Fe-based nanocrystalline soft magnetic alloy core

Abstract

To provide an Fe-based soft magnetic alloy magnetic core which is low in percentage of Al content, and which shows a high magnetic permeability in a high frequency region.SOLUTION: An Fe-based nanocrystalline soft magnetic alloy magnetic core is composed of a magnetic core arranged by winding a ribbon made of Fe-based nanocrystalline soft magnetic alloy containing amorphous phases and crystal grains, of which the magnetic strain at 20°C is less than 0 ppm. The Fe-based nanocrystalline soft magnetic alloy has a composition represented by the following compositional formula (I): (Fe1-x-ySixAly)100-a-b-cMaM'bCuc(I). In the compositional formula, M represents one or more elements selected from a group consisting of Nb, W, Zr, Hf, Ti and Mo, M' represents one or more elements selected from a group consisting of B, C and P, and a, b and c satisfy 2.0≤a≤5.0, 3.0<b<10.0 and 0<c<3.0 in units of atom%, and x and y meet 0.170≤x≤0.320 and 0.010≤y≤0.045, and 15.5<x×(100-a-b-c) is satisfied.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a magnetic core of an Fe-based nanocrystalline soft magnetic alloy. [Background technology]

[0002] With the active promotion of high performance, miniaturization, and weight reduction of electrical and electronic devices and information and communication equipment, there is a demand for miniaturization and increased efficiency of power supply devices used in these various types of equipment. Magnetic components used in power converters can generally be miniaturized by increasing the conversion frequency, but magnetic components for noise filters, such as common mode choke coils, cannot be miniaturized except by increasing the permeability of the material. In recent years, with the miniaturization and reduction of various electronic devices, there has been a growing demand for miniaturization of power conversion components such as noise filters. Therefore, there is a strong desire to improve the permeability of magnetic materials used in high-frequency ranges, particularly in common-mode choke coils.

[0003] To date, progress has been made in developing magnetic materials that exhibit excellent high-frequency characteristics. For example, Fe-Si-B-Cu-Nb soft magnetic alloys with Fe as the main component (Patent Document 1) and Fe-Si-Al soft magnetic alloys are widely known. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 64-79342 [Overview of the project] [Problems that the invention aims to solve]

[0005] Magnetic materials generally achieve high permeability by bringing both magnetostriction λ and crystalline magnetic anisotropy K to near zero. Patent Document 1 describes how a Fe-Si-B-Cu-Nb soft magnetic alloy is given a nanocrystalline structure to average out and reduce crystalline magnetic anisotropy, resulting in improved permeability compared to conventional materials. However, the crystalline composition is Fe-Si, and the crystalline magnetic anisotropy within individual crystals is not zero, and even averaging it out does not necessarily result in zero anisotropy.

[0006] Furthermore, conventionally, to ensure the processability of Fe-based alloys, a low Al content is desirable, as excessively high Al content can reduce the strength of the Fe-based alloy or cause breakage during processing. However, reducing the Al content in Fe-Si-Al soft magnetic alloys makes it difficult to achieve near-zero crystalline magnetic anisotropy, thus reducing permeability. Therefore, Fe-Si-Al soft magnetic materials must contain a certain amount of Al (for example, 4-6 atomic percent or more), leaving the problem of difficulty in achieving a balance between strength, processability, and permeability.

[0007] In view of the above problems, the present invention aims to provide a Fe-based soft magnetic alloy core that has a low Al content and exhibits high magnetic permeability in the high-frequency range. [Means for solving the problem]

[0008] As a result of repeated studies to solve the above problems, the inventors of the present invention have found that by using an Fe-based soft magnetic alloy with a specific composition having a low Al content as the material constituting the magnetic core, and by making the magnetostriction of the magnetic core a negative value, an Fe-based soft magnetic alloy magnetic core exhibiting high permeability in the high-frequency range can be obtained, leading to the present invention. In other words, the gist of the present invention is as follows.

[0009] [1] A magnetic core is formed by winding a ribbon made of an Fe-based nanocrystalline soft magnetic alloy containing amorphous phase and crystalline grains, The magnetostriction at 20°C is less than 0 ppm. An Fe-based nanocrystalline soft magnetic alloy core in which the Fe-based nanocrystalline soft magnetic alloy has a composition represented by the following compositional formula (I). (Fe 1-x-y Si x Al y ) 100-a-b-c M a M’ b Cu c (I) (In the compositional formula (I), M is one or more elements selected from the group consisting of Nb, W, Zr, Hf, Ti, and Mo; M’ is one or more elements selected from the group consisting of B, C, and P; a, b, and c are in atomic %, 2.0 ≦ a ≦ 5.0, 3.0 < b < 10.0, and 0 < c < 3.0; x and y are 0.170 ≦ x ≦ 0.320 and 0.010 ≦ y ≦ 0.045; 15.5 < x × (100 - a - b - c).) [2] The Fe-based nanocrystalline soft magnetic alloy core according to [1], wherein in the compositional formula (I), 0.250 < x ≦ 0.320. [3] The Fe-based nanocrystalline soft magnetic alloy core according to [1] or [2], wherein M is Nb and M’ is B. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide an Fe-based soft magnetic alloy core having a low Al content and showing a high magnetic permeability in a high-frequency region. [Brief Description of the Drawings]

