range from room temperature (RT) to 600°C at a heating rate of 600°C/hr. can be measured by The heat treatment temperature is desirably in the range of 350 to 450°C, preferably 390 to 430°C, although it depends on the crystallization temperature of the nanocrystalline alloy forming the granular structure. The heat treatment temperature is the highest temperature reached after heating, and when this temperature is held for a predetermined time, it is also the holding temperature.

The heat treatment time is desirably 1 second to 3 hours, preferably 1 second to 300 seconds in a continuous furnace, and 300 seconds to 2 hours (7200 seconds) in a batch furnace. The heat treatment time is the time held at the heat treatment temperature.

The average heating rate in the temperature range of 300°C or higher in heat treatment (average heating rate until reaching the target heat treatment temperature) is 0.001 to 1000°C/second, preferably 0.5 to 500°C/second for a continuous furnace. , preferably in the range of 0.006 to 0.08°C/sec for a batch type furnace. When the heating rate is within the above range, excessive temperature rise due to self-heating caused by crystallization of the alloy is prevented, significant overshoot with respect to the setting of the heat treatment temperature is suppressed, and the magnetism of the obtained powder is suppressed. Degradation of characteristics can be prevented.

(4) Alloy composition The composition of the nanocrystalline alloy may be any composition that enables FeSi crystals to form a columnar structure and contains Si, B, and Cu. An alloy composition suitable for obtaining a nanocrystalline alloy with a columnar structure by the atomization method is exemplified below, but the alloy composition is not limited thereto. In the particle size distribution of the magnetic core powder obtained by the atomization method, the alloy composition may be such that large-diameter particles form FeSi crystals with a columnar structure, and small-diameter particles form FeSi crystals with a granular structure.

The composition of the nanocrystalline alloy is Fe _100-abcdefgh Cu _a Si _b B _c M _{d Cre} 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 and M is 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 terms of atomic %. If the Cu content is too small, the effect of addition cannot be obtained, and conversely, if the Cu content is too high, the saturation magnetic flux density is lowered. When Cu _is excessive, crystallization proceeds too much during the cooling process. Precipitation is likely to occur, which may deteriorate the soft magnetic properties. The Cu content is more preferably 1.0% or more, still more preferably 1.1% or more, and most preferably 1.2% or more so as to provide a sufficient number density of Cu clusters in the cooling process of atomization. Further, the Cu content is more preferably 1.8% or less, more 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 terms of atomic %. In addition, it is known to have the effect of promoting amorphousization of nanocrystalline alloys, and in the cooling process, it has the effect of enhancing the ability to form amorphous by being present together with B. In addition, it has the effect of suppressing the precipitation of coarse crystal grains in the cooling process. If the Si content is too low, the effect of addition cannot be obtained, while if the Si content is too high, the saturation magnetic flux density will decrease. On the other hand, the lower limit of the Si content is more preferably 3.0%, since the ordered arrangement of Fe ₃ Si tends to occur. To obtain a high saturation magnetic flux density, the Si content is more preferably 10.0% or less, even more 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 quenching. 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 to form an 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. . Also, when the B content is high, the volume fraction of the residual amorphous phase in the structure after crystallization increases, leading to deterioration of 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. is more preferred, and 18.0% or less is most preferred.

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

Cr is preferably 2.0% or less (including 0) in atomic %. Although it is not essential for obtaining FeSi crystals with a columnar structure, it is an effective element for improving the corrosion resistance of nanocrystalline alloys. When the powder is produced by the atomization method, the Cr content is preferably 0.1% or more, more preferably 0.3% or more, in order to obtain the effect of preventing the inside from being oxidized. On the other hand, when used alone, it acts antiferromagnetically, and when mixed with Fe atoms, it weakens the ferromagnetism of Fe and causes a decrease in the saturation magnetic flux density. Therefore, the upper limit of the Cr content is preferably 1.5%. , and most preferably 1.1%.

Sn is preferably 1.5% or less (including 0) in atomic %. Although it is not essential for obtaining FeSi crystals with a columnar structure, it is an effective element for assisting the formation of Cu clusters. By adding a small amount, Sn atoms gather first in the process of crystallization, and Cu atoms diffusing around them gather to lower the potential energy to form clusters. Considering the effect of Cu as an auxiliary agent for cluster formation, the upper limit of the Sn content preferably does not exceed the Cu content. Further, since Sn is a non-magnetic 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%, most preferably 0.05%.

