JPWO2019208768A1 - Powder for magnetic core, magnetic core and coil parts using the same - Google Patents

Abstract

For a magnetic core including particles of a first Fe-based alloy having a region where a nano-sized FeSi crystal has a columnar structure, and particles of a soft magnetic material having a metal structure different from the particles of the first Fe-based alloy Powder. The columnar structure is composed of a plurality of linear FeSi crystals arranged along substantially one direction and an amorphous phase existing between the linear FeSi crystals, and the linear FeSi crystals exist in parallel. It has a striped pattern that appears.

Description

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

  Switching power supplies include various electronic devices that require power supply, such as 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 is required to have low power consumption from the viewpoint of energy saving as well as size and weight reduction.

  In addition, with the high integration of transistors due to the fine wiring of LSIs (Large Scale Integrated Circuits) used in electronic devices, the breakdown voltage of the transistors decreases and the current consumption increases, which lowers the operating voltage and increases the operating voltage. Currentization is progressing. Along with this, a power supply circuit such as a DC-DC converter that supplies power to the LSI is also required to cope with a reduction in the operating voltage of the LSI and a large current. For example, the lower operating voltage of the LSI narrows the voltage range in which it operates normally, so if the supply voltage from the power supply circuit fluctuates (ripple), it may exceed or fall below the power supply voltage range of the LSI. Therefore, measures to increase the switching frequency of the power supply circuit have come to be taken because of the unstable operation of the power supply circuit.

  Fe-based amorphous alloys, nanocrystalline alloys, pure alloys, which are suitable for miniaturization, operate in magnetic cores used for coil components with high excitation magnetic flux density in high frequency regions against high frequencies and large currents in power circuits. Powders of metal-based 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 the atomization method, which is less likely to cause shape anisotropy in magnetic properties when formed into a magnetic core, and has good fluidity in molding the magnetic core, is preferably used.

  Among the metal-based soft magnetic materials, the saturation magnetic flux density is high, the coercive force is small, and as a soft magnetic material capable of low magnetostriction, a Fe-based alloy, FeSi crystals having a fine bcc structure in the structure The nanocrystalline alloys of the above are conventionally known. In general, nanocrystalline alloys have uniform and ultra-fine crystal grains (for example, grain size of about 10 nm), the main phase is FeSi crystals of bcc structure, and the structure has an amorphous phase around them. (Hitachi Metals Co., Ltd., Finemet (registered trademark) Microstructure, [April 18, 2018 search], Internet <URL: http://www.hitachi-metals.co.jp/product/finemet/fp04 .htm>). For example, Japanese Patent Laid-Open No. 2004-349585 discloses that such a nanocrystalline alloy is obtained as a powder by a water atomizing method. Further, JP-A-2016-25352 and JP-A-2017-110256 disclose that nanocrystalline alloy powder is produced by a gas atomizing method and a high-speed rotating water atomizing method.

  A magnetic core used for a coil component is required to have an inductance of the magnetic core excited by an alternating current superposed with a direct current, which maintains an initial value up to a high current value, and whose decrease is suppressed, that is, an excellent superposition characteristic.

  Nanocrystalline alloy has a structure in which randomly oriented FeSi crystal grains in a ferromagnetic phase are dispersed, and the crystal grain size is smaller than the magnetic correlation length (approximately the domain wall width, which is several tens of nm). The crystal magnetic anisotropy is in a state close to zero, and is highly sensitive to an external magnetic field. A magnetic core using such a nanocrystalline alloy has 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 superposition characteristics has been required. .

  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 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 where a nano-sized FeSi crystal has a columnar structure, and a metal structure different from the first Fe-based alloy particle. It is a powder for magnetic cores containing particles of

  In the magnetic core powder, it is preferable that the particles of the first Fe-based alloy include a plurality of regions having different column directions of FeSi crystals in different extending directions.

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

In the magnetic powder, in the X-ray diffraction spectrum measured using Kα characteristic X-ray of Cu, with respect to the peak intensity P1 of the diffraction peak of the FeSi crystal having the bcc structure near 2θ = 45 °, bcc around 2θ = 56.5 ° 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.

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

In the powder for magnetic core, 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 (however, 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, Are numerical values that satisfy 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.) It is preferable to have.

