JP2013207008A - Method of producing r-t-b-based permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the orientation of a porous magnet produced by using the HDDR method.SOLUTION: A molding having a density of 3.5-5.2 g/cmand magnetic anisotropy is produced by molding powder of an R-T-B-based alloy (R is a rare earth element containing 50 atom% or more of Nd and/or Pr, T is Fe, or Fe and Co) having 50%volume center grain size (D) of 1-10 μm, and including a RTB phase, in a magnetic field. This method includes a first heat treatment step for progressing the sintering of the molding by heating and holding the molding in vacuum or an argon atmosphere, a second heat treatment step for progressing the hydrogenation and disproportionation reaction, and a third heat treatment step for forming a porous body by progressing the dehydrogenation and recombination reaction. Sintering is progressed by the first heat treatment step, so that the density of the molding is 5.7-6.4 g/cmwhen the second heat treatment step is started.

Description

  The present invention relates to a method for manufacturing an R-T-B permanent magnet having a porous structure manufactured by the HDDR method.

R-T-B type permanent magnets typical as high performance permanent magnets (R is a rare earth element containing Nd and / or Pr of 50 atomic% or more, T is Fe, or Fe and Co) is a ternary tetragonal compound It has a structure containing the R ₂ T ₁₄ B phase as a main phase and exhibits excellent magnetic properties. In R-T-B permanent magnets, it is known that the coercive force is improved by reducing the crystal grain size of the R ₂ T ₁₄ B phase, which is the main phase. As a method for obtaining an RTB-based permanent magnet having an average crystal grain size of 1 μm or less, an HDDR (Hydrogenation-Disposition-Desorption-Recombination) processing method is known.

  “HDDR” means a process of sequentially performing hydrogenation and disproportionation, dehydrogenation and recombination. The known HDDR treatment is performed, for example, by holding an R-T-B alloy ingot or powder at a temperature of 500 ° C. to 1000 ° C. in a hydrogen atmosphere or a mixed atmosphere of a hydrogen gas and an inert gas. Alternatively, after hydrogen is occluded in the powder (hydrogen occlusion treatment), dehydrogenation treatment is performed at a temperature of 500 ° C. to 1000 ° C. until, for example, a vacuum atmosphere with a hydrogen pressure of 13 Pa or less, or an inert atmosphere with a hydrogen partial pressure of 13 Pa or less. And then cooled.

In the above treatment, the following reaction usually proceeds. That is, by the hydrogen storage treatment, hydrogenation and disproportionation reaction (both are referred to as “HD reaction”. Example of reaction formula: Nd ₂ Fe ₁₄ B + 2H ₂ → 2NdH ₂ + 12Fe + Fe ₂ B) progresses and is fine. An organization is formed. Next, by performing the dehydrogenation treatment, dehydrogenation and recombination reaction (both are referred to as “DR reaction”. Example of reaction formula: 2NdH ₂ + 12Fe + Fe ₂ B → Nd ₂ Fe ₁₄ B + 2H ₂ ) An alloy containing an R ₂ Fe ₁₄ B phase is obtained.

  The RTB-based alloy powder produced by the HDDR process has a large coercive force and magnetic anisotropy. A method for producing an RTB-based alloy powder by HDDR processing is disclosed in, for example, Patent Document 1 and Patent Document 2. According to the HDDR treatment, a permanent magnet powder having a very fine crystal grain size of 0.1 μm to 1 μm can be obtained.

  Furthermore, in recent years, an R-T-B alloy powder finely pulverized to an average particle size of less than 10 μm is molded to produce a green compact, and a porous material produced by subjecting the green compact to HDDR treatment. A bulk magnet (hereinafter referred to as a porous magnet) has been developed and disclosed in Patent Document 3. Since this porous magnet is subjected to HDDR treatment on fine powder having an average particle size of less than 10 μm, the HDDR reaction can proceed in a short time, and as a result, the HDDR reaction can proceed uniformly. Therefore, the squareness of the demagnetization curve is excellent.

  Patent Document 4 discloses that the permanent magnet powder obtained by the HDDR process can be bulked by a hot molding method such as hot pressing.

JP-A-1-132106 JP-A-2-4901 International Publication No. 2007/135981 JP-A-4-253304

  According to the description of Patent Document 3, an anisotropic porous magnet is produced by subjecting the green compact molded while applying a magnetic field to HDDR treatment. However, it cannot be said that the degree of orientation is sufficiently large.

  The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is an RTB-based permanent magnet having a higher degree of orientation and a residual magnetic flux density than conventional porous magnets. Is to provide.

