Patent Application
20140102595
1. Field of the Invention
The present invention relates to an Fe-based amorphous alloy applied to, for example, dust cores of transformers and choke coils for power supplies.
2. Description of the Related Art
Dust cores used in booster circuits of hybrid vehicles and the like, and reactors, transformers, and choke coils used in power generation and transformer stations are produced by powder compaction of Fe-based amorphous alloy powder and binders. A metallic glass having good soft magnetic properties can be used as the Fe-based amorphous alloy.
However, in the related art, there were no Fe—Cr—P—C—B—Si-system Fe-based amorphous capable of exhibiting a high saturation magnetic flux density Bs (in particular, about 1.5 T or higher) while exhibiting a glass transition temperature (Tg).
US2012/0092111, U.S. Pat. No. 7,132,019, Japanese Examined Patent Application Publication No. 7-93204, and Japanese Unexamined Patent Application Publication No. 2010-10668 disclose compositions of Fe—Cr—P—C—B—Si-based soft magnetic alloys but do not disclose an Fe—Cr—P—C—B—Si-based soft magnetic alloy capable of exhibiting a high saturation magnetic flux density Bs of about 1.5 T or higher while exhibiting a glass transition temperature (Tg).
The present invention provides an Fe-based amorphous alloy capable of exhibiting a high saturation magnetic flux density Bs while exhibiting a glass transition temperature (Tg), and a dust core made using an Fe-based amorphous alloy powder.
An aspect of the present invention provides an Fe-based amorphous alloy having a composition represented by formula (Fe100-a-b-c-d-eCraPbCcBdSie (a, b, c, d, and e are in terms of at %)), where 0 at %≦a≦1.9 at %, 1.7 at %≦b≦8.0 at %, 0 at %≦e≦1.0 at %, and an Fe content (100-a-b-c-d-e) is 77 at % or more, 19 at %≦b+c+d+e≦21.1 at %, 0.08≦b/(b+c+d)≦0.43, 0.06≦c/(c+d)≦0.87, and the Fe-based amorphous alloy has a glass transition point (Tg).
Preferably, 0.75 at %≦c≦13.7 at % and 3.2 at %≦d≦12.2 at %. As a result, the glass transition temperature (Tg) can reliably emerge.
The B content d is preferably 10.7 at % or less. The P content b is preferably 7.7 at % or less. Preferably, b/(b+c+d) is 0.16 or more. Preferably, c/(c+d) is 0.81 or less. As a result, an amorphous structure can be formed, a saturation magnetic flux density Bs of 1.5 T or higher can be reliably achieved, and a glass transition temperature (Tg) can stably emerge.
Preferably, 0 at %≦e≦0.5 at %. As a result, the Tg can be decreased.
Preferably, 0.08≦b/(b+c+d)≦0.32 and 0.06≦c/(c+d)≦0.73.
Preferably, 4.7 at %≦b≦6.2 at %. Preferably, 5.2 at %≦c≦8.2 at % and 6.2 at %≦d≦10.7 at %. The B content d is more preferably 9.2 at % or less. Preferably, 0.23≦b/(b+c+d)≦0.30 and 0.32≦c/(c+d)≦0.87. Here, the Fe-based amorphous alloy is preferably produced by a water atomization method. As a result, the alloy can be appropriately made amorphous (amorphization) and a glass transition temperature (Tg) can reliably emerge. Typically, an Fe-based amorphous alloy produced by a water atomization method can only exhibit a saturation magnetic flux density Bs of 1.4 T or lower. According to the present invention, the saturation magnetic flux density Bs of the Fe-based amorphous alloy produced by a water atomization method can be increased to about 1.5 T or higher. The water atomization method is a simple process for obtaining a uniform and substantially spherical magnetic alloy powder and the magnetic alloy powder obtained by this method can be mixed with a binder such as a binder resin and processed into dust cores having various shapes through press forming techniques. In the present invention, a dust core having a high saturation magnetic flux density can be obtained by adjusting the alloy composition as described above.
A saturation magnetic flux density Bs of 1.5 T or higher can be stably obtained when 4.7 at %≦b≦6.2 at %, 5.2 at %≦c≦8.2 at %, 6.2 at %≦d≦9.2 at %, 0.23≦b/(b+c+d)≦0.30, and 0.36≦c/(c+d)≦0.57.
