Soft magnetic alloy powders, powder cores, and magnetic components

Abstract

To provide a soft magnetic alloy powder, a powder-compact magnetic core and a magnetic component that can realize a high withstand voltage and a high m value.SOLUTION: Provided is a soft magnetic alloy powder having a particle body made of a soft magnetic alloy containing Fe and Co and a surface layer portion located on the surface side of the particle body. The surface layer portion has at least 1 or more Si concentration maximum point and at least 1 or more Co concentration maximum point. Setting the maximum point located closest to the particle center side among the at least 1 or more Si concentration maximum points as a first Si maximum point LSimax, the distance from the interface between the particle body and the surface layer portion to LSimax as DSi, the maximum point located closest to the particle center side among the at least 1 or more Co concentration maximum points as a first Co maximum point LComax, and the distance from the interface to LComax as DCo, DSi≤DCo is satisfied.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic alloy powder, a dust core, and a magnetic component. [Background technology]

[0002] Magnetic components such as inductors, transformers, and choke coils are widely used in the power supply circuits of various electronic devices. In recent years, reducing energy loss and improving power supply efficiency in power supply circuits has become increasingly important in the move toward a low-carbon society, and there is a demand for more efficient and energy-efficient magnetic components.

[0003] To meet the above requirements for magnetic components, it is essential to improve the relative permeability of the magnetic core contained in the magnetic component. To improve the relative permeability of the magnetic core, it is necessary to increase the packing rate of the magnetic powder contained in the magnetic core. Therefore, in the field of magnetic components, various attempts have been made to improve the packing rate of the magnetic core. For example, Patent Document 1 discloses that the packing rate can be improved by increasing the circularity of the magnetic powder. Furthermore, Patent Document 2 discloses a technology for increasing the packing rate of the magnetic powder by using a mixed powder of coarse powder and fine powder.

[0004] However, increasing the filling rate of magnetic powder increases the number of contact points between magnetic particles, which tends to decrease the withstand voltage of the magnetic core. In other words, there is a trade-off between filling rate (relative permeability) and withstand voltage. Furthermore, as the filling rate increases, differences in the number of contact points per particle arise, which increases the variation in withstand voltage due to differences in the number of contact points, and the m value, which indicates the degree of variation, tends to decrease. Therefore, there is a need to develop technology that can achieve high withstand voltage and a high m value even when the filling rate of magnetic powder is increased. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-073947 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-012630 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a soft magnetic alloy powder, a dust core, and a magnetic component that can achieve a high withstand voltage and a high m value. [Means for solving the problem]

[0007] In order to achieve the above object, the soft magnetic alloy powder according to the present invention comprises: A particle body made of a soft magnetic alloy containing Fe and Co, and a surface layer portion located on the surface side of the particle body, the surface layer portion has a maximum point of Si concentration of at least 1 and a maximum point of Co concentration of at least 1, The maximum point located closest to the particle center among the maximum points of Si concentration of at least 1 is designated as the first Si maximum point L Si max year, The L Si max The distance to Si year, The maximum point located closest to the particle center among the maximum points of Co concentration of at least 1 is designated as the first Co maximum point L Co max year, The interface to the L Co max The distance to Co As, D Si ≦D Co Meet the following.

[0008] By using soft magnetic alloy powder having the above characteristics, it is possible to improve the withstand voltage and m value compared to conventional materials while maintaining a high relative permeability.

[0009] Preferably, DSi <D Co Meet the following.

[0010] Preferably, the surface layer is an oxide phase.

[0011] Preferably, the surface layer portion has a Si oxide phase containing an oxide of Si, Said L Si max is present in the Si oxide phase.

[0012] Preferably, the surface layer portion has a Co oxide phase containing an oxide of Co, Said L Co max is present in the Co oxide phase, A part of the Co oxide phase overlaps a part of the surface side of the Si oxide phase. Alternatively, the Co oxide phase may be located closer to the surface than the Si oxide phase.

[0013] The soft magnetic alloy powder of the present invention can be used for various magnetic parts without any particular limitations, and in particular, can be suitably used as a material for powder magnetic cores in magnetic parts such as inductors, transformers, and choke coils. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a soft magnetic alloy powder according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a main part of a region II shown in FIG. [Figure 3A] FIG. 3A is a graph simulating an example of line analysis data. [Figure 3B] FIG. 3B is a graph simulating an example of line analysis data. [Figure 4A] FIG. 4A is a graph simulating an example of line analysis data. [Figure 4B] FIG. 4B is a graph simulating an example of line analysis data. [Figure 5] FIG. 5 is a schematic cross-sectional view showing an example of a dust core containing the soft magnetic alloy powder shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing an example of a magnetic component having a powder magnetic core. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below based on the embodiments shown in the drawings.

[0016] As shown in FIG. 1 , the soft magnetic alloy powder 1 of this embodiment includes first particles 1a having a surface layer portion 10. In addition to the first particles 1a, the soft magnetic alloy powder 1 may also include other particles that do not have the surface layer portion 10, and the other particles may have a different composition or particle size from the first particles 1a. The proportion of the first particles 1a in the soft magnetic alloy powder 1 may be appropriately determined depending on the application of the soft magnetic alloy powder 1, and is not particularly limited. For example, the mass proportion of the first particles 1a can be 10% to 100%, and preferably 60% to 90%.

[0017] The average particle size of the soft magnetic alloy powder 1 is not particularly limited and can be, for example, 0.5 μm to 150 μm, and preferably 0.5 μm to 25 μm. When the soft magnetic alloy powder 1 contains other particles that do not have a surface layer portion 10, the average particle size of the first particles 1a is preferably 5 μm or more, and the average particle size of the other particles is preferably less than 5 μm.

