JP2018174314A - 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 11 and grain boundaries 12, where R represents one or more kinds of rare earth elements, 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 R-T-B based sintered magnet 1 has a magnet surface layer portion 1a, and a magnet center portion 1b located on an inner side of the magnet surface layer portion. A crystal orientation degree of the primary-phase grains 11 in the magnet surface layer portion 1a having a magnetic pole face is lower than a crystal orientation degree of the primary-phase grains 11 in the magnet center portion 1b.SELECTED DRAWING: Figure 1

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, T is one or more transition metal elements essential for Fe or Fe and Co, B is boron,
The RTB-based sintered magnet has a magnet surface layer part and a magnet center part located inside the magnet surface layer part,
The crystal orientation degree of the main phase particles in the magnet surface layer portion having the magnetic pole surface is lower than the crystal orientation degree of the main phase particles in the magnet central portion.

  Since the RTB-based sintered magnet according to the present invention has the above-described characteristics, it is possible to obtain an RTB-based sintered magnet with improved magnetic characteristics and low cost.

In the RTB-based sintered magnet according to the present invention, the R is one or more rare earth elements that essentially require the heavy rare earth element RH,
A part of the main phase particles contained in the magnet surface layer part 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 may be sufficient.

The RTB-based sintered magnet according to the present invention includes a low RH crystal phase in the core portion,
The low RH crystal phase may be composed of the R ₂ T ₁₄ B crystal, and the RH concentration may be relatively low with respect to the RH concentration in the entire main phase particle.

  The RTB-based sintered magnet according to the present invention may further include a nonmagnetic R-rich phase in the core portion.

It is the schematic of the cross section perpendicular | vertical to the magnetic pole surface in the magnet surface layer part vicinity with the magnetic pole surface of the RTB type sintered magnet which concerns on one Embodiment of this invention. 1 is a schematic view of non-uniform reverse core shell main phase particles according to an embodiment of the present invention. FIG.

  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, T is one or more transition metal elements essential for Fe or Fe and Co, and B is boron. R preferably contains a heavy rare earth element RH. 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 It becomes easy to suppress the precipitation of Fe and the like, and to suppress the deterioration of magnetic properties. If 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. is there.

  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 mass% or less, the squareness ratio (Hk / Hcj) tends 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 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. 1, the RTB-based sintered magnet 1 according to the present embodiment has a crystal orientation direction of the main phase particles 11 (low crystal orientation main phase particles 11 a) in the magnet surface layer portion 1 a (FIG. 1). Unlike the main phase particles 11 (highly crystallized main phase particles 11b) in the magnet central portion 1b, the direction of the arrow is not fixed. That is, in the RTB-based sintered magnet 1 according to this embodiment, the crystal orientation degree of the main phase particles 11 in the magnet surface layer portion 1a is lower than the crystal orientation degree of the main phase particles 11 in the magnet center portion 1b.

  Here, it is considered that the lower the degree of crystal orientation, the higher the coercive force and the lower the magnetization. The cause is considered as follows.

First, the magnetization direction of the R-T-B system sintered magnet is set to 0 °, and the angle in the c-axis direction of the main phase particles 11 made of R ₂ T ₁₄ B crystal with respect to this is set to θ (°). The saturation magnetization of the main phase particle 11 is Js. When the external magnetic field is applied from the direction of 0 °, the saturation magnetization component of the main phase particle 11 in the magnetic field direction is Js × cos θ. Here, it is considered that θ decreases and Js × cos θ decreases as the degree of crystal orientation decreases. Therefore, even if the main phase particle 11 is reversed in magnetization, the influence on the magnetization reversal of the main phase particle 11 adjacent to the main phase particle 11 is reduced. That is, it is considered that the coercive force is increased and the magnetization (residual magnetic flux density) is decreased by decreasing the degree of crystal orientation.

  Here, the present inventors have found that the coercive force of the entire RTB-based sintered magnet is greatly influenced by the coercive force of the portion close to the magnet surface of the RTB-based sintered magnet. It was. On the other hand, the present inventors have found that the magnetization (residual magnetic flux density) of the entire RTB-based sintered magnet is not greatly influenced only by the magnetization (residual magnetic flux density) near the magnet surface. Furthermore, the coercive force of the entire RTB-based sintered magnet is close to the magnet surface (magnetic pole surface) perpendicular to the easy magnetization axis among the surfaces present in the RTB-based sintered magnet. The present inventors have found that it is greatly influenced by the coercive force of the portion. The magnetic pole surface refers to the surface of the magnet through which main lines of magnetic force generated by the magnet pass.

