JP7155813B2 - 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 and always contains Nd, T is Fe or Fe and Co, and B is boron) has the highest 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.

RTB based sintered magnets are composed of a main phase mainly composed of an R ₂ T ₁₄ B compound and a grain boundary phase located at the grain boundary portion of the main phase. The R ₂ T ₁₄ B compound, which is the main phase, is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field, and forms the basis of the properties of the RTB system sintered magnet.

At high temperatures, irreversible thermal demagnetization occurs because the coercive force H _cJ (hereinafter sometimes simply referred to as “H _cJ ”) of the RTB sintered magnet decreases. Therefore, RTB sintered magnets used in motors for electric vehicles are particularly required to have a high _HcJ .

In the RTB system sintered magnet, part of the light rare earth element RL (for example, Nd and Pr) contained in R in the R ₂ T ₁₄ B compound is replaced with the heavy rare earth element RH (for example, Dy and Tb). The substitution is known to improve the H _cJ . The _HcJ improves as the amount of RH substitution increases.

However, when RH is substituted for RL in the R ₂ T ₁₄ B compound, the H _cJ of the RTB system sintered magnet is improved, while the residual magnetic flux density B _r (hereinafter sometimes simply referred to as “B _r ”) existing) will decrease. In particular, RH such as Dy has a problem that the supply is not stable and the price fluctuates greatly because the resources are scarce and the places of production are limited. Therefore, in recent years, there has been a demand for improving _HcJ while minimizing the use of RH.

Patent Document 1 discloses an RTB-based rare earth sintered magnet having a high coercive force while suppressing the Dy content. 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

In the RTB rare earth sintered magnet disclosed in Patent Document 1, although a high H _cJ can be obtained while the Dy content is reduced, there is a problem that the _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.

Various embodiments of the present invention provide methods for producing RTB-based sintered magnets having high B _r and high H _cJ while reducing the RH content.

In an exemplary embodiment of the method for producing an RTB based sintered magnet of the present disclosure, R: 27.5% by mass or more and 33.0% by mass or less (R is at least one rare earth element, Nd must be included), B: 0.85% by mass or more and 0.97% by mass or less, T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T in terms of mass ratio is Fe Pr: 65% by mass or more and 97% by mass or less (30% by mass of Pr can be replaced by another rare earth element), and Ga: 3% by mass or more and 35% by mass % or less (50% by mass or less of Ga can be replaced with Cu) and prepared by an atomizing method, and mixing the main alloy powder and the Pr-Ga alloy powder. Then, a step of producing a mixed powder in which the mass ratio of the Pr—Ga alloy powder to the entire mixed powder is 1% by mass or more and 10% by mass or less, molding in a magnetic field, and molding a compact of the mixed powder at 950 ° C. and a sintering step of sintering at a sintering temperature of not less than 1120 ° C., and when the sintering temperature in the sintering step is T ° C. and the sintering time is t seconds, 5 × (1120-T ) ² <t<10×(1120−T) ² holds.

In one embodiment, where [T] is the content of T expressed in mass% and [B] is the content of B expressed in mass%, the RTB based sintered magnet has a ratio of [T]/ It satisfies the relationship 55.85>14[B]/10.8.

In one embodiment, the content of Nd in the Pr--Ga alloy powder is equal to or less than the content of unavoidable impurities.

According to the embodiment of the present disclosure, after producing a compact of a mixed powder in which Pr—Ga alloy powder produced by the atomization method is added to the main alloy powder in an appropriate mass ratio, this compact is produced under specific conditions. Therefore, RTB based sintered magnets having high B _r and H _cJ can be produced even if the content of heavy rare earth elements such as Dy is reduced.

1 is a cross-sectional view schematically showing an enlarged part of an RTB based sintered magnet. FIG. FIG. 1B is a schematic cross-sectional view further enlarging the inside of the broken-line rectangular region of FIG. 1A. 4 is a flow chart showing an example of steps in a method for manufacturing a RTB based sintered magnet according to an embodiment of the present disclosure; 4 is a graph showing the relationship between sintering temperature T and sintering time t.

