JP2021158205A - R-t-b based permanent magnet - Google Patents

Abstract

To provide an R-T-B based permanent magnet which has a high coercive force at a high temperature and which is hardly demagnetized at a high temperature.SOLUTION: A permanent magnet contains a rare earth element R (containing at least Nd), a transition metal element T (containing at least Fe) and B. The permanent magnet comprises: a plurality of primary-phase grains 4 containing Nd, T and B; and grain boundary phases 6 included in grain boundaries among the primary-phase grains. A part of the primary-phase grains 4 is configured of a coarse primary-phase grain 4A, and another part of the primary-phase grains 4 is configured of fine primary-phase grains 4B smaller, in grain size, than the coarse primary-phase grains 4A. In a section of the permanent magnet, a grain size of the coarse primary-phase grain 4A is 100 μm or larger and 1000 μm or smaller. The number of coarse primary-phase grains 4A per unit area in the section is 0.1/cm2 or more and 1/cm2 or less. In the section, the median diameter of the fine primary-phase grains 4B is 1 μm or larger and 5 μm or smaller.SELECTED DRAWING: Figure 2

Description

The present invention relates to RTB-based permanent magnets containing at least a rare earth element R, a transition metal element T and boron B.

Since RTB permanent magnets have excellent magnetic characteristics, they are used in motors or actuators mounted on hybrid vehicles, electric vehicles, electronic devices, home appliances, and the like. RTB permanent magnets used in motors and the like are required to have a high coercivity in a high temperature environment.

As a method for improving the coercive force (HcJ) of RTB-based permanent magnets at high temperatures, some of the light rare earth elements (Nd or Pr) constituting the _{R 2} T _{14 B phase can be used as Dy or Tb.} substituted with a heavy rare-earth element, it is known to improve the magnetic anisotropy of the R 2 _T 14 _B phase. In recent years, the demand for high coercive force type RTB permanent magnets that require a large amount of heavy rare earth elements is rapidly expanding.

However, heavy rare earth elements are unevenly distributed in specific areas as resources, and their production is limited. Therefore, heavy rare earth elements are more expensive than light rare earth elements, and their supply is not stable. Therefore, there is a demand for RTB-based permanent magnets having a high coercive force at high temperatures even when the content of heavy rare earth elements is low.

For example, Patent Document 1 below discloses an example of a permanent magnet having a high coercive force without using a heavy rare earth element. The permanent magnet described in Patent Document 1 includes R ₂ T ₁₄ B crystal particles which _{are the main phases and a grain boundary phase between the R 2} T ₁₄ B crystal particles, and the main phase crystal particles in an arbitrary cross section of the permanent magnet. When the cross-sectional area distribution of is evaluated by a histogram, the cross-sectional area distribution of the main phase crystal particles is a distribution having at least one peak on each side of the average value of the cross-sectional areas.

JP-A-2015-38950

However, when the content of heavy rare earth elements in the RTB permanent magnets is low, it is difficult to achieve a sufficiently high coercive force in a high temperature environment where an in-vehicle drive motor or the like is exposed, and the high temperature environment. It was difficult to sufficiently suppress the demagnetization of the RTB-based permanent magnets below.

An object of the present invention is to have a high coercive force at a high temperature and to be difficult to demagnetize at a high temperature even when the content of heavy rare earth elements in the RTB permanent magnet is small. It is to provide a system permanent magnet.

The RTB-based permanent magnet according to one aspect of the present invention is an RTB-based permanent magnet containing a rare earth element R, a transition metal element T and B, and is an RTB-based permanent magnet. Contains at least Nd as R, the RTB-based permanent magnet contains at least Fe as T, and the RTB-based permanent magnet contains a plurality of mains including Nd, T and B. It comprises a phase particle (main phase grain) and a grain boundary phase contained in a grain boundary (grain boundary) between a plurality of main phase particles, and some of the main phase particles have a coarse main phase. The particles (cоarse main phase grain), and the other main phase particles are fine main phase particles (fine main phase grain) having a particle size smaller than the particle size (grain phase grain) of the coarse main phase particles, and are R-. The particle size of the coarse main phase particles in one cross section of the TB-based permanent magnet is 100 μm or more and 1000 μm or less, and the number of coarse main phase particles per unit area in the above cross section is 0.1 piece / cm ² or more. It is 1 piece / cm ² or less, and the median diameter of the fine main phase particles in the above cross section is 1 μm or more and 5 μm or less.

The RTB-based permanent magnet according to one aspect of the present invention may further contain Ga.

RTB-based permanent magnets are 29.50 to 33.00% by mass R, 0.70 to 0.95% by mass B, 0.03 to 0.60% by mass Al, 0.01 to 1.50% by mass Cu, 0.00 to 3.00% by mass Co, 0.10 to 1.00% by mass Ga, 0.05 to 0.30% by mass C, 0.03 to 0. It may consist of 40% by weight O and the balance, which may be Fe alone or Fe and other elements.

The total content of heavy rare earth elements in the RTB permanent magnets may be 0.00% by mass or more and 1.00% by mass or less.

According to the present invention, even when the content of heavy rare earth elements in the RTB permanent magnet is small, the RTB has a high coercive force at a high temperature and is difficult to be demagnetized at a high temperature. System permanent magnets can be provided.

(A) in FIG. 1 is a schematic perspective view of an RTB-based permanent magnet according to an embodiment of the present invention, and (b) in FIG. 1 is (a) in FIG. It is a schematic view (arrow view in the bb line direction) of the cross section of the RTB system permanent magnet shown in. FIG. 2A is a schematic enlarged view of a part (region IIa) of the cross section of the RTB-based permanent magnet shown in FIG. 1B, and is shown in FIG. b) is a schematic enlarged view of a part (region IIb) of a cross section of a conventional RTB-based permanent magnet that does not contain coarse main phase particles. FIG. 3 is a part of a cross section of the RTB-based permanent magnet according to the first embodiment of the present invention, and is an image taken with an optical microscope. FIG. 4 is a part of a cross section of the RTB-based permanent magnet according to the first embodiment of the present invention, and is an image taken by a scanning electron microscope.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, equivalent components are labeled with equivalent reference numerals. The present invention is not limited to the following embodiments. All of the "permanent magnets" described below mean "RTB-based permanent magnets".

(permanent magnet)
The permanent magnet according to this embodiment contains at least a rare earth element (R), a transition metal element (T) and boron (B). Permanent magnets may further contain gallium (Ga). Since the permanent magnet contains Ga, a transition metal-rich phase, which will be described later, is likely to be formed as a grain boundary phase. The permanent magnet may be a sintered magnet.

Permanent magnets contain at least neodymium (Nd) as the rare earth element R. In addition to Nd, the permanent magnet may further contain another rare earth element R. Other rare earth elements R include scandium (Sc), ytterbium (Y), lantern (La), cerium (Ce), placeozim (Pr), samarium (Sm), lutetium (Eu), gadolinium (Gd), and terbium (Tb). ), Dysprosium (Dy), Holmium (Ho), Elbium (Er), Thulium (Tm), Ytterbium (Yb), and Lutetium (Lu).

Permanent magnets contain at least iron (Fe) as the transition metal element T. The permanent magnet may contain both Fe and cobalt (Co) as the transition metal element T. The permanent magnet may contain only Fe as the transition metal element T.

