JP7228096B2 - Method for producing RTB based sintered magnet - Google Patents

Description

The present invention relates to a method for producing an RTB based sintered magnet.

RTB based sintered magnets (R is at least one rare earth element, T is at least one transition metal element and always contains Fe, and B is boron) is the most popular among permanent magnets. Known as a high-performance magnet, it is used in various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances. . As used herein, rare earth elements refer to at least one element selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanides. Here, the lanthanoid is a general term for 15 elements from lanthanum to lutetium.

An RTB based sintered magnet consists of a main phase consisting mainly of an R ₂ T ₁₄ B compound and a grain boundary phase located at the grain boundary portion of this main phase (hereinafter sometimes simply referred to as "grain boundary"). It is configured. The R ₂ T ₁₄ B compound is a ferromagnetic phase with high magnetization and forms the basis of the properties of RTB system sintered magnets.

RTB based sintered magnets have a problem of irreversible thermal demagnetization due to a decrease in coercive force H _cJ (hereinafter sometimes simply referred to as “coercive force” or “H _cJ ”) at high temperatures. Therefore, RTB sintered magnets used in motors for electric vehicles in particular are required to have a high H _cJ even at high temperatures, that is, to have a higher H _cJ at room temperature.

In the RTB sintered magnet, part of the light rare earth elements (mainly Nd and/or Pr) contained in R in the R ₂ T ₁₄ B compound are replaced with heavy rare earth elements (mainly Dy and/or Tb). The substitution is known to improve the H _cJ . _HcJ improves with an increase in the substitution amount of the heavy rare earth element.

However, when the light rare earth element in the R ₂ T ₁₄ B compound is replaced with a heavy rare earth element, the H _cJ of the RTB system sintered magnet is improved, while the residual magnetic flux density B _r (hereinafter simply “B _r ” in some cases) decreases. In addition, heavy rare earth elements, especially Dy, have problems such as unstable supply and large price fluctuations due to the fact that their resources are scarce and their places of production are limited. Therefore, in recent years, there has been a demand from users to improve _HcJ without using heavy rare earth elements as much as possible.

Patent Document 1 discloses an RTB-based rare earth sintered magnet in which the coercive force is increased while the Dy content is reduced. The composition of this sintered magnet is limited to a specific range in which the amount of B is relatively small compared to the generally used RTB alloy, and is selected from Al, Ga, and Cu. It contains more than one kind of metal element M. As a result, the R _{2 T 17} phase is generated at the grain boundary, and the volume ratio of the transition metal-rich phase (R ₆ T ₁₃ M) formed at the grain boundary from this R ₂ T 17 phase is increased _. improves.

WO2013/008756

The method described in Patent Document 1 is noteworthy in that it can increase the coercive force of the RTB system sintered magnet while suppressing the content of the heavy rare earth element. However, there is a problem that _Br is greatly reduced. In recent years, there has also been a demand for RTB based sintered magnets having a higher _HcJ for applications such as motors for electric vehicles. Further, the demand for RTB based sintered magnets is expected to greatly expand in the future, especially for use in motors for electric vehicles. Therefore, it is necessary not only to reduce heavy rare earth elements but also to diversify the use of rare earth elements. As a specific means, it is possible to use La (and Ce) which is relatively abundant among rare earth elements.

Embodiments of the present disclosure use La and provide a method for manufacturing RTB based sintered magnets with high B _r and high H _cJ while reducing the content of heavy rare earth elements.

In an exemplary embodiment, the method for producing an RTB based sintered magnet of the present disclosure includes the steps of preparing an R1-T1-B based sintered body and preparing an R2-Ga-Cu based alloy. and at least part of the surface of the R1-T1-B-based sintered body is brought into contact with at least part of the R2-Ga-Cu-based alloy, and in a vacuum or inert gas atmosphere at 450 ° C. or higher and 500 ° C. or lower. In the R1-T1-B based sintered body, R1 is at least one of rare earth elements and always contains at least one of Nd and Pr, and the content of R1 is 27 mass% or more and 35 mass% or less of the entire R1-T1-B based sintered body, T1 is Fe or at least one of Co, Al, Mn, Si and Fe, and the Fe content of the entire T1 is 80 mass% or more. and the molar ratio of T1 to B ([T1] / [B]) is more than 14.0 and 15.0 or less, and in the R2-Ga-Cu-based alloy, R2 is at least one rare earth element , La must be included, the content of R2 is 70 mol% or more and 90 mol% or less of the entire R2-Ga-Cu-based alloy, and the ratio of La to the entire rare earth element is the R1-T1-B-based sintered body is higher than the ratio of La to the entire rare earth element, the content of Ga is 5 mol% or more and 20 mol% or less of the entire R2-Ga-Cu alloy, and the content of Cu is the entire R2-Ga-Cu alloy. is 5 mol % or more and 20 mol % or less.

