JPH04703A - Permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a magnet whose temperature characteristic is good and whose magnetic characteristic is good by a method wherein an isotropic powder obtained by a liquid quenching method is mixed with an anisotropic powder obtained by crushing an anisotropic magnet and the mixture is heated, compressed and solidified. CONSTITUTION:A flakelike powder is obtained, by a liquid qeunching method, from an alloy which is composed of 13 atomis % each of Nd and Pr, 16 atomic % of Co, 6 atomic % of B and Fe as the residual part. The powder is magnetically isotropic. On the other hand, an isotropic power is obtained from an alloy which is composed of 15 atomic % each of Nd and Pr, and Fe as the residual part. The powder is housed in a space 12 in a metal mold 11, heated and compressed by an inductive heating method to obtain a mass at a full density. Then, a plastic deformation is caused, and a thin mass whose cross-sectional area is 2.5 times is obtained. The mass is magnetically anisotropic. The isotropic powder and the anisotropic powder are blended in a mixture ratio of 80:20; this mixture is housed in a space 33 which is constituted of a nonconductive ceramic die 31 and a conductive ceramic electrode punch 32; a pressure is exerted; in addition, a vacuum atmosphere is produced; a DC voltage is applied. After that, when the pressure is increased, the temperature of the powders inside a cavity is raised; the powders are cooled and a magnet whose outside diameter is 20mm is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to rare earth iron permanent magnets. More specifically, a flaky and magnetically isotropic powder of R-FeCo-B alloy obtained by an ultra-quenching method is used as a starting material, and a quasi-anisotropic powder having a high residual magnetic flux density that cannot be obtained with isotropy is used. Regarding sex magnets.

BACKGROUND OF THE INVENTION Two types of rare earth iron magnets have been published using different manufacturing methods. One is a powder metallurgy method invented by Jumen Tokusoku Metal Co., Ltd. and disclosed in Japanese Patent Publication No. 61-34242, and is related to magnetically anisotropic magnets. The other is JP 60-100402 from GM.
The method is disclosed in No. 1, using a flaky powder with a fine crystal structure obtained by a liquid ultra-quenching method as a starting material,
These are isotropic and anisotropic magnets obtained by hot press method and/or die up setting method.

In either method, the magnetic properties of the anisotropic magnet are the same, and B Hmax can exhibit 3 C) to 35 MGOe.

Problems to be Solved by the Invention However, these magnets have the disadvantage that their temperature characteristics are significantly lower than those of the S m -Co magnets that have been used up to now. Specifically, Br knee 0.12
%/℃, He j knee 0.6%/℃, while S
For m-Co, the Br knee is 0.04%/°C and the Hc j knee is 0.3%/°C. This is an essential problem with this alloy, and it is not easy to improve it. Therefore,
It is unsuitable for applications such as electric motors used in high-temperature environments.

On the other hand, the isotropic magnet proposed in JP-A-60-100402 maintains a fine crystal structure even though it is the same alloy, so its temperature characteristics are considerably improved compared to anisotropic magnets. Br knee 0.10%/℃, H
c j knee 0.42%/'°C. Therefore, it is also possible to use it in a high temperature atmosphere as described above. However, this magnet is magnetically isotropic and has a limit to its magnetic properties, and may not be able to be used due to insufficient magnetic properties to meet the needs of modern motors that require both miniaturization and high performance. be.

In view of the above problems, the present invention provides a magnet with good temperature characteristics (and good magnetic characteristics).

Means for Solving the Problems In order to solve the above conventional problems, the present invention mixes an isotropic powder obtained by a liquid quenching method and an anisotropic powder obtained by pulverizing an anisotropic magnet. We have discovered a magnet that solidifies under heat and compression, has good temperature characteristics, and has good magnetic properties.

More specifically, an alloy having a basic composition of R-Fe-Co-B is made into a flaky powder having a fine crystal structure by a melt spinning method, and is heat-treated as necessary to adjust the crystal grain size.

The powder is made into a full-density magnetically isotropic mass using a hot pressing method, and further compressed using a die-up setting method to cause plastic deformation to become a magnetically anisotropic mass. A magnetically anisotropic powder was obtained by mechanical grinding. This powder is mixed with the above-mentioned isotropic powder, placed in a molding cavity, caused to generate electric discharge in a vacuum of 10" Torr or more, and then directly applied with electric current and uniaxial pressure to obtain a full-density magnet. It is.