The manufacturing method of the R-T-B system permanent magnet of the present invention is a R-T-B system alloy having a 50% volume center particle size (D ₅₀ ) 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 a powder of Fe, or Fe and Co), and by molding the powder in a magnetic field, 3.5 g / cm ³ The step of producing a magnetically anisotropic molded body at a density of 5.2 g / cm ³ or less and sintering the molded body by heating and holding the molded body in a vacuum or argon atmosphere. A first heat treatment step to be performed, and after the first heat treatment step, the molded body is mixed with hydrogen or hydrogen and an inert gas at a temperature of 650 ° C. or more and 950 ° C. or less and lower than the temperature of the first heat treatment step. By maintaining the atmosphere, hydrogenation And a second heat treatment step in which the disproportionation reaction proceeds, and after the second heat treatment step, the molded body is maintained in a vacuum of 650 ° C. or higher and 950 ° C. or lower or in an inert gas atmosphere, whereby dehydrogenation and re-treatment are performed. Including a third heat treatment step in which a binding reaction proceeds to form a porous body, and the density of the molded body at the start of the second heat treatment step is 5.7 g / cm ³ or more and 6.4 g / cm ³ or less. Thus, the sintering of the molded body is advanced by the first heat treatment step.

In one embodiment, the density of the porous body after the third heat treatment is 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

  In one embodiment, the first heat treatment step has a temperature of 875 ° C. or higher and 1020 ° C. or lower, and a holding time of 1 minute or longer and 10 hours or shorter.

In one embodiment, the porous body is further compacted by hot forming at a temperature of 500 ° C. or higher and 900 ° C. or lower until the density becomes 7.4 g / cm ³ or higher.

The RTB-based permanent magnet of the present invention is produced by the above manufacturing method, and has a density of 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

  According to the present invention, the density of the molded body is increased by the heat treatment step (first heat treatment step) before the HDDR treatment, and the orientation degree of the main phase before the HDDR treatment is increased with the sintering from the molded body before the heat treatment. Can also be increased. For this reason, the degree of orientation in the porous magnet obtained by the HDDR process is improved.

It is a flowchart which shows an example of the manufacturing method of the RTB system permanent magnet by this invention. It is a figure which shows the hot press apparatus which can be used suitably by embodiment of this invention.

  The inventor found that the reason why the degree of orientation of the porous magnet disclosed in Patent Document 3 is relatively low is that small particles contained in a molded body (compact) produced by molding powder in a magnetic field. It was thought that the degree of orientation was low. Relatively small particles are weak in the force received from a magnetic field when molding in a magnetic field to produce a molded body, and are less likely to be oriented than larger particles. For this reason, it exists in the tendency for an orientation degree to fall, so that particle | grains are small among the particles contained in a molded object. However, in the case of a sintered magnet prepared by sintering such a molded body at a high temperature, small particles having a low degree of orientation are bonded to larger particles during the sintering process, and grain growth occurs. At this time, it is considered that grain growth occurs so that the direction of the easy axis of small particles is aligned with the direction of the easy axis of large particles. As a result, the sintered magnet has the effect of improving the degree of orientation during the sintering process.

  The present inventor believes that the HDDR process for forming the porous structure is performed at a temperature lower than that of the normal sintering process, so that the above-described grain growth does not occur, and as a result, the degree of orientation accompanying the sintering. I thought that the improvement effect might not be manifested. In the present invention, before the HDDR process is started, an additional heat treatment for obtaining an effect of improving the degree of orientation is performed.

  FIG. 1 is a flowchart showing an example of a method for producing an RTB-based permanent magnet according to the present invention.

In the example shown in FIG. 1, first, an RTB-based alloy (R is Nd and / or Pr) having a 50% volume center particle size (D ₅₀ ) of 1 μm or more and less than 10 μm and including an R ₂ T ₁₄ B phase. A rare earth element containing 50 atomic% or more, T is Fe, or Fe and Co) is prepared (step S1).

By molding this powder in a magnetic field, a molded body (green compact) having magnetic anisotropy at a density of 3.5 g / cm ³ or more and 5.2 g / cm ³ or less is produced (step S2). . The “density” in this specification refers to a value measured at room temperature (about 20 ° C. to about 30 ° C.). For this reason, the value displayed as “density” regarding the molded body that has risen to a temperature higher than room temperature by each heat treatment step is not a density value at that temperature but a value when measured at room temperature.

A first heat treatment step is performed in which the molded body thus produced is heated and held in a vacuum or an argon atmosphere (step S3). By this first heat treatment step, sintering of the molded body is advanced. In order to obtain the effect of improving the degree of orientation accompanying the above-mentioned sintering, the density of the molded body when starting the second heat treatment step by lowering the temperature to the temperature of the second heat treatment step after the first heat treatment step is important, This value is set to 5.7 g / cm ³ or more and 6.4 g / cm ³ or less. The value of this density is also a value measured at room temperature. However, when the first heat treatment step and the second heat treatment step are performed continuously, the treatment is performed when the temperature is lowered to the temperature of the second heat treatment step after the first heat treatment step. The treatment temperature and time may be set in advance so that the density value when the temperature is lowered to room temperature falls within this range.

  Next, the hydrogenation and disproportionation reactions proceed by holding the molded body in a mixed atmosphere of hydrogen or hydrogen and an inert gas at a temperature of 650 ° C. or higher and 950 ° C. or lower than the temperature of the first heat treatment step. A second heat treatment step is performed (step S4).

