Metal treatment – Stock – Magnetic
Reexamination Certificate
1999-05-14
2002-07-30
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C075S244000
Reexamination Certificate
active
06425961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite hard magnetic material provided with excellent magnetization and temperature characteristics as well as good magnetic characteristics, and a method for producing the same.
2. Description of the Related Art
While a Sm—Co system sintered magnet, Fe—Nd—B system sintered magnet and Fe—Nd—B system sintered magnet have been known in the art as magnetic materials having good performance superior to ferrite magnets, many researches are now under way aiming at novel alloy magnets such as a Fe—Sm—N system magnet having improved performance.
However, these magnetic materials require 10 atomic percentage (referred to at % hereinafter) or more of Nd or 8 at % or more of Sm to be contained, rendering a higher production cost than ferrite magnets owing to their higher content of expensive rare earth elements.
Although the ferrite magnets is more cheaply produced than these rare earth magnets, magnetic characteristics of the former have not been satisfactory, facilitating a demand for developing inexpensive magnetic materials that exhibit superior hard magnetism to the ferrite magnets.
For solving the problems as described above, the inventors of the present invention have invented hard magnetic materials (nano-composite Fe—M—B system magnets), as disclosed in Japanese Unexamined Patent Publication No.9-143641, that can be produced with low cost and have excellent hard magnetic characteristics containing one or more of elements among Fe, Co and Ni as main component as well as elements R comprising one or a plurality of rare earth elements, elements M comprising one or a plurality of Zr, Nb, Ta and Hf, and boron B, wherein 50% or more, preferably 60% or more, of the texture is composed of a fine crystalline phase with a mean crystal grain size of 100 nm or less with a balance of amorphous phases, the fine crystalline being mainly composed of bcc-Fe, Fe—B compounds including solid solution elements and/or Fe
14
R
2
B
1
(R represents one or more elements among rare earth elements).
The inventors of the present invention have also invented hard magnetic materials (nano-composite Sm—Co system magnets), as hard magnetic materials provided with excellent hard magnetic characteristics disclosed in Japanese Examined Patent Publication No. 9-332134, having an amorphous phase and a fine crystalline phase containing Co as a main component as well as at least one or a plurality of elements Q among P, C, Si and B; Sm; one or a plurality of elements M among Nb, Zr, Ta and Hf; one or a plurality of elements R among Sc, Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; and one or a plurality of elements X among Al, Ge, Ga, Cu, Ag, Pt and Au.
The nano-composite Fe—M—B system magnet as described above is an inexpensive magnet that have large remanent magnetization (Ir) and good magnetization characteristics besides having superior corrosion resistance to conventional Nd—Fe—B magnets. However, the magnet has so small coercive force (iHc) of about 2 to 5 kOe that permeance coefficient is largely decreased when coercive force is decreased at high temperature. Accordingly, when the magnet is used for a constituting material of a sensor such as a throttle position sensor (an angle sensor) that is usually used at high a temperature, the sensor output tends to drift because magnetization is varied due to temperature changes.
While the coercive force (iHc) is large, temperature change of magnetization characteristics is small and corrosion resistance is good in the nano-composite Sm—Co magnets, their remnant magnetization (Ir) as well as remanence ratio are so unsatisfactory that they can not be used for the constituting materials of the foregoing sensor that requires high magnetization characteristics, along with being high cost owing to their high content of expensive rare earth elements as in the Fe—Nd—B system sintered magnets.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention for solving the problems as hitherto described is to provide a hard magnetic material that contains relatively a small amount of expensive rare earth elements and has excellent magnetization and temperature characteristics as well as good hard magnetic characteristics, and a method for producing the same.
For the purpose of providing a hard magnetic material containing relatively a small amount of expensive rare earth elements and has excellent magnetization and temperature characteristics as well as good hard magnetic characteristics and a method for producing the same, the nano-composite Fe—M—B system magnets and nano-composite Sm—Co system magnets are especially noticed. It have been therefore presumed through collective studies and considerations that the foregoing problems would be solved by producing the hard magnetic materials using both of nano-composite Fe—M—B system hard magnetic powders and nano-composite Sm—Co system hard magnetic powders.
Usually, when a hard magnetic material is produced by mixing two kinds of hard magnetic powders having different compositions with each other, steps representing the characteristics of the two kinds of hard magnetic powders are thought to be formed in the B-H loop of this hard magnetic material. Accordingly, a B-H loop without any steps can not be obtained when a hard magnetic material is produced using two kinds of the hard magnetic powders having different compositions with each other, rendering a difficulty in obtaining a hard magnetic material having an averaged characteristics between one hard magnetic powder and the other hard magnetic powder. Therefore, no production methods of the hard magnetic material using both of the nano-composite Fe—M—B system and nano-composite Sm—Co system hard magnetic powders have not yet been established, thereby the foregoing assumption have never been proved nor applied for practical uses.
It was made clear, through further studies and considerations for completing the present invention, that a composite hard magnetic material, containing relatively a small amount of expensive rare earth elements and have excellent magnetization and temperature characteristics along with being provided with good hard magnetic characteristics without any steps in the B-H loop could be obtained by mixing, followed by consolidating, an alloy powder comprising an amorphous phase as a principal phase and containing at least Co and Sm, and an alloy powder comprising an amorphous phase as a principal phase and containing at least Fe and/or Co, rare earth elements R and B.
Accordingly, the object of the present invention is to provide a composite hard magnetic material, wherein a composite powder prepared by mixing an alloy powder comprising an amorphous phase as a principal phase and containing at least Co and Sm, and an alloy powder comprising an amorphous phase as a principal phase and containing at least Fe and/or Co, rare earth elements R and B are mixed and consolidated.
Preferably, the composite powder is consolidated by taking advantage of a phenomenon occurred when the phase in the alloy powder comprising an amorphous phase as a principal phase is crystallized.
In the composite hard magnetic material according to the present invention, a hard magnetic powder containing a main component Co and at least Sm and comprising a fine crystalline phase as a principal phase with a mean crystal grain size of 100 nm or less, and a hard magnetic powder containing at least Fe and/or Co, rare earth elements R, and B and comprising a fine crystalline phase as a principal phase with a mean crystal grain size of 100 nm or less are mixed and consolidated.
It is preferable that the composite hard magnetic material according to the present invention has a remnant magnetization (Ir) of 0.6T or more, the ratio between saturation magnetization (Is) and remnant magnetization (Ir) of 0.6T or more and coercive force (iHc) of 2 to 9 kOe.
According to the composite hard magnetic material of the present invention as hitherto described, the alloy powder comprising an am
Inoue Akihisa
Kojima Akinori
Makino Akihiro
Yamamoto Yutaka
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Sheehan John
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