[0011] [Figure 1] It is a graph showing the relationship between the inductance change rate of the Fe-based nanocrystalline soft magnetic alloy core obtained in Experimental Examples 1 to 3 and the ambient temperature. [Figure 2] It is a graph showing the relationship between the inductance change rate of the Fe-based nanocrystalline soft magnetic alloy core obtained in Experimental Examples 4 to 6 and the ambient temperature. [Figure 3] It is a graph showing the relationship between the inductance change rate of the Fe-based nanocrystalline soft magnetic alloy core obtained in Experimental Examples 7 to 9 and the ambient temperature. [Figure 4]This graph shows the relationship between the rate of change in inductance of Fe-based nanocrystalline soft magnetic alloy cores obtained in Experimental Examples 10-12 and the ambient temperature. [Figure 5] This graph shows the relationship between relative permeability and crystallinity of Fe-based nanocrystalline soft magnetic alloy cores obtained in Experimental Examples 1-12. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. The following description of the constituent elements is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents unless it exceeds the gist of the invention. Furthermore, when the lower and upper limits of a numerical range are described separately in this specification, the numerical range may be a combination of any lower limit and any upper limit.

[0013] 1. Fe-based nanocrystalline soft magnetic alloy core An Fe-based nanocrystalline soft magnetic alloy core (hereinafter sometimes simply referred to as "magnetic core") according to one embodiment of the present invention is a magnetic core formed by winding a ribbon made of an Fe-based nanocrystalline soft magnetic alloy containing amorphous phase and crystalline grains. The Fe-based nanocrystalline soft magnetic alloy core according to this embodiment is made of a material with a higher Si content and lower Al content compared to conventionally used Fe-Si-Al magnetic alloys, and has a negative magnetostriction at 20°C, resulting in high permeability in the high-frequency range and suppression of problems such as breakage during processing.

[0014] In addition, in this specification, a high magnetic permeability in the high-frequency region means at least one of the following: the magnetic permeability in the high-frequency region is high under normal temperature conditions, which is the practical temperature of the magnetic core, and when the ambient environmental temperature is changed, the magnetic permeability in the high-frequency region is maximized under normal temperature conditions. Regarding the former, for example, when the relative magnetic permeability in the high-frequency region under normal temperature conditions is 23,000 or more, preferably 24,000 or more, more preferably 25,000 or more, still more preferably 26,000 or more, and particularly preferably 27,000 or more, it is defined that the magnetic permeability in the high-frequency region is high. Also, in this specification, the normal temperature is set to 20°C.

[0015] In this specification, "relative magnetic permeability" may be used as an index for evaluating "magnetic permeability". Also, in this specification, the magnetic permeability in the high-frequency region is evaluated based on the magnetic permeability at a frequency of 100 kHz, and the magnetic permeability in the low-frequency region is evaluated based on the magnetic permeability at a frequency of 1 kHz.

[0016] The relative magnetic permeability of the Fe-based nanocrystalline soft magnetic alloy magnetic core is calculated, for example, by measuring the inductance of a coil wound around the Fe-based nanocrystalline soft magnetic alloy magnetic core and based on the following formula (1). μr = μ / μ0 (1) μr: relative magnetic permeability μ0: magnetic permeability of vacuum = 4π×10 -7 [H / m] μ: magnetic permeability [H / m] = Ll / A / N 2 L: inductance [H] l: magnetic path length [m] A: core effective cross-sectional area [m 2 N: number of turns

[0017] 1-1. Fe-based nanocrystalline soft magnetic alloy ribbon The Fe-based nanocrystalline soft magnetic alloy ribbon forming the magnetic core is made of an Fe-based nanocrystalline soft magnetic alloy. The Fe-based nanocrystalline soft magnetic alloy contains crystal grains composed of an amorphous phase and a crystalline phase. Clusters may be dispersed in the amorphous phase.

[0018] 1-1-1. Composition of Fe-based nanocrystalline soft magnetic alloys Fe-based nanocrystalline soft magnetic alloys have a composition represented by the following compositional formula (I) (hereinafter sometimes referred to as "composition (I)"). However, this composition may contain unavoidable impurities such as Cr and Mn in the remainder after excluding Si, Al, M, M', and Cu. (Fe 1-x-y Si x Al y ) 100-a-b-c M a M' b Cu c (I)

[0019] (M) In compositional formula (I), M is one or more elements selected from the group consisting of Nb, W, Zr, Hf, Ti, and Mo, and is preferably Nb. Nb is thought to have the effect of refining the precipitated crystal grains by forming an amorphous phase grain boundary layer together with B during nanocrystallization, or by forming clusters and suppressing the growth of crystal grains through interaction with elements such as Cu.

[0020] (M') In compositional formula (I), M' is one or more elements selected from the group consisting of B, C, and P, preferably B. One or more elements selected from the group consisting of B, C, and P are necessary in a certain amount together with Si to facilitate the formation of an amorphous structure in which the constituent elements are uniformly dispersed.