Thereafter, this molded body is kept in a vacuum of 650 ° C. or higher and 950 ° C. or lower or an inert gas atmosphere to advance dehydrogenation and recombination reaction, and the density is 6.0 g / cm ³ or more and 6.8 g / cm ^3. A third heat treatment step for forming the following porous body is performed (step S5).

The porous body obtained by this method has a density of 6.0 g / cm ³ or more and 6.8 g / cm ³ or less, which is 90% or less of the true density (about 7.6 g / cm ³ ). Although there are gaps, the individual particles are bonded to each other and exhibit sufficient mechanical strength and excellent magnetic properties.

  Hereinafter, an embodiment is described in detail about a manufacturing method of a RTB system permanent magnet by the present invention.

<Raw material alloy>
First, an RTB-based alloy (raw material alloy) including an R ₂ T ₁₄ B phase that is a hard magnetic 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 RTB-based alloy (raw material 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 desirably 12 atom% or more and 30 atom% or less, and more desirably 13 atom% or more and 18 atom% or less of the entire raw material alloy. Moreover, the coercive force can be improved by setting a part of R to 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 of the entire 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 raw material alloy is preferably produced by a strip casting method that can reduce the amount of α-Fe phase that adversely affects magnetic properties, but can also be produced by a book mold method, a centrifugal casting method, an atomizing method, or the like. it can. 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 at a temperature of usually 900 ° C. or higher in a vacuum or an inert atmosphere.

<Crushing>
Next, the raw material powder is produced by pulverizing the raw material alloy by a known method. In this embodiment, first, a raw material alloy is coarsely pulverized using a mechanical crushing method such as a jaw crusher or a hydrogen occlusion pulverizing method to produce a 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 a raw material powder having a 50% volume center particle size (D ₅₀ ) 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.

From the viewpoint of handling, the 50% volume center particle size (D ₅₀ ) of the raw material powder is 1 μm or more. This is because when the 50% volume center particle size (D ₅₀ ) is less than 1 μm, the raw material 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 preferable to set the 50% volume center particle size (D ₅₀ ) to 3 μm or more. From the viewpoint of improving the mechanical strength of the molded body, the preferable upper limit of the 50% volume center particle size (D ₅₀ ) is 9 μm, and the more preferable upper limit is 8 μm.

<Molded body (green compact)>
Next, the raw material alloy powder is molded to produce a molded body. The step of molding the molded body is performed, for example, under a pressure of 10 MPa to 200 MPa, for example, in a magnetic field of 0.4 MA / m to 16 MA / m (static magnetic field, pulse magnetic field, etc.). Molding can be performed by a known powder press apparatus. The compact density (green compact density) when removed from the powder press device is ^{3.5g / cm 3 ~5.2g / cm 3} .

  It should be noted that R 'metal and / or R'-M alloy powder is separately prepared and mixed with the pulverized powder, or R-T-B alloy and R' metal or R'- You may grind | pulverize, after mixing M type | system | group alloy. Here, “R ′” is a rare earth element containing Y, but is preferably composed of one or more of Nd, Pr, Dy, and Tb. “M” is at least one element selected from the group consisting of Al, Ga, Cu, Co, Ni, Cr, Fe, Si, and Ge. At least a part of R ′ and / or M, which are components of these R ′ and / or R′-M type alloys, are diffused and introduced into the grain boundaries of the main phase after the third heat treatment, thereby contributing to an improvement in coercive force. R ′ and R′-M alloys (hereinafter referred to as “diffusion materials”) may contain inevitable impurities.

  The composition ratio of the rare earth element R ′ in the R′-M-based alloy is preferably 25 atomic percent or more and less than 100 atomic percent, more preferably 30 atomic percent or more and 80 atomic percent or less, and 40 atomic percent or more and 70 atomic percent. It is further desirable that it is at most atomic%.

  The alloy used for these diffusing materials can be prepared 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.

  The particle size of the R ′ metal or R′-M alloy powder used for the diffusion material is preferably 1 μm or more and 30 μm or less.

  It is desirable to carry out the raw material alloy crushing step and the molded body forming step while suppressing oxidation of the raw material powder. In order to suppress the oxidation of the raw material powder, it is desirable to carry out each process and the handling between the processes in an inert atmosphere in which the amount of oxygen is suppressed as much as possible. Specifically, it is desirable to suppress the oxygen content of the molded body before the third heat treatment step to be 1% by mass or less, and it is more desirable to suppress the oxygen content to be 0.6% by mass or less.

<First heat treatment process>
Next, a first heat treatment is performed on the molded body obtained by the molding process.

The first heat treatment step is a step of increasing the density by advancing sintering of a molded body (a green compact) molded using the raw material powder in order to obtain the above-described effect of improving the degree of orientation. Since the density of the molded body may be further improved after the first heat treatment step and the temperature is lowered to the temperature of the second heat treatment step, in the present invention, the temperature is lowered to the temperature of the second heat treatment step. The density at the start of the process is important, and the temperature and time of the first heat treatment step are set so that the density at that time is 5.7 g / cm ³ or more and 6.4 g / cm ³ or less. In this sintering process, the orientation degree of the main phase R ₂ T ₁₄ B phase is improved. If the density of the sample at the start of the second heat treatment step is less than 5.7 g / cm ³ , the effect of improving the degree of orientation accompanying sintering cannot be sufficiently obtained, and 6.4 g / cm ³ (true density is 7.6 g / cm ³ ). ³ ), the density is excessively improved, and so-called closed pores that do not communicate with the outside of the magnet are locally generated. This is because it is difficult to carry out uniformly, and in severe cases, the sample is cracked due to non-uniform storage of hydrogen.

