Patent Application
20050254989
This application claims priority to prior Japanese patent application JP 2004-146595, the disclosure of which is incorporated herein by reference.
This invention relates to a high-frequency core mainly using a soft magnetic material and an inductance component using the core.
Heretofore, generally as a material of a high-frequency core, soft ferrite, high-silicon steel, an amorphous metal, a powder core, and the like have mainly been used. The reason why the above-mentioned materials are used is as follows. In case of the soft ferrite, the material itself has a high specific resistance. In case of other metal materials, the material may be formed into a thin plate or a powder so as to reduce an eddy current although the material itself has a low specific resistance. The above-mentioned materials are selectively used depending upon a working frequency or an intended use. Summarizing the reason therefor, the material high in specific resistance, such as the soft ferrite, has a low saturation magnetic flux density while the material high in saturation magnetic flux density, such as the high-silicon steel, has a low specific resistance. Thus, a magnetic material having both of a high saturation magnetic flux density and a high specific resistance is not yet provided.
In the meanwhile, following dramatic progress in reduction in size and improvement in function of various electronic apparatuses in recent years, inductance components, such as a coil and a transformer are required to be reduced in size and to have an inductance under a large direct current. In order to satisfy the above-mentioned demand, it is necessary to simultaneously improve a saturation magnetic flux density and a high-frequency loss characteristic of the core. Further, due to copper loss resulting from an electric resistance of a winding coil, heat generation of the coil or the transformer is increased. Therefore, it is also desired to provide a method for suppressing temperature elevation.
In case of the soft ferrite, improvement of the saturation magnetic flux density is considered but, actually, no substantial improvement is made. In case of the high-silicon steel or the amorphous metal, the material itself has a high saturation magnetic flux density. However, in order to adapt to a high-frequency band, the material must be formed into a thinner plate as the frequency band is higher. A multilayer core using such material is lowered in space factor, which may result in decrease in saturation magnetic flux density.
Further, in case of the powder core, it may be possible to achieve a high specific resistance by inserting an insulating material between fine powder particles and to achieve a high saturation magnetic flux density by high-density molding. However, there are difficult problems to solve. That is, a method of improving saturation magnetization of a soft magnetic powder used therefor and a method of forming a high-density molded body while maintaining insulation between powder particles are not established at present.
In order to remedy the above-mentioned problems, in particular, the problem that a magnetic material having both of a saturation magnetic flux density and a high specific resistance is difficult to obtain, proposal is made of a powder core and a method of producing the same in which a metallic glass powder is used as a soft magnetic powder, mixed with an insulating material, and formed into a molded body at a temperature not lower than a normal temperature so as to obtain a soft magnetic material having a high permeability with a relatively excellent frequency characteristic (see Japanese Unexamined Patent Application Publication (JP-A) No. 2001-189211, hereinafter referred to as a patent document 1).
Herein, there are various kinds of alloy compositions collectively called a metallic glass. However, alloy compositions used as the soft magnetic material are restricted to Fe-based alloys which are generally classified into a PePCBSiGa alloy composition and a FeSiBM (M being a transition metal) alloy composition.
The patent document 1 uses the former, i.e., an alloy having the FePcBSiGa alloy composition and discloses that, by the use of this soft magnetic material, excellent magnetic characteristics capable of achieving a high specific resistance and a high saturation magnetic flux density are obtained. It is noted here that the latter, i.e., the FeSiBM alloy composition is also disclosed (see Japanese Unexamined Patent Application Publications (JP-A) Nos. 2002-194514 and H11-131199, hereinafter referred to as patent documents 2 and 3, respectively). Further, it is also disclosed to use the soft magnetic material for a core (see Japanese Unexamined Patent Application Publication (JP-A) No. H11-74111, hereinafter referred to as a patent document 4).
On the other hand, it is disclosed to form a winding coil and a metal powder into an integral structure with a reduced size so that d.c. superposition characteristics are improved (see Japanese Unexamined Patent Application Publications (JP-A) Nos. H04-286305 and 2002-305108, hereinafter referred to as patent documents 5 and 6, respectively).
In case of the above-mentioned soft magnetic materials suitable as the high-frequency core, for example, in case of the FePCBSiGa alloy composition disclosed in the patent document 1, magnetic characteristics including a high permeability with a relatively excellent frequency characteristic are obtained. In this case, however, it is necessary to use an expensive metal such as Ga. This results in a problem that the material itself is high in cost and, therefore, promotion of industrial application is inhibited.
On the other hand, in the FeSiBM alloy composition disclosed in the patent documents 2 and 3 and considered about application to the core in the patent document 4, the material itself is excellent in economical efficiency. However, in these patent documents, no technique for obtaining a high specific resistance and a high magnetic flux density is shown (this is presumably because a method of forming a powder and a method of forming a molded body which are suitable for the alloy composition are not found). Thus, at present, it is difficult to use the material for the high-frequency core and an inductance component using the same.