[0021] (a, b, and c) a, b, and c represent the atomic percentages of M, M', and Cu in the composition formula (I), respectively. a is usually 2.0 or higher, preferably greater than 2.0, more preferably 2.5 or higher, and even more preferably 3.0 or higher, and also usually 5.0 or lower, preferably less than 5.0, more preferably 4.5 or lower, and even more preferably 4.0 or lower. It is most preferable that a be around 3.0. b is usually greater than 3.0, preferably 4.0 or more, more preferably 4.5 or more, and even more preferably 5.0 or more, and is also usually less than 10.0, preferably 9.5 or less, more preferably 9.0 or less, and even more preferably 8.0 or less. c is usually greater than 0, preferably 0.3 or more, more preferably 0.5 or more, and even more preferably 1.0 or more, and also usually less than 3.0, preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.8 or less.

[0022] By setting a, b, and c within the above ranges, it becomes easier to form crystal grains with a small average grain size, reducing the magnetic anisotropy of the Fe-based nanocrystalline soft magnetic alloy, and thus improving the relative permeability of the magnetic core. Furthermore, because the crystal grains can be refined in this way, it is also possible to improve the soft magnetic properties such as coercivity of the Fe-based nanocrystalline soft magnetic alloy.

[0023] When M' is B, setting b to the above range ensures amorphous formation ability, suppresses the deposition of Fe-B binary compounds with inferior magnetic properties, and enables the realization of excellent soft magnetic properties. Furthermore, since c is within the above range, amorphous formation ability is ensured, making it easier to produce amorphous alloys by the ultra-rapid cooling method described later. In addition, since c is within the above range, Cu-containing clusters are more easily formed uniformly in the amorphous phase prior to the crystallization of α-Fe(Si,Al), and these clusters can act as crystal nuclei to form fine crystal grains.

[0024] (x and y) x and y represent the molar amounts of Si and Al, respectively, when the molar amounts of Fe, Si, and Al in the Fe-based nanocrystalline soft magnetic alloy are set to 1. Furthermore, the molar amount of Fe when the molar amounts of Fe, Si, and Al in the Fe-based nanocrystalline soft magnetic alloy are set to 1 is expressed as 1-(x+y).

[0025] x is usually 0.170 or higher, preferably 0.200 or higher, more preferably 0.230 or higher, and even more preferably greater than 0.250, and also usually 0.320 or lower, preferably 0.300 or lower, and more preferably 0.280 or lower. y is usually 0.010 or higher, preferably 0.012 or higher, more preferably 0.014 or higher, even more preferably 0.016 or higher, and also usually 0.045 or lower, preferably 0.040 or lower, more preferably 0.035 or lower, even more preferably 0.030 or lower, and particularly preferably 0.025 or lower.

[0026] By keeping x within the above range, amorphous formation ability is ensured, facilitating the production of amorphous alloys by the ultra-rapid cooling method described later. Furthermore, excessive increases in crystalline magnetic anisotropy within the crystal grains are suppressed, enabling the realization of good soft magnetic properties. Furthermore, when y satisfies the above numerical range, the crystalline magnetic anisotropy of the crystalline phase of the Fe-Si-Al ternary alloy within the crystal grains is reduced, thereby reducing the crystalline magnetic anisotropy of the Fe-based nanocrystalline soft magnetic alloy and improving soft magnetic properties such as permeability and coercivity. In addition, the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy can also be reduced. Therefore, by setting x and y within the above range, it is possible to improve the relative permeability of the Fe-based nanocrystalline soft magnetic alloy.

[0027] (Si content in composition (I)) The Fe-based nanocrystalline soft magnetic alloy in this embodiment has a higher Si content compared to conventionally used Fe-Si-Al magnetic alloys. The Si content in composition (I) is calculated by the following formula (i). Si content in composition (I) [atomic %] = x × (100 - abc) (i) The Si content in composition (I) is not particularly limited as long as it satisfies the ranges of x, a, b, and c described above, but is usually greater than 15.5 atomic%, preferably 16.0 atomic% or more, more preferably 17.0 atomic% or more, particularly preferably 18.0 atomic% or more, and also preferably 28.0 atomic% or less, more preferably 27.0 atomic% or less, and even more preferably 26.0 atomic% or less.

[0028] (Al content in composition (I)) The Fe-based nanocrystalline soft magnetic alloy in this embodiment has a lower Al content compared to conventionally used Fe-Si-Al magnetic alloys. In this embodiment, the low Al content in the Fe-based nanocrystalline soft magnetic alloy makes it less prone to breakage during processing. Furthermore, in this embodiment, the negative magnetostriction of the magnetic core improves the permeability in the high-frequency range, thus enabling a balance between strength, processability, and permeability.

[0029] The Al content in composition (I) is calculated using the following formula (ii). Al content in composition (I) [atomic %] = y × (100 - abc) (ii) The Al content in composition (I) is not particularly limited as long as it satisfies the ranges of y, a, b, and c described above, but is preferably 0.9 atomic% or more, more preferably 1.0 atomic% or more, even more preferably 1.2 atomic% or more, particularly preferably 1.5 atomic% or more, and also preferably less than 4.0 atomic%, more preferably 3.5 atomic% or less, even more preferably 3.0 atomic% or less, particularly preferably 2.5 atomic% or less.