FIG. 1A is a schematic cross-sectional view enlarging a part of an RTB based sintered magnet, and FIG. 1B is a cross-sectional view schematically showing a further enlarged broken-line rectangular area in FIG. 1A. is. In FIG. 1A, 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. 1A and 1B, 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 As shown in FIG. 1B, the grain boundary phase 14 consists of a two-grain grain boundary phase 14a in which two R ₂ T ₁₄ B compound grains (grains) are adjacent to each other, and a grain boundary phase 14a in which three R ₂ T ₁₄ B compound grains are adjacent to each other. field triple point 14b.

The R ₂ T ₁₄ B compound, which is the main phase 12, is a ferromagnetic material 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).

As described in Patent Document 1, the amount of B is less than that of a general RTB-based sintered magnet, that is, the amount of B is less than the stoichiometric ratio of the R ₂ T ₁₄ B type compound. Then, when Ga is added, a transition metal-rich phase (RT-Ga phase) containing Ga is generated in the grain boundary phase 14 to improve H _cJ .

As a result of intensive studies by the present inventors, since the RT-Ga phase has magnetization, among the two grain boundaries 14a and the grain boundary triple points 14b of the RTB sintered magnet, It was found that the presence of a large amount of RT-Ga phase at the two-grain boundary 14a, which is considered to mainly affect H _cJ , hinders improvement of H _cJ . It was also found that together with the formation of the RT-Ga phase, an R--Ga phase, which is considered to have a lower magnetization than the RT--Ga phase, was also formed at the two-grain boundary 14a. Therefore, in order to obtain an RTB system sintered magnet having a high _HcJ , although it is necessary to generate the RT-Ga phase, it is necessary to generate a large amount of the R-Ga phase at the grain boundaries 14a of the two grains. thought it was important.

As a result of experiments by the present inventors, Pr--Ga alloy powder (atomized powder) produced by the atomizing method was mixed with powder of the main alloy of RTB-based sintered magnets, and a molded body of this mixed powder was obtained. It was found that R and Ga can be introduced into the two-grain boundaries 14a without being introduced into the interior of the main phase crystal grains 12 by executing the sintering process under predetermined conditions after producing the R and Ga. Thus, according to the embodiment of the present invention, a large amount of R--Ga phase can be generated at the grain boundaries of two grains.

As described above, the RTB sintered magnet has a structure in which powder particles of the main alloy for forming the main phase are bonded by sintering, and is mainly composed of the R ₂ T ₁₄ B compound. It is composed of a main phase and a grain boundary phase located at the grain boundary portion of the main phase. Since the melting point of the Pr--Ga alloy is lower than the sintering temperature, the powder particles of the Pr--Ga alloy melt during the sintering process and mainly constitute the grain boundary phase of the RTB system sintered magnet. do.

Incidentally, the Pr--Ga alloy has poor pulverizability. Therefore, if the Pr--Ga alloy is subjected to normal hydrogen pulverization and fine pulverization, pulverization takes a long time, which poses a problem in mass production. If the Pr--Ga alloy with hydrogen occluded is finely pulverized, the pulverizability is improved, but hydrogen may remain in the resulting sintered magnet, degrading the magnetic properties. Therefore, when utilizing hydrogen absorption, it is necessary to release hydrogen sufficiently by lengthening the sintering time or raising the sintering temperature so as not to leave hydrogen as much as possible. However, under such sintering conditions, R and Ga diffuse into the main phase crystal grains, making it impossible to obtain a high _HcJ .

In the embodiment of the present disclosure, the use of atomized Pr—Ga alloy powder makes it possible to obtain powder particles (for example, particles having a particle size of 106 μm or less) without pulverization. Since it is not necessary to release the hydrogen occluded by the alloy during the sintering process, there is no need to lengthen the sintering time or raise the sintering temperature. As a result, it was possible to select sintering conditions suitable for modifying the grain boundary phase with R and Ga to improve the magnetic properties.

