JPH03153006A - Permanent magnet and raw material therefor - Google Patents

Abstract

PURPOSE:To obtain a permanent magnet whose residual flux density is high and whose anisotropy degree is good by a method wherein, in a permanent magnet formed while an R-Fe-B-based alloy (where R is one or more kinds of rare-earth elements including Y) formed by quenching a molten metal is made magnetically anisotropic by a plastic working operation, a range of an average crystal particle diameter and a volume partial rate of coarse and large crystal particles are prescribed. CONSTITUTION:While a shape measured by using a picture of a fracture is regarded as a disk having the central axis in the c-axis direction, a volume is found; a diameter of a sphere having a volume equal to the disk is regarded as a crystal particle diameter. A degree of anisotropy by a plastic working operation differs according to the crystal particle diameter. Especially when an average crystal particle diameter is set to 0.1 to 0.5mum and a volume partial rate of crystal particles exceeding a crystal particle diameter of 0.5mum is set to less than 20%, it is possible to manufacture a permanent magnet whose residual flux density is 90% or higher of a saturation magnetization and whose anisotropy degree is good.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an R-Fe-B permanent magnet (R is a rare earth element).

[Conventional technology]

In the rare ±1 rrm stone market, R-Fe-B sintered magnets (JP-A-59-46008) are widely put into practical use due to their high magnetic properties and lower price than conventional Sm-Co magnets. . On the other hand, R-Fe-B basic processed magnets using ultra-quenching process or casting process and hot plastic working (
JP-A-60-1゜0402) has also been widely studied, and has been shown to have better thermal stability than sintered magnets, and magnets with a smaller thickness in the direction of easy magnetization can obtain higher magnetic properties than sintered magnets. It has the following characteristics. Furthermore, a plastically worked magnet using an ultra-quenching process has the advantage that it can be used as a raw material for anisotropic bonded magnets having high magnetic properties. (Unexamined Japanese Patent Publication No. 63232301) Like this,
In permanent magnets using plastic working, we manufacture magnets with a high energy product by using R-Fe-B alloys in which the coercive force of quenched ribbons (powder, flakes) is controlled to 3 kOe or less as raw materials. A method has been proposed (Japanese Patent Application Laid-open No. 1983-
152110).

[Problem to be solved by the invention]

However, according to experiments conducted by the present inventors, the reason why the residual magnetic flux density of plastically worked magnets using quenched flakes with a coercive force of 3 kOe or less was low was due to abnormal grain growth at the interface between the quenched flakes. It has become clear that coarse crystal grains with a crystal grain size exceeding 0.7 μm inhibit anisotropy due to plastic flow.

[Means to solve the problem]

The present invention uses the following technical means to solve the above problems.

That is, in a permanent magnet in which an R-Fe-B alloy (R is one or more rare earth elements including Y) created by rapid cooling of a molten metal is made magnetically anisotropic by plastic working, the average crystal grain size is 0. The above object has been achieved by using a permanent magnet characterized in that the volume fraction of crystal grains having a crystal grain size of 1 μm or more and 0.5 μm or less and a crystal grain size exceeding 0.7 μm is less than 20%.

The composition of the above alloy is RvFewcoxByMz (R is one or more rare earth elements including Y, M is Ga.

Zn, Si+ Al, Nb, Zr, Hf, Mo, P!
One or more elements consisting of C, Cu, Ni and unavoidable impurities), 11≦v≦18, w=100
-u-x-y-z, 0≦x≦304≦y≦11. O≦Z
It is preferable that ≦3.

In addition, the coercive force of the alloy before plastic working at room temperature is 3k.
It is preferable that the permanent magnet raw material is characterized in that the volume fraction of crystal grains exceeding Oe and the crystal grain size exceeding 0.7 μm is less than 20%. It is preferable that the surface roughness is 3 μm or less.

