JP4895027B2 - R-T-B sintered magnet and method for producing R-T-B sintered magnet - Google Patents

Description

  In the present invention, R-T-B (R is one or more selected from rare earth elements including Y (yttrium), and T is one or more transitions in which Fe or Fe and Co are essential. The present invention relates to a metal element, B is a boron) -based sintered magnet and a method for producing the same.

Among sintered magnets, RTB-based sintered magnets are used in various electrical equipment because they have excellent magnetic properties and Nd, which is the main component, is abundant and relatively inexpensive. Yes.
However, the RTB-based sintered magnet having excellent magnetic characteristics also has some technical problems to be solved. One of them is that since the thermal stability is low, the coercive force is greatly lowered with the temperature rise. For this reason, by adding heavy rare earth elements typified by Dy, Tb, and Ho, the coercive force at room temperature is increased, so that it can be maintained at a level that does not hinder the use even if the coercive force is lowered by the temperature rise. For example, it is proposed in Patent Document 1 (Japanese Patent Publication No. 5-10806).

The RTB-based sintered magnet is composed of a sintered body including at least main phase crystal grains made of an R ₂ T ₁₄ B compound and a grain boundary phase containing more R than the main phase. The proposal of the optimum concentration distribution of heavy rare earth elements in the main phase crystal grains having a large influence on the magnetic properties and the control method therefor are disclosed in Patent Document 2 (JP-A-7-122413) and Patent Document 3 (JP-A 2000-188213). No.).

Patent Document 2 describes a main phase mainly composed of an R ₂ T ₁₄ B compound (R is one or more rare earth elements, T is one or more transition metals), and an R-rich phase (R is In a sintered magnet whose main constituent phase is one or more of rare earth elements, it is proposed that heavy rare earth elements are distributed at a high concentration in at least three places in the R ₂ T ₁₄ B crystal grains. . The R-T-B system sintered magnet of Patent Document 2 is composed of an R-T-B alloy having an R ₂ T ₁₄ B compound as a main constituent phase and an RT eutectic containing at least one heavy rare earth element. An RT alloy having an area ratio of 50% or less is obtained by pulverizing and mixing, molding, and sintering. This R-T-B alloy preferably has an R ₂ T ₁₄ B compound as a main constituent phase, and has a composition of 27 wt% ≦ R ≦ 30 wt%, 1.0 wt% ≦ B ≦ 1.2 wt%, T: bal. It is recommended to do.

Patent Document 3 discloses a first R ₂ T ₁₄ B type main phase crystal grain having a heavy rare earth element concentration higher than that of the grain boundary phase, and a _second R ₂ T ₁₄ B type main phase crystal grain having a concentration lower than that of the grain boundary phase. It is disclosed that an RTB-based sintered magnet having a structure containing R ₂ T ₁₄ B type main phase crystal grains has a high residual magnetic flux density and a high maximum energy product.
In Patent Document 3, two or more types of RTB alloy powders having different contents of heavy rare earth elements such as Dy are mixed in order to obtain the above-described structure. In this case, the composition of each R-T-B alloy powder is such that the total amount of R elements is the same for each alloy powder. For example, in the case of Nd + Dy, one alloy powder is 29.0 wt% Nd + 1.0 wt% Dy (= 30.0 wt%), and the other alloy powder is 15.0 wt% Nd + 15.0 wt% Dy (= 30.0 wt%). To do. For elements other than the R element, the alloy powders are preferably substantially the same.

Japanese Patent Publication No. 5-10806 JP-A-7-122413 JP 2000-188213 A

The RTB-based sintered magnet according to Patent Document 2 has an obtained coercive force (iHc) of about 14 kOe, and further enhancement of the coercive force is desired.
The proposal disclosed in Patent Document 3 is an effective technique for improving the residual magnetic flux density and the maximum energy product of an R-T-B sintered magnet, but has a high residual magnetic flux density and coercive force. Difficult to do.
Since rare earth elements, particularly heavy rare earth elements, are scarce and expensive, it is required that the amount used for obtaining a predetermined effect be small. On the other hand, the appearance of higher-performance sintered magnets is always required. Therefore, an object of the present invention is to obtain an RTB-based sintered magnet having high magnetic properties while effectively utilizing heavy rare earth elements with little resources.