As illustrated in FIG. 2, the method for producing a RTB based sintered magnet according to the present disclosure includes a step S10 of preparing a main alloy powder for an RTB based sintered magnet, and an atomization method. and step S20 of providing powder of the fabricated Pr--Ga alloy. The order of the step S10 of preparing the main alloy powder and the step S20 of preparing the Pr--Ga alloy powder is arbitrary, and the main alloy powder and the Pr--Ga alloy powder produced in different places may be used. good. Further, the method for producing an RTB based sintered magnet according to the present disclosure includes a step of mixing the main alloy powder and the Pr—Ga alloy powder and compacting in a magnetic field (powder compacting step) S30, and and a step of sintering the mixed powder compact (sintering step) S40.

The main alloy powder in embodiments of the present disclosure is
R: 27.5% by mass or more and 33.0% by mass or less (R is at least one of rare earth elements and necessarily contains Nd),
B: 0.85% by mass or more and 0.97% by mass or less,
T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T is Fe in mass ratio),
contains

On the other hand, the Pr—Ga alloy powder in the embodiment of the present disclosure is
Pr: 65% by mass or more and 97% by mass or less, and Ga: 3% by mass or more and 35% by mass or less (50% by mass or less of Ga can be replaced with Cu),
contains

In the powder compacting step S30 in the embodiment of the present disclosure, when mixing the main alloy powder and the Pr—Ga alloy powder, the mass ratio of the Pr—Ga alloy powder to the entire mixed powder is 1% by mass or more and 10% by mass or less. do.

In the sintering step S40 in the embodiment of the present disclosure, the compact of the mixed powder is sintered at a sintering temperature of 950°C or higher and lower than 1120°C. Further, when the sintering temperature is T° C. and the sintering time is t seconds, the sintering conditions are adjusted so that the relationship of Equation 1 below is established.
5×(1120−T) ² <t<10×(1120−T) ² (Formula 1)

FIG. 3 is a graph showing the relationship between sintering temperature T and sintering time t. The dashed line in the graph is a curve showing 5×(1120−T) ² that defines the lower limit of sintering time t. On the other hand, the dotted line in the graph is a curve representing 10×(1120−T) ² that defines the upper limit of the sintering time t.

When the sintering temperature T is set to, for example, 1020° C., 5×(1120−T) ² that defines the lower limit of the sintering time t is 5×100 ² =50000 seconds, which is about 13 hours and 50 minutes. be. Also, 10×(1120−T) ² defining the upper limit of the sintering time t is 10×100 ² =100000 seconds, which is about 27 hours and 46 minutes. Therefore, if the sintering temperature T is 1020° C., the sintering time t is selected from the range of about 13 hours and 50 minutes to about 27 hours and 46 minutes.

According to the present disclosure, sintering is performed under the specific conditions for a powder compact produced by mixing the main alloy powder and the Pr—Ga alloy powder, whereby sintering and Formation of the R--Ga phase in the grain boundary phase proceeds appropriately. As a result, the grain boundary phase of the RTB system sintered magnet is reformed throughout the interior of the magnet to achieve high B _r and H _cJ . When Pr and Ga are diffused and introduced from the surface of the RTB based sintered magnet material into the interior after the RTB based sintered magnet material is produced by sintering, Pr and Ga are inevitably introduced. Since Ga concentration gradient occurs, even in the grain boundary phase of the RTB sintered magnet, the region near the surface of the RTB sintered magnet and the RTB sintered magnet There is a difference in the amount of R--Ga phase produced between the inside of the magnet and the inside of the magnet. However, according to the embodiments of the present disclosure, Pr and Ga are added from the stage before sintering and are present inside the powder compact, thus solving the problems of the conventional method.