[0030] 1-1-2. Crystal grains The crystal grains consist of a crystalline phase of an Fe-Si-Al ternary alloy having a body-centered cubic (bcc) structure, in which Si and Al are dissolved in the main Fe, and other elements may also be dissolved. The Fe-based nanocrystalline soft magnetic alloy can reduce crystalline magnetic anisotropy by including Al in its composition, and furthermore, because the crystal grains are fine, the crystalline magnetic anisotropy is averaged out and reduced, which is thought to improve the relative permeability. Furthermore, the crystal structure of the crystalline phase constituting the crystal grains can be identified by X-ray diffraction (XRD).

[0031] The average grain size of the crystal grains is not particularly limited as long as it is on the nanoscale, and is usually 9.0 nm or larger, and is usually 20.0 nm or smaller, preferably 12.0 nm or smaller, more preferably 11.3 nm or smaller, even more preferably 11.0 nm or smaller, and particularly preferably 10.0 nm or smaller. Alternatively, it is usually 9 nm or larger, and is usually 20 nm or smaller, preferably 12 nm or smaller, and more preferably 11 nm or smaller. The average grain size of the crystal grains can be set to a desired range by adjusting a, b, and c in composition (I). By keeping the average grain size of the crystal grains within the above range, the crystalline magnetic anisotropy is averaged out and reduced, and the effect of improving relative permeability tends to be greater. Furthermore, because the crystal grains are so fine, it is also possible to improve the soft magnetic properties such as relative permeability and coercivity of Fe-based nanocrystalline soft magnetic alloys.

[0032] The average grain size of the crystal grains can be determined by analyzing the Fe-based nanocrystalline soft magnetic alloy using an X-ray diffractometer (XRD) and following the formula (2) below. D = (K × λ) / (β × cosθ) (2) D: Crystal grain size [nm] K: Scherrer constant λ: Wavelength of X-ray [nm] β: Half-width [rad] θ: Bragg angle [rad]

[0033] 1-1-3. Clusters Clusters may be dispersed within the amorphous material. A cluster refers to an aggregate of atoms observed by a three-dimensional atom probe (3DAP). The clusters may be uniformly distributed or unevenly distributed within the Fe-based nanocrystalline soft magnetic alloy, but a uniform distribution is preferred.

[0034] The types of atoms constituting the clusters are not particularly limited as long as they are atoms other than Fe, which is the main component of the Fe-based nanocrystalline soft magnetic alloy, and may be one or more atoms selected from the group consisting of Si, Al, Nb, W, Zr, Hf, Ti, Mo, B, C, P, and Cu. Of these, the atoms constituting the clusters are preferably either Cu and Al or both, and more preferably both Cu and Al. Cu is an element that does not form a solid solution with Fe and therefore forms clusters, and Al is an element that readily forms a solid solution or compound with Cu and thus forms clusters.

[0035] When a cluster is composed of two or more types of atoms, each cluster may be an aggregate of one type of atom or an aggregate of two or more types of atoms, but it is preferable that it be an aggregate of two or more types of atoms.

[0036] For example, if the atoms constituting the cluster include both Cu and Al, then Cu clusters and Al clusters may be dispersed in the amorphous phase of the Fe-based nanocrystalline soft magnetic alloy, or clusters containing both Cu and Al may be dispersed, but it is preferable that clusters containing both Cu and Al are dispersed. Furthermore, in microstructural observation using a three-dimensional atom probe (3DAP), if the parts of the Cu distribution corresponding to clusters and the parts of the Al distribution corresponding to clusters overlap, it can be considered that clusters containing both Cu and Al are dispersed in the amorphous phase of the Fe-based nanocrystalline soft magnetic alloy.

[0037] As described later, Fe-based nanocrystalline soft magnetic alloys are manufactured by heat-treating an amorphous alloy to form clusters and crystal grains in the microstructure. Clusters are formed in the amorphous alloy in the early stages of heat treatment, and in addition to growing the crystal phase as crystal nuclei, they can also be dispersed around the crystal phase to suppress excessive crystal growth. This is thought to result in Fe-based nanocrystalline soft magnetic alloys containing crystal grains with small grain sizes. Furthermore, it is thought that the dispersion of fine clusters in the amorphous phase reduces the crystalline magnetic anisotropy, thereby improving the relative permeability of the Fe-based nanocrystalline soft magnetic alloy. Clusters composed of either or both Cu and Al are preferred because they exhibit this effect to a high degree.

[0038] The cluster number density in Fe-based nanocrystalline soft magnetic alloys is typically 1.65 × 10⁻⁶. -4 / nm 3 Preferably 1.90 × 10 -4 / nm 3 The above is more 2.15 × 10 -4 / nm 3 More preferably 2.50 × 10 -4 / nm 3 That is all, and also, normally 7.30 × 10 -4 / nm 3 The following is preferably 5.50 × 10 -4 / nm 3 More preferably, 3.00 × 10 -4 / nm 3 That's all. The cluster number density can be determined by using a 3D mapping obtained by 3D atom probe (3DAP) analysis of Fe-based nanocrystalline soft magnetic alloys to confirm the number of clusters per unit area. In this case, 20 atoms out of the atoms constituting the cluster... If one type of atom accounts for 20% or more of the total atoms, it shall be counted as one cluster of that atom. Furthermore, if two types of atoms account for 20% or more of the atoms constituting a cluster, it shall be counted as one cluster containing both of those two types of atoms.

