WO2014204106A1

WO2014204106A1 - Method for manufacturing permanent magnet

Info

Publication number: WO2014204106A1
Application number: PCT/KR2014/004647
Authority: WO
Inventors: 이성래; 김태훈; 장태석
Original assignee: 고려대학교 산학협력단
Priority date: 2013-06-18
Filing date: 2014-05-23
Publication date: 2014-12-24

Abstract

The present invention relates to a method for manufacturing an Nd-Fe-B-based permanent magnet having an improved coercive force while reducing the amount of Dy used. A method for manufacturing a permanent magnet according to an embodiment of the present invention may comprise the steps of: manufacturing powder including Nd, Fe, B, and Cu; manufacturing a shaped body by forming a specific magnetic field in the powder; sintering the shaped body at a specific sintering temperature; and subjecting the sintered, shaped body to heat treatment at a heat treatment temperature determined according to the content of Cu.

Description

Method of manufacturing permanent magnet

The present invention relates to a method of manufacturing a permanent magnet, and more particularly, to a method of manufacturing a Nd-Fe-B-based permanent magnet with improved coercivity while reducing the amount of Dy used.

Nd-Fe-B permanent magnets are increasingly used because of their excellent magnetic properties. Recently, in response to environmental problems, as the application of magnets is expanded to home appliances, industrial equipment, electric vehicles, and wind power generation, the performance of Nd-Fe-B magnets has been increasing.

As an index of magnet performance, the residual magnetic flux density and the magnitude of the coercive force can be given. Increasing the residual magnetic flux density of the Nd-Fe-B-based sintered magnet is achieved by increasing the volume ratio of the Nd ₂ Fe ₁₄ B compound and improving the crystal orientation, and various processes have been improved so far. In terms of increasing coercivity, there are various approaches such as miniaturization of grains, using alloys with increased Nd amounts, or adding effective elements. Currently, the most common method is Dy or Tb. The composition alloy which substituted a part of Nd is used. By replacing Nd of the Nd ₂ Fe ₁₄ B compound with these elements, the anisotropic magnetic field of the compound increases and the coercive force also increases. On the one hand, substitution by Dy or Tb reduces the saturation magnetic polarization of the compound. Therefore, the reduction of the residual magnetic flux density cannot be avoided only by increasing the coercive force by the above method. In addition, since Tb and Dy are expensive metals, it is preferable to reduce the usage amount as much as possible.

Related prior art is Korean Patent Publication No. 10-2010-0097580. The Patent Publication No. 10-2010-0097580 discloses a method for producing a sintered magnet through repeated heat treatment and a sintered magnet manufactured therefrom.

However, Korean Patent Publication No. 10-2010-0097580 does not disclose a method of improving the coercive force and reducing the Dy content in manufacturing a permanent magnet.

Therefore, when manufacturing permanent magnets, research on a technique for improving coercivity while reducing expensive Dy content is required.

An object of the present invention is to provide a method for manufacturing a Nd-Fe-B-based permanent magnet with improved coercivity while reducing the amount of Dy used.

According to an embodiment of the present invention to achieve the above object, preparing a powder comprising Nd, Fe, B and Cu; Preparing a molded body by forming a specific magnetic field on the powder; Sintering the molded body at a specific sintering temperature; And performing a heat treatment of the sintered molded body at a heat treatment temperature determined according to the content of Cu.

In the method of manufacturing a permanent magnet according to an embodiment of the present invention, the Nd-Fe-B-based permanent magnet is manufactured by improving the coercivity while reducing the amount of Dy by varying the heat treatment temperature according to the Cu content as an additive. can do.

1 is a flowchart illustrating a method of manufacturing a permanent magnet according to an embodiment of the present invention.

FIG. 2 is a view for explaining strip casting and hydrogen treatment in the method of manufacturing the permanent magnet shown in FIG. 1.

3 is a view for explaining a process of grinding the master alloy of the manufacturing method of the permanent magnet shown in FIG.

4 is a view for explaining a process of manufacturing a molded body of the manufacturing method of the permanent magnet shown in FIG.

5 is a view for explaining the sintering (sintering) process of the method of manufacturing a permanent magnet shown in FIG.

6 to 7 are views for explaining the effect of the heat treatment after sintering in the method of manufacturing a permanent magnet according to an embodiment of the present invention.

8 shows that the sintering and heat treatment are performed by a common method in the manufacture of a permanent magnet.

9 is a graph showing the relationship between the Cu content and the coercive force.

10-11 show the Nd-rich triple point microstructure of a permanent magnet containing Cu.

