Rare earth sintered magnet and method for producing rare earth sintered magnet

Abstract

SOLUTION: To provide a rare earth sintered magnet that includes R2T14B main phase crystal particles (R is one or more elements selected from rare earth elements, and Nd is essential, T is one or more elements selected from transition elements, and Fe is essential), a two-grain grain boundary phase, and a grain boundary triple point, and all of these main phase crystal particles, the two-grain grain boundary phase, and the grain boundary triple point contain TiB2 crystals.EFFECT: According to the present invention, it is possible to obtain a high-performance rare earth sintered magnet that has both high HcJ and good squareness.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rare earth sintered magnet characterized by having a particularly high coercive force, and a method for manufacturing the same.

Background Art

[0002] R-T-B sintered magnets (hereinafter sometimes referred to as Nd magnets) are essential functional materials for energy saving and high functionality, and their application range and production volume are expanding year by year. For example, they are used in various motors for hybrid vehicles, electric vehicles, and home appliances. In these various applications, the high coercive force (hereinafter referred to as H cJ ) of the R-T-B sintered magnet is a great advantage, but for further improvement of heat resistance, an improvement in H cJ is required.

[0003] Conventionally, a large amount of heavy rare earths (mainly Dy) has been added as a method for increasing H cJ of the R-T-B sintered magnet. However, there has been a problem that the residual magnetic flux density B r (hereinafter referred to as B r ) decreases due to the addition of heavy rare earths. Therefore, in recent years, a grain boundary diffusion method, which is a method of diffusing heavy rare earth elements from the surface to the inside of the R-T-B sintered magnet to concentrate heavy rare earths in the outer shell portion of the main phase crystal grains, has been increasingly adopted to suppress the decrease in B r while obtaining a high H cJ .

[0004] However, heavy rare earths such as Dy have unstable supply due to reasons such as limited production areas, and there is a problem that the price fluctuates greatly. Therefore, there is a need for a technology to improve H cJ of the R-T-B sintered magnet without using heavy rare earth elements such as Dy as much as possible.

[0005] International Publication No. 2013 / 008756 (Patent Document 1) proposes preparing an R-T-B alloy such that its composition satisfies a predetermined relational expression, resulting in a composition with a lower B content than usual. According to this method, an R 2 T 17 phase is formed. Using this R 2 T 17 phase as a raw material, by sufficiently ensuring the volume fraction of the transition metal-rich phase (R 6 T 13 M) formed by reacting the rare earth element R and the metal element M, it is described that an R-T-B sintered magnet with a high coercivity can be obtained while suppressing the Dy content.

[0006] Further, in Japanese Patent Application Laid-Open No. 2015-179841 (Patent Document 2), an alloy powder with R: 27 to 35% by mass, B: 0.9 to 1.0% by mass, Ga: 0.15 to 0.6% by mass, and the balance being T, and a powder of titanium hydride are mixed, and then an R-T-B sintered magnet is manufactured. It is proposed that an R-T-B sintered magnet having a high coercivity and rectangularity can be obtained while suppressing a decrease in Br without using heavy rare earth elements as much as possible.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the R-T-B sintered magnet of Patent Document 1 above has a lower rectangularity than a general R-T-B sintered magnet, and there is a tendency for the rectangularity to decrease as H cJ increases.

[0009] In addition, in the R-T-B sintered magnet of Patent Document 2, although the rectangularity can be increased, since it is necessary to separately prepare and mix the hydride of Ti, there is a problem that the manufacturing cost increases due to an increase in the number of manufacturing steps.

[0010] The present invention has been made in view of the above problems, and regarding the R-T-B rare earth sintered magnet, without mixing two alloys, high H cJ and an object of the present invention is to provide a high-quality R-T-B rare earth sintered magnet having rectangularity.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that in the main phase crystal particles, the grain boundary between two particles, and the grain boundary triple point in the rare earth sintered magnet, all contain TiB 2 crystals, a rare earth sintered magnet having high H cJ and good rectangularity can be obtained. Also, regarding its manufacture, when casting an alloy melt having a predetermined composition to obtain a raw material alloy, by optimizing the temperature and cooling rate of the melt, high H cJ and the present invention has been completed by finding that the rare earth sintered magnet having good rectangularity can be manufactured.

