Patent Application
20180122540
The present invention relates to a soft magnetic alloy and a magnetic device.
Low power consumption and high efficiency have been demanded in electronic, information, communication equipment, and the like. Moreover, the above demands are becoming stronger for a low carbon society. Thus, reduction in energy loss and improvement in power supply efficiency are also required for power supply circuits of electronic, information, communication equipment, and the like. Then, improvement in saturation magnetic flux density and reduction in core loss (magnetic core loss) are required for the magnetic core of the ceramic element used in the power supply circuit. If the core loss is reduced, the loss of power energy is reduced, and high efficiency and energy saving are achieved.
Patent Document 1 discloses a Fe—B-M based soft magnetic amorphous alloy (M=Ti, Zr, Hf, V, Nb, Ta, Mo, and W). This soft magnetic amorphous alloy has favorable soft magnetic properties, such as a high saturation magnetic flux density, compared to a saturation magnetic flux density of a commercially available Fe amorphous material.
As a method of reducing the core loss of the magnetic core, it is conceivable to reduce coercivity of a magnetic material constituting the magnetic core.
However, an alloy composition of Patent Document 1 fails to contain an element capable of improving corrosion resistance, and is thereby extremely hard to be manufactured in the air. Moreover, even if the alloy composition of Patent Document 1 is manufactured by a water atomizing method or a gas atomizing method in a nitrogen atmosphere or an argon atmosphere, the alloy composition is oxidized by a small amount of oxygen in the atmosphere. This is also a problem with the alloy composition of Patent Document 1.
It is an object of the invention to provide a soft magnetic alloy or so simultaneously having a high corrosion resistance and excellent soft magnetic properties achieving both a high saturation magnetic flux density and a low coercivity.
To achieve the above object, the soft magnetic alloy according to the present invention is a soft magnetic alloy comprising a composition having a formula of ((Fe(1-(α+β))X1αX2β)(1-(a+b+c+d+e))MaBbPcCrdCue)1-fCf, wherein
X1 is one or more elements selected from a group of Co and Ni,
X2 is one or more elements selected from a group of W, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, N, O, and rare earth elements,
M is one or more elements selected from a group of Nb, Hf, Zr, Ta, Ti, Mo, and V, and
The soft magnetic alloy according to the present invention has the above-mentioned features, and thus easily has a structure to be a Fe based nanocrystalline alloy by a heat treatment. Moreover, the Fe based nanocrystalline alloy having the above-mentioned features has a high corrosion resistance. Moreover, the Fe based nanocrystalline alloy having the above-mentioned features is a soft magnetic alloy having favorable soft magnetic properties, such as a high saturation magnetic flux density and a low coercivity.
The soft magnetic alloy according to the present invention may satisfy 0.91≤1−(a+b+c+d+e)≤0.95.
The soft magnetic alloy according to the present invention may satisfy 0≤α{1−(a+b+c+d+e)}(1−f)≤0.40.
The soft magnetic alloy according to the present invention may satisfy α=0.
The soft magnetic alloy according to the present invention may satisfy 0≤β{1−(a+b+c+d+e)}(1−f)≤0.030.
The soft magnetic alloy according to the present invention may satisfy β=0.
The soft magnetic alloy according to the present invention may satisfy α=β=0.
The soft magnetic alloy according to the present invention may comprise a nanohetero structure composed of an amorphous phase and initial fine crystals, wherein the initial fine crystals exist in the amorphous phase.
The initial fine crystals may have an average grain size of 0.3 to 10 nm.
The soft magnetic alloy according to the present invention may comprise a structure composed of Fe based nanocrystals.
The Fe based nanocrystals may have an average grain size of 5.0 to 30 nm.
The soft magnetic alloy according to the present invention may comprise a ribbon shape.
The soft magnetic alloy according to the present invention may comprise a powder shape.
A magnetic device according to the present invention is composed of the above-mentioned soft magnetic alloy.
Hereinafter, an embodiment of the present invention will be described.
