JP6198103B2 - Manufacturing method of RTB-based permanent magnet - Google Patents

Description

  The present invention relates to a method for producing an R-T-B permanent magnet.

R-T-B type permanent magnets typical as high performance permanent magnets (R is a rare earth element containing Nd and / or Pr, T is Fe or a part of Fe substituted with Co, and B is boron) It includes an R ₂ T ₁₄ B phase (Nd ₂ Fe ₁₄ B type compound phase), which is a ternary tetragonal compound, as a main phase, and exhibits excellent magnetic properties, so that it is used in various applications.

In particular, in recent years, the demand for RTB-based permanent magnets used at high temperatures, such as drive motors for hybrid vehicles and electric vehicles, has been increasing. R-T-B permanent magnets used in such products are required to have a high coercive force. As a method for increasing the coercive force of an R-T-B system permanent magnet, a part of R of the R-T-B system permanent magnet is a heavy rare earth element such as Dy or Tb, so that the R ₂ T ₁₄ B phase ( It is generally known to increase the magnetocrystalline anisotropy of the main phase. However, heavy rare earth elements such as Dy and Tb are rare elements with small crustal abundance, and there is concern that the risk of resource depletion may become apparent in the future. R- without using Dy or Tb There is a need for a technique for increasing the coercive force of a T-B permanent magnet.

Among RTB-based permanent magnets, RTB-based sintered magnets manufactured by the powder metallurgy method can be used without using Dy or Tb by reducing the pulverized particle size of the raw material powder. It is known from Non-Patent Document 1 that magnetic force is improved. Also, HDDR (Hydrogenation-Deposition-Recombination-Recombination) processing method known as a method for refining the crystal grain size of the R ₂ T ₁₄ B phase to submicron size, which is difficult with powder metallurgy, is an R-T-B system. A permanent magnet is attracting attention as a technique that has a possibility of obtaining a higher coercive force without using Dy or Tb, and is disclosed in Non-Patent Document 2, for example.

The HDDR processing method means a process of sequentially performing hydrogenation and disproportionation, dehydrogenation and recombination, and is mainly different from R-T-B system. It has been adopted as a method for producing magnet powder for isotropic bonded magnets. According to the known HDDR treatment, first, an R-T-B alloy ingot or powder is maintained at a temperature of 700 ° C. to 1000 ° C. in an H ₂ gas atmosphere or a mixed atmosphere of an H ₂ gas and an inert gas. Then, hydrogen is occluded in the ingot or powder. Thereafter, such as _{H 2} pressure is 13Pa or less of vacuum atmosphere, or _{H 2} partial pressure is dehydrogenated at a temperature 700 ° C. to 1000 ° C. or less inert atmosphere 13Pa, then cooled.

  In the above treatment, the following reaction typically proceeds.

First, a hydrogenation and disproportionation reaction proceeds by a heat treatment that occludes hydrogen at a predetermined temperature to form a fine structure. Both hydrogenation and disproportionation reactions are collectively referred to as “HD reactions”. In a typical HD reaction, a reaction of Nd ₂ Fe ₁₄ B + 2H ₂ → 2NdH ₂ + 12Fe + Fe ₂ B proceeds.

Next, dehydrogenation and recombination reaction proceed by heat treatment for releasing hydrogen at a predetermined temperature. The dehydrogenation and recombination reactions are collectively referred to as “DR reactions”. In a typical DR reaction, for example, a reaction of 2NdH ₂ + 12Fe + Fe ₂ B → Nd ₂ Fe ₁₄ B + 2H ₂ proceeds. Thus, an alloy containing a fine R ₂ T ₁₄ B crystal phase is obtained.

  In this specification, the heat treatment for causing the HD reaction is referred to as “HD treatment”, and the heat treatment for causing the DR reaction is referred to as “DR treatment”. Further, performing both HD processing and DR processing is referred to as “HDDR processing”.

  The R-T-B type HDDR magnet powder (hereinafter referred to as “HDDR magnetic powder”) obtained by the HDDR treatment has a crystal grain size of 0.1 μm to 1 μm and has a large coercive force while being a powder, and is magnetic. Anisotropy is shown. However, it has been difficult to obtain magnetic powder having a coercive force that can withstand use in a drive motor for a hybrid vehicle or an electric vehicle only by the HDDR process. Moreover, the HDDR magnetic powder for bonded magnets had poor squareness of the demagnetization curve and poor heat resistance.

  In recent years, several methods for improving the coercive force of HDDR magnetic powder without using Dy or Tb have been proposed. For example, Patent Document 1 discloses HDDR magnetic powder and an R′-Al alloy (R ′ represents Nd and / or Pr). R'-Al alloy diffuses into HDDR magnetic powder and improves coercive force by heat treatment at 550 to 900 ° C. by mixing rare earth elements containing 90 atomic% or more with respect to the entire R ′ and not containing Dy and Tb) Is disclosed.

  Further, Patent Document 2 discloses a method for HDDR treatment using an RTB rare earth alloy powder having an average particle size of less than 10 μm as a green compact as a method for obtaining a bulk magnet while improving the squareness of HDDR magnetic powder. ing.

  By the way, in an RTB-based sintered magnet, an aging treatment (heat treatment at about 500 to 600 ° C. in a vacuum or an inert gas atmosphere) is usually performed after sintering or after further processing such as cutting and grinding. It is usually performed to improve the coercive force. Patent Document 3 describes an example of molding, sintering, and aging treatment of a raw material powder for an R-T-B system magnet, and describes that HDDR magnetic powder can be used as the raw material powder.

JP 2012-049492 A International Publication No. 2007/135981 JP-A-11-307379

K. Kobayashi, T. Takano, T. Sagawa, The Institute of Electrical Engineers of Japan, MAG-05-118 (2005) Satoshi Hirosawa, Takeshi Nishiuchi, Tadakatsu Okubo, Li Wangfang, Kazuhiro Hono, Jiro Yamazaki, Masaaki Takezawa, Kanetsu Sumiyama, Samasu Yamamuro, Journal of the Japan Institute of Metals vol. 73 p. 135 (2009)

As described in Patent Document 1, by mixing and heat-treating HDDR magnetic powder and R′-Al-based alloy powder, R′-Al-based alloy diffuses into the R ₂ T ₁₄ B phase grain boundary, Coercivity is improved. However, magnetic powder obtained by diffusing an R′-Al alloy into HDDR magnetic powder has a problem that the squareness of the demagnetization curve is poor.

  Moreover, although the squareness was improved by the method described in Patent Document 2, it was difficult for the obtained magnet to obtain a sufficient coercive force without using Dy.

  As described above, Patent Document 3 describes that HDDR magnetic powder can be used as a raw material powder in an example of molding, sintering, and aging treatment of a raw material powder for an R-T-B system magnet. There is no example of improving the coercive force by directly heat-treating the magnetic powder. When the inventors tried to perform an aging treatment on the HDDR magnetic powder under the same conditions as the sintered magnet, a sufficient coercive force improving effect could not be obtained.

  The subject of this invention is providing the RTB type permanent magnet which has sufficient coercive force and squareness without using Dy.

