Flat metal particle in which magnetic hard axis is oriented, molded body, inductor, and magnetic sheet

Abstract

The present invention provides flat metal particles that are metal particles of iron-based metal, for example, the flat metal particles being excellent in magnetic characteristics or the like even in a high frequency range.　In an inverse pole figure of the flat metal particles in a direction perpendicular to a flat surface by pole evaluation using X-ray diffraction, the pole density of (111) is higher than the pole density of (001), and the pole density of (111) is 2 or more.

Description

Flat metal particles with hard axis of magnetization aligned, compact, inductor, and magnetic sheet

[0001] The present invention relates to flat metal particles and to a molded article using the flat metal particles.

[0002] In metallic materials, texture (also called crystal texture) is controlled to improve their functionality. By controlling the texture, magnetic properties can be controlled and the materials are used in iron cores and the like.

[0003] For example, Patent Document 1 discloses a method for producing flat metal particles having a texture in which the crystal planes are controlled to a predetermined direction by subjecting a metal powder containing metal particles to mechanochemical processing such as pulverization. By imparting a texture to the metal in this way, it is possible to obtain the effect of improving the magnetic properties as shown in Patent Document 1.

[0004] Patent Document 1 and Non-Patent Document 1 disclose flat metal particles having a recrystallized texture in which the crystal planes are controlled in a predetermined direction, and a method for manufacturing the same. In particular, when the flat metal particles are made of an iron-based metal, applying the flat metal particles to the cores of electromagnetic application products such as motors and reactors can improve the magnetic permeability and magnetic flux density of the core.

[0005] Patent Document 2 discloses a crystal having a peak intensity ratio (peak intensity B / peak intensity A) of 0.5 or more between a peak intensity A of the (110) plane and a peak intensity B of the (001) plane in X-ray diffraction, a valley between diffraction peaks from the same crystal plane originating from Kα1 and Kα2, and a volume of 1.8 × 10 -12 m 3 The above flat metal particles and the like are disclosed.

[0006] JP 2020-70459 A JP 2022-146086 A

[0007] Satoshi Motodzuka et al., Formation of (001) Fiber Texture in Iron Powder and its Effect on Magnetic Properties and Crystal Orientation of the Powder Compact, ISIJ International, Vol.59 (2019), No.1, pp.192-200

[0008] The characteristics of this material structure, as disclosed in Patent Documents 1 and 2, improve core performance in the low-frequency region where the magnetization process is dominated by domain wall motion. However, in the high-frequency band, the magnetization process shifts from domain wall motion to magnetization rotation. In such high-frequency regions, a structure oriented along the hard axis of magnetization rather than the easy axis of magnetization can improve core performance. This is because in the magnetization process along the hard axis of magnetization, magnetization progresses only through magnetization rotation, which can suppress the occurrence of domain wall motion, which causes slow magnetization progression at high frequencies. Therefore, the inventors invented flat metal particles oriented along the hard axis of magnetization.

[0009] The present invention provides flat metal particles that have excellent magnetic properties, such as suppressing an increase in iron loss and a decrease in magnetic permeability in the high frequency range.

[0010] The present inventors have conducted extensive research to solve the above problems and have found that the following inventions meet the above objectives, thereby completing the present invention.

[0011] <1> A flat metal particle in which, in an inverse pole figure perpendicular to the flat surface, determined by pole point evaluation using X-ray diffraction, the pole density of (111) is higher than the pole density of (001), and the pole density of (111) is 2 or more. <2> A flat metal particle described in <1>, having an aspect ratio of 2 or more. <3> A compact formed by compressing the flat metal particle described in <1> or <2>, wherein the pole density of (111) is 2 or more when measured by electron backscatter diffraction method on a cross section parallel to the compression direction. <4> The compact described in <3>, which is an iron core for a high-frequency magnetic device. <5> An inductor having a coil wound around a compact which is the iron core described in <4>. <6> A magnetic sheet for an electronic device, comprising the flat metal particle described in <1> or <2>.

[0012] According to the present invention, flat metal particles and the like are provided that have excellent magnetic properties in the high frequency range where magnetization rotation is dominant.