A soft magnetic alloy according to the present embodiment has a composition whose Fe content, M content, B content, P content, Cr content, Cu content, and C content are respectively within specific ranges. Specifically, the soft magnetic alloy according to the present embodiment is a soft magnetic alloy comprising a composition having a formula of ((Fe(1-(α+β))X1αX2β)(1-(a+b+c+d+e))MaBbPcCrdCue)1-fCf, wherein
X1 is one or more elements selected from a group of Co and Ni,
X2 is one or more elements selected from a group of W, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, N, O, and rare earth elements,
M is one or more elements selected from a group of Nb, Hf, Zr, Ta, Ti, Mo, and V, and
The soft magnetic alloy having the above-mentioned composition is easily configured to be a soft magnetic alloy composed of an amorphous phase and containing no crystal phase composed of crystals whose average grain size is larger than 20 nm. When this soft magnetic alloy undergoes a heat treatment, Fe based nanocrystals are deposited easily. Then, the soft magnetic alloy containing the Fe based nanocrystals easily has favorable magnetic properties. Moreover, the soft magnetic alloy easily has corrosion resistance as well.
In other words, the soft magnetic alloy having the above-mentioned composition is easily configured to be a starting material of a soft magnetic alloy where Fe based nanocrystals are deposited.
The Fe based nanocrystals are crystals whose grain size is in nano order and crystal structure of Fe is bcc (body-centered cubic structure). In the present embodiment, Fe based nanocrystals whose average grain size is 5 to 30 nm are preferably deposited. Such a soft magnetic alloy where Fe based nanocrystals are deposited easily has a high saturation magnetic flux density and a low coercivity.
Incidentally, the soft magnetic alloy before a heat treatment may be completely composed of only an amorphous phase, but preferably comprises a nanohetero structure composed of an amorphous phase and initial fine crystals, whose grain size is 20 nm or less, wherein the initial fine crystals exist in the amorphous phase. When the soft magnetic alloy before a heat treatment has a nanohetero structure where initial fine crystals exist in an amorphous phase, Fe based nanocrystals are easily deposited during a heat treatment. In the present embodiment, the initial fine crystals preferably have an average grain size of 0.3 to 10 nm.
Hereinafter, respective constituents of the soft magnetic alloy according to the present embodiment will be described in detail.
M is one or more elements selected from a group of Nb, Hf, Zr, Ta, Ti, Mo, and V. M is preferably one or more elements selected from a group of Nb, Hf, and Zr. When M is one or more elements selected from the group of Nb, Hf, and Zr, coercivity decreases easily.
AM content (a) satisfies 0.020≤a≤0.060. The M content (a) is preferably 0.020≤a≤0.045. When the M content (a) is small, a crystal phase composed of crystals whose grain size is larger than 15 nm is easily generated in the soft magnetic alloy before a heat treatment, no Fe based nanocrystals can be deposited by a heat treatment, and coercivity is high easily. When the M content (a) is large, coercivity is high easily, and corrosion resistance is low easily.
AB content (b) satisfies 0.020≤b≤0.060. The B content (b) preferably satisfies 0.020≤b≤0.050. When the B content (b) is small, amorphous forming ability decreases easily. When the B content (b) is large, coercivity is high easily, and corrosion resistance is low easily.
AP content (c) satisfies 0≤c≤0.030. The P content (c) may satisfy c=0. That is, P may not be contained. When P is contained, coercivity decreases easily. The P content (c) preferably satisfies 0.010≤c≤0.020. When the P content (c) is large, saturation magnetic flux density decreases easily. On the other hand, when P is not contained (c=0), there is an advantage that saturation magnetic flux density is high, compared to when P is contained.
A Cr content (d) satisfies 0≤d≤0.050. The Cr content (d) may satisfy d=0. That is, Cr may not be contained. The Cr content (d) preferably satisfies 0.005≤d≤0.020. When the Cr content (d) is large, corrosion resistance improves easily, but saturation magnetic flux density decreases easily. On the other hand, when Cr is not contained (d=0), there is an advantage that saturation magnetic flux density is high, compared to when Cr is contained.