In the embodiment of the present invention, the R-T-B system permanent magnet has a 50% volume center particle diameter of 1 μm or more and less than 10 μm, and includes an R-T-B system alloy powder containing an R ₂ T ₁₄ B phase. (R is a rare earth element containing 50 atomic% or more of Nd and / or Pr, T is Fe, or Fe and Co), or an R ′ metal (R ′) having a particle size of less than 150 μm with respect to the RTB-based alloy powder Is one or more selected from Nd, Pr, Dy, and Tb) or an R′-M alloy (M is one or more selected from Al, Ga, Co, and Fe, R ′ is the entire R′-M alloy) A step of preparing a mixed powder in which a powder of 20 atomic percent or more and less than 100 atomic percent is mixed, a step of forming a green compact by molding the RTB-based alloy powder or mixed powder, and the green compact. In a hydrogen atmosphere of more than 10 kPa and less than 500 kPa, or hydrogen content A process in which a heat treatment is performed at a temperature of 650 ° C. to 900 ° C. in a mixed atmosphere of hydrogen of 10 kPa to 500 kPa and an inert gas, thereby causing hydrogenation and disproportionation reactions, and a hydrogen atmosphere of 2 kPa to 10 kPa Heat treatment at a temperature of 650 ° C. or higher and 900 ° C. or lower, thereby causing dehydrogenation and recombination reaction, and at a temperature of 650 ° C. or higher and 900 ° C. or lower with respect to the green compact in a vacuum or an inert atmosphere. A porous magnet is obtained by performing a heat treatment and thereby forming a grain boundary phase in the vicinity of the interface of the R ₂ T ₁₄ B phase crystal grains. Further, a densification step is performed to increase the density of the porous magnet to 96% or more of the true density by hot compression molding in a vacuum or an inert gas atmosphere, and then 800 ° C. or higher and 900 ° C. in a vacuum or an inert gas atmosphere. A grain boundary phase homogenization step in which heat treatment is performed at the following temperature is performed.

  In one embodiment, the temperature is raised from 200 ° C. to 600 ° C. in a hydrogen atmosphere in the temperature raising step before the HD step.

In one embodiment, the number density of Nd-rich phases (including an Nd oxide phase) having an area of 0.00006 μm ² or more and 0.785 μm ² or less in a cross section of the RTB-based permanent magnet is 2 / μm ² or more.

  According to the present invention, the conventional HDDR magnetic powder and the magnet powder that has been bulked by hot compression molding exhibit better squareness, and the conventional porous magnet and porous magnet are hot compression molded. Thus, it becomes possible to produce an RTB-based permanent magnet having a higher coercive force than a high-density magnet obtained in this way.

It is a figure which shows the hot press apparatus which can be used suitably by embodiment of this invention. It is the graph which showed the relationship between the heat processing temperature when a heat processing was performed with respect to the RTB type permanent magnet of this invention, and the sintered magnet of the same composition, and a coercive force. In Experimental example 2 of the Example of this invention, it is the figure which showed the relationship between the grain boundary phase homogenization heat processing temperature, and a coercive force. In Experimental example 4 of the Example of this invention, it is the figure which showed the relationship between the grain boundary phase homogenization heat processing temperature, and a coercive force. It is a cross-sectional processing photograph of the high-density magnet in the comparative example 33 of the Example of this invention. It is a cross-sectional processing photograph of the high-density magnet in the comparative example 36 of the Example of this invention. It is a cross-sectional processing photograph of the high-density magnet in the comparative example 40 of the Example of this invention. It is a cross-section processing photograph of the high-density magnet in Example 20 of the Example of this invention.

In the present invention, in a hydrogen atmosphere of more than 10 kPa and 500 kPa or less, or a mixed atmosphere of hydrogen and an inert gas having a hydrogen partial pressure of more than 10 kPa and 500 kPa or less with respect to the green compact obtained by the green compact manufacturing process described later Among them, heat treatment is performed at a temperature of 650 ° C. or more and 900 ° C. or less, thereby causing hydrogenation and disproportionation reactions (HD treatment step). Thereafter, a dehydrogenation reaction and a recombination reaction of the R-T-B system alloy powder to the R ₂ T ₁₄ B phase are performed by a heat treatment at a temperature of 650 ° C. to 900 ° C. in a hydrogen atmosphere of 2 kPa to 10 kPa. Is sufficiently advanced to reduce α-Fe residue (DR treatment step). Thereafter, the green compact is heat-treated at a temperature of 650 ° C. or higher and 900 ° C. or lower in a vacuum or an inert atmosphere, and a dehydrogenation reaction to the R-rich phase is advanced to convert the R-rich phase into R ₂ T ₁₄ B. A porous magnet is obtained by diffusing in the vicinity of the interface of the phase crystal grains to form a grain boundary phase (heat treatment for grain boundary phase formation). Thereafter, the porous magnet is densified to 96% or more of the true density by hot compression molding to obtain a high-density magnet. Then, heat treatment is performed on the high-density magnet at a temperature of 800 ° C. or higher and 900 ° C. or lower in a vacuum or in an inert atmosphere, and the R-rich phase segregated in the magnet is mainly diffused to the grain boundaries to make the distribution uniform. (Granular boundary phase homogenization).

  Hereinafter, a desirable embodiment is described in detail about the above-mentioned manufacturing process in the manufacturing method of the RTB system permanent magnet of the present invention.

<Green compact production process>
An R-T-B alloy powder is molded to produce a green compact. The R′-T-B alloy powder described later includes an R ′ metal (R ′ is one or more selected from Nd, Pr, Dy, Tb) or an R′-M alloy (M is Al, Ga, Co, Fe). A green compact may be produced by molding a mixed powder in which powders of one or more selected, R ′ is 20 atom% or more and 100 atom% or less of the entire R′-M alloy, are mixed in advance. The step of molding the green compact is desirably performed in a magnetic field (such as a static magnetic field or a pulsed magnetic field) of 0.4 MA / m to 16 MA / m by applying a pressure of 10 MPa to 200 MPa. Molding can be performed by a known powder press apparatus. Compact density (compact density) when removed from the powder press device ^is 3.5g / cm ³ ~5.2g / cm 3 order.

  You may perform said shaping | molding process, without applying a magnetic field. When magnetic field orientation is not performed, an isotropic porous magnet is finally obtained. However, in order to obtain higher magnetic characteristics, it is desirable to execute a molding process while performing magnetic field orientation and finally obtain an anisotropic porous magnet.

  Inside the green compact, gaps in which hydrogen gas can move and diffuse in the HDDR process to be performed later exist with a sufficient size between the powder particles. Moreover, in this invention, since the raw material powder whose 50% volume center particle size is 1 micrometer or more and less than 10 micrometers is used, it is easy for hydrogen to move the whole in a powder particle. Therefore, the HD reaction and DR reaction in the HDDR process can be advanced in a short time. Thus, since the structure after the HDDR process is homogenized, there are obtained advantages that high magnetic properties, particularly good squareness can be obtained, and the time required for the HDDR process can be shortened.

<HDDR processing>
Next, the HDDR process is performed on the green compact obtained by the green compact manufacturing step. In the present embodiment, the HDDR process includes four steps: a temperature raising step, an HD treatment step, a DR treatment step, and a grain boundary phase formation heat treatment step.