Furthermore, in order to make the surface roughness of the R-Fe-B alloy 3 μm or less, the molten metal quenching is performed by a twin roll method, the molten metal quenching is performed in a vacuum or under a pressure lower than atmospheric pressure, Preferably, the molten metal quenching is performed in He or Ne gas.

In the present invention, the R-Fe-B alloy has R2 as the main phase.
Fe14B or R2 (F e , Co) 14B
means an alloy with By rapidly cooling molten metal using a molten metal quenching method such as a single roll method, a twin roll method, or an ultrasonic gas atomization method, it is possible to create an alloy consisting of an amorphous state or fine crystals. By plastically working this alloy in the range of 600℃ to 850℃,
It is possible to create permanent magnets that are magnetically anisotropic. Here, magnetic anisotropy refers to a phenomenon in which the residual magnetic flux density differs depending on the measurement direction, and corresponds to the fact that the crystal axis direction is aligned in one direction due to plastic working.

The present inventors have found that the degree of anisotropy caused by plastic working differs depending on the crystal grain size. In particular, the average crystal grain size is 0.1 to 0.5 μm, and the crystal grain size is 0.7 μm.
It has been discovered that by setting the volume fraction of crystal grains exceeding Ta.

The average grain size varies greatly depending on the composition (particularly the amount of rare earth) and plastic working conditions (heating rate, working temperature, working time, etc.). Further, the anisotropic crystal grains are plate-shaped crystal grains that are short in the C-axis direction of a tetragonal crystal and long in the C-plane direction. In the present invention, the volume was determined from a shape determined from a photograph of the fracture surface as a disk having its central axis in the C-axis direction, and the diameter of a sphere having the same volume as this disk was defined as the crystal grain size. Further, the average crystal grain size is the average crystal grain size.

If the plastic working temperature is too low or the amount of rare earth is too small, there is no rare earth-rich low melting point liquid phase (melting point 580-690°C) that promotes grain growth, so grain growth is suppressed and the average The crystal grain size becomes 0.1 μm or less. If the average crystal grain size is less than 0.1 μm, the plastic deformability of the alloy is insufficient and the anisotropy of the crystal grains does not progress sufficiently.

It is difficult to increase the residual magnetic flux density to 90% or more of the saturation magnetization. , the average grain size increases.

When the average crystal grain size exceeds 0.5 μm, the crystal growth rate at the plastic working temperature largely depends on the size of the crystal grains, so that the variation in the crystal grain sizes becomes large. Coarse crystal grains are difficult to plastically deform and do not become anisotropic. Coarse crystal grains disturb the surrounding plastic flow and cause the easy magnetization directions of other crystal grains to vary. Therefore, it is difficult to increase the residual magnetic flux density to 90% or more of the saturation magnetization.

The average crystal grain size is within the above range (0.1 μm or more 0.5 μm
(below), crystal grains with a crystal grain size exceeding 0.7 μm (hereinafter referred to as coarse grains) interfere with anisotropy caused by plastic working. That is, in addition to the effect that the coarse crystal grains themselves do not become anisotropic, they also have the effect of disturbing the direction of plastic flow in the surrounding area.

Therefore, the smaller the number of coarse crystal grains, the better.

However, it is difficult to completely eliminate coarse crystal grains generated at the interface of the quenched flakes (powder) during the temperature raising process. By setting the volume fraction of coarse crystal grains to less than 20%, it is possible to create a magnet with a good degree of anisotropy and a residual magnetic flux density of 90% or more of the saturation magnetization.

In order to make the volume fraction of coarse grains less than 20%,
Coarse crystal grains in the rapidly cooled flakes (powder) created by the molten metal quenching method, coarse grains formed at the interface between rapidly cooled flakes (powders) during the heating process, areas where the amorphous phase rapidly crystallized during the heating process 20% of the sum of the three coarse grains generated from
It is requested that the amount be kept below. Therefore, there are desirable composition ranges, desirable quenched flakes (powders), desirable thermal histories for plastic working, and desirable plastic working conditions.

Desirable composition ranges for permanent magnets are as follows.

