JPH0391205A - Anisotropic permanent magnet - Google Patents

Abstract

PURPOSE:To obtain an inexpensive Nd anisotropic permanent magnet having a high temperature characteristic by shaping an alloy of R-Fe-Co-B fundamental composition into flake powder by the melt spin method and heat-treating the powder to make an anisotropic magnet. CONSTITUTION:An alloy consisting of for example 13at.% of Nd and Pr, 17.8at.% of Co, 5.8at.% of B, and Fe is quenched and solidified by the melt spin method and shaped into flake powder and crystal grains are made by heat treatment. The flake is put into a space 3 defined by a ceramic cavity 1 and a pair of electromagnetic punches 2 and 2', a pressure is exerted on the electromagnetic punches 2 and 2' to produce a higher vacuum atmosphere, DC voltage is applied, a direct current is directly passed, and cooling is carried out to obtain a permanent magnet. The relative density of the magnet is 95% or higher, the residual magnetic flux density thereof is 9.5KG or higher, and the intrinsic coercive force thereof is 10KOe or more. The temperature coefficient of the residual magnetic flux density is -0.09%/ deg.C or lower and that of the intrinsic coercive force is -0.5%/ deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to permanent magnets having magnetic anisotropy. More specifically, the present invention relates to an anisotropic permanent magnet having both high residual magnetic flux density and thermal stability, which uses rare earth and iron flakes obtained by ultra-quenching as a starting material.

BACKGROUND OF THE INVENTION It has been published that rare earth and iron-based anisotropic magnets having the same composition can be obtained using different techniques.

One was developed by Sumitomo Special Metals in 1986.
This is a powder metallurgy method disclosed in No. 34242. The other method is disclosed by GM in Japanese Patent Application Laid-Open No. 60100402, and is a hot press and die up setting method that uses a liquid ultra-quenching method as a starting step. Any of the magnets can exhibit characteristics of B Hmax 30 to 40 M G Oe.

These magnets have been highly anticipated because they have superior magnetic properties compared to Sm--Co magnets, which are rare earth magnets that have been used in the past, and have the advantage of being cheaper for resource reasons.

Generally, there are two types of temperature demagnetization of permanent magnets: reversible demagnetization and irreversible demagnetization. Reversible demagnetization is the temperature characteristic of residual magnetic flux density △B r
/Br, and is related to the Curie temperature of the alloy, and is conventionally used Sm-C
While it is -0.04%/℃ for o-based anisotropic magnets,
The Nd system anisotropy was initially -0.19% for the Nd-FeB alloy.
/℃, which is the value of ferrite magnet -0.18%/℃
The value is close to .

The Curie temperature of this Nd-Fe-B is about 3100C. Therefore, attempts were made to improve the temperature characteristics by increasing the Curie temperature, and specifically, it was discovered that the Curie temperature could be increased by replacing a portion of Fe with Co. FIG. 7 shows the relationship between Co amount and Curie temperature. By substituting a part of Fe with Co in this manner, reversible demagnetization is improved and the possibility of use even at high temperatures of 100°C to 120°C is increased.

Irreversible demagnetization is typified by the temperature characteristics of the intrinsic coercive force, and it is not sufficient to simply improve the Curie temperature; it also depends on the absolute value of the intrinsic coercive force (an example is shown in Figure 8). , the higher the Curie temperature and the larger the initial value of the intrinsic coercive force, the more the temperature characteristic of the intrinsic coercive force △H
c j / Hc j improves. (Note that this result applies to an anisotropic case, specifically a flake-like powder magnet that is rapidly solidified using a liquid quenching method and whose crystal grains are adjusted to 40 nm to 400 nm by appropriate heat treatment.)
Problems to be Solved by the Invention However, when an anisotropic magnet is produced from this raw material by the hot press method and die up setting method, the intrinsic coercive force is
In the case of isotropic powder, 17KOe was reduced to 10KOe.
e, and △Hcj/Hcj is -0,35~
-0.4%/℃ was -0.58% to -0.
This significantly worsens to 6%/℃. In other words, both a decrease in the intrinsic coercive force itself and a decrease in temperature characteristics occur in an anisotropic magnet. Therefore, although it is superior to S m -Co at room temperature, when used at high temperatures such as 100°C to 120°C, it may not be able to maintain its superiority compared to S m -Co. The field of application is limited because it has the disadvantage that it can sometimes be reversed.

In view of the above problems, the present invention provides an anisotropic Nd-based permanent magnet that is inexpensive and has good temperature characteristics.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the present invention aims to control the growth of crystal grains in the process of solidifying flaky powder having a fine crystal structure and making it anisotropic. By devising heating means for anisotropy and anisotropy, an anisotropic magnet with good temperature characteristics was discovered.