[0012] That is, the present invention provides the following rare earth sintered magnet and a method for manufacturing the same. 1. 12 to 17 atomic % of R (R is at least one or more selected from rare earth elements), 0.1 to 3 atomic % of M 1 (M 1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi), 0.05 to 1 atomic % of M 2 (M 2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and Ti is essential), 4.8 to 6.5 atomic % of B, 1.5 atomic % or less of carbon, 1.5 atomic % or less of oxygen, 0.5 atomic % or less of nitrogen, and the balance T (T is one or more elements selected from iron group elements), and has a composition of R 2 T 14 B main phase crystal grains child and A rare earth sintered magnet including a two-particle grain boundary phase formed between main phase crystal particles adjacent to each other and a grain boundary triple point surrounded by three or more main phase crystal particles, wherein any of the main phase crystal particles, the two-particle grain boundary phase, and the grain boundary triple point contains TiB 2 crystals, characterized by being a rare earth sintered magnet. 2. The TiB2 The crystal is AlB 2 type crystal structure, and the rare earth sintered magnet of 1. 3. The TiB 2 crystal has a flat hexagonal column shape, and the average value of the thickness in the height direction of the hexagonal column shape is 10 to 60 nm, and the rare earth sintered magnet of 1 or 2. 4. said M 2 is any one of 1 to 3 rare earth sintered magnets containing 0.05 atomic % or more of Ti and 0.05 atomic % or more of Zr. 5. 10 to 90 volume % of the total grain boundary phase composed of the two-particle grain boundary and the grain boundary triple point is R 6 T 13 M 1 is any one of 1 to 4 rare earth sintered magnets that is a phase. 6. Any one of 1 to 5 rare earth sintered magnets in which the average crystal grain size, which is the average value of the equivalent circle diameters calculated from the cross-sectional areas of the main phase crystal grains, is 4 μm or less. 7. Any one of 1 to 6 rare earth sintered magnets in which the total content of Dy, Tb, and Ho is 0 to 5.0 atomic %. 8. A method for manufacturing a rare earth sintered magnet including a casting step of casting an alloy melt having a predetermined composition to obtain a raw material alloy, a pulverizing step of pulverizing the raw material alloy to prepare alloy fine powder, a molding step of compacting the alloy fine powder under magnetic field application to obtain a molded body, and a heat treatment step of heat treating the molded body to obtain a sintered body. The casting step is a step of heating the alloy melt to 1480 to 1600 ° C and then cooling it by controlling the average cooling rate to 500 ° C to 100 to 1200 ° C / second. The heat treatment step includes a sintering step of holding the molded body in a temperature range of 950 ° C to 1200 ° C for 0.5 to 20 hours. A method for manufacturing a rare earth sintered magnet, characterized by this.

Advantages of the Invention

[0013] According to the present invention, a high-performance rare earth sintered magnet having high H cJ and good rectangularity can be obtained.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0015] As described above, in the main phase crystal particles, two-particle grain boundary phases, and grain boundary triple points of the rare earth sintered magnet of the present invention, all contain TiB 2 crystals.

[0016] First, regarding the entire magnet, the rare earth sintered magnet of the present invention is a so-called R-T-B-based rare earth sintered magnet, which is not particularly limited, but contains 12 to 17 atomic% of R, 0.1 to 3 atomic% of M 1 , 0.05 to 1.0 atomic% of M 2 , 4.8 to 6.5 atomic% of B, 1.5 atomic% or less of carbon, 1.5 atomic% or less of oxygen, 0.5 atomic% or less of nitrogen, and the balance of T, and preferably has a composition.