(Temperature raising process)
The temperature raising step is a step of heating the green compact to the processing temperature of the HD processing step with respect to the green compact obtained in the green compact manufacturing step. The temperature raising step is performed in a hydrogen gas atmosphere having a hydrogen partial pressure of 10 kPa or more and 500 kPa or less, or a mixed atmosphere of hydrogen gas and an inert gas (Ar, He, etc.), an inert gas atmosphere, or in a vacuum. In order to prevent the HD reaction of the RTB-based alloy powder from proceeding at a low temperature during the temperature rise and lowering the degree of orientation, the temperature of the green compact is increased to 600 ° C. in an atmosphere containing hydrogen. Then, after 600 ° C., the temperature may be raised in an inert gas atmosphere or in a vacuum.

(HD processing process)
The HD processing step to be performed next is a step of obtaining a disproportionated structure by performing an HD reaction of the R ₂ T ₁₄ B phase in a hydrogen atmosphere. At this time, the magnetic anisotropy of the finally obtained magnet can be increased by appropriately controlling the temperature and the hydrogen partial pressure in the HD processing step. The temperature of the HD processing step is 650 ° C. or higher and 900 ° C. or lower. If it is less than 650 degreeC, it will take time for disproportionation to fully advance. If the temperature exceeds 900 ° C., the disproportionated structure becomes coarse, and the texture of the R ₂ T ₁₄ B phase obtained by the subsequent DR treatment step becomes coarse, resulting in a decrease in magnetic properties, particularly coercive force. In particular, from the viewpoint of suppressing grain growth, it is more desirable to set the temperature of the HD processing step to 900 ° C. or lower.

The hydrogen partial pressure in the HD treatment process is more than 10 kPa and 500 kPa or less. If the hydrogen partial pressure is less than 10 kPa, it takes too much time for the disproportionation of the R ₂ T ₁₄ B phase to proceed sufficiently, which may lead to a decrease in productivity. The lower limit of the hydrogen partial pressure is desirably 20 kPa. Further, when the hydrogen partial pressure exceeds 500 kPa, a special apparatus may be required for the treatment. The upper limit of the hydrogen partial pressure is desirably 150 kPa or less. When the hydrogen partial pressure exceeds 150 kPa, hydrogen occlusion occurs abruptly, and the green compact may crack due to volume expansion accompanying hydrogen occlusion.

The time required for the HD processing step is preferably 10 minutes or more and 5 hours or less. If it is less than 10 minutes, the disproportionation of the R ₂ T ₁₄ B phase may not proceed sufficiently. Further, when the time exceeds 5 hours, the disproportionated structure becomes coarse, and thus the recombination structure after the DR treatment process becomes coarse, which may cause a decrease in magnetic properties, particularly coercive force. More desirably, it is 15 minutes or more and 2 hours or less.

(DR treatment process)
Next, the DR treatment step to be performed is a heat treatment at a temperature of 650 ° C. or more and 900 ° C. or less in a hydrogen atmosphere of 2 kPa or more and 10 kPa or less, causing dehydrogenation and recombination reaction of the R—T—B system alloy powder, and R ₂ T ₁₄ Generate phase B by recombination reaction. In order to obtain a high coercive force, 3 kPa or more and 8 kPa or less are more preferable.

Suppresses dehydrogenation reaction from R-hydride to R-rich phase of R-TB alloy powder by changing DR treatment atmosphere from conventional vacuum and inert gas atmosphere to hydrogen atmosphere of 2 kPa to 10 kPa However, by sufficiently proceeding only with the dehydrogenation reaction and the recombination reaction into the R ₂ T ₁₄ B phase, it is possible to reduce the residue of the α-Fe phase existing in the conventional treatment. The remaining R hydride undergoes a dehydrogenation reaction in the subsequent grain boundary phase forming heat treatment step, and diffuses the R-rich phase into the grain boundaries of the R ₂ T ₁₄ B phase crystal grains.

  A hydrogen atmosphere of 2 kPa or more and 10 kPa or less can be realized by, for example, evacuating the inside of the heat treatment apparatus while controlling the exhaust speed by a vacuum pump or the like and balancing with hydrogen generated by dehydrogenating the green compact after the HD treatment process. .

The temperature of the DR treatment process is 650 ° C. or higher and 900 ° C. or lower. If it is less than 650 degreeC, dehydrogenation reaction does not occur substantially. In addition, when the temperature exceeds 900 ° C., the recombined R ₂ T ₁₄ B phase grows as crystal grains, leading to a decrease in magnetic properties, particularly coercive force. Further, the time required for the DR treatment step is about 15 minutes, and the recombination reaction of the R ₂ T ₁₄ B phase is completed. Therefore, 15 minutes or more is desirable. By treating for 30 minutes or more, the effect of further improving the coercive force is obtained. It is more desirable because it can. On the other hand, if the treatment is performed for a long time, it leads to an increase in production cost, and thus it is preferably 10 hours or less, and more preferably 3 hours or less.

The R ₂ T ₁₄ B phase generated in the DR treatment step typically forms a texture having an average crystal grain size of 0.1 μm or more and 1.0 μm or less.

  Further, the hydrogen in the heat treatment apparatus may be replaced by flowing an inert gas between the HD treatment process and the DR treatment process for about several minutes. As a result, a large amount of hydrogen does not flow into the pump when the heat treatment apparatus is evacuated by the vacuum pump in the DR treatment process, and the treatment can be performed safely.

(Grain boundary phase formation heat treatment process)
Next, the grain boundary phase forming heat treatment step is carried out by holding at 650 ° C. or more and 900 ° C. or less in a vacuum or an inert atmosphere, so that an R hydride or R′-M alloy contained in the RTB-based alloy powder. A dehydrogenation reaction of the powder occurs, a liquid phase rich in R is generated, and a grain boundary phase (rare earth-rich phase) is formed at the crystal grain boundary of the R ₂ T ₁₄ B phase to develop a coercive force. Furthermore, a sintering reaction also occurs at the same time, resulting in a porous permanent magnet.

  When the green compact is formed by mixing the R′-M alloy powder, the grain boundary phase (rare earth rich phase) is formed more uniformly than when the R′-M alloy powder is not mixed. Therefore, a high coercive force can be obtained.

The atmosphere of the grain boundary phase forming heat treatment step is preferably a reduced pressure atmosphere by evacuating while introducing an inert gas in order to suppress oxidation during the treatment from the viewpoint of coercive force. The temperature in the grain boundary phase forming heat treatment step is 650 ° C. or higher and 900 ° C. or lower. If it is less than 650 degreeC, dehydrogenation reaction does not occur substantially. On the other hand, if the temperature exceeds 900 ° C., the R ₂ T ₁₄ B phase grows and the magnetic properties, particularly the coercive force, are reduced. The time required for the grain boundary phase forming heat treatment step is preferably 5 minutes or more and 10 hours or less, and more preferably 10 minutes or more and 1 hour or less.

<Porous magnet>
By the HDDR treatment, a porous magnet having a density of 3.5 g / cm ³ or more and 7.0 g / cm ³ or less is obtained. In this porous magnet, there is a void having a major axis of about 10 μm communicating with the three-dimensional network between the powder particles bonded to each other in the HDDR processing step. The individual powder particles constituting the green compact are combined with adjacent powder particles by the HDDR process to form a three-dimensional structure exhibiting rigidity, and fine Nd ₂ Fe ₁₄ B in each powder particle. A texture of the type crystal phase is formed. The density of the R-T-B type porous magnet of the present invention is 3.5 g / cm ³ or more and 7.0 g / cm ³ or less, but the particles are bonded to each other even when there are gaps between the powder particles. Demonstrate sufficient mechanical strength and excellent magnetic properties.