  The heat treatment temperature in the first heat treatment step is not particularly limited as long as the density of the molded body is set within the above range, and varies depending on the composition of the raw material alloy, but is usually in the temperature range from 875 ° C. to 1020 ° C. Set within. If the temperature is lower than 875 ° C., the effect of improving the degree of orientation accompanying sintering may not be sufficiently obtained. If the temperature exceeds 1020 ° C., the density is excessively improved, and it is difficult to uniformly perform the HDDR process performed thereafter. Because there is a possibility of becoming. A more preferable range is 900 ° C. or higher and 1000 ° C. or lower. Further, by setting the temperature of the first heat treatment to be, for example, 10 ° C. higher than the temperature of the second heat treatment, the sintering can be advanced in a shorter time, and the effect of improving the degree of orientation of the present invention can be obtained efficiently.

  The heat treatment time of the first heat treatment step is not particularly limited as long as the density of the molded body is set within the above range, and varies depending on the composition of the raw material alloy, etc., but is usually in the temperature range of 1 minute to 10 hours. Set within. If it is less than 1 minute, the effect of improving the degree of orientation accompanying sintering may not be sufficiently obtained, and holding for more than 10 hours may cause a decrease in productivity. A more preferable range is 5 minutes or more and 5 hours or less.

  Note that the atmosphere of the first heat treatment is an inert gas atmosphere such as vacuum or argon.

  It is preferable to use a vacuum or an inert gas as the temperature rising atmosphere until the first heat treatment. Hydrogen can also be used in a temperature range of 650 ° C. or lower, but in this case, if the first heat treatment step is not performed in a sufficiently dehydrogenated state, sintering does not proceed, and the effect of improving the degree of orientation of the present invention is achieved. I can't get it.

  In addition, if it exposes to hydrogen atmosphere at the temperature exceeding 650 degreeC in a temperature rising process, since a hydrogenation-disproportionation reaction (HD reaction) will advance, the orientation degree improvement effect of this invention cannot be acquired.

<Second heat treatment step>
Next, the second heat treatment step to be performed is a step of obtaining a disproportionated structure by 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 second heat treatment step.

The temperature of the second heat treatment step is 650 ° C. or more and 950 ° C. or less, and is lower than the temperature of the first heat treatment. It is preferably 10 ° C. or lower than the temperature of the first heat treatment step. Below 650 ° C., it takes too much time to complete disproportionation. When the temperature exceeds 950 ° C., the disproportionated structure becomes coarse, and the texture of the R ₂ T ₁₄ B phase obtained by the subsequent third heat treatment step becomes coarse, leading to a decrease in magnetic properties, particularly coercive force. A more preferable temperature is 700 ° C. or higher and 900 ° C. or lower, and a more preferable temperature is 750 ° C. or higher and 870 ° C. or lower.

The hydrogen partial pressure in the second heat treatment step is desirably 20 kPa or more. When the hydrogen partial pressure is less than 20 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. Further, when the hydrogen partial pressure exceeds 500 kPa, hydrogen occlusion occurs abruptly, and there is a possibility that the molded body may crack due to volume expansion accompanying hydrogen occlusion, and a special apparatus is required for processing. Therefore, it is desirable that it is 500 kPa or less. A more preferable hydrogen partial pressure is 150 kPa or less.

The time required for the second heat treatment step is desirably 10 minutes or more and 5 hours or less. If it is less than 10 minutes, 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 the recombination structure after the third heat treatment step 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.

<Third heat treatment process>
Next, in the third heat treatment step to be performed, dehydration reaction of the RH _x phase is caused by holding at 650 ° C. or more and 950 ° C. or less in a vacuum (10 kPa or less) or an inert atmosphere, and the R ₂ T ₁₄ B phase is recombined. To generate. The R ₂ T ₁₄ B phase produced at this time usually forms a texture having an average crystal grain size of 0.1 μm or more and 1.0 μm or less. In addition, a dehydrogenation reaction from RHx that has not been used for recombination 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. Coercive force. At this time, a sintering reaction also occurs at the same time, resulting in a porous permanent magnet.

The temperature of the third heat treatment step is 650 ° C. or higher and 950 ° C. or lower. Below 650 ° C., it takes too much time to complete dehydrogenation. On the other hand, when the temperature exceeds 950 ° C., the recombined R ₂ T ₁₄ B phase grows in crystal grains, leading to a decrease in magnetic properties, particularly coercive force. A more preferable temperature is 750 ° C. or higher and 900 ° C. or lower. The time required for the third heat treatment step is preferably 5 minutes or more and 10 hours or less, and more preferably 10 minutes or more and 2 hours or less.

