JP2018174312A - R-T-B based sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an R-T-B based sintered magnet which is low cost and enables the increase in residual magnetic flux density and coercive force.SOLUTION: An R-T-B based sintered magnet 1 comprises RTB crystal as primary-phase grains, where R represents one or more kinds of rare earth elements, including a heavy rare earth element RH as an essential element, T represents one or more kinds of transition metal elements, including Fe or Fe and Co as an essential element, and B represents boron. The primary-phase grains are partially composed of inverted core shell primary-phase grains 11. The inverted core shell primary-phase grains 11 each have a core part 11a and a shell part 11b. When a total RH concentration (at%) in the core part 11a is denoted by C, and a total RH concentration (at%) in the shell part 11b is denoted by C, C/C>1.0. The abundance rate of the inverted core shell primary-phase grains 11 at the grain boundaries 12 in a magnet surface layer portion is larger than that in a magnet center portion.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an RTB-based sintered magnet.

  As shown in Patent Document 1, it is known that an RTB-based sintered magnet has excellent magnetic properties. At present, further improvement in magnetic properties is desired.

  As a method for improving the magnetic properties, particularly the coercive force, of an RTB-based sintered magnet, a method (one alloy method) in which a heavy rare earth element is included as R at the stage of producing a raw material alloy is known. Further, there is a method (two alloy method) in which a main phase alloy containing no heavy rare earth element and a grain boundary phase alloy containing heavy rare earth element are mixed and sintered after pulverization. Furthermore, as described in Patent Document 2, after the RTB-based sintered magnet is manufactured, the heavy rare earth element is diffused through the grain boundary by attaching and heating the heavy rare earth element on the surface. There is a method (grain boundary diffusion method).

  In the one alloy method described above, since the heavy rare earth element is present in the main phase particles, the maximum energy product may be reduced. In the two-alloy method, heavy rare earth elements in the main phase particles can be reduced, and a decrease in the maximum energy product can be suppressed. In the grain boundary diffusion method, the concentration of heavy rare earth elements can be increased only in a region very close to the grain boundary in the main phase particles, and the concentration of heavy rare earth elements inside the main phase particles can be reduced. That is, main phase particles having a general core-shell structure can be obtained. A general core-shell structure is a structure in which the concentration of heavy rare earth elements in the core portion is lower than the concentration of heavy rare earth elements in the shell portion covering the core portion. Thereby, it is possible to increase the coercive force as compared with the two-alloy method and suppress the decrease in the maximum energy product. Furthermore, the amount of expensive heavy rare earth elements used can be suppressed.

  Patent Document 3 discloses that the concentration of heavy rare earth elements in the core portion is higher than the concentration of heavy rare earth elements in the shell portion in order to improve the coercive force as compared with the conventional RTB-based sintered magnet. Techniques involving phase particles are described.

JP 59-46008 A International Publication No. 2006/043348 Japanese Patent Laid-Open No. 2006-154219

  However, at present, there is a demand for further improvement in coercive force and cost reduction.

  An object of this invention is to obtain the RTB type sintered magnet which improves a magnetic characteristic and is low-cost.

In order to achieve the above object, an RTB-based sintered magnet according to the present invention includes:
An RTB-based sintered magnet including main phase particles made of R ₂ T ₁₄ B crystal,
R is one or more rare earth elements essential for the heavy rare earth element RH, T is one or more transition metal elements essential for Fe or Fe and Co, and B is boron,
Some of the main phase particles are reverse core shell main phase particles,
The reverse core shell main phase particles have a core portion and a shell portion,
The total RH concentration (at%) in the core part is defined as C _RC ,
All RH concentration at the shell portion (at%) in the case of the _{C RS,}
C _RC / C _RS > 1.0,
The existence ratio of the reverse core shell main phase particles is larger in the magnet surface layer than in the magnet center.

  The RTB-based sintered magnet according to the present invention has the above-described characteristics, thereby improving the magnetic characteristics and providing a low-cost magnet.

The RCTB sintered magnet according to the present invention may have _CRC / _CRS > 1.5.

The RTB-based sintered magnet according to the present invention is
Some of the main phase particles are core-shell main phase particles,
The core-shell main phase particles have a core part and a shell part,
The total RH concentration (at%) in the core part is represented by _CNC ,
When the total RH concentration (at%) in the shell portion is C _NS ,
C _NC / C _NS <1.0 may be sufficient.

The RTB-based sintered magnet according to the present invention is
A core-shell particle layer mainly composed of the core-shell main phase particles and a reverse core-shell particle layer mainly composed of the reverse core-shell main phase particles may be included.

The RTB-based sintered magnet according to the present invention is
The core-shell particle layer and the reverse core-shell particle layer may be arranged in this order from the magnet center to the magnet surface layer.

The RTB-based sintered magnet according to the present invention is
A part of the main phase particles is a non-core shell main phase particle having no core-shell structure, and is an RTB-based sintered magnet including a non-core shell particle layer mainly composed of the non-core shell main phase particles. And
The non-core shell particle layer, the core shell particle layer, and the reverse core shell particle layer may be arranged in this order from the magnet center to the magnet surface layer.

It is the schematic of the cross section of the RTB type sintered magnet which concerns on one Embodiment of this invention. It is the schematic of the cross section of the RTB type sintered magnet which concerns on one Embodiment of this invention. It is the schematic of the cross section of magnet surface layer vicinity of the RTB system sintered magnet which concerns on one Embodiment of this invention.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

  <RTB-based sintered magnet>

The RTB-based sintered magnet 1 according to this embodiment includes main phase particles made of R ₂ T ₁₄ B crystals. R is one or more rare earth elements essential for the heavy rare earth element RH, T is one or more transition metal elements essential for Fe or Fe and Co, and B is boron. Furthermore, Zr may be included. Note that the rare earth element contained as R means Sc, Y, and a lanthanoid element belonging to Group 3 of the long-period periodic table. The heavy rare earth element RH means Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

Although there is no restriction | limiting in particular in content of R, 25 mass% or more and 35 mass% or less may be sufficient, Preferably it is 28 mass% or more and 33 mass% or less. When the content of R is 25% by mass or more, R ₂ T ₁₄ B crystals that are the main phase particles of the R-T-B-based sintered magnet 1 are sufficiently easily generated, and α- having a soft magnetism Precipitation of Fe or the like is suppressed, and deterioration of magnetic properties is easily suppressed. When the R content is 35% by mass or less, the residual magnetic flux density Br of the RTB-based sintered magnet 1 tends to be improved.

  The content of B in the RTB-based sintered magnet according to this embodiment may be 0.5% by mass or more and 1.5% by mass or less, and preferably 0.8% by mass or more and 1.2% or less. It is not more than mass%, more preferably not less than 0.8 mass% and not more than 1.0 mass%. When the content of B is 0.5% by mass or more, the coercive force Hcj tends to be improved. Moreover, when the B content is 1.5% by mass or less, the residual magnetic flux density Br tends to be improved.