A Cu content (e) satisfies 0≤e≤0.030. The Cu content (e) may satisfy e=0. That is, Cu may not be contained. When Cu is contained, coercivity decreases easily. The Cu content (e) preferably satisfies 0.005≤e≤0.030. When the Cu content (e) is large, amorphous forming ability decreases, and an amorphous phase cannot be maintained. On the other hand, when Cu is not contained (e=0), there is an advantage that saturation magnetic flux density is high, compared to when Cu is contained.
There is no limit to a Fe content (1−(a+b+c+d+e)), but 0.91≤1−(a+b+c+d+e)≤0.95 is preferably satisfied. When 0.91≤1−(a+b+c+d+e) is satisfied, saturation magnetic flux density is improved easily. When 1−(a+b+c+d+e)≤0.95 is satisfied, amorphous forming ability improves, coercivity decreases, and soft magnetic properties are favorable easily.
A C content (f) satisfies 0<f≤0.040. The C content (f) preferably satisfies 0.001≤f≤0.040, and more preferably satisfies 0.005≤f≤0.030. When f=0 is satisfied, that is, when C is not contained, a crystal phase composed of crystals whose grain size is larger than 15 nm is easily generated in the soft magnetic alloy before a heat treatment, no Fe based nanocrystals can be deposited by a heat treatment, and coercivity is high easily. Even if the crystal phase is not generated, a soft magnetic alloy finally obtained easily has a large coercivity. When the C content (f) is too large, the crystal phase is generated easily.
In the soft magnetic alloy according to the present embodiment, a part of Fe may be substituted with X1 and/or X2.
X1 is one or more elements selected from a group of Co and Ni. A X1 content (a) may satisfy α=0. That is, X1 may not be contained. The number of atoms of X1 is preferably 40 at % or less provided that the number of atoms of an entire composition is 100 at %. That is, 0≤a {1−(a+b+c+d+e)}(1−f)≤0.40 is preferably satisfied.
X2 is one or more elements selected from a group of W, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, N, O, and rare earth elements. A X2 content (β) may satisfy β=0. That is, X2 may not be contained. The number of atoms of X2 is preferably 3.0 at % or less provided that the number of atoms of an entire composition is 100 at %. That is, 0≤β {1−(a+b+c+d+e)}(1−f) 0.030 is preferably satisfied.
The substitution amount of Fe with X1 and/or X2 is half or less of Fe based on the number of atoms. That is, 0≤α+β≤0.50 is satisfied. When α+β>0.50 is satisfied, a Fe based nanocrystalline alloy is hard to be obtained by a heat treatment.
Incidentally, the soft magnetic alloy according to the present embodiment may contain elements other than the above-mentioned elements as inevitable impurities. For example, 1 wt % or less of the inevitable impurities may be contained with respect to 100 wt % of the soft magnetic alloy.
Hereinafter, a manufacturing method of the soft magnetic alloy according to the present embodiment will be described.
The soft magnetic alloy according to the present embodiment is manufactured by any method. For example, a ribbon of the soft magnetic alloy according to the present embodiment is manufactured by a single roll method. The ribbon may be a continuous ribbon.
In the single roll method, first, pure metals of respective metal elements contained in a soft magnetic alloy finally obtained are prepared and weighed so that a composition identical to that of the soft magnetic alloy finally obtained is obtained. Then, the pure metals of each metal element are molten and mixed, and a base alloy is prepared. Incidentally, the pure metals are molten by any method. For example, the pure metals are molten by high-frequency heating after a chamber is evacuated. Incidentally, the base alloy and the Fe based nanocrystals finally obtained normally have the same composition.
Next, the prepared base alloy is heated and molten, and a molten metal is obtained. The molten metal has any temperature, and may have a temperature of 1200 to 1500° C., for example.
In the single roll method, the thickness of the ribbon to be obtained can be mainly controlled by controlling a rotating speed of a roll, but can be also controlled by controlling a distance between a nozzle and the roll, a temperature of the molten metal, or the like. The ribbon has any thickness, and may have a thickness of 10 to 80 μm, for example.
The ribbon is preferably an amorphous material containing no crystals whose grain size is larger than 15 nm at the time of a heat treatment mentioned below. The amorphous ribbon undergoes a heat treatment mentioned below, and a Fe based nanocrystalline alloy can be thereby obtained.