The patent documents 5 and 6 disclose reduction in size of the coil. However, because an existing soft magnetic metal material is used, reduction of loss is not sufficient.
It is an object of this invention to provide an inexpensive high-frequency core made of a soft magnetic material having a high saturation magnetic flux density and a high specific resistance and to provide an inductance component using the same.
According to one aspect of the present invention, there is provided a high-frequency core which includes a molded body obtained by molding a mixture of a soft magnetic metallic glass powder and a binder in an amount of 10% or less in mass ratio with respect to the soft magnetic metallic glass powder. The soft magnetic metallic glass powder has an alloy composition represented by (Fe1-aCoa)100-x-y-z-q-r(M1-pM′p)xTyBzCqAlr(0<a<0.50, 0<p<0.5, 2 atomic %<x<5 atomic %, 8 atomic %<y<12 atomic %, 12 atomic %<z<17 atomic %, 0.1 atomic %<q<1.0 atomic %, 0.2 atomic %<r<2.0 atomic % and 25<(x+y+z+q+r)<30, M being at least one selected from Zr, Nb, Ta, Hf, Mo, Ti, V, Cr, and W, M′ being at least one selected from Zn, Sn, and R (R being at least one element selected from rare earth metals including Y), T being at least one selected from Si and P).
According to another aspect of the present invention, there is provided an inductance component which includes the high-frequency core and at least one turn of winding wound around the core.
According to still another of the present invention, there is provided an inductance component which includes the high-frequency core and at least one turn of winding coil wound around the core.
This invention will be described in detail.
As a result of extensive studies, the present inventors have found out that, if an alloy composition of (Fe1-aCoa)100-x-y-z-q-r(M1-pM′p)xTyBzCqAlr(0<a<0.50, 0<p<0.5, 2 atomic %<x<5 atomic %, 8 atomic %<y<12 atomic %, 12 atomic %<z<17 atomic %, 0.1 atomic %<q<1.0 atomic %, 0.2 atomic %<r<2.0 atomic % and 25<(x+y+z+q+r)<30, M being at least one selected from Zr, Nb, Ta, Hf, Mo, Ti, V, Cr, and W, M′ being at least one selected from Zn, Sn, and R (R being at least one element selected from rare earth metals including Y), T being at least one selected from Si and P) is selected as a soft magnetic metallic glass powder excellent in economic efficiency, the powder excellent in magnetic characteristics and glass forming performance is obtained. In the present invention, “rare earth metals including Y” represent the group consisting of lanthanum series elements, such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and another element of Y It has also been found out that, if a powder core is obtained by subjecting the powder to oxidization or insulating coating and then forming the powder into a molded body by an appropriate molding method using a die or the like, the powder core is a high-permeability powder core exhibiting an excellent permeability over a wide band and an excellent performance which has never been achieved, and that, as a result, a high-frequency core made of a soft magnetic material having a high saturation magnetic flux density and a high specific resistance can be produced at a low cost.
Further, it has been found out that an inductance component obtained by providing the high-frequency core with at least one turn of winding is inexpensive and has a high performance as never before.
The present inventors also found out that, by limiting a particle size of the soft magnetic metallic glass powder represented by the above-mentioned composition formula, the powder core is excellent in core loss at a high frequency.
Further, it has been found out that an inductance component obtained by providing the high-frequency core with at least one turn of winding is inexpensive and has a high performance as never before. It is also found out that, by press forming in the state where a winding coil is embedded in a magnetic body to form an integral structure, an inductance component adapted to a high-frequency large-current application is obtained.
In order to increase the specific resistance of the molded body, the alloy powder before molding may be subjected to oxidizing heat treatment in atmospheric air. In order to form the molded body having a high density, molding may be carried out at a temperature not lower than a softening point of the resin as the binder. In order to achieve a higher density of the molded body, molding may be carried out in a supercooled liquid temperature range of the alloy powder.
Specifically, the soft magnetic metallic glass powder has an alloy composition represented by a formula (Fe1-aCoa)100-x-y-z-q-r(M1-pM′p)xTyBzCqAlr(0<a<0.50, 0<p<0.5, 2 atomic %<x<5 atomic %, 8 atomic %<y<12 atomic %, 12 atomic %<z<17 atomic %, 0.1 atomic %<q<1.0 atomic %, 0.2 atomic %<r<2.0 atomic % and 25<(x+y+z+q+r)<30, M being at least one selected from Zr, Nb, Ta, Hf, Mo, Ti, V, Cr, and W, M′ being at least one selected from Zn, Sn, and R (R being at least one element selected from rare earth metals including Y), T being at least one selected from Si and P). The molded body is obtained by molding a mixture of the soft magnetic metallic glass powder and a binder of a predetermined amount in mass ratio with respect to the soft magnetic metallic glass powder.