[0013] FIG. 1 is an overview diagram of the hard magnetization axis, etc. of the flat metal particles of the present invention. FIG. 2 is an image of a particle related to the flat metal particles, etc. of the embodiment. FIG. 3 is a diagram for explaining the influence of the forming conditions of the metal particles of the embodiment. FIG. 4 is a diagram for explaining the structural characteristics of the metal particles of the embodiment. FIG. 5 is a diagram for explaining the appearance of a compression molded body made from the flat metal particles of the embodiment. FIG. 6 is a diagram for explaining the structural characteristics of a compression molded body made from the flat metal particles of the embodiment. FIG. 7 is a diagram for explaining the magnetic characteristics of a compression molded body made from the flat metal particles of the embodiment. FIG. 8 is a diagram for explaining the magnetic characteristics of a compression molded body made from the flat metal particles of the embodiment.

[0014] The following describes in detail an embodiment of the present invention, but the following description of the constituent elements is one example (typical example) of an embodiment of the present invention, and the present invention is not limited to the following content unless the gist of the present invention is changed. Note that when the expression "to" is used in this specification, it is used as an expression including the numerical values ​​before and after it.

[0015] [Flat metal particles of the present invention] The flat metal particles of the present invention are flat metal particles in which, in an inverse pole figure perpendicular to the flat surface as determined by pole point evaluation using X-ray diffraction, the pole density of (111) is higher than the pole density of (001), and the pole density of (111) is 2 or more.

[0016] When used in an iron core, the flat metal particles of the present invention have the properties of an iron core made of iron powder, which has excellent core loss and magnetic permeability characteristics in the high frequency range.

[0017] Conventional flat metal particles with an easy axis of magnetization oriented have excellent magnetic properties in the low-frequency range, but are not necessarily advantageous in the high-frequency range. As shown in Figure 1, in the magnetic anisotropy of iron crystals, <001> is the easy axis of magnetization, while <111> is the hard axis of magnetization. In the case of ordinary flat iron powder, the orientation of the hard axis of magnetization <111> of each crystal grain is random. The inventor has invented flat iron-based metal particles with a controlled hard axis direction, in which magnetization proceeds through magnetization rotation, which governs the magnetization process in the high-frequency range.

[0018] In the low-frequency region, the magnetization of a material progresses due to domain wall motion, but at high frequencies, the domain walls are unable to follow the applied magnetic field, hindering the progression of magnetization. On the other hand, magnetization rotation can follow the external magnetic field up to higher frequency regions. Therefore, in order to improve the magnetic properties of a material in the high-frequency region, it is important to control the hard axis of magnetization rather than the easy axis of magnetization.

[0019] [Flat Metal Particles] The present invention will be described in more detail below. First, the flat metal particles will be described.

[0020] [Flat surface] The flat metal particle has a flat surface. The flat surface refers to a surface perpendicular to the thickness direction of the flattened particle. The flat surface is preferably flat. The flat surface may also be a curved surface. Such a flat surface is a surface formed by plastic deformation, for example, by subjecting the metal particle to a compression treatment or the like.

[0021] [Thickness] The thickness of the flat metal particles of the present invention is preferably 250 μm or less. Such a thickness is suitable as a material for aligning the orientation during molding of a compact. If the thickness is greater than this, the metal particles before flattening may be large, which may reduce the efficiency of pulverization or make it difficult to form a compact of the particles into the desired shape. The lower limit of the thickness may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more. The upper limit of the thickness may be 100 μm or less, or 80 μm or less.

[0022] [Aspect ratio] The flat metal particles of the present invention preferably have an aspect ratio, which is the particle size divided by the thickness, of 2 or more. The particle size is calculated based on a plane perpendicular to the thickness direction. The particle size d is calculated by considering it as a circle circumscribing the outline of the flat surface. The thickness of the particle observed from a cross section including the direction perpendicular to the flat surface is taken as the thickness t.

[0023] The aspect ratio may be 3 or more, 5 or more, or 10 or more. There is no particular upper limit to the aspect ratio, but if the aspect ratio is too high, the particle size d will be too large or the thickness t will be too small, resulting in excessive flattening. Therefore, the upper limit to the aspect ratio may be set to 1000 or less. The upper limit to the aspect ratio may also be 800 or less, or 500 or less.

[0024] [X-ray Diffraction Pattern] The flat metal particles of the present invention have a texture in which the hard axis of magnetization is oriented perpendicular to the flat surface of the particle. This texture can be characterized as follows.