Incidentally, any method can be used for confirming whether the ribbon of the soft magnetic alloy before a heat treatment contains crystals whose grain size is larger than 15 nm. For example, a normal X-ray diffraction measurement can confirm an existence of crystals whose grain size is larger than 15 nm.
In the ribbon before a heat treatment, no initial fine crystals, which have a particle size of less than 15 nm, may be contained, but the initial fine crystals are preferably contained. That is, the ribbon before a heat treatment preferably has a nanohetero structure composed of an amorphous phase and the initial fine crystals existing in this amorphous phase. Incidentally, the initial fine crystals have any particle size, but preferably have an average grain size of 0.3 to 10 nm.
The existence and average grain size of the above-mentioned initial fine crystals are observed by any method, such as by obtaining a restricted visual field diffraction image, a nano beam diffraction image, a bright field image, or a high resolution image using a transmission electron microscope with respect to a sample thinned by ion milling. When using a restricted visual field diffraction image or a nano beam diffraction image, with respect to diffraction pattern, a ring-shaped diffraction is formed in case of being amorphous, and diffraction spots due to crystal structure are formed in case of being non-amorphous. When using a bright field image or a high resolution image, an existence and an average grain size of the initial fine crystals can be confirmed by visually observing the image with a magnification of 1.00×105 to 3.00×105.
The roll has any temperature and rotating speed, and the chamber has any atmosphere. The roll preferably has a temperature of 4 to 30° C. for amorphization. The faster a rotating speed of the roll is, the smaller an average grain size of the initial fine crystals is. The roll preferably has a rotating speed of 25 to 30 m/sec. for obtaining initial fine crystals whose average grain size is 0.3 to 10 nm. The chamber preferably has an air atmosphere in view of cost.
The Fe based nanocrystalline alloy is manufactured under any heat conditions. Favorable heat treatment conditions differ depending on a composition of the soft magnetic alloy. Normally, a heat treatment temperature is preferably about 400 to 600° C., and a heat treatment time is preferably about 0.5 to 10 hours, but preferable heat treatment temperature and heat treatment time may be in a range deviated from the above ranges depending on the composition. The heat treatment is carried out in any atmosphere, such as an active atmosphere of air and an inert atmosphere of Ar gas.
An average grain size of an obtained Fe based nanocrystalline alloy is calculated by any method, and can be calculated by observation using a transmission electron microscope, for example. The crystal structure of bcc (body-centered cubic structure) is also confirmed by any method, and can be confirmed using an X-ray diffraction measurement, for example.
In addition to the above-mentioned single roll method, a powder of the soft magnetic alloy according to the present embodiment is obtained by a water atomizing method or a gas atomizing method, for example. Hereinafter, a gas atomizing method will be described.
In a gas atomizing method, a molten alloy of 1200 to 1500° C. is obtained similarly to the above-mentioned single roll method. Thereafter, the molten alloy is sprayed in a chamber, and a powder is prepared.
At this time, the above-mentioned favorable nanohetero structure is obtained easily with a gas spray temperature of 4 to 30° C. and a vapor pressure of 1 hPa or less in the chamber.
After the powder is prepared by the gas atomizing method, a heat treatment is conducted at 400 to 600° C. for 0.5 to 10 minutes. This makes it possible to promote diffusion of atoms while the powder is prevented from being coarse due to sintering of each particle, reach a thermodynamic equilibrium state for a short time, remove distortion and stress, and easily obtain a Fe based soft magnetic alloy whose average grain size is 10 to 50 nm.
An embodiment of the present invention has been accordingly described, but the present invention is not limited to the above-mentioned embodiment.
The soft magnetic alloy according to the present embodiment has any shape, such as a ribbon shape and a powder shape as described above. The soft magnetic alloy according to the present embodiment may also have a block shape.
The soft magnetic alloy (Fe based nanocrystalline alloy) according to the present embodiment is used for any purpose, such as for magnetic devices, particularly magnetic cores, and can be favorably used as a magnetic core for inductors, particularly power inductors. In addition to magnetic cores, the soft magnetic alloy according to the present embodiment can be also favorably used for thin film inductors, magnetic heads, and the like.