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

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

Other unavoidable impurities contained in the nanocrystalline alloy may include S, O, N, and the like. The contents of unavoidable impurities are preferably 200 ppm or less for S, 5000 ppm or less for O, and 1000 ppm or less for N, respectively.

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

Although the composition suitable for obtaining a nanocrystalline alloy having FeSi crystals with a columnar structure is shown above, conventional nanocrystalline alloys having FeSi crystals with a granular structure can also be obtained with that alloy composition.

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

When used as a metal composite material, the coil may be embedded in a mixture containing magnetic core powder and a binder for integral molding. For example, if a thermoplastic resin or a thermosetting resin is appropriately selected for the binder, a metal composite core (coil component) in which a coil is easily sealed can be easily formed by known molding means such as injection molding. Alternatively, a mixture containing magnetic core powder and a binder may be formed into a sheet-like magnetic core by known sheet forming means such as a doctor blade method. Alternatively, a mixture containing magnetic core powder and a binder may be used as the amorphous shield material.

In addition, in the magnetic core powder of one embodiment of the present invention, the nanocrystalline alloy powder in which FeSi crystals form a columnar structure includes an Fe-based amorphous alloy, pure iron, Fe—Si, and Fe—Si—Cr crystals. Other soft magnetic powders such as powders of metal-based soft magnetic materials may be added and used.

In either case, the resulting magnetic core has excellent magnetic properties with improved DC superimposition properties, and is suitably used for inductors, noise filters, choke coils, transformers, reactors, and the like.

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

After atomization, Fe, Cu, Si, B, Nb, Cr, Sn and C are weighed so that the alloy compositions of composition A and composition B shown below are obtained, placed in an alumina crucible and heated by a high frequency induction heating device. It was placed in a vacuum chamber and evacuated, and then melted by high-frequency induction heating in an inert atmosphere (Ar) under reduced pressure. After that, the molten metal was cooled to produce ingots of two kinds of master alloys.

[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

The obtained ingot was then remelted and the molten metal was pulverized by a high speed combustion flame atomization method. The atomizing device used consists of a container for containing the molten metal, a pouring nozzle provided in the center of the bottom of the container and communicating with the inside of the container, and a flame jet capable of injecting a flame jet toward the molten metal flowing downward from the pouring nozzle. It is equipped with a jet burner (manufactured by Hard Kogyo Co., Ltd.) and cooling means for cooling the pulverized molten metal. The flame jet is configured to crush molten metal to form molten metal powder, and each jet burner is configured to project a flame at supersonic or near-sonic speed as a flame jet. The cooling means has a plurality of cooling nozzles capable of injecting a cooling medium toward the pulverized molten metal. Water, liquid nitrogen, liquefied carbon dioxide gas, or the like can be used as the cooling medium.

The flame jet temperature was set to 1300°C, and the drooping speed of the raw material molten metal was set to 5 kg/min. Water was used as a cooling medium and was sprayed from a cooling nozzle in the form of a liquid mist. The cooling rate of the molten metal was adjusted by adjusting the injection amount of water from 4.5 liters/min to 7.5 liters/min.

The obtained powders of composition A and composition B were classified with a centrifugal air classifier (Nisshin Engineering TC-15), and two types of composition A with different average particle sizes d50 (the larger d50 is No. 1, and the smaller one was designated as No. 2 powder), and one kind of composition B (designated as No. *3 powder) for a magnetic core. The particle size of the obtained magnetic core powder was measured by the following evaluation method.

[Powder particle size]
From the volume-based particle size distribution measured by a laser diffraction scattering particle size distribution analyzer (Horiba LA-920) and measured by the laser diffraction method, the cumulative % from the small diameter side is 10% by volume, 50% by volume, and Particle sizes d10, d50 and d90 were obtained, which were 90% by volume. Fig. 3 shows the particle size distribution of No.1 to *3 powders.

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

[Saturation magnetization and coercive force]
The sample powder was placed in a container and magnetization was measured using a VSM (Vibrating Sample Magnetometer, VSM-5 manufactured by Toei Kogyo Co., Ltd.). The saturation magnetization at 100°C and the coercive force at Hm = 40 kA/m were obtained.