An Fe-based amorphous alloy according to this embodiment has a composition represented by formula (Fe100-a-b-c-d-eCraPbCcBdSie (a, b, c, d, and e are in terms of at %)), where 0 at %≦a≦1.9 at %, 1.7 at %≦b≦8.0 at %, and 0 at %≦e≦1.0 at %. The Fe content (100-a-b-c-d-e) is 77 at % or more, 19 at %≦b+c+d+e≦21.1 at %, 0.08≦b/(b+c+d)≦0.43, and 0.06≦c/(c+d)≦0.87.
As described above, the Fe-based amorphous alloy according to this embodiment is a metallic glass containing Fe as a main component and Cr, P, C, B, and Si added at the above-described compositional ratio.
The Fe-based amorphous alloy according to this embodiment is amorphous, has a glass transition temperature (Tg), and achieves a high saturation magnetic flux density Bs. Moreover, a structure having high corrosion resistance can be obtained.
In the description below, the contents of the respective constitutional elements in Fe—Cr—P—C—B—Si are first described.
The Fe content in the Fe-based amorphous alloy of this embodiment is the remainder when the Cr, P, C, B, and Si contents are subtracted from Fe—Cr—P—C—B—Si. In the compositional formula described above, the Fe content is expressed as (100-a-b-c-d-e). The Fe content is preferably high in order to obtain a high Bs and is to be 77 at % or more. However, if the Fe content is excessively high, the Cr, P, C, B, and Si contents become excessively low and emergence of the glass transition temperature (Tg) and formation of an amorphous structure may be adversely affected. Thus the Fe content is preferably 81 at % or lower and more preferably 80 at % or lower.
The Cr content a in Fe—Cr—P—C—B—Si is specified to be within the range of 0 at %≦a≦1.9 at %. Chromium (Cr) accelerates formation of a passive layer on particle surfaces and improves corrosion resistance of the Fe-based amorphous alloy. For example, in forming Fe-based amorphous alloy powder through a water atomization method, occurrence of corroded parts at the time the molten alloy directly comes into contact with water or in the step of drying the Fe-based amorphous alloy powder after the water atomization can be prevented. Meanwhile, addition of Cr decreases the saturation magnetic flux density Bs and tends to increase the glass transition temperature (Tg). Accordingly, it is effective to suppress the Cr content a to a minimum level. A Cr content a is preferably set to be within the range of 0 at %≦a≦1.9 at % since then a saturation magnetic flux density Bs of about 1.5 T or higher can be reliably obtained.
Moreover, the Cr content a is preferably set to be 1 at % or lower. Thus, a saturation magnetic flux density Bs as high as 1.55 T or higher and 1.6 T or higher can be reliably obtained in some cases while the glass transition temperature (Tg) is maintained at a low temperature.
The P content b in Fe—Cr—P—C—B—Si is specified to be within the range of 1.7 at %≦b≦8.0 at %. Thus, a high saturation magnetic flux density Bs of about 1.5 T or higher can be achieved. Moreover, the glass transition temperature (Tg) easily emerges. According to the related art, as shown by the patent literatures etc., the P content has been set relatively high, such as at about 10 at %; however, in this embodiment, the P content b is set lower than in the related art. Phosphorus (P) is a semimetal related to formation of an amorphous structure. However, as described below, a high Bs can be achieved and formation of an amorphous structure can be appropriately accelerated by adjusting the total content of P and other semimetals.
In order to obtain a higher saturation magnetic flux density Bs, the P content b is set to be within the range of 7.7 at % or less and preferably 6.2 at % or less. The lower limit of the P content b is preferably changed according to the production method as described below. For example, in order to produce an Fe-based amorphous alloy by a water atomization method, the P content b is preferably set to 4.7 at % or more. Crystallization easily occurs at a P content b less than 4.7 at %. In contrast, in order to produce an Fe-based amorphous alloy by a melt spinning method, the lower limit can be set at 1.7 at % or about 2 at %. If the emphasis is on the ease of forming an amorphous structure while causing a glass transition temperature (Tg) to emerge reliably, the lower limit of the P content b is set at about 3.2 at %. In the melt spinning method, the upper limit of the P content b is set to 4.7 at % and is preferably about 4.0 at % so as to achieve a high saturation magnetic flux density Bs.