[0017] The above R is at least one selected from rare earth elements, and it is preferably essential to contain Nd. The ratio of Nd in R is preferably 60 atomic% or more, and more preferably 75 atomic% or more. The content of R is not particularly limited, but from the viewpoint of suppressing an extreme decrease in H cJ and B r of the rare earth sintered magnet, it is preferably 12 to 17 atomic%, and more preferably 13 to 16 atomic%. Note that Dy, Tb, and Ho may not be contained in R, and when contained, the total amount of Dy, Tb, and Ho is preferably 5.0 atomic% or less (0 to 5.0 atomic%) with respect to the entire rare earth sintered magnet.

[0018] The above M 1 is composed of one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi. The content of M 1 is not particularly limited, but from the viewpoint of ensuring a good abundance ratio of the R-Fe(Co)-M 1 grain boundary phase to obtain a sufficient improvement effect of H cJ and suppressing deterioration of the rectangularity of the magnet and a decrease in B r , 0.1 to 3 atomic% is preferable, and 0.5 to 2.5 atomic% is more preferable.

[0019] The above M 2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, and Ti is essential. M 2 The content of M is not particularly limited, but from the viewpoint of stably forming borides and suppressing abnormal grain growth during sintering, 0.05 to 1.0 atomic% is preferable, and 0.1 to 0.5 atomic% is more preferable. As a result, it becomes possible to sinter at a relatively high temperature during production, leading to an improvement in squareness and an enhancement of magnetic properties.

[0020] Here, although not particularly limited, the above M 2 preferably contains 0.05 atomic% or more of Ti and 0.05 atomic% or more of Zr, and more preferably, Ti is 0.1 atomic% or more and Zr is 0.2 atomic% or more.

[0021] The above B is not particularly limited, but R 1.1 Fe 4 B 4 By forming a compound phase, so-called B-rich phase, it is possible to prevent the increase of H cJ and from the viewpoint of ensuring the volume fraction of the main phase and maintaining good magnetic properties, it is preferably 4.8 to 6.5 atomic%, and more preferably 5.0 to 6.2 atomic%.

[0022] In addition, for the rare earth sintered magnet of the present invention, it is desirable that the contents of oxygen, carbon, and nitrogen are less, but it is difficult to completely avoid contamination during the manufacturing process. The oxygen content is preferably 1.5 atomic% or less, particularly 1.2 atomic% or less, especially 1.0 atomic% or less, and most preferably 0.8 atomic% or less. The carbon content is preferably 1.5 atomic% or less, particularly 1.3 atomic% or less. The nitrogen content is preferably 0.5 atomic% or less, particularly 0.3 atomic% or less. In addition, as impurities, it is acceptable to contain elements such as H, F, Mg, P, S, Cl, and Ca at 0.1 mass% or less, but it is preferable that these elements are also less.

[0023] The above-mentioned T is one or more elements selected from iron group elements, and it is preferable that Fe is contained as this T, and Co may be further contained. Although the amount of T is the remainder, its content is preferably 70 to 80 atomic%, and particularly preferably 75 to 80 atomic%. As described above, Co may or may not be contained, but for the purpose of improving the Curie temperature and corrosion resistance, it may be contained in T at 10 atomic% or less, preferably 5 atomic% or less of the composition of the entire rare earth sintered magnet. Co substitution exceeding 10 atomic% will cause a significant decrease in H cJ and is not preferable.

[0024] The average crystal grain size of the rare earth sintered magnet of the present invention is preferably 4 μm or less, and the degree of orientation of the c-axis, which is the magnetization easy axis of the R 2 Fe 14 B particles is preferably 98% or more. The average crystal grain size can be measured by the following procedure. First, after polishing the cross-section of the sintered magnet until it becomes mirror-like, it is immersed in an etching solution such as a Vilella solution (a mixed solution with a glycerin:nitric acid:hydrochloric acid mixing ratio of 3:1:2) to selectively etch the grain boundary phase, and the cross-section is observed with a laser microscope. Based on the obtained observation image, the cross-sectional area of each particle is measured by image analysis, and the diameter as an equivalent circle is calculated. Then, the average particle size is determined based on the data of the area fraction occupied by each particle size. The average particle size is the average of a total of about 2,000 particles in 20 different images. The control of the average crystal grain size of the sintered body can be performed by adjusting the average particle size of the rare earth sintered magnet alloy fine powder during fine pulverization.