FIG. 1A is a schematic perspective view of a rectangular parallelepiped permanent magnet 2 according to the present embodiment. FIG. 1B is a schematic view of a permanent magnet 2 having a cross section of 2cs. FIG. 2A is an enlarged view of a part (region II) of the cross section 2cs of the permanent magnet 2. The shape of the permanent magnet 2 is not limited to a rectangular parallelepiped. For example, the shape of the permanent magnet 2 is, for example, a cube, a rectangle (plate), a polygonal column, an arc segment, a fan, an annular sector, a sphere, a disk, a cylinder, a cylinder, a ring, or a capsule. good. The cross-sectional shape of the permanent magnet 2 may be, for example, polygonal, arc (chord), bow, arch, C-shaped, or circular.

As shown in (a) in FIG. 2, the permanent magnet 2 includes a plurality of (many) main phase particles 4. The main phase particle 4 contains at least Nd, T and B. The main phase particles 4 may contain crystals of _{R 2} T _{14 B.} The crystals of R ₂ T ₁₄ B may be single crystals or polycrystals. The main phase particles 4 may consist only of crystals of _{R 2} T _{14 B.} R ₂ T ₁₄ B, for _{example, (Nd 1-x Pr x} ) 2 (Fe 1-y Co y) may be expressed as ₁₄ B, x may be 0 or more and less than 1, y is 0 or 1 May be less than. The main phase particles 4 may contain other elements in addition to Nd, T and B. The composition in the main phase particles 4 may be uniform. The composition in the main phase particles 4 may be non-uniform. For example, the concentration distributions of Nd, T, and B in the main phase particles 4 may have a gradient.

Some of the main phase particles 4 are coarse main phase particles 4A, and the other main phase particles 4 are fine main phase particles 4B having a particle size smaller than the particle size of the coarse main phase particles 4A. That is, all of the rest of all the main phase particles 4 except for the coarse main phase particles 4A are the fine main phase particles 4B.

The particle size (diameter) of the coarse main phase particles 4A may be the equivalent circle diameter of the coarse main phase particles 4A. For example, the particle size of each coarse main phase particle 4A may be expressed as ^{(4A / π) 1/2.} A is the cross-sectional area of the coarse main phase particles 4A measured in one cross section 2cs of the permanent magnet 2. (4A / π) ^1/2 corresponds to the diameter of a circle having an area of A (circle equivalent diameter). That is, the particle size of the coarse main phase particles 4A may be the Heywood diameter calculated from the cross-sectional area A of the coarse main phase particles 4A. For the measurement of the cross-sectional area A of the coarse main phase particles 4A, an image of one cross section 2cs of the permanent magnet 2 may be taken by an optical microscope. The dimensions of the field of view of the optical microscope may be, for example, 1.6 mm in length × 2.0 mm in width. As shown in FIG. 3, the coarse main phase particles 4A may be identified based on the difference in brightness (contrast) in the image of the cross section 2cs of the permanent magnet 2. The dark part in the center of FIG. 3 is the cross section of the coarse main phase particles 4A. The fine main phase particles 4B and the grain boundary phase 6 are present around the coarse main phase particles 4A (bright portion). The cross-sectional area A of the coarse main phase particles 4A may be measured using image analysis software. As the image analysis software, for example, Mac-View manufactured by Mountech Co., Ltd. may be used. The particle size of the coarse main phase particles 4A may be the maximum width of the coarse main phase particles 4A measured in one cross section 2cs of the permanent magnet 2.

The particle size (diameter) of the fine main phase particles 4B may be the equivalent circle diameter of the fine main phase particles 4B. For example, the particle size of each micromain phase particle 4B may be expressed as ^{(4B / π) 1/2.} B is the cross-sectional area of the fine main phase particles 4B measured in one cross section 2cs of the permanent magnet 2. (4B / π) ^1/2 corresponds to the diameter of a circle having an area of B (circle equivalent diameter). That is, the particle size of the fine main phase particles 4B may be the Heywood diameter calculated from the cross-sectional area B of the fine main phase particles 4B. For the measurement of the cross-sectional area B of the fine main phase particles 4B, an image of one cross section 2cs of the permanent magnet 2 may be taken by a scanning electron microscope (SEM). The dimensions of the field of view of the SEM may be, for example, 38.1 μm in length × 50.8 μm in width. As shown in FIG. 4, the fine main phase particles 4B and the grain boundary phase 6 are identified based on the difference in brightness (contrast) in the image of the cross section 2cs of the permanent magnet 2. The dark part in FIG. 4 is a cross section of the fine main phase particles 4B. The bright part in FIG. 4 is a cross section of the grain boundary phase 6. The image of the cross section 2cs of the permanent magnet 2 may be binarized based on the brightness of the reflected electron images of the fine main phase particles 4B and the grain boundary phase 6 respectively. By binarization, the fine main phase particles 4B and the grain boundary phase 6 are accurately identified, and the cross-sectional area B of each of the fine main phase particles 4B is measured. The binarization of the image of the cross section 2cs of the permanent magnet 2 may be performed by the above-mentioned image analysis software or human power. The cross-sectional area B of the fine main phase particles 4B may be measured using the image analysis software described above.

The permanent magnet 2 has a grain boundary located between a plurality of main phase particles 4. The permanent magnet 2 may have a plurality (many) grain boundaries. The permanent magnet 2 may have multiple grain boundary points as grain boundaries. The grain boundary multiple points are grain boundaries surrounded by three or more main phase particles 4. The permanent magnet 2 may include a plurality of (many) grain boundary multiple points. The permanent magnet 2 may have a two-particle grain boundary as the grain boundary. The two-particle grain boundary is a grain boundary located between two adjacent main phase particles 4. The permanent magnet 2 may have a plurality (many) two-particle boundaries.

The grain boundaries include the grain boundary phase 6. The presence of the grain boundary phase 6 between two or more adjacent main phase particles 4 divides the magnetic coupling between the main phase particles 4. That is, two or more adjacent R ₂ T ₁₄ B crystal grains are separated from each other via the grain boundary phase 6 having low magnetization. As a result, the coercive force of the permanent magnet 2 in the high temperature environment is improved, and the demagnetization of the permanent magnet 2 is suppressed in the high temperature environment. The grain boundaries may be filled with grain boundary phases 6.

The smaller the particle size of the main phase particles 4 contained in the permanent magnet 2, the smaller the surface area of each main phase particle 4, and the lower the frequency of generation of magnetization reversal nuclei (inverted magnetic domains) on the surface of the main phase particles 4. As a result, the coercive force of the permanent magnet 2 at high temperature increases, and the demagnetization of the permanent magnet 2 at high temperature is suppressed. Further, since each main phase particle 4 is coated with the non-magnetic grain boundary phase 6, the magnetic bond between the adjacent main phase particles 4 is divided by the grain boundary phase 6. The thicker the grain boundary phase 6, the easier it is for the magnetic coupling between the main phase particles 4 to be broken. As a result, the coercive force of the permanent magnet 2 at high temperature increases, and the demagnetization of the permanent magnet 2 at high temperature is suppressed. In particular, when the content of B in the permanent magnet 2 is relatively low, it is desirable to divide the magnetic coupling between the main phase particles 4 by the grain boundary phase 6. The thickness of the grain boundary phase 6 is not always uniform, and the thickness of the grain boundary phase 6 is not limited. For example, the thickness of the grain boundary phase 6 may be 10 nm or more and 100 nm or less.