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

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

  The powder for magnetic core of the present invention can improve the direct current superposition characteristics when used as a magnetic core. Further, it is possible to provide a magnetic core and a coil component using the magnetic powder.

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

  Hereinafter, a powder for a magnetic core according to an embodiment of the present invention, a magnetic core using the powder, and a coil component will be specifically described. However, the present invention is not limited to these. In addition, in some or all of the drawings, portions unnecessary for description are omitted, and there are portions illustrated in an enlarged or reduced form for ease of description. Further, the dimensions and shapes shown in the description, the relative positional relationship of the constituent members, and the like are not limited to these unless otherwise specified. Further, in the description, the same name or reference numeral indicates the same or the same member, and the detailed description may be omitted even if it is illustrated.

[1] Powder for magnetic core The present invention has led to the discovery of a nanocrystalline alloy having a novel crystallographic structure structure while the inventors have been earnestly researching a nanocrystalline soft magnetic material, and a study to utilize its properties. It is a thing. In order to facilitate understanding of the invention, a nanocrystalline alloy having a novel crystallographic structure will be described in detail.

(1) Texture Structure Conventional nanocrystalline alloys are obtained by crystallizing from an amorphous phase with Cu clusters (Cu-rich region) as the starting point, and the average crystal grain size is, for example, 30 nm or less. The structure is such that FeSi crystal grains of the ferromagnetic phase oriented in the direction are dispersed in the amorphous phase. That is, in the conventional nanocrystalline alloy, nanosized FeSi crystals have a granular structure. Grain growth of FeSi crystals occurs in arbitrary directions and becomes random precipitation, and does not have a regular precipitation morphology. The 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 with a novel texture, nanosized FeSi crystals form a columnar texture. The columnar structure is a structure in which a plurality of linear FeSi crystals lined up along substantially 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 have a columnar structure. In the nanocrystalline alloy 100 having this columnar structure, the linear FeSi crystals 200 are present in parallel lines and appear as a striped structure, and the amorphous phase 250 exists between the linear FeSi crystals 200. Has become.

  FIG. 2 is a schematic diagram for explaining the structure of the linear FeSi crystal 200 observed in the structure structure of FIG. The linear FeSi crystal 200 has a bead shape having a columnar structure and a large number of constrictions. The portion between the constrictions has a substantially elliptic spherical shape, and a plurality of substantially elliptic spherical portions are connected to form a columnar shape. The short diameter of the approximately elliptical spherical part is about 10 to 20 nm, and the long diameter is nano-sized with 20 to 40 nm. The length of the linear FeSi crystal 200 varies, but is, for example, 200 nm or more, and it is considered that the length varies due to 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.

  In the conventional nanocrystal structure including the FeSi crystal having a granular structure, as described above, the apparent crystal magnetic anisotropy is in a state close to zero, and the sensitivity to an external magnetic field is high. A magnetic core made of an alloy is characterized by high magnetic permeability and small loss.

  On the other hand, in the columnar structure which is a novel structure structure, the FeSi crystal is a long columnar structure having a length in the extension direction longer than its width. A structure having a FeSi crystal having a columnar structure exhibits greater magnetic anisotropy than a structure having a FeSi crystal having a conventional granular structure, which increases coercive force, decreases magnetic permeability, and causes loss. It is expected that there will be an increase and that the desired soft magnetic characteristics cannot be obtained. For such a problem, the present inventors, in the alloy structure, to have a plurality of regions having different stretching directions of FeSi crystals, that is, the stretching directions of the FeSi crystals are aligned in each region. Although it has regularity, the elongation direction of the FeSi crystal is different in each region, the linear FeSi crystal is discontinuous between adjacent regions, and by making the crystal structure with no regularity in the whole alloy We found that it could be improved.