[0018] The average particle size can be measured by various particle size analysis methods, such as laser diffraction, but is preferably measured using a particle image analyzer, Morphologi G3 (manufactured by Malvern Panatical). Using the Morphologi G3, soft magnetic alloy powder 1 is dispersed using air, the projected area of ​​the particles constituting the powder is measured, and a particle size distribution based on the equivalent circle diameter is obtained from the projected area. The particle size at which the cumulative relative frequency on a volume basis or number basis reaches 50% in the obtained particle size distribution can then be calculated as the average particle size. When soft magnetic alloy powder 1 is contained in a magnetic core, the average particle size can be calculated by observing the cross section using an electron microscope (SEM, STEM, etc.) and measuring the equivalent circle diameter of the particles contained in the cross section.

[0019] Fig. 2 is an enlarged cross-sectional view of the surface vicinity of a first particle 1a. As shown in Fig. 2, the first particle 1a has a particle body 2 and a surface layer portion 10 located on the surface side of the particle body 2. In this embodiment, the "surface side" means the side closer to the outside of the particle in the direction from the particle center toward the particle surface.

[0020] (Particle body 2) The particle body 2 is a base portion that occupies at least 90 vol% or more of the volume of the first particle 1a. Therefore, the average composition of the first particle 1a can be considered to be the composition of the particle body 2, and the crystal structure of the first particle 1a can be considered to be the crystal structure of the particle body 2. Note that the volume ratio of the particle body 2 can be replaced with an area ratio, and the particle body 2 occupies at least 90% or more of the cross-sectional area of ​​the first particle 1a.

[0021] The particle body 2 has a soft magnetic alloy composition containing Fe and Co, and the specific alloy composition is not particularly limited. For example, the particle body 2 can be a crystalline soft magnetic alloy such as an Fe-Co alloy, an Fe-Co-V alloy, an Fe-Co-Si alloy, or an Fe-Co-Si-Al alloy. Alternatively, from the viewpoint of reducing the coercive force of the soft magnetic alloy powder 1, the particle body 2 preferably has an amorphous or nanocrystalline alloy composition.

[0022] Examples of amorphous or nanocrystalline soft magnetic alloys include Fe-Co-PC based alloys, Fe-Co-B based alloys, and Fe-Co-B-Si based alloys. (Fe (1-(α+β)) Co α Ni β ) (1-(a+b)) X1 a X2 b It is preferable that the alloy has a composition that satisfies the above, and by having the above composition, an amorphous, heteroamorphous or nanocrystalline crystal structure is easily obtained.

[0023] In the above composition formula, X1 is one or more elements selected from B, P, C, Si, and Al. X2 is one or more elements selected from Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ga, Ag, Zn, S, Ca, Mg, V, Sn, As, Sb, Bi, N, O, Au, Cu, rare earth elements, and platinum group elements. Rare earth elements include Sc, Y, and lanthanides, and platinum group elements include Ru, Rh, Pd, Os, Ir, and Pt. α, β, a, and b are atomic ratios, and these atomic ratios preferably satisfy the following requirements:

[0024] The content (α) of Co relative to Fe is 0.005≦α≦0.700, or may be 0.010≦α≦0.600, 0.030≦α≦0.600, or 0.050≦α≦0.600. When α is within the above range, the saturation magnetic flux density Bs and corrosion resistance of the soft magnetic alloy powder 1 are improved. From the viewpoint of improving Bs, it is preferable that 0.050≦α≦0.500. As α increases, corrosion resistance tends to improve, but if α is too large, Bs is likely to decrease.

[0025] Furthermore, the content (β) of Ni relative to Fe can be, for example, 0≦β≦0.200. That is, the soft magnetic alloy need not contain Ni, or may be 0.005≦β≦0.200. From the viewpoint of improving Bs, it may be 0≦β≦0.050, 0.001≦β≦0.050, or 0.005≦β≦0.010. As β increases, corrosion resistance tends to improve, but if β is too large, Bs decreases.

[0026] Furthermore, when the sum of the atomic ratios of the elements constituting the soft magnetic alloy is 1, the atomic ratio (1-(a+b)) of the total content of Fe, Co, and Ni is preferably 0.720≦(1-(a+b))≦0.950, and more preferably 0.780≦(1-(a+b))≦0.890. Satisfying this requirement makes it easier to improve Bs. Also, when 0.720≦(1-(a+b))≦0.890, it is easier to obtain an amorphous state, and the coercive force is more likely to decrease.

[0027] X1 may be contained as an impurity or may be intentionally added. The content (a) of X1 is preferably 0≦a≦0.200. From the viewpoint of improving Bs, it is preferably 0≦a≦0.150.

[0028] X2 may be contained as an impurity or may be intentionally added. The content (b) of X2 is preferably 0≦b≦0.200. From the viewpoint of improving Bs, it is preferable that 0≦b≦0.150, and more preferably 0≦b≦0.100.

[0029] The composition of the particle body 2 (i.e., the composition of the first particle 1a) can be analyzed, for example, by inductively coupled plasma optical emission spectroscopy (ICP). In this case, if it is difficult to determine the oxygen content by ICP, impulse heating melt extraction can be used in combination. Furthermore, if it is difficult to determine the carbon content and sulfur content by ICP, infrared absorption can be used in combination.

[0030] In addition to ICP, composition analysis may be performed using an EDX (energy dispersive X-ray analysis) or EPMA (electron probe microanalyzer) attached to an electron microscope. For example, composition analysis using ICP may be difficult for the soft magnetic alloy powder 1 contained in a powder magnetic core containing a resin component. In such cases, composition analysis may be performed using EDX or EPMA. Furthermore, if detailed composition analysis is difficult using any of the above methods, composition analysis may be performed using 3DAP (three-dimensional atom probe). When using 3DAP, the composition of the particle body 2 can be measured while excluding the effects of resin components, surface oxidation, etc. in the analyzed region. This is because 3DAP allows the average composition to be measured by setting a small region (e.g., a region of Φ20 nm × 100 nm) within the first particle 1a.