Further, in the embodiment of the present disclosure, the Pr--Ga alloy powder is produced by the atomization method. Powders produced by the atomization method are sometimes called "atomized powders".

The atomization method, which is also called a molten metal atomization method, is one type of powder production method, and includes known atomization methods such as a gas atomization method and a plasma atomization method. For example, according to the gas atomization method, a metal or alloy is melted in a melting furnace to form a molten metal, which is sprayed into an inert gas atmosphere such as nitrogen or argon to solidify. Since the sprayed molten metal scatters as fine droplets, it is cooled at a high speed and solidified. Since the powder particles produced each have a spherical shape, no pulverization is necessary. The size of powder particles produced by the atomization method is distributed, for example, in the range of 10 μm to 200 μm.

According to the atomization method, since the droplets of the molten alloy to be sprayed are small and the surface area of each droplet is relatively large relative to its weight, the cooling rate is high. As such, the powder particles formed are amorphous or microcrystalline. These powder particles may additionally be heat-treated before mixing to crystallize amorphous particles.

The particle size of the Pr--Ga alloy powder can be adjusted by sieving. Further, if the amount of powder excluded by sieving is within 10% by mass, the effect is small, so the powder may be used without sieving.

After the sintering step, an additional heat treatment may be performed at a temperature below the sintering temperature in a vacuum or inert gas atmosphere. Other steps, such as a cooling step, may be performed between the sintering step S40 and the step of performing the additional heat treatment.

An RTB based sintered magnet manufactured by the manufacturing method of the present disclosure has, for example, the following composition.
R: 27.5% by mass or more and 34.0% by mass or less (R is at least one rare earth element and always contains at least one of Nd and Pr),
B: 0.85% by mass or more and 0.93% by mass or less,
Ga: 0.20% by mass or more and 0.70% by mass or less,
Cu: 0.05% by mass or more and 0.70% by mass or less, and T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T in terms of mass ratio is Fe), And when [T] is the content of T expressed in mass% and [B] is the content of B expressed in mass%, [T]/55.85>14[B]/10.8 To establish.

The composition of each alloy will be described in more detail below.

1. Composition of Main Alloy (R) The content of R is 27.5 to 33.0% by mass. R is at least one of rare earth elements, and necessarily contains Nd. If the R content is less than 27.5% by mass, the liquid phase is not sufficiently formed during the sintering process, making it difficult to sufficiently densify the sintered body. On the other hand, even if R exceeds 33.0% by mass, the effect of the present invention can be obtained, but the alloy powder becomes very active during the manufacturing process of the sintered body, and the alloy powder is significantly oxidized and ignited. 33.0% by mass or less is preferable. R is more preferably 28% by mass to 33.0% by mass, even more preferably 29% by mass to 33% by mass. The content of the heavy rare earth element RH is preferably 5% by mass or less. In the embodiment of the present invention, high B _r and high H _cJ can be obtained _without using the heavy rare earth element RH. can.

(B) The content of B is 0.85 to 0.97% by mass. A high B _r and a high H _cJ can be obtained by mixing the main alloy powder containing 0.85 to 0.97% by mass of B with the Pr—Ga alloy powder and sintering the mixture. If the B content is less than 0.85% by mass, _{Br may decrease, and if it exceeds 0.97% by mass, HcJ may} decrease. Also, part of B can be replaced with C.

(Ga) The content of Ga in the main alloy powder is 0 to 0.8% by mass. In the present invention, by adding Pr—Ga alloy powder to the main alloy powder, Ga is introduced into the grain boundary phase, so the main alloy powder has a relatively small amount of Ga (or does not contain Ga). . If the Ga content exceeds 0.8% by mass, the magnetization of the main phase may decrease due to Ga contained in the main phase, making it impossible to obtain a high _Br . Preferably, the Ga content is 0.5% by mass or less. A higher _Br can be obtained.

