JP7180089B2 - 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) have 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 with 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 preparing a Pr—Ga alloy powder produced by an atomizing method, and at least part of the surface of the green compact. and a sintering step of sintering the green body coated with the Pr--Ga alloy powder on at least a part of the surface.

In one embodiment, when the sintering temperature in the sintering step is T° C. and the sintering time is t seconds, T<1120 and 5×(1120−T) ² <t<10×(1120− T) The relationship of ² is established.

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 an embodiment of the present disclosure, the Pr—Ga alloy powder produced by the atomization method is applied to the surface of the green compact of the alloy powder, and then the Pr—Ga alloy powder is applied to the surface and the compact is sintered. Therefore, Pr and Ga are diffused in the grain boundaries that are in a liquid phase during the process of sintering the green body, and the _HcJ can be improved. Since the concentrations of Pr and Ga inside the grains of the main phase are low, the decrease in _Br is also suppressed. Therefore, even if the content of heavy rare earth elements such as Dy is reduced, RTB based sintered magnets having high B _r and H _cJ can be produced.

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 dashed-line rectangular area 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 the 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 applied to the surface of a green compact formed from main alloy powder of RTB sintered magnets. After that, by executing the sintering process under predetermined conditions, it was found that almost no R and Ga could be introduced into the interior of the main phase crystal grains 12 and could be introduced into the two grain boundaries 14a. 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 Pr--Ga alloy powder particles melt during the sintering process. Therefore, Pr and Ga mainly constitute the grain boundary phase of the RTB system sintered magnet being formed by sintering from the green compact.

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.

In the manufacturing method of the RTB system sintered magnet according to the present disclosure, as illustrated in FIG. 2, the main alloy powder for the RTB system sintered magnet is compressed in an oriented magnetic field. It includes a step S10 of preparing a "green compact" and a step S20 of preparing a Pr--Ga alloy powder produced by the atomization method. The order of the step S10 of preparing the green compact of the main alloy powder and the step S20 of preparing the Pr—Ga alloy powder is arbitrary, and the green compact of the main alloy powder and the Pr- Ga alloy powder may be used. Furthermore, the method for manufacturing an RTB based sintered magnet according to the present disclosure includes a step of applying Pr—Ga alloy powder to part or all of the surface of a green compact of main alloy powder (application step) S30; - A step of sintering the green compact with the Ga alloy powder applied to the surface (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

A compact (green compact) is produced by compressing the above main alloy powder in a magnetic field.

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 coating step S30 in the embodiment of the present disclosure, the mass ratio of the Pr—Ga alloy powder to the green compact is set to 1% by mass or more and 10% by mass or less.

In the sintering step S40 in the embodiment of the present disclosure, the green compact is sintered. In one embodiment, when the sintering temperature is T° C. and the sintering time is t seconds, T<1120, and
The sintering conditions are adjusted so that the relationship of Equation 1 below is established.
T<1120, and
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. The sintering temperature is preferably 950°C or higher and lower than 1120°C.

According to the embodiment of the present disclosure, sintering is performed under the above specific conditions while the Pr—Ga alloy powder is applied to the surface of the green compact formed from the above main alloy powder. During the sintering process, Pr--Ga phase formation 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 . After an RTB based sintered magnet material is produced by sintering, when Pr and Ga are diffused and introduced from the surface of this RTB based sintered magnet material into the inside, RT- Even within the grain boundary phase of the B-based sintered magnet, the Pr—Ga phase is present in the region near the surface of the RTB-based sintered magnet and the interior of the RTB-based sintered magnet. There will be a difference in the amount produced. However, according to the embodiments of the present disclosure, Pr and Ga are applied to the surface of the green compact from the stage before sintering, so the problems of the conventional method are resolved.

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 coating to crystallize the amorphous material.

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.

The RTB based sintered magnet produced by the production method of the present disclosure has the following composition.