  In addition, if the FeSi crystal has a columnar structure, the magnetic moment tends to be oriented in the elongation direction, and since the structure is in the nano-order, high sensitivity to the magnetic field remains. When the process of rotating the magnetic moment of Fe in the direction of the easy axis of magnetization is modeled by using a spring connected to the easy axis of magnetization, the magnetic field in the stretching direction is balanced by the orientation of the linear FeSi crystal and the sensitivity to the magnetic field. Due to its high saturation property, the magnetic moment rotates in parallel with the magnetic field in the vertical magnetic field, but its rotation is limited by the spring, and when the magnetic field is removed, the magnetic moment rapidly moves in the easy axis direction. It is thought 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 lasts up to a high magnetic field, a magnetic core using a nanocrystalline alloy having a FeSi crystal with a columnar structure has a large saturation magnetization due to the FeSi crystal. It is considered that the high incremental magnetic permeability μΔ can be maintained up to a large current (high magnetic field) while being obtained.

(2) Powder for magnetic core Based on such knowledge, the inventors of the present invention, while proceeding with further studies, powder of a nanocrystalline alloy having a novel columnar structure, and a nanocrystalline alloy having a conventional granular structure. Powder and / or powder of other soft magnetic material is used as a mixed powder to utilize / complement each different magnetic characteristic, and when used as a magnetic core, increase in magnetic core loss and decrease in magnetic permeability It has been found that a powder for magnetic cores that improves the superimposition characteristics can be obtained while suppressing.

  Although the mechanism of the appearance of columnar structures in nanocrystalline alloys has not been clarified, FeSi crystals with columnar structures precipitate FeSi crystals starting from Cu clusters in the amorphous phase, similar to FeSi crystals with conventional granular structures. (Crystallization). In the study so far, the conventional FeSi crystals having a granular structure are exclusively formed from the amorphous phase by heat treatment, whereas the FeSi crystals having a columnar structure are formed in the cooling process in which the molten metal is cooled and alloyed. This is different from the conventional nanocrystal structure formation.

In forming the columnar structure, the cooling rate during alloy production and the distribution of the cooling rate within the alloy (velocity gradient between the surface layer part and the central part of the alloy particles) are important, and they 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 / sec or more, and (sub-μm) ³ to (several μm) in a volume unit of ³ It is required to generate regions having different stress distributions inside the alloy. In particular, it is considered that the cooling rate at around 500 ° C. affects the cooling process of the molten metal.

  In the preparation of the nanocrystalline alloy powder having the FeSi crystals having the columnar structure, the manufacturing method, conditions, etc. are not limited as long as the above requirements can be satisfied. For example, the conventional method used to prepare a nanocrystalline alloy powder having FeSi crystals having a granular structure, such as a gas atomizing method, a water atomizing method, or a high-speed water jet atomizing method, which uses water or gas as a means for pulverizing a molten metal Alternatively, it may be powdered by an atomizing method such as a high-speed combustion flame atomizing method in which a flame is jetted 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 the production of nanocrystalline alloy particles having a columnar structure. The high-speed combustion flame atomizing method is not so general as other atomizing methods, but 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 from 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 gas.

  It is known that the particles obtained by the atomization method have a substantially spherical shape, and the cooling rate greatly depends on the particle size. When a crushed molten metal passes through a liquid or gas (for example, water, He or steam) having a higher heat exchange efficiency than the atmosphere at a high speed, the surface thereof is cooled at a high cooling rate. When the 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 first solidifies and the central portion that solidifies later. The larger the diameter of the obtained alloy particles, the more remarkable the variation in the cooling rate.

According to the above-mentioned high-speed combustion flame atomizing method, in the initial stage of the cooling process, the crushed molten metal is rapidly cooled into an alloy in a supercooled glass state, which is cooled for self-relaxation of strain due to volume difference. In the particles in the process, regions having different stress distributions are produced in volume units of (sub-μm) ³ to (several μm) ³ . It is considered that the respective regions are in a state of being mutually stressed by the restraining force from the surrounding regions. Further, when the crystalline phase and the amorphous phase are separated in the cooling process, when the precipitation of FeSi crystal starts from the Cu cluster as the starting point from the amorphous phase in the state where the stress is applied, the amorphous phase is triggered by it. Due to the effect of creep behavior accompanied by atomic migration of the crystalline phase, the edge of the FeSi crystal caused the formation of the next crystal grain, the crystal grain growth proceeded in the stress direction, and the lattice was continuously connected at the atomic level. It is considered that crystal growth occurs in a bead shape.