In order to improve the coercive force, the anisotropic magnetic field of the main phase crystal grains is required to be high. The anisotropic magnetic field varies depending on the selected rare earth element. Among the R ₂ T ₁₄ B compounds, the Tb ₂ T ₁₄ B compound in which Tb is selected as the heavy rare earth element exhibits the highest anisotropic magnetic field, and Dy is selected. The Dy ₂ T ₁₄ B compound exhibits the next highest anisotropic magnetic field. Therefore, considering only the coercive force, an RTB-based sintered magnet in which Tb is selected as the heavy rare earth element may be used. However, this RTB-based sintered magnet has the following problems. That is, the Tb ₂ T ₁₄ B compound has a low saturation magnetization, which is disadvantageous in terms of residual magnetic flux density. Tb is expensive. Therefore, in order to minimize the use of expensive Tb, Tb increases the concentration of the periphery of the main phase crystal grains. That is, the coercive force can be improved while suppressing a decrease in the residual magnetic flux density in the region by making Tb not present in the region surrounded by the peripheral edge or by making it small even if it exists. Furthermore, in order to minimize the use of expensive Tb, it is effective to use Dy together. The present invention is based on such knowledge, and R ₂ T ₁₄ B compound (R is one or more selected from rare earth elements including Y, T is essential for Fe, Fe and Co 1 R- containing main grains mainly containing Tb and Dy as heavy rare earth elements and at least one of Nd and Pr as light rare earth elements. It is a TB sintered magnet, and in the cross section of the crystal grain, Tb has a high concentration at the periphery in the crystal grain and is unevenly distributed at the periphery in the crystal grain, and Dy is substantially uniform in the crystal grain. In the region surrounded by the periphery in the crystal grains, Tb is an RTB -based sintered magnet characterized in that the concentration is lower than Dy . This R-T-B system sintered magnet has R: 25-37 wt%, B: 0.5-4.5 wt%, one or two of Al and Cu: 0.02-1.0 wt%, Co : 4 wt% or less, with the balance being Fe and inevitable impurities, Tb content 0.5-2.0 wt%, Dy content 0.3-5.5 wt%.

Also, in the R-T-B based sintered magnet of the present invention, Tb is allowed to be present in a region surrounded by the peripheral edge, so as to present only the periphery, that is unevenly distributed in the crystal grains Is most preferred. The peripheral region is preferably from the surface of the crystal grain to a depth of 3 to 40% of the diameter of the crystal grain, and the Tb concentration in the region surrounded by the peripheral part is preferably 0.1 wt% or less.
The amount of oxygen contained in the RTB-based sintered magnet of the present invention is preferably 2000 ppm or less.

The above-described RTB-based sintered magnet of the present invention can be manufactured by using a so-called mixing method. In this mixing method, an RTB alloy mainly composed of an R ₂ T ₁₄ B compound and an RT alloy mainly composed of R and T are separately prepared, mixed, molded, and sintered. Is the gist. Then, by supplying Tb from the RT alloy, it becomes possible to obtain crystal grains having a high Tb concentration at the periphery. That is, the present invention relates to an R ₂ T ₁₄ B compound (R is one or more selected from rare earth elements including Y, and T is one or more transition metals essentially including Fe, Fe, and Co). An R-T-B based sintered magnet mainly containing crystal grains containing at least one of Tb and Dy as heavy rare earth elements and Nd and Pr as light rare earth elements. A method for forming an RTB alloy powder mainly composed of an R ₂ T ₁₄ B compound and an RT alloy powder mainly composed of R and T in a magnetic field, and molding in a magnetic field And a step of sintering the molded body obtained in step Tb is supplied from the RT alloy powder, Dy is supplied from the RTB alloy powder, and Nd is selected as the light rare earth element. Nd is supplied only from the R-T-B alloy powder. To provide a method of manufacturing a R-T-B based sintered magnet, wherein Rukoto. Dy can also be supplied from an RT alloy powder .

  As described above, according to the present invention, the most effective Tb for improving the coercive force is obtained by increasing the concentration of the peripheral edge of the main phase crystal grains, thereby enjoying the effect of improving the coercive force with the minimum amount of Tb used. However, the region surrounded by the periphery can obtain a high residual magnetic flux density due to the low concentration of Tb. Therefore, it is possible to combine high coercive force and high residual magnetic flux density while effectively using expensive Tb.