Herein, description will be made of the alloy composition of the soft magnetic metallic glass powder. Fe as a main component is an element contributing to magnetism and is essential in order to achieve a high saturation magnetic flux density. A part of Fe may be replaced by Co in a ratio of 0 to 0.5. Such substitute component has an effect of improving a glass forming performance and is further expected to have an effect of improving the saturation magnetic flux density. The total amount of Fe and the substitute element is within a range not smaller than 70 atomic % and not greater than 75 atomic % with respect to a whole of the alloy powder. This is because, unless the amount is 70 atomic % or more, the saturation magnetic flux density is too low and the usefulness is lost and, if the amount is greater than 75 atomic %, the permeability of the core and the core loss are degraded due to crystallization.
The element M is a transition metal element necessary to improve the glass forming performance and is at least one selected from Zr, Nb, Ta, Hf. Mo, Ti, V, Cr, and W. The content of the element M is not smaller than 2 atomic % and not greater than 5 atomic %.
This is because if the content is smaller than 2 atomic %, the glass forming performance is decreased and the permeability and the core loss are remarkably deteriorated and, if the content exceeds 5 atomic %, the saturation magnetic flux density is decreased and the usefulness is lost. By replacing the ratio of 0 to 0.5 of the element M by Zn, Sn, R (R being at least one element selected from rare earth metals including Y), the ratio of Fe and Co can be increased without deteriorating the glass forming performance, so that the saturation magnetic flux density can be Improved.
Si and B are elements which are essential in order to produce the soft magnetic metallic glass powder. The amount of Si is within a range not smaller than 8 atomic % and not greater than 12 atomic %. The amount of B is within a range not smaller than 12 atomic % and not greater than 17 atomic %. This is because, if the amount of Si is smaller than 8 atomic % or greater than 12 atomic % or if the amount of B is smaller than 12 atomic % or greater than 17 atomic %, the glass forming performance is degraded and a stable soft magnetic glass powder can not be produced. Herein, Si may be replaced by P.
Al and C have an effect of forming the powder into a spherical shape upon preparing the powder by various atomizing techniques as far as these elements are used within the range of the alloy composition of this invention together with other constituent elements. As regards the amounts to be added, if the amount of Al is smaller than 0.2 atomic %, the effect of forming the powder of a spherical shape is small. If the amount of Al is greater than 2.0 atomic %, amorphous forming performance is deteriorated. Similarly, if the amount of C is smaller than 0.1 atomic %, the effect of forming the powder of a spherical shape is small. If the amount of C is greater than 1.0 atomic %, amorphous forming performance is deteriorated. Al and C may be used alone or in combination.
The soft magnetic metallic glass powder is produced by water atomization or gas atomization. Preferably, at least 50% of particle sizes are not smaller than 10 μm. In particular, the water atomization is established as a method of producing the alloy powder at a low cost and in a large amount. To be able to produce the powder by this method is a very large advantage in industrial application. However, in case of a conventional amorphous composition, the alloy powder of 10 μm or more is crystallized so that the magnetic characteristics are significantly deteriorated. As a result, the product yield is seriously deteriorated so that the industrial application is prevented. On the other hand, the soft magnetic metallic glass powder according to this invention is easily vitrified (amorphized) if the particle size is 150 μm or less. Therefore, the product yield is high. Thus, the soft magnetic metallic glass powder of this invention is highly advantageous in view of the cost. In addition, in the alloy powder produced by water atomization, an appropriate oxide coating film is already formed on a powder surface. Therefore, by mixing a resin with the alloy powder and molding the mixture to form a molded body, a core having a high specific resistance is easily obtained.
In either of the alloy powder produced by water atomization and the alloy powder produced by gas atomization, a more excellent oxide coating film is formed if heat treatment is carried out in atmospheric air under a temperature condition not higher than a crystallization temperature of the alloy powder used. In this event, the specific resistance of the core can be increased so that the core loss of the core can be reduced.
On the other hand, for an inductance component intended for higher-frequency applications, an eddy current loss can be reduced by the use of a metal powder having a very small particle size. However, with an alloy composition known in the art, oxidation of the powder during production is remarkable if the average diameter is 30 μm or less. Therefore, predetermined characteristics are difficult to obtain in the powder produced by a typical water atomization apparatus. However, the metallic glass powder is excellent in corrosion resistance of the alloy and is therefore advantageous in that the powder reduced in amount of oxygen and having excellent characteristics can relatively easily be produced even if the powder is very small.
Next, the method of molding the molded body will be described. Basically, a binder such as a silicone resin in an amount of 10% in mass ratio is mixed with the soft magnetic metallic glass powder. Using a die or by molding, the molded body is obtained. The molded body serves as a high-frequency core having a powder filling rate of 50% or more, a magnetic flux density of 0.5 T or more upon application of a magnetic field of 1.6×104 A/m, and a specific resistance of 1×104 cm. Herein, the amount of the binder is 10% or less in mass ratio. This is because, if the amount exceeds 10%, the saturation magnetic flux density becomes equivalent to or lower than that of ferrite and the usefulness of the core is lost.