[0039] By keeping the cluster number density within the above range, that is, by allowing many small clusters to exist, the spacing between clusters becomes narrower. As a result, the growth of the crystalline phase that forms with the clusters as crystal nuclei is suppressed, and an Fe-based nanocrystalline soft magnetic alloy containing crystal grains with a small average grain size can be obtained. Consequently, the relative permeability of the Fe-based nanocrystalline soft magnetic alloy is improved. The cluster number density can be adjusted by varying the composition of the Fe-based nanocrystalline soft magnetic alloy. For example, to form clusters containing both Cu and Al, this can be adjusted by changing c, y, and y × (100-abc) in compositional formula (I).

[0040] 1-1-4. Size of Fe-based nanocrystalline soft magnetic alloy ribbons The thickness and width of the Fe-based nanocrystalline soft magnetic alloy ribbon are not particularly limited as long as it can be wound to form a magnetic core of a practical shape. For example, the thickness of the ribbon may typically be between 8 μm and 16 μm, and the width of the ribbon may typically be between 5 mm and 25 mm.

[0041] 1-2. Magnetostriction The Fe-based nanocrystalline soft magnetic alloy core according to this embodiment exhibits magnetostriction of less than 0 ppm, i.e., negative magnetostriction. As described above, it has been generally accepted in this field that, in order to improve the permeability of magnetic materials, the magnetostriction should be brought close to zero. However, contrary to this understanding, the inventors have found that in the case of a magnetic core composed of the above-mentioned Fe-based nanocrystalline soft magnetic alloy, even if a high relative permeability is observed in the low-frequency region when the magnetostriction at practical temperature conditions is set to zero, the relative permeability does not reach its maximum in the high-frequency region. The inventors have then discovered that by setting the magnetostriction of the magnetic core at practical temperature conditions to a negative value instead of zero, the permeability in the high-frequency region of an Fe-based nanocrystalline soft magnetic alloy of a specific composition can be maximized. The above-mentioned practical temperature conditions refer to the room temperature (20°C) at which the magnetic core is used.

[0042] The magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core is negative, specifically, usually less than 0 ppm, preferably -0.25 ppm or less, and more preferably -0.5 ppm or less. Furthermore, the lower limit of the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core is preferably -2.0 ppm or more, more preferably -1.5 ppm or more, and even more preferably -1.0 ppm or more, from the viewpoint of further increasing the permeability in the high-frequency region under room temperature conditions.

[0043] The magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core according to this embodiment can be measured by the strain gauge method. Specifically, first, a strain gauge is attached to the surface of the sample to be measured, and a magnetic field of 600 Oe is applied in the longitudinal direction of the strain gauge axis. Next, the relative magnetostriction obtained by measuring the change in the length of the sample before and after the application of the magnetic field is taken as the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core. Magnetostriction measurements are performed at 20°C. The measurement sample may be a ribbon wound from an Fe-based nanocrystalline soft magnetic alloy core and cut into strips, or it may be a sample obtained by cutting a ribbon into strips before nanocrystallization and performing nanocrystallization (heat treatment) under the same conditions as when manufacturing the Fe-based nanocrystalline soft magnetic alloy core.

[0044] The inventors speculate that the reason the relative permeability in the high-frequency range is improved due to the magnetostriction at room temperature being within the above range for Fe-based nanocrystalline soft magnetic alloy cores is as follows. The relative permeability of the magnetic core changes depending on the ambient temperature. As shown in the examples described later, in this embodiment, when the composition of the Fe-based nanocrystalline soft magnetic alloy is kept constant, the high-frequency range The ambient temperature at which the relative permeability is maximum (maximum point) in the high-frequency region is higher than the ambient temperature at which the relative permeability is maximum in the low-frequency region. In other words, because the Fe-based nanocrystalline soft magnetic alloy core according to this embodiment is made of an Fe-based nanocrystalline soft magnetic alloy having the composition represented by composition formula (I), the maximum point of relative permeability in the high-frequency region shifts to a higher temperature than the maximum point of relative permeability in the low-frequency region. Considering this behavior of relative permeability, if the ambient temperature at which the relative permeability is maximum in the low-frequency region is below room temperature, it is considered that the relative permeability in the high-frequency region will be maximum at room temperature. Furthermore, if the magnetostriction of the core at room temperature is a negative value, it is presumed that the ambient temperature at which the relative permeability is maximum in the low-frequency region will be below room temperature, and the relative permeability in the high-frequency region can be maximized.

[0045] There is a correlation between the magnetostriction of the magnetic core, the composition of the Fe-based nanocrystalline soft magnetic alloy, the relative permeability of the magnetostriction at 20°C, and the degree of crystallinity of the Fe-based nanocrystalline soft magnetic alloy. Therefore, by adjusting the composition and degree of crystallinity of the Fe-based nanocrystalline soft magnetic alloy, it is possible to adjust the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core to the above range and improve the relative permeability in the high-frequency range. Specifically, the composition and degree of crystallinity of the Fe-based nanocrystalline soft magnetic alloy should be appropriately selected based on the verification shown in "Verification of the relationship between alloy composition, degree of crystallinity, and relative permeability" in the examples described later.