[0031] When a cross section near the surface of the first particle 1a is subjected to line analysis using EDX or EELS (electron energy loss spectroscopy), the particle body 2 can be recognized as a region where the Fe concentration and Co concentration are stable (see FIG. 3A). Furthermore, for example, the average composition obtained by mapping analysis of the particle body 2 can be used as the composition of the first particle 1a. In this case, the mapping analysis is performed using EDX or EELS, and the measurement location is a region 100 nm or more away from the surface of the first particle 1a in the depth direction (the region corresponding to the particle body 2), and the measurement field of view may be a range of approximately 256 nm × 256 nm.

[0032] The crystalline structure of the particle body 2 (i.e., the crystalline structure of the first particle 1a) can be crystalline, nanocrystalline, or amorphous, and is preferably nanocrystalline or amorphous from the viewpoint of reducing coercive force. For example, the amorphization degree X of the particle body 2 is preferably 85% or more. A crystalline structure with an amorphization degree X of 85% or more is a structure that is mostly amorphous or a heteroamorphous structure. Here, a heteroamorphous structure means a structure in which a small amount of crystals are present in an amorphous state. That is, in this embodiment, the term "amorphous crystalline structure" means a crystalline structure with an amorphization degree X of 85% or more that may contain crystals within a range that satisfies the amorphization degree X.

[0033] In the case of a heteroamorphous structure, the average crystal grain size of the crystals present in the amorphous material is preferably 0.1 nm or more and 10 nm or less. In this embodiment, "nanocrystalline" refers to a crystal structure having an amorphization degree X of less than 85% and an average crystal grain size of 100 nm or less (preferably 3 nm to 50 nm), and "crystalline" refers to a crystal structure having an amorphization degree X of less than 85% and an average crystal grain size of more than 100 nm.

[0034] The degree of amorphization X can be measured by X-ray crystal structure analysis using XRD. Specifically, the powder of the first particles 1a is subjected to 2θ / θ measurement by XRD to obtain a diffraction chart. In this case, the measurement range of the diffraction angle 2θ is set to a range in which a halo derived from the amorphous material can be confirmed, and preferably, for example, 2θ=30° to 60°.

[0035] Next, profile fitting is performed on the diffraction chart using the Lorentz function shown in the following equation (2). In this profile fitting, it is preferable to set the error between the integrated intensity actually measured by XRD and the integrated intensity calculated using the Lorentz function to within 1%. This profile fitting calculates the crystalline scattering integrated intensity Ic and the amorphous scattering integrated intensity Ia. The crystalline scattering integrated intensity Ic and the amorphous scattering integrated intensity Ia obtained here are then introduced into the following equation (1) to determine the degree of amorphization X.

[0036] X = 100 - (Ic / (Ic + Ia) × 100) ... (1) Ic: Crystalline scattering integrated intensity Ia: Amorphous scattering integrated intensity

number

[0037] The method for measuring the degree of amorphousness X is not limited to the method using XRD, but may be measured by EBSD (crystal orientation analysis) or electron beam diffraction.

[0038] (Surface layer 10) The surface layer 10 is a region in which the content of constituent elements of the soft magnetic alloy, such as Fe and Co, differs from that of the particle body 2. The surface layer 10 covers at least a part of the outer periphery of the particle body 2. In the cross section of the first particle 1a, the coverage of the surface layer 10 with respect to the particle body 2 is not particularly limited, but can be, for example, 50% or more, and more preferably 80% or more.

[0039] The surface layer portion 10 can be analyzed by observing a cross section near the surface of the first particle 1a with a STEM (scanning transmission electron microscope) or a TEM (transmission electron microscope) and performing line analysis using EDX or EELS. In line analysis, as shown in FIG. 2, a measurement line ML is drawn in a direction substantially perpendicular to the particle surface, and component analysis is performed at predetermined intervals along the measurement line to obtain the concentration distribution of the constituent elements near the surface. In this case, the measurement interval for component analysis is preferably 1 nm, and raw data measured at 1 nm intervals is preferably averaged to remove noise. More specifically, in the averaging process, it is preferable to average the measured values ​​at a total of five points, including the two adjacent points before and after each measurement point, to obtain an interval average value. The interval average value at each measurement point is then plotted to obtain a graph of the concentration distribution.

[0040] For example, the graphs shown in Figures 3A and 3B are examples of line analysis data in the vicinity of the surface of the first particle 1a. For convenience of explanation, two graphs (Figures 3A and 3B) are shown, but both Figures 3A and 3B show the same measurement example. The horizontal axis of the graph represents the distance from a specific point (interface 21), with the direction from the specific point toward the particle surface (outside of the particle) being the positive direction and the direction from the specific point toward the inside of the particle being the negative direction. The vertical axis of the graph represents the content of the constituent elements (Fe, Co, and Si).

[0041] 3A, in the particle body 2, the concentrations of constituent elements such as Fe, Co, and Si are stable within a range of about ±1 at% of the average concentration. On the surface side of the particle body 2, there exists a region where the concentrations of the constituent elements vary differently from those in the particle body 2, and this region is the surface layer 10. In this embodiment, a change point CP in the concentration distribution of each constituent element is identified, and the change point located closest to the particle's innermost (particle center) among the change points CP of the multiple constituent elements is designated as the "interface 21" between the particle body 2 and the surface layer 10.

[0042] Specifically, a method for identifying the change point CP and the interface 21 will be described. First, in the concentration distribution of each constituent element, a horizontal line AL is drawn that coincides with the average concentration in the particle body 2. Then, an approximate straight line TL is drawn in the region where the concentration of the constituent element monotonically increases or decreases from the particle body 2 toward the particle surface. The intersection of this horizontal line AL and the approximate straight line TL is taken as the change point CP in the concentration distribution of each constituent element. In FIG. 3A, the change point CP of Fe Fe and the change point CP of Co Co and the change point CP of Si Si Among them, the change point CP of Fe Fe is located at the innermost part of the particle. Therefore, in the graph of Fig. 3A, the change point CP Fe The position where the line 22 exists is taken as the interface 21, and the interface 21 is set as the zero point on the horizontal axis of the graph.