R: 27.5% by mass or more and 34.0% by mass or less (R is at least one of rare earth elements 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,
Al: 0.05% by mass or more and 0.40% by mass or less, and T: 61.5% by mass or more (T is Fe and Co and 90% or more of T is Fe in mass ratio), 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. By applying Pr—Ga alloy powder to the surface of the green compact formed from the main alloy powder containing 0.85 to 0.97% by mass of B and sintering it, high _Br and high H _cJ can be obtained. 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, Ga is introduced into the grain boundary phase by applying Pr—Ga alloy powder to the green compact of the main alloy powder, so that the amount of Ga in the main alloy powder is relatively small (or contains Ga not). 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 normally 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, containing Ti, V, Cr, Mn, Ni, Si, La, Ce, Sm, Ca, Mg, O (oxygen), N (carbon), C (nitrogen), 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, a raw material alloy produced by a strip casting method or the like is pulverized to 1 μm or more and 10 μm or less using a jet mill or the like, molded in a magnetic field, and sintered at a temperature of 900° C. or more and 1100° C. or less. can be prepared by

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 main alloy powder that constitutes the green compact satisfies Equation (2).
[T]/55.85>14 [B]/10.8 Formula 2

By satisfying this inequality (1), the B content is less than that of a general RTB based sintered magnet. 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 inequality (1) 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, if 70% by mass of Pr (30% by mass of Ga) in a Pr--Ga alloy, up to 21% by mass of Nd can be substituted. That is, Pr is 49% by mass and Nd is 21% by mass. The same applies to Dy, Tb and Cu.

By applying a Pr--Ga alloy powder having Pr and Ga within the above range on the surface of the green compact of the main alloy powder, Pr and Ga are concentrated in the grain boundary phase in the sintering process and distributed throughout the magnet. It can be dispersed in the grain boundary phase. 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.

3. Application of Pr--Ga alloy powder The Pr--Ga alloy powder is produced by the atomization method and has a spherical shape, so that it can be easily applied uniformly. Application of the Pr--Ga alloy powder can be done by any method. For example, the Pr--Ga alloy powder may be applied by spraying it on the surface of the molded body, or the Pr--Ga alloy powder may be dispersed in a solvent and the resulting slurry may be applied to the sintered body.

The coating amount is such that the mass ratio of the Pr--Ga alloy powder to the entire green compact coated with the Pr--Ga alloy powder is 1% by mass or more and 10% by mass or less.

An additional heat treatment may be performed on the sintered magnet obtained by the embodiment of the present disclosure 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 R—Ga alloy powder, and the RTB system sintered magnet were also measured in the same manner. 0.05% by mass of zinc stearate as a lubricant was added to the obtained main alloy powder with respect to 100% by mass of the finely pulverized powder, mixed, and compacted in a magnetic field to obtain a compact (green 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.

Next, an R—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 R--Ga alloy powder was 106 μm or less.

Next, R--Ga alloy powder (No. a) was applied by spraying on the surface of the green compact. The mass ratio of the Pr--Ga alloy powder to the entire green compact coated with the Pr--Ga alloy powder was 3% by mass.

The green compact coated with the Pr--Ga alloy powder 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 sintered magnets were checked, they were all (No. 1 to 9) Nd: 22.52%, Pr: 9.67%, B: 0.88%, Co : 0.87%, Al: 0.1%, Cu: 0.22%, Ga: 0.49%, Zr: 0.1%, Fe: around 64.89% (mass%), 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, in the same manner as in Example 1, R—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 R--Ga alloy powder was 106 μm or less.

Next, under the conditions shown in Table 6, the main alloy powder and the R--Ga alloy powder were put into a V-type mixer and mixed to prepare a mixed alloy powder (pulverized powder). No. 11 is No. C (main alloy powder) and No. a (R--Ga alloy powder), and the mass ratio of the R--Ga alloy powder to the entire mixed powder is 1% by mass. No. 12 to 21 are similarly described. Also, No. No. 10 contained only the main alloy powder and did not mix the R--Ga alloy powder. The pre-mixed alloy powder was compacted in the same manner as in Example 1 to obtain a compact. The compact thus obtained was sintered at 1040° C. for 36000 seconds (10 hr). The sintering temperature and the sintered magnet 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). 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. 11 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 B _r and high H _cJ , whereas R—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 .

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 green compact of 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;
a step of applying the Pr—Ga alloy powder to at least part of the surface of the green compact;
a sintering step of sintering the green compact having the Pr—Ga alloy powder applied to at least part of the surface 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 manufacturing 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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