  T may be Fe alone or a part of Fe may be substituted with Co. The content of Fe in the RTB-based sintered magnet according to the present embodiment is a substantial balance when the inevitable impurities, O, C, and N are removed from the RTB-based sintered magnet. is there. The Co content is preferably 0% by mass to 4% by mass, more preferably 0.1% by mass to 2% by mass, and 0.3% by mass to 1.5% by mass. More preferably. The transition metal element other than Fe or Fe and Co is not particularly limited, and examples thereof include Ti, V, Cr, Mn, Ni, Cu, Zr, Nb, Mo, Hf, Ta, and W. Further, a part of the transition metal element included as T may be replaced with an element such as Al, Ga, Si, Bi, Sn, for example.

  When the RTB-based sintered magnet 1 contains one or two selected from Al and Cu, the content of one or two selected from Al and Cu is 0.02 mass respectively. % Or more and 0.60% by mass or less is preferable. By containing one or two selected from Al and Cu in an amount of 0.02 to 0.60% by mass, the coercive force and moisture resistance of the RTB-based sintered magnet 1 can be improved. The temperature characteristic tends to be improved. The content of Al is preferably 0.03% by mass or more and 0.40% by mass or less, and more preferably 0.05% by mass or more and 0.25% by mass or less. Further, the Cu content is preferably more than 0% by mass and 0.30% by mass or less, more preferably more than 0% by mass and 0.20% by mass or less, and further preferably 0.03% by mass to 0.15% by mass.

  The RTB-based sintered magnet 1 can further contain Zr. The Zr content may be more than 0% by mass and 0.25% by mass or less. By containing Zr within the above range, abnormal growth of main phase particles can be suppressed in the manufacturing process of the sintered magnet, mainly in the sintering process. Therefore, the structure of the obtained sintered body (RTB-based sintered magnet 1) becomes uniform and fine, and the magnetic properties of the obtained sintered body tend to be improved. In order to obtain the above effects better, the content of Zr may be 0.03% by mass or more and 0.25% by mass or less.

  Further, the content of C in the RTB-based sintered magnet 1 is preferably 0.05% by mass or more and 0.30% by mass or less. When the C content is 0.05% by mass or more, the coercive force tends to be improved. When the C content is 0.30% by mass or less, the coercive force (Hcj) and the squareness ratio (Hk / Hcj) tend to be sufficiently high. Hk is the magnetic field strength when the magnetization in the second quadrant of the magnetic hysteresis loop (4πI-H curve) is 90% of the residual magnetic flux density (Br). The squareness ratio is a parameter representing the ease of demagnetization due to the action of an external magnetic field or temperature rise. When the squareness ratio is small, the demagnetization due to the action of the external magnetic field and the temperature rise increases. In addition, the magnetic field strength required for magnetization increases. In order to obtain a better coercive force and squareness ratio, the C content is preferably set to 0.10% by mass or more and 0.25% by mass or less.

  Further, the content of O in the R-T-B system sintered magnet 1 is preferably 0.03% by mass or more and 0.40% by mass or less. When the content of O is 0.03% by mass or more, the corrosion resistance tends to be improved. When the content is 0.40% by mass or less, a liquid phase is easily formed during sintering, and the coercive force tends to be improved. In order to improve the corrosion resistance and the coercive force, the content of O may be 0.05% by mass or more and 0.30% by mass or less, or 0.05% by mass or more and 0.25% by mass or less.

  Further, the N content in the R-T-B system sintered magnet 1 is preferably 0% by mass or more and 0.15% by mass or less. When the N content is 0.15% by mass or less, the coercive force tends to be sufficiently improved.

  The RTB-based sintered magnet 1 may contain inevitable impurities such as Mn, Ca, Ni, Cl, S, and F in an amount of about 0.001% by mass to 0.5% by mass.

  As a method for measuring the oxygen content, carbon content, and nitrogen content in the RTB-based sintered magnet, a conventionally known method can be used. The amount of oxygen is measured, for example, by an inert gas melting-non-dispersive infrared absorption method, the amount of carbon is measured, for example, by combustion in an oxygen stream-infrared absorption method, and the amount of nitrogen is, for example, an inert gas melting- Measured by thermal conductivity method.

No particular limitation on the particle size of the main phase particles consisting of R ₂ T ₁₄ B crystal, but typically is 1μm or more 10μm or less.

  The type of R is not particularly limited, but preferably includes Nd and Pr. Further, the type of heavy rare earth element RH is not particularly limited, but preferably includes one or both of Dy and Tb.

As shown in FIG. 1A and FIG. 2, the RTB-based sintered magnet 1 according to this embodiment includes a reverse core-shell particle layer 1 a mainly composed of reverse core-shell main phase particles 11, and mainly a core-shell main phase. It has a core-shell particle layer 1b made of particles 13. The inverted core-shell main phase particles 11 and the core-shell main phase particles 13 are main phase particles made of R ₂ T ₁₄ B crystals. Moreover, the grain boundary 12 may exist between each main phase particle.

  As shown in FIG. 2, the reverse core shell main phase particle 11 has a core part 11a and a shell part 11b covering the core part 11a. The core-shell main phase particles 13 have a core portion 13a and a shell portion 13b that covers the core portion 13a. In addition, the fact that each main phase particle has a core-shell structure, that is, a reverse core-shell main phase particle 11 or a core-shell main phase particle 13 is observed by using a SEM at a magnification of 1000 to 10,000 times. I can confirm.

  Specifically, a cross-section obtained by cutting the RTB-based sintered magnet 1 according to the present embodiment is mirror-polished, and then a reflected electron image is taken with an SEM. From the composition contrast generated in the reflected electron image, it can be determined whether each main phase particle is the core-shell main phase particle 13 or the reverse core-shell main phase particle 11. In general, the composition contrast becomes brighter (whiter) as the average atomic number of the observation target increases. Further, the heavy rare earth element RH has a larger atomic number than the elements contained in the other RTB-based sintered magnet 1. Therefore, the region where the concentration of heavy rare earth element RH is relatively high has a higher average atomic number than the region where the concentration of heavy rare earth element RH is relatively low. In the reflected electron image, a region having a high RH concentration inside the main phase particle becomes brighter (whiter) than a region having a low RH concentration. From the above, it is possible to determine whether each main phase particle is the core-shell main phase particle 13 or the reverse core-shell main phase particle 11 based on the position of the bright part inside the main phase particle.

Here, the reverse core shell main phase particles 11 are main phase particles made of the R ₂ T ₁₄ B crystal, and the total RH concentration (at%) in the core portion 11a is C _RC and the total RH concentration in the shell portion 11b ( the at%) in the case of the _{C RS,} a main phase particles is a C _{RC /} C RS> 1.0.

  That is, the reverse core-shell main phase particle 11 is a main phase particle in which the total RH concentration in the core portion 11a is higher than the total RH concentration in the shell portion 11b, contrary to the generally known core-shell main phase particles. is there.

There are no particular restrictions on the measurement locations of _CRC and _CRS . For example, it can be as follows.

First, the reverse core-shell main phase particles 11 whose concentration is to be measured are observed with a transmission electron microscope (TEM), and the diameter having the maximum length is specified. Next, two intersections between the diameter and the grain boundary are specified. Then, it is possible to measure the total RH concentration in the region of 20 nm × 20 nm centered on the midpoint of the two points of intersection, the total RH concentration _{C RC} in the core portion.

