Metal treatment – Stock – Magnetic
Reexamination Certificate
2002-02-28
2003-11-18
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C420S435000
Reexamination Certificate
active
06648990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Co-base magnetic alloy having excellent high-frequency magnetic properties, which is used in members of countermeasure against noise such as zero phase reactors and electro-magnetic shielding materials, inverter transformers, choke coils for active filters, antennas, smoothing choke coils, saturable reactors, power supplies for laser, pulse power magnetic members for accelerators, and so on. It also relates to high performance magnetic members made of the Co-base magnetic alloy.
2. Description of the Prior Art
Ferrite, amorphous alloys, nano-granular thin film materials, and so on have been known as magnetic materials for high frequency applications. The ferrite materials are unsuitable for high power applications in a high frequency range in which an operating magnetic flux density increases and a temperature rises, because the ferrite materials exhibit low saturation magnetic flux density and inferior temperature characteristics.
Because of large magnetostriction, Fe-base amorphous alloys have problems that magnetic properties are deteriorated under stress and that a large noise is generated in a use, wherein, for example, currents of an audio-frequency range are superimposed.
On the other hand, a Co-base amorphous alloy is thermally unstable. Therefore, if the Co-base amorphous alloy, which exhibits good properties for high-frequency applications, is used in applications which requires a high power, there will arise a problem that high-frequency magnetic properties are deteriorated because a large property change against time occurs.
An Fe-base nanocrystalline alloy is excellent in soft magnetic properties. Therefore, it is used for a magnetic core of common mode choke coils, high-frequency transformers, pulse transformers, etc. As typical alloy compositions thereof, there have been known an Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—Si—B alloy, Fe—Cu—(Nb, Ti, Zr, Hf, Mo, W, Ta)—B alloy, and so on which are disclosed in JP-B2-4-4393 (corresponding to U.S. Pat. No. 4,881,989) and JP-A-242755. In general, these Fe-base nanocrystalline alloys are prepared by nanocrystalizing amorphous alloys by annealing, which are fabricated by quenching an alloy from a liquid phase or a gaseous phase. A single roll method, a twin roll method, a centrifugal quenching method, a method of rotary spinning in a liquid, an atomizing process, and a cavitation method are known as typical rapid quenching methods from the liquid phase. Further, known examples of rapid quenching methods from the gaseous phase include a sputtering method, a vapor deposition method, an ion plating method, and so on.
The Fe-base nanocrystalline alloy is prepared by nanocrystalizing the amorphous alloy prepared by the above methods by annealing, which is thermally stable not like as an amorphous alloy, and which has been known that it exhibits high saturation magnetic flux density which is substantially the same as those of the Fe-base amorphous alloy, and exhibits excellent soft magnetic properties and low magnetostriction. Further, it has been known that the nanocrystalline alloy exhibits a small property change against time and also excellent temperature characteristics.
When the Fe-base nanocrystalline soft magnetic alloy is compared with a conventional soft magnetic material having generally the same saturation magnetic flux density, the alloy exhibits higher magnetic permeability and lower magnetic core loss, so that it is excellent in soft magnetic properties. However, an optimum operating frequency range for use in the transformer is around several tens of kilohertz for thin strip materials, and the properties are not sufficient for applications in the high frequency. Moreover, when the alloy is used as members of counter-measure against noise, particularly a large effect is obtained at 1 MHz or less. Therefore, there has been a demand for materials superior in the property even in a higher frequency range. With regard to the members of countermeasure against noise for the high current, it is necessary to prevent the saturation of the magnetic core and the unstable operation. From this viewpoint, there has been a demand for a material which indicates a magnetization curve with a low squareness ratio and exhibits a superior property in a high-frequency range. In these uses, a high-permeability material having a relative magnetic permeability of several tens of thousands in a low-frequency region has a problem that the magnetic core material is magnetically saturated and that a sufficient property cannot be obtained in the high frequency range.
With regard to a magnetic switch for use in a saturable reactor, accelerator, and so on, there has been a demand for a magnetic core material which has a high squareness ratio and low magnetic core loss in order to improve controllability, compression ratio, and efficiency.
In order to solve the above problems, a thin film for reducing an eddy current loss, a high electric resistance granular thin film, and so on have been examined. However, the granular thin film with high electric resistance has a limitation in increasing a volume of the magnetic material, and it is difficult to use the thin film as the magnetic core material for a magnetic switch, transformer, choke coil, and so on in a pulse power applications handling a high energy and a large-capacity inverter.
Therefore, even for the thin strip material whose volume is easily increased, or a bulk material, there has been a strong demand for a material superior in the magnetic property in a higher frequency range as the magnetic core material.
The Fe-base nanocrystalline soft magnetic alloy manufactured by crystallizing an amorphous alloy thin strips by the heat treatment generally shows a high magnetic permeability in a frequency range of several hundreds of kilohertz or less, and exhibits a rather high value of a quality factor Q as one of important properties of the material for coil members. However, a sufficiently high Q cannot be obtained in a megahertz (MHz) or higher range, even when the alloy is heat-treated in a magnetic field and a magnetic anisotropy is induced in the alloy. Moreover, there are problems of a magnetic saturation of the material by superimposed direct-current or by an unbalanced signal, when the material is used in the choke coil for a three-phase power line.
As the Co-base nanocrystalline alloy, an alloy disclosed in JP-A-3-249151 (corresponding to U.S. Pat. No 5,151,137) is known. However, the disclosed alloy contains a large amount of borides. There are problems that even with the heat treatment in the magnetic field, a high Q in the high frequency range, and a sufficiently low squareness ratio, or a sufficiently high squareness ratio cannot be obtained.
SUMMARY OF THE INVENTION
To solve the above problems, as a result of intensive studies, the present inventors have found a Co-base magnetic alloy which has excellent high-frequency magnetic properties in the megahertz (MHz) range.
The Co-base magnetic alloy has a chemical composition represented by the following general formula, by atomic %: (Co
1-a
Fe
a
)
100-y-c
M′
y
X′
c
, where M′ is at least one element selected from the group consisting of V, Ti, Zr, Nb, Mo, Hf, Sc, Ta and W; X′ is at least one element selected from the group consisting of Si and B; and a, y and c satisfy the formulas of a<0.35, 1.5≦y≦15, and 4≦c≦30, respectively. At least a part of the alloy structure of the Co-base magnetic alloy consists of crystal grains having an average grain size of not more than 50 nm. The present invention is based on finding that the above Co-base magnetic alloy, having a relative initial permeability of not more than 2000, exhibits excellent high frequency magnetic characteristics in the megahertz (MHz) range.
The Co-base magnetic alloy is prepared by quenching a molten metal having the above chemical composition by means of a rapid quenching technique such as a single roll method to produce an amorphous alloy. The amorphou
Hitachi Metals Ltd.
Sheehan John
Sughrue & Mion, PLLC
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