(M) The content of M is 0 to 2% by mass. M is at least one of Cu, Al, Nb, and Zr, and the effect of the present invention can be exhibited even if it is 0% by mass. can be done. H _cJ can be improved by containing Cu and Al. Cu and Al may be positively added, or those that are unavoidably introduced in the raw material used or the manufacturing process of the alloy powder may be utilized. Also, by containing Nb and Zr, abnormal grain growth of crystal grains during sintering can be suppressed. Preferably, M necessarily contains Cu and contains 0.05 to 0.30% by mass of Cu. This is because the H _cJ can be further improved by containing 0.05 to 0.30% by mass of Cu.

(T) T is Fe or Fe and Co. Fe preferably accounts for 90% or more of T in mass ratio. Part of Fe can be replaced with Co. However, if the substitution amount of Co exceeds 10% of the total T by mass ratio, _Br decreases, which is not preferable. The content of T is 61.5% by mass or more. If the T content is less than 61.5% by mass, Br may decrease significantly. Preferably, T is the balance.

The main alloy powder in the present disclosure includes unavoidable impurities that are usually contained in alloys such as didymium alloys (Nd-Pr), electrolytic iron, and ferroboron and during the manufacturing process, and small amounts of elements other than the above (R, B , Ga, M, and T). For example, Ti, V, Cr, Mn, Ni, Si, La, Ce, Sm, Ca, Mg, O (oxygen), N (nitrogen), C (carbon), Mo, Hf, Ta, W, etc. You may

The main alloy powder can be prepared using a general RTB based sintered magnet manufacturing method typified by Nd—Fe—B based sintered magnets. For example, after pulverizing a raw material alloy produced by a strip casting method or the like to a particle size _D50 of 1 μm or more and 10 μm or less (preferably a particle size _D50 of 3 μm or more and 8 μm or less) using a jet mill or the like , can be prepared by molding in a magnetic field and sintering at a temperature between 900°C and 1100°C.

If the pulverized particle size of the raw material alloy (volume median value = D ₅₀ measured by the air dispersion laser diffraction method) is less than 1 μm, it is extremely difficult to produce pulverized powder, and the production efficiency is greatly reduced. I don't like it. On the other hand, if the pulverized particle size exceeds 10 μm, the crystal grain size of the finally obtained main alloy powder for sintered RTB magnets becomes too large, making it difficult to obtain a high _HcJ , which is not preferable. .

Preferably, the primary alloy powder satisfies Equation 2.
[T]/55.85>14[B]/10.8 (Formula 2)

By satisfying this formula 2, the B content becomes smaller than that of general RTB based sintered magnets. General RTB sintered magnets have a [T]/55.85 (atomic weight of Fe) so that Fe phase and R ₂ T ₁₇ phase do not form in addition to R ₂ T ₁₄ B phase, which is the main phase. is less than 14 [B] / 10.8 (atomic weight of B) ([T] is the content of T expressed in mass%, [B] is the content of B expressed in mass% is).

In a preferred embodiment of the present disclosure, unlike general RTB sintered magnets, [T]/55.85 (atomic weight of Fe) is higher than 14 [B]/10.8 (atomic weight of B). is defined by Equation 2 so that As for T in the main alloy powder, the atomic weight of Fe is used because Fe is the main component.

2. Composition of Pr—Ga alloy powder (Pr) Pr in the Pr—Ga alloy powder is 65 to 97% by mass of the entire Pr—Ga alloy. 30% by mass or less of this Pr can be replaced with other rare earth elements. Specifically, 30 mass % or less of Pr can be replaced with Nd, and 20 mass % or less of Pr can be replaced with Dy and/or Tb.

(Ga) Ga accounts for 3% to 35% by mass of the entire Pr--Ga alloy, and 50% by mass or less of Ga can be replaced with Cu. The Pr--Ga alloy may contain unavoidable impurities.