The molded body may be obtained by preparing a mixture of the soft magnetic metallic glass powder and the binder in an amount of 5% or less in mass ratio with respect to the soft magnetic metallic glass powder and compression-molding the mixture using a die. In this case, the molded body has a powder filling rate of 70% or more, a magnetic flux density of 0.75 T or more when a magnetic field of 1.6×104 A/m is applied, and a specific resistance of 1 Ωcm or more. When the magnetic flux density is 0.75 T or more and the specific resistance is 1 Ωm or more, the characteristics are more excellent as compared with a Sendust core and the usefulness is further improved.
Further, the molded body may be obtained by preparing a mixture of the soft magnetic metallic glass powder and the binder in an amount of 3% or less in mass ratio with respect to the soft magnetic metallic glass powder and compression-molding the mixture using a die under a temperature condition not higher than a softening point of the binder. In this case, the molded body has a powder filling rate of 80% or more, a magnetic flux density of 0.9 T or more when a magnetic field of 1.6×104A/m is applied, and a specific resistance of 0.1 Ωcm or more. When the magnetic flux density is 0.9 T or more and the specific resistance is 0.1 Ωm or more, the characteristics are more excellent as compared with any powder core commercially available at present and the usefulness is further improved.
Further, the molded body may be obtained by preparing a mixture of the soft magnetic metallic glass powder and the binder in an amount of 1% or less in mass ratio with respect to the soft magnetic metallic glass powder and compression-molding the mixture in a supercooled liquid temperature range of the soft magnetic metallic glass powder. In this case, the molded body has a powder filling rate of 90% or more, a magnetic flux density of 1.0 T or more when a magnetic field of 1.6×104 A/m is applied, and a specific resistance of 0.01 Ωcm or more. When the magnetic flux density is 1.0 T or more and the specific resistance is 0.01 Ωm or more, the magnetic flux density is substantially equivalent to that of a multilayer core including an amorphous metal and a high-silicon steel plate in a practical region. However, the molded body herein obtained is small in hysteresis loss and high in specific resistance so that the core loss characteristic is much superior. Thus, the usefulness as a core is further improved.
Furthermore, after molding, the molded body as the high-frequency core may be subjected to heat treatment under a temperature condition not higher than the Curie point as a strain-relieving heat treatment. In this event, the core loss is further reduced and the usefulness as a core is further improved. Herein, it is desired that SiO2 is contained at least in a part of an intermediate material between particles of the alloy powder in order to maintain insulation between the particles (alternatively, all of the intermediate material may be SiO2).
If an inductance component is produced by providing the above-mentioned high-frequency core with at least one turn of winding after a gap is formed at a part of a magnetic path if necessary, a product exhibiting high permeability in a high magnetic field and having excellent characteristics is produced.
Hereinafter, this invention will be described further in detail with reference to the drawing.
If a powder core is produced by molding a mixture of a soft magnetic metallic glass powder having the above-mentioned metallic glass composition and having the maximum particle size of 45 μm or less in mesh size and the average diameter of 30 μm or less and a binder in an amount of 10% or less in mass ratio with respect to the soft magnetic metallic glass powder, the powder core exhibits an extremely low loss characteristic at a high frequency and has an excellent performance never before achieved. By providing the powder core with a winding, the inductance component excellent in Q characteristic is obtained.
Further, by press-molding a magnetic body with a winding coil embedded therein to form an integral structure, an inductance component adapted to a large high-frequency current is obtained.
Herein, the reason why the powder particle size is defined will be described in detail. If the maximum particle size exceeds 45 μm in mesh size, the Q characteristic in a high-frequency region is deteriorated. Further, unless the average diameter is 30 μm or less, the Q characteristic at 500 kHz or more does not exceed 40. Further, unless the average diameter is 20 μm or less, the Q value at 1 MHz or more is not 50 or more. The metallic glass powder is advantageous in that, since the specific resistance of the alloy itself is twice to ten times higher than conventional materials, the Q characteristic is high even at the same particle size. If the same Q characteristic is sufficient, a usable particle size range is widened so as to reduce a powder production cost.
Now, the high-frequency core according to this invention and the inductance component using the same will be described in conjunction with several examples and comparative examples, including production processes.
At first, as a powder preparing step, pure metal element materials including Fe, Si, B. Nb, Al, C, and substitute elements therefor or, if desired, various mother alloys were weighed so as to obtain predetermined compositions. By the use of these materials, various kinds of soft magnetic alloy powders were produced by water atomization generally used. It is noted here that a misch metal is a mixture of rare earth metals. Herein, a mixture of 30% La, 50% Ce, 15% Nd, and the balance other rare earth element or elements was used.