[0025] The structure of the rare earth sintered magnet of the present invention has an R 2 T 14 B phase as the main phase, and includes a two-particle grain boundary phase formed between adjacent main phase crystal particles and a grain boundary triple point surrounded by three or more main phase crystal particles. The above two-particle grain boundary phase and grain boundary triple point are composed of R 6 T 13 M 1 1 phase, R-M 1 phase, M 2 -B 2It may contain phases. In the present invention, TiB is present in the above-mentioned main phase, within the two-particle grain boundary phase, and at the grain boundary triple point. 2 It contains crystals.

[0026] The above TiB 2 crystals have an AlB 2 type crystal structure, and this identification can be carried out by STEM-EDX. The crystal shape is a flat hexagonal prism shape, and it is preferable that the average value of the thickness in the height direction of the hexagonal prism shape is 10 to 60 nm. Although the reason why the properties of the rare earth sintered magnet are improved by adopting such a structure is not necessarily clear, it is presumed as follows. That is, the above TiB 2 crystals precipitate in the main phase, within the two-particle grain boundary phase, and at the grain boundary triple point, and function not only as an effect to suppress abnormal grain growth of the sintered body but also as a spacer to weaken the magnetic coupling between the main phase particles, contributing to the improvement of the coercivity and the rectangularity.

[0027] Such a tissue form is considered to be obtained by adding Ti to produce an alloy. Also, Ti in the cast alloy is dissolved in the main phase, and it is considered that TiB 2 precipitates in the main phase, within the grain boundary phase, and at the grain boundary triple point.

[0028] In addition, the two-particle grain boundary phase and the grain boundary triple point preferably contain an R 6 T 13 M 1 1 phase in a volume ratio of 10 to 90%, more preferably 50 to 80%. By setting such a range, a sufficiently high H cJ can be obtained, and a large decrease in B r can be suppressed.

[0029] Here, although not particularly limited, in the above R 6 T 13 M 1 1 phase, M 1 is such that Si occupies 0.5 to 50 atomic% in M 1 and M 1The remainder is one or more elements selected from Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi, or Ga is M 1 occupies 1.0 to 80 atomic % in, and M 1 the remainder is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi, or Al is M 1 occupies 0.5 to 50 atomic % in, and M 1 the remainder is preferably one or more elements selected from Si, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi.

[0030] These elements can stably form intermetallic compounds (such as R 6 Fe 13 Ga 1 and R 6 Fe 13 Si 1 etc.), and can replace each other at the M 1 sites. Even if the elements at the M 1 sites are combined, no significant difference is observed in the magnetic properties. Practically, the quality is stabilized by reducing the variation in magnetic properties, and the cost is reduced by reducing the addition amount of expensive elements.

[0031] In addition to the above main phase, two-particle grain boundary phase, and grain boundary triple points, the rare earth sintered magnet of the present invention may further contain an R-rich phase and a phase composed of inevitable elements mixed in during the manufacturing process such as R oxides, R carbides, R nitrides, R halides, and R acid halides.

[0032] Next, a method for manufacturing the rare earth sintered magnet of the present invention will be described. The method for manufacturing the rare earth sintered magnet of the present invention manufactures the rare earth sintered magnet of the present invention, pulverizes an alloy having a predetermined composition, compact-presses it under the application of a magnetic field, and then sinter it.

[0033] According to the manufacturing method of the present invention, each step in manufacturing an alloy for an R-Fe-B-based rare earth sintered magnet can basically be carried out in the same manner as the ordinary powder metallurgy method. That is, although not particularly limited, usually, a raw material having a predetermined composition is melted, and the alloy melt is cast to obtain a raw material alloy (casting step), the raw material alloy is pulverized to prepare alloy fine powder (pulverizing step), the alloy fine powder is compacted under the application of a magnetic field (forming step), and the formed body is heat-treated to obtain a sintered body (heat treatment step). Here, the heat treatment step includes a sintering step of sintering the formed body, and may further include a heat treatment step of heat-treating the sintered magnet. Further, the above-mentioned pulverizing step may include a rough pulverizing step of obtaining rough pulverized powder and a fine pulverizing step of obtaining fine powder.