As described above, the coercive force and demagnetization of the permanent magnet 2 at high temperature are the particle size of the main phase particles 4, the coverage of the main phase particles 4 by the grain boundary phase 6, and the grain boundary phase covering the main phase particles 4. It depends on the thickness of 6. In order to improve the coercive force based only on the particle size of the main phase particles 4 and suppress demagnetization, the median diameter of the fine main phase particles 4B is as small as possible, and the permanent magnet 2 uses the coarse main phase particles 4A. It is preferable not to include it. However, the inventor intentionally contains an appropriate amount of coarse main phase particles 4A in the permanent magnet 2, so that the coercive force of the permanent magnet 2 at a high temperature is increased and the demagnetization of the permanent magnet 2 at a high temperature is suppressed. I found that. The reason (hypothesis) is that in the sintering process described later, sufficient grains for coating the fine main phase particles 4B from the components of the grain boundary phase 6 that should have been formed in the region occupied by the coarse main phase particles 4A. This is because the boundary phase 6 is formed. The mechanism (hypothesis) that the coercive force at high temperature increases and the demagnetization at high temperature is suppressed is explained as follows.

(A) in FIG. 2 is a part of a cross section of the permanent magnet 2 according to the present embodiment. The permanent magnet 2 according to the present embodiment includes both coarse main phase particles 4A and fine main phase particles 4B as main phase particles 4. (B) in FIG. 2 is a part of a cross section of a conventional permanent magnet. The conventional permanent magnet contains only the fine main phase particles 4B as the main phase particles 4.
It is assumed that the total volume of the main phase particles 4 in the permanent magnet 2 according to the present embodiment is equal to the total volume of the main phase particles 4 in the conventional permanent magnet. Further, it is assumed that the total volume of the grain boundary phase 6 in the permanent magnet 2 according to the present embodiment is equal to the total volume of the grain boundary phase 6 in the conventional permanent magnet.
Since the particle size (median diameter) of the fine main phase particles 4B is smaller than the particle size of the coarse main phase particles 4A, the specific surface area (surface area per unit volume) of the fine main phase particles 4B is that of the coarse main phase particles 4A. Greater than specific surface area. Therefore, when the volume of one coarse main phase particle 4A is the same as the total volume of the plurality of fine main phase particles 4B, the volume of the grain boundary phase 6 required for coating the one coarse main phase particle 4A is plural. It is smaller than the total volume of the grain boundary phase 6 required for coating all of the fine main phase particles 4B.
Since the permanent magnet 2 according to the present embodiment includes not only the fine main phase particles 4B but also the coarse main phase particles 4A, the total surface area of the main phase particles 4 in the permanent magnet 2 according to the present embodiment is the conventional permanent. It is smaller than the total surface area of the main phase particles 4 (fine main phase particles 4B) in the magnet. In other words, the volume of the grain boundary phase 6 required to cover the surface of all the main phase particles 4 in the conventional permanent magnet covers the surface of all the main phase particles 4 in the permanent magnet 2 according to the present embodiment. It is larger than the volume of the grain boundary phase 6 required for this. However, as described above, the total volume of the grain boundary phase 6 that can cover the surface of the main phase particles 4 is limited to a certain amount. Therefore, the surface of the main phase particles 4 in the conventional permanent magnet is less likely to be covered by the grain boundary phase 6 than the surface of the main phase particles 4 in the permanent magnet 2 according to the present embodiment. In other words, the surface of the main phase particles 4 in the permanent magnet 2 according to the present embodiment is more likely to be reliably covered by the grain boundary phase 6 than the surface of the main phase particles 4 in the conventional permanent magnet. For the same reason, the thickness of the grain boundary phase 6 covering the main phase particles 4 in the permanent magnet 2 according to the present embodiment is larger than the thickness of the grain boundary phase 6 covering the main phase particles 4 in the conventional permanent magnet. ..
As described above, since the permanent magnet 2 according to the present embodiment includes not only the fine main phase particles 4B but also the coarse main phase particles 4A, the coverage of the main phase particles 4 by the grain boundary phase 6 is likely to increase. The thickness of the grain boundary phase 6 that covers the main phase particles 4 tends to increase. As a result, the magnetic bond between the main phase particles 4 is easily broken by the grain boundary phase 6, the coercive force of the permanent magnet 2 at a high temperature increases, and the demagnetization of the permanent magnet 2 at a high temperature is suppressed.

The particle size of the coarse main phase particles 4A in one cross section 2cs of the permanent magnet 2 is 100 μm or more and 1000 μm or less. That is, the coarse main phase particles 4A may be defined as the main phase particles 4 having a particle size (circle equivalent diameter) measured in one cross section 2cs of the permanent magnet 2 of 100 μm or more and 1000 μm or less. When the particle size of the coarse main phase particles 4A is less than 100 μm, the grain boundary phase 6 formed between the fine main phase particles 4B tends to be thin. As a result, the coercive force at high temperature tends to decrease, and the permanent magnet 2 tends to be demagnetized at high temperature. When the permanent magnet 2 is manufactured through a sintering process under various conditions such that the particle size of the coarse main phase particles 4A exceeds 1000 μm, the fine main phase particles 4B grow excessively and the fine main phase particles 4B grow excessively. The median diameter of 4B easily exceeds the upper limit value described later. As a result, the coercive force at high temperature tends to decrease, and the permanent magnet 2 tends to be demagnetized at high temperature. Therefore, it is preferable that the permanent magnet 2 does not include the main phase particles 4 having a particle size (corresponding to a circle) measured in one cross section 2cs of the permanent magnet 2 larger than 1000 μm. In order to increase the coercive force at high temperature and suppress the demagnetization of the permanent magnet 2 at high temperature, the particle size of the coarse main phase particles 4A may be 110 μm or more and 970 μm or less.

The number of coarse main phase particles 4A per unit area of one cross section 2cs of the permanent magnet 2 is 0.10 / cm ² or more and 1.00 / cm ² or less. For example, the area of one section 2cs of the permanent magnet 2 is represented as (Scs) cm ^2, represented the number of coarse main phase particles 4A exposed in one section 2cs of the permanent magnet 2 and _{(N A)} pieces , _N A / Scs is 0.10 pieces / cm ² or more 1.00 pieces / cm ² or less. The "coarse grain frequency" described below means the number of coarse main phase particles 4A per unit area of one cross section 2cs of the permanent magnet 2. When the coarse particle frequency is ^{greater than 1.00 particles / cm 2} , the number of fine main phase particles 4B is relatively reduced. As a result, the coercive force at high temperature tends to decrease, and the permanent magnet 2 tends to be demagnetized at high temperature. When the coarse grain frequency is ^{less than 0.10 grains / cm 2} , the coverage of the main phase particles 4 by the grain boundary phase 6 tends to decrease, and the thickness of the grain boundary phase 6 covering the fine main phase particles 4B tends to decrease. .. As a result, the coercive force at high temperature tends to decrease, and the permanent magnet 2 tends to be demagnetized at high temperature. Increasing the coercive force at high temperatures, in order to suppress demagnetization of the permanent magnet 2 at a high temperature, coarse grains frequency may be 0.98 0.11 pieces / cm ² or more pieces / cm ² or less .. By observing a part or the whole of the cross section 2cs of the permanent magnet 2 with an optical microscope or the naked eye, the number of coarse main phase particles 4A existing in the cross section 2cs of the permanent magnet 2 may be measured. When the number of coarse main phase particles 4A is measured, the dimensions of the field of view of the optical microscope may be adjusted so that the entire coarse main phase particles 4A are within the field of view.