When the amount of R (one type or combination of two or more types of rare earth elements including Y) is 1 lat%, plastic working is rotational because there is no rare earth-rich liquid phase component, and sufficient storage is required. If magnetic force cannot be obtained and R exceeds 18 at%, the amount of the main phase decreases, and coarse crystal grains exceeding 0.7 μm are likely to occur, resulting in a decrease in residual magnetic flux density. Therefore, 11≦R≦
It was set at 18. In particular, when 13≦R≦15, it is possible to simultaneously achieve high residual magnetic flux density and coercive force, which is desirable.

When the amount of B is 4 at%, the main phase of the water-based magnet is Nd.
The 2Fe14B phase is not completely formed, and both the residual magnetic flux density and coercive force are low. Furthermore, when the amount of B exceeds 11 at %, the residual magnetic flux density decreases due to the appearance of phases that are unfavorable in terms of magnetic properties.

Therefore, the amount of B was set to 4≦y≦11. A particularly preferred range for residual magnetic flux density and coercive force is 5≦y≦7.

Although the Curie point improves by adding Go, the anisotropy constant of the main phase decreases, making it impossible to obtain a high coercive force. Therefore, the amount of Go was set to 30 at% or less. Moreover, when the amount of Go exceeds 20 at%, plastic working becomes gradually difficult.

For this reason, it is more desirable to control Go to 20 at% or less.

Additional elements include Ga, Zn, Sx, AI+Nb, Z
The reason why r, Hf, Mo, P, C, and Cu were selected is as follows. Gat Zn, Si, A of 3at% or less
l, Nb, Zr, Hf, and MotP are effective in improving coercive force. Addition of more than 3 at% significantly reduces coercive force. C mixed into raw materials during the reduction process of rare earths and boron is
If it is 3 at% or less, the coercive force will not be reduced. Cu improves corrosion resistance without significantly changing magnetic properties. Ga also has the effect of improving corrosion resistance.

Desirable quenched flakes (powders) are as follows.

The coercive force of the R-Fe-B alloy created by the molten metal quenching method at room temperature exceeds 3 kOe, and the grain size is 0.7 μm.
It is desirable that the volume fraction of grains exceeding Are known. (R, C, Ruhl
Mat, Sci, Eng., 1 (1967), ρ3
13) When the coercive force at room temperature is 3 kOe or less, the contact area between the flakes increases when the flakes are compressed and densified because the flakes are thin. If the flake thickness is thin, the quenching atmosphere gas is likely to be drawn in, resulting in increased surface roughness. For these reasons, the area of the flake interface increases in the compressed and densified state, and the amount of coarse crystal grains at the flake interface increases. When the coercive force at room temperature is 3 koe or less, it contains a large amount of amorphous, and coarse crystal grains are likely to be generated during the heating process.

Therefore, it is desirable that the thin piece coercive force is 3 kOe or more, while the coarse crystal grains contained inside the thin piece are 20 kOe or more.
Must be less than %. It is more desirable that the coarse crystal grains be 10% or less.

In order to suppress the generation of coarse crystal grains at the flake interface, it is desirable that the surface roughness of the quenched flake be 3 μm or less.

The reason is that by reducing the surface roughness to 3 μm or less,
This is because the free space at the flake interface can be reduced and the amount of coarse crystal grains generated at the flake interface can be reduced. In order to improve such surface roughness, it is effective to reduce gas entrainment on the surface of the quenched flake. Specific methods include creating quenched flakes using a twin-roll method, creating quenched flakes under reduced pressure, and using Ar, which has a smaller atomic weight than the commonly used Ar.
An effective method is to create a quenched flake in an inert gas such as He or Ne that does not cause entrainment. In the case of quenched flakes produced by the twin-roll method, the thickness of the flakes increases, which reduces the area of the flake interface in the compressed and densified state, and has the advantage of reducing the number of coarse crystal grains generated at the flake interface.