The Si content e in Fe—Cr—P—C—B—Si is specified to be within the range of 0 at %≦e≦1.0 at %. Addition of Si is considered to contribute to improving the ability of forming an amorphous structure. However, as the Si content e is increased, the glass transition temperature (Tg) tends to increase or vanish, thereby inhibiting formation of an amorphous structure. Accordingly, the Si content e is 1.0 at % or less and preferably 0.5 at % or less.
In this embodiment, the total content (b+c+d+e) of semimetal elements P, C, B, and Si is specified to be in the range of 19 at % or more and 21.1 at % or less. Because the P and Si contents b and e are within the above-described ranges, the range of the total content (c+d) of elements C and B is determined Furthermore, as described below, because the range of c/(c+d) is specified as below, neither the C content nor the B content is 0 at % and there are particular compositional ranges for these elements.
When the total content (b+c+d+e) of the semimetals P, C, B, and Si is 19 at % to 21.1 at %, a high saturation magnetic flux density Bs of about 1.5 T or higher can be obtained while an amorphous structure can be formed.
In this embodiment, the compositional ratio of P in P, C, and B, [b/(b+c+d)], is specified to be within the range of 0.08 or more and 0.43 or less. Thus, a glass transition temperature (Tg) can emerge and a high saturation magnetic flux density Bs of about 1.5 T or higher can be achieved.
In this embodiment, the compositional ratio of C in C and B, [c/(c+d)], is specified to be within the range of 0.06 or more and 0.87 or less. In this manner, the Bs can be increased and the ability to form an amorphous structure can be enhanced. Moreover, a glass transition temperature (Tg) emerges appropriately.
In sum, the Fe-based amorphous alloy of this embodiment exhibits a glass transition temperature (Tg) and a high saturation magnetic flux density Bs, in particular, a Bs of about 1.5 T or higher.
The Fe-based amorphous alloy of this embodiment can be produced in a ribbon shape by a melt spinning method. During this process, the limit thickness of the amorphous alloy is as large as about 150 to 180 μm. For example, for FeSiB-based amorphous alloys, the limit thickness is about 70 to 100 μm. Thus, according to this embodiment, the thickness can be about twice the thickness of the FeSiB-based amorphous alloys or more.
The ribbon is pulverized into a powder and used in manufacturing the dust cores and the like. Alternatively, an Fe-based amorphous alloy powder can be produced by a water atomization method or the like.
It is easier to achieve a high Bs by producing a ribbon-shaped Fe-based amorphous alloy through a melt spinning method than by producing the alloy through a water atomization method. However, even if an Fe-based amorphous alloy powder is obtained by a water atomization method, it is possible to achieve a high saturation magnetic flux density Bs of about 1.5 T or higher as shown by the experimental results below.
A preferable composition for producing an Fe-based amorphous alloy by a melt spinning method will now be described.
In this embodiment, the C content c is preferably set to be 0.75 at % or more and 13.7 at % or less and the B content d is preferably set to be 3.2 at % or more and 12.2 at % or less. Carbon (C) and boron (B) are both a semimetal and addition of C and B can enhance the ability to form an amorphous structure; however, if the contents of these elements are excessively small or large, the glass transition temperature (Tg) may vanish or even if a glass transition temperature (Tg) emerges, the composition adjusting ranges for other elements become very narrow. Accordingly, for stable emergence of a glass transition temperature (Tg), the C and B contents are preferably within the compositional ranges described above. The C content c is more preferably 12.0 at % or less. The B content d is more preferably 10.7 at % or less.
The compositional ratio of P in P, C, and B, [b/(b+c+d)], is preferably 0.16 or more. The compositional ratio of C in C and B, [c/(c+d)], is more preferably 0.81 or less. In this manner, the Bs can be increased and the ability to form an amorphous structure can be enhanced. Moreover, a glass transition temperature (Tg) can reliably emerge.
In this embodiment, it is possible to increase the saturation magnetic flux density Bs of the Fe-based amorphous alloy produced by a melt spinning method to 1.5 T or higher. It becomes possible to obtain a saturation magnetic flux density Bs of 1.6 T or higher by adjusting the compositional ratio of P in P, C, and B, [b/(b+c+d)], to 0.08 or more and 0.32 or less and the compositional ratio of C in C and B, [c/(c+d)], to 0.06 or more and 0.73 or less. More preferably, c/(c+d) is 0.19 or more.