The median diameter (d50) of the fine main phase particles 4B in one cross section 2cs of the permanent magnet 2 is 1.0 μm or more and 5.0 μm or less. That is, the median diameter of the main phase particles 4 excluding the coarse main phase particles 4A is 1.0 μm or more and 5.0 μm or less. The smaller the median diameter of the fine main phase particles 4B, the more the coercive force of the permanent magnet 2 at high temperature increases, and the demagnetization of the permanent magnet 2 at high temperature is suppressed. When the median diameter of the fine main phase particles 4B is larger than 5.0 μm, the coercive force at high temperature tends to decrease, and the permanent magnet 2 tends to be demagnetized at high temperature. Manufacture of permanent magnets containing micromain phase particles 4B with a median diameter of less than 1.0 μm is difficult at the current state of the art. In order to increase the coercive force at high temperature and suppress the demagnetization of the permanent magnet 2 at high temperature, the median diameter of the fine main phase particles 4B is 1.0 μm or more and 4.0 μm or less, 1.0 μm or more and 3.0 μm. Below, 2.0 μm or more and 5.0 μm or less, 2.0 μm or more and 4.0 μm or less, 2.0 μm or more and 3.0 μm or less, 2.5 μm or more and 3.5 μm or less, or 2.98 μm or more and 3.04 μm or less. May be good.

The median diameter of the fine main phase particles 4B is calculated based on the particle size distribution of the fine main phase particles 4B. The particle size distribution of the fine main phase particles 4B is a number-based particle size distribution (number distribution). The number N _B of the minute main phase particles 4B constituting the particle size distribution may be, for example, 100 or more 200 or less. That, N _B number of fine main phase particles 4B exposed to the cross-section 2cs permanent magnet 2 is chosen randomly from the particle size of the fine primary phase particles 4B in cross section 2cs permanent magnet 2 (equivalent circle diameter), The median diameter of the fine main phase particles 4B may be calculated. N _B number of fine main phase particles 4B其s particle size may be measured in the area (field of view) that does not contain coarse primary phase grains 4A of the one section 2cs of the permanent magnet 2.

The technical scope of the present invention is not limited by the mechanism described above.

The grain boundary multiple points or two-particle grain boundaries may include a transition metal-rich phase as the grain boundary phase 6. The transition metal rich phase may be a phase containing R, T and Ga and satisfying the following formula T1. The transition metal rich phase may be a phase containing _{R 6} T _{13 Ga.} The transition metal-rich phase may be a phase consisting of only _{R 6} T _{13 Ga.} R ₆ T ₁₃ Ga may be, for example, Nd ₆ Fe ₁₃ Ga. Since the permanent magnet 2 contains a transition metal rich phase, the coercive force of the permanent magnet 2 at a high temperature is likely to be improved.
1.50 ≦ ([Fe] + [Co]) / [R] ≦ 3.00 (T1)
[Fe] in the above formula T1 is the concentration of Fe at the grain boundary, [Co] in the above formula T1 is the concentration of Co in the grain boundary, and [R] in the above formula T1 is the concentration of Co in the grain boundary. The concentration of R in, and the unit of each of [Fe], [Co] and [R] is atomic%.

The grain boundary multiple points or two-particle grain boundaries may include an R-rich phase as the grain boundary phase 6. The R-rich phase may be a phase containing at least R and satisfying the following formulas R1 and R2. The R-rich phase may contain only Fe among Fe and Co as the transition metal element T. The R-rich phase may contain both Fe and Co as the transition metal element T. The R-rich phase does not have to contain the transition metal element T. The R-rich phase may contain O. The R-rich phase does not have to contain O.
0.00 ≦ ([Fe] + [Co]) / [R] <1.50 (R1)
0.00≤ [O] / [R] <0.35 (R2)
[Fe] in the above formula R1 is the concentration of Fe at the grain boundary, [Co] in the above formula R1 is the concentration of Co in the grain boundary, and [O] in the above formula R2 is the concentration of Co in the grain boundary. [R] in the above formulas R1 and R2 is the concentration of R at the grain boundary, and the units of [Fe], [Co], [O] and [R] are respectively. , Atomic%.

Some grain boundary phases 6 may be other phases different from the transition metal-rich phase and the R-rich phase. The other phase may be, for example, a rare earth oxide phase. The rare earth oxide phase may be a phase containing an oxide of R or a phase consisting of only an oxide of R. [O] / [R] in the rare earth oxide phase may be 0.35 or more.

Transition metal-rich phases, R-rich phases and other phases are completely different phases that are objectively and clearly identified based on differences in composition. The transition metal-rich phase, the R-rich phase, and the other phases are also identified based on the contrast between light and dark even in the image of the cross section 2cs of the permanent magnet 2 taken by SEM. Only one of the transition metal-rich phase, the R-rich phase and the other phases tends to be present at one grain boundary multiple point. However, at one grain boundary multiple point or one two-particle grain boundary, two or more kinds of phases may be present among the transition metal rich phase, the R rich phase and the other phase.

The total volume ratio of the main phase particles 4 in the permanent magnet 2 is not particularly limited, but may be, for example, 75% by volume or more and less than 100% by volume.

The permanent magnet 2 having the above-mentioned technical features can have a sufficiently high coercive force at a high temperature even when it does not contain a heavy rare earth element. However, in order to further increase the coercive force of the permanent magnet 2 at a high temperature, the permanent magnet 2 may contain a heavy rare earth element. However, if the content of heavy rare earth elements is too high, the residual magnetic flux density tends to decrease. For example, the total content of heavy rare earth elements in the permanent magnet 2 may be 0.00% by mass or more and 1.00% by mass or less. By refraining from using heavy rare earth elements as much as possible, the resource risk of using heavy rare earth elements can be reduced. Heavy rare earth elements are selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), formium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). It may be at least one kind.

The composition of each of the main phase particles 4 and the grain boundary phase 6 described above may be specified by analyzing the cross section 2cs of the permanent magnet 2 using an energy dispersive X-ray spectrometer (EDS).

The overall specific composition of the permanent magnet 2 will be described below. However, the range of composition of the permanent magnet 2 is not limited to the following. As long as the above-mentioned effects of the present invention can be obtained, the composition of the permanent magnet 2 may be outside the range of the following composition.

The content of R in the permanent magnet may be 29.50 to 33.00% by mass. When the permanent magnet contains a heavy rare earth element as R, the total content of all the rare earth elements including the heavy rare earth element may be 29.5 to 33% by mass. When the R content is in this range, the residual magnetic flux density and the coercive force tend to increase. When the R content is too small, main phase particles (R ₂ T ₁₄ B) are difficult to form, and an α-Fe phase having soft magnetism is likely to be formed. As a result, the coercive force tends to decrease. On the other hand, when the R content is too large, the volume ratio of the main phase particles becomes low, and the residual magnetic flux density tends to decrease. Since the volume ratio of the main phase particles is high and the residual magnetic flux density is likely to be high, the R content may be 30.00 to 32.50% by mass. Since the residual magnetic flux density and the coercive force tend to increase, the total ratio of Nd and Pr to the total rare earth element R may be 80 to 100 atomic% or 95 to 100 atomic%.

The content of B in the permanent magnet may be 0.70 to 0.95% by mass. Since the content of _{B is smaller than the stoichiometric ratio of the composition of the main phase represented by R 2} T ₁₄ B, the transition metal rich phase is likely to be formed and the coercive force is likely to be improved. If the content of B is too small, easy R ₂ T ₁₇ phase precipitates tend to coercive force is reduced. On the other hand, when the content of B is too large, it is difficult to sufficiently form the transition metal rich phase, and the coercive force tends to decrease. Since the residual magnetic flux density and the coercive force are likely to increase, the content of B may be 0.75 to 0.90% by mass or 0.80 to 0.88% by mass.