Next, as a molded body preparing step, each of the alloy powders was classified into those having a powder size of 45 μm or less. Thereafter, a silicone resin as a binder was mixed in an amount of 4% in mass ratio. Then, by the use of a die with a groove having an outer diameter of hope φOUT=27 mm×an inner diameter φIN=14 mm, various kinds of molded bodies were formed by applying a pressure of 1.18 GPa (about 12 t/cm2) at a room temperature so that the height was equal to 5 mm.
Further, the various kinds of molded bodies were subjected to resin curing. Thereafter, the weight and the size of each molded body were measured. Then, an appropriate number of turns of winding was provided to prepare various kinds of inductance components (having the shape illustrated in
Next, for each of various samples of the inductance components, the permeability was obtained from the inductance value at 100 kHz by the use of an LCR meter. Further, by the use of a d.c. magnetic characteristics measuring instrument, measurement was made of the saturation magnetic flux density when a magnetic field of 1.6×104 A/m was applied. In addition, upper and lower surfaces of each core were polished and measurement by X-ray diffraction (XRD) was carried out to observe a phase. The results shown in Table 1 were obtained.
Table 1 shows composition ratios of the samples. Further, an XRD pattern obtained by XRD measurement is judged as a glass phase if only a broad peak specific to the glass phase was detected, as a (glass+crystal) phase if a sharp peak attributable to a crystal was observed together with a broad peak, and as a crystal phase if only a sharp peak was observed without a broad peak.
For those samples of the compositions with the glass phase, a glass transition temperature and a crystallization temperature were measured as thermal analysis by DSC to confirm that a supercooled liquid temperature range ΔTx was 30 K or higher for all those samples. Herein, ×Tx=Tx−Tg, where Tx represents crystallization temperature, and Tg represents glass transition temperature. The specific resistance was measured for the molded bodies (cores) by two-terminal d.c. measurement. As a result, it was confirmed that all samples exhibited excellent specific resistances not lower than 1 Ωcm.
The temperature elevation rate of DSC was 40 K/min. From the examples 1 to 3 and the comparative examples 1 and 2, it is understood that the core having a glass phase is obtained if the amount of Nb is 3 to 6%.
However, it is seen that the magnetic flux density is as low as 0.70 T or less in the comparative example 2 where the amount of Nb is 6%.
From the examples 4 to 9 and the comparative examples 3 to 6, it is understood that the core having a glass phase is obtained if the amount of Si is 8 to 12, the amount of B is 12 to 17, and the amount of Fe is 70 to 75.
From the examples 10 to 14 and the comparative example 7, it is understood that, by replacing a part of Fe with Co, the metallic glass powder is obtained even if the amount of Nb is 2%. However, it is seen that, if the replaced amount exceeds 0.5, the effect of improving the magnetic flux density is not obtained. It is also understood that the similar effect is obtained by the use of Ta or Mo instead of Nb.
From the examples 15 and 16 and the comparative example 8, it is understood that the saturation magnetic flux density is improved by replacing Nb by Zn but the glass phase can not be formed if the replacement ratio exceeds 0.5.
As to the total amount of Zn and Nb, it is understood that 5% or less is appropriate from the examples 17 and 18 and the comparative example 9. From the examples 19 and 20, it is understood that the similar effect is obtained if Sn or a misch metal is added instead of Zn.
From the examples 21 to 23, it is understood that the similar effect is obtained if a part of Fe is replaced by Co and that the similar effect is obtained if Ta or Mo is used instead of Nb. As shown in the examples 24 to 26 and the comparative examples 11 and 12, Al may be added in a ratio of 2.0 or less and C may be added in a ratio of 1.0 or less. However, if a greater amount is added, an ability of forming an amorphous structure is remarkably deteriorated.
An alloy powder having a composition of (Fe0.8Co0.2)73Si9B14.5Nb2Al1.0C0.5 was prepared by water atomization. The powder thus obtained was classified into those having a size of 75 μm or less. XRD measurement was carried out to confirm a broad peak specific to a glass phase.
Next, thermal analysis by DSC was carried out to measure a glass transition temperature and a crystallization temperature to find out that ΔTx was 35K. Then, the powder was heat treated at 450° C. lower than the glass transition temperature for 0.5 hour in atmospheric air to form oxide on the surface of the powder. Next, the powder was mixed with 10%, 5%, 2.5%, 1%, and 0.5% silicone resin. By the use of a die of φ27×φ14, these powders were molded under three conditions at a room temperature, at 150° C. higher than a softening temperature of the resin, and at 550° C. in a supercooled liquid temperature range of this metallic glass powder. The powder filling rate, the magnetic flux density by d.c. magnetic characteristics measurement, and the d.c. specific resistance were measured. The results are shown in Table 2.