<Hot compression molding of porous magnet>
The porous magnet obtained by the above method is densified by hot compression molding such as hot pressing, and has a texture of R ₂ T ₁₄ B phase with an average crystal grain size of 0.1 μm to 1 μm. Get a high density magnet. An example of a specific embodiment will be shown below for densification by hot compression molding. Hot compression on the porous magnet can be performed using a known hot compression technique. For example, hot compression molding such as hot pressing, SPS (spark plasma sintering), HIP, and hot rolling can be performed. Especially, the hot press and SPS which are easy to obtain a desired shape can be used suitably. Hereinafter, a procedure for performing hot pressing will be described.

  In the present embodiment, a hot press apparatus having the configuration shown in FIG. 1 is used. This apparatus includes a die (die) 27 having an opening in the center, an upper punch 28a and a lower punch 28b for pressurizing a porous magnet, and drive units 30a and 30b for raising and lowering these punches 28a and 28b. I have.

  A porous magnet (indicated by reference numeral “10” in FIG. 1) produced by the method described above is loaded into the mold 27 shown in FIG. At this time, it is desirable to perform loading so that the orientation direction and the pressing direction coincide. The mold 27 and the punches 28a and 28b are formed of a material that can withstand the heating temperature and the applied pressure in the atmosphere gas to be used. As such a material, carbon or cemented carbide such as tungsten carbide is desirable. In addition, the anisotropy can be increased by setting the outer dimension of the porous magnet 10 to be smaller than the opening dimension of the mold 27. Next, the mold 27 loaded with the porous magnet 10 is set in a hot press apparatus. The hot press apparatus preferably includes a chamber 26 that can be controlled to a vacuum (1.3 Pa or less) or an inert atmosphere. In the chamber 26, for example, a heating device such as a carbon heater by resistance heating and a cylinder for pressurizing and compressing the porous magnet are provided.

  After filling the chamber 26 with a vacuum or an inert gas atmosphere, the mold 27 is heated by a heating device, and the temperature of the porous magnet 10 loaded in the mold 27 is increased to 600 ° C. to 900 ° C., 9.8 The porous magnet 10 is pressurized with a pressure P of ˜294 MPa. It is desirable that the pressurization to the porous magnet 10 is started after the temperature of the mold 27 reaches a set level. If the mold temperature is not sufficiently high, the porous magnet may be cracked during pressurization, or the degree of orientation of the resulting high-density magnet may deteriorate. While maintaining the pressure at 600 ° C. to 900 ° C. for 10 minutes or more while cooling, it is cooled. After the magnet, which has been densified by heat compression, is cooled to a low temperature (about 100 ° C. or less) that does not oxidize due to contact with the atmosphere, the magnet of this embodiment is taken out of the chamber. Thus, an RTB-based high density magnet can be obtained from the above porous magnet.

  The density of the obtained magnet reaches 96% or more of the true density. In addition, according to the present embodiment, in the final crystal phase texture, the crystal grains in which the ratio b / a of the shortest particle diameter a to the longest particle diameter b of each crystal grain is less than 2 are 50 of the total crystal grains. It exists by volume% or more. In this respect, the magnet of the present embodiment is greatly different from the conventional anisotropic bulk magnet by hot plastic working described in, for example, Japanese Patent Laid-Open No. 02-39503. In such a crystal structure of a magnet, flat crystal grains in which the ratio b / a between the shortest particle diameter a and the longest particle diameter b exceeds 2 are dominant.

<Granular boundary phase homogenization heat treatment process of high-density magnet>
A grain boundary phase homogenization process is performed with respect to the high-density magnet obtained by hot compression molding. Specifically, heat treatment is performed at a temperature of 800 ° C. or more and 900 ° C. or less in a vacuum or an inert gas (Ar, He, etc.) atmosphere, and the R-rich phase segregated in the high-density magnet is diffused to the grain boundaries. Homogenize the distribution. The time required for the heat treatment is preferably 5 minutes or more and 5 hours or less, more preferably 10 minutes or more and 1 hour or less.

  Hereinafter, the effect of the grain boundary phase homogenization heat treatment process in the high-density magnet of the present invention will be described by comparing with the heat treatment for the sintered magnet.

FIG. 2 shows the relationship between the heat treatment temperature and the coercive force when heat treatment is performed at a temperature of 450 ° C. to 950 ° C. for a high-density magnet in the embodiment of the present invention and a sintered magnet of the same composition as a comparison. It is the shown graph. As shown in FIG. 2, the coercive force of the high-density magnet of the present invention, in which the hydrogen partial pressure is controlled in the DR treatment step and heat treatment is performed at a reduced Ar pressure (grain boundary phase formation heat treatment) and then densified by hot compression molding. When (H _cJ ) is heat-treated at 450 ° C. to 950 ° C. (grain boundary phase homogenization heat treatment), it takes a maximum value in the vicinity of 450 ° C. to 550 ° C., and is slightly improved compared to before heat treatment. Since this phenomenon occurs in the vicinity of the same temperature even in sintered magnets having the same composition, it is considered that this phenomenon is similar to the aging treatment generally performed in sintered magnets. Thereafter, the coercive force (H _cJ ) takes a minimum value in the vicinity of 700 ° C., then increases again from 800 ° C., and takes a maximum value in the vicinity of 900 ° C. The coercive force (H _cJ ) obtained at this time is nearly 200 kA / m higher than that of a sintered magnet having the same composition, and it can be seen that a high coercive force can be obtained without using Dy. This phenomenon in which the coercive force (H _cJ ) is improved at a temperature of 800 ° C. to 900 ° C. is a phenomenon that cannot be seen with a sintered magnet having the same composition, and can only be seen with a high-density magnet obtained by the production method of the present invention. It is a phenomenon.

<Additional heat treatment process>
You may perform an additional heat processing process with respect to the high-density magnet which performed the grain boundary phase homogenization process. Specifically, heat treatment is performed at a temperature of 450 ° C. or higher and 650 ° C. or lower in a vacuum or an inert gas (Ar, He, or the like) atmosphere. The time required for the heat treatment is preferably 5 minutes or more and 5 hours or less, more preferably 10 minutes or more and 1 hour or less.

  Hereinafter, in the manufacturing method of the RTB-based permanent magnet according to the present invention, the RTB-based alloy powder and the RTB-based alloy powder are mixed with the R ′ metal or R′-M-based alloy powder. Preferred embodiments of the powder will be described in detail.

<R-T-B alloy>
First, an R—T—B system alloy including an R ₂ T ₁₄ B phase, which is a hard magnetic phase, and a rare earth-rich phase as a main phase is prepared. Here, “R” is a rare earth element and contains Nd and / or Pr by 50 atomic% or more. The rare earth element R in this specification may contain yttrium (Y). T is Fe or Fe and Co. This R-T-B alloy preferably contains 50% or more of the R ₂ T ₁₄ B phase by volume. Most of the rare earth element R contained in the raw material alloy constitutes the R ₂ T ₁₄ B phase and the rare earth rich phase, but a part constitutes R ₂ O ₃ and other phases.