The permanent magnet may contain aluminum (Al). The Al content in the permanent magnet may be 0.03 to 0.60% by mass, or 0.03 to 0.30% by mass or less. When the Al content is in the above range, the coercive force and corrosion resistance of the permanent magnet are likely to be improved.

The content of Cu in the permanent magnet may be 0.01 to 1.50% by mass, or 0.03 to 1.00% by mass, or 0.05 to 0.50% by mass. When the Cu content is in the above range, the coercive force, corrosion resistance and temperature characteristics of the permanent magnet can be easily improved. Since the coercive force tends to increase, the Cu content may be 0.01 to 0.50% by mass.

The content of Co in the permanent magnet may be 0.00 to 3.00% by mass. Like Fe, Co may be a transition metal element T constituting the _{main phase particles (crystal grains of R 2} T _{14 B).} Since the permanent magnet contains Co, the Curie temperature of the permanent magnet can be easily improved. Further, when the permanent magnet contains Co, the corrosion resistance of the grain boundary phase is likely to be improved, and the corrosion resistance of the entire permanent magnet is likely to be improved. Since these effects can be easily obtained, the content of Co in the permanent magnet may be 0.30 to 2.50% by mass.

The content of Ga may be 0.10 to 1.00% by mass, or 0.25 to 0.80% by mass. If the Ga content is too low, the transition metal rich phase is not sufficiently formed and the coercive force tends to decrease. When the Ga content is too high, the transition metal-rich phase tends to be excessively formed, the volume ratio of the main phase particles decreases, and the residual magnetic flux density tends to decrease. Since the residual magnetic flux density and the coercive force tend to increase, the Ga content may be 0.20 to 0.80% by mass.

Permanent magnets may contain carbon (C). The content of C in the permanent magnet may be 0.05 to 0.30% by mass, or 0.10 to 0.25% by mass. If the content of C is too small, easy R ₂ T ₁₇ phase precipitates tend to coercive force is reduced. If the C content is too high, the transition metal rich phase is not sufficiently formed and the coercive force tends to decrease. Since the coercive force is easily improved, the C content may be 0.10 to 0.25% by mass.

The content of oxygen (O) in the permanent magnet may be 0.03 to 0.40% by mass. If the O content is too low, the corrosion resistance of the permanent magnet tends to decrease, and if the O content is too high, the coercive force tends to decrease. Since the corrosion resistance and the coercive force are easily improved, the content of O may be 0.05 to 0.30% by mass or 0.05 to 0.25% by mass.

Permanent magnets may contain nitrogen (N). The content of N in the permanent magnet may be 0.00 to 0.15% by mass. If the N content is too high, the coercive force tends to decrease.

Fe may be the only residue after removing the above-mentioned elements from the permanent magnet. Alternatively, the balance obtained by removing the above-mentioned elements from the permanent magnet may be Fe and other elements. In order for the permanent magnet to have sufficient magnetic properties, the total content of elements other than Fe in the balance may be 5% by mass or less with respect to the total mass of the permanent magnet.

Permanent magnets may contain zirconium (Zr). The content of Zr in the permanent magnet may be 0.00 to 1.50% by mass, 0.03 to 0.80% by mass, or 0.10 to 0.60% by mass. Zr suppresses abnormal grain growth of main phase particles (crystal grains) in the manufacturing process (sintering process) of a permanent magnet, makes the structure of the permanent magnet uniform and fine, and improves the magnetic properties of the permanent magnet.

Permanent magnets may contain titanium (Ti). The content of Ti in the permanent magnet may be 0.00 to 1.50% by mass, 0.03 to 0.80% by mass, or 0.10 to 0.60% by mass. Ti suppresses abnormal grain growth of main phase particles (crystal grains) in the manufacturing process (sintering process) of the permanent magnet, makes the structure of the permanent magnet uniform and fine, and improves the magnetic properties of the permanent magnet.

Permanent magnets are at least one selected from the group consisting of manganese (Mn), calcium (Ca), nickel (Ni), silicon (Si), chlorine (Cl), sulfur (S) and fluorine (F) as unavoidable impurities. May be contained. The total content of unavoidable impurities in the permanent magnet may be 0.001 to 0.50% by mass.

The composition of the entire permanent magnet described above is specified by, for example, fluorescent X-ray (XRF) analysis, high frequency inductively coupled plasma (ICP) emission spectrometry, and inert gas melting-non-dispersive infrared absorption (NDIR) method. good.

The permanent magnet according to this embodiment may be applied to a motor, an actuator or the like. For example, permanent magnets include hybrid vehicles, electric vehicles, hard disk drives, magnetic resonance imaging (MRI), smartphones, digital cameras, flat-screen TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators and wind power generators. It is used in various fields such as machines.

(Manufacturing method of permanent magnet)
In the following, a method for manufacturing a sintered magnet will be described as an example of the above-mentioned method for manufacturing a permanent magnet.

A raw material alloy is produced from the metal (raw material metal) containing each element constituting the above-mentioned permanent magnet by a strip casting method or the like. The raw material metal may be, for example, a simple substance of a rare earth element (elemental metal), an alloy containing a rare earth element, pure iron, ferrobolon, or an alloy containing these. These raw metal are weighed to match the desired permanent magnet composition.

As the raw material alloy, one kind of raw material alloy may be used. That is, the permanent magnet may be manufactured by the one-alloy method. When one kind of raw material alloy is used, the composition of the raw material alloy may be substantially the same as the composition of the finally obtained permanent magnet. As the raw material alloy, a plurality of types of raw material alloys may be used. For example, a main phase alloy and a grain boundary phase alloy may be used as the raw material alloy. That is, the permanent magnet may be manufactured by the dialloy method. The main phase particles in the permanent magnet are derived from the main phase alloy. The grain boundary phase in the permanent magnet is derived from the grain boundary phase alloy. However, the composition of the main phase particles in the permanent magnet does not always match the composition of the main phase alloy, and the composition of the grain boundary phase in the permanent magnet does not necessarily match the composition of the grain boundary phase alloy. This is because the compositions of the main phase alloy and the grain boundary phase alloy can be changed in the sintering step and the aging treatment step described later.

A raw material alloy powder is prepared by pulverizing the above raw material alloy by the following method.

When only one type of raw material alloy is used in the production of permanent magnets, a part of the raw material alloy is pulverized in two steps of a coarse pulverization step and a fine pulverization step to form a fine powder. Become. The balance of the raw material alloy is pulverized only by the coarse pulverization step to become a coarse powder. In the coarse crushing step, for example, a crushing method such as a stamp mill, a jaw crusher, or a brown mill may be used. The coarse pulverization step may be carried out in an atmosphere of an inert gas. After occluding hydrogen in the raw material alloy, the raw material alloy may be crushed. That is, hydrogen storage pulverization may be performed as a coarse pulverization step. In the pulverization step, for example, a jet mill may be used.