  In the RTB-based sintered magnet 1 according to the present embodiment, the coercive force in the magnet surface layer portion 1a is increased by reducing the degree of crystal orientation of the main phase particles 11 in the magnet surface layer portion 1a having the magnetic pole face. . In the RTB-based sintered magnet 1 according to the present embodiment, the main phase particles 11 (low crystal orientation main phase particles 11a) in the magnet surface layer portion 1a have a crystal orientation degree in the magnet center portion 1b. 11 (highly crystallized main phase particles 11b) is lower than the degree of crystal orientation, so that high magnetic properties can be obtained. 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. Note that a plane perpendicular to the direction in which a magnetic field is applied during molding may be referred to as a C plane in this technical field. Further, in the RTB-based sintered magnet 1 according to the present embodiment, the C surface and the magnetic pole surface coincide with each other, but the C surface and the magnetic pole surface may not necessarily coincide with each other.

In the RTB-based sintered magnet 1 according to the present embodiment, a part of the main phase particles 11 included in the magnet surface layer portion 1a may be reverse core shell main phase particles. The inverted core-shell main phase particles have a core portion and a shell portion. The shell portion covers the core portion. Core and the shell is composed of the R _{2 T} 14 _B crystal, but different composition from each other. Specifically, the RH concentration differs between the core portion and the shell portion. Whether or not each main phase particle 11 is a particle having a core-shell structure can be confirmed by observing at a magnification of 1000 to 10,000 using a SEM.

  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. Whether the main phase particles are core-shell main phase particles or reverse core-shell main phase particles can be determined from the composition contrast generated in the reflected electron image. 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 a core-shell main phase particle or a reverse core-shell main phase particle according to the position of the bright part inside the main phase particle.

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

  That is, the reverse core-shell main phase particles are main phase particles having a higher total RH concentration in the core portion than a total RH concentration in the shell portion, contrary to the generally known core-shell main phase particles.

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 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.

  Further, the total RH concentration relative to the total R concentration in the core portion of the reverse core-shell main phase particles is not particularly limited, but is generally about 30% to 80% in atomic ratio. There is no particular limitation on the total RH concentration relative to the total R concentration in the shell portion of the reverse core-shell main phase particles, but the atomic ratio is generally about 10% to 30%.

  In addition, although the shell part covers the entire surface of the core part of the reverse core shell main phase particles, the shell part does not need to cover the entire surface of the core part, and may cover 60% or more of the surface of the core part. . The core part and the shell part can be distinguished by SEM.

  The RTB-based sintered magnet 1 according to the present embodiment includes a reverse core shell main phase particle, so that a permanent magnet having a high residual magnetic flux density and a coercive force even when the amount of heavy rare earth element RH is reduced. It becomes. The mechanism by which the above effect is obtained by including the inverted core-shell main phase particles is considered to be the mechanism shown below.

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

  In the RTB-based sintered magnet 1 according to this embodiment, the abundance ratio of the reverse core shell main phase particles with respect to all main phase particles is preferably higher in the magnet surface layer portion 1a than in the magnet center portion 1b. .

  The inverted core-shell main phase particles contain more heavy rare earth element RH in the core portion. Therefore, the reverse core shell main phase particles themselves have low residual magnetic flux density and saturation magnetization. Since the reverse core-shell main phase particles have a low saturation magnetization, even if a certain reverse core-shell main phase particle has a magnetization reversal, the influence on the magnetization reversal of the main phase particles adjacent to the reverse core-shell main phase particle is small. That is, since the reverse core shell main phase particles are mainly present in the magnet surface layer portion 1a of the RTB-based sintered magnet 1, transmission of reverse magnetic domains generated from the magnet surface is suppressed. Therefore, the coercive force of the RTB-based sintered magnet 1 is further improved due to the presence of the reverse core shell main phase particles in the magnet surface layer portion 1a.