The desirable thermal history is as follows. The temperature range for good plastic working is 600°C to 850°C, and the magnet raw material needs to be quickly heated to this temperature range. Since the time required for the temperature to become homogenized differs depending on the size of the object to be heated, there is no uniquely good temperature increase rate. Generally, in the low temperature range below 600℃, 10~b 1~b In order to suppress coarse grains, the temperature of the mold for plastic working should be made as homogeneous as possible to improve the homogeneity of the sample temperature. Need to improve.

Furthermore, the shorter the holding time after the temperature has been homogenized and reached a predetermined temperature, the fewer coarse crystal grains will be produced.

Desirable plastic working conditions are as follows.

Plastic working strain is required to be at least 50%. By applying a strain of 60% or more, it is possible to create a plastically worked magnet that has clearly higher characteristics than a sintered magnet of the same shape. A high residual magnetic flux density can be obtained at a strain rate in the range of 10-4 to 1O-2 s-1, but from an economical point of view, it is desirable to increase the strain rate.

(Hereinafter, blank space) [Example] Example 1 Composition formula N d 14F e73c o6B6G a 1
(Displayed as atomic %, same below) 0.2k of raw material weighed
g was melted using an arc melting furnace in an Ar atmosphere to produce a master alloy. The master alloy was placed in a transparent quartz nozzle with a hole at the bottom and set on a Be-Cu roll. After the chamber containing the roll was evacuated to 5 x 10-3 Torr, Ar gas was introduced to 380 Torr. After remelting the master alloy using high frequency,
Circumferential speed of 25 m/s due to Ar pressure of 250 g/cm2
The molten metal was spouted onto the rolls rotated by EC. The molten metal was rapidly cooled and solidified into flakes. The average thickness was 26 μm, the surface roughness was 2.8 μm, and the coercive force was 3.6 kOe. As a result of observing the fractured surface of the thin section, no coarse crystal grains exceeding 0.7 μm were observed.

The obtained flakes were cold molded to produce a cylindrical molded body (150 g) with a diameter of 28 mm. This molded body was compressed and densified at 710° C. using a vacuum hot press until the relative density became 98% or more to produce a consolidated magnet. Next, the densified sample was held at 71°C without side restraints.
A plastically worked magnet was produced by compressing the magnet by 74% in the axial direction at 0°C. The average strain rate was 4×10−3 s−1.

The obtained magnet had a diameter of about 60 mm, a thickness of about 7.3 mm, and the direction of easy magnetization was in the thickness direction.

The average characteristics of a 70kOe pulse magnetized magnet are:

Residual magnetic flux density 12.75kG, coercive force 19.6, ○e,
Energy product ((BH)max) 39゜3 MG
It was Oe. The fracture surface of the magnet was observed, and the average crystal grain size and the proportion of coarse crystal grains were determined. 0.32μm, respectively.
It was 8.2%. As a comparative example, a magnet was created in the same manner except that the peripheral speed of the roll during quenching was 40 m/secC. The average characteristics of a 70 kOe pulse magnetized magnet are: residual magnetic flux density 11.1 kG, coercive force 19.6 kOe,
(BH) max 26MGOe. The fracture surface of the magnet was observed, and the average crystal grain size and the proportion of coarse crystal grains were determined.

They were 0.28 μm and 26%, respectively.

Example 2 Same as Example 1 except for changing the circumferential speed,
Created a magnet. Table 1 shows the thin piece coercive force (koe), average grain size after plastic working, proportion of coarse grains, and magnetic properties.
It can be seen that a high (BH)max can be obtained by increasing the flake coercive force to more than 3 kOe.

(Hereinafter, blank spaces) Table 1 Example 3 A magnet was created in the same manner as in Example 1 except that the plastic working temperature was changed. Table 2 shows the average grain size, proportion of coarse grains, and magnetic properties after plastic working.

In order to obtain a high (BH)max, the plastic working temperature is 60
0°C to 850°C is desirable.