The composition ratio of the rare earth element R is preferably 10 atomic percent or more and 30 atomic percent or less, and more preferably 12 atomic percent or more and 17 atomic percent or less of the entire raw material alloy. In the case of mixing an R′-M-based alloy, which will be described later, a rare earth-rich phase mass of 1 μm or more can be reduced in the structure after HDDR treatment when the content is 12 atomic% or more and 14 atomic% or less. Moreover, the grain growth of the R ₂ T ₁₄ B phase during HDDR treatment can be suppressed, and at the same time, the constituent ratio of the R ₂ T ₁₄ B phase can be increased. As a result, improvement in the squareness of _HcJ and the demagnetization curve can be expected. Furthermore, it is possible to improve the magnetization when hot compression molding is performed. In addition, since it is a rare element, it should be avoided to use a large amount, but the coercive force can be improved by using a part of R as Dy and / or Tb.

  The composition ratio of B is preferably 3 atomic percent or more and 15 atomic percent or less, more preferably 5 atomic percent or more and 8 atomic percent or less, and further preferably 5.5 atomic percent or more and 7.5 atomic percent or less. A part of B may be substituted with C, but the amount of substitution is preferably 10 atomic% or less with respect to the amount of B before substitution.

  “T” occupies the remainder and is Fe or Co substituted for Fe and part of Fe. The amount of substitution is desirably 50 atomic% or less with respect to the total amount of T. Further, the total amount of Co with respect to the entire raw material alloy is preferably 20 atomic% or less, and more preferably 5 atomic% or less from the viewpoint of cost and the like. High magnetic properties can be obtained even when Co is not contained at all, but more stable magnetic properties can be obtained when Co of 0.5 atomic% or more is contained.

  In order to obtain effects such as improvement of magnetic characteristics, elements such as Al, Ti, V, Cr, Ga, Nb, Mo, In, Sn, Hf, Ta, W, Cu, Si, Zr, and Ni may be added as appropriate. Good. However, since an increase in the amount of addition causes a decrease in saturation magnetization in particular, the total amount is preferably 10 atomic% or less. The raw material alloy may contain inevitable impurities.

  The R-T-B alloy is preferably produced by a strip casting method that can reduce the amount of α-Fe phase that adversely affects the magnetic properties. However, the book casting method, centrifugal casting method, atomizing method, etc. Can also be made. For the purpose of homogenizing the structure of the raw material alloy, heat treatment may be performed on the raw material alloy before pulverization. Such heat treatment can be performed in a vacuum or inert gas atmosphere, typically at a temperature of 1000 ° C. or higher.

<R-T-B alloy powder>
When the obtained RTB-based alloy is not mixed with an R′-M-based alloy described later, it is coarsely pulverized using a mechanical pulverization method such as a jaw crusher or a hydrogen occlusion pulverization method. A roughly pulverized powder of about 1000 μm is prepared. The coarsely pulverized powder is finely pulverized by a jet mill or the like to produce an RTB-based alloy powder having a 50% volume center particle size of 1 μm or more and less than 10 μm.

The 50% volume center particle size (D ₅₀ ) can be measured by a gas flow dispersion type laser diffraction method. When the 50% volume center particle size is at a level where it can be clearly confirmed that it is within the desired range, the particle size of the arbitrarily extracted powder may be easily confirmed by observation with an electron microscope.

<R 'metal or R'-M alloy (diffusion material)>
An R ′ metal or an R′-M alloy is prepared. Here, “R ′” is a rare earth element, and is at least one rare earth element selected from the group consisting of Nd, Pr, Dy, and Tb. “M” is at least one element selected from the group consisting of Al, Ga, Co, and Fe. The R′-M alloy is decomposed into R ′ hydride (R′H _x ) and R′-M compounds (R′M, R′M _2, etc.) in the hydrogen storage treatment described later. It is desirable to select “M” so that the melting point of the R′-M compound sometimes generated is higher than the heat treatment temperature of HD treatment described later. The diffusing material may contain inevitable impurities.

  The composition ratio of the rare earth element R ′ in the R′-M alloy is 20 atomic% or more and less than 100 atomic%, preferably 25 atomic% or more and less than 100 atomic%, and 40 atomic% or more and 98 atomic% or less. It is more desirable that it is 60 atomic% or more and 90 atomic% or less.

  The R ′ metal or the R′-M alloy can be produced by a known method such as a book mold method, a centrifugal casting method, an atomizing method, a strip casting method, or a liquid superquenching method.

  Furthermore, the R′-M alloy produced by these methods should store hydrogen at a temperature of 900 ° C. or less in a hydrogen atmosphere of 10 kPa or more or in a mixed atmosphere of hydrogen and inert gas having a hydrogen partial pressure of 10 kPa or more. Thus, diffusion of the R′-M alloy to the RTB alloy powder in the temperature raising step of the HDDR process can be suppressed. By this hydrogen storage treatment, the R′-M alloy is decomposed into a hydride of R ′ and an R′-M compound. Since the melting point of the hydride of R ′ is higher than the processing temperature in the HD processing step, the diffusion of the R′-M alloy into the RTB-based alloy powder can be suppressed.

  In addition, in the temperature rising step of the HDDR process described above, the temperature is increased to 600 ° C. in an atmosphere containing hydrogen to hydrogenate the green compact, and then the temperature of 600 ° C. or higher is in an inert gas atmosphere or in a vacuum. Similarly, by increasing the temperature, it is possible to suppress diffusion of the R′-M alloy during the temperature increase into the RTB-based alloy powder.

<Mixed powder>
When mixing the R′-M alloy, a mixed powder is prepared in advance by mixing the RTB alloy and the R′-M alloy. At that time, the RTB-based alloy and the R′-M-based alloy may be separately pulverized and mixed, or the mixture of the RTB-based alloy and the R′-M-based alloy may be pulverized. .

  When the R-T-B type alloy and the R′-M-type alloy are separately pulverized, the R-T-B type alloy is first roughened using a mechanical crushing method such as a jaw crusher or a hydrogen occlusion crushing method. Crushing to produce coarsely pulverized powder having a size of about 50 μm to 1000 μm. The coarsely pulverized powder is finely pulverized by a jet mill or the like to produce an RTB-based alloy powder having a 50% volume center particle size of 1 μm or more and less than 10 μm.

  On the other hand, the R′-M alloy is coarsely pulverized using a mechanical pulverization method, a hydrogen occlusion pulverization method, or the like to produce an R′-M alloy powder having a size of less than 150 μm, for example. When the diffusing material is pulverized, a solid lubricant and / or a liquid lubricant may be added for the purpose of improving the pulverization property. The size of the R′-M type alloy powder may be classified by using the sieve specified in JIS Z 8801-1 by the method described in JIS Z 2510 and adjusted to a desired particle size range. The 50% volume center particle size of the system alloy powder is also determined by measuring by an air flow dispersion type laser diffraction method or confirmed by an electron microscope.

  The produced RTB-based alloy powder and R′-M-based alloy powder are mixed by a known powder mixing method to obtain a mixed powder.