Next, one intersection is selected from the two intersections. Then, the total RH concentration in a region of 20 nm × 20 nm centering on the point entering the reverse core shell main phase particle side is measured along the diameter having the maximum length from the intersection, and the total RH in the shell portion is measured. The concentration _CRS can be set.

On the other hand, the core-shell main phase particle 13 is a main phase particle composed of the R ₂ T ₁₄ B crystal, and the total RH concentration (at%) in the core portion 13a is C _NC and the total RH concentration (at) in the shell portion 13b. %) and when the _{C NS,} a main phase particles is a C _{NC /} C NS <1.0.

  That is, the core-shell main phase particles 13 are main-phase particles having a lower total RH concentration in the core portion 13a than in the total RH concentration in the shell portion 13b, as in the generally known core-shell main phase particles.

Although there is no restriction | limiting in particular in the measurement location of _CNC and _CNS , For example, a measurement location can be set similarly to _CRC and _CRS .

  The total RH concentration with respect to the total R concentration in the core portion 11a of the reverse core-shell main phase particle 11 is not particularly limited, but is generally about 30% to 80% in atomic ratio. The total RH concentration relative to the total R concentration in the shell portion 11b of the reverse core shell main phase particle 11 is not particularly limited, but is generally about 10% to 30% in terms of atomic ratio.

  The total RH concentration relative to the total R concentration in the core portion 13a of the core-shell main phase particle 13 is not particularly limited, but is generally about 0% or more and 10% or less in terms of atomic ratio. The total RH concentration relative to the total R concentration in the shell portion 13b of the core-shell main phase particle 13 is not particularly limited, but is generally about 10% to 30% in terms of atomic ratio.

  As described above, normally, the core portion 11a of the reverse core shell main phase particle 11 has the highest total RH concentration with respect to the total R concentration, and the core portion 13a of the core shell main phase particle 13 has the lowest total RH concentration with respect to the total R concentration. In addition, in the shell part 11b of the reverse core-shell main phase particle 11 and the shell part 13b of the core-shell main phase particle 13, the total RH concentration does not change greatly with respect to the total R concentration.

  In FIG. 2, the shell 11b covers the entire surface of the core portion 11a in the reverse core shell main phase particles 11, but the shell 11b does not need to cover the entire surface of the core 11a, and the surface of the core 11a. Of 60% or more. The core part 11a and the shell part 11b can be distinguished by SEM. The same applies to the core-shell main phase particles 13.

  The RTB-based sintered magnet 1 according to the present embodiment includes a reverse core shell main phase particle 11 and thus becomes a permanent magnet having high magnetic characteristics even when the amount of heavy rare earth elements is reduced. The mechanism by which the above effect is obtained by including the inverted core-shell main phase particles 11 is considered to be the following mechanism.

  The reverse core shell main phase particles 11 contain more RH than the shell portion 11b, so that the anisotropic magnetic field is increased in the core portion 11a. Therefore, it is considered that the anisotropic magnetic field changes at the interface between the core portion 11 a and the shell portion 11 b of the reverse core shell main phase particle 11. It is considered that the pinning force increases due to the change of the anisotropic magnetic field in the above-described reverse core-shell main phase particles 11. Therefore, it is considered that the RTB-based sintered magnet 1 including the reverse core shell main phase particles 11 has improved coercive force.

  As shown in FIGS. 1A and 2, the abundance ratio of the reverse core shell main phase particles 11 with respect to all main phase particles is higher in the magnet surface layer than in the magnet center. And it is preferable that the reverse core-shell particle layer 1a mainly composed of the reverse core-shell main phase particles 11 exists in the magnet surface layer portion.

  The inverted core-shell main phase particle 11 contains a lot of heavy rare earth elements RH in the core portion 11a. Therefore, the reverse core shell main phase particles 11 themselves have low residual magnetic flux density and saturation magnetization. Since the reverse core shell main phase particle 11 has a low saturation magnetization, even if a certain reverse core shell main phase particle 11 is reversed in magnetization, the influence on the magnetization reversal of the main phase particle adjacent to the reverse core shell main phase particle 11 is small. That is, the reverse core-shell particle layer 1a mainly composed of the reverse core-shell main phase particles 11 is present in the magnet surface layer portion of the R-T-B system sintered magnet 1, thereby transmitting the reverse magnetic domain generated from the magnet surface. It is suppressed. Therefore, since the reverse core shell main phase particles 11 are present more in the magnet surface layer portion and the reverse core shell particle layer 1a is present in the magnet surface layer portion, the coercive force of the RTB-based sintered magnet 1 is further improved. To do.

In the inverted core-shell main phase particles 11 included in the RTB-based sintered magnet 1 according to the present embodiment, C _RC / C _RS > 1.5 is preferable, and C _RC / C _RS > 3.0 It is more preferable that In the inverted core-shell main phase particles 11, the more the heavy rare earth element RH is present in the core portion 11a than in the shell portion 11b, the above effect is increased and the coercive force is further improved, which is preferable.

  In the present embodiment, the magnet surface layer portion refers to a region of 5 μm or more and 150 μm or less from the magnet surface toward the inside of the magnet. The magnet center portion refers to a portion inside the magnet surface layer portion. Moreover, the reverse core shell particle layer 1a does not need to exist in all the magnet surface layer parts of the RTB-based sintered magnet 1, and may exist only in a part of the magnet surface layer part. Further, as shown in FIG. 2, the reverse core shell particle layer 1 a indicates a layer in which the reverse core shell main phase particles 11 are present. The core-shell particle layer 1b is a layer in which the core-shell main phase particles 13 are present and the reverse core-shell main phase particles 11 are not present.

  There is no restriction | limiting in particular in the thickness of the reverse core shell particle layer 1a. The thickness is preferably 10 μm or more and 100 μm or less.

  Further, in the RTB-based sintered magnet according to the present embodiment, as shown in FIG. 1A, the core-shell particle layer 1b and the reverse core-shell particle layer 1a are arranged in this order from the magnet central portion toward the magnet surface layer portion. You can leave. Moreover, you may consist only of the reverse core-shell particle layer 1a and the core-shell particle layer 1b.

<Method for producing RTB-based sintered magnet>
Next, the manufacturing method of the RTB system sintered magnet concerning this embodiment is explained.

  In the following description, an RTB-based sintered magnet manufactured by powder metallurgy and having a heavy rare earth element diffused at grain boundaries will be described as an example. The method for manufacturing the magnet is not particularly limited, and other methods can be used.

  The manufacturing method of the R-T-B system sintered magnet according to the present embodiment includes a forming step of forming a raw material powder to obtain a formed body, and a sintering step of sintering the formed body to obtain a sintered body. And an aging step of holding the sintered body at a temperature lower than the sintering temperature for a certain period of time.

  Hereinafter, although the manufacturing method of a RTB system sintered magnet is demonstrated in detail, what is necessary is just to use a well-known method about the matter which is not specified.

[Preparation process of raw material powder]
The raw material powder can be produced by a known method. In this embodiment, an R-T-B system sintered magnet is manufactured by one alloy method using one kind of raw material alloy mainly composed of R ₂ T ₁₄ B phase, but a two alloy method using two kinds of raw material alloys. You may manufacture by. Here, the composition of the raw material alloy is controlled to be the composition of the finally obtained RTB-based sintered magnet.