[0025] The structure of the flat metal particles of the present invention is understood using an inverse pole figure obtained by analyzing the pole measurement results obtained by X-ray diffraction from the flat metal particles using the ODF (Crystal Orientation Distribution Function) method. The pole density is determined using an inverse pole figure perpendicular to the flat surface of the flat metal particle. In this case, the pole density of (111) is higher than the pole density of (001). Furthermore, the pole density of (111) is 2 or more. Iron-based particles exhibiting such a characteristic structure have a uniform direction of the hard magnetization axis and can rapidly progress magnetization in the high frequency range.

[0026] The pole density of (001) should be lower than the pole density of (111), and is more preferably 2 or less, and may be 1.5 or less, or 1.3 or less. The lower the pole density of (001), the higher the orientation of the hard magnetization axis, and the greater the improvement effect. The pole density of (111) is 2 or more, and more preferably 2.5 or more, and may be 2.8 or more, or 3.0 or more. There is no particular upper limit to the pole density of (111), but taking into consideration manufacturing efficiency and the like, it may be 20 or less, 15 or less, or 10 or less. The higher the pole density of (111), the higher the orientation of the hard magnetization axis, and the greater the improvement effect.

[0027] The flat metal particles of the present invention are used as raw materials for powdered iron cores, etc. The flat metal particles are an aggregate of a large number of particles. In the present invention, the volume, thickness, aspect ratio, etc. of the particles are average values ​​of the powder of the particles. When calculating this average value, particles with a particle size d of 10 μm or less that are difficult to identify even when observed under a microscope are excluded, and the average value can be calculated from the average value of, for example, 30 randomly selected particles.

[0028] [Metal Particles] Regarding the flat metal particles of the present invention, the flat metal particles having a texture have a body-centered cubic lattice structure. The composition of the metal particles is not particularly limited. Metal particles used in powder iron cores and powder magnetic cores are preferably used. Iron-based alloy particles, which are particles of iron-based alloys, are preferably used as the metal particles. Examples of iron-based alloys include silicon steel, iron-silicon-chromium alloys, iron-aluminum-silicon alloys, iron-cobalt alloys, iron-cobalt-vanadium alloys, iron-vanadium alloys, and chromium-iron alloys. Silicon steel, iron-silicon-chromium alloys, and iron-aluminum-silicon alloys are more preferred. These alloys are iron-based ferromagnetic alloys that exhibit excellent soft magnetic properties and high saturation magnetic flux densities, which can contribute to the miniaturization of devices, etc. Furthermore, these alloys are preferred because the magnetic properties can be controlled according to the application by utilizing the crystal orientation within the flat powder and the particle orientation due to the flat shape.

[0029] [Molded Articles] Various molded articles can be produced using the flat metal particles of the present invention. A preferred embodiment of the present invention is a powder iron core including a structure in which the flat metal particles of the present invention are coated with an insulating film. When molded articles using the flat metal particles of the present invention are produced, for example, as powder iron cores using iron-based particles, the orientation of the hard axis of magnetization is controlled, resulting in small hysteresis loss and eddy current loss. The magnetic permeability is maintained even at high frequencies, such as tens of kHz or more, hundreds of kHz or even several MHz, resulting in excellent magnetic properties. This powder iron core is highly effective for use in electromagnetic application products such as transformers and reactors, contributing to improving the functionality of these electromagnetic application products.

[0030] [Compressed iron powder core] The compressed iron powder core is not particularly limited as long as it is composed of the above-mentioned flat metal particles and formed into a predetermined shape. For example, it contains soft magnetic alloy powder and a resin binder, and the soft magnetic alloy particles constituting the flat metal particles are fixed into a predetermined shape by being bonded to each other via the resin. The compressed iron powder core may also be composed of a mixed powder of the above-mentioned flat metal particles and another magnetic powder and formed into a predetermined shape.

[0031] [Magnetic Component (Inductor)] The magnetic component is not particularly limited as long as it includes the above-mentioned powdered iron core. For example, it may be a magnetic component in which an air-core coil wound with wire is embedded inside a powdered iron core of a predetermined shape, or a magnetic component in which wire is wound a predetermined number of times around the surface of a powdered iron core of a predetermined shape.