  From the viewpoint of handling, it is desirable that the 50% volume center particle size of the RTB-based alloy powder and the R′-M-based alloy powder is 1 μm or more, respectively. This is because when the 50% volume center particle size is less than 1 μm, the mixed powder easily reacts with oxygen in the air atmosphere, increasing the risk of heat generation and ignition due to oxidation. In order to make the handling easier, it is desirable to set the 50% volume center particle size to 3 μm or more. The 50% volume center particle size of the diffusing material powder is preferably 10 μm or more from the viewpoint of suppressing oxidation. From the viewpoint of improving the mechanical strength of the molded body, the desirable upper limit of the 50% volume center particle size of the RTB-based alloy powder is 9 μm, and the more desirable upper limit is 8 μm. Further, from the viewpoint of uniformity of the HDDR reaction, the particle diameter of the R′-M alloy powder is less than 150 μm.

  By grinding the RTB-based alloy and the R′-M-based alloy separately, the 50% volume center particle size of the RTB-based alloy powder is 1 μm or more and less than 10 μm. The 50% volume center particle diameter of the R′-M alloy powder, which easily reacts with oxygen, can be suppressed.

  In the case of pulverizing a mixture of an R-T-B type alloy and an R′-M-type alloy, the mixture of the R-T-B type alloy and the R′-M type alloy is first mechanically pulverized by a jaw crusher or the like. A coarsely pulverized powder having a size of about 50 μm to 1000 μm is prepared by coarsely pulverizing using a method or a hydrogen storage and pulverization method. The coarsely pulverized powder is finely pulverized by a jet mill or the like to produce a mixed powder having a 50% volume center particle size of 1 μm or more and less than 10 μm. The RTB-based alloy and the R′-M-based alloy may be mixed as coarsely pulverized powder having a size of about 50 μm to 1000 μm, respectively, and the mixed coarsely pulverized powder may be finely pulverized.

  When the 50% volume center particle size of the mixed powder is less than 1 μm, the mixed powder easily reacts with oxygen in the air atmosphere, increasing the risk of heat generation and ignition due to oxidation. In order to make the handling easier, it is desirable to set the 50% volume center particle size to 3 μm or more. From the viewpoint of improving the mechanical strength of the green compact, a desirable upper limit of 50% volume center particle size is 9 μm, and a more desirable upper limit is 8 μm.

  By pulverizing the mixture of the RTB-based alloy and the R′-M-based alloy, a mixed powder in which the RTB-based alloy and the diffusion material are uniformly mixed can be easily produced.

The mixing ratio of the R-T-B type alloy and the R′-M-type alloy is (R-T-B type alloy) :( diffusion material) = m: 1 (5 ≦ m ≦ 100) in weight ratio. Is desirable. When m is less than 5, the ratio of the R′-M alloy is excessively increased, which causes a decrease in the volume ratio of the main phase R ₂ T ₁₄ B phase, resulting in a decrease in residual magnetic flux density. there is a possibility. On the other hand, if m exceeds 100, the effect of adding the R′-M alloy may be hardly obtained.

  The total amount of rare earth elements R and R ′ in the mixed powder is preferably 10 atomic percent or more and 30 atomic percent or less, and more preferably 12 atomic percent or more and 17 atomic percent or less of the entire mixed powder. In addition, the total amount of rare earth elements R and R ′ in the mixed powder is more preferably 15 atomic% or less of the entire mixed powder because it is easy to remove from the mold after hot pressing.

  The green compact molding step and the RTB-based alloy or R′-M-based alloy pulverizing step suppress the oxidation of the RTB-based alloy powder or the R′-M-based alloy powder. It is desirable to do. In order to suppress the oxidation of the RTB-based alloy powder or the R′-M-based alloy powder, it is desirable that each process and handling between the processes be performed in an inert atmosphere in which the amount of oxygen is suppressed as much as possible. The amount of oxygen in the green compact before the DR treatment is preferably suppressed to 1% by mass or less, and more preferably to 0.6% by mass or less.

The RTB-based permanent magnet of the present invention can evaluate the dispersion state of the Nd-rich phase characteristic in the structure by the following method. The magnet is cut with a cross section polisher (for example, device name: SM-09010, manufactured by JEOL), and the reflected electron image of the processed cross section is used with FE-SEM (for example, device name: JSM-7001F, manufactured by JEOL). Shoot at a magnification of 5000 times. In the reflected electron image, the contrast of the Nd ₂ Fe ₁₄ B phase that is the main phase is dark, and the Nd-rich phase (including the Nd oxide phase) that is the grain boundary phase is displayed brightly. Image editing software (for example, product name: Photoshop Elements) from the area of 24 μm × 18 μm (actual size) to the Nd-rich phase 3 point using the captured 5000 × image.
9 and manufactured by Adobe Systems). Further, the number density and the total area of the Nd-rich phase triple point are measured by image analysis software (for example, product name: WinROOF, manufactured by Mitani Corporation). At that time, the Nd-rich phase of less than 0.00006 μm ^{2 and} the Nd-rich phase of more than 0.785 μm ² are considered to hardly contribute to the improvement of the coercive force, and are excluded. The R-T-B-based permanent magnet of the present invention is to present number density of Nd-rich phase having an area of 0.00006Myuemu ² more 0.785Myuemu ² or less 2 / [mu] m ² or more by the above method Is evaluated as a feature.

  An RTB-based alloy having the composition shown in Table 1 below was prepared, and a high-density magnet was manufactured by the manufacturing method of the above-described embodiment. Hereinafter, a method for producing a high-density magnet in this experimental example will be described.

(Experimental example 1)
First, an RTB-based alloy having the composition of B1 in Table 1 was produced by a strip cast method. The obtained alloy was coarsely pulverized into a powder having a particle size of 425 μm or less by the hydrogen storage / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain an RTB system having a 50% volume center particle size of 4.2 μm. An alloy powder was obtained. The 50% volume center particle size was measured by a laser diffraction particle size distribution measuring device (manufactured by Sympatec, HEROS / RODOS, hereinafter all measured by the same device).
Next, the R-T-B system alloy powder was filled in a die of a press machine, and a pressure of 32 MPa was applied in a direction perpendicular to the magnetic field in a magnetic field of 1.2 MA / m to produce a green compact. The density of the green compact was 4.2 g / cm ³ when calculated based on dimensions and weight.

Next, HDDR processing was performed on the green compact. The green compact was heated to 860 ° C. at a heating rate of 14 ° C./min in a 100 kPa argon flow, and then the atmosphere was switched to a hydrogen flow of 100 kPa, and then kept at 860 ° C. for 120 minutes for HD processing. The process was performed. Then, while maintaining at 860 ° C., the atmosphere was switched to Ar and maintained for 2 minutes to replace the atmosphere in the heat treatment apparatus. Next, the Ar gas is stopped and the inside of the heat treatment apparatus is evacuated with a vacuum pump, and the hydrogen pressure generated in the green compact is adjusted to maintain the hydrogen pressure in the heat treatment apparatus at 4.0 kPa and held for 60 minutes. Processing steps were performed. Subsequently, it hold | maintained for 10 minutes in the argon air pressure-reduced to 5.3 kPa with 860 degreeC, and the grain boundary phase formation heat treatment process was performed. Then, it cooled to room temperature in 100 kPa argon flow, and the porous magnet was obtained. When the density was calculated from the size and weight of the produced porous magnet, it was 5.55 g / cm ³ .

Further, the porous magnet was heated to 800 ° C. in a cemented carbide mold and subjected to hot compression treatment (hot pressing) at a pressure of 50 MPa for 20 minutes, whereby a high density of 7.52 g / cm ^{3 was} achieved. A magnet was obtained. After magnetizing the produced high-density magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 2 (Comparative Example 1).