<Porous body>
By the HDDR treatment, a porous body (RTB porous magnet) having a density of 6.0 g / cm ³ or more and 6.8 g / cm ³ or less and magnetically anisotropic is obtained.

In this porous body, there are voids having a major axis of 1 μm or more and 20 μm or less that communicate with each other between the powder particles interconnected in the first heat treatment step and the second and third heat treatment steps (HDDR treatment steps). . The individual powder particles that made up the compact (green compact) are combined with adjacent powder particles by the first, second, and third heat treatments to form a three-dimensional structure that exhibits sufficient mechanical strength. In addition, a fine Nd ₂ Fe ₁₄ B type crystal phase texture is formed in each powder particle.

The density of the RTB-based porous magnet obtained by the production method of the present invention is 6.0 g / cm ³ or more and 6.8 g / cm ³ or less. The particles combine to exhibit sufficient mechanical strength and excellent magnetic properties.

  In this embodiment, since the HDDR process is performed on the molded body (compact) after the molding process, the powder molding is not performed after the HDDR process. For this reason, it does not occur after HDDR processing that the magnetic powder is pulverized by pressurization for molding, and high magnetic characteristics can be obtained as compared with a bonded magnet that compresses HDDR powder.

<Hot compression molding of porous body>
The porous body obtained by the above method can be used as it is as a bulk permanent magnet, but it is further densified by using hot compression molding such as a hot press method, and the average crystal grains A high-density magnet having a texture of R ₂ T ₁₄ B phase with a diameter of 0.1 μm or more and 1 μm or less can be obtained.

  An example of a specific embodiment will be shown below for densification by hot compression molding. Hot compression with respect to a porous body can be performed using a known hot compression technique. For example, hot compression molding such as hot pressing, SPS (Spark Plasma Sintering), HIP (Hot Isostatic Press), 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 this embodiment, a hot press apparatus having the configuration shown in FIG. 2 is used. The apparatus includes a die (die) 27 having an opening in the center, an upper punch 28a and a lower punch 28b for pressurizing the porous body, and driving units 30a and 30b for raising and lowering the punches 28a and 28b. ing.

  The porous body produced by the method described above (indicated by reference numeral “10” in FIG. 2) 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. Note that anisotropy can be increased by setting the outer dimensions of the porous body 10 to be smaller than the opening dimensions of the mold 27. Next, the mold 27 loaded with the porous body 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 body 10 are provided.

  After filling the chamber 26 with a vacuum or an inert atmosphere, the mold 27 is heated by a heating device, the temperature of the porous body 10 loaded in the mold 27 is increased to 500 ° C. to 900 ° C., and 9.8 to 294 MPa. The porous body 10 is pressurized with a pressure P of. It is desirable that pressurization of the porous body 10 is started after the temperature of the mold 27 reaches a set level. If the temperature of the mold is not sufficiently high, there is a possibility that the porous body is cracked during pressurization, or the degree of orientation of the resulting high-density magnet is deteriorated. While maintaining the pressure at 500 ° C. to 900 ° C. for 10 minutes or more, the sample 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, the RTB-based high-density magnet of the present embodiment can be obtained from the porous body 10 described above.

The density of the magnet thus obtained reaches 95% or more of the true density. Specifically, it can be densified until the density is 7.4 g / cm ³ or more. 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.

  Moreover, densification can also be advanced by heat-processing the said porous body 10 at 750-1000 degreeC in inert gas atmosphere, such as a vacuum or argon. The time for this heat treatment is usually from 5 minutes to 10 hours. The pressure when using an inert gas atmosphere is usually 500 kPa or less, more preferably 100 kPa or less.

(Experimental example 1)
A rapidly solidified alloy having a composition of Nd _13.7 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 (mol%) was produced by strip casting. The obtained rapidly solidified 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 a 50% volume center particle size (D ₅₀ ) of 4.2 μm. A fine powder was obtained. In this example, the 50% volume center particle size (D ₅₀ ) was measured by an air flow dispersion type laser diffraction type particle size distribution measuring device (manufactured by Sympatec, HEROS / RODOS).

Next, this powder was filled in a mold 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 molded body. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

Next, the molded body is heated to a temperature T ₁ shown in Table 1 at a rate of temperature increase of 13 ° C./min in an argon flow of 0.1 MPa (atmospheric pressure), and then held at T ₁ for a time t _1. The first heat treatment was performed.

  Subsequently, after the temperature was decreased to 860 ° C. at a temperature decrease rate of −10 ° C./min, the temperature was maintained at 860 ° C. for 30 minutes, and then the atmosphere was switched to 0.1 MPa hydrogen flow and maintained for 2 hours to A second heat treatment was carried out to advance the chemical-disproportionation reaction (HD reaction).

  In addition, in order to evaluate the sample density at the start of the second heat treatment, after removing the oxide layer present on the surface of the molded body obtained by stopping the treatment just before the second heat treatment and cooling to room temperature by grinding, Table 1 shows the results of measuring the dimensions and weight and calculating the density from the obtained values.