In one embodiment, La in the R2-Ga-Cu alloy is 50 mol% or more of the total R2.

In one embodiment, R2 in the R2-Ga-Cu alloy is La (including impurities).

In one embodiment, the total content of R2, Ga and Cu in the R2-Ga-Cu alloy is 80 mass% or more.

In one embodiment, the step of preparing the R1-T1-B-based sintered body includes pulverizing the raw material alloy so that the particle size _D50 is 3 μm or more and 10 μm or less, and then sintering by orienting in a magnetic field. Including doing.

According to embodiments of the present disclosure, it is possible to provide a method for producing a RTB based sintered magnet having high B _r and high H _cJ while using La and reducing the content of heavy rare earth elements. can.

4 is a flow chart showing an example of steps in a method for manufacturing a sintered RTB magnet according to the present disclosure; 1 is a schematic diagram showing a main phase and a grain boundary phase of an RTB based sintered magnet. FIG. FIG. 2B is a schematic diagram further enlarging the inside of the broken-line rectangular area of FIG. 2A. FIG. 4 is an explanatory view schematically showing an example of the arrangement of the R1-T1-B-based sintered body and the R2-Ga-Cu-based alloy in the heat treatment step; No. 1 is a photograph of a cross section near the surface of a sintered body of 1-4 (Example of the invention) observed with a scanning electron microscope. No. 1 is a photograph of a cross section of 800 μm region from the surface of 1-4 (example of the present invention) observed with a scanning electron microscope. No. 1 is a photograph of a cross section of the central portion of 1-4 (example of the present invention) observed with a scanning electron microscope. No. FIG. 10 is a diagram showing the result of EDX analysis of the cross section near the surface of the sintered body of 1-4 (example of the present invention). No. FIG. 10 is a diagram showing the results of EDX analysis of a cross section of a region of 800 μm from the surface of 1-4 (example of the present invention). No. FIG. 10 is a diagram showing the result of EDX analysis of the cross section of the central portion of 1-4 (example of the present invention).

In the present disclosure, rare earth elements may be collectively referred to as "R". When referring to a particular element or group of elements among the rare earth elements R, the designations "R1" and "R2", for example, are used to distinguish them from other rare earth elements. In addition, in the present disclosure, all transition metal elements including Fe are denoted as “T”. When both the specific element or element group of the transition metal element T and the specific element or element group other than the transition metal element that easily replaces the Fe site of the main phase are included, the symbol "T1" is used. Distinguished from other transition metal elements.

As shown in FIG. 1, the method for producing an RTB based sintered magnet according to the present disclosure includes step S10 of preparing an R1-T1-B based sintered body, and preparing an R2-Ga-Cu based alloy. and step S20. The order of the step S10 of preparing the R1-T1-B-based sintered body and the step S20 of preparing the R2-Ga-Cu-based alloy is arbitrary, and each R1-T1-B system manufactured at a different place A sintered body and an R2--Ga--Cu alloy may also be used.

In the present disclosure, RTB system sintered magnets before and during heat treatment are referred to as R1-T1-B system sintered bodies, and R1-T1-B system sintered bodies after heat treatment are simply RT- It is called a B-based sintered magnet.

In the R1-T1-B system sintered body, the following (1) to (3) are established.
(1) R1 is at least one of rare earth elements and always contains at least one of Nd and Pr, and the content of R1 is 27 mass% or more and 35 mass% or less of the entire R1-T1-B based sintered body.
(2) T1 is Fe or at least one of Co, Al, Mn, and Si and Fe, and the content of Fe with respect to the entire T1 is 80 mass% or more.
(3) The molar ratio of T1 to B ([T1]/[B]) is more than 14.0 and 15.0 or less.

The molar ratio of T1 to B in the present disclosure ([T1] / [B]) is the analysis value (mass%) of each element (Fe or at least one of Co, Al, Mn, Si and Fe) that constitutes T1. is divided by the atomic weight of each element, and the sum of those values (a) and the ratio (a/ b).

The fact that the molar ratio of T1 to B ([T1]/[B]) exceeds 14.0 means that the content ratio of B is lower than the stoichiometric composition ratio of the R ₂ T ₁₄ B compound. there is In other words, in the R1-T1-B system sintered body, the amount of B is relatively small with respect to the amount of T1 used to form the main phase (R ₂ T ₁₄ B compound).