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

  As shown in FIG. 2, the RTB-based sintered magnet according to the present embodiment includes a core portion 110 a and a shell portion 110 b and includes a non-homogeneous reverse core shell including a low RH crystal phase 210 therein. Main phase particles 110 may be included. As shown in FIG. 2, a plurality of low RH crystal phases 210 may exist in one non-uniform reversed core shell main phase particle 110. The size of one low RH crystal phase 210 is not particularly limited, but is preferably 5% or more and 30% or less in terms of a cross-sectional area with respect to the non-uniform reversed core-shell main phase particles 110.

  The inclusion of the low RH crystal phase 210 inside the main phase particles can be confirmed using SEM and TEM.

The low RH crystal phase 210 is an R ₂ T ₁₄ B crystal phase in which the concentration of the heavy rare earth element RH is lower than the main phase existing around the low RH crystal phase 210. More specifically, the total RH concentration (at%) / total RL concentration (at%) in the low RH crystal phase 210 is L1, and the total RH concentration (at%) in the main phase existing around the low RH crystal phase / When the total RL concentration (at%) is N1, it is an R ₂ T ₁₄ B crystal phase in which N1−L1 ≧ 0.5.

The presence of the low RH crystal phase 210 can be confirmed by SEM, SEM-EDS, TEM, and TEM-EDS. Specifically, it can be visually confirmed by SEM that some foreign phase is present in the main phase particles, and it can be confirmed by TEM that the foreign phase is an R ₂ T ₁₄ B crystal phase. L1 can be specified by TEM-EDS.

  Furthermore, in the RTB-based sintered magnet 1 according to the present embodiment, the content ratio of the non-uniform inverted core-shell main phase particles 110 in the main phase particles 11 is higher in the magnet surface layer portion 1a than in the magnet center portion 1b. It is preferable that there are more.

Specifically, r _{s (%)} of the existence ratio of the main phase grains containing low RH crystalline phase 210 in the magnet surface layer portion 1a, the existence ratio of main-phase particles comprising the low RH crystalline phase in the magnet central portion 1b r _{When c} (%), r _s −r _c ≧ 20% is preferable.

  The RTB-based sintered magnet according to the present embodiment has a large number of non-uniform reverse core shell main phase particles 110, particularly in the magnet surface layer portion 1a, thereby improving the residual magnetic flux density and the coercive force.

It is considered that the non-uniform reverse core-shell main phase particle 110 has the low RH crystal phase 210, and thus the anisotropic magnetic field changes abruptly in the non-uniform reverse core-shell main phase particle 110. The pinning force increases due to this sudden change in the anisotropic magnetic field. As a result, it is considered that the coercive force is improved. Further, the presence of a large number of such non-uniform reversed core shell main phase particles 110 in the magnet surface layer portion 1a suppresses transmission of reversed magnetic domains generated from the magnet surface. Therefore, the coercive force of the RTB-based sintered magnet 1 can be improved with a small amount of heavy rare earth element RH used. Furthermore, since the amount of heavy rare earth element RH used can be reduced, the residual magnetic flux density can be improved. Further, the presence of the plurality of low RH crystal phases 210 in one non-uniform reverse core shell main phase particle 110 makes it possible to suppress the domain wall movement from any direction. Furthermore, since the low RH crystal phase 210 is an R ₂ T ₁₄ B-based crystal phase like the surrounding main phase, crystal matching can be achieved. For this reason, generation | occurrence | production of distortion is suppressed and the coercive force improvement effect becomes large.

  Preferably, the low RH crystal phase 210 is substantially free of heavy rare earth element RH. “Substantially does not contain” means that the atomic ratio of RH / R in the low RH crystal phase 210 is 0.03 or less.

  When the low RH crystal phase 210 does not substantially contain heavy rare earth RH, the effect of including the low RH crystal phase 210 is further increased.

  In addition, as shown in FIG. 2, the non-uniform inverted core-shell main phase particles 110 preferably further include a nonmagnetic R-rich phase 230 therein. In addition, a plurality of nonmagnetic R-rich phases 230 may be present in one non-uniform reverse core shell main phase particle 110. The size of one nonmagnetic R-rich phase 230 is not particularly limited, but is preferably 5% or more and 15% or less in terms of a cross-sectional area ratio with respect to the non-uniform reversed core-shell main phase particles 110. .

Specifically, the nonmagnetic R-rich phase 230 is an R-rich phase having an R content of 70 atomic% to 100 atomic%. Further, the nonmagnetic R-rich phase 230 is not an R ₂ T ₁₄ B-based crystal phase.

