Soft magnetic alloy powder, compacted magnetic core and coil components

Abstract

To provide a soft magnetic alloy powder having good saturation magnetization and a coercive force capable of reducing core loss while maintaining good permeability and DC superposition characteristics of a dust core including the soft magnetic alloy powder.SOLUTION: The soft magnetic alloy powder includes soft magnetic alloy particles. The soft magnetic alloy particles include Fe and Si. The soft magnetic alloy particles are composed of a plurality of crystallites and a crystal grain boundary between a plurality of crystallites. The crystallites have a portion where Si is segregated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to soft magnetic alloy powder, compacted magnetic core, and coil components. [Background technology]

[0002] Patent Document 1 describes an invention of a metallic magnetic material comprising soft magnetic alloy particles made of Fe and Si. This metallic magnetic material includes a layer containing a high concentration of Si between the soft magnetic alloy particles.

[0003] Patent Document 2 describes an invention of soft magnetic alloy particles containing Fe and Ni. These soft magnetic alloy particles consist of a plurality of crystallites and grain boundaries between the crystallites, with a high-resistance layer present at the grain boundaries. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-143700 [Patent Document 2] Japanese Patent Publication No. 2018-206835 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a soft magnetic alloy powder that has good saturation magnetization and coercivity, and furthermore, can reduce core loss while improving the permeability and DC superposition characteristics of a compacted magnetic core containing the soft magnetic alloy powder. [Means for solving the problem]

[0006] To achieve the above objective, the soft magnetic alloy powder of the present invention is a soft magnetic alloy powder containing soft magnetic alloy particles, The soft magnetic alloy particles contain Fe and Si, The soft magnetic alloy particles consist of a plurality of crystallites and grain boundaries between the plurality of crystallites. The crystallite is characterized by the presence of regions where Si is segregated.

[0007] The soft magnetic alloy powder according to the present invention has the above-mentioned characteristics, which enable good saturation magnetization and coercivity. Furthermore, it is possible to reduce core loss while improving the permeability and DC superposition characteristics of the compacted magnetic core containing the soft magnetic alloy powder.

[0008] The soft magnetic alloy particles may contain only Fe, Si, and unavoidable impurities.

[0009] The Si content in the soft magnetic alloy particles may be 3.0% by mass or more and 11.0% by mass or less.

[0010] The compacted magnetic core of the present invention contains the above-mentioned soft magnetic alloy powder.

[0011] The coil component of the present invention includes the above-mentioned powdered magnetic core. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of soft magnetic alloy particles according to this embodiment. [Figure 2] This is a COMPO image of soft magnetic alloy particles from sample No. 3. [Figure 3] This is a Si mapping image of soft magnetic alloy particles from sample No. 3. [Figure 4] This is a binarized image of Figure 3. [Figure 5] This is a COMPO image of soft magnetic alloy particles from sample No. 6. [Figure 6] This is a Si mapping image of soft magnetic alloy particles from sample No. 6. [Figure 7] This is a binarized image of Figure 6. [Figure 8] This is a COMPO image of soft magnetic alloy particles from sample No. 7. [Figure 9]It is an Si mapping image of the soft magnetic alloy particles of Sample No. 7. [Figure 10] It is an image obtained by binarizing FIG. 9.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present invention will be described based on the drawings, but the embodiments of the present invention are not limited to the following embodiments.

[0014] The soft magnetic alloy powder according to the present embodiment contains soft magnetic alloy particles 2. As shown in FIG. 1, the soft magnetic alloy particles 2 are composed of a plurality of crystallites 4 and grain boundaries 4a existing between the crystallites 4.

[0015] The soft magnetic alloy particles 2 contained in the soft magnetic alloy powder according to the present embodiment are characterized in that there are sites where Si is segregated in the crystallites 4. Hereinafter, the site where Si is segregated may be simply referred to as an Si segregation part.