In the R2-Ga-Cu alloy, the following (4) to (6) are established.
(4) R2 is at least one of the rare earth elements and always contains La, the content of R2 is 70 mol% or more and 90 mol% or less of the entire R2-Ga-Cu alloy, and La relative to the entire rare earth element is higher than the ratio of La to the total rare earth elements in the R1-T1-B sintered body.
(5) The content of Ga is 5 mol % or more and 20 mol % or less of the entire R2-Ga-Cu alloy.
(6) The content of Cu is 5 mol % or more and 20 mol % or less of the entire R2-Ga-Cu alloy.

The method for producing an _RTB based sintered magnet according to the present _disclosure uses R1 - At least part of the surface of the T1-B sintered body is brought into contact with the R2-Ga-Cu alloy, and as shown in FIG. Step S30 of performing heat treatment is performed. As a result, an RTB based sintered magnet having high B _r and high H _cJ can be obtained.

First, the basic structure of the RTB system sintered magnet will be described.

RTB sintered magnets have a structure in which raw material _alloy powder particles are bonded by _sintering . It consists of a grain boundary phase located

FIG. 2A is a schematic diagram showing the main phase and grain boundary phase of an RTB based sintered magnet, and FIG. 2B is a schematic diagram further enlarging the broken-line rectangular region of FIG. 2A. In FIG. 2A, as an example, an arrow with a length of 5 μm is shown for reference as a reference length indicating the size. As shown in FIGS. 2A and 2B, the RTB system sintered magnet has a main phase 12 mainly composed of an R ₂ T ₁₄ B compound and a grain boundary phase 14 located at the grain boundary portion of the main phase 12. It consists of Further, as shown in FIG. 2B, the grain boundary phase 14 includes a two-particle grain boundary phase 14a in which two R ₂ T ₁₄ B compound particles (grains) are adjacent to each other, and three or more R ₂ T ₁₄ B compound particles. includes adjacent grain boundary triple points 14b.

The R ₂ T ₁₄ B compound, which is the main phase 12, is a ferromagnetic phase with high saturation magnetization and anisotropic magnetic field. Therefore, in an RTB based sintered magnet, B _r can be improved by increasing the abundance ratio of the R ₂ T ₁₄ B compound that is the main phase 12 . In order to increase the abundance ratio of the R ₂ T ₁₄ B compound, the R amount, T amount, and B amount in the raw material alloy are adjusted to the stoichiometric ratio of the R ₂ T ₁₄ B compound (R amount: T amount: B amount = 2:14:1). When the amount of B or the amount of R for forming the R ₂ T ₁₄ B compound is below the stoichiometric ratio, generally a ferromagnetic material such as an Fe phase or an R ₂ T ₁₇ phase is generated in the grain boundary phase 14. , H _cJ drops sharply. However, as in the method described in Patent Document 1, the amount of B is less than the stoichiometric ratio of the R ₂ T ₁₄ B compound, and one or more selected from Al, Ga, and Cu When the metal element M is included, a transition metal-rich phase (eg, RT-Ga phase) is generated at the grain boundary from the R ₂ T ₁₇ phase, and a high H _cJ can be obtained. However, in the method described in Patent Document 1, _Br is greatly reduced.

In the method for producing an RTB based sintered magnet of the present disclosure, at least a part of the surface of the R1-T1-B based sintered body having a specific composition that is a low B composition has an abundance of rare earth elements By contacting an R2-Ga-Cu alloy containing La as R2, which is relatively rich in , and performing heat treatment, R2 containing La and Ga and Cu are diffused inside the magnet. As a result of investigation by the inventors, it was found that the content of R2 in the R2-Ga-Cu alloy is such that the ratio of La to the total rare earth elements is higher than the ratio of La to the total rare earth elements of the R1-T1-B sintered magnet body. also be raised. Then, when La is present in R2 in such a ratio and heat treatment is performed at a very narrow specific temperature (450° C. or more and 500° C. or less), grain boundary diffusion is promoted, and a thick double layer containing Ga is formed. It was found that grain boundaries can be easily formed even inside the sintered body. This makes it possible to use La and obtain high _Br and high H _cJ while reducing the content of heavy rare earth elements. It was also found that in the case of Ce, which is relatively abundant among rare earth elements like La, it is difficult to achieve effects similar to those of the present disclosure (high _Br and high H _cJ ). That is, the present disclosure realizes high _Br and high H _cJ by heat-treating an alloy containing R2 containing La and Ga and Cu at a very narrow specific temperature and diffusing it into a sintered body with the above specific composition. I have found what I can do.

(Step of preparing R1-T1-B based sintered body)
First, the composition of the sintered body in the step of preparing the R1-T1-B system sintered body (hereinafter sometimes simply referred to as "sintered body") will be described.

