Patent Application
20080142121
This application claims benefit of Japanese Patent Application No. 2006-338094 filed on Dec. 15, 2006, and Japanese Patent Application No. 2007-210306 filed on Aug. 10, 2007, which are hereby incorporated by reference.
1. Field of the Disclosure
Embodiments of the present disclosure relate to Fe-based amorphous magnetic alloys and magnetic sheets. In particular, embodiments of the present disclosure relate to an Fe-based amorphous magnetic alloy having a large imaginary part μ″ of complex permeability for use in a highly flexible magnetic sheet and a magnetic sheet incorporating the Fe-based amorphous magnetic alloy.
2. Description of the Related Art
Generally, alloys based on TM-Al—Ga—P—C—B—Si (TM represents a transition metal element such as Fe, Co, or Ni) and/or other similar element form amorphous phases and become amorphous soft magnetic alloys by being quenched in a molten state. Techniques for fabricating magnetic materials with excellent magnetic properties may be developed by optimizing the composition of the amorphous soft magnetic alloys. An Fe-based amorphous magnetic alloy has been developed where the alloy may be used as a magnetic material with excellent magnetic properties, in particular, a magnetic material having a large imaginary part μ″ of complex permeability (refer to Japanese Unexamined Patent Application Publication No. 2002-226956).
Portable electronic devices such as cellular phones and laptop computers are increasingly used. These portable electronic devices face problems of electromagnetic wave interference, and there is increasing need for measures for preventing generation of unwanted high-frequency electromagnetic waves. In order to suppress unwanted electromagnetic waves, attaching a magnetic sheet to an electronic device that generates unwanted electromagnetic waves is effective. This magnetic sheet is prepared by forming particles of several to several tens of micrometers in size from the above-described Fe-based amorphous magnetic alloy by a water atomization process or the like, flattening the particles, kneading the resulting particles with a matrix material (insulating resin) such as polyethylene chloride serving as a binder, and forming the resulting mixture into sheets of several tens to several hundred micrometers in thickness by a doctor blade technique. This magnetic sheet preferably has a complex permeability with a large imaginary part μ″ in the operation frequency band.
The imaginary part μ″ of complex permeability of the Fe-based amorphous magnetic alloy may be increased by annealing. The problem associated with this is that when the glass transition temperature (Tg), the crystallization temperature (Tx), and the melting temperature (Tm) of the Fe-based amorphous magnetic alloy are high, the annealing temperature must be also high. Accordingly, when the Fe-based amorphous magnetic alloy is used in the magnetic sheet, the matrix material may become thermally decomposed and deteriorated, resulting in embrittlement of the magnetic sheet.
Embodiments of the present disclosure provides an Fe-based amorphous magnetic alloy having relatively low glass transition temperature, crystallization temperature, and melting temperature such that the annealing temperature may be low, and a magnetic sheet having excellent flexibility even after annealing.
An Fe-based amorphous magnetic alloy of the present disclosure may contain 4 at. % or less of a low temperature annealing-enabling element M and 10 at. % or less of Ni. The total amount of the low temperature annealing-enabling element M and Ni may be 2 at. % or more and 10 at. % or less.
According to this composition, the Fe-based amorphous magnetic alloy may exhibit relatively low glass transition temperature (Tg), crystallization temperature (Tx), and melting temperature (Tm) and excellent flexibility suitable for use in a magnetic sheet.
The Fe-based amorphous magnetic alloy of the present disclosure may include at least one of tin (Sn), Indium (In), zinc (Zn), gallium (Ga), and aluminum (Al) as the low temperature annealing-enabling element M.
Additionally, in another embodiment, the Fe-based amorphous magnetic alloy may contain 1 at. % or more and 4 at. % or less of the low temperature annealing-enabling element M and 1 at. % or more and 10 at. % or less Ni. According to this composition, an Fe-based amorphous magnetic alloy having amorphous structures may be more stably produced.
The Fe-based amorphous magnetic alloy may have a composition represented by a compositional formula Fe100−a−b−x−y−z−w−tMaNibCrxPyCzBwSit, where the parameters may be as follows: 0<a≦4 at. %, 0<b≦10 at. %, 0≦x≦4 at. %, 6 at. %≦y≦13 at. %, 2 at. %≦z≦12 at. %, 0≦w≦5 at. %, and 0≦t≦4 at. %.