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

Table 1 shows the results obtained. Note that the samples whose numbers are marked with "*" in Table 1 are reference examples.

As a result of confirming the diffraction spectrum by the X-ray diffraction method, it was found that the diffraction peak of the FeSi crystal with the bcc structure and However, only a halo pattern was observed in one type of B composition powder for magnetic core (No.*3 powder ₎ , and the diffraction peaks of FeSi and Fe ₂ B crystals were Not confirmed. In addition, by TEM observation, a striped structure in which linear FeSi crystals are continuous at intervals was confirmed in the two powders of composition A. This structure was also observed in the powder after heat treatment, which will be described later.

Next, in an electric heat treatment furnace in which the atmosphere can be adjusted, 100 g of three magnetic core powders No. 1 to *3 put in a SUS container were heat treated in a N ₂ atmosphere with an oxygen concentration of 0.5% or less. The heat treatment was carried out by increasing the temperature at a rate of 0.006° C./second, reaching the holding temperature shown in Table 2, holding at this holding temperature for 1 hour, and then stopping the heating and cooling in the furnace.

After heat treatment, No. 1 to *3 powders were measured for saturation magnetization, coercive force, and diffraction spectrum by X-ray diffraction using the same evaluation method as described above. Table 2 shows the results obtained.

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

From FIG. 5, a columnar structure (striped structure) in which shading appears alternately in parallel lines in the observation field was confirmed. By spot diffraction measurement by TEM and composition mapping, it was specified that the linear dark portions with low brightness are FeSi crystals, and the light portions with high brightness are amorphous phases. In addition, from FIG. 6 of another field of view, a region of striped texture and a region where a dark portion with low brightness looks like a dot-like texture were observed. In each region, the dark portions with low brightness were FeSi crystals, and the light portions with high brightness were amorphous phases. Upon further detailed observation, it was found that FeSi crystals were formed linearly in all regions and looked like stripes or dots depending on the direction of appearance on the observed surface. In other words, one particle has regions in which groups of FeSi crystals extend in different directions, and each region has a columnar structure in which FeSi crystals are precipitated in almost one direction. In this one region, the linear FeSi crystals are oriented in the same direction and have regularity. When viewed as a whole, the particles had a non-regular structure.

In elemental distribution mapping, brighter colors indicate more target elements. From the results shown in FIGS. 7, 8, and 9, where Si, B, and Cu are respectively mapped in the same field of view, Si and Cu are concentrated in the region corresponding to the linear FeSi crystal, and the linear FeSi crystal It is confirmed that B is concentrated in the region corresponding to the amorphous phase between . Also, Fe (not shown) was confirmed throughout, but it was confirmed that the concentration was high in the region where Si and Cu were concentrated.

Through spinodal decomposition of linear FeSi crystals and amorphous phase, Fe and Si are used to form FeSi crystals. It is thought that phase separation progresses so that the concentration becomes relatively high, and a periodic concentration modulation structure appears.

In powder No. 2, when observing multiple particles with a particle size corresponding to d90, a striped columnar structure area similar to the structure observed in FIGS. 5 and 6 was observed, but No.* In the powder of No. 3, no striped columnar structure region was observed, and the grain structure was such that FeSi crystal grains with a grain size of about 30 nm, which is the conventional structure, were dispersed in the amorphous phase.

Observation of a plurality of particles with particle diameters corresponding to d10 of No. 1 to *3 powders after heat treatment revealed that they all had a granular structure, which is a conventional structure. In other words, it can be seen that the magnetic core powders of Nos. 1 and 2 are powders in which the powder of the nanocrystalline alloy with a granular structure and the powder of the nanocrystalline alloy with a columnar structure are mixed. On the other hand, the powder of No. *3 of the reference example does not contain a nanocrystalline alloy powder with a columnar structure, and is a powder of a conventional nanocrystalline alloy with a granular structure.