[0016] The Si segregation part is considered to be a part with a higher electrical resistance compared to the part other than the Si segregation part of the crystallite 4. When the Si segregation part is included in the crystallite 4, the electrical resistance in the crystallite 4 increases. By increasing the electrical resistance in the crystallite 4, the generation of eddy currents in the crystallite 4 is suppressed. As a result, the powder compact core produced using the soft magnetic alloy powder containing the soft magnetic alloy particles 2 having an Si segregation part in the crystallite 4 has particularly good permeability at high frequencies and low core loss. In particular, when the crystal grain size of the crystallite 4 is large, the effect of suppressing the generation of eddy currents due to the presence of the Si segregation part in the crystallite 4 becomes greater.

[0017] Also, an Si segregation part may exist at the grain boundary 4a. When the Si segregation part is included in the grain boundary 4, it is considered that the electrical resistance at the grain boundary 4a increases. By increasing the electrical resistance at the grain boundary 4a, the generation of eddy currents in the soft magnetic alloy particles 2 is suppressed.

[0018] It is particularly preferable that Si segregation zones exist at both the crystallites 4 and the grain boundaries 4a. A compacted magnetic core made using soft magnetic alloy powder containing soft magnetic alloy particles 2 in which Si segregation zones exist at both the crystallites 4 and the grain boundaries 4a exhibits particularly good magnetic permeability at high frequencies and low core loss.

[0019] There are no particular restrictions on the average particle size of the soft magnetic alloy particles 2, but for example, it is between 1 μm and 50 μm. Similarly, there are no particular restrictions on the average crystallite diameter of the crystallites 4, but for example, it is between 0.5 μm and 20 μm.

[0020] The soft magnetic alloy particles 2 contain at least Fe and Si. Other elements may be included in amounts that do not significantly affect the properties of the soft magnetic alloy powder containing the soft magnetic alloy particles 2. For example, the other elements may be included in amounts of 5.0 mass% or less, or 1.0 mass% or less, respectively. Alternatively, the other elements may be included in a total of 10.0 mass% or less, or 2.0 mass% or less.

[0021] However, if the soft magnetic alloy particles 2 contain Ni, the crystallites 4 are less likely to contain Si segregation regions. Also, raw materials containing Ni are expensive. Therefore, the Ni content is preferably 5.0% by mass or less, and preferably 0.5% by mass or less.

[0022] The soft magnetic alloy particles 2 may contain only Fe, Si, and unavoidable impurities. In this case, the content of unavoidable impurities may be 2.0% by mass or less, or 1.0% by mass or less.

[0023] There are no particular restrictions on the Si content in the soft magnetic alloy particles 2. It may be 2.0% by mass or more and 12.0% by mass or less, or 3.0% by mass or more and 11.0% by mass or less. A Si content of 2.0% by mass or more or 3.0% by mass or more makes it easier to lower the coercivity of the soft magnetic alloy powder containing the soft magnetic alloy particles 2. It also makes it easier to reduce the core loss of the compacted magnetic core containing the soft magnetic alloy powder. A Si content of 12.0% by mass or less or 11.0% by mass or less makes it easier to increase the saturation magnetization of the soft magnetic alloy powder containing the soft magnetic alloy particles 2. It also makes it easier to improve the permeability and DC superposition characteristics of the compacted magnetic core containing the soft magnetic alloy powder.

[0024] The fact that the soft magnetic alloy particles 2 consist of multiple crystallites 4 and grain boundaries 4a existing between the crystallites 4 can be confirmed by observing the backscattered electron image (COMPO image) obtained by EPMA. Figure 2 shows the COMPO image of the soft magnetic alloy particles according to this embodiment. There are no particular restrictions on the magnification of the COMPO image; any magnification and resolution that allows the above-mentioned microstructure of the soft magnetic alloy particles to be confirmed is acceptable. For example, the magnification can be between 500x and 5000x.