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

  When the particle size exceeds 10 μm, typically around 20 μm, the difference in cooling rate between the inside and the outside becomes large, and the strain due to the time difference of the volume change during cooling is accumulated. However, FeSi crystals having a columnar structure are likely to precipitate from the relatively slow inside.

  Based on such knowledge, as long as the powder contains particles having a particle size of at least 10 to 20 μm, even if it is a powder obtained by a single atomization treatment, it is possible to obtain a nanocrystalline alloy having a FeSi crystal with a columnar structure. A powder containing the powder and a powder of a nanocrystalline alloy having FeSi crystals having a granular structure can be used. Further, if the particles are classified, the ratio of the nanocrystalline alloy powder having a columnar structure and the nanocrystalline alloy powder having a granular structure can be made different.

The nanocrystalline alloy having FeSi crystals having a columnar structure may partially include a crystalline phase other than FeSi crystals as long as the magnetic properties required of the magnetic core powder are satisfied. The crystal phase other than the FeSi crystal is exemplified by Fe ₂ B crystal which has a high magnetocrystalline anisotropy and is considered to be a phase which deteriorates the soft magnetic characteristics. For example, the peak intensity ratio (P2 / P1) of the peak intensity P2 of the diffraction peak of the Fe ₂ B crystal of the bcc structure to the peak intensity P1 of the diffraction peak of the FeSi crystal of the bcc structure described below (P2 / P1) (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 nanocrystalline alloy powder 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 may be crystallized. A powder obtained by mixing a powder which later becomes a nanocrystalline alloy having a granular structure and a powder of a nanocrystalline alloy having a columnar structure and which has been subjected to a heat treatment for crystallization may be used. 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 is a mixture of 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 up to around 600 ° C. Any heating furnace can be used without any particular problem. For example, it can be carried out by a batch type electric furnace or a mesh belt type continuous electric furnace. It is preferable that the atmosphere can be adjusted if oxidation is prevented.

The heat treatment conditions in such heat treatment may be set appropriately so as not to increase the crystal phase that deteriorates the soft magnetic characteristics such as Fe ₂ B crystal other than FeSi crystal 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 having a granular structure. Note that the crystallization start temperature is a differential scanning calorimeter (DSC) using a differential scanning calorimeter (DSC), in the temperature range of room temperature (RT) to 600 ℃, the thermal analysis of the powder at a heating rate of 600 ℃ / hr It can be measured by The heat treatment temperature depends on the crystallization temperature of the nanocrystalline alloy forming the grain structure, but is preferably in the range of 350 to 450 ° C, preferably 390 to 430 ° C. The heat treatment temperature is the highest temperature reached after the temperature is raised, and is also the holding temperature when the temperature is held for a predetermined time.

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

  The average heating rate in the temperature range of 300 ° C or higher in the heat treatment (average heating rate until reaching the target heat treatment temperature) is 0.001 to 1000 ° C / sec, preferably 0.5 to 500 ° C / sec for a continuous furnace. The range of 0.006 to 0.08 ° C / sec is preferable for a batch type furnace. When the temperature rising rate is within the above range, it prevents excessive temperature rise due to self-heating caused by crystallization of the alloy, and suppresses overshoot significantly against setting of heat treatment temperature, resulting in magnetic properties of the obtained powder. It is possible to prevent deterioration of characteristics.

(4) Alloy composition The composition of the nanocrystalline alloy may be any composition that enables columnar organization of FeSi crystals and contains Si, B and Cu. Examples of alloy compositions suitable for obtaining a nanocrystalline alloy having a columnar structure by the atomization method are shown below, but the invention is not limited thereto. In the particle size distribution of the magnetic core powder obtained by the atomization method, an alloy composition may be used in which particles having a large particle diameter form columnar structure FeSi crystals and particles having a small particle diameter form FeSi crystals having a particle 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 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 It is a numerical value to be satisfied, 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 structure FeSi crystals. It is also an element that contributes to the formation of a granular structure. The Cu content in atomic% is preferably 0.8% or more and 2.0% or less. If the Cu content is low, the effect of addition cannot be obtained, and conversely, if it is high, the saturation magnetic flux density decreases. When Cu is excessive, crystallization in the cooling process progresses too much, the residual amorphous phase having the effect of suppressing crystal grain growth is deficient, and coarsening of crystal grains and high magnetic anisotropy of Fe ₂ B Precipitation is likely to occur, which may deteriorate the soft magnetic properties. In the cooling process of atomization, 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 give a sufficient number density of Cu clusters. Further, the Cu content is more preferably 1.8% or less, further preferably 1.5% or less.