The present invention will be described in detail and specifically below.
<Organization>
The RTB-based sintered magnet of the present invention is mainly composed of R ₂ T ₁₄ B compound and crystal grains containing Tb and Dy as heavy rare earth elements and Nd as light rare earth elements. And a sintered body including at least a grain boundary phase containing more R than the main phase.
The present invention is characterized by the distribution of Tb and Dy in the crystal grains constituting the main phase. That is, Tb has a high peripheral concentration in the main phase crystal grains, and Dy has a substantially uniform concentration in the crystal grains. This is referred to as a first form. In the present invention, whether or not the concentration of Dy is substantially uniform in the crystal grains is substantially uniform if the concentration difference is within 15%, as shown in an example described later. In the present invention, Tb may have a high peripheral edge concentration in the main phase crystal grains, and Dy may have a high peripheral edge concentration in the main phase crystal grains. This is referred to as a second form. Hereinafter, it demonstrates, referring drawings.
FIG. 1 schematically shows the concentration distribution of Tb and Dy in crystal grains in the first embodiment. The horizontal axis direction indicates the position of crystal grains, and the vertical axis direction indicates the concentration of Tb or Dy. In the first embodiment, as shown in FIG. 1, Tb has a high concentration at the periphery of the crystal grains, but is low in a region surrounded by the periphery (indicated as the inside in FIGS. 1 and 2).
The difference between the Tb concentration at the periphery and the Tb concentration in the region surrounded by the periphery is preferably as large as possible. Ideally, Tb exists only at the periphery of the crystal grain. When Tb is present at the periphery of the crystal grains in this way, the effect of improving the coercive force is easily exhibited. That is, the Tb ₂ Fe ₁₄ B compound has a higher anisotropic magnetic field than the R ₂ Fe ₁₄ B compound using other heavy rare earth elements including the Dy ₂ Fe ₁₄ B compound, and this Tb ₂ Fe ₁₄ B compound is mainly used. By being concentrated on the periphery of the phase crystal grains, the coercive force is efficiently improved with a minimum amount of Tb. On the other hand, since the saturation magnetization of Tb is lower than that of the Nd ₂ Fe ₁₄ B compound, if there is a large amount of Tb in the region surrounded by the periphery, the contribution to the coercive force is small and the residual magnetic flux density is reduced. It becomes a factor to make.

On the other hand, in the first embodiment, Dy has a substantially uniform concentration distribution within the crystal grains. Moreover, the concentration is lower than the concentration of Tb at the periphery. That is, the area surrounded by the periphery has low Tb and Dy concentrations. The concentration of R as a whole R ₂ T ₁₄ B compound is essentially uniform. Therefore, the concentration of the light rare earth element consisting of at least one of Nd and Pr is higher in the region surrounded by the periphery than in the periphery, and in the region surrounded by the periphery, the saturation magnetization is improved and the high residual magnetic flux is increased. Density can be obtained.

  In the above, Dy is assumed to be distributed substantially uniformly in the crystal grains. However, as shown in FIG. 2, Dy may have a higher peripheral density. The improvement in coercive force due to Dy can also be positively utilized. However, it is not ideal that Dy exists only at the periphery like Tb. This is because the coercive force is lowered in this way as shown in the examples described later.

  In the present invention, it is not necessary that all the crystal grains constituting the sintered body have the above-described structure, and the ratio of the crystal grains having the structure to the total number of crystal grains is 30% or more. That's fine. When the proportion of crystal grains having the structure is less than 30%, the effect of improving the coercive force is reduced. Preferably it is 60% or more, more preferably 80% or more.

  The peripheral region having a high Tb concentration is preferably from the crystal grain surface to a depth of 3 to 40% of the crystal grain diameter. When the region having a high Tb concentration is less than 3% with respect to the grain size of the crystal grains, a remarkable improvement in coercive force cannot be expected. On the other hand, when the region has a thickness exceeding 40% of the grain size of the main phase crystal grains, the region having a relatively low Tb is reduced, so that the residual magnetic flux density is lowered.

<Chemical composition>
Next, the desirable chemical composition of the RTB-based sintered magnet of the present invention will be described. The chemical composition here refers to the chemical composition after sintering.
The RTB-based sintered magnet of the present invention contains 25 to 37 wt% of rare earth element (R). Here, R in the present invention has a concept including Y (yttrium). Therefore, R is selected from one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. , Tb and Dy are necessarily included.
When the amount of R is less than 25 wt%, the R ₂ T ₁₄ B compound, which is the main phase of the R-T-B system sintered magnet, is not sufficiently produced, and α-Fe having soft magnetism is precipitated, resulting in coercive force. Is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A desirable amount of R is 28 to 35 wt%, and a more desirable amount of R is 29 to 33 wt%.

  Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as R is Nd. Since Pr also has a function equivalent to that of Nd, part or all of Nd can be replaced with Pr. On the other hand, the RTB-based sintered magnet of the present invention necessarily contains Tb and Dy as heavy rare earth elements in order to improve the coercive force. Here, the present invention allows heavy rare earth elements (Ho, Er, Tm, Yb and Lu) other than Tb and Dy to be contained.

Among rare earth elements, the Tb ₂ Fe ₁₄ B compound and the Dy ₂ Fe ₁₄ B compound have a high anisotropic magnetic field, which is effective for improving the coercive force of the RTB-based sintered magnet. In particular, a Tb ₂ Fe ₁₄ B compound containing Tb has the highest anisotropic magnetic field and is most preferable for improving the coercive force. However, since Tb is rare and expensive compared to Dy, it is preferable to reduce its content. The present invention meets this demand and realizes the above-described crystal grain structure by using not only Tb but also Dy. As a result, the coercive force and the residual magnetic flux density can be combined when the Tb content is 0.5 to 2.0 wt% and the Dy content is 0.3 to 5.5 wt%. The contents of Tb and Dy in consideration of cost are preferably Tb: 0.5 to 1.5 wt% and Dy: 0.3 to 4.5 wt%. When importance is attached to the coercive force, the content of Dy is preferably 2.5 to 5.5 wt%.

  The RTB-based sintered magnet of the present invention contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.

  The RTB-based sintered magnet of the present invention can contain one or two of Al and Cu in a range of 0.02 to 1.0 wt%. By containing one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained sintered magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.5 wt%, and the more desirable amount of Al is 0.05 to 0.35 wt%. Further, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.12 wt%.

  The RTB-based sintered magnet of the present invention contains Co of 4 wt% or less (excluding 0), preferably 0.1 to 2.0 wt%, and more preferably 0.3 to 1.0 wt%. can do. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

The RTB-based sintered magnet of the present invention allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is desirable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is desirably 5000 ppm or less, further 3000 ppm or less , and more preferably 2000 ppm or less . This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

<Manufacturing method>
The RTB-based sintered magnet of the present invention can be manufactured by mixing and using at least two kinds of raw material alloys having different alloy compositions. In this case, an R-T-B alloy mainly composed of an R ₂ T ₁₄ B phase and an RT alloy mainly composed of R and T are used. In the following, an example in which an RTB alloy and an RT alloy are used will be described. However, an embodiment in which RTB alloys having different compositions are mixed is not excluded.

In the present invention, in order to increase the concentration of Tb at the periphery of the crystal grains constituting the main phase, it is a basic requirement that the RT alloy contains Tb. Tb contained in the RT alloy diffuses to the periphery of the crystal grains (RTB alloy) during sintering. The RTB alloy does not contain Tb or has a lower concentration than the RT alloy even if it is contained. Dy is essential to be contained in the RTB alloy, but may be contained in the RT alloy. When Nd is selected as the light rare earth element, Nd is supplied only from the RTB alloy powder. When Pr is selected as the light rare earth element, Pr is supplied from the R-T-B alloy powder or supplied from the R-T-B alloy powder and the RT alloy powder.

Both the above R-T-B alloy and R-T alloy can be produced by strip casting or other known melting methods in a vacuum or an inert gas, preferably in an Ar atmosphere.
The RTB alloy can contain Cu and Al as constituent elements in addition to rare earth elements, Fe, Co and B. The chemical composition of the R-T-B alloy is appropriately determined according to the chemical composition of the R-T-B sintered magnet desired to be finally obtained, but preferably 25 to 40 wt% R-0.8 to 2 0.0 wt% B-0.03 to 0.3 wt% Al-bal. The composition range of Fe.

Also, the RT alloy can contain Cu and Al in addition to the rare earth element, Fe and Co. The chemical composition of the RT alloy is also appropriately determined according to the chemical composition of the RTB-based sintered magnet to be finally obtained. Preferably, it is preferably 26 to 70 wt% R-0.3 to 40 wt% Co. -0.03-5.0 wt% Cu-0.03-2.0 wt% Al-bal. The composition range of Fe.
In order to obtain the structure of the present invention described above, the RT alloy necessarily includes Tb, but Dy and other R may also be included. However, the rare earth element R contained in the RT alloy is preferably only Tb.