In the rough crushing step, after crushing the raw material alloy, the raw material alloy may be classified so that the particle size of the raw material alloy is less than 1000 μm. That is, in the coarse pulverization step, a crude powder having a particle size of less than 1000 μm (cоarse powder) may be produced from the raw material alloy. The coarse powder may be a precursor of coarse main phase particles contained in a permanent magnet. The coarse powder may become coarse main phase particles through a sintering step and an aging treatment step described later. Therefore, the particle size of the coarse powder may be substantially the same as the particle size of the coarse main phase particles. That is, the particle size of the coarse main phase particles in the permanent magnet may be controlled by adjusting the particle size of the coarse powder in the coarse pulverization step. The particle size or particle size distribution of the coarse powder may be measured by, for example, a laser diffraction / scattering type particle size distribution measuring device. A plurality of coarse main phase particles may be formed by separating one alloy particle (for example, a secondary particle) constituting the coarse powder into a plurality of particles in a subsequent step. Therefore, the particle size of some of the alloy particles constituting the coarse powder may be larger than the particle size of the coarse main phase particles.

In the fine pulverization step following the coarse pulverization step, a part of the coarse powder obtained in the coarse pulverization step is further pulverized. In the fine pulverization step, the crude powder is pulverized until the median diameter (d50) of the crude powder becomes 1 μm or more and less than 5 μm. That is, in the fine pulverization step, a fine powder having a median diameter of 1 μm or more and less than 5 μm (fine powder) is produced from the crude powder. The fine powder may be a precursor of fine main phase particles contained in a permanent magnet. The fine powder may become fine main phase particles through the sintering step and the aging treatment step described later. Therefore, the median diameter of the fine powder may be substantially the same as the median diameter of the fine main phase particles. That is, the median diameter of the fine main phase particles in the permanent magnet may be controlled by adjusting the median diameter of the fine powder in the fine pulverization step. The median diameter of the fine powder is calculated based on the particle size distribution of the fine powder. The particle size distribution of the fine powder may be a particle size distribution based on the volume of the fine powder. The particle size distribution of the fine powder may be measured by, for example, a laser diffraction / scattering type particle size distribution measuring device.

A raw material alloy powder may be prepared by mixing the crude powder and the fine powder obtained by the above method. The relative mass of the crude powder with respect to 100 parts by mass of the fine powder is 0.02 parts by mass or more and 0.10 parts by mass or less. That is, a raw material alloy powder may be obtained by adding a crude powder of 0.02 parts by mass or more and 0.10 parts by mass or less to 100 parts by mass of a fine powder. The "crude powder addition amount" described below means the relative mass of the crude powder with respect to 100 parts by mass of the fine powder. When the amount of coarse powder added is less than 0.02 parts by mass, the frequency of coarse particles in the permanent magnet tends to be less than ^{0.1 grain / cm 2.} When the amount of coarse powder added is larger than 0.10 parts by mass, the frequency of coarse particles in the permanent magnet tends to exceed ^{1 piece / cm 2.}

When a plurality of types of raw material alloys are used, each raw material alloy may be pulverized separately and then mixed. For example, when a permanent magnet is manufactured by the two-alloy method, a main phase crude powder may be prepared from the main phase alloy by the above-mentioned coarse grinding step. Further, it may be prepared from a part of the main phase crude powder to the main phase fine powder by the above-mentioned coarse pulverization step and fine pulverization step. Then, the main phase alloy powder may be prepared by adding the main phase crude powder to the main phase fine powder in the above amount of the crude powder addition. Further, the grain boundary phase alloy powder (grain boundary phase fine powder) may be prepared from the grain boundary phase alloy by the above-mentioned coarse pulverization step and fine pulverization step. Then, the raw material alloy powder may be prepared by mixing the main phase alloy powder and the grain boundary phase alloy powder in a predetermined ratio. The predetermined ratio is a ratio in which the overall composition of the raw material alloy powder substantially matches the composition of the target permanent magnet.

The particle size distribution of the raw material alloy powder obtained by the above method may have at least two peaks. The particle size corresponding to the first peak of the two peaks may be substantially the same as the median diameter of the fine powder or the median diameter of the fine main phase particles in the permanent magnet. The particle size corresponding to the second peak of the two peaks may be substantially the same as the particle size of the coarse powder or the particle size of the coarse main phase particles in the permanent magnet. The intensity (frequency) of the first peak may be higher than the intensity (frequency) of the second peak. In other words, the integral of the first peak may be greater than the integral of the second peak. Since the particle size distribution of the raw material alloy powder has the above two peaks, it is easy to obtain a permanent magnet having the above technical features relating to the coarse main phase particles and the fine main phase particles. The particle size distribution of the raw material alloy powder may be a volume-based particle size distribution. The particle size distribution of the raw material alloy powder may be measured by, for example, a laser diffraction / scattering type particle size distribution measuring device.

By molding the raw material alloy powder obtained by the above method in a magnetic field, a molded product (green compact) can be obtained. For example, a molded product can be obtained by pressurizing the raw material alloy powder with the mold while applying a magnetic field to the raw material alloy powder in the mold. The pressure exerted by the mold on the raw material alloy powder may be 30 to 300 MPa. The strength of the magnetic field applied to the raw material alloy powder may be 950 to 1600 kA / m.

In the sintering step, the above-mentioned compact is heated at a predetermined sintering temperature in a vacuum or an atmosphere of an inert gas. As a result, the molded product is sintered and a sintered body is obtained. The particle size of the coarse main phase particles in one cross section of the permanent magnet is 100 μm or more and 1000 μm or less, and the number of coarse main phase particles per unit area in the above cross section is 0.1 piece / cm ² or more and 1 piece / cm. ^As long as the size is 2 or less and the median diameter of the fine main phase particles in the above cross section is 1 μm or more and 5 μm or less, the grain growth of each of the fine powder and the coarse powder may proceed during the sintering process, and the fine powders may grow together. Sintering, sintering of coarse powders, and sintering of fine powders and coarse powders may proceed during the sintering process.

Sintering conditions may be appropriately set according to the composition of the target permanent magnet, the crushing method of the raw material alloy, the particle size, and the like. The sintering temperature Ts may be, for example, 1000 to 1090 ° C. The sintering time may be 1 hour or more and 24 hours or less. If the sintering temperature is too low, the molded product is not sufficiently sintered, and it is difficult for the sintered body to have sufficient magnetic properties and mechanical strength. When the sintering temperature is higher than 1090 ° C., the sintering and grain growth of the raw material alloy powder (main phase alloy powder) are likely to proceed excessively. Therefore, when the sintering temperature is higher than 1090 ° C., the particle size of the coarse main phase particles tends to exceed 1000 μm, and the median diameter of the fine main phase particles tends to increase. As a result, the coercive force of the permanent magnet at high temperature tends to decrease, and the permanent magnet tends to be demagnetized at high temperature.

An aging treatment step following the sintering step may be carried out. In the aging treatment step, the sintered body is heated at a predetermined aging treatment temperature in a vacuum or an atmosphere of an inert gas. The aging treatment temperature may be lower than the sintering temperature. For example, the aging treatment temperature may be 450 ° C. or higher and 940 ° C. or lower, or 470 ° C. or higher and 920 ° C. or lower. The aging treatment step may consist of a first aging treatment and a second aging treatment following the first temporary aging treatment. In the first temporary effect treatment, the sintered body may be heated at the first temperature T1. In the second aging treatment, the sintered body may be heated at the second temperature T2. The first temperature T1 may be higher than the second temperature T2. The first temperature T1 may be 700 to 940 ° C or 800 to 920 ° C. The second temperature T2 may be 450 to 570 ° C or 470 to 540 ° C.