Next, a preferable composition for producing an Fe-based amorphous alloy by a water atomization method is described.
The P content b is preferably 4.7 at %≦b≦6.2 at %. In this manner, amorphization can stably occur and a high saturation magnetic flux density Bs of about 1.5 T or higher can be obtained. The phrase “about 1.5 T or higher” means that the saturation magnetic flux density Bs may be a value slightly lower than 1.5 T and more specifically may be about 1.45 T which can be rounded to 1.5 T. In particular, it has been difficult for an Fe-based amorphous alloy produced by a water atomization method to achieve a saturation magnetic flux density Bs of 1.4 T or higher. However, according to this embodiment, a saturation magnetic flux density Bs of about 1.5 T or higher, which is significantly higher than that achieved by the related art, can be stably achieved.
The C content c is preferably 5.2 at % or more and 8.2 at % or less and the B content d is preferably 6.2 at % or more and 10.7 at % or less. The B content d is more preferably 9.2 at % or less. Carbon (C) and boron (B) are both a semimetal and addition of these elements can enhance the ability to form an amorphous structure; however, if the contents of these elements are excessively small or large, the glass transition temperature (Tg) may vanish or even if a glass transition temperature (Tg) emerges, the composition adjusting ranges for other elements become very narrow. As shown by the experimental results below, adjusting the contents as described above makes it possible to achieve amorphization and stably obtain a saturation magnetic flux density Bs of about 1.5 T or higher.
Preferably, 0.23≦b/(b+c+d)≦0.30 and 0.32≦c/(c+d)≦0.87. As shown by the experimental results below, it becomes possible to achieve amorphization and stably obtain a saturation magnetic flux density Bs of about 1.5 T or higher.
For the Fe-based amorphous alloy produced by a water atomization method, more preferably, 4.7 at %≦b≦6.2 at %, 5.2 at %≦c≦8.2 at %, 6.2 at %≦d≦9.2 at %, 0.23≦b/(b+c+d)≦0.30, and 0.36≦c/(c+d)≦0.57. Thus, a high saturation magnetic flux density Bs of 1.5 T or higher can be stably obtained.
As shown by the experiments described below, the Fe-based amorphous alloy produced by a water atomization method tends to show a lower saturation magnetic flux density Bs than the Fe-based amorphous alloy produced by a melt spinning method. This is presumably due to contamination in raw materials used and the influence of powder oxidation during atomization, for example.
In the case where an Fe-based amorphous alloy is produced by a water atomization method, the compositional range for forming an amorphous structure tends to be narrow compared to the melt spinning method. However, the experiments described below show that even the Fe-based amorphous alloy produced by the water atomization method can exhibit a high saturation magnetic flux density Bs of about 1.5 T or higher while being amorphous as with those produced by a melt spinning method.
In particular, Fe-based amorphous alloys produced by typical water atomization methods have had a low saturation magnetic flux density Bs of 1.4 T or lower; however, according to this embodiment, it becomes possible for the alloys to achieve a saturation magnetic flux density Bs of about 1.5 T or higher.
The composition of the Fe-based amorphous alloy of this embodiment can be analyzed with ICP-MS (inductively coupled plasma mass spectrometer) or the like.
In this embodiment, a powder of the Fe-based amorphous alloy represented by the compositional formula above is mixed with a binder and solidified so as to form a ring-shaped dust core 1 shown in
Examples of the binder include liquid or powdery resin and rubber such as epoxy resin, silicone resin, silicone rubber, phenolic resin, urea resin, melamine resin, PVA (polyvinyl alcohol), and acrylic acid, liquid glass (Na2O—SiO2), oxide glass powder (Na2O—B2O3—SiO2, PbO—B2O3—SiO2, PbO—BaO—SiO2, Na2O—B2O3—ZnO, CaO—BaO—SiO2, Al2O3—B2O3—SiO2, and B2O3—SiO2), and glassy substances produced by sol-gel methods (those mainly composed of SiO2, Al2O3, ZrO2, TiO2, and the like).
Zinc stearate, aluminum stearate, and the like can be used as a lubricant. The mixing ratio of the binder is 5 mass % or less and the lubricant content is about 0.1 mass % to 1 mass %.