  First, a raw material metal corresponding to the composition of the raw material alloy according to the present embodiment is prepared, and a raw material alloy corresponding to the present embodiment is produced from the raw material metal. There is no restriction | limiting in particular in the preparation methods of raw material alloy. For example, a raw material alloy can be produced by a strip casting method.

  After producing the raw material alloy, the produced raw material alloy is pulverized (grinding step). The pulverization process may be performed in two stages or in one stage. There is no particular limitation on the grinding method. For example, it is carried out by a method using various pulverizers. For example, the pulverization process is performed in two stages, a coarse pulverization process and a fine pulverization process, and the coarse pulverization process can be performed, for example, by hydrogen pulverization. Specifically, after hydrogen is stored in the raw material alloy at room temperature, dehydrogenation can be performed in an Ar gas atmosphere at 400 ° C. or higher and 650 ° C. or lower, 0.5 hour or longer and 2 hours or shorter. The fine pulverization step can be performed using, for example, a jet mill or a wet attritor after adding oleic acid amide, zinc stearate or the like to the coarsely pulverized powder. There is no restriction | limiting in particular in the particle size of the finely pulverized powder (raw material powder) obtained. For example, fine pulverization can be performed so that the particle diameter (D50) is a fine pulverized powder (raw material powder) having a particle size of 1 μm to 10 μm.

[Molding process]
In the forming step, the finely pulverized powder (raw material powder) obtained in the pulverizing step is formed into a predetermined shape. Although there is no limitation in particular in a shaping | molding method, in this embodiment, finely pulverized powder (raw material powder) is filled in a metal mold | die, and it pressurizes in a magnetic field.

  The pressing at the time of molding is preferably performed at 30 MPa or more and 300 MPa or less. The applied magnetic field is preferably 950 kA / m or more and 1600 kA / m or less. The shape of the molded body obtained by molding finely pulverized powder (raw material powder) is not particularly limited. For example, the shape of the RTB-based sintered magnet is a desired shape such as a rectangular parallelepiped, a flat plate, or a column. It can be made into an arbitrary shape accordingly.

[Sintering process]
A sintering process is a process of sintering a molded object in a vacuum or inert gas atmosphere, and obtaining a sintered compact. The sintering temperature needs to be adjusted depending on various conditions such as composition, pulverization method, difference in particle size and particle size distribution, etc., but for the molded body, for example, 1000 ° C. or higher and 1200 ° C. in vacuum or in the presence of an inert gas. It sinters by performing the process heated at 1 degreeC or less for 1 to 10 hours. Thereby, a high-density sintered body (sintered magnet) is obtained.

[Aging process]
The aging treatment step is performed by heating the sintered body (sintered magnet) after the sintering step at a temperature lower than the sintering temperature. There is no particular limitation on the temperature and time of the aging treatment, but for example, it can be performed at 450 ° C. or higher and 900 ° C. or lower for 0.2 hours or longer and 3 hours or shorter. This aging treatment step may be omitted.

  Further, the aging treatment process may be performed in one stage or in two stages. When performing in two stages, for example, the first stage is 700 ° C. to 900 ° C. for 0.2 hours to 3 hours, and the second stage is 450 ° C. to 700 ° C. for 0.2 hours to 3 hours. Also good. Alternatively, the first stage and the second stage may be performed continuously, or after the first stage, the second stage may be performed by cooling to near room temperature and then reheating.

[Reverse core shell main phase particle generation process]
There is no restriction | limiting in particular in the production | generation method of the reverse core shell main phase particle | grains in this embodiment. For example, reverse core-shell main phase particles can be obtained through the following decomposition step, grain boundary diffusion step, and recrystallization step.

[Disassembly process]
The decomposition step is a step of decomposing and disproportionating main phase particles mainly composed of R ₂ T ₁₄ B crystals present in the magnet surface layer portion. The conditions of the decomposition step are not particularly limited as long as the main phase particles mainly composed of R ₂ T ₁₄ B crystals existing in the magnet surface layer portion can be decomposed.

For example, the main phase particles mainly present in the surface layer of the magnet by heating at about 600 ° C. to 900 ° C. for about 5 minutes to about 60 minutes in an inert atmosphere containing H ₂ gas, CO gas, or N ₂ gas. Occludes H ₂ , CO or N ₂ to cause decomposition and disproportionation.

By controlling the concentration of H ₂ gas, CO gas or N ₂ gas, heating temperature and / or heating time, the thickness of the region where the main phase particles are disproportionated is controlled, and finally the reverse core-shell particles obtained The layer thickness can be controlled.

  Moreover, the main phase particles existing in the magnet surface layer part can be decomposed and disproportionated also by heating at about 300 ° C. to 500 ° C. for about 20 minutes to about 60 minutes in an oxidizing atmosphere containing an oxidizing gas. it can.

[Diffusion treatment process]
In this embodiment, following the decomposition step, there is further a diffusion treatment step for diffusing heavy rare earth elements. The diffusion treatment can be carried out by applying a heat treatment after attaching a compound containing a heavy rare earth element to the surface of the sintered body subjected to the decomposition step. There is no particular limitation on the method for attaching the compound containing heavy rare earth element, and for example, the compound can be attached by applying a slurry containing heavy rare earth element. In this case, the above-mentioned C _RC / C _RS can be controlled by controlling the application amount of the slurry and the concentration of the heavy rare earth element contained in the slurry.

  However, the method for attaching the heavy rare earth element is not particularly limited. For example, there are methods using vapor deposition, sputtering, electrodeposition, spray coating, brush coating, jet dispenser, nozzle, screen printing, squeegee printing, sheet construction method and the like.

  The heavy rare earth compound is preferably particulate. The average particle diameter is preferably 100 nm or more and 50 μm or less, and more preferably 1 μm or more and 10 μm or less.

  As the solvent used for the slurry, a solvent capable of uniformly dispersing the heavy rare earth compound without dissolving it is preferable. For example, alcohol, aldehyde, ketone and the like can be mentioned, and ethanol is particularly preferable.

  There is no restriction | limiting in particular in content of the heavy rare earth compound in a slurry. For example, it may be 50% by weight or more and 90% by weight or less. The slurry may further contain components other than the heavy rare earth compound as necessary. For example, a dispersant for preventing aggregation of heavy rare earth compound particles can be used.

By performing the above diffusion treatment step on the sintered body subjected to the decomposition step, the main phase particles existing in the magnet surface layer portion are decomposed and disproportionated in addition to the grain boundaries of the entire sintered body. In the region, a liquid phase is generated as the melting point decreases, and the heavy rare earth element RH diffuses into the liquid phase. And since R ₂ T ₁₄ B crystal containing heavy rare earth element RH as R is easier to produce than R ₂ T ₁₄ B crystal not containing heavy rare earth element RH as R, the liquid phase containing diffused heavy rare earth element is partially Thus, R ₂ T ₁₄ B is crystallized and mainly becomes the core portion of the reverse core shell main phase particles finally obtained.

The conditions for the diffusion treatment step are not particularly limited, but it is preferably performed at 650 ° C. to 1000 ° C. for 1 hour to 24 hours. By setting the temperature and time within the above ranges, it becomes easy to increase the ratio of the heavy rare earth element RH taken into the liquid phase. Further, during the diffusion treatment step, each component contained in the H ₂ gas, CO gas, N ₂ gas, or oxidizing gas is released.