  The presence of the nonmagnetic R-rich phase 230 in the main phase particles can be confirmed by SEM, SEM-EDS, TEM, and TEM-EDS. Specifically, the presence of some foreign phase in the main phase particles can be visually confirmed with an SEM image, and the R content in the foreign phase can be specified by TEM-EDS.

  By including the non-magnetic R-rich phase 230 inside the non-uniform reversed core-shell main phase particle 110, a large number of large anisotropic magnetic field gaps can be generated inside the particle. Therefore, the transmission of the domain wall motion from any direction can be suppressed, and the coercive force of the RTB-based sintered magnet can be improved.

Further, when the RTB-based sintered magnet 1 according to the present embodiment includes the non-uniform reverse core-shell main phase particles 110 including the low RH crystal phase 210 and the nonmagnetic R-rich phase 230, the magnet center portion It is preferable that the magnet surface layer portion 1a includes more non-uniform reverse core shell main phase particles 110 than 1b. Specifically, the ratio of the main phase particles including the low RH crystal phase 210 and the nonmagnetic R-rich phase 230 in the magnet surface layer portion 1a is r _sh (%), and the low RH crystal phase 210 and the nonmagnetic R in the magnet center portion. When the existing ratio of the main phase particles including the rich phase 230 is r _ch (%), it is preferable that r _sh −r _ch ≧ 20%.

  Further, as shown in FIG. 2, in the non-uniform inverted core-shell main phase particle 110, it is preferable that the core portion 110 a includes the low RH crystal phase 210 and the nonmagnetic R-rich phase 230. When the core part 110a includes the low RH crystal phase 210 and the nonmagnetic R rich phase 230, the effect of improving the coercive force is further increased.

<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.

[Crystal orientation reduction step]
There is no particular limitation on the method for reducing the degree of crystal orientation of the main phase particles in the present embodiment. For example, the degree of crystal orientation can be lowered through the following decomposition step, grain boundary diffusion step, and recombination step.

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

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. H ₂ , CO, or N ₂ is occluded and disproportionated to make it finer.

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 become finer is controlled, and the finally obtained low crystal orientation degree The layer thickness can be controlled.

  In addition, the main phase particles existing in the magnet surface layer portion are disproportionated and refined by heating in an oxidizing atmosphere containing an oxidizing gas at about 300 ° C. to 500 ° C. for about 20 minutes to 60 minutes. be able to.

[Diffusion treatment process]
In the present embodiment, following the decomposition step, there is further a diffusion treatment step for diffusing rare earth elements. The diffusion treatment is performed by attaching a compound containing a rare earth element (hereinafter sometimes simply referred to as a rare earth compound) or the like to the surface of the sintered body subjected to the decomposition step and then performing a heat treatment. Can do. There is no particular limitation on the method for attaching the compound containing the rare earth element, and for example, the compound can be attached by applying a slurry containing the rare earth element. The type of rare earth element to be diffused is arbitrary, but heavy rare earth elements are preferred. When diffusing heavy rare earth elements, the above-mentioned C _RC / C _RS can be controlled by controlling the amount of slurry applied and the concentration of heavy rare earth elements contained in the slurry.

  However, the method for attaching the 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.

  When applying the slurry, the 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 in the slurry, a solvent that can be uniformly dispersed without dissolving the rare earth compound 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 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 rare earth compound as necessary. For example, a dispersant for preventing aggregation of rare earth compound particles can be used.

  By performing the above diffusion treatment step on the sintered body that has been subjected to the decomposition step, in addition to the grain boundaries of the entire sintered body, also inside the refined particles present mainly in the magnet surface layer part, Rare earth elements will diffuse.

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 easier to increase the proportion of the rare earth element taken into the refined particles. Further, during the diffusion treatment step, each component contained in the H ₂ gas, CO gas, N ₂ gas, or oxidizing gas is released.

[Recombination process]
By passing through the recombination process after the diffusion treatment process, the particles that have been refined are recombined to generate R ₂ T ₁₄ B crystals. However, even if recombination occurs, the degree of crystal orientation does not return to the value before decomposition, and the degree of crystal orientation decreases. The recombination step is performed, for example, by performing rapid cooling at a rate of 50 ° C./min to 500 ° C./min. There is no particular limitation on the cooling rate, but if the cooling rate is too high, it tends to be microcrystals containing a large amount of amorphous, and if the cooling rate is too low, the core portion 110a and the shell portion of the reverse core shell main phase particle 110 are present. The interface with 110b tends to be unclear.