Further subjected to grain boundary phase homogenization heat treatment step of 60min at 700 ° C. to 950 ° C. at ¹⁰ -2 Pa in a vacuum of high-density magnets, and cooled to room temperature in vacuo. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 2. As shown in Table 2, the coercive force decreased when the heat treatment was performed at 700 ° C. and 950 ° C. (Comparative Example 2 and Comparative Example 3) with respect to the magnet not subjected to heat treatment (Comparative Example 1). When the heat treatment was performed at ˜900 ° C. (Examples 1 to 3), the coercive force was improved.

(Experimental example 2)
The temperature up to the HD treatment step was raised to 600 (° C.) at a rate of 14 ° C./min in a 100 kPa hydrogen stream, and then the atmosphere was switched to a 100 kPa argon stream, followed by 860 ° C. A porous magnet A (heat treatment step of the present invention) was produced in the same manner as in Experimental Example 1 except that the temperature was increased at a temperature increase rate of 14 ° C./min. In addition, after the HD treatment step, after switching to Ar flow and holding for 2 minutes to replace the atmosphere in the heat treatment apparatus, the flow is kept at 860 ° C. in an argon flow reduced to 5.3 kPa for 60 minutes. A porous magnet B (conventional DR processing step) was produced in the same manner as the porous magnet A except that the DR treatment step was performed and the grain boundary phase formation heat treatment step was not performed. When the density was calculated from the size and weight of the produced porous magnet, the porous magnet A was 5.77 g / cm ³ and the porous magnet B was 5.85 g / cm ³ , respectively.

Further, the porous magnet A was heated to 800 ° C. in a cemented carbide mold and subjected to hot compression treatment (hot pressing) at a pressure of 50 MPa for 20 minutes. A high density magnet of 7.51 g / cm ³ was obtained from cm ³ and porous magnet B. After magnetizing the produced high-density magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 3 (Comparative Example 4) and Table 4 (Comparative Example 10).

Further, the high-density magnet was heat-treated at 450 ° C. to 950 ° C. for 60 minutes in a vacuum of 10 ⁻² Pa or less, and cooled to room temperature in vacuum. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results for porous magnet A are shown in Table 3. Table 4 shows the result of the porous magnet B. Furthermore, the figure which showed the relationship between the grain boundary phase homogenization heat processing temperature of the porous magnet A and the porous magnet B, and a coercive force ( _HcJ ) is shown in FIG. As shown in Table 3, Table 4, and FIG. 3, the hydrogen partial pressure was controlled in the DR treatment step and heat treatment was performed at Ar reduced pressure (grain boundary phase formation heat treatment), and then the density was increased by hot compression molding. The coercive force (H _cJ ) of the high-density magnet takes a maximum value at least between 450 ° C. and 550 ° C. when heat-treated at 450 ° C. to 950 ° C. (grain boundary phase homogenization heat treatment), and is slightly improved compared to before heat treatment. To do. This phenomenon is similar to the heat treatment (so-called aging treatment) for improving the coercive force generally performed in the RTB-based sintered magnet as described later in Experimental Example 5 because the temperature range is substantially the same. It is considered a phenomenon. At higher temperatures, the coercive force (H _cJ ) takes a minimum value around 700 ° C., then increases again from 800 ° C., and _{reaches a} maximum value around 900 ° C. This phenomenon is a phenomenon that is not seen in a high-density magnet obtained from the porous magnet B produced by the conventional DR treatment process or an RTB-based sintered magnet as will be described later in Experimental Example 5. This is a phenomenon that can be seen only in the high-density magnet obtained by the manufacturing method of the invention.

Further, the high-density magnets of Examples 4 to 6 in Table 3 were subjected to additional heat treatment at 500 ° C. for 60 minutes in a vacuum of 10 ⁻² Pa or less, and cooled to room temperature in vacuum. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 5. As shown in Table 5, it can be seen that the coercive force is further improved by the additional heat treatment at 500 ° C.

(Experimental example 3)
A porous magnet was produced in the same manner as in Experimental Example 2, except that the temperatures of the HD treatment process and DR treatment process were changed to 820 ° C., 840 ° C., and 880 ° C. When the density is calculated from the size and weight of the produced porous magnet, the sample at 820 ° C. is 5.26 g / cm ³ , the sample at 840 ° C. is 5.48 g / cm ³ , and the sample at 840 ° C. is 5.92 g / cm ³ . ³ .

Furthermore, the porous magnet was heated to 800 ° C. in a cemented carbide mold and subjected to a hot compression treatment (hot press) for 20 minutes at a pressure of 50 MPa, so that 7.51 g / cm from any sample. ³ high density magnets were obtained. After magnetizing the produced high-density magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 6 (Comparative Examples 17 to 19).

Further, the high-density magnet was heat-treated at 900 ° C. for 60 minutes in a vacuum of 10 ⁻² Pa or less, and cooled to room temperature in vacuum. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 6 (Examples 10 to 12). Table 6 also shows the results of Comparative Example 4 and Example 6 for comparison. As shown in Table 6, it can be seen that the coercive force is greatly improved by the grain boundary phase homogenization heat treatment regardless of the temperature of the HD treatment process and the DR treatment process.

(Experimental example 4)
An RTB-based alloy having a composition of B2 to B6 shown in Table 1 was produced by strip casting. The obtained alloy was coarsely pulverized into a powder having a particle size of 425 μm or less by the hydrogen storage / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain an RTB system having a 50% volume center particle size of 4.2 μm. An alloy powder was obtained.

Further, an alloy having a composition (atomic%) of Nd ₇₀ Al ₃₀ was produced by a melt spinning method. Specifically, the alloy was melted and sprayed from a quartz nozzle having an orifice diameter of 0.8 mmφ onto a copper roll rotating at a roll peripheral speed of 20 m / s to obtain a ribbon-like alloy. These alloys are heated to 400 ° C. in a hydrogen gas stream, occluded with hydrogen, pulverized by mechanical pulverization, classified using a mesh having an opening of 53 μm, and an Nd—Al alloy having a size of 53 μm or less. A powder was obtained. In addition, it confirmed by observation with an electron microscope that the particle size of the obtained diffusing material powder was clearly 1 μm or more. The obtained RTB-based alloy powder and Nd-Al alloy powder were mixed using an agate mortar at a mixing ratio of RTB-based alloy powder: Nd-Al alloy powder = 14: 1 (weight ratio). As a result, a mixed powder was obtained.

Next, the mixed powder was filled in a die of a press machine, and a green compact was produced by applying a pressure of 32 MPa in a direction perpendicular to the magnetic field in a magnetic field of 1.2 MA / m. The density of the green compact was 4.3 g / cm ³ when calculated based on dimensions and weight.

Next, the green compact was subjected to HDDR treatment by the same method as in Experimental Example 2 to obtain a porous magnet. When the density was calculated from the size and weight of the produced porous magnet, it was 5.84 g / cm ³ .