After press-forming, the dust core is heat-treated to relax the stress strain on the Fe-based amorphous alloy powder. In this embodiment, the glass transition temperature (Tg) of the Fe-based amorphous alloy powder can be decreased and thus the optimum heat-treatment temperature of the core can be made lower than that typically required. The “optimum heat-treatment temperature” means a heat-treatment temperature for a core compact at which the stress strain on the Fe-based amorphous alloy powder can be effectively relaxed and the core loss can be minimized
Fe-based amorphous alloys having compositions shown in Table 1 in Appendix were produced by a melt spinning method so as to have a ribbon shape. In particular, a ribbon was obtained in an Ar atmosphere at a reduced pressure by a single roll method involving ejecting a melt of Fe—Cr—P—C—B—Si from a crucible nozzle onto a rotating roll to conduct rapid cooling. The ribbon production conditions were set as follows. The distance (gap) between the nozzle and the roll surface was about 0.3 mm; the peripheral speed of the rotating roll was about 2000 m/min, and the ejection pressure was set to about 0.3 kgf/cm2. The thickness of each ribbon obtained was about 20 to 25 μm.
All samples in Table 1 were confirmed to be amorphous with an XRD (X-ray diffraction analyzer). The Curie temperature (Tc), the glass transition temperature (Tg), the crystallization onset temperature (Tx), and the melting temperature (Tm) were measured with a DSC (differential scanning calorimeter) (heating rate was 0.67 K/sec for Tc, Tg, and Tx and 0.33 K/sec for Tm).
The saturation magnetic flux density Bs and the saturation mass magnetization σs in Table 1 were measured with a VSM (vibrating sample magnetometer) under application of a 10 kOe magnetic field. The density D shown in Table 1 was measured by the Archimedean method. The figures in the columns of Table 1 were rounded if they were indivisible. Thus, for example, “0.52” has a range of 0.515 to 0.524.
The graphs indicating dependency of the saturation magnetic flux density Bs, the saturation mass magnetization as, the Curie temperature (Tc), the glass transition temperature (Tg), the crystallization onset temperature (Tx), ΔTx, the melting temperature (Tm), the reduced glass transition temperature (Tg/Tm), and Tx/Tm in Table 1 on the composition are shown in
It was found that the Fe-based amorphous alloys of Comparative Examples shown in Table 1 either have a lower saturation magnetic flux density Bs than in Examples or have no glass transition temperature (Tg) if they are capable of exhibiting a high saturation magnetic flux density Bs.
In contrast, the Fe-based amorphous alloys of Examples shown in Table 1 exhibited a glass transition temperature (Tg) and a high saturation magnetic flux density Bs of about 1.5 T or higher. In particular, Nos. 43 to 53, No. 57, No. 62, No. 65, No. 67, No. 77, No. 79, No. 81, and No. 82 samples were found to exhibit a saturation magnetic flux density Bs exceeding 1.6 T.
In sum, it was found that Examples exhibited a high saturation magnetic flux density Bs and a high ability to form an amorphous structure attributable to the presence of a glass transition temperature (Tg) and ΔTx associated therewith. Accordingly, an Fe-based amorphous alloy having a high saturation magnetic flux density can be easily obtained even when the cooling conditions and the like are relaxed.
The reduced glass transition temperature (Tg/Tm) and Tx/Tm are preferably high in order to obtain a high ability to form an amorphous structure. It was found that a reduced glass transition temperature (Tg/Tm) of 0.50 or more and Tx/Tm of 0.53 or more can be achieved in Examples.
Experiments related to saturation magnetic flux density Bs and other alloy properties: water atomization method
Fe-based amorphous alloys having compositions shown in Table 2 were produced by a water atomization method.
The melt temperature (temperature of the melted alloy) for obtaining powders was 1500° C. and the water ejection pressure was 80 MPa.
The mean particle size (D50) of the Fe-based amorphous alloy powders produced by the water atomization method was 10 to 12 μm. The mean particle size was measured with a Microtrac particle size distribution analyzer MT300EX produced by Nikkiso Co., Ltd.
Of the samples shown in Table 2, Nos. 84 to 90 were confirmed to be a mixture of crystalline and amorphous phases and Nos. 91 to 97 were confirmed to be amorphous with an XRD (X-ray diffraction analyzer).
