Method for producing soft magnetic particles

Abstract

To provide a manufacturing method of a soft magnetic particle having smaller coercive force and capable of contributing to reduction of iron loss (in particular, hysteresis loss) of a magnetic core.SOLUTION: A manufacturing method of a soft magnetic particle includes: a pulverization step of machine pulverization of a ribbon including a soft magnetic alloy (mainly, ferroalloy) in an amorphous state or a nanocrystal state to obtain raw material pieces; and a treatment step of making the raw material pieces contact process liquid to obtain flakes being the raw material pieces each with a surface layer part removed. The flakes thus obtained are in a state where a residual strain or an oxide layer caused on a vicinity of a surface (surface layer part) of the raw material pieces by the machine pulverization is removed, so that coercive force is likely to be smaller. Such flakes have, for instance, granularity of 500 μm or less. Furthermore, such flakes have a long granular cross section, and an aspect ratio being a ratio of a maximum length to a maximum thickness is 5 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing soft magnetic particles. [Background technology]

[0002] Electromagnetic devices such as electric motors, generators, various actuators, and transformers include a magnetic core (soft magnetic material / soft magnet) on which an alternating magnetic field acts. Magnetic cores can be broadly categorized into laminates of insulatingly coated electromagnetic steel sheets and compacts of insulatingly coated soft magnetic particles (powder cores). Recently, powder cores have come into widespread use because they offer a high degree of freedom in shape and can reduce high-frequency loss (hereinafter simply referred to as "iron loss" regardless of the material of the magnetic core). The soft magnetic particles (powders) used in such powder cores are described, for example, in the following patent documents: [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2005-281805 [Patent Document 2] Patent Publication No. 2006-302958 [Patent Document 3] WO2009 / 139368 [Patent Document 4] Patent Publication No. 2020-77845 [Patent Document 5] Patent Publication No. 2020-96167 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Documents 1 and 2 contain descriptions related to Fe-based atomized powder, while Patent Documents 3 to 5 contain descriptions related to pulverized powder of Fe-based amorphous alloy ribbon. Amorphous or nanocrystalline pulverized powder has a higher saturation magnetic flux density and a lower coercive force than Fe-based atomized powder, and is therefore expected to be used in dust cores with high magnetic properties and low iron loss.

[0005] However, the coercive force of such pulverized powder is correspondingly larger than that of the ribbon itself before pulverization, and conventional methods such as adjusting the pulverization atmosphere and heat treatment after pulverization have not been able to sufficiently reduce the coercive force of the pulverized powder.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a new manufacturing method etc. that can reduce the coercive force of soft magnetic particles. [Means for solving the problem]

[0007] As a result of intensive research to solve this problem, the inventors have succeeded in obtaining flakes (pulverized powder) with significantly reduced coercive force by chemically removing (polishing) at least a portion of the surface (surface layer) of particles (soft magnetic particles) obtained by pulverizing an amorphous alloy ribbon. By expanding on this result, the present invention, which will be described below, has been completed.

[0008] <<Method for manufacturing soft magnetic particles>> (1) The present invention is a method for producing soft magnetic particles, comprising a grinding step in which a ribbon made of an amorphous or nanocrystalline soft magnetic alloy is mechanically ground to obtain raw material pieces, and a processing step in which the raw material pieces are brought into contact with a processing liquid to obtain thin pieces by removing the surface layer of the raw material pieces.

[0009] (2) According to the method for producing soft magnetic particles of the present invention (also simply referred to as the "production method"), it is possible to obtain flakes (soft magnetic particles) with a small coercive force. The reason for this is presumed to be as follows.

[0010] The raw material pieces obtained by mechanically pulverizing ribbons made of amorphous or nanocrystalline soft magnetic alloys have a higher coercive force than the ribbons themselves. This is thought to be due to the residual strain (processing strain, etc.) introduced at least near the surface (surface layer) of the raw material pieces by mechanically pulverizing the ribbons, or the oxidation of the exposed new surface (shear surface of the raw material pieces).

[0011] In the manufacturing method of the present invention, at least a portion of the surface (surface layer) of such raw material pieces is chemically removed with a treatment solution. This removes at least a portion of the residual strain and oxide layer, which are factors that increase the coercive force. As a result, it is believed that the coercive force of the flakes (soft magnetic particles) of the present invention is reduced.

[0012] 《Soft magnetic particles》 The present invention can also be understood as a soft magnetic particle (or soft magnetic powder). For example, the present invention can be a soft magnetic particle consisting of flakes of a soft magnetic alloy, the soft magnetic alloy being amorphous or nanocrystalline, and the flakes having an elongated cross section with at least rounded corners. Flakes with an elongated cross section in which the corners, which are the parts that increase the coercive force, are rounded (removed), tend to have a low coercive force. The present invention can also be understood as a soft magnetic powder that is an aggregate of soft magnetic particles.