As seen from Table 2, the specific resistance has a value as high as ≧104 comparable to that of a ferrite core when the amount of the binder exceeds 5%. Because no special effect is obtained even if the molding temperature is elevated, molding at the room temperature is sufficient. Next, when the amount of the binder is equal to 5%, the specific resistance as high as 100 Ωcm or more is obtained and molding at the room temperature is sufficient. Next, it is understood that, when the content of the binder is equal to 2.5%, the powder filling rate is dramatically improved, the magnetic flux density is high, and the specific resistance of 10 Ωcm or more is obtained if molding is carried out at 150° C. Next, it is understood that, when the amount of the binder is 1% and 0.5%, the powder filling rate is dramatically improved, the saturation magnetic flux density is high, and the specific resistance of 0.1 Ωcm or more is obtained if molding is carried out at 550° C.
In an example 28, an alloy powder having a composition of Fe72Si9B14.5Nb3Al1.0C0.5 was prepared by water atomization. Thereafter, the powder thus obtained was classified into those having a particle size of 75 μm or less. Then, XRD measurement was carried out to confirm a broad peak specific to a glass phase.
Further, thermal analysis by DSC was carried out to measure a glass transition temperature and a crystallization temperature to confirm that a vitrification start temperature range or a supercooled liquid temperature range ΔTx was 35K. Then, the powder was kept at a temperature condition of 450° C. lower than the glass transition temperature and heat treated for 0.5 hour in atmospheric air to form oxide on the surface of the powder.
Next, the powder with oxide formed thereon was mixed with, in mass ratio, 10%, 5%, 2.5%, 1%, and 0.5% silicone resin as a binder. By the use of a die with a groove having an outer diameter φOUT=27 mm×an inner diameter φIN=14 mm, these powders were molded by applying a pressure of 1.18 GPa (about 12 t/cm2) as a molding pressure under three different temperature conditions, i.e., at a room temperature, at 150° C. higher than a softening temperature of the resin, and at 550° C. in a supercooled liquid temperature range of the soft magnetic metallic glass powder, so that the height was equal to 5 mm. Thus, various kinds of molded bodies were produced.
Next, the various kinds of molded bodies thus obtained were subjected to resin curing. Thereafter, the weight and the size of each molded body were measured. Then, an appropriate number of turns of winding was provided to prepare various kinds of inductance components (having the shape illustrated in
Then, for each of various samples (Nos. 1-15) of the inductance components, the powder filling rate %, the magnetic flux density (at 1.6×104 A/m) by d.c. magnetic characteristics measurement, and the d.c. specific resistance Ωcm were measured. The results shown in Table 3 were obtained.
As seen from Table 3, the specific resistance has a value as high as ≧104 comparable to that of a ferrite core when the amount of the binder (the amount of the resin) exceeds 5%. It is understood that no special effect is obtained even if the molding temperature is elevated and that the molding condition around the room temperature is sufficient. Further, it is understood that, when the amount of the resin is equal to 5%, the specific resistance as high as 100 Ωcm or more is obtained and that molding at the room temperature is similarly sufficient.
Further, it is understood that, when the amount of the resin is equal to 2.5%, the powder filling rate is dramatically improved, the magnetic flux density is high, and the specific resistance of 10 Ωcm or more is obtained if molding is carried out at 150° C. In addition, it is understood that, when the amount of the resin is 1% and 0.5%, the powder filling rate is dramatically improved, the saturation magnetic flux density is high, and the specific resistance of 0.1 Ωcm or more is obtained if molding is carried out at 550° C.
By the use of the sample No. 12 in the example 27, the inductance characteristic was measured in comparison with various core materials. Further, a core prepared by the use of the same alloy powder and the same production process was heat treated at 500° C. for 0.5 hour in a nitrogen atmosphere to obtain another sample. The inductance characteristic of this sample is also shown. For standardization of the inductance value, the permeability was obtained for comparison. The core materials compared were Sendust, 6.5% silicon steel, and an iron-based amorphous metal.
Note)
*Power specification with a gap inserted at a part of a magnetic path.
As seen from the above Table 4, the inductance component of this invention has a magnetic flux density equivalent to that of the inductance component using the amorphous metal and exhibits a core loss characteristic lower than that of the inductance component using Sendust. Therefore, the inductance component of this invention can be used as a very excellent inductance component. It has been confirmed that, in the inductance component using the heat-treated core, the permeability and the core loss are further improved.
In an example 30, an inductance component was produced by the use of a material corresponding to the sample No. 12 in the example 28. Further, another inductance component was prepared using a high-frequency core produced by the same alloy powder and the same production process and heat treated at 500° C. for 0.5 hour in a nitrogen atmosphere. Further, for comparison, inductance components (including the structure having a gap at a part of a magnetic path as shown in
As seen from the above Table 5, the inductance component of this invention has a magnetic flux density substantially equivalent to that of the inductance component using the Fe-based amorphous metal as a core and yet exhibits a core loss lower than that of the inductance component using Sendust as a core. Therefore, the inductance component of this invention has a very excellent characteristic. It has been confirmed that, in the inductance component using the heat-treated core, the permeability and the core loss are further improved and more excellent characteristics are achieved.