  As mentioned above, as a manufacturing method of the RTB system sintered magnet concerning this embodiment, at least the decomposition process which decomposes | disassembles and refines the main phase particle | grains of a magnet surface layer part, a rare earth element is used for the refined particle | grains. It is important that the grain boundary diffusion process for diffusing and the recombination process for recombining the refined particles are performed in this order. Thereby, a crystal orientation degree can be reduced in the magnet surface layer part of a RTB system sintered magnet. The methods and conditions of the above decomposition step, grain boundary diffusion step, and recombination step are merely examples. The decomposition process may be any process that decomposes and refines the main phase particles on the surface layer of the magnet. The grain boundary diffusion step is not limited as long as the rare earth element can be diffused into the refined particles. The recombination process only needs to recombine the refined particles. In addition, reverse core-shell particle | grains can also be produced | generated in a magnet surface layer part through said decomposition | disassembly process, a grain-boundary diffusion process, and a recombination process.

[Reaging process]
The reaging treatment step is performed by heating the sintered magnet after the recombination 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.

  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. Furthermore, 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 finely 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 listed in Table 1, H, Si, Ca, La, Ce, Cr, etc. 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 1-14 shown below and Comparative Examples 1-4 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 disproportionate and refine the main phase particles present mainly in the surface layer of the magnet. The magnetic pole surface (C surface) of the sintered magnet is a surface of 20 mm × 20 mm.

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. Then, Tb was diffused into the refined main phase particles.

  After the heat treatment, quenching was performed at a cooling rate of 200 ° C./min to recombine the refined particles.

  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 having 8% by volume of CO and 92% by volume of Ar, and the main phase particles mainly present on the magnet surface layer are unevenly distributed. And refined.

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 subsequently, heat treatment was performed at 950 ° C. for 5 hours. And Tb was diffused even inside the refined particles.

  After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recombine the refined particles.

  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 atmosphere 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 portion are not treated. Leveled and refined.

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 subsequently, heat treatment was performed at 950 ° C. for 5 hours. And Tb was diffused even inside the refined particles.

  After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recombine the refined particles.

  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 to disproportionate main phase particles present mainly in the magnet surface layer. Refined.

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 subsequently, heat treatment was performed at 950 ° C. for 5 hours. And Tb was diffused even inside the refined particles.

  After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recombine the refined particles.

  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)
The sintered magnet obtained by the above process was held in an H ₂ gas atmosphere at 750 ° C. for 10 minutes to disproportionate and refine the main phase particles present mainly in the magnet surface layer.

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 the slurry was applied, heat treatment was performed at 770 ° C. for 5 hours while flowing Ar at atmospheric pressure, and subsequently, heat treatment was performed at 820 ° C. for 5 hours. And Tb was diffused even inside the refined particles.

  After the heat treatment, it was rapidly cooled at a cooling rate of 200 ° C./min to recombine the refined particles.

  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 12)
TbH ₂ particles (average particle diameter D50 = 5 [mu] m), except that was replaced by NdH ₂ particles (average particle diameter D50 = 5 [mu] m) was performed in the same manner as in Example 1. In addition, Nd was made to adhere so that the weight of Nd to apply | coat with respect to the weight of a sintered magnet might be 0.5 weight%.

(Example 13)
Example 1 except that Tb was adhered by applying a slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) were dispersed in ethanol only to both magnetic pole faces (C face) of the sintered magnet. Implemented. 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 14)
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.

(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 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 the sintered magnet manufacturing process, sintered body alloys (raw material alloys) B and C were prepared so as to have the compositions shown in Table 1. 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, 7-11,13 and the comparative examples 1 and 4 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)
The same operation as in Example 12 was carried out except that the main phase particles present in the surface layer portion of the sintered magnet were not disproportionated or refined.

(Comparative Example 4)
Example except that Tb was adhered by applying slurry in which TbH ₂ particles (average particle diameter D50 = 5 μm) were dispersed in ethanol to four surfaces except both magnetic pole surfaces (C surface) of the sintered magnet. 1 was 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%.