[0043] As shown in FIG. 3B, the surface layer 10, which is the fluctuation region, has at least one Si concentration maximum and at least one Co concentration maximum in the concentration distribution in the direction substantially perpendicular to the particle surface. Here, in this embodiment, a local maximum is a point where the concentration distribution switches from an increasing trend to a decreasing trend in the positive direction from the interface 21 toward the surface. In other words, a local maximum is an extreme value in a local region where the concentration of a predetermined element changes in a convex manner. There may be multiple local maxima, and a local maximum does not necessarily coincide with the maximum value in the entire surface layer 10 (global maximum).

[0044] Among the maximum points of the Si concentration of at least 1, the maximum point closest to the interface 21 (i.e., the maximum point located closest to the particle center) is designated as the first Si maximum point L Si max In the graph of Figure 3B, L Si max On the other hand, the maximum point of the Co concentration of at least 1 that is closest to the interface 21 is designated as the first Co maximum point L Co max In the graph of Figure 3B, L Co max are indicated by black circles.

[0045] In the concentration distribution near the surface as shown in FIG. 3B, Si max Distance to D Si From the interface 21 to L Co max Distance to D Co Then, D Si and D Co The relationship between Si ≦D Co and D Si <D Co It is preferable that:

[0046] As described above, the surface layer 10 is L Si max and L Co max and D Si ≦D Co By satisfying the above, the magnetic core containing the soft magnetic alloy powder 1 of this embodiment can improve the withstand voltage while maintaining a high relative permeability. Also, the variation in withstand voltage can be reduced (i.e., the m value can be increased), enabling stable production of magnetic components. In particular, when the surface layer 10 is D Si <D Co By satisfying these conditions, the withstand voltage and m value can be further improved.

[0047] The above-mentioned D Si and D Co The relationship between Co -D Si", "D Co -D Si " is 0 nm or more, preferably more than 0 nm, more preferably 3 nm or more, and even more preferably 5 nm or more. Co -D Si The upper limit of " is not particularly limited, but can be set to, for example, 30 nm or less, or may be set to 10 nm or less. Si The value of and D Co The value of is not particularly limited, and for example, D Si is preferably 20 nm or less, and D Co is preferably 30 nm or less.

[0048] Although Figures 3A and 3B show the concentration distributions of Fe, Co, and Si, the surface layer portion 10 may contain elements other than the above elements that constitute the average composition of the first particle 1a, such as Cr, Al, B, and P.

[0049] The surface layer 10 may be a metal phase, an oxide phase, a metal compound phase other than an oxide, or the like, and preferably contains an oxide phase. When the surface layer 10 contains an oxide phase, a higher concentration of oxygen is detected in the surface layer 10 than in the particle body 2. For example, the graphs shown in Figures 4A and 4B are examples of line analysis data for the surface layer 10 containing an oxide phase.

[0050] As shown in Fig. 4A, when the oxygen concentration in the surface layer 10 is higher than that in the particle body 2, the surface layer 10 contains an oxide phase. In Fig. 4A, the Si concentration peak and the Co concentration peak overlap with the high oxygen concentration region, and the surface layer 10 contains a Si oxide phase 12 containing an oxide of Si and a Co oxide phase 14 containing an oxide of Co.

[0051] The Si oxide phase 12 is a region where the Si concentration is higher than that of the particle body 2 and where a convex peak for the Si concentration exists. Si max is located in the Si oxide phase 12. The Co oxide phase 14 is a region where a convex peak related to the Co concentration exists, and L Comax is located within the Co oxide phase 14. In FIG. 4A, a part of the Co oxide phase 14 overlaps a part of the Si oxide phase 12. The positional relationship between the Si oxide phase 12 and the Co oxide phase 14 is not limited to the state shown in FIG. 4A, and the Co oxide phase 14 may be located closer to the surface than the Si oxide phase 12, as shown in FIG. 4B. That is, in the surface layer portion 10 of the first particle 1a, L Si max Position and L Co max The position of Si ≦D Co As shown in FIGS. 4A and 4B, the Si oxide phase 12 and the Co oxide phase 14 may or may not overlap each other.

[0052] When the surface layer portion 10 has a structure of oxide phases (12, 14) as shown in FIG. 4A or FIG. 4B, the withstand voltage and m value of the magnetic core can be further improved.

[0053] Each of the oxide phases (12, 14) may contain, in addition to Si, Co, and O, elements that make up the average composition of the first particles 1a, such as Fe, Cr, Al, B, and P.

[0054] Furthermore, in the soft magnetic alloy powder 1 of this embodiment, the thickness T of the surface layer portion 10 is not particularly limited, but is preferably 1 nm or more and 30 nm or less, and more preferably 5 nm or more and 20 nm or less. The thickness T of this surface layer portion 10 can be calculated as the distance from the interface 21 to the outer surface 10a of the surface layer portion 10. In measuring the thickness T, the interface 21 can be identified based on the change point CP as described above, and the outer surface 10a may be identified by the method shown below.

[0055] For example, in the graph of Fig. 3A, the outer surface 10a of the surface layer portion 10 constitutes the outermost surface of the first particle 1a. In this case, since the outermost particle surface can be visually recognized in a TEM image or a STEM image, by comparing the TEM image or the STEM image with the graphs of concentration distribution shown in Figs. 3A and 3B, the outer surface 10a in the graphs of concentration distribution can be identified.