[0034] First, in the above-mentioned casting step, metals or alloys as raw materials for each element are weighed so as to have the predetermined composition in the present invention described above, and for example, the raw materials are melted by high-frequency melting, and the alloy melt is cooled and cast to produce a raw material alloy. As described above, the rare earth sintered magnet of the present invention can be produced by adding Ti when producing the alloy. More specifically, in the above-mentioned casting step, when melting the above-mentioned raw material having a predetermined composition containing Ti, after raising the temperature of the alloy melt to 1480 to 1600 °C, preferably 1500 to 1550 °C, the average cooling rate up to 500 °C is controlled to 100 to 1200 °C / second, preferably 500 to 1000 °C / second, and then cooled. By doing so, an alloy structure in which Ti is dissolved in the main phase can be formed. When the cooling rate is less than 100 °C / second, coarse TiB 2 crystals precipitate during the cooling process, so that a magnet in which fine TiB2 crystals are dispersed cannot be obtained. On the other hand, when the cooling rate exceeds 1200 °C / second, chill crystals and an amorphous phase are generated in the alloy structure, and the magnetic properties of the magnet deteriorate.

[0035] The above-mentioned pulverization process is, for example, a multi-stage process including a coarse pulverization process and a fine pulverization process. In the coarse pulverization process, for example, a jaw crusher, a brown mill, a pin mill, or hydrogenation pulverization is used. In the case of an alloy produced by strip casting, hydrogenation pulverization is usually applied to obtain coarse powder coarsely pulverized to, for example, 0.05 to 3 mm, particularly 0.05 to 1.5 mm.

[0036] In the above-mentioned fine pulverization process, a lubricant is added to the coarse powder obtained in the coarse pulverization process, and fine pulverization is performed using a method such as jet mill pulverization.

[0037] In the production method of the present invention, in this fine pulverization process, fine pulverization is performed so that the average particle size of the fine powder preferably ranges from 0.5 to 3.5 μm. In this case, the more preferable average particle size of the fine powder is 1.0 to 3.0 μm, and still more preferably 1.5 to 2.8 μm. The lower limit value of 0.5 μm is a set value from the viewpoint of suppressing oxidation and nitridation of the fine powder and obtaining good H cJ and the upper limit value of 3.5 μm is a set value from the viewpoint of obtaining sufficient H cJ . Note that the average particle size of the powder refers to the median diameter in the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0038] The above-mentioned fine powder thus prepared is pressure-molded in a magnetic field to obtain a molded body, and such a molded body is heat-treated to obtain a sintered body, thereby obtaining a sintered magnet.

[0039] In the molding process, a magnetic field of 400 to 1600 kA / m may be applied, and the alloy powder may be pressure-molded with a compression molding machine while being oriented in the direction of the easy magnetization axis.

[0040] In the sintering process, the molded body obtained in the molding process is sintered in a high vacuum or in a non-oxidizing atmosphere such as Ar gas. In the present invention, this sintering operation is performed by holding in a temperature range of 950°C to 1200°C, preferably 1000 to 1150°C, for 0.5 to 20 hours, preferably 3 to 10 hours. As a result, Ti dissolved in the main phase becomes TiB2 As a result, a magnet structure precipitated in the main phase, grain boundary phase, and grain boundary triple points can be obtained. When the sintering temperature is less than 950 °C, the densification of the compact does not proceed sufficiently. When it exceeds 1200 °C, abnormal grain growth occurs. When the holding time is less than 0.5 hours, the precipitation amount of TiB 2 crystals becomes insufficient. When it exceeds 20 hours, the coarsening of TiB 2 crystals occurs.