Other parameters may also be provided. For example, in one embodiment, the parameters may be as follows: 1≦a≦4 at. %, 1≦b<10 at. %, 2<a+b≦10 at. %, 1≦x≦8 at. %, 6≦y≦11 at. %, 6≦z≦11 at. %, 0≦w≦2 at. %, and 0≦t<2 at. %). In another embodiment, the parameters may be as follows: 1.5≦a≦3.5 at. %, 2≦b≦7 at. %, 3≦a+b≦9.5, and 2≦x≦4 at. %.
A magnetic sheet of the present disclosure may include a matrix material and the Fe-based amorphous magnetic alloy described above, the Fe-based amorphous magnetic alloy being contained in the matrix material.
In this manner, the magnetic sheet may have a large imaginary part μ″ of complex permeability in the operation frequency band and excellent flexibility.
Also, the magnetic sheet may be annealed at a temperature of 400° C. or less.
Embodiments of the present disclosure will now be described in detail with reference to attached drawings.
The Fe-based amorphous magnetic alloy of the present disclosure may contain 4 at. % or less of an element M that enables low-temperature annealing (also referred to as “low temperature annealing-enabling element M” hereinafter) and 10 at. % or less of Ni, where the total content of M and Ni is 2 at. % or more and 10 at. % or less. The low temperature annealing-enabling element M may be an element that may decrease the glass transition temperature (Tg), the crystallization temperature (Tx), and the melting temperature (Tm) of the Fe-based amorphous magnetic alloy once it is used in combination with Ni.
The low temperature annealing-enabling element M may have a melting temperature lower than that of Fe. It is considered that incorporation of the low temperature annealing-enabling element M and Ni in the Fe-based alloy shifts the overall thermal profile toward the lower temperature side, and the Tg, Tx, and Tm become tower than those of existing Fe-based alloys. Examples of the low temperature annealing-enabling element M may include tin (Sn), Indium (In), zinc (Zn), gallium (Ga), and aluminum (Al).
The Fe-based amorphous magnetic alloy of the present disclosure may be represented by formula Fe100−a−b−x−y−z−w−tMaNibCrxPyCzBwSit (where 0<a≦4 at. % 0<b≦10 at. %, 0≦x≦4 at. % 6 at. %≦y≦13 at. %, 2 at. %≦z≦12 at. %, 0≦w≦5 at. %, and 0≦t≦4 at. %)
As described above, the low temperature annealing-enabling element M used in combination with Ni may decrease the crystallization temperature (Tx) and the melting temperature (Tm). As a result, the annealing temperature may be decreased. The amount a of the low temperature annealing enabling element M may be 0≦a≦4 at. % in the above formula from the point of view of yielding an amorphous state. The total content of the M and Ni may be 2 at. % or more and 10 at. % or less, and/or more specifically, 3 at. % or more and 9.5 at. % or less.
Substitution of Fe by Ni may decrease the glass transition temperature (Tg), the crystallization temperature (Tx), and the melting temperature (Tm) From the standpoint of achieving preferable saturation magnetization and melting temperature (Tm), the Ni content b may be 0≦b≦10 at. %, and/or more specifically, 2 at. %≦b≦7 at. % in the above-described formula.
The Cr content x may be 0≦x≦8 at. %, and/or more specifically, 2 at. %≦x≦4 at. % in the above formula from the standpoints of achieving optimal corrosion resistance, thermal stability, and saturation magnetization of the alloy. The corrosion resistance in salt water immersion may be improved by adding 4 at. % of Cr. Since the amorphous phase may be stably produced and the magnetization intensity (σs) may be decreased by increasing the melting temperature (Tm), the Cr content may be 4 at. %.
The P content y may be preferably 6 at. %≦y≦13 at. %, and/or more specifically, 6 at. %≦y≦11 at. % in the above formula from the viewpoint that the P content may be relatively near the Fe—P—C (Fe79.4P10.8C9.8) eutectic composition.
The C content z may be 2 at. %≦z≦12 at. %, and/or more specifically, 6 at. %≦z≦11 at. % in the above formula from the viewpoint that the C content is preferably near the Fe—P—C (Fe79.4P10.8C9.8) eutectic composition.
The B content w may be 0≦w≦5 at. %, and/or more specifically, 0≦w≦2 at. % in the above formula since B increases the glass transition temperature (Tg), the crystallization temperature (Tx) and the melting temperature (Tm). In order to enhance the amorphous phase formation ability, the B content may also be 1≦w≦2 at. %.
The Si content t may be 0≦t≦4 at. % and/or more specifically, 0≦t≦2 at. % in the above formula since Si increases the glass transition temperature (Tg), the crystallization temperature (Tx) and the melting temperature (Tm). As with B, the Si content may be 1≦t≦2 at. % to enhance amorphous phase formation ability.
