Metal treatment – Stock – Magnetic
Reexamination Certificate
2002-05-17
2004-10-05
Sheehan, John P. (Department: 1742)
Metal treatment
Stock
Magnetic
C075S244000, C310S159000, C310S173000, C310S179000, C148S101000, C148S102000, C164S462000, C164S463000, C164S479000
Reexamination Certificate
active
06800145
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth magnet alloy, a manufacturing method thereof and a product applied with the rare earth magnet alloy and, more particularly, to a technology for simply and easily manufacturing an anisotropic exchange spring magnet having an excellent magnetic property.
Magnets to be used in motors involve a Nd—Fe—B type permanent magnet, having high magnetic properties, which has been proposed to be manufactured by a melting technique (refer to M. Sagawa et al.: Japanese Journal of Applied Physics 26 (1987) 785) and a ultra cooling technique (refer to R. W. Lee: Applied Physics Letter 46 (1985) 790). In order to improve a coercive force by forming fine crystals in the magnet, an attempt has been proposed to use a HDDR treatment (refer to T. Takeshita et al.: Proc. 10th Int. Workshop on Rare Earth Magnets and Their Application, Kyoto, (1989) 551). Further, another technique has been proposed to add one or more of elements of Co, Ga, Zr and Hf to cause the resulting magnet powder to have an anisotropy. With such a structure, theoretically, the Nd—Fe—B type permanent magnet tends to have preferable magnet properties.
However, the Nd—Fe—B type magnet in such a structure is nearing to a theoretical limiting value of magnetic properties.
For this reason, a development for a following generation's magnet with improved several performances is required and so a great attention is recently focused onto an exchange spring magnet (refer to E. F. Kneller and R. Hawig: IEEE Transaction Magnetics 27 (1991) 3588). The exchange spring magnet is comprised of compositions which include hard magnetic phases (hereinafter suitably referred to as hard phases) and soft magnetic phases (hereinafter suitably referred to as soft phases) that are finely dispersed in the order of several tens nm scale, with magnetizations of the both phases combining with one another due to an exchanging mutual reaction to preclude the magnetization of the soft phase not to be easily reversed to cause the magnet to totally serve as a single hard phase, and is also referred to as a nanocomposite magnet. In the compositions of Sm
2
Co
17
N
3
/Fe—Co, theoretically, it is reported that the presence of the anisotropic property given to the magnet allows the magnet to have the maximum energy product of a value such as (BH)
max
=137 MGOe (refer to R. Skomski and J. M. D. Corey: Physical Review B48 (1993) 15812).
“R. Coehoorn et al.: Journal de Physique 49 (1988)” discloses a method of manufacturing Nd
2
Fe
14
B/Fe
3
B type exchange spring magnet. Also, Japanese Patent Application Laid-Open Publication No. H7-173501, Japanese Patent Application Laid-Open Publication No. H7-176417 and “L. Withanasam et al.: Journal of Applied Physics 76 (1994) 7065” disclose methods for manufacturing Nd
2
Fe
14
B/Fe type exchange spring magnet.
However, since a melt spun technique and a mechanical alloying (MA) technique disclosed in the above literatures have a difficulty in aligning a crystalline direction, only an isotropic exchange spring magnet is obtained. It is hard to say that the related art techniques take a full advantage of the benefits of the characteristic of the exchange spring magnet.
Now, manufacturing methods for an anisotropic exchange spring magnet have heretofore been proposed such as a method for heating Nd—Fe—B amorphous metal in a strong magnetic field to form crystals (refer to Japanese Patent Application Laid-Open Publication No. H11-8109), a method for hot working a thin strip alloy to be rapidly cooled such that hard and soft phases are finely dispersed to be deposited (refer to Japanese Patent Application Laid-Open Publication No. H11-97222), and a method for rapidly increasing the temperature of a thin strip alloy to be rapidly cooled to directly achieve hot processing for one-axis deformation (refer to Japanese Patent Application Laid-Open Publication No. 2000-235909).
SUMMARY OF THE INVENTION
However, the anisotropic exchange spring magnets manufactured in such related art methods still face insufficient results in the magnetic properties, and there has heretofore been a long-awaited realization for manufacturing the anisotropic exchange spring magnet in a more simple and easy fashion.
The present invention has been made with the above view and has an object to provide a rare earth magnet alloy, a method for manufacturing such a rare earth magnet alloy suitable for simply and easily producing an anisotropic exchange spring magnet having excellent magnetic properties, and also products applied with such a rare earth magnet alloy.
That is, upon study of various attempts and studies made by the present inventors, it has been revealed that the use of a procedure, wherein the rare earth magnet alloy, which is magnetically isotropic as a whole but includes regions (hereinafter suitably referred to as partly anisotropic regions) in each of which the hard phases (single crystal particles) and soft phases (single crystal particles) are finely dispersed and the hard phases have axes of easy magnetization that is aligned in one direction, is used as a starting material and then such a starting material is crushed to a particle size of equal to or less than the sizes of the partly anisotropic regions, enables a production of the anisotropic exchange spring magnet having excellent magnetic properties. That is, the present invention has been completed while realistically establishing various process conditions of such a procedure. More particularly, by crushing such a magnet alloy to a particle size of equal to or less than the sizes of the partly anisotropic regions so as to obtain magnetic powder and then pressing the powder of the crushed alloy in a magnetic field, it is possible to obtain a pressed powder body having the magnetic anisotropy. And, by subjecting the resulting pressed powder body to a sintering process under a condition such that the crystalline sizes are not in enlarged, the anisotropic exchange spring magnet having the excellent magnetic properties are reliably and easily obtained.
According to one aspect of the present invention, there is provided Nd—Fe—B type rare earth magnet alloy comprising: hard magnetic phases each of which has a size equal to or less than 80 nm; soft magnetic phases each of which has a size equal to or less than 80 nm, with the hard and soft magnetic phases being present in a mixed structure; and partly anisotropic regions wherein axes of easy magnetization of the hard magnetic phases are aligned in one direction, each of the partly anisotropic regions having a size equal to or greater than 0.1 &mgr;m.
Further, the present invention provides a method of manufacturing a Nd—Fe—B type rare earth magnet alloy, which comprises: preparing an ingot of Nd—Fe—B type rare earth magnet composition; obtaining a molten mass of the ingot of the Nd—Fe—B type rare earth composition; and subjecting the molten mass to a rapid cooling treatment to obtain an alloy of Nd—Fe—B type rare earth magnet. Here, the alloy of Nd—Fe—B type rare earth magnet comprises: hard magnetic phases each of which has a size equal to or less than 80 nm; soft magnetic phases each of which has a size equal to or less than 80 nm, with the hard and soft magnetic phases being present in a mixed structure; and partly anisotropic regions wherein axes of easy magnetization of the hard magnetic phases are aligned in one direction, each of the partly anisotropic regions having a size equal to or greater than 0.1 &mgr;m.
Furthermore, the present invention provides a method of manufacturing an anisotropic exchange spring magnet, which comprises: preparing an alloy of Nd—Fe—B type rare earth magnet; crushing the alloy of Nd—Fe—B type rare earth magnet to a size equal to or less than the size of each of the partly anisotropic regions to obtain magnet powder; pressing the magnet powder in a magnetic field to obtain a pressed powder body; and subjecting the pressed powder body to a pressing and sintering treatment in a discharge plasma to obtain a bulk magnet. Here, the all
Ono Hideaki
Shimada Munekatsu
McDermott Will & Emery LLP
Nissan Motor Co,. Ltd.
Sheehan John P.
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