More specifically, an alloy whose basic composition is R-Fe-Co-B is made into a flaky powder with a fine crystal structure by a well-known melt spin method, and heat treated as necessary to reduce the crystal grain size. adjust.

The flaky powder is placed in a molding cavity, and 101
This involves causing a discharge in a vacuum of more than Torr, then directly applying current, and applying uniaxial pressure at the same time.

The flaky powder generates Joule heat through electrical discharge and direct energization, softens as it heats up to a predetermined temperature, and is compressed to full density due to the applied uniaxial pressure, causing plastic deformation at the same time. Magnetically anisotropic. R
An alloy with a basic composition of -Fe-Co-B has crystals oriented by plastic deformation and has magnetic anisotropy, and the direction of the anisotropy is parallel to the direction of plastic deformation, specifically, the direction of compression. anisotropic. The magnet of the present invention undergoes plastic deformation due to heating and compression to achieve full density, which causes it to become anisotropic, but since the heating means is a direct energization method, it can reach a predetermined temperature in a short time. Since the growth of crystal grains is suppressed, a pinning phenomenon occurs in magnetization, resulting in a so-called pinning coercive force mechanism. The relative density of the magnet is 95
% or less, anisotropy may not occur because plastic deformation is less likely to occur due to heating and compression. In addition, the basic composition determines the magnetic properties at room temperature, and at the same time, especially Co
is an important alloy component because it increases the Curie temperature of the alloy, improves the temperature characteristics of residual magnetic flux density, and at the same time improves the temperature characteristics of coercive force, and the main focus of the present invention is to provide a magnet with good temperature characteristics. Therefore, C○ addition is an important component of the present invention. Furthermore, since the magnet has a fine crystal structure due to the control of crystal grains, which is a feature of the present invention,
Its coercive force structure is limited to the pinning type, and it uses a heating method that can be processed in a short time, so the starting material
JP-A No. 60-100402 and “Rare earths blooming as industrial materials” Nikkei New Materials August 2, 1987
As described in item 63 of the 4th issue, it is not necessary that the starting material be a flaky powder that is rapidly solidified and has a fine crystalline structure including some amorphous, and has already been used by IIGM in the US for resin bonded magnets. MQP-C, MQ on sale
It is also possible to use a crystallized flake-like powder such as PD. However, in view of the purpose of the present invention, which is to provide an inexpensive magnet, the use of flake powder containing amorphous requires time for crystallization in the magnet manufacturing process, and processing cannot be done in a short time. However, it should be limited to crystallized flakes because it increases manufacturing costs.

In addition, Nd-Fe-Co-B magnets have a density of 10
The residual magnetic flux density at 0% is a maximum of 8400G.

Although there is no clear definition as to where the boundary between isotropy and anisotropy lies, using the example shown in JP-A No. 5,611,203, it can be interpreted that they are about 10% equivalent. If you stand on this point, 8.4KG x 1.1 = 9
．． It is considered that up to 24KG, it should be treated as isotropic even if some anisotropy occurs and the properties are improved. Therefore, the residual magnetic flux density of the anisotropic magnet of the present invention is 9
．． Limited to 5KG or more.

Examples Example 1 Examples of the present invention will be described below with reference to the drawings.

Nd and Pr are 13 at% Co17.8 at% B5.
An alloy with 8 atomic % residual Fe is rapidly solidified by a conventional method to form a flake powder, and by heat treatment, crystal grains of 40 to 400
nm. The flakes were placed in a ceramic cavity (with an inner diameter of 20 mm) as shown in Figure 2.
1) into a space (3) consisting of a pair of electrode punches (2, 2'), and a pair of electromagnetic punches (2, 2').
kgf/c! Apply a pressure of 10-' to 1
A vacuum atmosphere of O-2 Torr and a pulse width of 40 m5e
Apply a DC voltage of 20V for 60 seconds at c, and then
Direct current of 1.5 KA is applied for 40 to 60 seconds, and at the same time a pair of electromagnetic punches (2, 21 pressure is applied to 300 kg f
/cn? raised to. Finally, the temperature of the powder inside the cavity reached 700-750°C.