[0046] Furthermore, the degree of crystallinity of Fe-based nanocrystalline soft magnetic alloys can be determined by analysis using an X-ray diffraction (XRD) instrument (for example, Rigaku Corporation's Ultima IV). For this purpose, XRD analysis is performed on the magnetic core of an Fe-based nanocrystalline soft magnetic alloy, and the degree of crystallinity can be calculated from the peak areas of the crystalline component and the amorphous component in the obtained XRD pattern based on the following equation (3).

[0047]

number

[0048] 2. Method for manufacturing Fe-based nanocrystalline soft magnetic alloy cores The method for producing the Fe-based nanocrystalline soft magnetic alloy core according to this embodiment is not particularly limited, and known methods may be used as appropriate. Known methods include, for example, a method that includes an amorphous alloy ribbon production step in which an amorphous alloy ribbon is produced by rapidly solidifying a molten metal having a predetermined composition using an ultra-rapid cooling method, and a heat treatment step in which the amorphous alloy is nanocrystallized by heat treatment.

[0049] 2-1. Process for manufacturing amorphous alloy ribbons In the above method, the alloy used for the ultra-rapid quenching method is one having the same composition as the target Fe-based nanocrystalline soft magnetic alloy, that is, an alloy having the composition represented by compositional formula (I).

[0050] In the amorphous alloy ribbon manufacturing process, it is desirable that the temperature of the molten metal during rapid cooling be approximately 50°C to 300°C higher than the melting point of the alloy. The rapid cooling method is not particularly limited, and known methods such as the single-roll method, double-roll method, rotating liquid-based prevention method, gas atomization method, and water atomization method can be employed. The preparation of amorphous alloy ribbons by the ultra-rapid quenching method may be carried out under an oxidizing atmosphere such as air, under an inert gas atmosphere such as argon, helium, or nitrogen, or under vacuum conditions. Furthermore, amorphous alloy ribbons obtained by the ultra-rapid cooling method are preferable to be free of crystalline phases. However, it may also contain a crystalline phase in part.

[0051] The amorphous alloy ribbon obtained in the amorphous alloy ribbon fabrication process may be wound after nanocrystallization to create a magnetic core, but it is preferable to wind it before nanocrystallization to create a magnetic core material, and then heat-treat this magnetic core material to induce nanocrystallization. This is because although the alloy shows good workability at the amorphous alloy stage, its workability decreases after nanocrystallization due to heat treatment.

[0052] 2-2. Heat Treatment Process The heat treatment temperature in the heat treatment process is not particularly limited as long as it is above the crystallization start temperature of the alloy, and is usually 450°C or higher, but may be 500°C or higher, 510°C or higher, 520°C or higher, 530°C or higher, or 540°C or higher. Furthermore, the upper limit of the heat treatment temperature is usually 700°C or lower, but may be 650°C or lower, or 600°C or lower. Note that the heat treatment temperature refers to the highest temperature reached during the heat treatment. The holding time at the heat treatment temperature depends on the size of the amorphous alloy ribbon, etc., but from the viewpoint of uniformly heating the entire alloy and productivity, it is usually 5 minutes or more, but may be 8 minutes or more or 10 minutes or more, and is usually 5 hours or less, but may be 3 hours or less, 2 hours or less, or 1 hour or less.

[0053] Furthermore, the heat treatment process may be carried out in an oxidizing atmosphere such as air, in an inert gas atmosphere such as argon, helium, or nitrogen, or under vacuum conditions, but it is preferable to carry it out in an inert gas atmosphere. Furthermore, in order to improve the permeability of the magnetic core, a magnetic field may be applied to the amorphous alloy ribbon during the heat treatment process, for example, in accordance with the method described in International Publication No. 2022 / 019335.

[0054] As described above, the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy core according to this embodiment is adjusted by the composition and crystallinity of the Fe-based nanocrystalline soft magnetic alloy. Therefore, various heat treatment conditions such as heat treatment temperature and holding temperature are selected according to the composition of the Fe-based nanocrystalline soft magnetic alloy and the desired crystallinity.

[0055] 3. Applications of Fe-based nanocrystalline soft magnetic alloy cores The Fe-based nanocrystalline soft magnetic alloy core according to this embodiment can be used in reactors, common mode choke coils, transformers, communication pulse transformers, motors, generators, and the like. Of these, the Fe-based nanocrystalline soft magnetic alloy core according to this embodiment is particularly suitable for applications requiring high relative permeability at high frequencies, such as common mode choke coils, zero-phase reactors, current transformers, and ground fault sensors. [Examples]

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0057] <Experimental Examples 1-12> Alloy ribbons were prepared from molten metal with the composition shown in Table 1 using the single-roll method. Specifically, a master alloy was obtained by melting and mixing pure metals of each element, weighed to achieve the composition shown in Table 1, using the arc melting method. The resulting molten alloy was then ejected onto a roll rotating at a peripheral speed of 50 m / s under reduced pressure in an argon gas atmosphere to produce ribbons with a width of 5 mm and a thickness of 10 μm.

