JP2011100881A - Method for manufacturing nanocomposite magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a nanocomposite magnet with satisfactory magnetic characteristics without generating a coarse crystal grain due to crystallization in sintering. <P>SOLUTION: In the method for manufacturing the nanocomposite magnet, the temperature of a quenched alloy is raised to the temperature below crystallization temperature by rapidly raising temperature under pressure for sintering. The quenched alloy is composed of a quench composition comprising a hard magnetic phase and soft magnetic phase and whose crystalline organization is 85 wt.%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a nanocomposite magnet in which hard magnetic nanoparticles and soft magnetic nanoparticles are combined.

  Nanocomposite magnets have a hard magnetic / soft magnetic two-phase composite structure. By making the soft magnetic phase ultrafine particles of several nanometers, exchange coupling works between the hard soft magnetic phases, greatly increasing residual magnetization and saturation magnetization. The property of being able to increase is drawing attention.

  As a method for producing a bulk body having such a nanostructure, a method in which a powder or ribbon obtained by rapidly cooling a melt having a predetermined composition is used as a raw material.

  That is, Patent Document 1 proposes a method in which an amorphous quenching ribbon is used and anisotropy is directly made in the presence of a liquid phase by warm uniaxial deformation (electric current powder rolling method).

  Patent Document 2 proposes a method for manufacturing an exchange spring magnet (nanocomposite magnet) by using an amorphous quenching ribbon and performing heat treatment in a hydrogen atmosphere and discharge plasma sintering.

  Patent Document 3 proposes a method of manufacturing an exchange spring magnet (nanocomposite magnet) by using an amorphous quenching ribbon, pulverizing it, and performing discharge plasma sintering.

Patent Document 4 proposes a method for producing a bulk exchange spring magnet by pulverizing a quenched ribbon, filling the obtained powder into a shape, and performing discharge plasma sintering at a predetermined sintering pressure and temperature. Has been. Patent Document 5 proposes that in the above technique, discharge plasma sintering is performed at a temperature of 500 to 650 ° C. and a pressure of 3.1 to 6.0 ton / cm ² .

  However, Patent Documents 1 to 5 do not disclose the amorphous / crystalline ratio constituting the quenched structure.

  Patent Document 6 proposes a method in which the volume ratio of amorphous contained in the raw material powder of the nanocomposite magnet is 50% or more, and this is hot-molded to form a bulk nanocomposite magnet. In order to perform hot forming, plastic deformability is required, and for this reason, the amorphous ratio is increased.

  Similarly, Patent Document 7 discloses a method of sintering using an amorphous sintering raw material under a pressure of 20 to 80 MPa.

  However, in order to bring the sintered density close to the true density, it is necessary to raise the sintering temperature. When a rapidly quenched powder or quenched ribbon with a lot of amorphous material is sintered, the amorphous part is slightly crystallized. There is a problem that the crystal structure is not mixed but a coarse crystal grain is mixed, and the magnetic properties (particularly the coercive force) of the obtained sintered body are lowered.

JP 2000-235909 A JP 2002-339018 A JP 2002-343659 A JP 2001-093723 A JP 2003-264115 A JP 2004-339527 A JP 2000-348919 A

  An object of the present invention is to provide a method for producing a nanocomposite magnet having good magnetic properties without generating coarse crystal grains by crystallization during sintering.

  In order to achieve the above object, a method for producing a nanocomposite magnet according to the present invention comprises a rapidly cooled alloy comprising a hard magnetic phase and a soft magnetic phase and having a crystal structure of 85% by weight or more under pressure. The temperature is raised to a temperature equal to or lower than the crystallization temperature by rapid heating and is sintered.

  Since a rapidly cooled alloy having a crystal structure of 85% by weight or more is used as a raw material and sintered at a temperature lower than the crystallization temperature by rapid heating, coarse crystal grains are not generated, and good magnetic properties can be secured.