[Recrystallization process]
Through the recrystallization step after the diffusion treatment step, the liquid phase that has not been crystallized in the grain boundary diffusion step out of the liquid phase in which the heavy rare earth element RH is taken in is also crystallized to form R ₂ T ₁₄ B crystals. . The recrystallization step is performed, for example, by performing rapid cooling at a rate of 50 ° C./min to 500 ° C./min. By the recrystallization step, the liquid phase existing around the R ₂ T ₁₄ B crystal having a high content of the heavy rare earth element RH crystallized in the diffusion treatment step is also crystallized. Furthermore, in the recrystallization step, the heavy rare-earth element content RH begins to occur from more _R 2 _{T 14} B crystal, the content of the heavy rare-earth element RH is less _R 2 _{T 14} B crystal of the heavy rare-earth element RH It tends to be formed around R ₂ T ₁₄ B crystals having a high content. As a result, reverse core shell main phase particles are formed. There is no particular limitation on the cooling rate, but if the cooling rate is too high, it tends to be a microcrystal containing a large amount of amorphous and subphases. And the shell portion 11b tend to be unclear.

As mentioned above, as a manufacturing method of the RTB system sintered magnet concerning this embodiment, at least a decomposition process which decomposes and disproportionates main phase particles of a magnet surface layer part, generates a liquid phase, and makes the liquid phase It is important that the grain boundary diffusion step for diffusing heavy rare earth elements and the recrystallization step for crystallizing the liquid phase around the partially crystallized R ₂ T ₁₄ B crystal are performed in this order. Thereby, a reverse core shell main phase particle can be generated in the magnet surface layer part of a RTB system sintered magnet, and a reverse core shell particle layer can be formed. The methods and conditions of the above decomposition step, grain boundary diffusion step, and recrystallization step are merely examples. The decomposition step may be a step for decomposing and disproportionating the main phase particles in the magnet surface layer portion. The grain boundary diffusion step only needs to generate a liquid phase and diffuse heavy rare earth elements into the liquid phase. The recrystallization step only needs to generate reverse core shell main phase particles by recrystallization and form a reverse core shell particle layer.

  For the main phase particles not decomposed and disproportionated in the decomposition step, a shell portion is formed by the heavy rare earth element RH diffused at the grain boundary in the grain boundary diffusion step, and becomes a normal core-shell main phase particle. Form.

[Reaging process]
The reaging treatment step is performed by heating the sintered magnet after the recrystallization step at a temperature lower than the maximum temperature of the diffusion treatment step. There is no particular limitation on the temperature and time of the re-aging treatment, but for example, the re-aging treatment can be performed at 450 ° C. to 800 ° C. for 0.2 hours to 3 hours.

  The RTB-based sintered magnet obtained by the above steps may be subjected to surface treatment such as plating, resin coating, oxidation treatment, or chemical conversion treatment. Thereby, corrosion resistance can further be improved.

  Furthermore, a magnet obtained by cutting and dividing the RTB-based sintered magnet according to this embodiment can be used.

  Specifically, the RTB-based sintered magnet according to the present embodiment is suitably used for applications such as a motor, a compressor, a magnetic sensor, and a speaker.

  In addition, the RTB-based sintered magnet according to this embodiment may be used alone, or two or more RTB-based sintered magnets may be combined and used as necessary. . There is no particular limitation on the bonding method. For example, there are a mechanical bonding method and a resin mold bonding method.

  By combining two or more RTB-based sintered magnets, a large RTB-based sintered magnet can be easily manufactured. A magnet in which two or more RTB-based sintered magnets are combined is preferable for applications requiring particularly large RTB-based sintered magnets, such as IPM motors, wind power generators, large motors, and the like. Used.

  Note that the present invention is not limited to the embodiment in which the core-shell particle layer 1b and the reverse core-shell particle layer 1a are arranged in this order from the magnet central portion toward the magnet surface layer portion as in the above-described embodiment. Various modifications can be made within the range.

  For example, as shown in FIG. 1B, an R-T-B system in which a non-core-shell particle layer 1c composed only of non-core-shell main phase particles having no core-shell structure is present in the magnet central portion in addition to the core-shell particle layer 1b. Embodiments of the sintered magnet 10 are conceivable. And you may arrange in order of the non-core-shell particle layer 1c, the core-shell particle layer 1b, and the reverse core-shell particle layer 1a toward the magnet surface layer part from the magnet center part. Moreover, you may consist only of the reverse core-shell particle layer 1a, the core-shell particle layer 1b, and the non-core-shell particle layer 1c. In addition, it can confirm that main phase particle | grains do not have a core-shell structure when a core-shell structure is not observed, when observing by 1000-times or more magnification of 1000 times or less using SEM.

  When the non-core shell particle layer 1c is present (FIG. 1B), the residual magnetic flux density Br tends to be higher than when the non-core shell particle layer 1c is not present (FIG. 1A).

  There is no particular limitation on the method for allowing the non-core shell particle layer 1c to exist. For example, there are a method of adjusting the amount of heavy rare earth element deposited in the grain boundary diffusion step, and a method of shortening the diffusion treatment time in the grain boundary diffusion step.

  Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

(Sintered magnet manufacturing process)
Nd, electrolytic iron, and a low carbon ferroboron alloy were prepared as raw materials. Further, Al, Cu, Co, and Zr were prepared in the form of a pure metal or an alloy with Fe.

  An alloy for a sintered body (raw material alloy) was prepared by strip casting for the raw material metal so that the composition of the sintered magnet became a composition shown in alloy A of Table 1 described later. The content (% by weight) of each element shown in Table 1 is a value when the total content of Nd, B, Al, Cu, Co, Zr and Fe is 100% by weight. Moreover, the alloy thickness of the raw material alloy was set to 0.2 mm or more and 0.6 mm or less.

  Next, hydrogen was occluded by flowing hydrogen gas to the raw material alloy at room temperature for 1 hour. Next, the atmosphere was switched to Ar gas, dehydrogenation treatment was performed at 450 ° C. for 1 hour, and the raw material alloy was pulverized with hydrogen. Further, after cooling, a sieve having a particle size of 400 μm or less was obtained using a sieve.

  Next, 0.1% oleic amide by weight was added as a grinding aid to the raw material alloy powder after hydrogen grinding and mixed.

  Subsequently, it was pulverized in a nitrogen stream using a collision plate type jet mill device to obtain fine powder (raw material powder) having an average particle diameter of about 4 μm. The average particle diameter is an average particle diameter D50 measured with a laser diffraction particle size distribution meter.

  For elements not described in Table 1, H, Si, Ca, La, Ce, Cr, and the like may be detected. Si is mainly mixed from the ferroboron raw material and the crucible during melting of the alloy. Ca, La, and Ce are mixed from rare earth materials. Moreover, Cr may be mixed from electrolytic iron.

The obtained fine powder was molded in a magnetic field to produce a molded body. The applied magnetic field at this time is a static magnetic field of 1200 kA / m. The pressing force during molding was 120 MPa. The magnetic field application direction and the pressurizing direction were orthogonal to each other. When the density of the molded body at this time was measured, the density of all the molded bodies was in the range of 4.10 Mg / m ³ or more and 4.25 Mg / m ³ or less.