[0058] Next, the resulting ribbon is wound to create a magnetic winding with an outer diameter of 13 mm, an inner diameter of 12 mm, and a height of 5 mm. We obtained a core. The resulting wound magnetic core was then subjected to heat treatment under a nitrogen atmosphere under the conditions shown in Table 2 to fabricate an Fe-based nanocrystalline soft magnetic core.

[0059] [Evaluation of relative permeability] In the experimental example, a core made of Fe-based nanocrystalline soft magnetic alloy was loaded into a resin case, and then a coil was fabricated by winding 0.5 mm diameter copper wire three times around the resin case. Using an impedance analyzer (Keysight, E4990A), the inductance of the obtained coil was measured at frequencies of 1 kHz or 100 kHz and Hm = 0.4 A / m or less, and the relative permeability of the Fe-based nanocrystalline soft magnetic alloy core was determined based on the above equation (1). The magnetic path length l was 39 mm, and the effective cross-sectional area A was 1.8 mm². 2 The number of turns N is 3. The results are shown in Table 2.

[0060] [Measurement of crystallinity] The Fe-based nanocrystalline soft magnetic alloy cores fabricated in the experimental example were analyzed using an XRD analyzer (Ultima IV, Rigaku Corporation). The crystalline components in the obtained XRD patterns were analyzed. The degree of crystallinity was calculated from the peak area and the peak area of ​​the amorphous component based on the above formula (3). The results are shown in Table 2.

[0061] [Measurement of magnetostriction] The alloy ribbon prepared in the experimental example was cut into strips, and a measurement sample was obtained by heat treatment under the same conditions as the heat treatment of the wound magnetic core in the experimental example. A strain gauge was attached to the surface of this measurement sample, and a magnetic field of 600 Oe was applied in the longitudinal direction of the strain gauge axis. The change in the length of the measurement sample before and after the application of the magnetic field was measured, and the relative strain was determined. The results are shown in Table 2.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Evaluation of the temperature dependence of relative permeability] In the experimental example, a Fe-based nanocrystalline soft magnetic alloy core was fabricated and then placed in a resin case. A coil was then constructed by winding 0.5 mm diameter copper wire three times around the resin case. The inductance Ls of the obtained coil was measured using an impedance analyzer (Keysight E4990A) at frequencies of 1 kHz and Hm = 0.4 A / m or less, under varying ambient temperatures. Subsequently, the rate of change ΔLs of inductance Ls at each ambient temperature was calculated, using the inductance Ls at 20°C as the baseline. The relationship between the inductance change rate ΔLs [%] and ambient temperature is shown in Figures 1 to 4. Since relative permeability is proportional to inductance, the larger ΔLs, the higher the relative permeability, and the relative permeability of the magnetic core is also at its maximum (maximum) at the ambient temperature where ΔLs is at its maximum. In Figures 1-4, the maximum points of ΔLs are indicated by arrows. However, if the maximum point of ΔLs is below the lower limit of the ambient temperature at which the measurement was performed (-60°C), the ambient temperature at which ΔLs reaches its maximum point is considered to be that lower limit.

[0065] The magnetostriction of Fe-based alloys within crystal grains is temperature-dependent; as the ambient temperature rises, the magnetostriction decreases from a positive value to a negative value. Therefore, as the ambient temperature rises from a low temperature, the magnetostriction within the crystal grains decreases, and the relative permeability of the Fe-based nanocrystalline soft magnetic alloy is maximized when the magnetostriction approaches zero.

[0066] Comparing the results of experimental examples 7-9 in Figure 3, we can see that the lower the crystallinity of the Fe-based nanocrystalline soft magnetic alloy, the greater the relative permeability of the magnetic core when the ambient temperature is high enough to reduce magnetostriction. This holds true for both low frequencies (1 kHz) and high frequencies (100 kHz). Furthermore, in Figure 3, the relative permeability at 1 kHz and 100 kHz are shown for the magnetic core of the same experimental example. Comparing this to the relative permeability at kHz, it can be seen that at 100 kHz, the ambient temperature at which the relative permeability is maximum is higher than the ambient temperature at which the relative permeability is maximum at 1 kHz. As can be seen from Figures 1, 2, and 4, these trends are observed not only in Experimental Examples 7-9, but also in Experimental Examples 1-3, 4-6, and 10-12, where the composition of the Fe-based nanocrystalline soft magnetic alloy differs from that of Experimental Examples 7-9 in terms of x in compositional formula (I).

[0067] From the above, it is considered that, for a magnetic core using an Fe-based nanocrystalline soft magnetic alloy of composition (I) as a constituent material, in order to maximize the relative permeability in the high-frequency region at the practical temperature of room temperature (20°C), the ambient temperature at which the relative permeability in the low-frequency region is maximized must be below room temperature. Furthermore, in order to maximize the relative permeability in the low-frequency region at temperatures below room temperature, the magnetostriction of the Fe-based nanocrystalline soft magnetic alloy magnetic core at room temperature must be a negative value.