12 is a diagram for comparing the microstructure of the Nd-rich grain boundary phase with different Cu content.

13 to 14 are diagrams for explaining the relationship between the Cu content and the heat treatment temperature.

FIG. 15 shows the coercive force and residual magnetization change with the primary heat treatment temperature of the sintered magnet containing 0.5 at.% Cu.

FIG. 16 is a view illustrating a microstructure of a specimen when the heat treatment is performed at the heat treatment temperature shown in FIG. 8 and the heat treatment temperature shown in FIG. 15.

FIG. 17 is an image obtained by using high-resolution transmission electron microscopy (HRTEM) of FIG. 16 (b).

18 is a graph showing a change in magnetic properties according to the sintering temperature in accordance with an embodiment of the present invention.

19 is a graph showing the coercive force change according to the first heat treatment temperature change in accordance with an embodiment of the present invention.

Hereinafter, a method of manufacturing a permanent magnet and a permanent magnet according to an embodiment of the present invention will be described with reference to the drawings.

As used herein, the singular forms "a", "an" and "the" include plural forms unless the context clearly indicates otherwise. In this specification, terms such as “consisting of” or “comprising” should not be construed as necessarily including all of the various components or steps described in the specification, and some of the components or some steps It should be construed that it may not be included or may further include additional components or steps.

First, a powder containing Nd, Fe, B, and Cu may be manufactured (S110). The powder manufacturing process may include processes such as strip casting, hydrotreating, and grinding.

FIG. 2 is a view for explaining strip casting and hydrogen treatment in the method of manufacturing the permanent magnet shown in FIG. 1. In the following examples, the permanent magnet may be manufactured by varying the composition of other components depending on the content of Dy.

According to the first embodiment, a composition of _{_{_{_{_{Nd 12 .00 Dy 2 .70 Fe (}}}}} 76.45-x) Cu x B 6.00 M 2 .65 (x = 0.2, 0.3, 0.4, 0.5), (at.%, M = Co, Al, and Nb) strip-cast mother alloy may be prepared, and hydrogen treatment may be performed. Due to the process, the volume of the grain boundary may be changed, thereby facilitating crushing into single crystals.

Further, according to the second _{_{_{embodiment, Nd 32 .00 Fe (64.79-}}} x) Cu x B 0.97 M 2 .24 (Dy-free) (x = 0.2, 0.3, 0.4, 0.5), (at.%, M = Co, Al, and Nb) strip-cast mother alloy may be prepared, and hydrogen treatment may be performed. Due to the process, the volume of the grain boundary may be changed, thereby facilitating crushing into single crystals.

In addition, according to the third _{_{_{_{embodiment, Nd 29 .00 Dy 3 .00 Fe}}}} (64.79-x) Cu x B 0.97 M 2 .24 (3wt.% Dy-containing) (x = 0.2, 0.3, 0.4, 0.5) , (at.%, M = Co, Al, and Nb) to prepare a strip-cast master alloy, and may be subjected to a hydrogen treatment. Due to the process, the volume of the grain boundary may be changed, thereby facilitating crushing into single crystals.

The strip-cast master alloy shown in FIG. 2 may be ground using jet-milling. Due to the grinding process, a ferromagnetic powder having a single crystal can be produced.

Cu contained in the powder most effectively lowers the melting point of the Nd-rich phase. The content of Cu relative to the powder may be preferably 0.01 to 0.8 weight ratio. When the content of Cu in the powder exceeds 0.8 weight ratio, the density becomes low, and when the content of Cu in the powder is less than 0.01 weight ratio, the effect of Cu addition is insignificant.

When the ferromagnetic powder is manufactured, a molded body may be manufactured by forming a specific magnetic field on the powder (S120).

As shown, a green compact may be manufactured by applying pressure to the ferromagnetic powder while applying a specific magnetic field (for example, about 2.2T) to the powder. The produced molded article has easy magnetization axes aligned in one direction.

When the molded body is manufactured, the molded body may be sintered (S130).

As shown, the molded body may be sintered for a predetermined time under a specific atmosphere. For example, the molded body may be sintered at 1070 ° C to 1040 ° C for 4 hours in a vacuum atmosphere. The ideal sintering temperature and sintering time may vary depending on the composition and the atmosphere sintering furnace. Liquid phase sintering may be performed until densification is achieved by about 99%. Through the sintering process, an anisotropic magnet having a full density may be manufactured.

On the other hand, according to an embodiment of the present invention, the sintering temperature may vary depending on the content of copper.

After the sintering process, heat treatment may be performed (S140). The heat treatment may be performed once, but may be performed a plurality of times to improve properties.