Next, the compact was sintered to obtain a sintered magnet. The sintering conditions were held at 1060 ° C. for 4 hours. The sintering atmosphere was in a vacuum. At this time, the sintered density was in the range of 7.50 Mg / m ³ or more and 7.55 Mg / m ³ or less. Thereafter, a first aging treatment was performed for 1 hour at a first tempering temperature T1 = 900 ° C. in an Ar atmosphere and atmospheric pressure, and further a second aging treatment was performed for 1 hour at a second aging temperature T2 = 500 ° C. .

  The composition of the obtained sintered magnet was evaluated by fluorescent X-ray analysis. The content of B was evaluated by ICP. It was confirmed that the composition of the sintered magnet in each sample was as shown in Table 2. And the process of each Examples 1-22 and Comparative Examples 1-6 shown below was performed with respect to the obtained sintered magnet.

Example 1
After processing the sintered magnet obtained by the above process into a rectangular parallelepiped having a width of 20 mm, a length of 20 mm, and a thickness of 5 mm in the orientation direction, in an atmosphere gas in which hydrogen is 5 vol% and Ar is 95 vol% And maintained at 750 ° C. for 10 minutes to decompose and disproportionate main phase particles mainly present in the surface layer of the magnet.

Next, a slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet so that the weight of Tb is 0.5% by weight with respect to the weight of the sintered magnet. To attach Tb. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse Tb at the grain boundaries.

After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recrystallize R ₂ T ₁₄ B crystals from the liquid phase.

  Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure.

  The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Example 2)
The sintered magnet obtained by the above process is held at 700 ° C. for 10 minutes in an atmospheric gas containing 8% by volume of CO and 92% by volume of Ar, and main phase particles mainly present in the magnet surface layer are not decomposed. Leveled.

Next, a slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet so that the weight ratio of Tb to the weight of the sintered magnet is 0.5% by weight. Tb was made to adhere by application. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse Tb at the grain boundaries.

After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recrystallize R ₂ T ₁₄ B crystals from the liquid phase.

  Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure.

  The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Example 3)
The sintered magnet obtained by the above process is held at 650 ° C. for 30 minutes in an atmospheric gas containing 8% by volume of N _{2 and} 92% by volume of Ar, and main phase particles mainly present in the magnet surface layer part are decomposed. Disproportionated.

Next, a slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet so that the weight ratio of Tb to the weight of the sintered magnet is 0.5% by weight. Tb was made to adhere by application. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse Tb at the grain boundaries.

After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recrystallize R ₂ T ₁₄ B crystals from the liquid phase.

  Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure.

  The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

Example 4
The sintered magnet obtained by the above process is held at 400 ° C. for 30 minutes in an oxidizing atmosphere containing a gas adjusted to a water vapor partial pressure of 200 hPa, and the main phase particles mainly present in the magnet surface layer portion are decomposed unevenly. Turned into.

Next, a slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet so that the weight ratio of Tb to the weight of the sintered magnet is 0.5% by weight. Tb was made to adhere by application. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse Tb at the grain boundaries.

After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recrystallize R ₂ T ₁₄ B crystals from the liquid phase.

  Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure.

  The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Example 5)
TbH ₂ particles (average particle diameter D50 = 5 μm), TbH ₂ particles (average particle diameter D50 = 5 μm) and NdH ₂ particles (average particle diameter D50 = 5 μm) were converted to Tb: Nd = 80: 20 (atomic ratio). This was carried out in the same manner as in Example 1 except that the particles were mixed so as to be. Tb and Nd were attached so that the weight of Tb was 0.5% by weight with respect to the weight of the sintered magnet.

(Example 6)
TbH ₂ particles (average particle diameter D50 = 5 μm), TbH ₂ particles (average particle diameter D50 = 5 μm) and NdH ₂ particles (average particle diameter D50 = 5 μm) were converted to Tb: Nd = 70: 30 (atomic ratio). This was carried out in the same manner as in Example 1 except that the particles were mixed so as to be. Tb and Nd were attached so that the weight of Tb was 0.5% by weight with respect to the weight of the sintered magnet.

(Example 7)
The same operation as in Example 1 was performed except that the holding time in an atmosphere gas containing 5% by volume of hydrogen and 95% by volume of Ar was set to 20 minutes.

(Example 8)
The same operation as in Example 1 was performed except that the holding time in an atmosphere gas containing 5% by volume of hydrogen and 95% by volume of Ar was set to 30 minutes.

Example 9
The same procedure as in Example 1 was performed except that the cooling rate after the heat treatment was 50 ° C./min.

(Example 10)
The same procedure as in Example 1 was performed except that the cooling rate after the heat treatment was 500 ° C./min.

(Example 11)
TbH ₂ particles (average particle size D50 = 5 μm), TbH ₂ particles (average particle size D50 = 5 μm) and NdH ₂ particles (average particle size D50 = 5 μm) were converted to Tb: Nd = 30: 70 (atomic ratio). This was carried out in the same manner as in Example 1 except that the particles were mixed so as to be. Tb and Nd were attached so that the weight of Tb was 0.5% by weight with respect to the weight of the sintered magnet.

(Example 12)
TbH ₂ particles (average particle size D50 = 5 μm), TbH ₂ particles (average particle size D50 = 5 μm) and NdH ₂ particles (average particle size D50 = 5 μm) were converted to Tb: Nd = 50: 50 (atomic ratio). This was carried out in the same manner as in Example 1 except that the particles were mixed so as to be. Tb and Nd were attached so that the weight of Tb was 0.5% by weight with respect to the weight of the sintered magnet.

(Example 13)
The same operation as in Example 2 was performed except that the holding temperature in an atmospheric gas containing 8% by volume of CO and 92% by volume of Ar was set to 600 ° C.

(Example 14)
After applying the slurry, it was carried out in the same manner as in Example 1 except that the heat treatment at 950 ° C. for 10 hours was performed only once while flowing Ar at atmospheric pressure to diffuse Tb at the grain boundaries.