[0013] 《Soft magnetic material》 The present invention can also be understood as a member (soft magnetic material) using soft magnetic particles. For example, the present invention may be a soft magnetic material obtained by binding the above-mentioned soft magnetic particles at a temperature below the crystallization temperature. The binding of the soft magnetic particles may be in a state where the shape is maintained by an anchor effect due to plastic deformation of the soft magnetic particles, or in a state where the shape is maintained by a binder (adhesive, base material made of resin or metal, etc.).

[0014] The surface of the soft magnetic particles may be coated with an insulating layer. If an insulating layer (including a binder) exists between the soft magnetic particles (at the grain boundaries), the resistivity of the soft magnetic material increases, thereby reducing eddy current loss in an alternating magnetic field. A typical example of a soft magnetic material is a magnetic core (for example, a powder core formed by compressing soft magnetic powder) that constitutes at least a part of a magnetic circuit.

[0015] "others" (1) In this specification, the term "amorphous" means that the pattern obtained by X-ray diffraction analysis (XRD) of a thin strip or flake is halo-shaped (broad). For example, this refers to an XRD pattern in which the strongest peak is a broad peak on the (110) plane and no other significant peaks are observed.

[0016] "Nanocrystalline" refers to a state in which, when the metal structure of a ribbon or flake is observed under a microscope, the maximum length of each crystal grain is less than 1 μm (or even 100 nm or less, or 50 nm or less). In this case, the entire material may be composed of nanocrystals, or an amorphous phase may be interposed between the nanocrystals (a state in which the nanocrystals are dispersed in the amorphous phase (parent phase)).

[0017] (2) Unless otherwise specified, "x to y" in this specification includes a lower limit of x and an upper limit of y. Any numerical value included in the various numerical values ​​or ranges described in this specification may be used as a new lower limit or upper limit to create a new range such as "a to b."

[0018] Unless otherwise specified, "x to y μm" in this specification means x μm to y μm. The same applies to other units (nm, etc.). [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a photograph of an example of raw material pieces and flakes observed under a microscope. [Figure 2] FIG. 10 is a scatter diagram illustrating the relationship between the etching time of the raw material pieces and the coercive force of the flakes. [Figure 3] FIG. 2 is a schematic diagram showing how raw material pieces are thinned by etching. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in more detail by illustrating embodiments of the invention. One or more configurations arbitrarily selected from this specification may be added to the configuration of the present invention. The contents described in this specification may be applied to the soft magnetic particles (powder), soft magnetic material, and manufacturing methods thereof according to the present invention. Configurations relating to manufacturing methods may also be configurations relating to products. Which embodiment is best depends on the target, required performance, etc.

[0021] Thin Ribbon The ribbon is made of an amorphous or nanocrystalline soft magnetic alloy. Soft magnetic alloys usually have a ferromagnetic element such as Fe, Ni, or Co as a base material. A typical example is an iron alloy. The iron alloy may contain B, Si, Cu, P, Nb, C, Al, Cr, Ti, or Mo. Taking into consideration the saturation magnetic flux density and the desired structure (amorphous or nanocrystalline formation), the iron alloy preferably contains 90 to 96 mass % of Fe relative to the total mass.

[0022] Typical iron alloys include Fe-Si-BP-Cu alloys, Fe-Si-BP-Cu-C alloys, Fe-Si-B-Cu-Nb alloys, and Fe-Ni-B alloys.

[0023] The ribbon may have any form (thickness, width, shape, etc.) as long as it is amorphous or nanocrystalline. For example, the ribbon usually has a thickness of about 5 to 100 μm, 10 to 60 μm, or even 20 to 40 μm. The ribbon may be produced by any method, but may be produced by, for example, a rapid solidification method (single roll liquid cooling method, etc.).

[0024] <Crushing process> The pulverization step is performed by mechanical pulverization, in which shear force, impact force, etc. are mechanically applied to the ribbon to shred the ribbon. Examples of pulverization devices that can be used include cutter mills, feather mills, pulverizers, and cyclone mills. The pulverization device is selected in consideration of, for example, the desired particle size of the raw material pieces or flakes, pulverization efficiency, etc., and it is preferable that the pulverization device has fewer grinding elements.

[0025] The mechanical pulverization may be carried out in an atmosphere of an inert gas (nitrogen, rare gas, etc.), but may also be carried out in an air atmosphere, taking into consideration the treatment steps after the pulverization step.

[0026] The ribbon may be preheated to about 200 to 350°C, or even about 250 to 300°C, before being crushed. This heat treatment embrittles the ribbon, improving its crushability (embrittling step). The heat treatment may be performed in air, but is preferably performed in a vacuum or inert gas in order to prevent surface oxidation.