FIG. 1 is a schematic diagram showing a manufacturing process according to the present invention in which a rapidly cooled ribbon is manufactured by a melt spinning method, and coarsely pulverized and sintered. FIG. 2 is a schematic diagram showing XRD charts for the quenched ribbon (1) amorphous and (2) crystalline manufactured in Example 1. FIG. FIG. 3 is a schematic view showing a method for separating the quenched ribbon into an amorphous one and a crystalline one. FIG. 4 is a schematic diagram showing a procedure for sintering the coarsely pulverized quenched ribbon (ribbon). FIG. 5 is a graph showing magnetization curves for a sintered body and an unsintered quenched ribbon. FIG. 6 is a graph showing the relationship between the ratio of the crystalline material constituting the sintered raw material and the ratio of the characteristics to the crystalline quenched ribbon. 7 is a photograph showing a transmission electron microscope (TEM) image of a crystalline ribbon used as a sintering raw material in Example 2. FIG. FIG. 8 is a photograph showing transmission electron microscope (TEM) images of a sintered body sintered at various temperatures and an unsintered quenched ribbon.

  In the method of the present invention, excellent magnetic properties equivalent to those of a crystalline quenched ribbon are achieved by using a sintering raw material having a crystalline content of 85% by weight or more, and the coercive force Hc is reduced as compared with the quenched ribbon. Within 10%, the decrease in residual magnetic flux density Br is within 5%. In particular, when a sintered raw material having a crystalline weight of 100% is used, both Hc and Br can have excellent magnetic properties with a decrease of 5% or less with respect to the crystalline quenched ribbon.

  By the method of the present invention, it is possible to obtain a binder-free magnet in which rare earth alloy magnet powders or ribbons produced by rapid cooling are bonded without a resin. Since no binder is used, the magnetic properties are good and it can be used even at high temperatures.

  A liquid quenching method such as melt spinning or atomizing is preferable as a method for producing a quenched alloy as a sintering raw material because it can achieve a fine structure accompanied by single domain grain formation. The crystal grain size of the quenched alloy is desirably 10 nm to 200 nm for the hard magnetic phase as the main phase and 1 nm to 100 nm for the soft magnetic phase.

  The quenched ribbon obtained by the liquid quenching method is coarsely pulverized and used for sintering. In general, the particle size is desirably 200 μm or less.

  As the sintering method, rapid temperature increase such as a hot press method, a discharge plasma method, and an electric current sintering method is desirable. Sintering is performed by heating and holding under pressure.

  Sintering is desirably performed at a temperature of 500 to 650 ° C. and a pressure of 200 MPa or more.

The typical composition of the quenched alloy i.e. sintered material applying the method of the present invention, is represented by the general formula _{R x Q y M z T 100} -x-y-z, R, Q, M, T is
R: one or more rare earth metals,
Q: at least one of B and C,
M: at least one selected from the group consisting of Ti, Al, Si, V, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, Pb,
T: Fe or a part of Fe substituted with at least one of Co and Ni,
And the above x, y, z are
2 ≦ x ≦ 11.8,
1 ≦ y ≦ 22,
0 ≦ z ≦ 10
The filling,
The hard magnetic phase as the main phase is R ₂ T ₁₄ M, and the soft magnetic phase is a compound of αFe or Fe and B or C.

[Example 1]
According to the present invention, a nanocomposite magnet having the following composition was produced.

Hard magnetic phase: (Nd ₂ Fe ₁₄ B) _0.99 Ga _0.01
Soft magnetic phase: αFe
Hard magnetic phase: soft magnetic phase = 8: 2
<Production of quenching ribbon>
Nd, Fe, FeB, and Ga were weighed in accordance with the above composition, and an alloy ingot was produced in an arc melting furnace.

  As shown in FIG. 1 (1), an alloy ingot is melted at a high frequency in a furnace in an Ar gas atmosphere reduced to 50 kPa or less, and a molten steel is sprayed onto a copper roll to rapidly cool the ribbon. Was made. FIG. 1 also shows all steps of (1) quenching ribbon production → (2) coarse pulverization → (3) sintering.