R1 is at least one of rare earth elements and always contains at least one of Nd and Pr. In order to improve the H _cJ of the R1-T1-B based sintered body, a small amount of commonly used heavy rare earth elements such as Dy, Tb, Gd and Ho may be contained. However, according to the manufacturing method according to the present disclosure, a sufficiently high H _cJ can be obtained without using a large amount of heavy rare earth elements. Therefore, the content of the heavy rare earth element is preferably 1 mass% or less in the R1-T1-B based sintered body, more preferably 0.5 mass% or less, and does not contain (substantially 0 mass% ) is more preferred.

The content of R1 is 27 mass% or more and 35 mass% or less of the entire R1-T1-B based sintered body. If the content of R1 is less than 27 mass%, the liquid phase is not sufficiently formed during the sintering process, making it difficult to sufficiently densify the R1-T1-B based sintered body. On the other hand, even if the R1 content exceeds 35 mass %, the effect of the present disclosure can be obtained, but the alloy powder becomes very active during the manufacturing process of the R1-T1-B based sintered body. As a result, significant oxidation or ignition of the alloy powder may occur, so the content is preferably 35 mass% or less. The content of R1 is more preferably 27.5 mass % or more and 33 mass % or less, and further preferably 28 mass % or more and 32 mass % or less.

T1 is Fe or at least one of Co, Al, Mn, and Si and Fe, and the content of Fe in the entire T1 is 80 mass% or more. That is, T1 may consist of only Fe, or may consist of at least one of Co, Al, Mn and Si and Fe. However, the content of Fe with respect to the entire T1 is 80 mass% or more. If the Fe content is less than 80 mass%, _Br and _HcJ may decrease. Here, "the content of Fe in the entire T1 is 80 mass% or more" means, for example, when the content of T1 in the R1-T1-B system sintered body is 70 mass%, the R1-T1-B system sintered It means that 56 mass% or more of the body is Fe. Preferably, the content of Fe with respect to the entire T1 is 90 mass% or more. This is because higher _Br and higher _HcJ can be obtained. When Co, Al, Mn, and Si are contained, the preferable content is 5.0 mass% or less for Co, 1.5 mass% or less for Al, and 0.2 mass% or less for each of Mn and Si.

The molar ratio of T1 to B ([T1]/[B]) is more than 14.0 and 15.0 or less.

If the molar ratio of T1 to B ([T1]/[B]) is 14.0 or less, a high _HcJ cannot be obtained. On the other hand, if the molar ratio of T1 to B ([T1]/[B]) exceeds 15.0, _Br may decrease. The molar ratio of T1 to B ([T1]/[B]) is preferably 14.3 or more and 15.0 or less. Higher _Br and higher _HcJ can be obtained. Also, the content of B is preferably 0.85 mass % or more and less than 0.95 mass % of the entire R1-T1-B based sintered body.

In addition to the above elements, the R1-T1-B based sintered body contains Ga, Cu, Ag, Zn, In, Sn, Zr, Nb, Ti, Ni, Hf, Ta, W, Ge, Mo, V, Y, La, Ce, Sm, Ca, Mg, Cr, H, F, P, S, Cl, O, N, C and the like may be contained. The contents of Ga, Cu, Ag, Zn, In, Sn, Zr, Nb, and Ti are each 0.5 mass% or less, Ni, Hf, Ta, W, Ge, Mo, V, Y, La, Ce, Each of Sm, Ca, Mg and Cr is preferably 0.2 mass % or less, H, F, P, S and Cl are preferably 500 ppm or less, O is 6000 ppm or less, N is 1000 ppm or less, and C is 1500 ppm or less. The total content of these elements is preferably 5 mass % or less of the entire R1-T1-B based sintered body. If the total content of these elements exceeds 5 mass % of the entire R1-T1-B based sintered body, it may not be possible to obtain high B _r and high H _cJ .

Next, the process of preparing the R1-T1-B system sintered body will be described. The step of preparing the R1-T1-B system sintered body can be prepared using a general manufacturing method typified by RTB system sintered magnets. The R1-T1-B sintered body is obtained by pulverizing the raw material alloy so that the particle size D ₅₀ (the volume center value obtained by the measurement by the air dispersion laser diffraction method = D ₅₀ ) is 3 μm or more and 10 μm or less, It is preferable to sinter by orientation in a magnetic field. To give an example, a raw material alloy produced by a strip casting method or the like is pulverized using a jet mill device or the like so that the particle size _D50 is 3 μm or more and 10 μm or less, then molded in a magnetic field, and the temperature is 900 ° C. or higher. It can be prepared by sintering at temperatures below 1100°C. If the particle diameter _D50 of the raw material alloy is less than 3 μm, it is extremely difficult to produce pulverized powder, and production efficiency is greatly reduced, which is not preferable. On the other hand, if the grain size _D50 exceeds 10 μm, the crystal grain size of the finally obtained R1-T1-B based sintered body becomes too large, making it difficult to obtain a high _HcJ , which is not preferable. The particle size _D50 is preferably between 3 μm and 5 μm.