The raw alloy, R-T-B alloy and R-T alloy, are pulverized separately or together. The pulverization process is generally divided into a coarse pulverization process and a fine pulverization process.
First, in the coarse pulverization, the raw material alloy is pulverized until the particle diameter is about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after hydrogen storage / release treatment.
After the coarse pulverization process, the process proceeds to the fine pulverization process. The coarsely pulverized powder having a particle size of about several hundred μm is finely pulverized until the average particle size becomes 3 to 8 μm. A jet mill can be used for fine pulverization.

  When the raw material alloys are pulverized separately in the fine pulverization step, the finely pulverized raw material alloy powders are mixed in a nitrogen atmosphere. The mixing ratio of the raw material alloy powder can be selected from the range of 50:50 to 97: 3 by weight. The mixing ratio in the case of pulverizing two kinds of raw material alloys together is the same. By adding about 0.01 to 0.3 wt% of additives such as zinc stearate and oleic acid amide at the time of fine pulverization, the orientation during molding can be improved.

Next, the raw material alloy mixed powder is formed in a magnetic field. The molding in the magnetic field may be performed at a pressure of about 0.7 to 2.0 ton / cm ² (69 to 196 MPa) in a magnetic field of 12.0 to 17.0 kOe (955 to 1353 kA / m).
After molding in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of a particle size and a particle size distribution, what is necessary is just to sinter at 1000-1150 degreeC for about 1 to 5 hours.
After sintering, the obtained sintered body can be subjected to an aging treatment. This step is an important step in controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by the heat treatment at around 600 ° C., the aging treatment at around 600 ° C. is preferably performed when the aging treatment is performed in one stage.

The raw material alloys shown in Table 1 were produced by strip casting.
As shown in Table 1, the first embodiment contains Tb in the RT alloy and Dy and Nd in the RTB alloy, whereas the first comparative example contains Tb and Nd in R. In the -T-B alloy, Dy is contained in the RT alloy. In the second embodiment, Tb and Dy are contained in the RT alloy, and Dy and Nd are contained in the RTB alloy. On the other hand, in the 2-1 comparative example, Tb and Nd are contained in the R-T alloy. In the TB alloy, Dy is contained in the RT alloy. In the 2-2nd comparative example, Tb and Dy are contained in the RT alloy, and Nd is contained in the RTB alloy.

Each alloy was occluded with hydrogen at room temperature, and then subjected to hydrogen pulverization treatment in which an dehydrogenation treatment was performed at 600 ° C. for 1 hour in an Ar atmosphere. This experiment was performed in a low oxygen process in which the atmosphere from the recovery after hydrogen treatment to the introduction into the sintering furnace was suppressed to an oxygen concentration of less than 100 ppm in order to suppress the oxygen content of the sintered body to 2000 ppm or less.
0.1% oleic acid amide was added to the hydrogen pulverized powder as an additive, and pulverized by a jet mill using high-pressure nitrogen gas to produce a pulverized powder having an average particle diameter of 4 μm.
The finely pulverized powder made of the produced RTB alloy and the finely pulverized powder made of the RT alloy were blended at a ratio shown in Table 1 and mixed.
The obtained mixed powder was molded at a pressure of 1.5 ton / cm ² (147 MPa) in a magnetic field of 15 kOe (1200 kA / m) to obtain a molded body. The molded body was sintered at 1090 ° C. for 4 hours in a vacuum and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 600 ° C. × 1 hour (both in an Ar atmosphere).
About the obtained RTB system rare earth magnet, the residual magnetic flux density (Br) and the coercive force (HcJ) were measured with a BH tracer. Further, composition analysis was performed after the obtained sintering. The results are shown in Table 2.
The cross section of the obtained sintered body was subjected to element mapping using an EPMA (Electron Prove Micro Analyzer) in the range of 100 μm × 100 μm. Then, based on the EPMA mapping analysis results, the number of main phase crystal grains included in the observation field of 100 μm × 100 μm and the number of crystal grains in which Tb is unevenly distributed in the peripheral part are obtained, and the number of crystal grains in which Tb is unevenly distributed in the peripheral part is obtained. The number ratio was calculated.