(Example 15)
The same procedure as in Example 1 was performed except that TbH ₂ particles (average particle size D50 = 5 μm) were replaced with TbF ₃ particles (average particle size D50 = 5 μm). In addition, Tb was made to adhere so that the weight of Tb with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 16)
The same operation as in Example 1 was performed except that TbH ₂ particles (average particle diameter D50 = 5 μm) were replaced with Tb ₂ O ₃ particles (average particle diameter D50 = 5 μm). In addition, Tb was made to adhere so that the weight of Tb with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 17)
Except for replacing TbH ₂ particles (average particle diameter D50 = 5 μm) with a Tb—Fe compound [Tb: Fe = 80: 20 (atomic ratio)] (average particle diameter D50 = 5 μm), the same as in Example 1. Carried out. In addition, Tb was made to adhere so that the weight of Tb with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 18)
TbH ₂ particles (average particle diameter D50 = 5 [mu] m), except substituting the DyH ₂ particles (average particle diameter D50 = 5 [mu] m) were carried out in the same manner as in Example 1. In addition, Dy was made to adhere so that the weight of Dy with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 19)
The same procedure as in Example 1 was performed except that TbH ₂ particles (average particle diameter D50 = 5 μm) were replaced with DyF ₃ particles (average particle diameter D50 = 5 μm). In addition, Dy was made to adhere so that the weight of Dy with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 20)
Except that TbH ₂ particles (average particle diameter D50 = 5 μm) are replaced with Dy—Fe compound [Dy: Fe = 80: 20 (atomic ratio)] (average particle diameter D50 = 5 μm), the same as in Example 1. Carried out. In addition, Dy was made to adhere so that the weight of Dy with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 21)
Example 21 was carried out in the same manner as Example 1 except that the composition of the sintered magnet before grain boundary diffusion was the composition shown in Table 1. Specifically, a raw material alloy G was produced. Then, pulverization, molding, sintering and aging treatment were performed in the same manner as in Example 1 to obtain sintered magnets having the compositions shown in Table 2. Thereafter, in the same manner as in Example 1, the main phase particles present in the magnet surface layer portion were decomposed and disproportionated, and Tb diffusion treatment was performed. Thereafter, recrystallization and reaging treatment were performed in the same manner as in Example 1. The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Example 22)
Example 22 was carried out in the same manner as Example 1 except that the composition of the sintered magnet before grain boundary diffusion was the composition shown in Table 1. Specifically, a raw material alloy H was produced. Then, pulverization, molding, sintering and aging treatment were performed in the same manner as in Example 1 to obtain sintered magnets having the compositions shown in Table 2. Thereafter, in the same manner as in Example 1, the main phase particles present in the magnet surface layer portion were decomposed and disproportionated, and Tb diffusion treatment was performed. Thereafter, recrystallization and reaging treatment were performed in the same manner as in Example 1. The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Comparative Example 1)
A slurry in which TbH ₂ particles (average particle size D50 = 5 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet obtained by the above-described sintered magnet manufacturing step, and the weight of Tb relative to the weight of the sintered magnet is 0.00. Tb was made to adhere by applying to 5 wt%. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse Tb at the grain boundaries. And it cooled rapidly with the cooling rate of 200 degrees C / min after the said heat processing.

  Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure.

  The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Comparative Example 2)
In Comparative Example 2, sintered body alloys (raw material alloys) B and C were prepared so as to have the compositions shown in Table 1 in the sintered magnet manufacturing process. The raw material alloy B and the raw material alloy C shown in Table 1 were pulverized with hydrogen and then mixed so that the weight ratio was 9: 1. Thereafter, pulverization, molding, sintering and aging treatment were performed in the same manner as in Example 1 to obtain sintered magnets having the compositions shown in Table 2. In addition, it confirmed that the composition of the said sintered magnet became the same as the composition of the sintered magnet of Examples 1-4, 7-10 and the comparative example 1 after the said diffusion process.

  The sintered magnet after the aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Comparative Example 3)
In Comparative Example 3, sintered body alloys (raw material alloys) D and E were prepared by a strip casting method so as to have a composition shown in Table 2 to be described later. The raw material alloy D and the raw material alloy E shown in Table 2 were pulverized with hydrogen and then mixed so that the weight ratio was 9: 1. Thereafter, pulverization, molding, sintering and aging treatment were performed in the same manner as in Example 1 to obtain sintered magnets having the compositions shown in Table 2.

  The sintered magnet after the aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Comparative Example 4)
In Comparative Example 4, a sintered body alloy (raw material alloy) was produced in the same manner as in Example 1 except that the composition of the finally obtained sintered magnet was the composition shown in Table 1. Specifically, the raw material alloy F was produced. Then, pulverization, molding, sintering and aging treatment were performed in the same manner as in Example 1 to obtain sintered magnets having the compositions shown in Table 2.

  The sintered magnet after the aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

(Comparative Example 5)
The same procedure as in Example 1 was performed except that the cooling rate in the recrystallization step after the diffusion treatment was 10 ° C./min.

(Comparative Example 6)
In Comparative Example 6, DyH ₂ particles (average particle diameter D50 = 5 μm) were dispersed in ethanol over the entire surface of the sintered magnet obtained so that the composition of the sintered magnet before grain boundary diffusion was the composition shown in Table 1. The slurry was applied so that the weight of Dy with respect to the weight of the sintered magnet was 1.0% by weight, thereby attaching Dy. After applying the slurry, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and then heat treatment was performed at 950 ° C. for 5 hours to diffuse grain boundaries. And it cooled rapidly with the cooling rate of 200 degrees C / min after the said heat processing. Thereafter, re-aging treatment was performed at 500 ° C. for 1 hour in an Ar atmosphere and atmospheric pressure. The sintered magnet after the re-aging treatment was evaluated for magnetic properties (residual magnetic flux density Br, coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer.

  Table 3 shows each of whether the decomposition process for decomposing the main phase particles present in the surface layer portion of the sintered magnet, the grain boundary diffusion process, and the rapid cooling after the grain boundary diffusion were performed. A mark was given when each process was performed, and a mark was marked when each process was not performed.

  Table 3 shows the results of evaluation of the magnetic properties (residual magnetic flux density Br, coercive force Hcj, and squareness ratio Hk / Hcj) for the RTB-based sintered magnets of the examples and comparative examples using a BH tracer. . The residual magnetic flux density Br was 1380 mT or more, and 1400 mT or more. The coercive force Hcj was 1800 kA / m or higher when Tb was diffused at grain boundaries, and 1830 kA / m or higher was further improved. When Dy was diffused at grain boundaries, 1600 kA / m or more was considered good, and 1620 kA / m or more was even better. The squareness ratio Hk / Hcj was determined to be good when it exceeded 0.90, and better when it was 0.95 or more.

  Moreover, the R-T-B system sintered magnets of the examples and comparative examples were cut in arbitrary cross sections, and the cross sections were observed. The abundance ratio of the reverse core shell main phase particles in the 20 μm portion from the magnet surface toward the inside of the magnet in the magnet surface layer was measured. The measurement of the existence ratio of the reverse core shell main phase particles in the magnet surface layer portion is performed on 10 main phase particles randomly selected from the main phase particles in the portion of 20 μm from the magnet surface toward the inside of the magnet. SEM and TEM-EDS were used. Moreover, the abundance ratio of the reverse core shell main phase particles in the magnet central part was measured. The abundance ratio of the reverse core shell main phase particles in the magnet central portion was measured using SEM and TEM-EDS for 10 main phase particles randomly selected from the main phase particles in the magnet central portion. The results are shown in Table 4.

Further, the reverse shell main phase particles present in the magnet surface part in each example was measured total RH concentration C _RS in the concentration C _RC and the shell of the entire RH in the core portion. And the ratio of the particle | grains which are _CRC / _CRS > 1.5 in each reverse core shell main phase particle | grain, and the ratio of the particle | grains which are _CRC / _CRS > 3.0 were computed using TEM-EDS. The results are shown in Table 4.

  In the reverse core-shell main phase particles 11 in this example, the measurement locations of the total RH concentration in the core portion 11a and the total RH concentration in the shell portion 11b are as follows.