[0041] Subsequent to the sintering process, although not particularly limited, a heat treatment process may be performed to heat treat at a temperature lower than the sintering temperature for the purpose of increasing H cJ . This post-sintering heat treatment may be performed by two-stage heat treatment of high-temperature heat treatment and low-temperature heat treatment, or only low-temperature heat treatment may be performed. In the high-temperature heat treatment in this post-sintering heat treatment, it is preferable to heat treat the sintered body at a temperature of 600 to 950 °C, and in the low-temperature heat treatment, it is preferable to heat treat at a temperature of 400 to 600 °C. During cooling, the cooling rate up to at least 400 °C is 5 to 100 °C / min, preferably 5 to 80 °C / min, more preferably 5 to 50 °C / min. When the cooling rate is less than 5 °C / min, R 6 T 13 M 1 1 phase segregates at the grain boundary triple points, and the magnetic properties may deteriorate significantly. On the other hand, when the cooling rate exceeds 100 °C / min, although the precipitation of the R 6 T 13 M 1 1 phase during the cooling process can be suppressed, the dispersibility of the R-M 1 phase in the structure is insufficient, and the squareness of the sintered magnet may deteriorate.

[0042] In addition, the obtained sintered magnet may be subjected to a grain boundary diffusion treatment using Dy or Tb. By reducing the nitrogen concentration to 800 ppm or less as described above, stable characteristics can be obtained without reducing the increase in H cJ after grain boundary diffusion.

Examples

[0043] Examples and comparative examples are shown below to more specifically explain the present invention, but the present invention is not limited thereto.

[0044] [Examples 1 to 5, Comparative Examples 1 to 4] Rare earth metals (Nd or dysprosium), electrolytic iron, Co, other metals and alloys were used, weighed to have a predetermined composition, melted in a high-frequency induction furnace in an argon atmosphere, and strip-cast on a water-cooled copper roll to produce alloy ribbons. At this time, the heating temperature and cooling rate of the molten alloy were changed in each example and comparative example. The conditions at that time are shown in Table 2. Next, the produced alloy ribbons were coarsely pulverized by hydrogenation to obtain coarse powders, and then 0.20% by mass of menthol was added as a lubricant to the coarse powders and mixed. Next, the obtained coarse powders were finely pulverized with a jet mill in a nitrogen stream to produce fine powders. Thereafter, these fine powders were filled into a mold of a molding device in an inert gas atmosphere, and pressure molding was performed in a direction perpendicular to the magnetic field while being oriented in a magnetic field of 15 kOe (1.19 MA / m). The obtained compacted powder compact was sintered in vacuo at 1030 to 1080 °C for 5 to 30 hours and cooled to 200 °C or lower. The obtained sintered body was heat-treated after sintering at 900 °C for 2 hours, cooled to 200 °C, and subsequently subjected to an aging treatment for 2 hours. The composition of the magnet is shown in Table 1.

[0045] The central part of each obtained sintered body was cut into a rectangular parallelepiped shape with a size of 18 mm × 15 mm × 12 mm to obtain a sintered magnet, and the magnetic properties of each such sintered magnet were measured using a B-H tracer. Table 2 shows the values of Examples 1 to 5 and Comparative Examples 1 to 4 respectively. Regarding the oxygen concentration of the sintered magnet, it was measured by the inert gas fusion infrared absorption method, regarding the nitrogen concentration by the inert gas fusion heat conduction method, and regarding the carbon concentration by the combustion infrared absorption method. Regarding the average crystal grain size D50 (μm), the cross-section parallel to the magnetization direction of the sintered magnet was polished until it became a mirror surface, immersed in a mixed solution of glycerin: nitric acid: hydrochloric acid = 3:1:2 to selectively etch the grain boundary phase of the cross-section, 25 cross-sectional images in a range of 85 × 85 μm were obtained with a laser microscope, and based on the obtained cross-sectional images, the cross-sectional area of each individual particle was measured by image analysis and determined as the area average of the diameters of each particle calculated as the equivalent circle diameter.