[0027] <<Processing process>> The treatment step is carried out by bringing the raw material pieces obtained by mechanically pulverizing the ribbon into contact with a treatment liquid. The treatment liquid may be an acidic or alkaline liquid. The treatment liquid may be selected depending on the alloy composition of the ribbon and the surface layer of the raw material pieces. For example, nital (an alcohol solution of nitric acid), or an acid solution obtained by diluting hydrochloric acid, sulfuric acid, or the like with pure water or alcohol can be used as the treatment liquid. In the case of nital, the nitric acid concentration (mass %) is preferably 1 to 20%, or even 3 to 15%, for example.

[0028] The contact of the raw material pieces with the treatment liquid may be carried out by immersion or spraying. The treatment time (contact time) is preferably, for example, 10 to 180 minutes, or more preferably 45 to 150 minutes. The concentration of the treatment liquid and the treatment time can be selected depending on the thickness of the surface layer to be removed and the treatment efficiency.

[0029] Raw material pieces and flakes The raw material pieces are pulverized ribbon pieces. The planar shape of the raw material pieces is not limited, but they are usually scale-like. The cross-sectional shape of the raw material pieces may be, for example, square (rectangular), oval (elliptical), needle-like, or the like. The maximum thickness of the raw material pieces (for example, the maximum length of the short side (uniaxial side) of the cross section) is usually approximately equal to the thickness of the ribbon. The maximum length of the raw material pieces (the maximum length of the long side (major axis side) of the cross section) is, for example, 25 to 750 μm, or even 50 to 500 μm. This maximum length usually corresponds to the particle size of the raw material pieces.

[0030] The flakes are, for example, formed by removing the surface layer of the raw material pieces (chemical polishing). Such flakes usually have a long grain cross section, with the corners removed and rounded compared to the cross section of the raw material pieces. Since the corners of the raw material pieces, which have large residual strain, are at least removed, flakes with a long grain cross section tend to have a small coercive force.

[0031] The maximum thickness of the flakes is, for example, about 5 to 75 μm, 10 to 50 μm, or 15 to 40 μm. The maximum length of the flakes is, for example, 20 to 600 μm or 40 to 500 μm. The aspect ratio, which is the ratio of the maximum length to the maximum thickness, is, for example, 5 or more, 7 or more, 10 or more, or 13 or more.

[0032] The size of each of the raw material pieces or flakes may be determined as the arithmetic mean value of the measurements of a plurality of particles arbitrarily extracted from the powder that is an aggregate of the raw material pieces or flakes.

[0033] 《Application》 Soft magnetic particles can be used in a variety of applications. For example, they are used in magnetic cores (cores / soft magnetic materials) for electric motors (including generators), actuators, transformers, induction heaters (IH), etc. In any case, the use of the soft magnetic particles according to the present invention makes it possible to achieve both high levels of magnetic properties and low iron loss (especially hysteresis loss). [Example]

[0034] The amorphous ribbon was mechanically crushed to obtain a raw material piece, and a sample (thin piece) was produced using the raw material piece, and various properties thereof were evaluated. The present invention will be described in more detail based on such a specific example.

[0035] Machine Shattering Effect The influence of mechanical pulverization on the coercive force was previously investigated as follows.

[0036] (1) Raw materials An amorphous ribbon was prepared as the raw material. Its alloy composition was Fe-2.4%Ni-3.1%B (composition: mass percentage). Its thickness was 34-37 μm, and its coercive force was 5 A / m. The ribbon thickness was measured with a micrometer. The ribbon coercive force was measured with a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.; simply referred to as "VSM") equipped with a Helmholtz coil.

[0037] (2) Mechanical crushing (crushing process) The above ribbon was mechanically pulverized in an air atmosphere at room temperature using one or more of the following pulverizers. Cutter mill: Manufactured by IKA Japan Co., Ltd. Feather Mill: Manufactured by Hosokawa Micron Corporation Pulperizer: Hosokawa Micron Corporation

[0038] The pulverized powder obtained using each device was classified using a sieve (mesh). In this example, the particles were sieved into four sizes: 75 μm or less, 75 to 150 μm, 150 to 250 μm, and 250 to 500 μm. Note that "y to x μm" means that the particles (powder) pass through a sieve with a mesh size of x (μm) but do not pass through a sieve with a mesh size of y (μm). In other words, it means that the maximum particle size is x μm or less (less than) and the minimum particle size is y μm or more (greater than). Unless otherwise specified, the "particle size" referred to in this specification is specified by such sieving. For example, "particle size x μm or less" means that the particles pass through a sieve with a mesh size of x (μm).

[0039] (3) Coercive force The coercive force of the pulverized pieces (raw material pieces) randomly extracted from each pulverized powder was measured using VSM. The results are summarized in Table 1.