In an example 31, an alloy powder having a composition of Fe72Si9B14.5Nb3Al1.0C0.5 was prepared by water atomization. Thereafter, the powder thus obtained was classified into those having a particle size of 45 μm or less. Then, XRD measurement was carried out to confirm a broad peak specific to a glass phase.
Further, thermal analysis by DSC was carried out to measure a glass transition temperature and a crystallization temperature to confirm that a supercooled liquid temperature range ΔTx was 35K. Then, powders obtained by water atomization and having alloy compositions represented by the following Table 6 were filtered by a standard sieve into the powders of 20 μm or less. These powders were mixed at ratios shown in Table 6.
Further, using the powders thus obtained, a silicone resin as a binder was mixed in an amount of 1.5% in mass ratio. By the use of a die with a groove having an outer diameter φOUT=27 mm×an inner diameter φIN=14 mm, these powders were molded at a room temperature by applying a pressure of 12 t/cm2 so that the height was equal to 5 mm. Thus, various kinds of molded bodies were produced. After molding, heat treatment was carried out in Ar at 500° C.
Next, the various kinds of molded bodies thus obtained were subjected to resin curing. Thereafter, the weight and the size of each molded body were measured. Then, an appropriate number of turns of winding was provided to prepare various kinds of inductance components (having the shape illustrated in
Then, for each of the various samples of the inductance components, the powder filling rate %, the permeability, and the core loss (20 kHz 0.1 T) were measured. The results shown in Table 6 were obtained.
As seen from Table 6, the inductance component of this invention is improved in powder filling rate by adding to the metallic glass powder the soft magnetic powder smaller in particle size, and is consequently improved in permeability. On the other hand, if the added amount exceeds 50%, the improving effect is weakened and the core loss characteristic is significantly degraded. Therefore, it is understood that the added amount is preferably 50% or less.
In an example 32, alloy powders having a composition of Fe73.5-q-rSi9B14.5Nb3CqAlr in which the ratio of q and r were variously changed were prepared by water atomization. Thus, powders having aspect ratios shown in Table 7 were prepared. Thereafter, the powders thus obtained were classified into those having a particle size of 45 μm or less. Then, XRD measurement was carried out to confirm a broad peak specific to a glass phase. Further, thermal analysis by DSC was carried out to measure a glass transition temperature and a crystallization temperature to confirm that a supercooled liquid temperature range ΔTx was 35K.
Further, using the powders thus obtained, a silicone resin as a binder was mixed in an amount of 3.0% in mass ratio. By the use of a die with a groove having an outer diameter φOUT=27 mm×an inner diameter φIN=14 mm, these powders were molded at a room temperature by applying a pressure of 1.47 GPa (15 t/cm2) so that the height was equal to 5 mm. Thus, various kinds of molded bodies were produced. After molding, heat treatment was carried out in Ar at 500° C.
Next, the various kinds of molded bodies thus obtained were subjected to resin curing. Thereafter, the weight and the size of each molded body were measured. Then, an appropriate number of turns of winding was provided to prepare various kinds of inductance components (having the shape illustrated in
Then, for each of the various samples of the inductance components, the powder filling rate % and the permeability were measured. The results shown in Table 7 were obtained.
As seen from Table 7, the inductance component of this invention is improved in permeability by increasing the aspect ratio of the metallic glass powder. On the other hand, if the aspect ratio exceeds 2.0, the initial permeability is high but the permeability under d.c. superposition is degraded. Therefore, it is understood that the aspect ratio of the powder is preferably 2 or less.
At first, as a powder preparing step, materials were weighed so as to obtain the composition of Fe72.0Si9B14.5Nb3C0.5Al1.0. By the use of the materials, soft magnetic alloy fine powders different in average diameter were prepared by high-pressure water atomization.
Next, as a molded body preparing step, the alloy powders thus obtained were filtered by various types of standard sieves to prepare powders shown in Table 8. Thereafter, a silicone resin as a binder was mixed in an amount of 3% in mass ratio. Then, by the use of a die of 10 mm×10 mm, each powder was molded, together with a winding coil having an outer diameter of φOUT=8, an inner diameter φIN=4 mm and a height of 2 mm and arranged so that, after molding, the winding coil is positioned at an exact center of a molded body, by applying a pressure of 490 MPa at a room temperature so that the height was equal to 4 mm. Thus, molded bodies were formed.
Next, resin curing was performed at 150° C. As to a sample No. 5, another sample was also prepared by heat treating the inductance component at 500° C. for 0.5 Hr in nitrogen.
