Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2001-07-13
2002-06-18
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S101000
Reexamination Certificate
active
06406559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic material capable of being used as a permanent magnet of high performance and the like and a manufacturing method thereof, and a bonded magnet using the same.
2. Description of the Related Art
As one kind of rare earth permanent magnets of high performance, Sm—Co based magnet, Nd—Fe—B based magnet and the like have been known. These magnets contain much Fe and Co, these elements contributing in enhancement of saturation magnetic flux density. Further, rare earth elements in these magnets, due to behavior of 4f electrons in crystal field, induce a very large magnetocrystalline anisotropy. Thereby increase of coercive force is attained, realizing magnets of high performance.
Such high performance magnets are being used mainly for speakers, motors, electric instruments such as measuring instruments. In recent years, demand for miniaturization of various kinds of electric instruments has become strong, in order to respond it, permanent magnets of more higher performance are expected. To this demand, a TbCu
7
type compound excellent in its magnetic property and compounds thereto nitrogen is made to be contained are proposed (refer to Japanese Patent Laid-Open Application No. Hei-6-172936, Japanese Patent Laid-Open Application No. Hei-9-74006 and the like).
A magnetic material having a phase in which a TbCu
7
type crystal structure (hereinafter refers to as TbCu
7
type crystal phase) is a principal phase is manufactured with the manufacturing process shown in the following. First, mother alloy is produced with melt-spun method or mechanical alloying method. Then, to this mother alloy, heat treatment is given with a main object to control its metallic texture. Further, by introducing nitrogen into interstitial sites of the principal phase, nitriding treatment with a main object to heighten the magnetocrystalline anisotropy of the principal phase is implemented.
The nitriding process is usually carried out in an atmosphere containing gas of nitrogen compounds such as nitrogen gas and ammonia. By heat treating in such an atmosphere containing nitrogen to make absorb it in the mother alloy, nitrogen is introduced in magnetic material. To make rapidly absorb nitrogen in the magnetic material, employment of gas containing hydrogen such as ammonia or a mixed gas of ammonia and hydrogen gas is known to be effective.
For instance, in Japanese Patent Laid-Open Applications No. Hei-2-57663 and Hei-3-16102, a manufacturing method of a magnetic material is disclosed wherein, by heat treating a mother alloy, of which a phase possessing a Th
2
Zn
17
type crystal structure (hereinafter referred to as Th
2
Zn
17
type crystal phase) is a principal phase, in a gas mixed ammonia gas and hydrogen gas with a partial pressure ratio of 1:2 to 1:3, nitrogen, further hydrogen is made contained in the aforementioned mother alloy.
However, upon manufacturing a magnetic material having a TbCu
7
type crystal phase as a principal phase, if heat the treatment of a mother alloy is carried out in a mixed gas of ammonia gas and hydrogen gas mixed with a partial pressure ratio of 1:2 to 1:3, too much nitrogen is absorbed, thereby amorphous portion increases to result in a problem of deteriorating magnetic characteristics.
Thus, in a magnetic material which has a TbCu
7
type crystal phase as a principal phase, upon a mother alloy being subjected to a nitriding treatment, a technology, which, without hindering rapid absorption of nitrogen, controls too much absorption of nitrogen, is demanded. Thereby, the amorphous portion in a magnetic material can be prevented from being increased.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is, upon carrying out nitriding treatment to a mother alloy in which a TbCu
7
type crystal phase is a principal phase, without hindering a rapid absorption of nitrogen, to suppress deterioration of magnetic characteristics due to too much absorption of nitrogen. In more specific, by suppressing increase of the amorphous phase due to too much absorption of nitrogen, it is to provide a magnetic material which made possible to obtain efficiently excellent magnetic characteristics and a bonded magnet using the same. Further, it is to provide a manufacturing method of a magnetic material which made possible to manufacture such a magnetic material efficiently with excellent reproducibility.
The present inventors, after much study with an intention to accomplish the aforementioned object, have found that, when a mother alloy having a TbCu
7
type crystal phase as a principal phase is subjected to nitriding treatment with a mixed gas containing ammonia gas and hydrogen gas, by remarkably reducing partial pressure of ammonia gas than that of hydrogen gas, without hindering rapid absorption of nitrogen, the amount of nitrogen intruding into crystal can be readily controlled. Incidentally, the main phase in the present invention is specified as a phase which occupies the maximum volume among the constituting crystalline phases and non-crystalline phases.
That is, a mother alloy which is manufactured with liquid rapid cooling method or mechanical alloying method and has a TbCu
7
type crystal phase as a principal phase can be made such fine as a grain diameter of, for instance, 50 nm or less. Such a micro-crystalline alloy, upon being subjected to the nitriding treatment with a mixed gas containing ammonia gas and hydrogen gas, compared with an alloy large in its grain diameter such as, for instance, Sm
2
Fe
17
alloy of which principal phase is Th
2
Zn
17
type crystal phase, too much nitrogen is prone to be absorbed. As a result, a magnetic material which has a TbCu
7
type crystal phase as a principal phase is supposed to be made amorphous readily.
Thus, when a micro-crystalline alloy of which the principal phase is a TbCu
7
type crystal phase is used as a mother alloy, by reducing partial pressure of ammonia gas, without increasing amorphous phase in magnetic material, nitrogen necessary and sufficient for an over-all crystal can be rapidly fed. Further, the obtained magnetic material contains a small quantity of hydrogen. In a magnetic material of which the principal phase is a TbCu
7
type crystal phase containing a small quantity of hydrogen, without lowering its manufacturing efficiency, excellent magnetic characteristics can be obtained with excellent reproducibility.
The present invention was accomplished based on such knowledge. That is, a magnetic material of the present invention is essentially consisting of a composition expressed by a general formula
R
1
X
R
2
Y
B
Z
N
U
H
V
M
100-X-Y-Z-C-V
(1)
(wherein, R
1
denotes at least one kind element selected from rare earth elements, R
2
denotes at least one kind element selected from Zr, Hf and Sc, M denotes one kind element selected from Fe and Co, X, Y, Z, U and V are numbers satisfying 2 at. %≦X, 0.01 at. %≦Y, 4≦X+Y≦20 at. %, 0≦Z≦10 at. %, 0.1≦U≦18 at. %, 0.01≦V≦10 at. %, respectively), the magnetic material is characterized in possessing a TbCu
7
type crystal phase as a principal phase.
A manufacturing method of the magnetic material of the present invention comprises a step of preparing a mother alloy of which the principal phase is a TbCu
7
type crystal phase, and a step of making contain nitrogen in the mother alloy by heat treating the mother alloy in a mixed gas containing ammonia gas and hydrogen gas and satisfying a partial pressure ratio of 3<P
y
/P
x
, when partial pressure of the ammonia gas is P
X
, that of the hydrogen gas is P
y
.
A bonded magnet of the present invention is characterized in casting in a desired shape a mixture of the aforementioned magnetic material of the present invention and a binder.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, embodiments for carrying out the present invention will be described.
Magnetic material of the present invention has a composition expressed essentially by the aforementioned formula (1), and
Arai Tomohisa
Hashimoto Keisuke
Hirai Takahiro
Sakurada Shinya
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