  Some samples cracked. Table 1 shows the presence or absence of cracks. It is considered that the sample was cracked in the subsequent second heat treatment step because the sintering proceeded excessively in the first heat treatment step and the density during the second heat treatment became too high.

  Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example.

  Thereafter, the pressure is reduced to 4 kPa while maintaining the temperature at 860 ° C., and then the dehydrogenation-recombination reaction (DR) is performed by adjusting the pumping rate of hydrogen released from the sample so that the pressure in the furnace becomes constant at 4 kPa and holding for 1 hour. A third heat treatment was performed to proceed the reaction), and the sample was held in an argon flow of 5.33 kPa for 10 minutes, and then cooled to room temperature in an argon flow of 0.1 MPa to prepare a sample.

  Table 1 shows the results of measuring the dimensions and weight after removing the oxide layer present on the surface of the sample obtained after the third heat treatment by grinding, and calculating the density from the obtained values. In addition, since it was thought that the density of the sample in which the crack was seen cannot be evaluated correctly, the value is excluded from the table.

The sample in which no crack was observed was magnetized with a pulse magnetic field of 3.2 MA / m, and then the magnetic properties were measured with a BH tracer (device name: MTR-1412 (manufactured by Metron Giken)). The residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by measurement are shown. J _max is the maximum measured value of the magnetization of the sample when an external magnetic field is applied up to 1.6 MA / m in the magnetization direction of the magnetized sample. The larger the _Br / J _max , the better the degree of orientation. ing.

As shown in Table 1, in samples A1 to A3 in which the density at the start of the second heat treatment is 5.7 g / cm ³ or more and 6.4 g / cm ³ or less, the degree of orientation ( (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

On the other hand, in samples A4, A5, and A6 where the density at the start of the second heat treatment was less than 5.7 g / cm ³ , B _r / J _max , B _r , and (BH) _max were almost improved compared to the reference example. There wasn't. Further, in Sample A7 having a density of 6.57 g / cm ³ , the HDDR reaction does not proceed sufficiently because the densification has progressed too much, and as a result, (BH) _max is significantly lower than in Reference Example (A0). did. Furthermore, in Samples A8 and A9 that were subjected to the first heat treatment at a higher temperature or longer than Sample A7, sample cracking occurred.

(Experimental example 2)
Nd _14.5 Fe _bal. Co ₁ B _6.0 Ga _0.1 Cu _0.1 Al _0.5 (mol%) Except that a rapidly solidified alloy was used, coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 to obtain a 50% volume center particle size. A fine powder of (D ₅₀ ) 4.3 μm was obtained.

Next, a molded body was produced using this powder by the same method as in Experimental Example 1. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

Next, the molded body is heated to a temperature T ₁ shown in Table 2 at a temperature increase rate of 13 ° C./min in an argon gas atmosphere of 0.1 MPa (atmospheric pressure), and then held at T ₁ for a time t _1. The first heat treatment was performed.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 2. Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example.

  Some samples cracked. Table 2 shows the presence or absence of cracks. It is considered that the sample was cracked in the subsequent second heat treatment step because the sintering proceeded excessively in the first heat treatment step and the density during the second heat treatment became too high.

About the sample in which the crack was not seen, the density and the magnetic characteristic were measured by the same method as Experimental Example 1 after the third heat treatment. Table 2 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 2, in Samples B1 to B3 in which the density at the start of the second heat treatment is 5.7 g / cm ³ or more and 6.4 g / cm ³ or less, the degree of orientation (in comparison with the reference example (B0)) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

On the other hand, in sample B4 in which the density at the start of the second heat treatment was less than 5.7 g / cm ³ , B _r / J _max , B _r , (BH) _max were hardly improved as compared with the reference example. Further, in Sample B5 having a density of 6.55 g / cm ³ , the HDDR reaction did not proceed sufficiently because the densification progressed too much, and as a result, (BH) _max was significantly lower than in Reference Example (B0). did. Furthermore, in sample B6 subjected to the first heat treatment at a temperature higher than that of sample B5, the sample was cracked.

(Experimental example 3)
Nr _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 (mol%) Except that a rapidly solidified alloy was used, coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 to obtain a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

Next, a molded body was produced using this powder by the same method as in Experimental Example 1. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

Next, the molded body was heated in an atmosphere of argon at 0.1 MPa (atmospheric pressure) from room temperature to a temperature T ₁ shown in Table 3 in 1 hour, and then held at T ₁ for 1 hour to perform a first heat treatment. Went.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 3.

  Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example.

No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 3 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 3, the samples C1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (C0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.35 g / cm ³ .

(Experimental example 4)
Coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 except that a rapidly solidified alloy having a composition of Nd _13.7 Fe _bal. Co ₃ B _6.2 Ga _0.2 (mol%) was used, and a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

Next, a molded body was produced using this powder by the same method as in Experimental Example 1. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 600 ° C. for 42 minutes in a hydrogen gas atmosphere of 0.1 MPa (atmospheric pressure), then held at 600 ° C. for 30 minutes, and then 0.1 MPa (atmospheric pressure) argon The first heat treatment was performed by switching to flowing air and raising the temperature to 950 ° C. in 24 minutes and holding at 950 ° C. for 1 hour.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 4.

  Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example.

No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 4 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 4, the samples D1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (D0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.17 g / cm ³ .

(Experimental example 5)
Nr _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 (mol%) Except that a rapidly solidified alloy was used, coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 to obtain a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained. .

Next, a molded body was produced using this powder by the same method as in Experimental Example 1. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 600 ° C. for 42 minutes in a hydrogen gas atmosphere of 0.1 MPa (atmospheric pressure), then held at 600 ° C. for 30 minutes, and then 0.1 MPa (atmospheric pressure) argon The first heat treatment was performed by switching to flowing air and raising the temperature to 950 ° C. in 24 minutes and holding at 950 ° C. for 1 hour.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 5.

Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example. No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 5 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 5, the samples E1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (E0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.43 g / cm ³ .

(Experimental example 6)
Coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 except that a rapidly solidified alloy having a composition of Nd _13.7 Fe _bal. Co ₃ B _6.2 Ga _0.2 (mol%) was used, and a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

On the other hand, a rapidly solidified alloy having a composition of Nd ₇₀ Al ₃₀ (mol%) was produced by a melt spinning method. Specifically, the alloy was melted in a quartz nozzle having an orifice diameter of 0.8 mmΦ and sprayed onto a copper roll rotating at a roll peripheral speed of 20 m / sec to obtain a ribbon-like alloy. This alloy was pulverized by mechanical pulverization and classified using a sieve having an opening of 53 μm to obtain an Nd—Al alloy powder having a size of 53 μm or less.

Next, Nd _13.7 Fe _bal. Co ₃ B _6.2 Ga _0.2 alloy powder was mixed with Nd—Al alloy powder in a mass ratio of 50: 1, and then filled into a die of a press machine, and 0.64 MA / m A compact was produced by applying a pressure of 76 MPa in a direction parallel to the magnetic field. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 950 ° C. in 66 minutes in an argon flow of 0.1 MPa (atmospheric pressure) in 66 minutes, and then held at 950 ° C. for 1 hour to perform a first heat treatment.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 6.

Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example. No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 6 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 6, in the sample F1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (F0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.41 g / cm ³ .

(Experimental example 7)
Nr _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 (mol%) Except that a rapidly solidified alloy was used, coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 to obtain a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

On the other hand, a rapidly solidified alloy having a composition of Nd ₇₀ Al ₃₀ (mol%) was produced by the same method as in Experimental Example 6, and this alloy was pulverized and classified by the same method as in Experimental Example 6, and the size was 53 μm or less. Nd-Al alloy powder was obtained.

Next, Nd _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 alloy powder and Nd—Al alloy powder were mixed at a mass ratio of 50: 1, and then a molded body was produced in the same manner as in Experimental Example 6. . The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 950 ° C. in 66 minutes in an argon flow of 0.1 MPa (atmospheric pressure) in 66 minutes, and then held at 950 ° C. for 1 hour to perform a first heat treatment.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 7.

Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example. No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 7 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 7, the samples G1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (G0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.60 g / cm ³ .

(Experimental example 8)
Coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 except that a rapidly solidified alloy having a composition of Nd _13.7 Fe _bal. Co ₃ B _6.2 Ga _0.2 (mol%) was used, and a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

On the other hand, a rapidly solidified alloy having a composition of Nd ₇₀ Al ₃₀ (mol%) was produced by the same method as in Experimental Example 6, and this alloy was pulverized and classified by the same method as in Experimental Example 6, and the size was 53 μm or less. Nd-Al alloy powder was obtained.

Next, Nd _13.7 Fe _bal. Co ₃ B _6.2 Ga _0.2 alloy powder was mixed with Nd—Al alloy powder at a mass ratio of 50: 1, and a molded body was produced in the same manner as in Experimental Example 6. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 600 ° C. for 42 minutes in a hydrogen gas atmosphere of 0.1 MPa (atmospheric pressure), then held at 600 ° C. for 30 minutes, and then 0.1 MPa (atmospheric pressure) argon The first heat treatment was performed by switching to flowing air and raising the temperature to 950 ° C. in 24 minutes and holding at 950 ° C. for 1 hour.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 8.

Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example. No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 8 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 8, the samples H1 density of the second heat treatment at the start is in the 5.7 g / cm ³ or more 6.4 g / cm ³ or less, the degree of orientation as compared to Reference Example (H0) (B _r / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.54 g / cm ³ .

(Experimental example 9)
Nr _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 (mol%) Except that a rapidly solidified alloy was used, coarse pulverization and fine pulverization were performed in the same manner as in Experimental Example 1 to obtain a 50% volume center particle size (D ₅₀ ) A fine powder of 4.3 μm was obtained.

On the other hand, a rapidly solidified alloy having a composition of Nd ₇₀ Al ₃₀ (mol%) was produced by the same method as in Experimental Example 6, and this alloy was pulverized and classified by the same method as in Experimental Example 6, and the size was 53 μm or less. Nd-Al alloy powder was obtained.