The surface of the active mixed powder is cleaned and activated by plasma generated by electric discharge.

Next, direct electricity is applied to generate Joule heat, and the temperature is raised to a predetermined temperature. At the same time, when the powder is compressed to full density by the negative axis pressure, atomic bonds occur between the powders and solidify. In the magnet of the present invention, since activation by plasma and heating means by direct energization are employed in the manufacturing method, short-time processing is possible and growth of crystal grains of the mixed powder used is suppressed. It is known that in magnets made of this alloy, if the crystal grains are fine, a pinning phenomenon occurs at the grain boundaries in magnetization, resulting in a so-called pinning coercive force. Due to the manufacturing method used in conventional anisotropic magnets, the crystal grains become coarse and the coercive force becomes nucleation type. It is thought that this causes the temperature characteristics to deteriorate. In the magnet according to the present invention, the anisotropic powder to be mixed has this nucleation type coercive force, but the isotropic powder is of the pinning type, and in order to exhibit the pinning type as a whole, it is necessary to As is clear from FIG. 7, it is necessary to limit the mixing ratio of the anisotropic powder to 50% or less. This figure shows the characteristics of the magnet when the mixing ratio of anisotropic powder is changed. The residual magnetic flux density Br increases as the mixing ratio increases, reaches saturation at 50%, and is not improved even if the mixing ratio is increased further. This is considered to be because the anisotropic powder has a large particle size, so complete anisotropy is not achieved on a powder-by-powder basis. This problem can be solved by making the powder sufficiently small, but on the other hand, it is not appropriate because it causes a decrease in coercive force.Furthermore, coercive force decreases as the mixing ratio of anisotropic powder increases, and reaches 60%. Above, it becomes constant.This shows that when the mixing ratio is 60% or more, it becomes a nucleation type.From the balance between the coercive force Hcj and the residual magnetic flux density Br, the mixing ratio that achieves the purpose of the present invention is determined. should be limited to 20% to 50%.

Furthermore, even if the anisotropic powder used in the magnet of the present invention is made into an anisotropic mass by conventional powder metallurgy methods, the coercive force will be significantly reduced by pulverization, making it impractical. It is suitable to use isotropic flaky powder and grind it from an anisotropic mass obtained by hot pressing and die-up setting methods, but it is suitable to use isotropic flaky powder. There is no problem even if it is present as long as it has sufficient magnetic properties. However, one of the characteristics of the magnet of the present invention is that it imparts anisotropy without using a magnetic field, and this utilizes the characteristics of the shape of the powder used. The characteristic of this powder shape is that the isotropic powder is flaky because it is produced by a melt spinning method. Therefore, one of the important factors for anisotropic powder is that it is flaky.

Example The present invention will be explained below based on examples.