Si dissolves in Fe, which is the main component of the FeSi crystal, 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%. Further, it is known to have the effect of promoting the amorphization of the nanocrystalline alloy, and in the cooling process, when it is present together with B, it has the effect of enhancing the amorphous forming ability. Further, it has an effect of suppressing coarse crystal grain precipitation in the cooling process. If the Si content is low, the effect of addition cannot be obtained, while 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 is likely 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, most preferably 5.0% or less.

  B is known to have the effect of promoting 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 for forming an amorphous phase, and relatively coarse crystal grains of the order of micrometers are likely to precipitate, and good soft magnetic properties may not be obtained. . Further, when the B content is large, the volume fraction of the residual amorphous phase in the structure after crystallization becomes high, which leads to deterioration of magnetic characteristics such as saturation magnetization. Since the Fe content can be increased as the total content of Si and B is smaller, 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 preferable and 18.0% or less is the most preferable.

  M is one or more elements selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta and Mo. Columnar structure, or, although not essential in obtaining FeSi crystals of a granular structure, when heat-treating a powder obtained by mixing a powder of a nanocrystalline alloy having a granular structure and a powder of a nanocrystalline alloy of a columnar structure after crystallization, It is effective for uniformizing the grain size of FeSi crystals having 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). 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 not essential for obtaining FeSi crystals having a columnar structure, it is an effective element for improving the corrosion resistance of nanocrystalline alloys. In order to obtain the effect of preventing the inside from being oxidized when the powder is produced by the atomization method, the Cr content is preferably 0.1% or more, more preferably 0.3% or more. On the other hand, since it behaves antiferromagnetically as a simple substance and weakens the ferromagnetism of Fe by mixing with Fe atoms and causes a decrease in saturation magnetic flux density, the upper limit of the Cr content is more preferably 1.5%. , 1.1% is most preferable.

  Sn is preferably 1.5% or less (including 0) in atomic%. Although it is not essential for obtaining a FeSi crystal having a columnar structure, it is an element effective for assisting Cu cluster formation. When added in a small amount, Sn atoms first gather during the crystallization process, and Cu atoms diffusing further gather around the Sn atoms to form a cluster to lower the potential energy. Considering the effect of Cu as an auxiliary agent for cluster formation, it is preferable that the upper limit of the Sn content does not exceed the Cu content. Further, since it 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 to obtain FeSi crystals with columnar structure, but Ag separates in the molten metal and precipitates from the initial solidification of the nanocrystalline alloy after atomization, so that it becomes the nucleus of Cu clusters in the initial stage of heat treatment. Function. The preferable content of Ag is 0.2% or less (including 0) in atomic%.

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

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

  Fe is a main element that constitutes a 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% 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.

  Although the composition suitable for obtaining the nanocrystalline alloy having the FeSi crystals having the columnar structure has been shown above, the conventional nanocrystalline alloy having the FeSi crystals having the granular structure can be obtained with the alloy composition.

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

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

  Further, in the magnetic core powder according to one embodiment of the present invention, a powder of a nanocrystalline alloy in which FeSi crystals form a columnar structure is an Fe-based amorphous alloy, pure iron, Fe-Si, and a crystalline material of Fe-Si-Cr. Other soft magnetic powders such as the powder of the metal-based soft magnetic material may be added and used.