  The quenched ribbon (quenched ribbon) was collected, the crystal structure was analyzed by XRD, the magnetic properties were evaluated by VSM, and the crystal structure was observed by TEM.

FIG. 2 shows an example of the XRD chart. The quenched ribbons were individually amorphous and crystalline. As shown in FIG. 2 (1), when the quenched ribbon is amorphous, a broad pattern appears. However, as shown in FIG. 2 (2), the quenched ribbon is crystalline (in this case, polycrystalline). In this case, the peaks of the constituent phase Nd ₂ Fe ₁₄ B of the hard magnetic phase and the soft magnetic phase αFe appear clearly.

<Separation>
As shown in FIG. 3, the quenched ribbon is separated into a crystalline one and an amorphous one using a weak magnet. That is, among the quenching ribbon (1), the amorphous quenching ribbon is magnetized by the weak magnet and does not fall (2), and the crystalline quenching ribbon is not magnetized by the weak magnet and falls (3).

  In this way, using the separated crystalline / amorphous quenching ribbon, (A) 100% crystalline, (B) crystalline: amorphous = 65: 35, (C) crystalline by weight ratio. : Amorphous = 50:50 sample was prepared.

<Sintering>
Quenched ribbon samples A, B, and C were coarsely pulverized to a particle size of 200 μm or more, filled into a carbide die (inner diameter 10φ) as shown in FIG. As shown in FIG. 4 (2), a current was applied in the pressurizing direction through the cemented carbide punch while maintaining the pressurization, and heating was conducted. During energization heating, the displacement of the carbide punch was monitored. When the displacement in the compression direction stopped, the energization was stopped, and it was cooled to room temperature by natural heat dissipation.

  Table 1 summarizes the crystalline ratio (% by weight), the sintering pressure (MPa), and the sintering temperature (° C.) for the sintered bodies A, B, and C using the samples A, B, and C as raw materials.

  After cooling, the sintered body was taken out and the surface of the sintered body was polished, and then the magnetic properties were measured. The measurement results are summarized in Table 2. For comparison, the results of a crystalline rapidly quenched ribbon that is not sintered are also shown.

  FIG. 5 shows the magnetization curves of the sintered body A (100% crystalline) and the sintered body B (50% crystalline) compared to the magnetization curves of the unsintered crystalline quenching ribbon.

  FIG. 6 shows the relationship between the crystalline ratio of the sintered raw material and the characteristic ratio to the unsintered crystalline quenching ribbon.

  From these results, the sintered body A using the 100% crystalline quenching ribbon had both the residual magnetic flux density Br and the coercive force Hc decreased by about 2% compared to the unsintered quenching ribbon. It can be seen that the ratio rapidly decreases as the crystalline ratio of the sintered raw material decreases. From FIG. 6, it is necessary to set the ratio of the crystalline quenching ribbon in the sintered raw material to 85% or more in order to reduce the magnetic property within 10% of the unsintered crystalline quenching ribbon. is there.

[Example 2]
A nanocomposite magnet having the same composition as in Example 1 was produced.

<Production of quenching ribbon>
An ingot was prepared by arc furnace melting under the same procedure and conditions as in Example 1, and a quenched ribbon was prepared by a melt spinning method using a single roll (copper roll).

<Separation>
The crystalline / amorphous separation was performed with a weak magnet in the same manner as in Example 1, and only the crystalline quenching ribbon was used.

As a result of the crystal structure analysis by XRD of the quenched ribbon used, the peaks of the constituent phase Nd ₂ Fe ₁₄ B of the hard magnetic phase and the soft magnetic phase αFe are similar to those shown in FIG. It was confirmed that it appeared clearly.

FIG. 7 shows the transmission electron microscope (TEM) structure of the quenched ribbon used. It can be seen that the main phase (Nd ₂ Fe ₁₄ B) having a particle size of about 20 nm and the soft magnetic phase αFe are precipitated.