[0025] Furthermore, the presence of Si segregation regions at grain boundaries 4a and crystallite 4 can be confirmed by performing Si mapping using EPMA. Figure 3 shows the Si mapping image of the soft magnetic alloy particles shown in Figure 2. In this embodiment, regions with a Si concentration of 105% or more relative to the average Si concentration of the soft magnetic alloy particles are defined as Si segregation regions. The size of one Si segregation region is 0.4 μm. 2 That concludes the explanation. The size is 0.4 μm. 2 The portion less than the specified value is not considered a Si segregation region.

[0026] Figure 4 is a binarized image of the Si mapping image shown in Figure 3, divided into areas with a Si concentration of 105% or more relative to the average Si concentration of the soft magnetic alloy particles and areas with a Si concentration of less than 105%. By comparing Figure 2 and Figure 4, it is possible to confirm whether Si segregation zones exist at the grain boundaries and in the crystallites. As shown in Figures 3 and 4, Si segregation zones exist at the grain boundaries, and furthermore, Si segregation zones exist in a network-like structure in the crystallites.

[0027] Figures 2 to 4 show soft magnetic alloy particles with a Si content of 4.5 mass%. The soft magnetic alloy particles shown in Figures 2 to 4 are the soft magnetic alloy particles of sample No. 3, which will be described later. Figures 5 to 7 and 8 to 10 also show the COMPO image, Si mapping image, and binarized image of the Si mapping image of the soft magnetic alloy particles, respectively. The soft magnetic alloy particles shown in Figures 5 to 7 are the soft magnetic alloy particles of sample No. 6 (Si content of 6.5 mass%), which will be described later. The soft magnetic alloy particles shown in Figures 8 to 10 are the soft magnetic alloy particles of sample No. 7 (Si content of 8.0 mass%), which will be described later.

[0028] There are no particular restrictions on the proportion of Si segregation at the grain boundary 4a. In the cross-section of the soft magnetic alloy particle 2, it is preferable that the total area of ​​Si segregation at the grain boundary 4a is 70% or more of the total area of ​​the grain boundary 4a.

[0029] There are no particular restrictions on the proportion of Si segregation in the crystallite 4. In the cross-section of the soft magnetic alloy particle 2, it is preferable that the total area of ​​Si segregation in the crystallite 4 is 5% or more of the total area of ​​the crystallite 4.

[0030] Furthermore, an oxide film may be present on the particle surface 2a of the soft magnetic alloy particles 2. For example, the thickness of the oxide film may be 5.0 nm or less, or 3.0 nm or less. The thinner the oxide film, the easier it is for the hardness of the soft magnetic alloy particles 2 to decrease, and the easier it is for processability to improve. By improving the processability of the soft magnetic alloy particles 2, it becomes easier to improve the density of the compacted magnetic core containing the soft magnetic alloy particles 2.

[0031] The soft magnetic alloy powder according to this embodiment contains soft magnetic alloy particles 2 according to this embodiment. The soft magnetic alloy powder according to this embodiment does not have to consist only of soft magnetic alloy particles 2 according to this embodiment; it may also contain soft magnetic alloy particles that do not contain Si segregation regions in their crystallites. Preferably, the content of soft magnetic alloy particles containing Si segregation regions in their crystallites in the soft magnetic alloy powder according to this embodiment is 50% or more based on the number of particles. Furthermore, preferably, the content of soft magnetic alloy particles containing Si segregation regions in both the grain boundaries and the crystallites in the soft magnetic alloy powder according to this embodiment is 50% or more based on the number of particles.

[0032] The following describes an example of a method for producing soft magnetic alloy powder consisting of soft magnetic alloy particles according to this embodiment, but the method for producing soft magnetic alloy powder according to this embodiment is not limited to the method described below. In this embodiment, an aggregate of a substance containing multiple particles is used as the powder.

[0033] First, prepare the raw materials for the soft magnetic alloy powder. The raw materials can be individual metals or alloys. There are no particular restrictions on the form of the raw materials. For example, they can be ingots, chunks, or shots.

[0034] Next, the prepared raw materials are weighed and mixed. At this stage, the weighing is done so that the desired composition of soft magnetic alloy powder is ultimately obtained. Then, the mixed raw materials are melted and mixed to obtain a molten material. There are no particular restrictions on the equipment used for melting and mixing. For example, a crucible can be used.