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

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

  Fe, Cu, Si, B, Nb, Cr, Sn and C are atomized, then weighed so as to have the alloy composition of composition A and composition B shown below, and put into an alumina crucible for high-frequency induction heating. It was placed in a vacuum chamber to perform vacuuming, and then, under reduced pressure, it was melted by high frequency induction heating in an inert atmosphere (Ar). Then, the molten metal was cooled to prepare two 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 the high-speed combustion flame atomizing method. The atomizing device used is capable of injecting a flame jet toward a container for containing molten metal, a pouring nozzle provided at the center of the bottom of the container and communicating with the inside of the container, and a molten metal flowing downward from the pouring nozzle. It is equipped with a jet burner (made by HARD INDUSTRY CO., LTD.) And a cooling means for cooling the crushed molten metal. The flame jet is configured to be capable of crushing 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 sonic speed. The cooling means has a plurality of cooling nozzles configured to inject a cooling medium toward the crushed molten metal. Water, liquid nitrogen, liquefied carbon dioxide, or the like can be used as the cooling medium.

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

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

[Powder particle size]
Measured with a laser diffraction scattering type particle size distribution measuring device (LA-920 manufactured by Horiba Ltd.), from the volume-based particle size distribution measured by the laser diffraction method, cumulative% from the small diameter side is 10% by volume, 50% by volume and Particle diameters of d10, d50 and d90, which are 90% by volume, were obtained. Figure 3 shows the particle size distribution chart of No. 1 to * 3 powders.

  With respect to each of the obtained powders, the saturation magnetization, the coercive force, and the diffraction spectrum by the X-ray diffraction method were measured by the following evaluation methods.

[Saturation magnetization and coercive force]
The powder of the sample is put in the container and the magnetization is measured by VSM (Vibrating Sample Magnetometer, VSM-5 manufactured by Toei Industry Co., Ltd.). From the hysteresis loop, the magnetic strength is Hm = 800 kA / m. The saturation magnetization at the time and the coercive force under the condition of Hm = 40 kA / m were obtained.

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

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

As a result of confirming the diffraction spectrum by the X-ray diffraction method, it was found that in the two kinds of magnetic core powders (No. 1 and No. 2 powders) having different A composition average particle diameters, the diffraction peak of the FeSi crystal of the bcc structure and the bcc structure were observed. Although the diffraction peak of Fe ₂ B crystal was confirmed, only the halo pattern was observed in the one type of powder for magnetic core of B composition (powder of No. * 3), and the diffraction peaks of FeSi crystal and Fe ₂ B crystal were Not confirmed. In addition, the TEM observation confirmed a striped structure in which linear FeSi crystals were continuous at intervals in the two kinds 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, 100 g of three powders for magnetic cores No. 1 to * 3 put 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 by raising the temperature at a rate of 0.006 ° C./sec, reaching the holding temperature shown in Table 2 and then holding for 1 hour at this holding temperature, then stopping heating and cooling the furnace.

  Saturation magnetization, coercive force, and diffraction spectrum by X-ray diffractometry were measured for 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, after No. 1 ~ * 3 powder after heat treatment, a plurality of particles having a particle diameter corresponding to d10 and d90 are selected, embedded in a resin and cut and polished, and then the cross section is a transmission electron microscope (TEM / EDX: Transmission Electron Microscope / energy dispersive X-ray spectroscopy). FIG. 5 is a TEM photograph observed by polishing the cross section of the No. 1 particle corresponding to d90. FIG. 6 is a TEM photograph of another field of view observed under the same conditions. FIG. 7 is a photograph in which another field of view of the cross section of particles corresponding to d90 of No. 1 is observed and composition mapped with Si (silicon) element, and FIG. 8 is a photograph with composition mapped in B (boron) element, FIG. 9 is a photograph of composition mapping with Cu (copper) element.

  From FIG. 5, a columnar structure (striped pattern structure) in which light and shade alternately appear in parallel lines in the observation visual field was confirmed. By the spot diffraction measurement by TEM and composition mapping, it was identified that a dark portion with a low lightness observed linearly was a FeSi crystal and a light portion with a high lightness was an amorphous phase. Also, from FIG. 6 in another field of view, a region of a striped tissue and a region where a dark portion with low lightness looks like a dot-like tissue were observed. In each region, the dark part with low lightness was the FeSi crystal, and the light part with high lightness was the amorphous phase. Upon further detailed observation, it was found that FeSi crystals were formed in a linear shape in any of the regions, and appeared in a striped pattern or a dot-like shape in the direction in which they appeared on the observation surface. That is, each particle has a region in which the group of FeSi crystals extends in different directions, and in each region, the FeSi crystal has a columnar structure in which crystals are precipitated in substantially one direction. In this one region, the elongation directions of the linear FeSi crystals are aligned and have regularity, but the elongation directions of the FeSi crystals are different in each region, and the linear FeSi crystals become discontinuous between adjacent regions. However, the organization of the particles as a whole did not have regularity.