A magnet was created using Table 2 in the same manner as in Example 3. When the plastic working temperature was 600°C or lower, plastic deformation could not be achieved. Table 3 shows the average grain size, proportion of coarse grains, and magnetic properties after plastic working.
The plastic working temperature is 850℃ or less, which is high (BH).
max is shown.

Table 3 Example 4 Composition formula N d 12F e75c o6B6G a 1
Quenched flake Example 5 A magnet was produced in the same manner as in Example 1 except for changing the composition. The magnetic properties are shown in Table 4.

The average crystal grain size was in the range of 0.1 to 0.5 μm in all cases. Coarse grains were also less than 20%. A blank column indicates that plastic working could not be performed.

(Hereinafter, blank space) Table 4 It was within the range of 0.5 μm. 20% coarse grains
It was less than

Table 5 Example 6 Example 1 except that the composition formula is Nd14Febalco686Mx (M is an additive element) and the additive element is changed.
A magnet was created in the same way. The magnetic properties are shown in Table 5.

Note that the average crystal grain size was 0.1 stone in each case. Table 6 shows the surface roughness, proportion of coarse grains after plastic working, and magnetic properties of the rapidly cooled flakes. High when the surface roughness is 3 μm or less (
BH) max is obtained.

Table 6 Example 7 In order to change the surface roughness of the quenched flake, the same procedure as in Example 1 was carried out except that the ejection pressure was changed.Example 8: A quenched flake was created by changing the Ar pressure of the atmospheric gas to be quenched. A magnet was produced in the same manner as in Example 1. Table 7 shows the surface roughness, proportion of coarse grains after plastic working, and magnetic properties of the rapidly cooled flakes. The pressure of the quenching atmosphere is 760 T or
r or less is desirable.

Table 7 A piece was prepared, and a magnet was prepared in the same manner as in Example 1.

The surface roughness of the quenched flakes, the proportion of coarse grains after plastic working, and the magnetic properties are shown in Table 8, and it can be seen that high magnetic properties can be obtained by using the raw material powder prepared in He and Ne.

It should be noted that in a nitrogen atmosphere, it was not possible to create rapidly quenched flakes due to initial blockage of the nozzle.

Table 8 Example 9 Quenching groove by changing the type of atmospheric gas for quenching [Effects of the invention] As described above, the permanent magnet according to the present invention exhibits high magnetic properties and is useful.

Claims (7)

[Claims] (1) R-Fe-B alloy (R
is one or more kinds of rare earth elements (including Y) made magnetically anisotropic by plastic working, and the average crystal grain size is 0.1 μm or more and 0.5 μm or less, and the crystal grain size is 0.
．． A permanent magnet characterized in that the volume fraction of crystal grains exceeding 7 μm is less than 20%. (2) R-Fe-B alloy is R_vFe_wCO_x
B_yM_z (R is one or more rare earth elements including Y,
M is Ga, Zn, Si, Al, Nb, Zr, Hf, Mo
, one or more of the elements consisting of P, C, Cu, and Ni and unavoidable impurities), 11≦v≦18, w=
100-u-x-y-z, 0≦x≦30, 4≦y≦11
, 0≦z≦3. (3) The coercive force of the R-Fe-B alloy produced by the molten metal quenching method at room temperature exceeds 3 kOe, and the crystal grain size is 0.5 kOe.
A permanent magnet raw material characterized in that the volume fraction of crystal grains exceeding 7 μm is less than 20%. (4) The permanent magnet raw material according to claim 3, wherein the R-Fe-B alloy has a surface roughness of 3 μm or less. (5) The permanent magnet raw material according to claim 3, wherein the molten metal is rapidly cooled by a twin roll method. (6) Claim 3, characterized in that the quenching of the molten metal is carried out in a vacuum or in an inert gas atmosphere at a pressure lower than atmospheric pressure.
Permanent magnet raw materials listed in . (7) The permanent magnet raw material according to claim 3, wherein the molten metal is rapidly cooled in He gas or Ne gas.