The R1-T1-B based sintered body may be produced from one type of raw material alloy (single raw material alloy) as long as the above conditions are satisfied, or two or more types of raw material alloys may be used to produce them. may be produced by a method of mixing (blending method). Further, the obtained R1-T1-B based sintered body may be subjected to known machining such as cutting or cutting as necessary, and then subjected to the heat treatment described later.

(Step of preparing R2-Ga-Cu alloy)
First, the composition of the R2-Ga-Cu alloy in the step of preparing the R2-Ga-Cu alloy will be described. By containing R2, Ga, and Cu in the specific ranges described below, R2, Ga, and Cu in the R2-Ga-Cu alloy are sintered in the R1-T1-B system in the step of performing the heat treatment described later. It can be introduced inside the body.

R2 is at least one of rare earth elements, always contains La, and the content of R2 is 70 mol % or more and 90 mol % or less of the entire R2-Ga-Cu alloy. If the content of R2 is less than 70 mol %, there is a possibility that diffusion will not proceed sufficiently in the heat treatment described later. On the other hand, even if the content of R2 exceeds 90 mol %, the effect of the present disclosure can be obtained, but the alloy powder becomes very active during the manufacturing process of the R2-Ga-Cu alloy. As a result, the alloy powder may be significantly oxidized or ignited, so the content of R2 is preferably 90 mol % or less of the entire R2-Ga-Cu alloy. More preferably, the content of R2 is 75 mol % or more and 85 mol % or less. This is because a higher _HcJ can be obtained. In addition, as described above, while there is concern about the shortage of Nd supply, from the viewpoint of diversifying the use of rare earth elements, La in the R2-Ga-Cu-based alloy is preferably 50 mol% or more of the total R2. More preferably, R2 in the R2-Ga-Cu alloy is La (including impurities).

R2 has a higher ratio of La to the total rare earth elements than the ratio of La to the total rare earth elements of the R1-T1-B based sintered body. As a result, grain boundary diffusion is promoted, and Ga and Cu can be diffused inside the magnet. If the ratio of La is lower than the ratio of La to the total rare earth elements in the R1-T1-B sintered body, grain boundary diffusion is not promoted and the diffusion of Ga and Cu may remain near the surface of the sintered body. be. As a result, the amount of Ga—Cu introduced from the surface of the magnet into the inside is insufficient, and there is a possibility that a sintered RTB magnet having a high B _r and a high H _cJ cannot be obtained. Preferably, when [La]/[R1] in the R1-T1-B system sintered body is α and [La]/[R2] in the R2-Ga-Cu alloy is β, β/α ≧1.5.

Ga is 5 mol % or more and 20 mol % or less of the entire R2-Ga-Cu alloy. If Ga is less than 5 mol%, it is difficult for Ga and Cu in the R2-Ga-Cu-based alloy to be introduced into the R1-T1-B-based sintered body in the step of performing the heat treatment described later, and a high H _cJ can be obtained. I can't On the other hand, when Ga exceeds 20 mol %, _Br may decrease significantly. Ga is more preferably 5 mol % or more and 20 mol % or less. This is because higher _Br and higher _HcJ can be obtained.

Cu is contained in an amount of 5 mol % or more and 20 mol % or less of the entire R2--Ga--Cu alloy. If the Cu content is less than 5 mol%, a high _HcJ may not be obtained, and if the Cu content exceeds 20 mol%, the existence ratio of Ga at the grain boundary may decrease, so 20 mol% or less is preferable.

In addition to the above elements, the R2-Ga-Cu alloy contains Co, Al, Ag, Zn, Si, In, Sn, Zr, Nb, Ti, Ni, Hf, Ta, W, Ge, Mo, V, Y, La, Ce, Sm, Ca, Mg, Mn, Cr, H, F, P, S, Cl, O, N, C and the like may be contained.

Co may be contained in an amount of 0.5 mass % or more and 10 mass % or less for improving corrosion resistance. In addition, Al is 1.0 mass% or less, Ag, Zn, Si, In, Sn, Zr, Nb, and Ti are each 0.5 mass% or less, Ni, Hf, Ta, W, Ge, Mo, V, Y, La, Ce, Sm, Ca, Mg, Mn, Si, and Cr are each 0.2 mass% or less, H, F, P, S, and Cl are 500 ppm or less, O is 6,000 ppm or less, N is 1,000 ppm or less, and C is 1,500 ppm or less. content is preferred. However, when the total content of these elements exceeds 20 mass%, the content of R2, Ga, and Cu in the R2-Ga-Cu alloy decreases, and high _Br and high H _cJ cannot be obtained. there is a possibility. Therefore, the total content of R2, Ga and Cu in the R2-Ga-Cu alloy is preferably 80 mass% or more, more preferably 90 mass% or more.