[0035] Next, soft magnetic alloy powder is produced from the molten material. There are no particular restrictions on the method of producing soft magnetic alloy powder from the molten material, but for example, gas atomization, rotating disk method, and water atomization method can be used. Of these, in the gas atomization method, soft magnetic alloy powder can be produced by supplying the molten material as a continuous fluid through a nozzle or the like, and rapidly cooling the supplied molten material by impacting it with high-pressure gas.

[0036] Next, the obtained soft magnetic alloy powder is subjected to heat treatment. By performing the heat treatment under appropriate heat treatment conditions, Si segregation zones can be incorporated into the grain boundaries and crystallites.

[0037] The preferred heat treatment conditions vary depending on the composition of the target soft magnetic alloy powder, but typically the holding temperature during heat treatment is 800°C to 1100°C, preferably 800°C to 900°C. The holding time is 10 minutes to 3 hours, preferably 10 minutes to 2 hours.

[0038] Furthermore, the cooling rate to 300°C after heat treatment should be between 0.1°C / s and 100°C / s. There are no particular restrictions on the heat treatment atmosphere, but it is usually an inert gas atmosphere such as nitrogen or argon, or a vacuum.

[0039] In particular, by setting the holding temperature during heat treatment to a high temperature as described above, and the cooling rate to a fast rate as described above, Si segregation zones can be incorporated not only at the grain boundaries but also in the crystallites. If the cooling rate is too slow, it becomes easier to incorporate Si segregation zones at the grain boundaries, but it becomes more difficult to incorporate them in the crystallites. If the cooling rate is too fast, it becomes more difficult to incorporate Si segregation zones in both the grain boundaries and the crystallites. In other words, if the cooling rate is too fast, Si tends to be uniformly incorporated within the soft magnetic alloy particles.

[0040] If the holding temperature is too high, the crystallites tend to become coarse. If the holding temperature is too low, it becomes easier to include Si segregation zones at the grain boundaries, but it becomes more difficult to include Si segregation zones in the crystallites.

[0041] By the above method, a soft magnetic alloy powder consisting of soft magnetic alloy particles according to this embodiment can be obtained. Furthermore, a compacted magnetic core can be obtained using a method commonly used with the soft magnetic alloy powder according to this embodiment. There are no particular restrictions on the method for obtaining the compacted magnetic core.

[0042] A compacted magnetic core may be obtained using a soft magnetic alloy powder obtained by mixing the soft magnetic alloy powder according to this embodiment with other soft magnetic metal powders. There are no particular restrictions on the type of other soft magnetic metal powder. For example, a soft magnetic metal powder with a smaller average particle size than the soft magnetic alloy powder according to this embodiment can be used. The average particle size of the soft magnetic metal powder with a smaller average particle size may be 0.5 μm or more and 5 μm or less. There are no particular restrictions on the material of the soft magnetic metal powder with a smaller average particle size. For example, metals such as pure iron and alloys such as permalloy can be used.

[0043] There are no particular restrictions on the proportion of the soft magnetic alloy powder according to this embodiment when mixing it with the soft magnetic metal powder with a small average particle size. For example, it may be 50% by mass or more.

[0044] Coil components, such as inductors, reactors, and motors, can be obtained from the powdered magnetic core according to this embodiment using methods commonly employed. In particular, coil components with high saturation current, low coil resistance, and low loss at high frequencies can be obtained. Furthermore, when using the powdered magnetic core according to this embodiment, miniaturization of coil components is also easy. There are no particular restrictions on the method of obtaining the coil components. [Examples]

[0045] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0046] [Preparation of soft magnetic alloy powder] First, ingots, chunks, or shots of elemental Fe and elemental Si were prepared. Next, the elemental Fe and elemental Si were mixed to the Si content shown in Tables 1 and 2, and the mixture was placed in a crucible located in a gas atomizing apparatus. Then, in an inert atmosphere, the crucible was heated to over 1500°C by high-frequency induction using a work coil located outside the crucible, melting and mixing the ingots, chunks, or shots inside the crucible to obtain a molten material.