[0032] [Magnetic Sheet] The flat metal particles of the present invention can be used in magnetic sheets for electronic devices. The magnetic sheet can contain flat metal particles. Magnetic sheets are sheets for adjusting magnetism, such as electromagnetic wave shields for suppressing the effects of electromagnetic waves and magnetic flux concentrating plates for concentrating magnetic flux to improve density. These magnetic sheets can be coatings in which a coating liquid containing flat metal particles is applied to a substrate sheet, or resin sheets in which flat metal particles are dispersed in a resin such as polyimide. These coatings and resin sheets can be thin, but because the flat metal particles are flat, they are arranged in a horizontally spread manner, making it easy to align their orientation. In other words, they can be used as sheets in which the hard axis of magnetization is aligned.

[0033] [Electron Backscatter Diffraction (EBSD) Method] The molded body of the present invention preferably has a (111) pole density of 2 or more when a cross section parallel to the compression direction is evaluated by electron backscatter diffraction (EBSD) method. The pole density of a molded body such as an iron core is preferably measured by EBSD method. The (111) pole density measured by EBSD method is 2 or more, more preferably 2.5 or more, and may be 2.8 or more or 3.0 or more. There is no particular upper limit to the (111) pole density, but it may be 20 or less, 15 or less, or 10 or less, taking into consideration production efficiency, etc. The higher the (111) pole density, the higher the orientation of the hard magnetization axis, and the greater the improvement effect that can be obtained.

[0034] [Manufacturing method] Next, a method for manufacturing flat metal particles will be described. The method for manufacturing flat metal particles of the present invention can include a crushing step in which a general raw material powder of metal particles is crushed into iron-based particles using a lubricant, and an annealing step in which the crushed iron-based particles are annealed into a flat shape.

[0035] [Pulverization Step] In the pulverization step, metal particles as the starting material are pulverized using a ball mill or the like with a lubricant to obtain flat metal particles.

[0036] [Crushing Device, etc.] In the crushing step, the crushing treatment of the metal particles can be, for example, a mechanochemical treatment in which mechanical energy such as compressive force or frictional force is applied to the particulate material to induce mechanical and chemical interactions between the materials and deform the particle shape. The mechanochemical treatment is not particularly limited, and for example, a mechanical crushing device can be used. Examples include a bead mill, a planetary, rolling, or vibrating ball mill, a rocking mill, a tower mill, a mechanofusion, a jet mill, a hybridizer, a Henschel mixer, and a homomixer.

[0037] The material of the mill or other grinding container used in the grinding process is not limited, but it is preferably made of, for example, metal or metal oxide, because such materials can impart sufficient mechanical energy to the metal particles during the grinding process.

[0038] If a device that does not use spherical media, such as Mechanofusion (manufactured by Hosokawa Micron Corporation), is selected as the device for performing the pulverization process, there is no need to add spherical media, and the amount of spherical media introduced can be set to zero.

[0039] When selecting a device that uses spherical media, the material of the spherical media is not limited and can be selected depending on the size and material of the grinding container. Furthermore, when spherical media made of metal or metal oxide are used, sufficient mechanical energy can be imparted to the powder material during grinding. Furthermore, the size of the spherical media used in the grinding process is not particularly limited and can be selected depending on the size of the grinding container, etc.

[0040] [Lubricant] In the pulverization step, a lubricant is used in the pulverization treatment of the metal particles. The lubricant contains a lubricating substance that exhibits a lubricating function.

[0041] The lubricating function refers to reducing the coefficient of friction between the metal particles being pulverized and the object being pulverized (e.g., a spherical medium such as a ball). The use of a lubricant in the pulverization of metal particles can promote the flattening of iron-based particles during the pulverization process.

[0042] As the lubricant, for example, fatty acid esters, mineral oils, liquid saturated hydrocarbons, and polyethers can be used as liquid lubricants. Also, graphite, graphite fluoride, polytetrafluoroethylene, carbon fiber, molybdenum disulfide, mica, talc, boron nitride, and the like can be used. Furthermore, alcohols such as isopropyl alcohol can be used as auxiliary agents to improve fluidity. For example, the rust-preventive lubricant KURE5-56 (registered trademark), which is primarily made of mineral oil as an equivalent to mineral oil, liquid paraffin (liquid saturated hydrocarbon), which is a mixture of liquid saturated hydrocarbons, polyethylene glycol, which is a polyether, boron nitride, and isopropyl alcohol (IPA), can be used as lubricants when forming a recrystallized structure.