Nd and Pr are 13 atoms 0Q, CO is 16 at%, B
From an alloy with 6 atomic % and the balance Fe, crystal grains of 40 nm ~
A flaky powder having a diameter of 400 nm was obtained by a liquid ultra-quenching method. This powder was magnetically isotropic. On the other hand, from an alloy consisting of 15 atomic % of Nd and Pr, 15 atomic % of B, and the balance Fe, an isotropic powder was obtained in the same manner as the above powder, and
As shown in the figure, it is placed in the space (12) of the mold (4) and heated by induction heating to raise the temperature to 700 to 750'C.
It was compressed at a pressure of 2000 kgf/cd to obtain a full density mass. Next, as shown in Fig. 4, this mass is placed in a mold (21) whose cross-sectional area is 2.5 times larger, heated in the same manner as described above, and caused to undergo plastic deformation under a pressure of 100,100 O/cnt. It was made into a 2.5 times thinner mass. This mass exhibited magnetic anisotropy, and its characteristics were as shown in FIG. This mass was made into a powder of 50 to 300 μm by mechanical means in an argon gas atmosphere. The isotropic powder and this anisotropic powder are blended at a mixing ratio of 80.20, and as shown in FIG. 6, a non-conductive ceramic die (31) and a conductive ceramic electrode punch (
32) in the space (33) consisting of 50kgf/
Apply a pressure of ctj, further create a vacuum atmosphere of 10゛1 Torr, and apply a DC voltage of 20V for 60 seconds with a pulse width of 40m5ec.
Apply ec, then directly apply 1.5KA DC for 60s.
EC power is applied and at the same time the pressure of a pair of electrode punches is 300
The pressure was increased to kg f/cd. Finally, the temperature of the powder in the cavity was raised to 700-750°C. This was cooled to obtain a magnet with an outer diameter of 20 m. The magnetic properties of this magnet were measured using a conventional method, and the results shown in FIG. 1 were obtained. In the figure, curve 1 is the result of measurement in the compression direction, and curve 2 in the figure is the result of measurement in the direction perpendicular to the compression direction. As is clear from this figure, the magnet of this example exhibits anisotropy in the compression direction. Curve 3 in the figure is the characteristic of a magnet obtained using only isotropic powder, and curve 4 is obtained using only anisotropic powder in the same manner as in the example. B in the compression direction of the magnet in this example
Hmax is 1.2 times for isotropy and 0 for anisotropy.
．． It is 78. The characteristics were between conventional anisotropy and isotropy. The temperature characteristics of this magnet are Br10,
10%/°C, Hcj is -0.42%7/°C, which values are equivalent to the isotropic magnet shown by curve 3 in FIG. In addition, in the anisotropic magnet shown by curve 4, Br is -0
, 12%/°C, and Hcj was -0.60%/°C. Further, FIG. 2 shows the results of investigating the magnetizability of the magnet of this example. As is clear from the figure (the coercive force of this magnet is of the pinning type).

The temperature characteristics of Br are generally determined approximately by the Curie temperature of the alloy. On the other hand, the temperature characteristics of Hcj are determined by the coercive force mechanism, which is further
It is known that it depends on the size of crystal grains.

The final magnetic properties of the magnet of the present invention are determined by the magnetic properties of the magnetic powder used, so if magnetic powder with better properties than those used in the embodiments of the invention is used, the properties will be proportionally improved. do. In addition, in the examples, only Nd-based alloys have been described, but other alloys may be used as long as isotropic and anisotropic flaky powder can be obtained. Since the purpose is to provide a high-performance magnet, it is desirable that rare earth elements, iron, cobalt, and boron are constituent elements of the alloy.

Effects of the Invention As stated above, the permanent magnet of the present invention has magnetic properties exceeding isotropy, which could not be obtained with conventional magnets, and on the other hand, it has good temperature properties, which could not be achieved with anisotropy. By appropriately selecting the mixing ratio of anisotropic and isotropic powders, it is possible to select the characteristics of the magnet, making it possible to provide a high-performance magnet at a low price.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the magnetic properties of the magnet of the present invention, Figure 2 is a diagram showing the magnetization of the magnet of the present invention, and Figure 3 is a diagram showing the hot pressing method for making a full density mass using isotropic powder. Figure 4 is a diagram explaining the die-up setting method to turn an isotropic mass into an anisotropic mass, Figure 5 is a diagram showing the magnetic properties of an anisotropic mass, and Figure 6 is a diagram to explain the method. FIG. 7 is a diagram showing the method of manufacturing the magnet of the present invention, and is a diagram showing the relationship between the mixing ratio of powder used in the magnet of the present invention and magnetic properties.

Claims (5)

[Claims] (1) The basic composition is R-Fe-Co-B (R:Nd
A magnetically isotropic powder and a magnetically anisotropic powder made of one or more rare earth (including one or more kinds of rare earth) alloys as starting materials are directly discharged to a powder aggregate, and then a uniaxial Permanent magnets made into bulk by applying pressure and direct current to create atomic bonds between powders. (2) The permanent magnet according to claim 1, wherein the magnetically isotropic powder is in the form of flakes rapidly solidified by melt spinning. (3) The magnetically anisotropic powder was made by using the isotropic powder as a starting material and pulverizing a magnetically anisotropic aggregate made by the die-up set method. The permanent magnet according to claim 1. (4) The permanent magnet according to claim 1, wherein the anisotropic powder is flaky. (5) The permanent magnet according to claim 1, wherein the mixing ratio of the anisotropic powder is 20% to 50%.