For example, after sintering, heat treatment may proceed three times to improve properties. Ideal heat treatment conditions may vary depending on the composition and environment. Mainly, high temperature heat treatment and low temperature heat treatment can be divided into two processes.

According to one embodiment of the present invention, the heat treatment may be performed by varying the temperature according to the content of Cu. By performing the heat treatment at the heat treatment temperature determined according to the Cu content as described above, even if the amount of Dy (dysprosium) is reduced, the coercive force can be produced a permanent magnet. In addition, when the heat treatment is performed a plurality of times, the heat treatment may be performed at a heat treatment temperature determined according to the content of Cu only for the first heat treatment.

Hereinafter, the reason for changing the heat treatment temperature according to the sintering heat treatment effect and the content of Cu will be described through experiments.

6 shows a microstructure in which heat treatment is performed after sintering.

Post-sintering annealing is essential to improve the coercive force of Nd-Fe-B sintered magnets. That is, in order to reduce the Dy content, which is an expensive heavy rare earth element, heat treatment after sintering is one of very efficient methods. The coercive force of the sintered magnet is greatly affected by the microstructure of the nonmagnetic Nd-rich triple point and grain boundaries. The heat treatment effect is as follows.

First, continuity of the Nd-rich grain boundary phase may be improved through heat treatment. As a result, the coercive force is improved by suppressing the interchange coupling between adjacent ferromagnetic columnar phases.

In addition, the homogeneity of Nd-rich triple point and grain boundary phases is improved to reduce defects at the interface. As a result, the nucleation site of reverse domains is reduced, thereby improving coercivity.

A metastable C type Nd ₂ O ₃ triple point phase and a grain boundary phase are formed. Because of this, lattice mismatch with the columnar phase can be greatly reduced and the coercivity can be improved.

In improving the coercive force through heat treatment, addition of low melting point elements such as Al, Ga, Ag, Cu, etc. is very important. Among them, Cu is the most efficient because it lowers the melting point of the Nd-rich phase most efficiently.

7 is a view for explaining the effect of the heat treatment after sintering the powder containing Cu.

The effect of heat treatment after Cu addition is as follows.

first. The melting point of the Nd-rich phase is reduced to further improve the continuity and homogeneity of the grain boundary phase.

In addition, the non-magnetic properties of the Nd-rich triple point and the grain boundary phase are improved by the process decomposition reaction between Nd-Cu formed at about 520 ° C., so that the coercive force may be further improved.

Metastable C type Nd2O3 triple point and grain boundary phases are further promoted.

Excessive addition of Cu lowers the density of the sintered magnet. For example, if the Cu content exceeds about 0.8 at,%, the density of the sintered magnet is reduced.

The existing ideal Cu content is known to be about 0.1 to 0.2 at.%. However, it is not clear why the ideal Cu content is 0.1 ~ 0.2at.%.

The experimental example shown is a sintered magnet whose composition according to the first embodiment is Nd12.00Dy2.70Fe (76.45-x) CuxB6.00M2.65 (x = 0.2, 0.3, 0.4, 0.5), the composition according to the second embodiment Is Nd32.00 Fe (64.79-x) Cux B0.97 M2.24 (Dy-free) (x = 0.2, 0.3, 0.4, 0.5), (at.%, M = Co, Al, and Nb), and According to the third embodiment, the composition is Nd29.00 Dy3.00 Fe (64.79-x) Cux B0.97 M2.24 (3wt.% Dy-containing) (x = 0.2, 0.3, 0.4, 0.5), (at %, M = Co, Al, and Nb) is an experimental example for the sintering and heat treatment.

As shown, the sintering temperature is 1040 ° C ~ 1070 ° C (1070, 1060, 1050, 1040 ° C), the sintering time is 4 hours. In addition, the first heat treatment (PSA, Post-sintering annealing) temperature is 700 ℃ ~ 850 ℃ (850, 820, 790, 760, 730, 700 ℃), the heat treatment time is 2 hours. The secondary heat treatment temperature is 530 ° C., and the heat treatment time is 2 hours. The third heat treatment temperature is 500 ℃, the heat treatment time is 2 hours.

9 is a view showing a relationship between the content of Cu and the coercive force for the experimental example shown in FIG. 9 (a) relates to the first embodiment, FIG. 9 (b) relates to the second embodiment, and FIG. 9 (c) relates to the third embodiment.

According to FIG. 9 (a), as the Cu content increases, the coercive force also decreases (28.7-> 27.1 kOe). And the residual magnetization does not change significantly.