Next, Nd _14.2 Fe _bal. Co ₃ B _6.1 Ga _0.2 Cu _0.1 alloy powder was mixed with Nd—Al alloy powder at a mass ratio of 50: 1, and then a molded body was produced in the same manner as in Experimental Example 6. The density of the molded body was 4.2 to 4.5 g / cm ^{3 when} calculated based on dimensions and weight.

  Next, the molded body was heated from room temperature to 600 ° C. for 42 minutes in a hydrogen gas atmosphere of 0.1 MPa (atmospheric pressure), then held at 600 ° C. for 30 minutes, and then 0.1 MPa (atmospheric pressure) argon The first heat treatment was performed by switching to flowing air and raising the temperature to 950 ° C. in 24 minutes and holding at 950 ° C. for 1 hour.

  Subsequently, a second heat treatment and a third heat treatment were performed in the same manner as in Experimental Example 1 to prepare a sample.

  In addition, in order to evaluate the sample density at the start of the second heat treatment, the result of calculating the density of the molded body obtained by stopping the treatment immediately before the second heat treatment and cooling to room temperature in the same manner as in Experimental Example 1 Is shown in Table 9.

Moreover, the evaluation result of the sample produced without the 1st heat treatment process is also shown as a reference example. No cracks were seen in both samples. The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 9 shows the density, residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 9, the sample I1 having a density at the start of the second heat treatment of 5.7 g / cm ³ or more and 6.4 g / cm ³ or less has a degree of orientation (B _{r as} compared with the reference example (I0)). / J _max ) was found to be significantly improved. In addition, high _Br and (BH) _max were obtained because the density after the third heat treatment was higher than that of the reference example. The density at this time was 6.66 g / cm ³ .

(Experimental example 10)
A magnet produced under the same conditions as Samples A0 (Reference Example), A2 (Example), A3 (Example), and A6 (Comparative Example) in Experimental Example 1 was placed in a cemented carbide mold, and 800 ° C. After the temperature was raised to 50 MPa, it was held for 20 minutes in a state where a pressure of 50 MPa was applied, and hot pressing was performed, so that the density was increased to 7.4 g / cm ³ or more.

The density and magnetic properties of the obtained sample were measured by the same method as in Experimental Example 1. Table 10 shows the residual magnetic flux density (B _r ), orientation degree (B _r / J _max ), and maximum magnetic energy product ((BH) _max ) obtained by the measurement.

As shown in Table 1, in the samples A2 and A3 in which the degree of orientation after the third heat treatment was improved because the density during the second heat treatment was 5.7 g / cm ³ or more and 6.4 g / cm ³ or less, As shown in Table 10, the degree of orientation (B _r / J _max ) after hot pressing was significantly improved as compared with Reference Example (A0), and accordingly, a high _Br was obtained. On the other hand, in sample A6 in which the density during the second heat treatment was less than 5.7 g / cm ³ , only the degree of orientation and Br equivalent to those in Reference Example (A0) were obtained.

  Since the magnet produced by the present invention has a higher degree of orientation and residual magnetic flux density than conventional porous magnets, it is suitably used for various applications that require these characteristics.

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

Claims (5)

An RTB-based alloy having a 50% volume center particle size (D ₅₀ ) 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 a step of preparing a powder of Fe or Fe and Co);
Forming a molded body having magnetic anisotropy at a density of 3.5 g / cm ³ or more and 5.2 g / cm ³ or less by molding the powder in a magnetic field;
A first heat treatment step of proceeding sintering of the molded body by heating and holding the molded body in a vacuum or argon atmosphere;
After the first heat treatment step, the molded body is maintained in a mixed atmosphere of hydrogen or hydrogen and an inert gas at a temperature of 650 ° C. or more and 950 ° C. or less and lower than the temperature of the first heat treatment step. A second heat treatment step for promoting the dissociation and disproportionation reactions;
After the second heat treatment step, the molded body is held in a vacuum of 650 ° C. or higher and 950 ° C. or lower or an inert gas atmosphere to advance dehydrogenation and recombination reaction to form a porous body. Process,
Including
The sintering of the molded body is advanced by the first heat treatment process so that the density of the molded body at the start of the second heat treatment process is 5.7 g / cm ³ or more and 6.4 g / cm ³ or less. Manufacturing method of RTB-based permanent magnet. The density of the third heat treatment after the porous body is not more than 6.0 g / cm ³ or more 6.8 g / cm ^3, the manufacturing method of the R-T-B-based permanent magnet according to claim 1.   3. The method for producing an R—T—B system permanent magnet according to claim 1, wherein the first heat treatment step has a temperature of 875 ° C. or more and 1020 ° C. or less and a holding time of 1 minute or more and 10 hours or less. It densifies until it becomes a density of 7.4 g / cm ³ or more by carrying out hot forming at a temperature of 500 ° C. or more and 900 ° C. or less with respect to the porous body. Manufacturing method of RTB-based permanent magnet. An RTB-based permanent magnet produced by the manufacturing method according to claim 1 and having a density of 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

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