[0043] Furthermore, it is believed that the structure of the flat metal particles of the present invention is obtained because at least a portion of the lubricant is less likely to volatilize from the flat surfaces of the metal particles during the manufacturing process, thereby affecting the surface energy.The manufacturing process of the flat metal particles of the present invention includes a crushing process and a heat treatment.The crushing process introduces strain into the metal structure of the particles, and this structure recrystallizes in the subsequent heat treatment process, and the crystal orientation is determined by this recrystallization.The crystal orientation is determined so that the surface energy of the crystal plane on the particle surface is the lowest.In other words, the crystal orientation of the recrystallized structure can be controlled by controlling the surface energy of (111) using the heat treatment atmosphere or residual material on the particle surface.For this reason, it is believed that using the lubricant described above is effective.

[0044] When pulverizing, the raw material metal particles and lubricant may be mixed in such a way that the lubricant is in sufficient contact with the surfaces of the metal particles, and although this depends on the pulverizing device, it is possible to use an amount of lubricant sufficient to immerse the metal particles. The lubricant used in pulverization can be separated and removed when recovering the flattened metal particles or by annealing, and may remain on the surfaces of the flattened metal particles to the extent that it does not affect their physical properties.

[0045] [Annealing step] In the annealing step, the metal particles crushed into a flat shape in the crushing step are annealed (heat treated). By crushing the metal particles using a lubricant in the crushing step, lattice defects (processing strain) caused by crushing can be sufficiently removed, and the coercive force can be reduced.

[0046] [Annealing temperature and time] In the annealing step, the flattened metal particles may be annealed at a temperature equal to or higher than the recovery / recrystallization temperature of the metal particles, which varies depending on the composition of the metal particles (pure iron, various iron alloys), processing history, etc.

[0047] For example, in the case of silicon steel, the annealing atmosphere can be argon gas. Furthermore, since the crystal orientation of the metal particles of the present invention is presumably obtained by controlling the surface energy of the metal particles, the annealing temperature can be set to a temperature that reduces the (111) surface energy. The annealing temperature can be, for example, approximately 600 to 1000°C or approximately 650 to 800°C. If the temperature is significantly lower than 600°C, recrystallization may not occur. If the temperature is significantly higher than 1000°C, the metal particles may adhere to each other, losing their powder properties, or a metal structure significantly different from the target structure may be formed due to phase transformation, etc. Furthermore, the holding time at the annealing temperature can be approximately 15 minutes to 2 hours or approximately 30 minutes to 1.5 hours. Furthermore, cooling after the annealing temperature holding can be performed by furnace cooling, etc.

[0048] By this type of production, flat metal particles can be obtained that have a large size in the direction perpendicular to the thickness direction, include crystal grains that are composed of recrystallized crystals, and have crystal planes that are parallel to the flat surfaces of the particles.

[0049] The produced flat metal particles can be used after confirming whether they have the properties of the flat metal particles of the present invention by evaluating their X-ray diffraction patterns, etc.

[0050] Such flat metal particles can be made from iron-based particles, mixed with an appropriate binder such as an insulating material, coated with the binder, and then compressed to form a powder iron core. Such a powder iron core has excellent magnetic permeability and excellent magnetic properties that suppress increases in iron loss.

[0051] Furthermore, in terms of the saturation magnetic flux density of the flat metal particles of this embodiment configured as described above, Fe-6.5Si (silicon steel containing 6.5% silicon), a promising material for application in this embodiment, has a saturation magnetic flux density of 1.8T (tesla), while permalloy has a saturation magnetic flux density of 1.5T and ferrite has a saturation magnetic flux density of approximately 0.4T, demonstrating that the flat metal particles of this embodiment are superior. As a result, when an inductor made of permalloy or ferrite is created, if it is replaced with flat metal particles of Fe-6.5Si as in this embodiment, a volume reduction of approximately 16% for permalloy inductors and approximately 70% for ferrite inductors can be expected. Furthermore, in the case of an inverter using an inductor made with flat metal particles using Fe-6.5Si of this embodiment, heat generation is suppressed due to reduced iron loss, and it is expected that the amount of cooling water required to cool the inverter can be reduced.