According to FIG. 9 (b), the coercivity decreases with increasing Cu content (14.0-> 13.3 kOe). And the residual magnetization does not change significantly.

According to FIG. 9 (c), as the Cu content increases, the coercive force also decreases (20.5-> 20.1 kOe). And the residual magnetization does not change significantly.

Fig. 10 shows the microstructure on the Nd-rich triple point of a magnet containing 0.2 at.% Cu.

As shown, the microstructure forms a layer structure. The dark part has a composition of Nd ₄₀ Cu ₃₄ Co ₄ O ₂₂ and excess Cu is aggregated. In addition, the dark portion shows a C-TYPE Nd ₂ O ₃ crystal structure.

On the other hand, the bright part has a composition of Nd ₄₀ Cu ₆ Co ₇ O ₄₇ and a small amount of Cu is aggregated. The bright part shows hexagonal Nd ₂ O ₃ crystal structure, the most stable phase.

Excess Cu aggregation stabilizes the metastable C-TYPE Nd ₂ O ₃ phase. The excess Cu agglomeration mechanism in terms of layer structure is a process cracking reaction between Nd-Cu that can be formed during tertiary heat treatment.

Fig. 11 shows the microstructure on the Nd-rich triple point of a magnet containing 0.5 at.% Cu.

The microstructure of FIG. 11 also has a microstructure similar to that of FIG. 10.

Dark part has _{_{_{_{_{Nd 45 .2 Cu 36 .8 Co 2}}}}} .1 O ₁₅ composition of _0.9 and are aggregated an excess of Cu. But the dark structure is hexagonal Nd ₂ O ₃ , not C-TYPE Nd ₂ O ₃ .

Bright parts have a composition of Nd ₅₂ Cu ₁₁ _.6 _.8 _.6 Co ₁ O _34, and a small amount of Cu is aggregated. The bright part shows hexagonal Nd ₂ O ₃ crystal structure, the most stable phase.

12, it is possible to compare the microstructure of the Nd-rich grain boundary that plays the most important role in the coercivity.

12 (a) shows a case where the Cu content is 0.2 at.%, In which case an amorphous grain boundary phase of Nd ₂ O ₃ of C-TYPE is formed.

12 (b) shows a case where the Cu content is 0.5 at.%, In which case an amorphous grain boundary phase of hexagonal Nd ₂ O ₃ is formed.

It can be inferred that the coercivity is reduced due to the difference of crystal structure transformation state of Nd-rich phase.

13 shows an Nd-O binary phase diagram.

As shown, the addition of Cu lowers the melting point of the Nd-rich phase. This may mean that not only the melting point but also the phase transformation temperature decreases.

Changes in phase transformation temperature can be inferred from Dsc analysis and calculations.

It is a figure for demonstrating the relationship between content and heat processing temperature.

Figure 14 (a) shows the case where the Cu content is 0.2at.%. Overall, the temperature is lower than that of Cu-free, and the stable hexagonal Nd2O3 phase is stabilized at 850 ° C.

Figure 14 (b) shows a case where the Cu content is 0.2at.%. It can be seen that the overall phase transformation temperature is so low that the fcc-NdO phase, not the stable hexagonal Nd ₂ O ₃ phase, is stabilized at 850 ° C.

That is, the Nd ₂ O ₃ crystal of the metastable C-TYPE may be derived from the h-Nd ₂ O ₃ crystal structure. The two decisions are closely related to each other. Therefore, when excessive Cu is agglomerated into the invasive sites on the hexagonal Nd ₂ O ₃ , it may be transformed into C-TYPE Nd ₂ O ₃ crystals.

However, in the case of fcc-NdO having a rock salt structure, even if excessive Cu agglomerates with this crystal structure, it cannot be transformed into C-TYPE Nd ₂ O ₃ phase. There is no correlation between the two. Eventually it can be transformed into a stable hexagonal Nd ₂ O ₃ during the secondary tertiary heat treatment. In the magnet with 0.5 at.% Of Cu, hexagonal phases, not C-TYPEs, are observed despite excessive Cu agglomeration, thereby reducing the coercive force. Therefore, it is necessary to change the primary heat treatment temperature in accordance with the Cu content.

The coercivity is greatly improved when reduced from 850 ℃ to 790 ℃ (27.1-> 29.4 kOe). Thus, existing ideal trace amounts of Cu (addition of Cu in FIG. 8 embodiment) may not be ideal compositions.