  Table 3 shows whether a decomposition treatment for decomposing main phase particles present in the surface layer portion of each of the R-T-B system sintered magnets of Examples 1 to 11 and 14, and Comparative Examples 1 and 2 was performed, or grain boundary diffusion Each of the treatment was performed and the quenching was performed after the grain boundary diffusion was described. When each process was performed, “◯” was given, and when each process was not conducted, “X” was given. Furthermore, for each of the examples and comparative examples, RH was attached to both magnetic pole faces (C face) of the sintered magnet, and RH was attached to four faces excluding both magnetic pole faces (C face) of the sintered magnet. It was also described. When RH was made to adhere to each surface, it was marked with ○, and when RH was not made to adhere to each surface, × was marked.

  Further, the R-T-B system sintered magnets of Examples 1 to 11 and 14 and Comparative Examples 1 and 2 were evaluated for magnetic characteristics (residual magnetic flux density Br coercive force Hcj and squareness ratio Hk / Hcj) with a BH tracer. The results are shown in Table 3. The residual magnetic flux density Br was 1380 mT or more, and 1400 mT or more. The coercive force Hcj was 1790 kA / m or higher, and 1830 kA / m or higher was further improved. The case where the squareness ratio Hk / Hcj was 0.95 or more was considered good.

  Moreover, the crystal orientation degree was measured with the following method about the RTB system sintered magnet of each Example and the comparative example.

  First, the magnetic pole surface of the R-T-B system sintered magnet of each example and comparative example was mirror-polished. Thereafter, X-ray diffraction measurement of the mirror-polished surface was performed, and the degree of orientation was calculated by the Lotgering method based on the obtained diffraction peak. In the Lotgering method, based on the X-ray diffraction intensity I (00l) of the (00l) reflection component and the X-ray diffraction intensity I (hk0) of the (hk0) reflection component, the crystal orientation degree is expressed by the following equation (1). fc can be calculated.

  When the degree of orientation is calculated by the Lotgering method, only the orientation direction, that is, (00l) reflection component of the diffraction peaks is integrated on the molecular side. The component of the diffraction peak that deviates even slightly from the alignment direction is determined to be a component perpendicular to the alignment direction, that is, (hk0) reflection. That is, in the formula shown in the above equation 1, it is excluded from the numerator side and integrated on the denominator side. Therefore, the degree of orientation calculated compared to the actual degree of orientation is a considerably small value. In order to calculate the degree of orientation in line with actuality, it is preferable to perform vector correction on the diffraction peak, but in this embodiment, vector correction is not performed.

  The degree of crystal orientation of the magnetic pole face was calculated by the above method. Further, the thickness of the low crystal orientation layer was measured by the following method.

  The surface was polished 10 μm from the magnetic pole surface, and the mirror-polished surface was measured every 10 μm, and the degree of crystal orientation was calculated by the Lotgering method. The thickness of the portion where the degree of crystal orientation is reduced by 2% or more with respect to the degree of crystal orientation in the central part of the magnet is defined as the thickness of the low crystal orientation degree layer. In addition, the crystal orientation degree in the magnet central portion refers to the crystal orientation degree when the crystal orientation degree is highest among the crystal orientation degrees calculated every 10 μm. In addition, when the crystal orientation degree of the magnetic pole face does not decrease by 2% or more with respect to the crystal orientation degree in the magnet central portion, the low crystal orientation degree layer does not exist.

  Furthermore, the abundance ratio of the reverse core shell main phase particles in a portion of 20 μm from the magnetic pole surface toward the inside of the magnet in the magnet surface layer portion having the magnetic pole surface was measured. The measurement of the existence ratio of the reverse core shell main phase particles in the magnet surface layer portion was performed by randomly selecting 10 main phase particles in the portion of 20 μm from the magnetic pole surface toward the inside of the magnet in the magnet surface layer portion having the magnetic pole surface. The main phase particles were subjected to SEM and TEM-EDS. 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 on the magnet surface layer portion having a pole face, and the total RH concentration C _RS in the concentration C _RC and the shell of the entire RH in the core portion was measured using the TEM-EDS. 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 in Examples 1 to 11 and 14, the measurement locations of the total RH concentration in the core portion and the total RH concentration in the shell portion are as follows.