Hereinafter, a method for obtaining a magnetic device, particularly a magnetic core and an inductor, from the soft magnetic alloy according to the preset embodiment will be described, but is not limited to the following method. In addition to inductors, the magnetic core is used for transformers, motors, and the like.
For example, a magnetic core from a ribbon-shaped soft magnetic alloy is obtained by winding or laminating the ribbon-shaped soft magnetic alloy. When a ribbon-shaped soft magnetic alloy is laminated via an insulator, a magnetic core having further improved properties can be obtained.
For example, a magnetic core from a powder-shaped soft magnetic alloy is obtained by appropriately mixing the powder-shaped soft magnetic alloy with a binder and pressing this using a die. When an oxidation treatment, an insulation coating, or the like is carried out against the surface of the powder before the mixture with the binder, resistivity is improved, and a magnetic core further suitable for high-frequency regions is obtained.
The pressing method is not limited. Examples of the pressing method include a pressing using a die and a mold pressing. There is no limit to the kind of the binder. Examples of the binder include a silicone resin. There is no limit to a mixture ratio between the soft magnetic alloy powder and the binder either. For example, 1 to 10 mass % of the binder is mixed with 100 mass % of the soft magnetic alloy powder.
For example, 100 mass % of the soft magnetic alloy powder is mixed with 1 to 5 mass % of a binder and compressively pressed using a die, and it is thereby possible to obtain a magnetic core having a space factor (powder filling rate) of 70% or more, a magnetic flux density of 0.45 T or more at the time of applying a magnetic field of 1.6×104 A/m, and a resistivity of 1 Ω·cm or more. These properties are equivalent to or more excellent than those of normal ferrite core magnets.
For example, 100 mass % of the soft magnetic alloy powder is mixed with 1 to 3 mass % of a binder and compressively pressed using a die under a temperature condition that is equal to or higher than a softening point of the binder, and it is thereby possible to obtain a dust core having a space factor of 80% or more, a magnetic flux density of 0.9 T or more at the time of applying a magnetic field of 1.6×104 A/m, and a resistivity of 0.1 Ω·cm or more. These properties are more excellent than those of normal dust cores.
Moreover, a green compact constituting the above-mentioned magnetic core undergoes a heat treatment after pressing for distortion removal. This further decreases core loss. Incidentally, core loss of the magnetic core decreases by reduction in coercivity of a magnetic material constituting the magnetic core.
An inductance product is obtained by winding a wire around the above-mentioned magnetic core. The wire is wound by any method, and the inductance product is manufactured by any method. For example, a wire is wound around a magnetic core manufactured by the above-mentioned method at least in one or more turns.
Moreover, when using soft magnetic alloy particles, there is a method of manufacturing an inductance product by pressing and integrating a magnetic material incorporating a wire coil. In this case, an inductance product corresponding to high frequencies and large current is obtained easily.
Moreover, when using soft magnetic alloy particles, an inductance product can be obtained by carrying out firing after alternately printing and laminating a soft magnetic alloy paste obtained by pasting the soft magnetic alloy particles added with a binder and a solvent and a conductor paste obtained by pasting a conductor metal for coils added with a binder and a solvent. Instead, an inductance product where a coil is incorporated into a magnetic material can be obtained by preparing a soft magnetic alloy sheet using a soft magnetic alloy paste, printing a conductor paste on the surface of the soft magnetic alloy sheet, and laminating and firing them.
Here, when an inductance product is manufactured using soft magnetic alloy particles, in view of obtaining excellent Q properties, it is preferred to use a soft magnetic alloy powder whose maximum particle size is 45 m or less by sieve diameter and center particle size (D50) is 30 m or less. In order to have a maximum particle size of 45 m or less by sieve diameter, only a soft magnetic alloy powder that passes through a sieve whose mesh size is 45 m may be used.
The larger a maximum particle size of a soft magnetic alloy powder is, the further Q values in high-frequency regions tend to decrease. In particular, when using a soft magnetic alloy powder whose maximum particle diameter is more than 45 m by sieve diameter, Q values in high-frequency regions may decrease greatly. When Q values in high-frequency regions are not so important, however, a soft magnetic alloy powder having a large variation can be used. When a soft magnetic alloy powder having a large variation is used, cost can be reduced due to comparatively inexpensive manufacture thereof.