The saturation magnetic flux density Bs shown in Table 2 was measured with a VSM (vibrating sample magnetometer) under an application of 10 kOe magnetic field.
Three samples were chosen from Examples (those having amorphous powder structure) in Table 2 and indicated in Table 3 below. The curie temperature (Tc), the glass transition temperature (Tg), the crystallization onset temperature (Tx), and the melting temperature (Tm) of these samples were measured with DSC (differential scanning calorimeter) (heating rate was 0.67 K/sec for Tc, Tg, and Tx and 0.33 K/sec for Tm).
It was found from
However, as shown in
In all Examples shown in Table 2, a glass transition temperature (Tg) emerged.
The experimental results described above show that it is difficult to form an amorphous structure when the P content b is excessively small and the saturation magnetic flux density Bs decreases when the P content b is excessively large.
Based on the experimental results, the P content b in Examples was set to 1.7 at % or more and 8.0 at % or less. Since a water atomization method may be used to make an Fe-based amorphous alloy, the P content b is more preferably 4.7 at % or more and 6.2 at % or less in view of the experimental results shown in Table 3.
The Fe-based amorphous alloys shown in Tables 1 and 2 had a Si content e of 0 at % or 0.5 at %. It was found that even when the Si content e was 0 at %, a high Bs was achieved, a glass transition temperature (Tg) emerged, and formation of an amorphous structure was possible. In Examples, the range of the Si content e was set to 0 at % or more and 1.0 at % or less based on the assumption that the properties would not be much affected even when the maximum Si content e was set to a value slightly larger than that of the experiments because the content of at least one semimetal element selected from P, C, and B was lowered. A preferable range of the Si content e was set to 0 at % or more and 0.5 at % or less.
The Fe content (100-a-b-c-d-e) is preferably high in order to obtain a high saturation magnetic flux density Bs. In Examples, Bs was set to 77 at % or more. However, excessively increasing the Fe content decreases the Cr, P, C, B, and Si contents and may adversely affect the ability to form an amorphous structure, emergence of a glass transition temperature (Tg), and corrosion resistance. Thus, the maximum Fe content was set to 81 at % or less and preferably 80 at % or less.
The total content, (b+c+d+e), of P, C, B, and Si in Examples shown in Tables 1 and 2 was 19.0 at % or more and 21.1 at % or less.
The compositional ratio of P with respect to the total content of P, C, and B, [b/(b+c+d)], in Tables 1 and 2 was 0.08 or more and 0.43 or less.
The compositional ratio of C with respect to the total content of C and B, [b/(b+c)], in Tables 1 and 2 was 0.06 or more and 0.87 or less.
Based on Table 1, a preferable range of the C content c in Examples was set to 0.75 at %≦c≦13.7 at %. A preferable range of the B content d was set to 3.2 at %≦d≦12.2 at %.
As shown in
As shown in Table 1, the glass transition temperature (Tg) tends to vanish when the compositional ratio of P with respect to the total content of P, C, and B, [b/(b+c+d)], is low, in other words, as the compositional ratio of p is decreased. Thus, the preferable range of [b/(b+c+d)] was set to 0.16 or more.
As shown in Table 1 and
As shown in Table 1 and
It was also found that a saturation magnetic flux density Bs of 1.6 T or more can be obtained by adjusting the compositional ratio of P in P, C, and B, [b/(b+c+d)], to 0.08 or more and 0.32 or less and adjusting the compositional ratio of C in C and B, [c/(c+d)], to 0.06 or more and 0.73 or less. More preferably, c/(c+d) is 0.19 or more.
Preferable Compositional Range for Fe-Based Amorphous Alloys Produced by Water Atomization Method
As shown in Table 2 and
It was found that a saturation magnetic flux density Bs of about 1.5 T or higher can be stably obtained while achieving amorphicity by adjusting the C content c to 5.2 at % or more and 8.2 at % or less and a B content d to 6.2 at % or more and 10.7 at % or less. It was also found that the saturation magnetic flux density Bs can be more effectively stably increased by adjusting the B content d to 9.2 at % or less.