First, the reverse core-shell main phase particles 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 .

In addition, the existence ratio r _s (%) of particles including a low RH crystal phase in the magnet surface layer portion having the magnetic pole face of Examples 1 to 11 and Comparative Examples 1 and 2, and the low RH crystal phase in the magnet central portion The abundance ratio r _c (%) of the particles containing was measured using SEM, SEM-EDS, TEM and TEM-EDS. Specifically, 10 main phase particles were selected for each of the magnet surface layer portion and the magnet center portion having the magnetic pole face, and how many of the 10 particles contained a low RH crystal phase was measured. The results are shown in Table 4.

Further, for Examples 1 to 11 and 14, and Comparative Examples 1 and 2, the abundance ratio (r _sh ) (%) of particles containing a low RH crystal phase and a nonmagnetic R rich phase in the magnet surface layer portion having the pole face, and In addition, the abundance ratio (r _ch ) (%) of particles including a low RH crystal phase and a non-magnetic R-rich phase in the central part of the magnet was measured using SEM-EDS, TEM and TEM-EDS. The results are shown in Table 4.

  From Tables 1 to 4, the step of decomposing and refining the main phase particles of the magnet surface layer after sintering, the step of incorporating RH into the particles refined by grain boundary diffusion, and the particles incorporating RH by rapid cooling In the RTB-based sintered magnets of Examples 1 to 11 and 14 that have undergone the recombination step, the crystal orientation degree of the main phase particles in the magnet surface layer portion having the magnetic pole surface (C surface) is the main phase in the magnet central portion. It was lower than the degree of crystal orientation of the particles. The residual magnetic flux density Br, the coercive force Hcj, and the squareness ratio Hk / Hcj were preferable.

Further, in Examples 1 to 7, 9 to 11 and 14 in which the thickness of the low crystal orientation layer was 10 μm or more and 70 μm or less, the residual magnetic flux density Br was more preferable. Further, Examples 1 to 5, wherein the reverse core shell main phase particles are present, and the ratio of the reverse core shell main phase particles having C _RC / C _RS > 1.5 among the reverse core shell main phase particles is 90% or more. 7 and 8 had a more preferable coercive force Hcj.

Further, in Examples 1 to 11 and 14 where r _s −r _c ≧ 20%, preferable residual magnetic flux density Br and coercive force Hcj were obtained. Further, in Examples 1 to 5 and 7 where r _sh −r _ch ≧ 60%, more preferable residual magnetic flux density Br and coercive force Hcj were obtained.

  On the other hand, the step of decomposing and refining the main phase particles in the magnet surface layer after sintering, the step of incorporating RH into the particles refined by grain boundary diffusion, and the recombination of particles incorporating RH by rapid cooling In the comparative example which did not pass through the process to do, the crystal orientation degree of the magnet surface layer part did not fall. As a result, the residual magnetic flux density Br, the coercive force Hcj and / or the squareness ratio Hk / Hcj were inferior to those of Examples 1 to 11.

  In Comparative Example 1, since the step of decomposing and refining the main phase particles of the magnet surface layer portion after sintering was not performed, RH was not taken into the main phase particles even after undergoing grain boundary diffusion and rapid cooling, and the degree of crystal orientation decreased. There wasn't. In Comparative Example 2, as a result of producing a sintered magnet by the two-alloy method, the crystal orientation degree of the main phase particles in the magnet surface layer part and the crystal orientation degree of the main phase particles in the magnet central part became equal. As a result, the residual magnetic flux density Br, the coercive force Hcj, and the squareness ratio Hk / Hcj were inferior to those of Examples 1 to 11.

  Table 5 shows the results of comparing Example 12 and Comparative Example 3, and Table 6 shows the results of comparing Example 13 and Comparative Example 4.

  Table 5 shows whether Example 12 and Comparative Example 3 were subjected to decomposition treatment for decomposing main phase particles present in the surface layer portion of the R-T-B system sintered magnet, grain boundary diffusion treatment, and Each of the cases where rapid cooling was performed after grain boundary diffusion was described. When each process was performed, “◯” was given, and when each process was not conducted, “X” was given. Further, Table 5 shows the results of evaluation of magnetic characteristics (residual magnetic flux density Br coercive force Hcj and squareness ratio Hk / Hcj) using a BH tracer. In the comparison between Example 12 and Comparative Example 3 in which RH was not diffused at the grain boundary, the coercive force was 1250 kA / m or more.