[0047] Next, Fe-Si-based soft magnetic alloy powders with the Si content shown in Tables 1 and 2 were prepared by supplying molten material from a nozzle in the crucible and simultaneously rapidly cooling the supplied molten material by impacting it with a gas at 1 to 10 MPa. In all soft magnetic alloy powders, the average particle size of the soft magnetic alloy particles was set to 25 μm.

[0048] Furthermore, the obtained soft magnetic alloy powder was subjected to heat treatment. The heat treatment conditions for each experimental example described in Table 1 are shown in Table 1. In addition, the heat treatment conditions for each experimental example described in Table 2 were appropriately controlled within the range of: holding temperature: 800°C to 1100°C, holding time: 10 minutes to 3 hours, and cooling rate to 300°C after heat treatment: 0.1°C / s to 100°C / s.

[0049] [Preparation of powdered magnetic core] Granulated powder was prepared by adding epoxy resin as a binder to heat-treated soft magnetic alloy powder. The type and amount of epoxy resin added were determined appropriately according to the composition of each soft magnetic alloy powder. Using this granulated powder, a toroidal shape with an outer diameter of 18 mm, an inner diameter of 10 mm, and a height of 5 mm was formed at a molding pressure of 6 ton / cm². 2 The material was then molded. Next, the molded body was held at 180°C for 3 hours in an atmospheric environment to cure the resin, thereby obtaining a toroidal-shaped powder magnetic core.

[0050] [Evaluation of soft magnetic alloy powders] (Evaluation of magnetic properties) The saturation magnetization σs and coercivity Hc of the soft magnetic alloy powders in each experimental example were measured. σs was measured using a vibrating sample magnetometer (VSM) at a magnetic field of 1000 kA / m. Hc was measured using an Hc meter. The results are shown in Tables 1 and 2. A σs of 120 emu / g or higher was considered good, and 140 emu / g or higher was considered even better. A Hc of 1000 A / m or lower was considered good, and 800 A / m or lower was considered even better.

[0051] (Observation of Si segregation) The presence or absence of Si segregation zones at grain boundaries and crystallites was determined by observing the cross-section obtained by cross-polishing a compound made by kneading soft magnetic alloy powder with resin. Specifically, the positions of grain boundaries and crystallites in the soft magnetic alloy particles were identified from the COMPO image obtained by observing the compound at a magnification of 2000x using EPMA (JEOL JXA-8500F). Then, the presence or absence of Si segregation zones at grain boundaries and in the crystallites of the soft magnetic alloy particles was determined from the Si mapping image obtained by observing the compound at a magnification of 2000x using EPMA (JEOL JXA-8500F).

[0052] The measurement conditions for EPMA were: acceleration voltage 15.0kV, irradiation current 1.030 × 10⁻¹⁰ -7 A. The irradiation time was 40.00 ms, the number of measurement points was 200 × 200, and the measurement point interval was 0.20 μm. The Si content was calculated by assuming that the sum of the content of the four elements Si, P, O, and Fe was 100 mass%. P and O are included as unavoidable impurities. Furthermore, the composition of the parts other than the soft magnetic alloy particles is inaccurate because the parts other than the soft magnetic alloy particles contain a large amount of carbon (C) derived from the kneaded resin.

[0053] In this example, at least 10 soft magnetic alloy particles were observed in the cross-section obtained by polishing the cross-section of a compound obtained by kneading soft magnetic alloy particles with resin. In each example, the proportion of soft magnetic alloy particles with Si segregation zones at the grain boundaries and crystallites was 70% or more on a numerical basis. In contrast, in the comparative example of sample No. 1, no Si segregation zones were observed at either the grain boundaries or the crystallites. In the comparative example of sample No. 2, the proportion of soft magnetic alloy particles with Si segregation zones at the grain boundaries was 70% or more on a numerical basis, but no soft magnetic alloy particles with Si segregation zones at the crystallites were observed. The results are shown in Tables 1 and 2.