[0056] The first particle 1a may also have an insulating coating covering the surface layer portion 10. The insulating coating is a coating formed by coating or the like after the formation of the surface layer portion 10, and its average thickness is preferably 1 nm or more and 100 nm or less, more preferably 50 nm or less. The insulating coating may be recognized as a region with a contrast different from that of the particle body 2 and the surface layer portion 10 in a TEM image or STEM image. In this case, the outer surface 10a of the surface layer portion 10 can be identified based on the contrast in the TEM image or STEM image. Alternatively, the outer surface 10a of the surface layer portion 10 may be identified based on the concentration distribution of element M specific to the insulating coating. In the line analysis results, the concentration of the specific element M increases in the region where the surface layer portion 10 changes to the insulating coating, so the change point where the specific element M increases may be defined as the outer surface 10a of the surface layer portion 10.

[0057] (Method of manufacturing soft magnetic alloy powder 1) The following describes a method for producing the soft magnetic alloy powder 1 according to this embodiment. The soft magnetic alloy powder 1 according to this embodiment can be produced by producing powder by a well-known method and then performing a surface modification treatment.

[0058] The method for producing the soft magnetic alloy powder before the surface modification treatment is not particularly limited. For example, the soft magnetic alloy powder may be produced by an atomization method such as water atomization or gas atomization. Alternatively, the soft magnetic alloy powder may be produced by a synthesis method such as a CVD method using at least one of evaporation, reduction, and thermal decomposition of metal salts. Alternatively, the soft magnetic alloy powder may be produced by an electrolysis method or a carbonyl method. Furthermore, the soft magnetic alloy powder may be produced by pulverizing a thin ribbon or thin plate of the starting alloy. The produced powder may be classified as needed to adjust the particle size of the soft magnetic alloy powder.

[0059] Next, the soft magnetic alloy powder is subjected to a surface modification treatment to form a surface layer portion 10 on the surface of the first particle 1a. The surface modification method is not particularly limited, and may be a CVD method or a mechanochemical method. In this embodiment, it is particularly preferable to perform the surface modification treatment by the mechanochemical method in an atmosphere in which the oxygen partial pressure is controlled. The mechanochemical method will be described below.

[0060] A conventional method for surface treatment of soft magnetic alloy powder is to heat treat the powder to form an oxide film on the particle surface. However, in conventional heat treatments, it is necessary to adjust conditions such as temperature depending on the type of powder, making it difficult to uniformly control the composition and internal structure of the film.

[0061] On the other hand, the mechanochemical method is a method in which a mechanofusion device is applied to the surface modification of soft magnetic alloy powder. Mechanofusion devices have traditionally been used for coating various types of powder. The inventors have discovered that by using a mechanofusion device to form a surface phase of powder in a way that is different from conventional coating processes, it is possible to uniformly form a desired surface layer 10 on different types of powder.

[0062] In the mechanochemical method, the interior of the mechanofusion device is first prepared to have a desired oxidizing atmosphere. For example, a mixed gas of Ar gas and air is used as the atmospheric gas filled into the device, and the partial pressure of Ar gas and air in the mixed gas can be controlled to adjust the oxygen partial pressure inside the device. The oxygen partial pressure inside the device is preferably set to, for example, 100 ppm to 3000 ppm, more preferably 500 ppm to 3000 ppm, and even more preferably 500 ppm to 1000 ppm. Note that in the mixed gas, oxygen gas may be used instead of air, and an inert gas such as nitrogen gas or helium may be used instead of Ar gas.

[0063] Next, the soft magnetic alloy powder is introduced into the rotating rotor of the mechanofusion device, and the rotating rotor is rotated. A press head is installed inside the rotating rotor, and when the rotating rotor is rotated, the soft magnetic alloy powder is compressed in the gap between the inner wall surface of the rotating rotor and the press head. During this process, friction occurs between the soft magnetic alloy powder and the inner wall surface of the rotating rotor, causing the soft magnetic alloy powder to locally become hot. This frictional heat forms a surface layer 10 on the surface of the particle body 2. In particular, the above-mentioned mechanochemical method makes it easy to form a surface layer 10 containing oxide phases (12, 14).

[0064] In the mechanochemical method, it is preferable to control the oxygen partial pressure within an appropriate range, as well as the rotation speed of the rotating rotor and the gap between the inner wall surface of the rotating rotor and the press head. For example, a low rotation speed reduces the frictional heat generated, making it difficult to form the surface layer 10. On the other hand, a high rotation speed increases the compressive stress applied to the powder, making it easier to form the surface layer 10, but the particle body 2 and the surface layer 10 are more likely to be destroyed, which may result in a decrease in magnetic properties. Furthermore, if the gap between the inner wall surface of the rotating rotor and the press head is too large, the frictional heat generated decreases, making it difficult to form the surface layer 10. On the other hand, the narrower the gap between the inner wall surface of the rotating rotor and the press head, the greater the compressive stress applied to the powder, making it easier to form the surface layer 10, but making it easier to destroy the particle body 2 and the surface layer 10.

[0065] After the surface modification by the mechanochemical method, in order to remove the stress caused by the mechanochemical method, a heat treatment may be carried out in an atmosphere that does not change the surface structure.

[0066] Furthermore, when forming an insulating coating on the surface layer 10, a coating formation treatment such as phosphate treatment, mechanical alloying, silane coupling treatment, or hydrothermal synthesis may be performed after the surface modification treatment using the mechanochemical method. Examples of materials for the insulating coating to be formed include phosphates, silicates, soda-lime glass, borosilicate glass, lead glass, aluminosilicate glass, borate glass, and sulfate glass. Examples of phosphates include magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and examples of silicates include sodium silicate.

[0067] Through the above steps, the soft magnetic alloy powder 1 having the surface layer portion 10 is obtained.

[0068] (Uses of soft magnetic alloy powder 1) The soft magnetic alloy powder 1 according to this embodiment can be used for various magnetic parts without any particular limitations. In particular, the soft magnetic alloy powder 1 can be suitably used as a material for powder magnetic cores in magnetic parts such as inductors, transformers, and choke coils. Hereinafter, examples of powder magnetic cores and magnetic parts containing the soft magnetic alloy powder 1 will be described with reference to FIGS. 5 and 6.