  Table 6 shows whether Example 13 and Comparative Example 4 were subjected to a decomposition treatment for decomposing main phase particles present in the surface layer portion of the RTB-based sintered magnet, a grain boundary diffusion treatment, and Each of the cases where rapid cooling was performed after grain boundary diffusion was described. When each process was performed, “◯” was given, and when each process was not conducted, “X” was given. Furthermore, for each of the examples and comparative examples, RH was attached to both magnetic pole faces (C face) of the sintered magnet, and RH was attached to four faces excluding both magnetic pole faces (C face) of the sintered magnet. It was also described. When RH was made to adhere to each surface, it was marked with ○, and when RH was not made to adhere to each surface, × was marked. Further, Table 6 shows the results of evaluation of magnetic characteristics (residual magnetic flux density Br coercive force Hcj and squareness ratio Hk / Hcj) using a BH tracer.

  From Table 5, the step of decomposing and refining the main phase particles in the magnet surface layer after sintering, the step of incorporating Nd into particles refined by grain boundary diffusion, and the recombination of particles incorporating Nd by rapid cooling Example 12 which performed the process to improve coercive force Hcj and squareness ratio Hk / Hcj compared with the comparative example 3 which did not perform the process which decomposes | disassembles and refines | miniaturizes the main phase particle | grains of a magnet surface layer part after sintering. . Further, in Example 12, the degree of crystal orientation on the magnet surface decreased, whereas in Comparative Example 3, the degree of crystal orientation on the magnet surface did not decrease. That is, the step of decomposing and refining the main phase particles of the magnet surface layer after sintering, the step of incorporating Nd into the particles refined by the grain boundary diffusion, and the rapid cooling By performing the step of recombining the particles in which Nd has been taken in, the degree of crystal orientation on the magnet surface can be reduced, and the coercive force Hcj and the squareness ratio Hk / Hcj can be improved.

  From Table 6, the coercive force Hcj was greatly improved in Example 13 in which Tb was attached only to both magnetic pole surfaces, compared to Comparative Example 4 in which Tb was attached only to the four surfaces other than both magnetic pole surfaces. That is, it can be seen that the coercive force Hcj can be improved by incorporating RH into the magnetic pole surface (C surface) and reducing the crystal orientation of the main phase particles in the magnet surface layer portion having the magnetic pole surface. The coercive force of Example 13 was improved more than that of Example 1 because the amount of Tb deposited on the magnetic pole surface was larger in Example 13 than in Example 1, and the magnet surface layer having the magnetic pole surface was used. This is presumably because the degree of decrease in the degree of crystal orientation of the main phase particles in the part was large.

DESCRIPTION OF SYMBOLS 1 ... R-T-B system sintered magnet 1a ... Magnet surface layer part 1b (having a magnetic pole face) ... Magnet central part 11 ... Main phase particle 11a ... Low crystal orientation main phase particle 11b ... High crystal orientation main phase particle 12 ... Grain boundary 110 ... heterogeneous reverse core shell main phase particles 110a ... core part 110b ... shell part 210 ... low RH crystal phase 230 ... non-magnetic R rich phase

Claims (4)

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, T is one or more transition metal elements essential for Fe or Fe and Co, B is boron,
The RTB-based sintered magnet has a magnet surface layer part and a magnet center part located inside the magnet surface layer part,
An RTB-based sintered magnet characterized in that a crystal orientation degree of the main phase particles in a magnet surface layer portion having a magnetic pole surface is lower than a crystal orientation degree of the main phase particles in a magnet central portion. R is one or more rare earth elements that essentially require heavy rare earth elements RH;
A part of the main phase particles contained in the magnet surface layer part 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,}
The R-T-B system sintered magnet according to claim 1, wherein C _RC / C _RS > 1.0. The core portion includes a low RH crystal phase,
The R- of claim ₂ , wherein the low RH crystal phase is composed of the R ₂ T ₁₄ B crystal, and the concentration of the RH is relatively low with respect to the concentration of the RH in the entire main phase particle. TB sintered magnet.   The RTB-based sintered magnet according to claim 3, further comprising a nonmagnetic R-rich phase in the core portion.

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