When raising the temperature of the atmosphere from a temperature below Ts (eg, room temperature) to Ts to initiate the sintering process, the rate of temperature rise may be 0.1 to 20 ° C./min. The "atmospheric temperature" is the temperature of the atmosphere around the sintered body, for example, the temperature inside the heating furnace. When the temperature of the atmosphere is lowered from Ts to a temperature lower than T1 (for example, room temperature) after the sintering step, the temperature lowering rate may be 1 to 50 ° C./min. When raising the temperature of the atmosphere from a temperature below T1 (for example, room temperature) to T1 in order to start the first temporary effect treatment, the heating rate may be 0.1 to 20 ° C./min. When the temperature of the atmosphere is lowered from T1 to a temperature lower than T2 (for example, room temperature) after the first temporary effect treatment, the temperature lowering rate may be 1 to 50 ° C./min. When raising the temperature of the atmosphere from a temperature below T2 (for example, room temperature) to T2 in order to start the second aging treatment, the heating rate may be 0.1 to 50 ° C./min. After the first temporary aging treatment, the temperature of the atmosphere may be lowered from T1 to T2, and the second aging treatment may be carried out following the first temporary aging treatment. When the temperature of the atmosphere of the aging treatment is lowered from T2 to room temperature after the second aging treatment, the temperature lowering rate may be 1 to 50 ° C./min.

By the above method, a permanent magnet (sintered magnet) according to the present embodiment can be obtained.

When a permanent magnet containing a heavy rare earth element is produced, the heavy rare earth element or a compound thereof (for example, a hydride) may be attached to the surface of the above-mentioned sintered body, and then the sintered body may be heated. By this thermal diffusion treatment, heavy rare earth elements can be diffused from the surface of the sintered body to the inside. For example, the first temporary aging treatment and the second aging treatment may be carried out after the heat diffusion treatment is carried out after the sintering step. After performing the heat diffusion treatment after the first temporary aging treatment, the second aging treatment may be carried out.

The present invention is not limited to the above embodiment. For example, the RTB-based permanent magnet may be a hot-processed magnet (hоt-defоrmed magnet).

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

(Example 1)
[Making permanent magnets]
A raw material alloy was produced from the raw metal of the permanent magnet by the strip casting method. The composition of the raw material alloy was adjusted by weighing the raw material metal. The concentration of each element in the raw material alloy was adjusted so that the composition of the raw material alloy matched the composition of the permanent magnets shown in Table 1 below. R in Table 1 below means Nd and Pr. The concentrations of Nd, Pr, Fe, Co, Ga, Cu, Al and Zr were measured by fluorescent X-ray analysis. The concentration of B was measured by ICP emission spectrometry.

Each of the following steps from the hydrogen pulverization treatment to the sintering step was carried out in a non-oxidizing atmosphere in which the oxygen concentration was less than 100 ppm.

After occluding hydrogen in the raw material alloy, the raw material alloy was heated at 350 ° C. for 1 hour to dehydrogenate in an Ar atmosphere to obtain a crude powder. That is, hydrogen pulverization treatment was performed as a coarse pulverization step. By classifying the crude powder using a classifier, particles having a particle size of 1000 μm or more were removed from the coarse powder. That is, the maximum value of the particle size of the crude powder was adjusted to less than 1000 μm. A fine grinding step was performed using some crude powder. In the fine grinding step, oleic acid amide was added to the crude powder as a grinding aid and these were mixed. After the addition of oleic acid amide, the crude powder was pulverized using a jet mill to obtain a fine powder. The median diameter of the fine powder was adjusted to 2.8 μm. The median diameter of the fine powder was calculated based on the particle size distribution of the fine powder. The particle size distribution of the fine powder was a particle size distribution based on the volume of the fine powder. The maximum value of the particle size of the coarse powder was measured by a commercially available laser diffraction / scattering type particle size distribution measuring device. The particle size distribution of the fine powder was also measured by the above-mentioned laser diffraction scattering type particle size distribution measuring device.

A raw material alloy powder was prepared by mixing the crude powder and the fine powder obtained by the above method. The relative mass of the crude powder with respect to 100 parts by mass of the fine powder was 0.02 parts by mass. The "crude powder addition amount" described below means the relative mass of the crude powder with respect to 100 parts by mass of the fine powder.

In the molding process, the raw material alloy powder was filled in the mold. Then, a molded product was obtained by pressurizing the raw material powder at 120 MPa while applying a magnetic field of 1200 kA / m to the raw material powder in the mold.

In the sintering step, the molded product was heated at the sintering temperature Ts for 10 hours in vacuum and then rapidly cooled to obtain a sintered body. The sintering temperature Ts of Example 1 is shown in Table 2 below.

As the aging treatment step, the first aging treatment and the second aging treatment following the first temporary aging treatment were carried out. In both the first temporary treatment and the second aging treatment, the sintered body was heated in an Ar atmosphere.

In the first temporary effect treatment, the sintered body was heated at 900 ° C. (first temperature T1) for 60 minutes.

In the second aging treatment, the sintered body was heated at 520 ° C. (second temperature T2) for 60 minutes.

By the above method, the permanent magnet of Example 1 was obtained.

[Composition analysis of permanent magnets]
The composition of the entire permanent magnet was analyzed by fluorescent X-ray analysis and ICP emission analysis. The concentration of each element in the permanent magnet matched the values shown in Table 1 below.

[Measurement of magnetic characteristics]
At 150 ° C. (high temperature), the permanent magnet's coercive force HcJ and demagnetizing field Hk were measured. Hk is a demagnetizing field in which the magnetization J of the permanent magnet corresponds to 95% of the residual magnetic flux density Br. The unit of coercive force HcJ is kA / m. The unit of the demagnetizing field Hk is kA / m. A BH tracer was used to measure HcJ and Hk. HcJ and Hk of Example 1 are shown in Table 2 below. The higher the value of the demagnetizing field Hk, the more difficult it is for the permanent magnet to be demagnetized at high temperatures.

[Analysis of cross section of permanent magnet]
The permanent magnet was cut perpendicular to its magnetization direction. The cross section of the permanent magnet was milled by ion milling to remove impurities such as oxides formed on the cross section. The cross section of the permanent magnet was rectangular, and the dimensions of the entire cross section were 54 mm in length × 9.4 mm in width. A part of the cross section of the permanent magnet was photographed with an optical microscope. A cross section of a permanent magnet taken with an optical microscope is shown in FIG. As shown in FIG. 3, the permanent magnet contained coarse main phase particles 4A.

Subsequently, the region of the cross section of the permanent magnet in which the coarse main phase particles were absent was analyzed by a scanning electron microscope (SEM) and an energy dispersive X-ray spectroscopy (EDS) apparatus. As the SEM, a shotkey scanning electron microscope "SU5000" manufactured by Hitachi High-Technologies Corporation was used. As the EDS apparatus, "Energy Dispersive X-ray Analyzer EMAX Evolution / EMAX ENERGY (EMAX X-MaxN Detector Specification)" manufactured by HORIBA, Ltd. was used. The measurement conditions were set as follows.
Electron beam acceleration voltage: 15kV
Spot intensity: 30
Working distance: 10mm

A cross section of the permanent magnet photographed by SEM is shown in FIG. As shown in FIG. 4, the permanent magnet contained a large number of micromain phase particles 4B and a grain boundary phase 6 existing between the plurality of micromain phase particles 4B. Each fine main phase particles 4B _{was (Nd 1-x Pr x)} 2 (Fe 1-y Co y) of ₁₄ B crystal grains. x was 0 or more and less than 1, and y was 0 or more and less than 1. Further, some grain boundary phases 6 were transition metal-rich phases, and some other grain boundary phases 6 were R-rich phases. The composition of the coarse main phase particles 4A described above was also analyzed using EDS. The composition of the coarse main phase particles 4A was substantially the same as the composition of the fine main phase particles 4B.