In the present disclosure, “30% or less of Pr can be replaced with Nd” means that the content (mass%) of Pr in the Pr—Ga alloy is 100%, and 30% of which can be replaced with Nd. means For example, 70% by mass of Pr (30% by mass of Ga) in a Pr—Ga alloy can be substituted with up to 21% by mass of Nd. That is, Pr is 49% by mass and Nd is 21% by mass. The same is true for Dy, Tb, and Cu.

By mixing Pr--Ga alloy powder with Pr and Ga within the above ranges with the main alloy powder, Pr and Ga are concentrated in the grain boundary phase during the sintering process and dispersed in the grain boundary phase throughout the magnet. be able to. Part of Pr in the Pr—Ga alloy may be substituted with Nd, Dy and/or Tb, but if the amount of each substitution exceeds the above range, Pr is too small, so high _Br and high H _cJ cannot be obtained. Preferably, the Nd content of the Pr--Ga alloy is less than or equal to the incidental impurity content (approximately 1% by weight or less). Although 50% or less of Ga can be replaced with Cu, _HcJ may decrease when the amount of Cu replacement exceeds 50%.

The Pr--Ga alloy powder in the present disclosure is produced by the atomization method. Therefore, even without mechanical pulverization, it has a spherical shape as described above.

The sintered magnet thus obtained may be subjected to additional heat treatment for the purpose of further improving the magnetic properties. For example, one-step heat treatment may be performed at a temperature lower than the sintering temperature (400° C. or higher and 600° C. or lower). Alternatively, after performing the first heat treatment at a relatively high temperature (700 ° C. or higher and the sintering temperature or lower), the second heat treatment may be performed at a relatively low temperature (400 ° C. or higher and 600 ° C. or lower) (two-step Heat treatment). A specific example of the two-stage heat treatment may include a first heat treatment at a temperature of 750° C. or higher and 850° C. or lower for about 5 minutes to 500 minutes, and a second heat treatment at a temperature of 440° C. or higher and 550° C. or lower for about 5 minutes to 500 minutes. . Between the first heat treatment and the second heat treatment, cooling may be performed to room temperature, or to a temperature of 440° C. or higher and 550° C. or lower. The R ₆ T ₁₃ Ga phase generated during cooling after sintering can disappear by heat treatment at relatively high temperatures. _Reducing the amount of _R6T13Ga phase before the second heat treatment expands the grain boundary phase and can increase _HcJ . Also, heat treatment at relatively low temperatures can promote the formation of RT-Ga and R-Ga phases.

Any heat treatment is desirably performed in a vacuum atmosphere or an inert gas (helium, argon, etc.).

The present disclosure will be described in more detail by examples, but the disclosure is not limited thereto.

Example 1
About No. in Table 1. Each element was weighed so that the composition shown in A was obtained, and the alloy was cast by a strip casting method to obtain an alloy in the form of flakes. After hydrogen embrittlement was applied to the resulting flake-shaped alloy in a pressurized hydrogen atmosphere, dehydrogenation treatment was performed by heating to 550° C. in vacuum and cooling to obtain a coarsely pulverized powder. Next, 0.04% by mass of zinc stearate as a lubricant is added to the coarsely ground powder with respect to 100% by mass of the coarsely ground powder. , dry-milled in a nitrogen atmosphere to obtain a main alloy powder with a particle size _D50 of 4.3 μm. No. 1 in Table 1 shows the result of component analysis of the obtained main alloy powder. A. Each component in Table 1 was measured using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The compositions of the main alloy powder, the Pr--Ga alloy powder, and the RTB system sintered magnet were also measured in the same manner.

Next, a Pr--Ga alloy powder (No. a) of an alloy having the composition shown in Table 2 was produced by an atomizing method. The particle size of the obtained Pr--Ga alloy powder was 106 μm or less.