The Fe-based amorphous magnetic alloy may be used in a magnetic sheet. The magnetic sheet may contain a matrix material and the Fe-based amorphous magnetic alloy in the matrix material.
Examples of the matrix material may include silicone resin, polyvinyl chloride, silicone rubber, phenolic resin, melamine resin, polyvinyl alcohol, polyethylene chloride, and various types of elastomers. In particular, since the Fe-based amorphous magnetic alloy is blended into the resin solution to prepare sheets, a resin capable of making an emulsion of the Fe-based amorphous magnetic alloy may be the matrix material. An example of such a resin may be silicone resin. Note that addition of a lubricant containing a stearate or the like to the matrix material facilitates formation of flat magnetic materials, and an Fe-based amorphous magnetic alloy having a high aspect ratio may be obtained in this manner. As a result, the particles of the Fe-based amorphous magnetic alloy in the magnetic sheet may stack in the sheet thickness direction and may easily become oriented. The density may also increased. Accordingly, the imaginary part μ″ of the complex permeability increases, and the noise suppression characteristics may be improved.
The Fe-based amorphous magnetic alloy used in the magnetic sheet may be in the form of flat particles or powder. Powder or particles having an average aspect ratio (major axis/thickness) of 2.5 or more, and/or more specifically, 12 or more, may be preferred as such flat particles or powder from the standpoint of achieving an optimal degree of orientation and noise suppression characteristics. When the flat powder or particles have a higher degree of orientation, the density of the magnetic sheet and the imaginary part μ″ of the complex permeability may be increased, and thus the noise suppression characteristics may be improved. A high aspect ratio may suppress generation of eddy current, resulting in an increased inductance, and may increase the imaginary part μ″ of the complex permeability in the GHz band. From the standpoint of sheet production, the average aspect ratio is 80 or less and preferably 60 or less since sheet formation becomes difficult at an excessively large aspect ratio.
The magnetic sheet may be produced as follows. First, a melt of the Fe-based amorphous magnetic alloy may be sprayed into water and quenched to produce alloy particles (water atomization technique). Note that the technique for making the Fe-based amorphous magnetic alloy particles may not be limited to this water atomization technique, and various other techniques such as a gas atomization technique, a liquid quenching technique in which ribbons of quenched alloy melt are pulverized to form alloy powder, or other similar techniques, may also be employed. Processing conditions for the water atomization technique, the gas atomization technique, and the liquid quenching technique may be typical conditions selected according to the types of raw materials.
After the resulting Fe-based amorphous magnetic alloy particles are classified to make the particle size uniform, the alloy particles may be flattened with an attritor or the like as needed. The attritor may include a drum containing many balls used for disintegration and may process the Fe-based amorphous magnetic alloy particles to have a target flatness by mixing and agitating the Fe-based amorphous magnetic alloy powder with the balls. The flat particles of Fe-based amorphous magnetic alloy may also be obtained by the liquid quenching technique described above. The resulting Fe-based amorphous magnetic alloy particles may be heated to reduce the internal stress, if necessary.
Next, a magnetic sheet containing the Fe-based amorphous magnetic alloy may be made. In making the magnetic sheet, a liquid mixture containing a liquid matrix material of the magnetic sheet and the Fe-based amorphous magnetic alloy may be prepare and then the liquid mixture may be formed into sheets. The resulting magnetic sheet may then be annealed.
The experiments conducted to confirm the effects of the present disclosure will now be described.
Spherical particles 1 μm to 100 μm in size were prepared by the water atomization technique by using FePC as the base material and by adding M, Ni, Cr, B, Si, and/or other suitable elements to the base material. The particles were classified so that the average particle size (D50) was 22 to 25 μm, and the resulting particles were flattened with a disintegrator such as an attritor to form flat Fe-based amorphous magnetic alloy particles. The glass transition temperature (Tg), the crystallization temperature (Tx), and the melting temperature (Tm) of the particles were measured with a differential scanning calorimeter (DSC). The saturation magnetization (σs) was determined with a vibrating sample magnetometer (VSM).