[0040] As is clear from Table 1, it was found that even when the same crushing equipment was used, the smaller the particle size of the crushed pieces, the greater the coercive force. Furthermore, it was found that even when the particle size (distribution) is the same, the coercive force of the crushed pieces differs if the crushing equipment (crushing principle) and crushing conditions (crushing time, etc.) are different. Such coercive force is thought to indicate the degree of distortion, oxidation, etc. introduced into the crushed pieces by mechanical crushing of the ribbon.

[0041] "Making Slices" (1) Crushing process The above-mentioned ribbon was heated in the atmosphere at 275°C for 2 hours to embrittle the ribbon (embrittlement heat treatment step).

[0042] The heat-treated ribbon was pulverized for 3 minutes in the feather mill and then further pulverized in a pulverizer. The pulverized powder (raw material pieces) thus obtained was classified into 150 to 250 μm. The same heat-treated ribbon was pulverized for 10 minutes in the cutter mill, and the pulverized powder (raw material pieces) obtained was classified into 75 to 150 μm.

[0043] (2) Treatment process 1 g of each pulverized powder was added to 30 cc of processing solution, stirred, and left for approximately 30 to 180 minutes, after which the powder was washed with water. The processing solution used was an ethanol solution of nitric acid (Nital solution / acid etching solution). The nitric acid concentration was 5% or 10% (the concentration is the mass ratio to the total solution).

[0044] In this way, thin pieces (soft magnetic particles / samples 11 to 13 and sample 2 shown in Table 2) were obtained by etching the surface layer portion of the raw material pieces.

[0045] (3) Comparison sample A comparative sample (sample C2) was also prepared by subjecting the raw material to heat treatment (stress relief annealing) without etching. This heat treatment was carried out by heating at 400°C for 30 minutes in an Ar atmosphere.

[0046] <<Flake Form>> (1) Observation The above-mentioned flakes and raw material pieces were observed using a scanning electron microscope (SEM). Figure 1 shows examples of observed images of raw material pieces with a grain size of 150 to 250 μm and flakes obtained by etching them (samples 11 and 13).

[0047] (2) Measurement Within the field of view (1500 μm × 1000 μm) of the SEM image, the maximum thickness (maximum length in the minor axis direction) and maximum length (maximum length in the major axis direction) of each thin section were measured. For each sample, the arithmetic mean value of the maximum thickness (t) and the arithmetic mean value of the maximum length (L) were calculated, and their ratio (L / t: aspect ratio) was also calculated (see Figure 3). The results are also shown in Table 2.

[0048] <<Coercive force of thin film>> (1) For each sample, the coercive force (H0) of the raw piece (before treatment) and the coercive force (H) of the thin piece (after treatment) were measured using a VSM with a built-in Helmholtz coil, applying a maximum magnetic field of 200 Oe.

[0049] The coercive force (H0, H) of each sample thus obtained is shown in Table 2. The reduction rate of coercive force due to etching (100 × (H0-H) / H0) was also calculated and shown in Table 2.

[0050] (2) The coercive force of the thin sections obtained by varying the etching time was also measured in the same manner as for Samples 11 to 13 and Sample 2. The results are summarized in Figure 2.

[0051] "evaluation" As is clear from Figures 1 and 2 and Table 2, it was found that the coercive force can be significantly reduced by etching the raw material pieces. In particular, the reduction rate of the coercive force could be increased by increasing the concentration of the etching solution (treatment solution) or by extending the etching time (treatment time). Furthermore, as is clear from a comparison of Sample 2 and Sample C2, it was also found that etching reduces the coercive force more than heat treatment (annealing).

[0052] Table 2 shows that the presence or absence of etching affects not only the coercive force but also the flake morphology (especially the cross-sectional shape). In other words, it was found that etching produces thin flakes with a large aspect ratio and an elongated cross-section.

[0053] [Table 1]

[0054] [Table 2]

Claims

1. a crushing step of mechanically crushing a ribbon made of an amorphous or nanocrystalline soft magnetic alloy having a maximum crystal grain length of less than 1 μm to obtain raw material pieces; a treatment step of contacting the raw material pieces with a treatment liquid to obtain flakes by removing a surface layer portion of the raw material pieces, A method for producing soft magnetic particles that does not require annealing after the treatment step.

2. The soft magnetic particles are comprised of flakes having an elongated cross section with at least rounded corners, 2. The method according to claim 1, wherein the elongated cross section has an aspect ratio (L / t), which is the ratio of the maximum length (L) to the maximum thickness (t), of 5 or more.

3. A manufacturing method described in claim 1 or 2, wherein the soft magnetic particles have a particle size of 500 μm or less.

4. 3. The manufacturing method according to claim 2, wherein the long grain cross section has the maximum thickness (t) of 5 to 75 μm and the maximum length (L) of 20 to 600 μm.

5. The manufacturing method according to any one of claims 1 to 4, wherein the soft magnetic alloy is an iron alloy.

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