By observing the entire cross section of the permanent magnet with an optical microscope and the naked eye, the number of coarse main phase particles 4A existing in the cross section of the permanent magnet was measured. Further, the cross-sectional area A of each coarse main phase particle 4A was measured by analyzing the image of each coarse main phase particle 4A taken with an optical microscope using image analysis software. As the image analysis software, Mac-View manufactured by Mountech Co., Ltd. was used. The particle size (diameter equivalent to a circle) of each coarse main phase particle 4A was calculated from the cross-sectional area A of each coarse main phase particle 4A. The equivalent circle diameter of the coarse main phase particles 4A is expressed as ^{(4A / π) 1/2.} By the above method, the maximum value (maximum particle size) of the particle sizes of all the coarse main phase particles 4A found in the cross section of the permanent magnet was specified. The maximum particle size of the coarse main phase particles of the examples is shown in Table 2 below. Further, the number of coarse main phase particles 4A per unit area of the cross section of the permanent magnet was calculated. The "coarse grain frequency" described below means the number of coarse main phase particles 4A per unit area of the cross section of the permanent magnet. The coarse grain frequencies of Example 1 are shown in Table 2 below. The permanent magnet of Example 1 did not contain main phase particles having a particle size measured in cross section larger than 1000 μm.

By photographing a plurality of regions in the cross section of the permanent magnet with SEM, 170 micromain phase particles 4B existing in the cross section of the permanent magnet were randomly selected. The cross-sectional area B of each micromain phase particle 4B was measured by binarizing and analyzing the image taken by SEM using the above image analysis software. The particle size (circle equivalent diameter) of the fine main phase particles 4B was calculated from the cross-sectional area B of each of the fine main phase particles 4B. The equivalent circle diameter of the fine main phase particles 4B is expressed as ^{(4B / π) 1/2.} The median diameter d50 of the fine main phase particles 4B was calculated from the particle size (circle equivalent diameter) of the 170 fine main phase particles 4B. The median diameter d50 of the fine main phase particles of Example 1 is shown in Table 2 below.

(Examples 2 and 3 and Comparative Examples 1 to 4)
The raw material alloy powders of Examples 2 and 3 and Comparative Examples 2 and 3 were prepared with the amount of crude powder added as shown in Table 2 below. Permanent magnets of Examples 2 and 3 and Comparative Examples 2 and 3 were produced in the same manner as in Example 1 except for the amount of coarse powder added.

In the case of Comparative Example 1, a fine powder was obtained by pulverizing all the crude powders with a jet mill. That is, the raw material alloy powder of Comparative Example 1 consisted of only fine powder and did not contain coarse powder. Therefore, the amount of crude powder added in Comparative Example 1 was zero parts by mass. The permanent magnet of Comparative Example 1 was produced in the same manner as in Example 1 except that the raw material alloy powder did not contain the crude powder.

In the case of Comparative Example 4, fine powder was obtained by pulverizing all the crude powder with a jet mill. That is, the raw material alloy powder of Comparative Example 4 consisted of only fine powder and did not contain coarse powder. Therefore, the amount of crude powder added in Comparative Example 4 was zero parts by mass. The sintering temperature Ts of Comparative Example 4 was 1070 ° C. A permanent magnet of Comparative Example 1 was produced in the same manner as in Example 1 except for these matters.

Measurement and analysis were performed using the permanent magnets of Examples 2 and 3 and Comparative Examples 1 to 4 by the same method as in Example 1.

In any of Examples 2 and 3 and Comparative Examples 1 to 4, the permanent magnet contained a plurality of coarse main phase particles 4A, a plurality of fine main phase particles 4B, and a grain boundary phase 6. In each of Examples 2 and 3 and Comparative Examples 1 to 4, the compositions of the coarse main phase particles 4A, the fine main phase particles 4B, and the grain boundary phase 6 were substantially the same as in the case of Example 1. ..
HcJ and Hk of Examples 2 and 3 and Comparative Examples 1 to 4 are shown in Table 2 below.

The maximum particle sizes of the coarse main phase particles of Examples 2 and 3 and Comparative Examples 1 to 4 are shown in Table 2 below.
However, the permanent magnet of Comparative Example 1 did not contain coarse main phase particles. The permanent magnets of Examples 2 and 3 each did not contain main phase particles having a particle size measured in cross section larger than 1000 μm. On the other hand, the maximum particle size of the main phase particles contained in the permanent magnet of Comparative Example 4 was 1100 μm. In order to compare Comparative Example 4 with Examples 1 to 3 and Comparative Examples 1 to 3, only in the case of Comparative Example 4, not only the main phase particles having a particle size of 100 μm or more and 1000 μm or less, but also the particle size of 1000 μm or more. Larger principal phase particles were also classified as coarse principal phase particles. That is, only in the case of Comparative Example 4, in the calculation of the coarse particle frequency, the number of main phase particles having a particle size larger than 1000 μm was also measured as the number of coarse main phase particles.
The coarse grain frequencies of Examples 2 and 3 and Comparative Examples 1 to 4 are shown in Table 2 below.
The median diameter d50 of each of the fine main phase particles of Examples 2 and 3 and Comparative Examples 1 to 4 is shown in Table 2 below.

Since the RTB-based permanent magnet according to the present invention has excellent magnetic characteristics at high temperatures, it is applied to, for example, a motor mounted on a hybrid vehicle or an electric vehicle.

2 ... RTB-based permanent magnet, 2cs ... Cross section of RTB-based permanent magnet, 4 ... main phase particles, 4A ... coarse main phase particles, 4B ... fine main phase particles, 6 ... grain boundary phase.

Claims (4)

An RTB-based permanent magnet containing the rare earth element R and the transition metal elements T and B.
The RTB-based permanent magnet contains at least Nd as R and contains.
The RTB-based permanent magnet contains at least Fe as T and contains.
The RTB-based permanent magnet includes a plurality of main phase particles including Nd, T, and B, and a grain boundary phase contained in a grain boundary between the plurality of main phase particles.
Some of the principal phase particles are coarse principal phase particles.
The other main phase particles are micro-main phase particles having a particle size smaller than the particle size of the coarse main phase particles.
The particle size of the coarse main phase particles in one cross section of the RTB-based permanent magnet is 100 μm or more and 1000 μm or less.
The number of the coarse main phase particles per unit area of the cross section is 0.1 piece / cm ² or more and 1 piece / cm ² or less.
The median diameter of the fine main phase particles in the cross section is 1 μm or more and 5 μm or less.
RTB system permanent magnet. Contains more Ga,
The RTB-based permanent magnet according to claim 1. 29.50 to 33.00% by mass R,
0.70 to 0.95% by mass B,
0.03 to 0.60% by mass Al,
0.01-1.50% by mass Cu,
0.00-3.00% by mass of Co,
0.10 to 1.00% by mass of Ga,
0.05 to 0.30% by mass of C,
Consists of 0.03 to 0.40% by mass O and the balance
The balance is Fe only, or Fe and other elements.
The RTB-based permanent magnet according to claim 1 or 2. The total content of heavy rare earth elements is 0.00% by mass or more and 1.00% by mass or less.
The RTB-based permanent magnet according to any one of claims 1 to 3.

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