Next, the main alloy powder (No. A) and the Pr--Ga alloy powder (No. a) were put into a V-type mixer and mixed to prepare a mixed powder (fine pulverized powder). The mass ratio of the Pr--Ga alloy powder to the entire mixed powder was 3% by mass. 0.05% by mass of zinc stearate as a lubricant was added to the mixed powder with respect to 100% by mass of the finely pulverized powder, and the mixture was compacted in a magnetic field to obtain a compact. 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 compact was sintered at the sintering temperature and sintering time shown in Table 3. If the sintering time satisfies the formula 1 (5 × (1120-T) ² < t < 10 × (1120-T) ² ) of the present disclosure, it is indicated as ◯, and if it is not satisfied, it is indicated as ×. ing. Also, the sintering temperature and the sintered magnet were measured by attaching a thermocouple to the compact. The RTB sintered magnet after sintering is subjected to heat treatment in which it is held at 900°C in vacuum for 2 hours, then cooled to room temperature, then held at 500°C in vacuum for 2 hours, and then cooled to room temperature. RTB system sintered magnets (Nos. 1 to 9) were obtained. When the components of the obtained RTB based sintered magnets were checked, all (No. 1 to 9) were found to be Nd: 22.5%, Pr: 9.77%, B: 0.5% by mass ratio. 88%, Co: 0.87%, Al: 0.1%, Cu: 0.18%, Ga: 0.5%, Zr: 0.1%, Fe: 64.85%, and the present disclosure 2 ([T]/55.85>14[B]/10.8). The heat- _treated sintered magnets (samples No. 1 to 9) were _machined to prepare samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm. was measured. Table 3 shows the measurement results.

As shown in Table 3, the present invention examples all produced RTB sintered magnets having high B _r and high H _cJ . None of these comparative examples yielded RTB based sintered magnets with high B _r and high H _cJ .

Example 2
About No. 4 in Table 4. Each element was weighed so that the composition shown in B to I was obtained, and the alloy was cast by a strip casting method to obtain an alloy in the form of flakes. The resulting flake-like alloy was pulverized in the same manner as in Example 1 to obtain main alloy powder. Table 4 shows the composition of the obtained main alloy powder.

Next, similarly to Example 1, Pr--Ga alloy powders (Nos. a to e) of alloys having compositions shown in Table 5 were prepared by the atomization method. The particle size of the obtained Pr--Ga alloy powder was 106 μm or less.

Next, under the conditions shown in Table 6, the main alloy powder and the Pr--Ga alloy powder were put into a V-type mixer and mixed to prepare a mixed powder (pulverized powder). No. 11 is No. C (main alloy powder) and No. a (Pr--Ga alloy powder), and the mass ratio of the Pr--Ga alloy powder to the entire mixed powder is 1% by mass. No. 12 to 21 are similarly described. Also, No. No. 10 did not mix the Pr--Ga alloy powder with only the main alloy powder. The mixed powder was molded in the same manner as in Example 1 to obtain a molded body. The compact thus obtained was sintered at 1040° C. for 36000 seconds (10 hr). The sintering temperature and sintering time are within the scope of the present disclosure. The obtained sintered bodies were subjected to heat treatment in the same manner as in Example 1 to obtain RTB sintered magnets (Nos. 11 to 21). Also, No. No. 10 is the same as No. 1 except that only the main alloy powder was mixed with no Pr--Ga alloy powder. An RTB based sintered magnet was produced in the same manner as in Nos. 11 to 21. Table 7 shows the composition of the RTB system sintered magnet. When formula 2 of the present disclosure is satisfied, it is indicated by ◯, and when it is not satisfied, it is indicated by ×. RTB sintered magnets (samples No. 10 to 21) were machined to prepare samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and the characteristics of each sample (B _r and H _cJ ) was measured. Table 6 shows the measurement results.

As shown in Table 6, all the examples of the present invention _{produced RTB based sintered magnets with high Br and high HcJ ,} whereas Pr—Ga alloy powder was used. No No. No. 10 and No. 1 in which the mass ratio of the Pr—Ga alloy powder to the entire alloy powder exceeds 10% by mass. No. 16 and No. 1 where the Pr amount in the Pr—Ga alloy powder is off. 18 and no. None of the 19 comparative examples provided RTB based sintered magnets with high B _r and high H _cJ .