Furthermore, the density of 7.52 g / cm ³ (B2) is obtained by heating the porous magnet in a cemented carbide alloy mold to 800 ° C. and performing a hot compression treatment (hot pressing) for 20 minutes at a pressure of 50 MPa. 7.51 g / cm ³ (B3), density 7.46 g / cm ³ (B4), 7.48 g / cm ³ (B5), and density 7.49 g / cm ³ (B6). After magnetizing the produced high-density magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 7 (Comparative Example 20, Comparative Example 33, Comparative Examples 46 to 48).

Further, the high-density magnet was heat-treated at 450 ° C. to 950 ° C. for 60 minutes in a vacuum of 10 ⁻² Pa or less, and cooled to room temperature in vacuum. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 7. FIG. 4 shows the relationship between the grain boundary phase homogenization heat treatment temperature and the coercive force (H _cJ ) of the sample using the B2 alloy. As shown in Table 7 and FIG. 4, when the R′-M alloy is mixed, the coercive force (H _cJ ) takes a maximum value between 450 ° C. and 550 ° C. as in the case of Experimental Example 2. It can be seen that the temperature is slightly improved as compared with that before the heat treatment, then reaches a minimum value near 700 ° C., then increases again from 800 ° C., and reaches a maximum value near 900 ° C.

Further, after hot compression molding, Comparative Example 33 in which heat treatment was not performed, Comparative Example 36 in which heat treatment was performed at 500 ° C. and 650 ° C., Comparative Example 40, and Example 20 in which heat treatment was performed at 900 ° C. were cross-section polishers. (Device name: SM-09010, manufactured by JEOL Ltd.) was cut and a reflected electron image of the processed cross section was photographed at a magnification of 5000 using FE-SEM (device name: JSM-7001F, manufactured by JEOL Ltd.). The reflected electron images are shown in FIGS. In the reflected electron image, the contrast of the Nd ₂ Fe ₁₄ B phase that is the main phase is dark, and the Nd-rich phase that is the grain boundary phase is displayed brightly. Nd-rich phase 3 points are extracted from the image of the observation area 24 μm × 18 μm by binarization processing with image editing software (product name: Photoshop Elements 9, manufactured by Adobe Systems), and image analysis software (product name: WinROOF, Mitani Corporation) The number density and total area of the Nd-rich phase triple point were measured. The results are shown in Table 8. In addition, less than 0.0006 μm ² was excluded. The 900 ° C. heat-treated sample with high coercive force (Example 20) obtained a large number density of Nd-rich phase triple points having an area with an equivalent circle diameter of 1.0 μm or less. It can be seen that the Nd-rich phase is dispersed by the heat treatment at 900 ° C. and is more uniformly arranged around the main phase, thereby obtaining a structure exhibiting a high coercive force.

Further, the high-density magnets of Examples 13 to 23 (excluding 17 and 19) in Table 7 were subjected to additional heat treatment at 475 to 650 ° C. for 60 minutes in a vacuum of 10 ⁻² Pa or less, and cooled to room temperature in vacuum. did. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 9. As shown in Table 9, it can be seen that the coercive force is further improved by heat treatment at 475 to 650 ° C. after heat treatment at 800 ° C. to 900 ° C.

(Experimental example 5)
First, an RTB-based alloy having the composition of B1 in Table 1 was produced by a strip cast method. The obtained alloy was coarsely pulverized into a powder having a particle size of 425 μm or less by the hydrogen storage / disintegration method, and then the coarse powder was finely pulverized using a jet mill to obtain an RTB system having a 50% volume center particle size of 4.2 μm. An alloy powder was obtained.

Next, the R-T-B system alloy powder was filled in a die of a press machine, and a pressure of 32 MPa was applied in a direction perpendicular to the magnetic field in a magnetic field of 1.2 MA / m to produce a green compact. The density of the green compact was 4.2 g / cm ³ when calculated based on dimensions and weight.

  Next, the temperature of the green compact was raised to 1040 ° C. in an argon stream depressurized to 0.5 kPa and held for 240 minutes. Then, after cooling to 850 degreeC in 15 minutes, it cooled to room temperature in 100 kPa argon stream, and the sintered magnet was obtained.

When the density was calculated from the size and weight of the obtained sintered magnet, it was 7.53 g / cm ³ . After magnetizing the sintered magnet with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 10.

  Further, the sintered magnet was heat-treated at 450 ° C. to 950 ° C. for 60 minutes in a vacuum of 10 Pa or less, and cooled to room temperature in vacuum. After magnetizing the obtained sample with a pulse magnetic field of 3.2 MA / m, the magnetic properties were measured with a BH tracer (device name: MTR-1412 (Metron Giken Co., Ltd.)). The results are shown in Table 10. As shown in Table 10, it can be seen that the sintered magnet cannot obtain the effect of improving the coercive force by the heat treatment in the temperature range of 800 to 900 ° C., unlike the high-density magnet of the present invention.

  According to the present invention, the conventional HDDR magnetic powder and the magnet powder that has been bulked by hot compression molding exhibit better squareness, and the conventional porous magnet and porous magnet are hot compression molded. Thus, it becomes possible to produce an RTB-based permanent magnet having a higher coercive force than a high-density magnet obtained in this way.

10 Porous magnet 27 Mold (die)
28a Upper punch 28b Lower punch 30a Driving unit 30b Driving unit 26 Chamber

Claims (2)

An RTB-based alloy powder having a 50% volume center particle diameter of 1 μm or more and less than 10 μm and containing an R ₂ T ₁₄ B phase (R is a rare earth element containing 50 atomic% or more of Nd and / or Pr, T is Fe , Or Fe and Co), or an R ′ metal having a particle size of less than 150 μm with respect to the RTB-based alloy powder (R ′ is one or more selected from Nd, Pr, Dy, Tb) or R′-M. A step of preparing a mixed powder in which a powder of an alloy based alloy (M is one or more selected from Al, Ga, Co, Fe, and R ′ is 20 atomic% or more and less than 100 atomic% of the entire R′-M alloy) When,
Forming the green compact by molding the RTB-based alloy powder or mixed powder;
The green compact is subjected to heat treatment at a temperature of 650 ° C. or more and 900 ° C. or less in a hydrogen atmosphere of more than 10 kPa and 500 kPa or less, or in a mixed atmosphere of hydrogen and inert gas having a hydrogen partial pressure of more than 10 kPa and 500 kPa or less, thereby An HD treatment process that causes hydrogenation and disproportionation reactions;
A DR treatment step in which heat treatment is performed at a temperature of 650 ° C. or more and 900 ° C. or less in a hydrogen atmosphere of 2 kPa or more and 10 kPa or less, thereby causing dehydrogenation and recombination reaction;
Grain boundary phase formation in which the green compact is heat-treated at a temperature of 650 ° C. or higher and 900 ° C. or lower in a vacuum or an inert atmosphere, thereby forming a grain boundary phase in the vicinity of the interface of R ₂ T ₁₄ B phase crystal grains. A heat treatment step;
A densification step for increasing the density to 96% or more of the true density by hot compression molding at a temperature of 600 ° C. or higher and 900 ° C. or lower in a vacuum or an inert gas atmosphere;
The manufacturing method of the RTB type | system | group permanent magnet including the grain boundary phase homogenization process which heat-processes at the temperature of 800 to 900 degreeC in a vacuum or inert gas atmosphere. The manufacturing method of the RTB type | system | group permanent magnet of Claim 1 which heats up the temperature of 200 to 600 degreeC in a hydrogen atmosphere in the temperature rising process before the said HD process .