The resulting Fe-based amorphous magnetic alloy particles were mixed with a silicone resin to prepare a mixture having an Fe-based amorphous magnetic alloy content of 44 vol. %. The mixture was formed into noise suppression sheets (magnetic sheets) having a thickness of about 0.1 mm. The magnetic sheets were placed in an annealing furnace and annealed in an nitrogen atmosphere at an annealing temperature (Ta) of 300° C. to 420° C. (a temperature that may sufficiently increase the imaginary part (μ″) of the complex permeability or the fracture strain (λf)) The temperature profile was as follows: rate of temperature elevation: 10° C./min, retention time: 30 minutes. The magnetic sheets were then furnace-cooled. The imaginary part (μ″) of the complex permeability at 1 GHz of the resulting magnetic sheets was measured with an E4991A produced by Agilent. The fracture strain λf was measured by the process described below
As previously mentioned, the imaginary part μ″ of the complex permeability of the Fe-based amorphous magnetic alloy of the present disclosure may be increased by annealing. At an excessively high annealing temperature, the magnetic sheet prepared from the Fe-based amorphous magnetic alloy may undergo embrittlement. Embrittlement of the magnetic sheet may be evaluated in terms of flexibility based on fracture strain λf.
λf=t/(Df−t) (1)
where Df represents the fracture limit diameter and t represents the thickness of the magnetic sheet 12.
The magnetic sheet in a completely bent state (the state in which the magnetic sheet is folded in two without cracks) may have Df of 2 t and the maximum value of λf may be 1. The flexibility of the magnetic sheet may be rated on the basis of λf. The closer λf is to 1, the higher the flexibility of the magnetic sheet. In application, λf may be required to be at least 0.1 to facilitate handling, and λf may also be 0.2 or more. For example, in order for a magnetic sheet having a thickness of 0.1 mm to satisfy λf>0.1, the temperature of annealing the magnetic sheet may be 400° C. or less.
Annealing the magnetic sheet causes structural relaxation in the Fe-based amorphous magnetic alloy and releases the strain generated during sheet formation. In this manner, the imaginary part μ″ of the complex permeability may increase in the operation frequency band, and superior noise suppression effects may be achieved. In application, the imaginary part μ″ of the complex permeability may be 15 or more at 1 GHz.
The results are shown in Table 1. In the table, samples noted as “Ex.” may be within the range of the embodiments of the present disclosure and samples noted as “Co.” may be outside the range of the embodiments of the present disclosure. In the present disclosure, the melting temperature (Tm) may be relatively low to reduce the annealing temperature. In the table, the compositions that meet this requirement are given.
In Table 1, Sample Nos. 18 to 30 represent comparative examples in which the crystallization temperature (Tx) exceeds 720 K, the imaginary part (μ″) of the complex permeability is less than 15, or the fracture strain λf is less than 0.2. In contrast, Sample Nos. 1 to 17 all satisfy the required characteristics described above. In particular, the annealing temperature may be decreased to 400° C. (673 K) or lower if the crystallization temperature (Tx) is 720 K or less. Sample Nos. 2, 3, 5, 6, 8, and 15 exhibited μ″ exceeding 20, and their magnetic properties are also satisfactory. Sample No. 12 has λf reaching 0.5, and an imaginary part (μ″) of the complex permeability exceeding 20. Sample No. 12 has superior characteristics.
In the table, the samples having the glass transition temperature (Tg) column unfilled may be samples that do not have any glass transition temperature. Although a material having a glass transition temperature (Tg) forms an alloy that may easily form amorphous phases, the glass transition temperature (Tg) and the crystallization temperature (Tx) may tend to be high, and this may require higher annealing temperature. This tendency may be apparent from the results of Table 1.
In the graph, the profile indicated by square symbols may be based on samples not containing Ni but 0 to 5 at. % of Sn. That is, Sample Nos. 21, 22, and 23 in Table 1 are plotted in the ascending order of the Sn content.
The optimum amounts of the low temperature annealing-enabling element and Ni in the Fe-based amorphous magnetic alloy will now be described.
Spherical particles 1 μm to 100 μm in size were prepared by a water atomization technique from an alloy melt of Sample No. 16 in Table 1. The particles were classified so that the average particle size (D50) was 22 to 25 μm, and the resulting particles were flattened with a disintegrator such as an attritor to form flat Fe-based amorphous magnetic alloy particles. The glass transition temperature (Tg) and the crystallization temperature (Tx) of the Fe-based amorphous magnetic alloy were measured with DSC. The glass transition temperature (Tg) was not detected. The crystallization temperature (Tx) was 395° C. (668 K).