[0052] Furthermore, by fabricating an inductor using flat metal particles oriented in (111) as in this embodiment, the easy axis of magnetization disappears in the excitation direction, and magnetization rotation becomes more dominant in the magnetization process than domain wall motion. As a result, the dominance of magnetization rotation suppresses the rapid change in magnetic flux density over time due to domain wall motion, reducing the eddy current loss of the inductor. The coercive force of the inductor is also reduced. By using the flat metal particles of this embodiment, it is possible to achieve a reduction in magnetic anisotropy, etc., thereby reducing the coercive force of the inductor. From the above, materials oriented primarily in (111), such as the flat metal particles of this embodiment, can contribute to magnetic properties, particularly loss reduction, so that when an inductor is fabricated using the flat metal particles of this embodiment, heat generation, etc. can be reduced.

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not changed.

[0054] (Materials) (Iron-based metal particles) Silicon steel particles (Epson Atmix Corporation, product number: PIS65) (Lubricants) Lubricating oil (Kure Industries, product name: 5-56) Polyethylene glycol 200 (Fujifilm Wako Pure Chemical Industries, polyethylene glycol 200, Wako Grade 1) Liquid paraffin (Fujifilm Wako Pure Chemical Industries, liquid paraffin, special reagent grade)

[0055] Example 1 (Pulverization) Silicon steel particles (Epson Atmix Corporation, product number: PIS65) and lubricating oil (Kure Industries Co., Ltd., product name: 5-56) were added to a ball mill (Nissin Giken Co., Ltd., model number: NEV-MA-8) and pulverized.

[0056] The conditions for the ball mill treatment were as follows: the amount of silicon steel particles added to the mill was 5 g, the amount of lubricating oil added as a lubricant was 20 mL, 20 steel balls (made of SUJ-2) with a diameter of approximately 10 mm were used as spherical media, the ball mill operating speed was 6.4 rps, and the treatment time was 2.00 to 8.00 h.

[0057] The particles after pulverization were analyzed using an electron microscope (JCM-6000, manufactured by JEOL Ltd., etc.) and a powder X-ray diffractometer (Smartlab, manufactured by Rigaku Corporation). The analysis results are shown in Figures 2 to 4, respectively. Figure 2(a) is an image of silicon steel particles used as raw material before pulverization. Figure 2(b) is an image of flat metal particles after pulverization. Figure 2(c) is an image of the cross section of silicon steel particles used as raw material before pulverization. Figure 2(d) is an image of the cross section of flat metal particles after pulverization.

[0058] The shape of the flat metal particle was circumscribed around the outer shape in a direction perpendicular to the thickness direction, and the diameter of the disk was calculated as a disk with the same thickness as the flat metal particle. The obtained diameter was divided by the obtained thickness to calculate the aspect ratio. 30 particles were randomly selected for the measurement, and the average was taken. The results are shown in Figure 3. In this example, powder processed for 4.00 hours was subjected to the subsequent heat treatment and molding process. The average diameter of the disks was 237 μm. The average thickness was 7.3 μm. The aspect ratio was 32.

[0059] (Annealing) Next, the iron-based particles subjected to the above-mentioned pulverization treatment were subjected to an annealing treatment (heat treatment) in a tubular electric furnace (TMF-500N, manufactured by AS ONE Corporation). The annealing atmosphere was Ar, the annealing temperature was 700°C, the holding time at the annealing temperature was 1 hour, and the cooling after the temperature holding was furnace cooling.

[0060] The obtained iron-based particles were analyzed using a powder X-ray diffractometer (Smartlab, manufactured by Rigaku Corporation), and the resulting inverse pole figure is shown in Figure 4. According to this, the pole density of the (111) plane oriented parallel to the flat particles was as follows: - Iron-based particles before pulverization was 0.9 - Iron-based particles after pulverization was 2.3

[0061] (Evaluation of Molded Product) The raw material iron-based particles and the flat metal particles that had been subjected to the above-mentioned crushing treatment for 4.00 hours and then annealed were each compressed in a mold and molded into pellets with a diameter of 11.3 mm. The appearance is shown in Figure 5. The cross section was analyzed and evaluated using an electron microscope (JEOL, JIB-4600F) and an EBSD analyzer (TSL, OIM). The inverse pole figure map and inverse pole figure obtained by EBSD (electron backscatter diffraction) were evaluated on a cross section parallel to the compression direction of the pellet. The results are shown in Figure 6.

[0062] According to this, the pole density of the (111) plane oriented parallel to the flat particles was as follows: 1.1 for the iron-based particles before the crushing process, and 5.5 for the iron-based particles after the crushing process.