It was found that a saturation magnetic flux density Bs of about 1.5 T or higher can be obtained while achieving amorphicity by setting the compositional ratio of P with respect to the total content of P, C, and B, [b/(b+c+d)], to 0.23 or more and 0.30 or less and setting the compositional ratio of C with respect to the total content of C and B, [c/(c+d)], to 0.32 or more and 0.87 or less.
Based on the experimental results shown in Table 2 and
In the compositions shown in Tables 1 and 2, the Cr content is fixed at 1 at %. In the next experiment, the saturation magnetic flux density Bs and the same properties as those in Table 1 were measured by varying the Cr content a so as to specify the Cr content a.
In the experiment, Fe-based amorphous alloy ribbons having a composition of Fe78.9-aCraP3.2C8.2B9.2Si0.5 were obtained under the same production conditions as the samples shown in Table 1.
In the experiment, the Cr content a was varied from 0 at % to 6 at % and the same properties as those shown in Table 1 were measured. The experimental results are shown in Table 4 below.
As shown in Table 4 and
Based on this experiment, the Cr content a was set to be within the range of 0 at %≦a≦1.9 at %. A preferable Cr content a for obtaining good corrosion resistance was set to 0.5≦a≦1.9 at % although the saturation magnetic flux density Bs is slightly decreased in this range.
In the experiment, dust cores of Examples were prepared by using Fe-based amorphous alloy powder of No. 94 (Fe77.9Cr1P6.3C5.2B9.2Si0.5; Bs=1.5 T) shown in Table 2.
Dust cores of Comparative Examples were prepared by using Fe-based amorphous alloy powder (Bs=1.2 T) having a composition of Fe77.4Cr2P9C2.2B7.5Si4.9 or Fe-based amorphous alloy powder (Bs=1.35 T) having a composition of Fe77.9Cr1P7.3C2.2B7.7Si3.9.
In Examples and Comparative Examples, 1.4 wt % of a silicone resin and 0.3 wt % of a lubricant (fatty acid) were added to magnetic powder and mixed. The resulting mixture was dried for two days and pulverized. Then a toroidal core having an outer diameter of 20 mm, an inner diameter of 12 mm, and a thickness of 7 mm was prepared by press-forming (at a pressure of 20 ton/cm2).
The toroidal core obtained as such was heat-treated at 400° C. to 500° C. in a N2 atmosphere for 1 hour.
As shown in Table 5 below, the heat treatment temperature was adjusted so that the initial permeability (μ0) was substantially the same between Example 1 and Comparative Example 1, between Example 2 and Comparative Example 2, and between Example 3 and Comparative Example 3.
In the experiment, a wire was wound around each of the toroidal cores of Examples and Comparative Examples and the change in permeability μ was measured by applying a bias magnetic field to each core up to a maximum of 4130 A/m (DC superimposition characteristics).
Table 5 below shows the saturation magnetic flux density Bs, the initial permeability μ0, the permeability μ4130 under 4130 A/m bias, and μ4130/μ0 of each sample. The figures for μ4130/μ0 in Table 5 were rounded off to two decimal places.
As shown in Table 5, Example 1, Example 2, and Example 3 had the same powder composition and the same saturation magnetic flux density Bs; however, the heat-treatment temperature was changed so that the initial permeability μ0 was adjusted to be substantially the same as that of the corresponding comparative example.
The saturation magnetic flux density Bs in Comparative Example was lower than in Examples and was outside the compositional range of Examples.
Table 6 below shows the permeability μ of each sample relative the magnitude of the bias magnetic field.
The relationship between the bias magnetic field and the permeability μ of Example 1 and Comparative Example 1 is determined based on the experimental results of Table 6 and shown in
The lower the rate of decrease in permeability μ under application of a bias magnetic field, the better the DC superimposition characteristics.
Accordingly, it was found from the experimental results shown in
The dependency of μ4130/μ0 on Bs was also investigated on the basis of the experimental results shown in Table 5. The results are shown in
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-165020 | Jul 2011 | JP | national |
| 2012-151424 | Jul 2012 | JP | national |
This application is a Continuation of International Application No. PCT/JP2012/068975 filed on Jul. 26, 2012, which claims benefit of Japanese Patent Application No. 2011-165020 filed on Jul. 28, 2011 and No. 2012-151424 filed on Jul. 5, 2012. The entire contents of each application noted above are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/068975 | Jul 2012 | US |
| Child | 14134809 | US |