First, the reverse core-shell main phase particles 11 whose concentration is to be measured are observed with a transmission electron microscope (TEM), and the diameter having the maximum length is specified. Next, two intersections between the diameter and the grain boundary are specified. Then, by measuring the total RH concentration in the region of 20 nm × 20 nm centered on the midpoint of the two points of intersection, the total RH concentration _{C RC} in the core portion.

Next, one intersection is selected from the two intersections. Then, the total RH concentration in a region of 20 nm × 20 nm centering on the point entering the reverse core shell main phase particle side is measured along the diameter having the maximum length from the intersection, and the total RH in the shell portion is measured. Concentration _CRS .

  Furthermore, the abundance ratio of the core-shell main phase particles in the magnet surface layer was measured. The existence ratio of the core-shell main phase particles in the magnet surface layer portion is determined by SEM and TEM-EDS for 10 particles randomly selected from the main phase particles in the portion of 20 μm from the magnet surface toward the inside of the magnet. It measured using. Moreover, the abundance ratio of the core-shell particles in the central part of the magnet was measured. The existence ratio of the core-shell main phase particles in the central part of the magnet was measured using SEM and TEM-EDS for 10 particles randomly selected from the main phase particles in the central part of the magnet. The results are shown in Table 4.

  Furthermore, about each Example, the thickness of the reverse core-shell particle layer, the thickness of the core-shell particle layer, and the thickness of the non-core-shell particle layer was measured using SEM. The results are shown in Table 4. In addition, the thickness of each layer is the thickness per layer. When there were two or more layers, the average was calculated and the average value was taken as the thickness of each layer.

  Hereinafter, the method for measuring the thickness of each layer will be described more specifically. The RTB-based sintered magnets of each example and comparative example were cut in a cross section parallel to the orientation direction, the cross section was mirror-polished, and then observed with an electron microscope (SEM) at 1000 times. SEM observation was continuously performed from the magnet surface to the opposite magnet surface along the orientation direction. In the observed field of view, the region from when the reverse core-shell particles began to be observed until they were not observed was defined as the reverse core-shell particle layer mainly composed of the reverse core-shell main phase particles. And the thickness of the reverse core shell particle layer was estimated from the SEM image. Further, the region from the time when the reverse core-shell particles were not observed to the time when the core-shell particles were not observed in the observed visual field was defined as the core-shell particle layer mainly composed of the core-shell main phase particles. And the thickness of the core-shell particle phase was estimated. Further, a region where the reverse core-shell particles and the core-shell particles are not observed in the observed field of view is defined as a non-core-shell particle layer composed of non-core-shell main phase particles. And the thickness of the non-core shell particle layer was estimated.

  From Tables 1 to 4, the step of decomposing and disproportionating the main phase particles of the magnet surface layer after sintering, the step of generating a liquid phase by grain boundary diffusion and incorporating RH into the liquid phase, and the RH by rapid cooling In the RTB-based sintered magnets of Examples 1 to 22 that had undergone the step of recrystallizing the incorporated liquid phase, the reverse core-shell main phase particles were generated in the magnet surface layer portion to form the reverse core-shell particle layer. The residual magnetic flux density, coercive force, and squareness ratio were favorable results.

Further, among the examples in which Tb was grain boundary diffused, the thickness of the reverse core shell particle layer was 10 μm or more and 60 μm or less, and there were reverse core shell particles having C _RC / C _RS > 1.5, 9 to 10, 12 to 17, and 21 to 22 had more preferable residual magnetic flux density.

  In contrast, the step of decomposing and disproportionating the main phase particles in the magnet surface layer after sintering, the step of generating a liquid phase by grain boundary diffusion and incorporating RH into the liquid phase, and the step of quenching RH were incorporated. In the comparative example in which the liquid phase was not recrystallized, the reverse core shell main phase particles were not generated. As a result, the residual magnetic flux density, coercive force and / or squareness ratio were inferior to those of Examples 1 to 22.

  In Comparative Examples 1 and 6, since the step of decomposing and disproportionating the main phase particles in the magnet surface layer portion after sintering was not performed, the reverse core shell main phase particles were not generated even after undergoing grain boundary diffusion and rapid cooling. In Comparative Example 2, a sintered magnet was produced by the two-alloy method, but no reverse core shell main phase particles were produced. As a result, the residual magnetic flux density and the coercive force were inferior to those of Examples 1-17 and 21-22. In Comparative Examples 3 and 4, as a result of increasing the Tb content, the coercive force was good, but the residual magnetic flux density was inferior to those of Examples 1-17 and 21-22. Moreover, since the Tb content was increased, the sintered magnets of Comparative Examples 3 and 4 were also more expensive to manufacture than the sintered magnets of Examples 1 to 17 and 21 to 22. In Comparative Example 5, since the cooling rate in the recrystallization step after the diffusion treatment was too low, uniform main phase particles were formed, and reverse core shell main phase particles were not generated.

DESCRIPTION OF SYMBOLS 1,10 ... R-T-B system sintered magnet 1a ... Reverse core shell particle layer 1b ... Core shell particle layer 1c ... Non-core shell particle layer 11 ... Reverse core shell main phase particle 11a ... Core part (reverse core shell main phase particle)
11b ... Shell part (reverse core shell main phase particles)
12 ... Grain boundary 13 ... Core-shell main phase particles 13a ... Core part (core-shell main phase particles)
13b ... Shell part (core-shell main phase particles)

Claims (6)

An RTB-based sintered magnet including main phase particles made of R ₂ T ₁₄ B crystal,
R is one or more rare earth elements essential for the heavy rare earth element RH, T is one or more transition metal elements essential for Fe or Fe and Co, and B is boron,
Some of the main phase particles are reverse core shell main phase particles,
The reverse core shell main phase particles have a core portion and a shell portion,
The total RH concentration (at%) in the core part is defined as C _RC ,
All RH concentration at the shell portion (at%) in the case of the _{C RS,}
C _RC / C _RS > 1.0,
The RTB-based sintered magnet is characterized in that the abundance ratio of the reverse core shell main phase particles is larger in the magnet surface layer than in the magnet center. The R-T-B system sintered magnet according to claim 1, wherein C _RC / C _RS > 1.5. Some of the main phase particles are core-shell main phase particles,
The core-shell main phase particles have a core part and a shell part,
The total RH concentration (at%) in the core part is represented by _CNC ,
When the total RH concentration (at%) in the shell portion is C _NS ,
C _NC / C _NS <1.0, The _RTB -based sintered magnet according to claim 1 or 2 characterized by the above-mentioned.   The RTB-based sintered magnet according to claim 3, comprising a core-shell particle layer mainly composed of the core-shell main phase particles and a reverse core-shell particle layer mainly composed of the reverse core-shell main phase particles.   The RTB-based sintered magnet according to claim 4, wherein the core-shell particle layer and the reverse core-shell particle layer are arranged in this order from the magnet central portion toward the magnet surface layer portion. A part of the main phase particles is a non-core shell main phase particle having no core-shell structure, and is an RTB-based sintered magnet including a non-core shell particle layer mainly composed of the non-core shell main phase particles. And
The RTB-based sintered magnet according to claim 4, wherein the non-core-shell particle layer, the core-shell particle layer, and the reverse core-shell particle layer are arranged in this order from the magnet center to the magnet surface layer.

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