Next, the process of preparing the R2--Ga--Cu alloy will be described. The R2-Ga-Cu alloy can be produced by a raw material alloy preparation method employed in general manufacturing methods typified by Nd-Fe-B sintered magnets, such as die casting, strip casting and single casting. It can be prepared using a roll ultra-quenching method (melt spinning method), an atomizing method, or the like. Also, the R2-Ga-Cu alloy may be obtained by pulverizing the alloy obtained above by a known pulverizing means such as a pin mill. In order to improve the pulverizability of the alloy obtained as described above, the alloy may be subjected to heat treatment at 700° C. or less in a hydrogen atmosphere to contain hydrogen, and then pulverized.

(Step of performing heat treatment)
At least part of the surface of the R1-T1-B-based sintered body prepared above is brought into contact with at least part of the R2-Ga-Cu-based alloy, and in a vacuum or inert gas atmosphere, at 450 ° C. or more and 500 ° C. Heat treatment at the following temperature. As a result, a liquid phase containing R2 containing La and Ga and Cu is generated from the R2-Ga-Cu-based alloy, and the liquid phase passes through the grain boundaries of the R1-T1-B-based sintered body to the sintered body. Diffusion is introduced from the surface to the inside, and an RT-Ga phase is generated at the grain boundary. If the heat treatment temperature is less than 450° C., the amount of liquid phase containing R2 containing La and Ga and Cu may be too small to obtain high _Br and high _HcJ . On the other hand, if the temperature exceeds 500 ° C., the diffusion of the R2-Ga-Cu alloy into the R1-T1-B sintered body is inhibited for unknown reasons, and a high H _cJ may not be obtained. . The heat treatment temperature is preferably 460° C. or higher and 490° C. or lower. This is because higher _Br and higher _HcJ can be obtained. The heat treatment time is set to an appropriate value depending on the composition and dimensions of the R1-T1-B-based sintered body and R2-Ga-Cu-based alloy, the heat treatment temperature, etc., but is preferably 5 minutes or more and 24 hours or less, and 10 minutes or more. 20 hours or less is more preferable, and 30 minutes or more and 16 hours or less is even more preferable. Further, the heat treatment may be performed only once, or may be performed multiple times. In addition, it is preferable to prepare the R2-Ga-Cu alloy in an amount of 2 mass% or more and 30 mass% or less with respect to the weight of the R1-T1-B sintered body. If the R2-Ga-Cu based alloy is less than 2 mass% with respect to the weight of the R1-T1-B based sintered body, a high H _cJ may not be obtained. On the other hand, if it exceeds 30 mass%, _Br may decrease significantly.

The heat treatment can be performed by placing an R2-Ga-Cu alloy in an arbitrary shape on the surface of the R1-T1-B sintered body and using a known heat treatment apparatus. For example, the surface of the R1-T1-B based sintered body can be covered with a powder layer of R2-Ga-Cu based alloy and heat treated. For example, after applying a slurry in which an R2-Ga-Cu alloy is dispersed in a dispersion medium to the surface of the R1-T1-B sintered body, the dispersion medium is evaporated to obtain the R2-Ga-Cu alloy and the R1- It may be brought into contact with the T1-B system sintered body. Further, as shown in an experimental example to be described later, it is preferable that the R2-Ga-Cu based alloy is arranged so as to contact at least the surface of the R1-T1-B based sintered body perpendicular to the orientation direction. Examples of dispersion media include alcohols (ethanol, etc.), NMP (N-methylpyrrolidone), aldehydes, and ketones. Also, the heat-treated R1-T1-B-based sintered body may be subjected to known machining such as cutting and cutting.

The present invention will be explained in more detail by examples, but the present invention is not limited to them.

Experimental example 1
[Preparation of R1-T1-B based sintered body]
Using Nd metal, Pr metal, ferroboron alloy, and electrolytic iron (all metals have a purity of 99% or more), the sintered body is blended so that it has a composition of 1-A to 1-C shown in Table 1. , and the raw materials were melted and cast by a strip casting method to obtain raw material alloy flakes having a thickness of 0.2 to 0.4 mm. After hydrogen pulverization of the resulting flaky raw material alloy, a dehydrogenation treatment was performed by heating to 550° C. in vacuum and then cooling to obtain a coarsely pulverized powder. Next, 0.04 mass% of zinc stearate as a lubricant is added to the obtained coarsely pulverized powder with respect to 100 mass% of the coarsely pulverized powder, and mixed. Dry pulverization was carried out in an air stream to obtain a finely pulverized powder (alloy powder) having a pulverized particle diameter _D50 of 4 μm. The pulverized particle size _D50 is the volume center value (volume-based median diameter) obtained by the laser diffraction method using the air dispersion method.