[0069] (Powder magnetic core 40) The powder core 40 containing the soft magnetic alloy powder 1 is not particularly limited in terms of its external dimensions or shape, as long as it is formed into a predetermined shape. As shown in the schematic cross-sectional view of Fig. 5, the powder core 40 contains at least the soft magnetic alloy powder 1 and a resin 4 as a binder, and the constituent particles (1a, 1b) of the soft magnetic alloy powder 1 are bound together via the resin 4 to be fixed into a predetermined shape.

[0070] The soft magnetic alloy powder 1 in the powder core 40 may be composed only of first particles 1a having a surface layer portion 10, but is preferably composed of a mixture of the first particles 1a and fine particles 1b having an average particle size smaller than that of the first particles 1a, as shown in FIG. 5. In this case, the average particle size of the first particles 1a is preferably 5 μm or more, and the average particle size of the fine particles 1b is preferably less than 5 μm. The material of the fine particles 1b is not particularly limited, and can be, for example, pure iron or an Fe-Ni alloy. Although the fine particles 1b shown in FIG. 5 do not have an insulating coating, an insulating coating may be formed on the surface of the fine particles 1b.

[0071] There are no particular limitations on the ratio of first particles 1a to microparticles 1b in the powder magnetic core 40. For example, the mass ratio of "first particles 1a:microparticles 1b" can be in the range of 10:90 to 90:10, and preferably in the range of 60:40 to 90:10.

[0072] There are no particular limitations on the material of resin 4, and it can be, for example, a thermosetting resin such as epoxy resin. There are also no particular limitations on the content of resin 4 in powder magnetic core 40, and it is preferably, for example, 1.0 mass % to 2.5 mass %.

[0073] The filling rate of the soft magnetic alloy powder 1 in the powder core 40 can be controlled by manufacturing conditions such as the molding pressure and the content of the resin 4, and can be set to, for example, 70 vol% to 90 vol%. From the viewpoint of increasing the relative permeability, the filling rate of the soft magnetic alloy powder 1 is preferably 80 vol% or more.

[0074] In conventional powder magnetic cores, increasing the packing rate of the magnetic powder increases the relative permeability but decreases the withstand voltage, making it difficult to achieve both a high relative permeability and a high withstand voltage. In contrast, in the powder magnetic core 40 of this embodiment, the constituent particles (1a) of the soft magnetic alloy powder 1 have surface layers 10 with predetermined characteristics, making it possible to improve the withstand voltage and m value even at a packing rate as high as 80 vol% or more.

[0075] The method for manufacturing the powder magnetic core 40 is not particularly limited. For example, first particles 1a that have been subjected to a surface modification treatment using a mechanochemical method are mixed with fine particles 1b, and then the resulting mixed powder is kneaded with a thermosetting resin to obtain a resin compound. The resin compound is then filled into a mold and pressure-molded, and the thermosetting resin is then cured to obtain the powder magnetic core 40 shown in FIG. 5.

[0076] (Magnetic parts 100) In the magnetic component 100 shown in Fig. 6, the element body is constituted by a powder magnetic core 40 as shown in Fig. 5. A coil 50 is embedded inside the powder magnetic core 40, which is the element body, and ends 50a, 50b of the coil 50 are each drawn out to an end face of the powder magnetic core 40. In addition, a pair of external electrodes 60, 80 is formed on the end face of the powder magnetic core 40, and the pair of external electrodes 60, 80 are electrically connected to the ends 50a, 50b of the coil 50, respectively.

[0077] The magnetic component 100 of this embodiment is suitable for use as a power inductor in a power supply circuit, because the powder magnetic core 40 constituting the element body has good withstand voltage characteristics. Note that the magnetic component containing the soft magnetic alloy powder 1 is not limited to the form shown in Fig. 6, and may be a magnetic component in which a powder magnetic core of a predetermined shape has a wire wound on the surface thereof by a predetermined number of turns.

[0078] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways within the scope of the present invention. [Example]

[0079] The present invention will be described in more detail below based on specific examples. However, the present invention is not limited to the following examples. In the table below, sample numbers marked with * are comparative examples.

[0080] (Experiment 1) In Experiment 1, six types of soft magnetic alloy powders (Powder A to Powder F) shown in Table 1 were prepared. All of Powder A to Powder F were prepared by the following procedure.

[0081] First, pure metal raw materials such as Fe, Co, and other minor components were prepared and weighed so as to have the desired composition after melting. The weighed pure metal raw materials were then melted by high-frequency heating in a vacuum chamber to obtain a master alloy. Next, the prepared master alloy was heated to 1500°C to remelt, and then high-pressure water atomization was used to obtain a powder having the desired composition. After atomization, the obtained powder was classified by a predetermined method to adjust the particle size of the powder. The average particle size (D50) of Powders A to F prepared by the above method was all within the range of 15 μm to 25 μm.

[0082] [Table 1]

[0083] Next, each of Powders A to F was divided into a plurality of samples, and each sample was subjected to a surface treatment under one of the conditions shown in Table 2.

[0084] Under conditions 1 to 5, the powder samples were heat-treated while controlling the oxygen partial pressure within the range shown in Table 2. The heat treatment temperature was set within an optimum range depending on the composition of Powders A to F.

[0085] Under conditions 6 to 10, the powder samples were subjected to surface modification treatment by mechanochemical method. During this process, an AMS-Lab manufactured by Hosokawa Micron Corporation was used as the mechanofusion device, and the oxygen partial pressure in the rotor was controlled within the range shown in Table 2.

[0086] Under condition 11, a two-layer coating was formed on the surface of the particles constituting the powder sample using the following procedure. First, the cobalt phosphate aqueous solution and the powder sample were placed in a V-type mixer and thoroughly mixed. The powder sample was then removed from the mixer and thoroughly dried in the air. Next, the powder sample and a treatment liquid containing phosphate and a silica source were placed in the V-type mixer and thoroughly mixed. The powder sample was then removed from the mixer and thoroughly dried in the air at 150 to 250°C.