The compositions of the sintered bodies of the first example and the first comparative example are the same except for Tb and Dy, and the total amounts of Tb and Dy are the same, but the first comparative example is the first. The amount of Tb is larger than that in one embodiment. Therefore, in view of the anisotropic magnetic fields and the amount of Tb of Tb ₂ Fe ₁₄ B and Dy ₂ Fe ₁₄ B, the first comparative example should have a higher coercive force (HcJ) than the first example. is there. However, the coercive force (HcJ) of the first example is higher.

FIG. 3 shows the results of element mapping observation by EPMA (Electron Prove Micro Analyzer) of the cross sections of the sintered bodies of the first example and the first comparative example.
As shown in FIG. 3, in the first embodiment, Dy has a constant density in crystal grains and a substantially uniform concentration. As a result of EPMA mapping, quantitative analysis was performed on the peripheral portion and the region surrounded by the peripheral portion. As a result, the Dy concentration in the peripheral portion was 2.3 wt%, and the Dy concentration in the region surrounded by the peripheral portion was 2.0 wt%. The change rate is 13%. If this change rate is within 15%, it can be said that the Dy concentration is substantially uniform. On the other hand, since Tb has a pale peripheral color in the crystal grain and a deep color in the region surrounded by the peripheral edge, about 80% of the crystal grains in which Tb is unevenly distributed exist in the peripheral part of the crystal grain. confirmed. In the case of the crystal grains, the Tb concentration in the peripheral portion was 1.0 wt%, and the Tb concentration in the region surrounded by the peripheral portion was 0.1 wt% or less (not detected). On the other hand, in the first comparative example, Tb is almost uniform in the crystal grains, but there are about 80% of the crystal grains in which Dy exists only at the periphery in the crystal grains. As described above, the Tb concentration at the periphery in the crystal grains increases the concentration of Tb that forms the Tb ₂ Fe ₁₄ B compound having a high anisotropic magnetic field, so that the first embodiment has a higher coercive force (HcJ ) Is obtained.

  In the second example, the 2-1 comparative example, and the 2-2 comparative example, a sintered body having the same composition as that of the first example is produced using different raw material alloys. The second example contains both Tb and Dy in the RT alloy, and also contains Dy in the RTB alloy. The 2-1 comparative example is similar to the first comparative example in that R- The TB alloy contains Tb and the RT alloy contains Dy. The 2-2 comparative example is different from the second embodiment in that Dy is not contained in the RTB alloy.

As shown in Table 2, the second example showed almost the same characteristics as the first example. The 2-1 comparative example has a lower coercive force (HcJ) than the first comparative example, but this is considered to be because the Tb amount is smaller in the 2-1 comparative example than in the first comparative example. The
The 2-2 comparative example was carried out by predicting that the most ideal crystal grain concentration distribution was obtained. However, contrary to this prediction, the R-T-B alloy does not contain Tb and Dy, so the residual magnetic flux density (Br) is high, but the diffusion of Tb and Dy becomes uneven, grain growth occurs, and the coercive force (HcJ) resulted in a decrease.

  FIG. 4 shows the result of element mapping observation by EPMA (Electron Probe Micro Analyzer) of the second embodiment. Similar to the first embodiment, Dy is also present in the crystal grains, but is present at a high concentration at the periphery, and the Tb concentration is high at the periphery of the crystal grains. As described above, in order to increase the concentration at the periphery in the crystal grains, it is most effective to include the element in the RT alloy and not include the element in the RTB alloy. .

The point of using the alloy shown in Table 3 is that the composition of the sintered body is 25.1 wt% Nd-1.0 wt% Tb-5.0 wt% Dy-0.2 wt% Al-1.0 wt% Co-0.2 wt. % Cu-1.0 wt% B-bal. A sintered body was produced in the same manner as in Example 1 except that it was Fe and the low oxygen process was not performed.
Here, as shown in Table 3, the third example includes Tb and Dy in the RT alloy and Dy in the RTB alloy, whereas the third comparative example has Tb and Dy. Dy is contained in the RTB alloy and Dy is contained in the RT alloy.
About the obtained sintered compact, it carried out similarly to Example 1, and performed the magnetic characteristic and the composition analysis of the sintered compact. The results are shown in Table 4.