[0068] Since the magnetostriction of a magnetic core depends on the composition and crystallinity of the constituent materials, it is possible to make the magnetostriction of the magnetic core a negative value by adjusting the composition and crystallinity of the Fe-based nanocrystalline soft magnetic alloy. Therefore, the following study examines the composition and crystallinity of Fe-based nanocrystalline soft magnetic alloys that can produce a negative magnetostriction in the magnetic core.

[0069] [Verification of the relationship between alloy composition, crystallinity, and relative permeability] Figure 5 shows a graph plotting the results from Table 2, with the crystallinity of the Fe-based nanocrystalline soft magnetic alloy on the x-axis and the relative permeability of the magnetic core at 20°C on the y-axis, and an approximation curve drawn.

[0070] As can be seen from Figure 5, the relative permeability of the magnetic cores fabricated in the experimental examples increases as the degree of crystallinity of the Fe-based nanocrystalline soft magnetic alloy increases, and then decreases once the degree of crystallinity exceeds a certain level. The reason why the relative permeability of the magnetic core increases with increasing degree of crystallinity is thought to be that as crystallination progresses, the volume ratio of the negative magnetostrictive region (crystalline phase) in the alloy increases, and the magnetostriction of the magnetic core approaches zero. Furthermore, the reason why the relative permeability decreases once crystallination progresses beyond a certain level is thought to be that the positive magnetostrictive region (amorphous phase) decreases, the volume ratio of the negative magnetostrictive region increases further, and the magnetostriction of the magnetic core becomes excessively large in the negative direction.

[0071] The composition represented by composition formula (I) has a lower Al content and a higher Si content than conventionally used Fe-Si-Al magnetic alloys, and therefore tends to have greater crystalline magnetic anisotropy. Considering the relationship between relative permeability and crystallinity described above, it is considered particularly important to adjust the crystallinity to a desired range in order for the relative permeability of a magnetic core composed of such a material, where the crystalline magnetic anisotropy is not near zero, to show a maximum point at room temperature. Therefore, we will examine Figure 5 in more detail.

[0072] From the approximation curve drawn in the graph in Figure 5, it can be inferred that for each composition, the relative permeability is maximized at 1 kHz and 100 kHz, respectively, at the points indicated by the arrows in Figure 5. Therefore, by adjusting to the degree of crystallinity indicated by the arrow in the lower part of the graph in Figure 5, the relative permeability at 100 kHz is maximized under room temperature conditions, and the magnetostriction of the magnetic core at this time is thought to be a negative value. Furthermore, based on the above inferences and the plots in the graph, it can be considered that, when the composition of the Fe-based nanocrystalline soft magnetic alloy is represented by compositional formula (I), at both 1 kHz and 100 kHz, the higher the Si content in the Fe-based nanocrystalline soft magnetic alloy, the lower the degree of crystallinity at which the relative permeability of the magnetic core is maximized.

[0073] Furthermore, when comparing the relative permeability at 1 kHz and 100 kHz for each composition of Fe-based nanocrystalline soft magnetic alloy constituting the magnetic core, the Fe-based alloy with the highest relative permeability at 100 kHz The crystallinity of the nanocrystalline soft magnetic alloy is expected to be about 1-2% higher than that of the Fe-based nanocrystalline soft magnetic alloy that exhibits maximum relative permeability at 1 kHz.

[0074] The above verification demonstrated a relationship between the Si content, relative permeability at 20°C, and crystallinity in Fe-based nanocrystalline soft magnetic alloys. Therefore, based on such verification, the magnetostriction of the magnetic core at room temperature can be adjusted to a desired range by appropriately adjusting the composition and crystallinity of the Fe-based nanocrystalline soft magnetic alloy. Furthermore, this makes it possible to obtain a magnetic core with high relative permeability in the high-frequency range using an Fe-based nanocrystalline soft magnetic alloy with a low Al content.

Claims

1. A magnetic core is formed by winding a ribbon made of an Fe-based nanocrystalline soft magnetic alloy containing amorphous phases and crystalline grains, The magnetostriction at 20°C is less than 0 ppm. The Fe-based nanocrystalline soft magnetic alloy core has a composition represented by the following compositional formula (I). (F%) １－ｘ－ｙ Yes ｘ Al ｙ ) １００－ａ－ｂ－ｃ M ａ M' ｂ Cổ ｃ (I) (In compositional formula (I), M is one or more elements selected from the group consisting of Nb, W, Zr, Hf, Ti, and Mo; M' is one or more elements selected from the group consisting of B, C, and P; a, b, and c are atomic percent values ​​of 2.0 ≤ a ≤ 5.0, 3.0 < b < 10.0, and 0 < c < 3.0, respectively; x and y are 0.170 ≤ x ≤ 0.320 and 0.010 ≤ y ≤ 0.045; and 15.5 < x × (100 - a - b - c).)

2. The Fe-based nanocrystalline soft magnetic alloy core according to claim 1, wherein in the composition formula (I), 0.250 < x ≤ 0.

320.

3. The Fe-based nanocrystalline soft magnetic alloy core according to claim 1 or 2, wherein M is Nb and M' is B.

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