To the finely pulverized powder, 0.05 mass % of zinc stearate was added as a lubricant to 100 mass % of the finely pulverized powder. As the forming apparatus, a so-called orthogonal magnetic field forming apparatus (transverse magnetic field forming apparatus) in which the magnetic field application direction and the pressurizing direction are perpendicular to each other was used.

The obtained molded body is sintered in a vacuum at 1000° C. or higher and 1040° C. or lower (a temperature at which sintering causes sufficient densification is selected for each sample) for 4 hours and then quenched to sinter the R1-T1-B system. got a body The density of the obtained sintered body was 7.5 Mg/m ³ or more. Table 1 shows the composition of the obtained sintered body. Each component in Table 1 was measured using high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). As a result of measuring the oxygen content of the sintered bodies by the gas fusion-infrared absorption method, it was confirmed that all of them were around 0.4 mass %. "[T1]/[B]" in Table 1 is an analysis value (mass%) for each element (including unavoidable impurities, Fe, Al, Si, Mn in this experimental example) that constitutes T1. (a) obtained by dividing the atomic weight of the element and summing those values, and (b) obtained by dividing the analytical value (mass%) of B by the atomic weight of B is the ratio (a/b) to The same is true for all tables below. In addition, even if each composition of Table 1 is totaled, it does not become 100 mass%. This is because, as described above, the analysis method differs depending on each component, and furthermore, components other than those listed in Table 1 (for example, C (carbon), N (nitrogen), etc.) are present. The same applies to other tables.

[Preparation of R2-Ga-Cu alloy]
Using La metal, Ga metal, and Cu metal (all metals have a purity of 99% or more), the alloy is blended so that it has a composition of code 1-a shown in Table 2, and these raw materials are melted, A ribbon- or flake-shaped alloy was obtained by a single-roll ultra-quenching method (melt spinning method). The obtained alloy was pulverized in an argon atmosphere using a mortar and then passed through a sieve with an opening of 425 μm to prepare an R2-Ga-Cu alloy. Table 2 shows the composition of the obtained R2-Ga-Cu alloy.

[Heat treatment]
The R1-T1-B based sintered bodies of 1-A to 1-C in Table 1 were cut and machined into rectangular parallelepipeds of 4.4 mm×4.4 mm×4.4 mm (orientation direction). Next, as shown in FIG. 3, in a processing container 3 made of niobium foil, the surface perpendicular to the orientation direction (arrow direction in the figure) of the R1-T1-B system sintered body 1 is mainly R2- The R2-Ga-Cu-based alloy indicated by reference numeral 1-a shown in Table 2 is placed above and below each of the R1-T1-B-based sintered bodies indicated by reference numerals 1-A to 1-I so as to be in contact with the Si-based alloy 2. placed in

After that, using a tubular flow furnace, heat treatment was performed at the heat treatment temperature and time shown in Table 3 in reduced pressure argon controlled at 200 Pa, and then cooled. In order to remove the concentrated portion of the R2-Ga-Cu-based alloy present near the surface of each sample after heat treatment, the entire surface of each sample was cut by 0.2 mm using a surface grinder, and 4.0 mm × A cubic sample (RTB sintered magnet) of 4.0 mm×4.0 mm was obtained.

[Sample evaluation]
The residual magnetic flux density (B _r ) and coercive force (H _cJ ) of the samples obtained by BH tracer were measured. Table 3 shows the measurement results. As shown in Table 3, when the molar ratio of T1 to B in the R1-T1-B sintered body ([T1] / [B]) is set to 14.0 or more, and the heat treatment temperature is set to 450 ° C. or higher and 500 ° C. or lower , high characteristics were obtained.

Among the samples shown in Table 3, No. Scanning electron microscope (SEM: JSM-7800F manufactured by JEOL Ltd.) of the sintered body surface vicinity, 800 μm area from the surface, and the cross section of the central part of 1-4 (example of the present invention) is a backscattered electron image at an accelerating voltage of 5 kV. Acquired. The results are shown in Figures 4A-4C. A thick grain boundary of 100 nm or more was formed from the vicinity of the surface of the magnet to the center of the magnet.