Hereinafter, the present invention will be described based on examples.
Raw material metals were weighed so that alloy compositions of respective examples and comparative examples shown in the following tables were obtained, and were molten by high-frequency heating. Then, a base alloy was prepared.
Then, the prepared base alloy was heated and molten to be turned into a metal in a molten state at 1300° C. This metal was thereafter sprayed by a single roll method against a roll of 10° C. with a rotating speed of 30 m/sec. in the air, and ribbons were prepared. The ribbons had a thickness of 20 to 25 am, a width of about 15 mm, and a length of about 10 m.
Each of the obtained ribbons underwent an X-ray diffraction measurement for confirmation of existence of crystals whose grain size was larger than 15 nm. Then, it was considered that each of the ribbons was composed of an amorphous phase if there was no crystals whose grain size was larger than 15 nm, and that each of the ribbons was composed of a crystal phase if there was a crystal whose grain size was larger than 15 nm.
Thereafter, the ribbon of each example and comparative example underwent a heat treatment with conditions shown in the following tables. Each of the ribbons after the heat treatment was measured with respect to saturation magnetic flux density and coercivity. The saturation magnetic flux density (Bs) was measured using a vibrating sample magnetometer (VSM) in a magnetic field of 1000 kA/m. The coercivity (Hc) was measured using a DC-BH tracer in a magnetic field of 5 kA/m. In the present examples, a saturation magnetic flux density of 1.40 T or more was considered to be favorable, and a saturation magnetic flux density of 1.60 T or more was considered to be more favorable. In the present examples, a coercivity of 6.0 A/m or less was considered to be favorable, and a coercivity of 5.0 A/m or less was considered to be more favorable.
Moreover, the ribbon of each example and comparative example underwent a constant temperature and humidity test, and was evaluated with respect to corrosion resistance and observed how many hours no corrosion was generated with conditions of a temperature of 80° C. and a humidity of 85% RH. In the present examples, 3 hours or more were considered to be favorable, and 30 hours or more was considered to be more favorable.
Incidentally, unless otherwise stated, it was confirmed by an X-ray diffraction measurement and a transmission electron microscope that all examples shown below had Fe based nanocrystals whose average grain size was 5 to 30 nm and crystal structure was bcc.
Table 1 shows examples and comparative examples where B content (b), P content (c), Cr content (d), Cu content (e), C content (f), M content (a), and kind of M were changed. Incidentally, Comparative Example 11 is a conventional FeSiBCr amorphous alloy (composition formula: Fe73S10B15Cr2).
An example whose each component was within a predetermined range had a favorable constant temperature and humidity test result. Such an example also had favorable saturation magnetic flux density and coercivity.
On the other hand, in some of comparative examples whose any of each component was out of a predetermined range, a ribbon before a heat treatment was composed of a crystal phase, and coercivity after a heat treatment was significantly high. In these comparative examples, even if a ribbon before a heat treatment was composed of an amorphous phase, an obtained soft magnetic alloy was inferior to a soft magnetic alloy of examples with respect to saturation magnetic flux density and/or coercivity.
Table 2 shows examples where a part of Fe was substituted with X1 and/or X2 with respect to Example 3.
Favorable characteristics were exhibited even if a part of Fe was substituted with X1 and/or X2.
Table 3 shows examples where an average grain size of initial fine crystals and an average grain size of a Fe based nanocrystalline alloy were changed by changing a ratating speed of the roll and/or a heat treatment temperature with respect to Example 3.
When the initial fine crystals had an average grain size of 0.3 to 10 nm and the Fe based nanocrystalline alloy had an average grain size of 5 to 30 nm, both saturation magnetic flux density and coercivity were favorable, compared to when failing these ranges.
Table 4 shows examples carried out in the same conditions as Examples 3, 23, and 24 except that the kind of M was changed.
Favorable characteristics were exhibited even if the kind of M was changed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-213581 | Oct 2016 | JP | national |