The resulting Fe-based amorphous magnetic alloy particles were mixed into a silicone resin such that the Fe-based amorphous magnetic alloy content in the mixture was 44 vol. %. The mixture was formed into noise suppression sheets (magnetic sheets) having a thickness of about 0.1 mm. The magnetic sheets were placed in an annealing furnace and annealed in a nitrogen atmosphere at an annealing temperature (Ta) of 300° C. to 420° C. (573 to 693 K). The temperature profile was as follows: rate of temperature elevation: 10° C./min, retention time: 30 minutes. The magnetic sheets were then furnace-cooled. Thus, magnetic sheets of Examples were obtained.
The magnetic sheets annealed at the above-described temperature were analyzed to determine the imaginary part μ″ of the complex permeability at 1 GHz and the fracture strain λf. The results are shown in
As shown in
The relationship between the magnetic property and the flexibility was examined to demonstrate whether both magnetic property and the flexibility were at optimal levels at an annealing temperature of 300° C. to 400° C. (573 to 673 K). The results are shown in
The region A in
Flat alloy particles were prepared as in Example but from a magnetic alloy having a composition of No. 26 of Table 1 outside the range of the present disclosure. The glass transition temperature (Tg) and the crystallization temperature (Tx) of the resulting Fe-based amorphous magnetic alloy particles were examined as in Example. The glass transition temperature was 472° C. (745 K), and the crystallization temperature (Tx) was 503° C. (776 K).
The Fe-based amorphous magnetic alloy particles were mixed with a silicone resin to prepare a mixture having a Fe-based amorphous magnetic alloy content of 44 vol. %, and the mixture was formed into sheets as in Example. The sheets were annealed at Ta=300° C. to 420° C. (573 to 693 K) to obtain magnetic sheets of Sample No. 26. These magnetic sheets (Comparative Example 1) annealed at temperatures described above were analyzed as in Example to determine the imaginary part μ″ of the complex permeability at 1 GHz and the fracture strain λf. The results are shown in
As shown in
To investigate whether both the magnetic property and the flexibility were excellent, the relationship between the magnetic property and the flexibility of magnetic sheets annealed at 300° C. to 400° C. (573 to 673 K) was determined. The results are shown in
As shown in
A magnetic alloy having a composition of No. 27 of Table 1 outside the range of the present disclosure was used to form flat Fe-based amorphous magnetic alloy particles. The Fe-based amorphous magnetic alloy particles were analyzed as in Example to determine the glass transition temperature (Tg) and the crystallization temperature (Tx). The glass transition temperature (Tg) was 511° C. (784 K) and the crystallization temperature (Tx) was 561° C. (834 K).
The Fe-based amorphous magnetic alloy particles were mixed with a silicone resin to prepare a mixture having a Fe-based amorphous magnetic alloy content of 44 vol. %, and the mixture was formed into sheets. The sheets were annealed at Ta=300° C. to 420° C. (573 to 693 K) to prepare magnetic sheets of Comparative Example 2. Each magnetic sheet of Comparative Example 2 annealed at the above-described temperature was analyzed as in Example to determine the imaginary part μ″ of complex permeability at 1 GHz and the fracture strain λf. The results are shown in
As shown in
To investigate whether both the magnetic property and the flexibility were excellent, the relationship between the magnetic property and the flexibility of magnetic sheets annealed at 300° C. to 400° C. (573 to 673 K) was determined. The results are shown in
As shown in
The crystallization temperature (Tx) and the melting temperature (Tm) were measured while varying the Ni content x in the composition Fe74.4−xNixSn1.5Cr4P10.8B2Si1 from 0 to 12 at. %. The results are shown in Table 4 and
As shown in
The above results demonstrate that the Ni content may be 1 at. % or more and 10 at. % or less to stably obtain an amorphous alloy, and/or more specifically, 2 at. % or more and 7 at. % or less, if lowering of the melting temperature is also required.
The crystallization temperature (Tx) and the melting temperature (Tm) were measured while varying the Cr content x in the composition Fe74.4-xCrxSn1.5Ni6P10.6C6.3B2Si1 from 0 to 12 at. %. The results are shown in Table 5 and
As shown in
Thus, the Cr content may be 0 at. % or more and 8 at. % or less to increase the crystallization temperature (Tx). When corrosion resistance is necessary, such as when water atomization is employed, the Cr content may be required to be 2 at. % or more. Since this decreases saturation magnetization (σs), the Cr content may be limited to 4 at % or less.
The present disclosure is not limited by the embodiments and examples described above. Various modifications, alterations, and changes are possible without departing the range of the present disclosure. For example, the types and amounts of constituent components, the process of blending the materials, the process conditions, and the like may be varied within the range of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP 2006-338094 | Dec 2006 | JP | national |
| JP 2007-210306 | Aug 2007 | JP | national |
