Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1990-02-21
1992-03-31
Dean, R.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148105, H01F 4102
Patent
active
051004852
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
1. Background of the Invention
The present invention relates to a method for manufacturing permanents magnets of arbitrary shapes using thin flakes of a rare earth-Fe-B alloy metal as a raw material.
2. Description of the Prior Art
Thin flakes of an R-Fe-B alloy metal (R indicates one or more rare earth elements) in a nonequilibrium state, as a raw material, wherein R.sub.2 -Fe-B phases and amorphous phases are coexistent can be obtained by rapidly quenching an R-Fe-B alloy metal in a melted state at a quenching speed of 10.sup.4 .degree. C./sec or more and thereby, freezing at least a portion of the alloy metal in the melted state as it is. Accordingly, they are obtained only in such a flaky configuration having a thickness of 20 to 30 .mu.m and a length smaller than 20 mm. Therefore, in order to form permanent magnets of arbitrary shapes, it becomes necessary to solidify thin flakes gathered by a predetermined amount using a suitable method.
As solidifying means, there have been known a sintering method for sintering a mass of thin flakes at an ambient pressure and a hot press method wherein a mass of thin flakes is pressed while being heated.
However, the conventional method such as the sintering method or the hot press method has an disadvantage in that the magnetic properties are lowered since R.sub.2 Fe.sub.14 B phases grow too large due to a heating temperature higher than the crystallization temperature of the R-Fe-B alloy metal and a long heating time.
SUMMARY OF THE INVENTION
Accordingly, a main object of the present invention is to provide a manufacturing method capable of forming permanent magnets of arbitrary shapes without lowering the magnetic properties of R-Fe-B alloy metal in the nonequilibrium state wherein R.sub.2 Fe.sub.14 B phases and amorphous phases are coexistent.
The object of the present invention mentioned above is achieved by applying a pressure in an axial direction to a mass of thin flakes made of an R-Fe alloy metal, supplying an electric current thereto to generate Joule heat at contacting interfaces among the flakes and, bonding them into one piece by making them deform plastically at a high temperature. The Joule heat generated by supplying the current is propagated through respective contacting interfaces and particles become easy to deform plastically. Especially, atomic bonding is accelerated regarding atoms locating on the contacting interfaces since they are easily movable as the result of activation. Features of the present method exist in that the thickness of each membrane having a large electric resistance is smaller than several tens nm and in the supply of current and, thereby, in that the contacting interfaces can be bonded by the supply of current for several seconds without accompanying transition of the nonequilibrium state wherein R.sub.2 Fe.sub.14 B phases and amorphous phases are coexistent.
In the meanwhile, it is important and necessary for improving the magnetic properties of the R-Fe-B permanent magnet according to the present invention to promote rearrangement of particles upon bonding of contacting interfaces and to decrease vacancies by pressurizing the mass of particles upon supplying the electric current.
Further, it is desirable to make contacting interfaces among particles and/or between individual particle and a support member breakdown dielectrically by generating a discharge beforehand and, when the discharge is caused once, surfaces of contacting interfaces are cleaned up by impacts by electrons emitted from a cathode and ions generated at an anode. And, impact pressure by the discharge can yield particles distortions to increase the dispersion velocity of atoms. This enables efficient bonding.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a photograph showing a texture of solidified thin flakes of the permanent magnet obtained according to the preferred embodiment of the present invention,
FIGS. 2(a) and 2(b) are photographs showing crystal grains (R.sub.2 Fe.sub.14 B phases) of an original thin flake and the p
REFERENCES:
patent: 4957668 (1990-09-01), Plackard et al.
patent: 4963320 (1990-10-01), Saito et al.
Patent Abstracts of Japan, vol. 13, No. 453 (E-831)(3801) Oct. 12, 1989, & JP-A-1 175705 (Daido Steel Co. Ltd.), Jul. 12, 1989, *the whole document*.
Wada Masami
Yamashita Fumitoshi
Dean R.
Matsushita Electric - Industrial Co., Ltd.
Wyszomierski George
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