  Element distribution mapping shows that the lighter the color tone, the more target elements. From the results shown in FIG. 7, FIG. 8 and FIG. 9 in which Si, B, and Cu are composition-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 is obtained. It is confirmed that B is concentrated in the region corresponding to the amorphous phase between. Further, although Fe (not shown) was confirmed as a whole, it was confirmed that the concentration was high in the 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, which is difficult to enter into the crystalline phase, is concentrated in the amorphous phase. It is considered that the phase separation proceeds so that the concentration becomes relatively high, and a periodic concentration modulation structure appears.

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

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

Fe ₂ B crystals are likely to be formed in the amorphous phase in the nanocrystalline alloy particles having a columnar structure. Further, the more the proportion of particles containing Fe ₂ B crystals in the powder is, the stronger the peak of Fe ₂ B crystals is expressed. Therefore, the relative proportion of the proportion of particles having a columnar structure should be evaluated from the peak intensity. You can In the diffraction spectrum diagram shown in FIG. 4, the peaks of the FeSi crystal and the Fe ₂ B crystal were confirmed in both the powders of No. 1 and 2 of alloy composition A (after heat treatment). In the No. * 3 powder of alloy composition B (after heat treatment), the peak of the FeSi crystal was confirmed, but the peak of the Fe ₂ B crystal 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 for the No. 2 powder having a particle size distribution with a smaller diameter as a whole. Also, the coercive force of the No. 2 powder was smaller.

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

[Space factor (relative density)]
The annular magnetic core evaluated for magnetic measurement was heat-treated at 250 ° C. to decompose the binder to obtain a powder. From the weight of the powder and the size and mass of the annular magnetic core, calculate the density (kg / m ³ ) by the volumetric weight method, 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.

[Core loss]
An annular magnetic core is used as the object to be measured, and the primary side winding and the secondary side winding are wound 18 turns each, and the maximum magnetic flux density of 30 mT and the frequency of 2 MHz are measured by BW analyzer SY-8218 manufactured by Iwatsu Measurement Co., Ltd. The magnetic core loss (kW / m ³ ) was measured at room temperature (25 ° C) under the condition of.

[Initial permeability μi]
An annular magnetic core was used as the DUT, the conductor was wound 30 turns to form a coil component, and it was calculated by the following formula from the inductance measured at a frequency of 100 kHz at room temperature with an LCR meter (Agilent Technology Co., Ltd. 4284A). . 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: magnetic core cross-sectional area, and N: number of coil turns)

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

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

Claims (8)

  For a magnetic core including particles of a first Fe-based alloy having a region where a nano-sized FeSi crystal has a columnar structure, and particles of a soft magnetic material having a metal structure different from the particles of the first Fe-based alloy Powder. In the powder for magnetic core according to claim 1,
The particles of the first Fe-based alloy are magnetic core powders having a plurality of regions having different extending directions of FeSi crystals in the region forming 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 where nano-sized FeSi crystals form a grain structure. In the magnetic core powder according to any one of claims 1 to 3,
In the X-ray diffraction spectrum measured using the Kα characteristic X-ray of Cu, the peak intensity P1 of the diffraction peak of the FeSi crystal of bcc structure around 2θ = 45 ° is compared to the peak intensity P1 of the Fe ₂ B crystal of bcc structure around 2θ = 56.5 °. Powder for magnetic core having a peak intensity ratio (P2 / P1) of the peak intensity P2 of the diffraction peak of 0.05 or less. In the magnetic core powder according to any one of claims 1 to 4,
Powder for magnetic core having a coercive force of 350 A / m or less in an applied magnetic field of 40 kA / m. In the magnetic core powder according to any one of claims 1 to 5,
Particles of the first Fe-based alloy,
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 powder for magnetic core according to any one of claims 1 to 6 with a binder.   A coil component including the magnetic core according to claim 7 and a coil.