Fe ₂ B crystals are likely to be formed in the amorphous phase in nanocrystalline alloy particles with a columnar structure. In addition, since the peak of Fe ₂ B crystals appears more strongly as the abundance of particles containing Fe ₂ B crystals in the powder increases, the abundance of particles with a columnar structure can be relatively evaluated from the peak intensity can be done. In the diffraction spectrum diagram shown in FIG. 4, the peaks of FeSi crystals and the peaks of Fe ₂ B crystals were confirmed in both powders of Nos. 1 and 2 of alloy composition A (after heat treatment). In powder No.*3 of alloy composition B (after heat treatment), FeSi crystal peaks were confirmed, but Fe ₂ B crystal peaks were 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 for the No. 2 powder having a particle size distribution with a smaller diameter as a whole. In addition, the coercive force of the No. 2 powder was also smaller.

Add 5 parts each of silicone resin to 100 parts of No. 1 to *3 powders after heat treatment, knead, fill the molding die, and press 400 MPa with a hydraulic press molding machine to mold. An annular magnetic core of φ13.5 mm×φ7.7 mm×t2.0 mm was fabricated. The space factor, core loss, initial permeability, and incremental permeability of the manufactured magnetic core were evaluated. Table 3 shows the results. Also in Table 3, the samples using the magnetic core powder of the reference example are distinguished by adding * to their numbers.

[Space factor (relative density)]
A heat treatment was performed at 250° C. to decompose the binder to obtain a powder. Calculate the density (kg/m ³ ) by the volume weight method from the weight of the powder and the dimensions and mass of the annular magnetic core. The space factor (relative density) (%) of the magnetic core was calculated.

[Core loss]
An annular magnetic core was used as the object to be measured, and the primary and secondary windings were each wound with 18 turns. The magnetic core loss (kW/m ³ ) was measured at room temperature (25°C) under the following conditions.

[Initial permeability μi]
Using an annular magnetic core as the object to be measured, winding 30 turns of conducting wire to form a coil component, and using an LCR meter (4284A manufactured by Agilent Technologies), the inductance was measured at room temperature 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)/( _μ0 ×Ae× ^N2 )
(le: magnetic path length, L: sample inductance (H), μ ₀ : vacuum permeability = 4π×10 ^-7 (H/m), Ae: magnetic core cross-sectional area, and N: number of coil turns)

[Incremental permeability μΔ]
Using the coil components used for the initial permeability measurement, a DC applying device (42841A: manufactured by Hewlett-Packard) applied a DC magnetic field of 10 kA/m, and an LCR meter (4284A manufactured by Agilent Technologies, Inc.) ) 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 magnetic permeability μi was defined as the incremental magnetic permeability μΔ. A ratio μΔ/μi (%) was calculated from the obtained incremental magnetic permeability μΔ and initial magnetic permeability μi.

The magnetic cores using the magnetic core powders of No. 1 and No. 2 of the present invention had a sufficiently small change in magnetic permeability regardless of changes in current, and could exhibit stable DC superimposition characteristics at a substantially constant value. In addition, the magnetic core using the magnetic core powder No. 2, which had a small peak intensity ratio P2/P1, had a small core loss and a large 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 winding turns to obtain the required inductance, resulting in an increase in the external dimensions of the coil component. Therefore, it can be seen that the No. 2 powder is more advantageous in downsizing the coil component.

Claims (4)

an amorphous phase;
comprising nano-sized FeSi crystals,
At least part of the FeSi crystals form a region forming a columnar structure in which a plurality of linearly arranged lines are arranged in the amorphous phase .
Particles of nanocrystalline alloy. In the nanocrystalline alloy particles of claim 1,
A nanocrystalline alloy particle comprising a plurality of regions in which FeSi crystals extend in different directions in the region forming the columnar structure. In the nanocrystalline alloy particles according to claim 1 or 2,
Diffraction peak of Fe2B crystal with bcc structure near 2θ=56.5° against peak intensity P1 of diffraction peak of FeSi crystal with bcc structure near 2θ=45° in X-ray diffraction spectrum measured using Kα characteristic X-ray of Cu Particles of a nanocrystalline alloy having a peak intensity ratio (P2/P1) of the peak intensity P2 of 0.05 or less. In the nanocrystalline alloy particles according to any one of claims 1 to 3,
Alloy composition: Fe100-abcdefg-hCuaSibBcMdCreSnfAggCh (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 Nb, Ti, Zr, Hf, V, Ta, and one or more elements selected from the group consisting of Mo.).

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