[0054] [Evaluation of powdered magnetic core] (Measurement of permeability and DC superposition characteristics) For the compacted powder cores of each example and comparative example, the relative permeability μ' at a frequency of 1 MHz was measured. An RF impedance material analyzer (Agilent Technologies: 4991A) was used for the measurement of the relative permeability μ'. Also, the relative permeability μ' when the applied DC current is 0, that is, when no DC current is superimposed, is μ0, and the relative permeability μ' when a DC magnetic field of 20 kA / m is applied with a DC current superimposed is μ 20k and μ 20k / μ0 was calculated to evaluate the DC superposition characteristics. In this example, μ0 was considered good when it was 22.0 or more, and even better when it was 23.0 or more. Also, μ 20k / μ0 was considered good when it was 0.55 or more, and even better when it was 0.60 or more. The results are shown in Tables 1 and 2.

[0055] (Measurement of core loss (power loss) Pcv) For the compacted powder cores of each example and comparative example, the primary winding was wound 30 times and the secondary winding was wound 10 times. Then, Pcv was measured at a measurement frequency of 0.3 MHz and a magnetic flux density of 25 mT. Also, Pcv was measured at a measurement frequency of 3 MHz and a magnetic flux density of 10 mT. The measurement of Pcv was performed using a B-H analyzer (SY-8218 manufactured by Iwasaki Telecom Co., Ltd.). The Pcv measured at a measurement frequency of 0.3 MHz and a magnetic flux density of 25 mT was 600 kW / m 3 or less was considered good, and 500 kW / m 3 or less was considered even better. The Pcv measured at a measurement frequency of 3 MHz and a magnetic flux density of 10 mT was 2200 kW / m 3 or less was considered good, and 2000 kW / m 3 or less was considered even better. The results are shown in Tables 1 and 2.

[0056]

Table 1

[0057]

Table 2

[0058] Tables 1 and 2 show that each example in which the crystallites of the soft magnetic alloy particles contained Si segregation regions exhibited good magnetic properties. Furthermore, when compacted magnetic cores were fabricated from the soft magnetic alloy particles, they showed good relative permeability and DC superposition characteristics, and core loss was small at all frequencies.

[0059] Furthermore, when the Si content was 3.0 mass% or higher, the coercivity of the soft magnetic alloy powder and the core loss of the compacted magnetic core were particularly reduced. Also, when the Si content was 11.0 mass% or lower, the saturation magnetization of the soft magnetic alloy powder and the relative permeability μ' of the compacted magnetic core were particularly increased. In addition, the DC superposition characteristics of the compacted magnetic core were improved.

[0060] In contrast, when the crystallites of the soft magnetic alloy particles did not contain Si segregation regions (samples No. 1 and 2), the core loss at high frequencies worsened when compacted magnetic cores were fabricated from the soft magnetic alloy particles. [Explanation of Symbols]

[0061] 2...Soft magnetic alloy particles 2a...(soft magnetic alloy) particle surface 4. Crystallite 4a...grain boundary

Claims

1. A soft magnetic alloy powder containing soft magnetic alloy particles, The soft magnetic alloy particles contain Fe and Si, The soft magnetic alloy particles consist of a plurality of crystallites and grain boundaries between the plurality of crystallites. A soft magnetic alloy powder having regions in which Si is segregated within the crystallite.

2. The soft magnetic alloy powder according to claim 1, wherein the soft magnetic alloy particles consist only of Fe, Si, and unavoidable impurities.

3. The soft magnetic alloy powder according to claim 1 or 2, wherein the Si content in the soft magnetic alloy particles is 3.0% by mass or more and 11.0% by mass or less.

4. A compacted magnetic core comprising the soft magnetic alloy powder according to claim 1 or 2.

5. A coil component comprising a compacted magnetic core as described in claim 4.

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