Next, for each of the various samples of the inductance components, the inductance and the resistance were measured at various frequencies by the use of an LCR meter. From the measurements, the inductance value at 1 MHz, the peak frequency of Q, and the peak value of Q were obtained. The results shown in Table 8 were obtained.
Next, for the same samples of the inductance components, a power conversion efficiency was measured by the use of an evaluation kit for a typical DC/DC converter. The results are as follows. The measurement condition was an input of 12 V, an output of 5 V, a drive frequency of 300 kHz, and an output current of 1 A.
As seen from Table 8, in the inductance component of this invention, when the mesh particle size was 45 μm or less and the average diameter was 30 μm or less, the peak frequency of Q was 500 kHz or more and its value was 40 or more. At that time, the power conversion efficiency was as excellent as 80% or more. When the mesh particle size was 45 μm or less and the average diameter was 20 μm or less, the peak frequency of Q was 1 MHz or more and its value was 50 or more. At that time, the power conversion efficiency was as more excellent as 85% or more. Further, it is understood that, by heat treating the inductance component, the conversion efficiency is further improved.
As described above, in the high-frequency core according to this invention, an alloy composition of (Fe1-aCoa)100-x-y-z-q-r(M1-pM′p)xTyBzCqAlr(0<a<0.50, 0<p<0.5, 2 atomic %<x<5 atomic %, 8 atomic %<y<12 atomic %, 12 atomic %<z<17 atomic %, 0.1 atomic %<q<1.0 atomic %, 0.2 atomic %<r<2.0 atomic % and 25<(x+y+z+q+r)<30, M being at least one selected from Zr, Nb, Ta, Hf, Mo, Ti, V, Cr, and W, M′ being at least one selected from Zn, Sn, and R (R being at least one element selected from rare earth metals including Y), T being at least one selected from Si and P) is selected as a soft magnetic metallic glass powder excellent in economic efficiency. This makes it possible to obtain the powder excellent in magnetic characteristics, glass forming performance, and powder filling ability. Further, the powder is subjected to oxidization or insulating coating and molded by the use of a die or the like using an appropriate molding method to obtain a molded body. In this manner, the powder core is prepared. Therefore, a high-permeability powder core which exhibits excellent permeability characteristics over a wide band and which is never known is obtained. As a result, it is possible to economically produce a high-frequency core of a soft magnetic material having a high saturation magnetic flux density and a high specific resistance. Further, an inductance component comprising the high-frequency core and at least one turn of winding wound therearound is obtained as an economical and high-performance product which has never been obtained. Accordingly, this invention is extremely useful in industrial application.
In this invention, if the metallic glass powder having a maximum particle size of 45 μm or less in mesh size and an average diameter of 30 μm or less, more desirably 20 μm or less, is used, a powder core having an extremely low loss characteristic at a high frequency is obtained. An inductance component comprising the high-frequency core with at least one turn of winding wound therearound is extremely excellent in Q characteristic so that the power supply efficiency can be improved. Thus, this invention is very useful in industrial application.
Further, in this invention, the metallic glass powder having a maximum particle size of 45 μm or less in mesh size and an average diameter of 30 μm or less, more desirably 20 μm or less, is press-molded with a winding coil embedded in a magnetic body to form an integral structure. In this event, in addition to the excellent core characteristics specific to the metallic glass, heat generation resulting from an electric current flowing through the winding coil is radiated through the metal magnetic body. By the synergetic effect thereof, it is possible to obtain an inductance component increased in rated current for the same shape. Herein, the temperature of the strain-relieving heat treatment of the metallic glass powder is lower than a temperature above 600° C. which is believed as an upper limit of the allowable temperature for a copper wire and a coating material used in the winding coil. Therefore, by the heat treatment at a temperature not higher than 600° C., it is possible to obtain a coil remarkably reduced in loss. Therefore, as the powder forming the core having an integral structure of the winding coil and the powder, the alloy composition of this invention is very suitable.
As described above, the high-frequency core according to this invention is economically obtained by the use of the soft magnetic metallic glass material having a high saturation magnetic flux density and a high specific resistance. Further, the inductance component obtained by providing the core with the winding is excellent in magnetic characteristics in a high-frequency band as never before. Thus, a high-permeability powder core low in cost and high in performance as never before can be produced and is suitably used in a power supply component, such as a choke coil and a transformer, of various electronic apparatuses.
By the use of the high-frequency core obtained by molding the powder having a fine particle size in this invention, a higher-performance inductance component at a high frequency can be produced. Further, in the high-frequency core obtained by molding the powder having a fine particle size, press-molding may be carried out with the winding coil embedded in the magnetic body to form an integral structure. Thus, the inductance component small in size and adapted to a large current can be produced and is suitably used as an inductance component such as a choke coil and a transformer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-146595 | May 2004 | JP | national |