From these results, it was confirmed that a ribbon-like quenching structure was formed by the liquid quenching method, and a nanocomposite magnet of Nd ₂ Fe ₁₄ B / Fe was obtained.

<Sintering>
Sintering was performed in the same manner as in Example 1. However, the sintering pressure was set at two levels of 200 MPa and 300 MPa. The sintering conditions are shown in Table 1. The density and magnetic properties of the obtained sintered body were measured.

Table 3 shows the density and relative density (* 1) of the sintered body together with the conventional example (* 2). Table 4 shows the magnetic properties of the sintered body together with the unsintered quenched ribbon and the conventional example (* 2).

(* 1) Ratio to true density of 7.65 g / cm ³ (* 2) Conventional example: Source T. Saito et al., J. Mater. Res., 19, 2730 (2004); Composition Nd ₄ Fe _77.5 B _18.5

  As shown in Table 1, in the sintered bodies 1 to 4 according to the present invention, a value close to the true density is obtained as the sintered density. In particular, the sintered body 1 has a relative density of 97% and the sintered body 2 has a relative density. It can be seen that a density of 99% is obtained and the density is increased at a sintering pressure of 200 MPa or more. As a result, as shown in Table 2, the sintered bodies 1 to 4 according to the present invention have good magnetic properties.

  In contrast, Conventional Examples 1 and 2 have a low sintering pressure (50 MPa), so the density is low at a sintering temperature of 600 ° C. as shown in Table 1, and the sintering temperature is set to 700 ° C. to increase the density. However, as shown in Table 2, when the sintering temperature is set to 700 ° C. (conventional example 2), the magnetic characteristics are greatly deteriorated.

FIG. 8 shows changes in the transmission electron microscope (TEM) structure depending on the sintering temperature when the sintering pressure is 300 MPa (constant). Compared with the sintered body 2 having a sintering temperature of 600 ° C., the sintered body 4 having a sintering temperature of 700 ° C. has a larger αFe particle size (about 100 nm) and lower magnetic properties. Therefore, it can be seen that the sintering temperature is preferably 650 ° C. or lower. On the other hand, the structure of the sintered body 3 having a sintering temperature of 500 ° C. is the finest, but the density is relatively low at 7.11 g / cm ³ . However, this is a sufficient density for a bulk body. From this, it is desirable that the lower limit of the sintering temperature be 500 ° C.

From the results of this example, it was found that a sintering density of 7.11 g / cm ³ or more was obtained by setting the sintering pressure to 200 MPa or more and the sintering temperature to 500 ° C. to 650 ° C.

  According to the present invention, there is provided a method for producing a nanocomposite magnet having good magnetic properties without generating coarse crystal grains by crystallization during sintering.

Claims (3)

  Sintering a rapidly cooled alloy consisting of a hard magnetic phase and a soft magnetic phase and having a crystal structure of 85% by weight or more by raising the temperature to a temperature below the crystallization temperature by rapid heating under pressure. A method for producing a nanocomposite magnet.   The method for producing a nanocomposite magnet according to claim 1, wherein the sintering is performed at a temperature of 500 to 650 ° C. and a pressure of 200 MPa or more. The composition of the rapidly solidified alloy is represented by the general formula _{R x Q y M z T 100} -x-y-z, R, Q, M, T is
R: one or more rare earth metals,
Q: at least one of B and C,
M: at least one selected from the group consisting of Ti, Al, Si, V, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, Pb,
T: Fe or a part of Fe substituted with at least one of Co and Ni,
And the above x, y, z are
2 ≦ x ≦ 11.8,
1 ≦ y ≦ 22,
0 ≦ z ≦ 10
The filling,
The method for producing a nanocomposite magnet, wherein the hard magnetic phase as a main phase is R ₂ T ₁₄ M, and the soft magnetic phase is αFe or a compound of Fe and B or C.