[0046] When the cross-section of the sintered magnet produced in Example 1 was observed with an electron probe microanalyzer (EPMA), as shown in Fig. 1, R 2 T 14 B was the main phase, and a two-particle grain boundary phase formed between adjacent main phase crystal particles and a grain boundary triple point surrounded by three or more main phase crystal particles were observed. The above two-particle grain boundary phase and grain boundary triple point contain the R 6 T 13 M 1 1 phase, the R-M 1 1 phase, and the M 2 -B 2 phase. 75% by volume of the total grain boundary phase was the R 6 T 13 M 1 1 phase. Also, TiB 2 crystals were contained in the above main phase, two-particle grain boundary phase, and grain boundary triple point. When the above TiB 2 crystals were observed by STEM-EDX, as shown in Fig. 2(a), AlB 2It had a type crystal structure. Also, as shown in Fig. 2(b), the crystal shape was a flat hexagonal column shape, and it was found that the average value of the thickness, which was the height direction of the hexagonal column shape, was about 40 nm. Fig. 3 is a view of the cross section of the sintered magnet produced in Comparative Example 2 observed by EPMA, and it can be seen that ZrB 2 crystals are segregated within the grain boundary triple points.

[0047]

Table 1

[0048]

Table 2

[0049] As shown in Table 2 and Figs. 1 to 3, magnets containing TiB 2 crystals in the main phase, within the two-particle grain boundary phase, and within the grain boundary triple points have both high H cj and rectangularity and can be applied to various uses as high-performance magnets.

Claims

【Claim 1】 12 to 17 atomic % of R (R is at least one or more selected from rare earth elements), 0.1 to 3 atomic % of M1 (M1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi), 0.05 to 1 atomic % of M2 (M2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and Ti is essential), 4.8 to 6.5 atomic % of B, carbon of 1.5 atomic % or less, oxygen of 1.5 atomic % or less, nitrogen of 0.5 atomic % or less, and the balance T (T is one or more elements selected from iron group elements), and R 2 T 14 A rare earth sintered magnet including B main phase crystal particles, a two-particle grain boundary phase formed between adjacent main phase crystal particles, and a grain boundary triple point surrounded by three or more main phase crystal particles, wherein any of the inside of the main phase crystal particles, the inside of the two-particle grain boundary phase, and the inside of the grain boundary triple point contains TiB 2 crystals, characterized by the rare earth sintered magnet. Claim 2 The above-mentioned TiB 2 crystals are AlB 2 The rare earth sintered magnet according to claim 1, which has a type crystal structure. Claim 3 The above-mentioned TiB 2 The rare earth sintered magnet according to claim 1, wherein the shape of the crystal is a flat hexagonal column shape, and the average value of the thickness in the height direction of the hexagonal column shape is 10 to 60 nm. Claim 4 The rare earth sintered magnet according to claim 1, wherein M2 contains Ti of 0.05 atomic % or more and Zr of 0.05 atomic % or more. Claim 5 The rare earth sintered magnet according to claim 1, wherein 10 to 90% by volume of the total grain boundary phase composed of the two-particle grain boundaries and the grain boundary triple points is the R6T13M1 phase. Claim 6 The rare earth sintered magnet according to claim 1, wherein the average crystal grain size, which is the average value of the equivalent circle diameters calculated from the cross-sectional areas of the main phase crystal grains, is 4 μm or less. Claim 7 The rare earth sintered magnet according to claim 1, wherein the total content of Dy, Tb, and Ho is 0 to 5.0 atomic %. Claim 8 A method for manufacturing the rare earth sintered magnet according to claim 1, comprising: a casting step of casting a molten alloy having a predetermined composition to obtain a raw material alloy; a pulverizing step of pulverizing the raw material alloy to prepare alloy fine powder; a molding step of powder compacting the alloy fine powder under the application of a magnetic field to obtain a molded body; and a heat treatment step of heat treating the molded body to obtain a sintered body. The casting step is a step of heating the molten alloy to 1480 to 1600 °C and then cooling it while controlling the average cooling rate to 500 °C to be 100 to 1200 °C / second, and the heat treatment step includes a sintering step of holding the molded body in a temperature range of 950 °C to 1200 °C for 0.5 to 20 hours. A method for manufacturing a rare earth sintered magnet, characterized by this.

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