[0087] The coating treatment under condition 11 was only performed on samples separated from powder A. In the samples that underwent the coating treatment under condition 11, it was confirmed that a Co-containing coating was formed on the side in contact with the particle body, and that a Si-containing coating was formed on top of the Co-containing coating. Furthermore, the total thickness of the coating formed by the coating treatment under condition 11 (the sum of the thickness of the Co-containing coating and the Si-containing coating) was within the range of 5 nm to 10 nm.

[0088] [Table 2]

[0089] Next, powder samples that had been subjected to any one of the surface treatments under conditions 1 to 11 were used to produce powder cores according to the procedure described below. In Experiment 1, the powder samples that had been subjected to any one of the surface treatments under conditions 1 to 11 were used as main powders, and fine powders were mixed with the main powders to obtain magnetic powders for powder cores. For all samples in Experiment 1, an Fe-based soft magnetic alloy with an average particle size (D50) of 1 μm was used as the fine powder, and the mass ratio of the main powder to the fine powders was main powder:fine powder = 80:20.

[0090] The magnetic powder and epoxy resin were then kneaded to obtain a resin compound. The compounding ratio of the magnetic powder to the epoxy resin was controlled so that the resin content in the powder magnetic core was 2.5 wt% in all samples in Experiment 1. The resin compound was filled into a mold and pressed to obtain a toroidal molded body. In this case, the molding pressure was 1 to 10 ton / cm. 2The molding pressure was controlled within this range so that the filling rate of the magnetic powder was at least 80 vol% for all samples in Experiment 1. The above compact was then heat-treated at 180°C for 60 minutes to harden the epoxy resin in the compact, thereby obtaining a powder magnetic core with a toroidal shape (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 mm).

[0091] For each sample in Experiment 1, the prepared powder sample (main powder) and dust core were evaluated as follows.

[0092] (Analysis of the surface structure of the main powder) The surface structure of the soft magnetic alloy powders (main powders A to F) that had been subjected to a predetermined surface treatment was analyzed by line analysis using TEM-EDX. In this line analysis, the maximum point of Si concentration, L Si max The presence or absence of Co, the maximum point of Co concentration, L Co max The presence or absence of "D Co -D Si " was investigated.

[0093] (Filling rate of magnetic powder in powder core) The dimensions and mass of the produced powder magnetic core were measured, and the density ρ of the powder magnetic core was calculated from the dimensions and mass. Furthermore, assuming that the powder magnetic core was composed only of magnetic powder, the theoretical density of the powder magnetic core was calculated from the specific gravity of the magnetic powder. The density ρ was then divided by the theoretical density to calculate the packing fraction of the magnetic powder in the powder magnetic core.

[0094] (Relative permeability of powder magnetic core) A polyurethane copper wire (UEW wire) was wound around a toroidal powder magnetic core. The inductance of the powder magnetic core at a frequency of 100 kHz was measured using an LCR meter (4284A manufactured by Agilent Technologies), and the relative permeability (unitless) of the powder magnetic core was calculated based on the inductance.

[0095] (Voltage resistance characteristics of powder magnetic core) To measure the withstand voltage characteristics, a cylindrical test core was fabricated in the same manner as the toroidal core described above, and an In-Ga electrode was formed on each end face of the test core. Next, a voltage was applied to the test core using a withstand voltage tester (THK-2011ADMPT manufactured by Tama Densoku Co., Ltd.), and the voltage value when a current of 1 mA flowed was measured. The withstand voltage of the test core was then calculated by dividing the measured voltage value by the length of the test core (the distance between the end faces).

[0096] The above-mentioned withstand voltage measurements were performed on 20 test cores for each sample, and the average value of the 20 test cores was taken as the withstand voltage for each sample. The withstand voltage of each sample was then evaluated relative to the withstand voltage of the reference sample. Specifically, a powder core was prepared using powder that had not been subjected to the surface treatment shown in Table 2, and this powder core was used as the reference sample. Samples that exhibited a withstand voltage less than 1.3 times the withstand voltage of the reference sample were judged to be "fail (F)," samples that exhibited a withstand voltage between 1.3 and 1.5 times the withstand voltage of the reference sample were judged to be "good (G)," and samples that exhibited a withstand voltage of 1.5 times or more were judged to be "very good (VG)."

[0097] In addition, a Weibull plot was created using the voltage resistance data of the 20 test cores as a population, and the m value (unitless) of each sample was calculated from the Weibull plot. The m value is an index showing the degree of variation in voltage resistance, with a value of 3.0 or higher being considered good and a value of 5.5 or higher being considered particularly good.

[0098] The evaluation results of each sample in Experiment 1 are shown in Tables 3 to 8. Table 3 shows the evaluation results of the sample using powder A as the main powder, Table 4 shows the evaluation results of the sample using powder B as the main powder, Table 5 shows the evaluation results of the sample using powder C as the main powder, Table 6 shows the evaluation results of the sample using powder D as the main powder, Table 7 shows the evaluation results of the sample using powder E as the main powder, and Table 8 shows the evaluation results of the sample using powder F as the main powder. In each table, a "-" in the column for surface treatment method means that the surface treatment shown in Table 2 was not performed. Also, in each table, D Co -D Si The "-" in the column indicates that the surface layer of the main powder is L Si max or / and L Comax By not having D Co -D Si This means that it could not be measured.

[0099] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8]

[0100] As shown in Tables 3, 5, and 7, samples using Co-free primary powders (Powder A, Powder C, or Powder E) did not show improvement in withstand voltage characteristics, even when surface modification treatment was performed using the mechanochemical method. Furthermore, sample A-12, which underwent coating treatment under condition 11, showed an improvement in withstand voltage. However, for sample A-12, where 0 > (DCo-DSi), the withstand voltage varied widely, and the m value did not improve.