[0063] As shown in Figure 6, the cross section of the raw powder is composed of relatively isotropic particles, and the inverse pole figure map and inverse pole figure indicate that there is no strong crystal orientation in any particular direction. On the other hand, in the case of flat metal particles, the flat surfaces of the flat particles are oriented in the compression direction, i.e., perpendicular to the vertical direction of the figure. This is because the particles spontaneously oriented within the molding die due to their flatness. To achieve this orientation effect, the flat powder requires a certain aspect ratio. Furthermore, as can be seen from the inverse pole figure map and inverse pole figure, the (111) plane is oriented parallel to the flat surfaces.

[0064] (Evaluation and Comparison of Magnetic Properties) The raw iron-based particles and the above-mentioned crushed and heat-treated iron-based particles were coated with silicone resin (SR2400, manufactured by Dow Corning Toray Co., Ltd.), compressed in a mold, and molded into a ring shape with an outer diameter of 30 mm and an inner diameter of 20 mm. Primary and secondary windings were applied to this, and the AC magnetic properties were evaluated using a B-H analyzer (SY-8219, manufactured by Iwasaki Electric Co., Ltd.). Based on this, the frequency dependence of the loss per mass of the resulting ring core divided by frequency (Pc / f) is shown in Figure 7. This method is called the dual-frequency method, and the intercept of the graph is proportional to the hysteresis loss of the ring core, and the slope is proportional to the eddy current loss. For comparison, the characteristics of a ring core made of flat iron particles with the 001 orientation controlled parallel to the flat surface, produced using the method described in JP 2020-70459 A, are also shown.

[0065] The figure shows that compared to the raw iron particles, the ring core made from iron particles with the 001 plane oriented in the flat plane, which is the conventional technology, has a smaller intercept, i.e., a lower hysteresis loss, but the slope is the same, i.e., the eddy current loss is almost unchanged. In contrast, the ring core made from iron particles with the 111 plane oriented parallel to the flat plane has a lower slope of about 1 / 4, and it can be seen that the lower loss is more pronounced as the frequency increases.

[0066] As described above, it has become clear that by applying this technology, it is possible to create an iron core in which the (111) plane is oriented in the flat plane and the orientation of the hard axis of magnetization is controlled.

[0067] Example 2 (Polyethylene Glycol) Flat metal particles were produced in the same manner as in Example 1, except that "polyethylene glycol" was used instead of "lubricating oil (manufactured by Kure Industries, product name: 5-56)" during grinding.

[0068] Example 3 (Liquid Paraffin) Flat metal particles were produced in the same manner as in Example 1, except that liquid paraffin was used instead of lubricating oil (manufactured by Kure Industries, product name: 5-56) during grinding, by carrying out the same grinding and annealing processes.

[0069] The obtained flat metal particles were each compressed in a mold to form a pellet with a diameter of 11.3 mm. The cross section was analyzed and evaluated using an electron microscope (JEOL, JIB-4600F) and an EBSD analyzer (TSL, OIM). The EBSD inverse pole figure maps and inverse pole figures were evaluated on a cross section parallel to the compression direction of the pellet. The results are shown in Figure 8.

[0070] In Example 2, the (001) was 0.63 and the (111) was 3.30. In Example 3, the (001) was 0.54 and the (111) was 2.84. In Examples 2 and 3, the (111) axis, which is the hard magnetization axis, is oriented most flatly, and similar to the flat metal particles of Example 1, they have excellent properties in the high frequency range.

[0071] The flat metal particles of the present invention can be used in powder iron cores used in transformers, reactors, etc., and are therefore industrially useful.

Claims

1. Flat metal particles in which, in an inverse pole figure perpendicular to the flat surface, determined by pole point evaluation using X-ray diffraction, the pole density of (111) is higher than the pole density of (001), and the pole density of (111) is 2 or more.

2. Flat metal particles according to claim 1, having an aspect ratio of 2 or more.

3. A compact compressed from flat metal particles according to claim 1 or 2, in which the (111) pole density measured by electron backscatter diffraction in a cross section parallel to the compression direction is 2 or more.

4. The molded article according to claim 3, which is an iron core for a high-frequency magnetic device.

5. An inductor having a coil wound around the molded body which is the iron core according to claim 4.

6. A magnetic sheet for an electronic device comprising the flat metal particles according to claim 1 or 2.

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