By changing the primary heat treatment temperature according to the Cu content, the coercive force can be further improved. As a result, the coercive force of the sintered magnet can be improved without adding Dy. That is, Dy reduction type sintered magnets can be manufactured by inexpensive addition of Cu and optimization of heat treatment conditions according to its content.

Figure 16 (a) shows a microstructure subjected to the heat treatment at a heat treatment temperature of 850 ℃ conventional method, Figure 16 (b) shows a micro structure subjected to the heat treatment at a heat treatment temperature of 790 ℃ changed according to the Cu content.

The first heat treatment temperature was lowered to refine the grains. This may contribute to an improvement in coercivity.

Nd-rich triple-phase and grain boundary phases, as well as metastable C-TYPE Nd ₂ O ₃ with excessive Cu agglomeration, were formed again. This may contribute to an improvement in coercivity.

In addition, it can be seen through the illustrated embodiment that the heat treatment temperature is lowered as the Cu content is increased.

On the other hand, the permanent magnet produced according to another embodiment of the present invention changes the magnetic properties according to the sintering temperature at the time of filing.

18 is a graph showing a change in magnetic specificity according to sintering temperature in relation to an embodiment of the present invention.

18 (a) shows the change of the magnetic properties according to the sintering temperature of the permanent magnet according to the second embodiment, Figure 18 (b) shows the magnetic properties of the permanent magnet according to the sintering temperature of the second embodiment Indicates a change.

According to Fig. 18A, the coercive force tends to increase as the sintering temperature decreases. In addition, the coercive force of the Cu content (0.4, 0.5 wt%) is low, but the coercivity tends to increase with decreasing the primary heat treatment temperature and the sintering temperature. At the first heat treatment of 820 ° C, the coercive force of the specimen with the Cu content of 0.3 wt.% Is the highest. The maximum coercive force is obtained when the Cu content is 0.3 and the sintering temperature is 1050 ° C.

According to Fig. 18B, the coercive force tends to increase as the sintering temperature decreases. Especially in the case of 0.2, 0.3 wt% Cu added, the coercive force increases rapidly when the sintering temperature is reduced from 1070 ° C to 1060 ° C at the first heat treatment temperature of 850 ° C. Similarly, the highest coercive force comes from specimens with a Cu content of 0.3 wt.% (Sintering temperature 1050 ° C / primary heat treatment 790 ° C).

18 (b) and 18 (a), in the case of specimens added with 3 wt.% Of Dy, when the Cu content is high (0.5, 0.6 wt.%), The first heat treatment and the sintering temperature may be reduced. Coercivity does not increase significantly.

On the other hand, the permanent magnet produced by another embodiment of the present invention changes the coercive force according to the change in the first heat treatment temperature at the time of filing.

19 (a) shows the coercive force change according to the first heat treatment temperature change of the permanent magnet according to the second embodiment, Figure 18 (b) shows the coercive force according to the first heat treatment temperature change of the permanent magnet according to the second embodiment Indicates a change.

19 (a), as the Cu content increases, the optimum primary heat treatment temperature decreases. Also, as the sintering temperature decreases, the overall coercive force tends to increase.

19 (b), the optimal primary heat treatment temperature also tends to decrease as the Cu content increases. In addition, as shown in FIG. 19 (a), as the sintering temperature decreases, the overall coercive force tends to increase.

As described above, the method of manufacturing a permanent magnet according to an embodiment of the present invention is to change the sintering temperature or the heat treatment temperature according to the Cu content, thereby reducing the amount of expensive Dy and manufacturing the permanent magnet with improved coercivity. Can be.

The manufacturing method of the permanent magnet described above is not limited to the configuration and method of the embodiments described above, the embodiments are a combination of all or part of each embodiment selectively so that various modifications can be made It may be configured.

Claims

Preparing a powder comprising Nd, Fe, B, and Cu;

Preparing a molded body by forming a specific magnetic field on the powder;

Sintering the molded body at a specific sintering temperature; And

And heat-treating the sintered molded body at a heat treatment temperature determined according to the content of Cu.
The method of claim 1, wherein performing the heat treatment

And a plurality of heat treatments, and the heat treatment temperature determined according to the Cu content is a primary heat treatment of the plurality of heat treatments.
The method of claim 1, wherein the content of Cu

Method for producing a permanent magnet, characterized in that the weight ratio of 0.01 to 0.8 with respect to the powder.
According to claim 3, wherein the heat treatment temperature determined according to the content of Cu is

Method of producing a permanent magnet, characterized in that lowered as the content of Cu increases.
The method of claim 1, wherein the specific sintering temperature is

Method for producing a permanent magnet, characterized in that determined according to the content of Cu.