[0101] On the other hand, as shown in Tables 4, 6, and 8, the samples using the main powder containing Co (Powder B, Powder D, or Powder F) were subjected to surface modification treatment using the mechanochemical method, and the L Si max and L Co max was formed on the particle surface. Co -D Si ) exhibited high withstand voltage and high m value. Co -D Si) the sample that satisfied the condition obtained a relative permeability similar to that of the reference sample. Si max and L Co max and D Si ≦D Co By satisfying the above condition, it was found that the withstand voltage and m value can be improved while maintaining a high relative permeability. Co -D Si ) is satisfied, the withstand voltage and m value are further improved.

[0102] Note that 0≦(D Co -D Si ) it was confirmed that the surface layer of the soft magnetic alloy powder contained an oxide phase containing Si and an oxide phase containing Co.

[0103] (Experiment 2) In Experiment 2, a powder core was produced using a fine powder different from that used in Experiment 1 and a main powder (Powder B, Powder D, or Powder F). Specifically, in Experiment 2, an FeNi-based soft magnetic alloy powder with an average particle size (D50) of 1 μm was used as the fine powder. In Experiment 2, the experimental conditions other than the type of fine powder were the same as in Experiment 1, and the same evaluations were carried out as in Experiment 1. The evaluation results of Experiment 2 are shown in Tables 9 to 11. Note that Tables 9 to 11 show the evaluation results of Experiment 1, which used an Fe-based fine powder, along with the results of Experiment 2.

[0104] [Table 9] [Table 10] [Table 11]

[0105] The results in Tables 9 to 11 show that changing the type of fine powder can change the relative magnetic permeability. Si ≦D CoIn the samples that satisfied this condition, even if the relative permeability varied depending on the type of fine powder, the withstand voltage characteristics did not vary, and a high withstand voltage and a high m value were obtained.

[0106] (Experiment 3) In Experiment 3, the resin content in the powder magnetic core was changed. Specifically, epoxy resin was mixed with magnetic powder containing a specified main powder (powder B, powder D, or powder F) so that the resin content was 2.5 vol%, 2.0 vol%, 1.5 vol%, or 1.0 vol%. In Experiment 3, the experimental conditions other than the resin content were the same as in Experiment 1, and the same evaluations were performed as in Experiment 1. The evaluation results of Experiment 3 are shown in Tables 12 to 14.

[0107] [Table 12] [Table 13] [Table 14]

[0108] As shown in Tables 12 to 14, in the samples not having the surface layer portion 10, reducing the resin content improved the relative permeability, but resulted in a decrease in the withstand voltage and m value. Si ≦D Co In the sample having the surface layer 10 satisfying the above condition, a high withstand voltage and a high m value were obtained even when the resin content was reduced. Si ≦D Co It was found that in samples that satisfy the above condition, high relative permeability and high withstand voltage characteristics can be achieved even when the resin content is reduced.

[0109] (Experiment 4) In Experiment 4, an insulating coating made of a phosphate-based compound was formed on the particle surface of the primary powder (Powder B, Powder D, or Powder F) by phosphate treatment. Specifically, samples were prepared in which only the insulating coating was formed without mechanochemical treatment, and samples in which the insulating coating was formed after mechanochemical treatment. In all samples in Experiment 4, the average thickness of the insulating coating was in the range of 1 nm to 50 nm, and the resin content was 1.0 vol%. The other experimental conditions in Experiment 4 were the same as those in Experiment 1, and the same evaluations were performed as in Experiment 1. The evaluation results of Experiment 4 are shown in Table 15.

[0110] [Table 15]

[0111] From the results in Table 15, D Si ≦D Co It was found that the withstand voltage characteristics can be further improved by further forming an insulating coating on the outer surface of the surface layer portion 10 that satisfies the above. [Explanation of symbols]

[0112] 1 … Soft magnetic alloy powder 1a … 1st particle 2...particle body 10 … Surface layer part 10a … External surface 12...Si oxide phase 14... Co oxide phase 21 … Interface 1b … Fine powder 4... Resin 40 … powder magnetic core 50... Coil 50a,50b … end 60,80 … external electrode 100...Magnetic parts

Claims

1. The particle has a particle body made of a soft magnetic alloy containing Fe and Co, and a surface layer portion located on the surface side of the particle body, the soft magnetic alloy has a composition of Fe—Co—B—Si—C, Fe—Co—Nb—B—Si—Cu, or Fe—Co—Si, the surface layer portion has at least one or more maximum points of Si concentration and at least one or more maximum points of Co concentration, The maximum point located closest to the particle center among at least one of the maximum points of Si concentration is designated as the first Si maximum point L Si max year, The L Si max The distance to Si year, The maximum point located closest to the particle center among at least one of the maximum points of Co concentration is designated as the first Co maximum point L Co max year, The interface to the L Co max The distance to Co As, D Si ≦D Co Meet the soft magnetic alloy powder.

2. D Si <D Co The soft magnetic alloy powder according to claim 1, which satisfies the above.

3. 3. The soft magnetic alloy powder according to claim 1, wherein the surface layer portion is an oxide phase.

4. the surface layer portion has a Si oxide phase containing an oxide of Si, Said L Si max The soft magnetic alloy powder according to any one of claims 1 to 3, wherein is present in the Si oxide phase.

5. the surface layer portion has a Co oxide phase containing an oxide of Co, Said L Co max is present in the Co oxide phase, 5. The soft magnetic alloy powder according to claim 4, wherein a portion of the Co oxide phase overlaps a portion of the surface side of the Si oxide phase.

6. the surface layer portion has a Co oxide phase containing an oxide of Co, Said L Co max is present in the Co oxide phase, 5. The soft magnetic alloy powder according to claim 4, wherein the Co oxide phase is located closer to the surface than the Si oxide phase.

7. A dust core comprising the soft magnetic alloy powder according to any one of claims 1 to 6.

8. A magnetic part comprising the soft magnetic alloy powder according to any one of claims 1 to 6.

Images