Example 3
About No. 8 in Table 8. Each element was weighed so that the composition shown in J was obtained, and the alloy was cast by a strip casting method to obtain an alloy in the form of flakes. The resulting flake-like alloy was pulverized in the same manner as in Example 1 to obtain main alloy powder. Table 8 shows the composition of the obtained main alloy powder.

Next, in the same manner as in Example 1, Pr--Ga alloy powders (No. f and g) of alloys having compositions shown in Table 9 were prepared by the atomization method. The particle size of the obtained Pr--Ga alloy powder was 106 μm or less.

Next, under the conditions shown in Table 10, the main alloy powder and the Pr--Ga alloy powder were put into a V-type mixer and mixed to prepare a mixed powder (pulverized powder). No. 22 is No. J (main alloy powder) and No. f (Pr--Ga alloy powder), and the mass ratio of the Pr--Ga alloy powder to the entire mixed powder is 3% by mass. No. 23 is similarly described. The mixed powder was molded in the same manner as in Example 1 to obtain a molded body. The compact thus obtained was sintered at 1070° C. for 14400 seconds (4 hours). The sintering temperature and sintering time are within the scope of the present disclosure. The obtained sintered bodies were subjected to the same heat treatment as in Example 1 to obtain RTB sintered magnets (Nos. 22 and 23). Table 11 shows the composition of the RTB system sintered magnet. RTB sintered magnets (samples No. 22 and 23) were machined to prepare samples of 7 mm in length, 7 mm in width, and 7 mm in thickness, and the characteristics of each sample (B _r and H _cJ ) was measured. Table 10 shows the measurement results.

As shown in Table 10, all the invention examples yield RTB based sintered magnets having high B _r and high H _cJ .

According to the present invention, an RTB based sintered magnet having high B _r and high H _cJ can be produced. The sintered magnet of the present invention is suitable for various motors such as hybrid vehicle mounted motors exposed to high temperatures, home electric appliances, and the like.

Main phase 14 composed of 12 R ₂ T ₁₄ B compound Grain boundary phase 14a Two-grain grain boundary phase 14b Grain boundary triple point

Claims (3)

R: 27.5% by mass or more and 33.0% by mass or less (R is at least one of rare earth elements and necessarily contains Nd),
B: 0.85% by mass or more and 0.97% by mass or less,
T: 61.5% by mass or more (T is Fe and Co, and 90% or more of T is Fe in mass ratio),
providing a main alloy powder containing
Pr: 65% by mass or more and 97% by mass or less (30% by mass of Pr can be replaced by another rare earth element), and Ga: 3% by mass or more and 35% by mass or less (50% by mass or less of Ga can be replaced by Cu)
A step of preparing a Pr—Ga alloy powder containing and produced by an atomizing method;
The main alloy powder and the Pr--Ga alloy powder are mixed to prepare a mixed powder in which the mass ratio of the Pr--Ga alloy powder to the entire mixed powder is 1% by mass or more and 10% by mass or less. a molding step;
A sintering step of sintering the compact of the mixed powder at a sintering temperature of 950° C. or more and less than 1120° C.;
encompasses
When the sintering temperature in the sintering step is T ° C. and the sintering time is t seconds,
t≧3600, and
A method for producing an RTB based sintered magnet, wherein the relationship 5×(1120−T) ² <t<10×(1120−T) ² is established. Where [T] is the content of T expressed in mass% and [B] is the content of B expressed in mass%, the RTB based sintered magnet is:
[T]/55.85>14[B]/10.8
2. The method for manufacturing an RTB based sintered magnet according to claim 1, which satisfies the relationship of 3. The method for producing a RTB based sintered magnet according to claim 1, wherein the Nd content in said Pr--Ga alloy powder is equal to or less than the content of unavoidable impurities.

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