Furthermore, No. 1, which is an example of the present invention. Regarding the sintered body of 1-4, energy dispersive X-ray spectroscopic analysis of the vicinity of the surface, the 800 μm area from the surface, and the cross section of the central part by SEM (JSM-7800F manufactured by JEOL) accessory device (JED-2300 SD30 manufactured by JEOL) (EDS) was performed. The analysis points are 1, 4, 6, 7 and 8 in FIGS. 4A and 4B, and 1, 4, 5, 7 and 8 in FIG. 4C. The probe diameter for EDX analysis was set to 1 μm, and the average composition of the observation area was obtained from the analysis result of 200 μm square. The results are shown in Figures 5A-5C. As shown in FIGS. 5A to 5C, substitution of La into the main phase could hardly be confirmed. In addition, although grain boundary phases with multiple compositions were observed in each observation region, the molar ratio of La to rare earth element R in each phase was higher on the surface of the RTB system sintered magnet than on the inside. was In addition, in each observation region, a phase containing 25 mol % or more and 35 mol % or less of R and 55 mol % or more and 65 mol % or less of Fe was confirmed. Since this phase contains Ga and Cu, it is presumed to be an R ₆ Fe ₁₃ M (M is Ga, Cu, etc.) phase, and two or more composition phases with different La amounts within the same field of view. existed.

Experimental example 2
A plurality of R1-T1-B sintered bodies were produced in the same manner as in Experimental Example 1, except that the sintered body was mixed so as to have a composition of 2-A shown in Table 4. Table 4 shows the result of component analysis of the obtained sintered body.

An R2-Ga-Cu alloy was produced in the same manner as in Experimental Example 1, except that the alloy composition was blended so as to correspond to symbols 2-a to 2-m shown in Table 5.

After processing a plurality of R1-T1-B-based sintered bodies in the same manner as in Experimental Example 1, R2-Ga-Cu-based alloys 2-a to 2-m and 2-A in the same manner as in Experimental Example 1 were placed in contact with the R1-T1-B based sintered body, and heat treatment and processing were performed in the same manner as in Experimental Example 1 to obtain a sample (RTB based sintered magnet). The resulting sample was measured in the same manner as in Experimental Example 1 to obtain residual magnetic flux density (B _r ) and coercive force (H _cJ ). Table 6 shows the results. As shown in Table 6, RTB based sintered magnets having high magnetic properties were obtained by setting the R2-Ga-Cu based alloy within a specific range.

The RTB based sintered magnet obtained by the embodiment of the present invention is used in voice coil motors (VCM) of hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, etc. It can be suitably used for various motors and home electric appliances.

1 R1-T1-B-based sintered body 2 R2-Ga-Cu-based alloy 3 Processing vessel

Claims (5)

A step of preparing an R1-T1-B based sintered body;
A step of preparing an R2-Ga-Cu alloy;
At least part of the surface of the R1-T1-B-based sintered body is brought into contact with at least part of the R2-Ga-Cu-based alloy, and in a vacuum or inert gas atmosphere, at a temperature of 450 ° C. or higher and 500 ° C. or lower. including the step of performing heat treatment at
In the R1-T1-B based sintered body,
R1 is at least one of rare earth elements and necessarily contains at least one of Nd and Pr, and the content of R1 is 27 mass% or more and 35 mass% or less of the entire R1-T1-B based sintered body,
T1 is Fe or at least one of Co, Al, Mn, and Si and Fe, and the Fe content relative to the entire T1 is 80 mass% or more,
The molar ratio of T1 to B ([T1]/[B]) is more than 14.0 and 15.0 or less,
In the R2-Ga-Cu alloy,
R2 is at least one of the rare earth elements and necessarily contains La, the content of R2 is 70 mol% or more and 90 mol% or less of the entire R2-Ga-Cu alloy, and the ratio of La to the total rare earth elements is , higher than the ratio of La to the total rare earth elements of the R1-T1-B based sintered body,
The content of Ga is 5 mol% or more and 20 mol% or less of the entire R2-Ga-Cu alloy,
A method for producing an RTB system sintered magnet, wherein the Cu content is 5 mol % or more and 20 mol % or less of the entire R2-Ga-Cu system alloy. 2. The method for producing a RTB based sintered magnet according to claim 1, wherein La in said R2-Ga-Cu based alloy is 50 mol % or more of the total R2. 2. The method for producing a RTB based sintered magnet according to claim 1, wherein R2 in said R2-Ga-Cu based alloy is La (including impurities). 4. The method for producing a RTB based sintered magnet according to claim 1, wherein the total content of R2, Ga and Cu in said R2-Ga-Cu based alloy is 80 mass % or more. The step of preparing the R1-T1-B-based sintered body includes pulverizing the raw material alloy so that the particle size _D50 is 3 μm or more and 10 μm or less, and then sintering by orienting in a magnetic field. A method for producing an RTB based sintered magnet according to any one of claims 1 to 4.

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