By cooling this, a permanent magnet with an outer diameter of 20 mm and a permeance coefficient of 1 was obtained. The density of this magnet is
It was 7.70g/c-. Figure 1 shows the demagnetization characteristics of this magnet at room temperature. Curve 10 is parallel to the compression direction of this magnet. Curve 12 is the value measured perpendicularly, and curve 14 is the value measured in the VS direction for starting materials of the same composition.
Measurements were taken after magnetizing with Pctl and 50K Oe. Furthermore, when the thermal demagnetization characteristics △B r / Br and △Hcj / Hc j of this magnet were measured using a VSM, △B
r / B r -〇, 07%/℃, △Hej/He
j −−0.48%/°C. Further, the maximum energy product of this magnet at room temperature was 25.2 MGOe. When the initial magnetization curve of this magnet was determined, the results shown in FIG. 3 were obtained.

This curve is a result of the magnet shown in Comparative Example 1, and the coercive force mechanism is clearly different from that in Figure 5, and it is similar to the initial magnetization curve of the starting material of this example, confirming that it is a pinning type. It was done.

Example 2 The same two alloys as in Example 1 were rapidly solidified in the same manner as in Example 1 to obtain flaky powder. When the degree of crystallinity of this powder was examined using X-ray, it was confirmed that a portion of the powder contained amorphous matter.

Using this powder, a magnet with an outer diameter of 20 mm and Pctl was obtained in the same manner as in Example 1. The density of this magnet 0 is 7,69 g/c! Magnetic properties at room temperature are Br10.3KG, Hcj 14.7KOe, Hc
B8.85KOe, BHmax23.6MGOe, temperature characteristics are △Br/Br=-0.07%/℃, △Hcj/
Hcj--0.47%/°C.

Comparative Example 1 Using an alloy having the same composition as in Example 1, flake-like powder partially containing amorphous material as in Example was obtained. This powder was
A magnet with an outer diameter of 20 mmPcξ1 was obtained according to the method disclosed in Japanese Patent No. C)-100402. Figure 4 shows the demagnetization characteristics of this magnet at room temperature. In the figure, curve 16 is the anisotropic direction, curve 18 is the perpendicular direction, and curve 20 is the measurement result of the starting material. Furthermore, when the temperature characteristics of this magnet were measured, the ΔBr/Br--0.08-0 wire 08 showed a nucleation type as shown in FIG.

Comparative Example 2 Completely crystallized flake powder was prepared using the same alloy composition as in Example 1, and a similar magnet was obtained under the same conditions as in Comparative Example 1. Its density is 7.65g/cm? The magnetic properties at room temperature are shown in FIG. Compared to Figure 4, it is clear that Hc
j is decreasing. This is thought to be because the crystal grains became coarse during the magnet processing steps of hot pressing and die up setting.

Effects of the Invention The magnet of the present invention uses Nd and/or P, which are advantageous in terms of resources, compared to conventionally used SmCo-based anisotropic magnets.
The main components are r and Fe, and it can be used at high temperatures, which was impossible with conventional Nd-based anisotropic magnets due to poor temperature characteristics, and the manufacturing method also allows processing in a short time. In addition, starting materials can be those that are already available on the market at low cost for use in resin bonded magnets.
It has the advantage of being able to be supplied at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the demagnetization characteristics of Example 1 of the magnet of the present invention, FIG. 2 is a diagram showing the manufacturing method of the magnet of the present invention, and FIG. 3 is a diagram showing the initial magnetization characteristics of Example 1 of the magnet of the present invention. 4 is a diagram showing the demagnetization characteristics of the magnet of Comparative Example 1, FIG. 5 is a diagram showing the initial magnetization characteristics of Comparative Example 1, and FIG. 6 is a diagram showing the demagnetization characteristics of Comparative Example 2. Figure 7 is C. Figure 8 shows the relationship between the amount and the alloy Curie temperature.
It is a figure showing the relationship of j.

Claims (4)

[Claims] (1) The basic composition is R-Fe-Co-B, (R:Nd
The starting material is flakes or powder made by rapidly solidifying an alloy containing a new component for partial modification using a melt spinning method, and the relative density is 9.
5% or more, and the residual magnetic flux density is at least 9.5KG
As mentioned above, the unique coercive force is at least 10 KOe or more, the temperature coefficient of residual magnetic flux density is -0.09%/℃ or less, and the temperature coefficient of intrinsic coercive force is -0.5%/℃ or less. Directional permanent magnet. (2) The anisotropic permanent magnet according to claim 1, wherein the coercive force mechanism is of a pinning type. (3) The anisotropic permanent magnet according to claim 1, characterized in that a flake or powder produced by a melt spin method is heated by a discharge and/or direct energization method and simultaneously solidified by uniaxial pressure. (4) The anisotropic permanent magnet according to claim 3, wherein the flakes or powder produced by the melt spinning method are completely crystallized before being heated by electric discharge or direct energization.