As shown in Table 4, the compositions of the third example and the third comparative example are the same. And although both have the same residual magnetic flux density (Br), the coercive force (HcJ) is higher in the third embodiment.
In the same manner as in Example 1, element mapping observation by EPMA (Electron Prove Micro Analyzer) was performed on the third example and the third comparative example. As a result, in the third example, as in the second example, it was confirmed that Dy was almost uniform in the crystal grains, but Tb had about 80% of the particles existing only in the periphery of the crystal grains. . On the other hand, in the third comparative example, it was confirmed that Tb was almost uniform in the crystal grains, but Dy had about 80% of the crystal grains having a high peripheral density in the crystal grains.

The point of using the alloy shown in Table 5 is that the composition of the sintered body is 25.7 wt% Nd-2.0 wt% Tb-4.0 wt% Dy-0.2 wt% Al-2.0 wt% Co-0.1 wt. % Cu-0.1 wt% Ga-0.2 wt% Nb-1.0 wt% B-bal. A sintered body sample was produced in the same manner as in Example 2 except that it was Fe.
Here, as shown in Table 5, the fourth example contains Tb in the RT alloy and Dy in the RTB alloy, whereas the fourth comparative example contains Tb and Dy. In the RTB alloy, Dy is further contained in the RT alloy.
About the obtained sintered compact, it carried out similarly to Example 1, and performed the magnetic characteristic and the composition analysis of the sintered compact. The results are shown in Table 6.

As shown in Table 6, the compositions of the sintered bodies in the fourth example and the fourth comparative example are the same. And although both have the same residual magnetic flux density (Br), the coercive force (HcJ) is higher in the fourth embodiment.
In the same manner as in Example 1, element mapping observation by EPMA (Electron Prove Micro Analyzer) was performed on the fourth example and the fourth comparative example. As a result, in the fourth example, as in the second example, it was confirmed that Dy was almost uniform in the crystal grains, but Tb had about 80% of the grains existing only in the periphery of the crystal grains. . On the other hand, in the fourth comparative example, it was confirmed that Tb was almost uniform in the crystal grains, but Dy had about 80% of the crystal grains having a high peripheral density in the crystal grains.

  As described above, according to the present invention, a high coercive force (HcJ) and a high residual magnetic flux density (Br) can be provided even if the amount of Tb having a high anisotropic magnetic field is reduced as compared with Dy. This also means that a higher coercive force (HcJ) can be obtained if the amount of Tb is the same.

It is a figure which shows typically the structure of the crystal grain of the RTB type sintered magnet by this invention. It is a figure which shows typically the structure of the crystal grain of the other RTB system sintered magnet by this invention. It is a figure which shows the result of the element mapping observation by EPMA (Electron Probe Micro Analyzer) of the sintered compact cross section of 1st Example, and the sintered compact cross section of a 1st comparative example. It is a figure which shows the result of the element mapping observation by EPMA (Electron Probe Micro Analyzer) of the sintered compact cross section of 2nd Example.

Claims (5)

R ₂ T ₁₄ B compound (R is one or more selected from rare earth elements including Y, T is one or more transition metal elements essential for Fe, Fe and Co) ,And,
An RTB-based sintered magnet including, as a main phase, crystal grains containing at least one of Tb and Dy as heavy rare earth elements and Nd and Pr as light rare earth elements,
In the cross section of the crystal grain,
Tb has a high concentration at the periphery in the crystal grains and is unevenly distributed at the periphery in the crystal grains,
Dy is distributed substantially uniformly in the crystal grains,
In the region surrounded by the periphery in the crystal grain, Tb has a lower concentration than Dy,
The RTB-based sintered magnet includes R: 25-37 wt%, B: 0.5-4.5 wt%, one or two of Al and Cu: 0.02-1.0 wt%, Co : 4 wt% or less, the balance being Fe and inevitable impurities, Tb content is 0.5 to 2.0 wt%, Dy content is 0.3 to 5.5 wt% R-T-B system sintered magnet. The peripheral region is from the surface of the crystal grain to a depth of 3 to 40% of the diameter of the crystal grain, and the Tb concentration in the region surrounded by the peripheral part is 0.1 wt% or less. The RTB-based sintered magnet according to claim 1 , wherein the RTB-based sintered magnet is provided. 3. The RTB-based sintered magnet according to claim 1, wherein the amount of oxygen contained in the RTB-based sintered magnet is 2000 ppm or less. R ₂ T ₁₄ B compound (R is one or more selected from rare earth elements including Y, T is one or more transition metal elements essential for Fe, Fe and Co) ,And,
A method for producing an RTB-based sintered magnet comprising, as a main phase, crystal grains containing at least one of Tb and Dy as heavy rare earth elements and Nd and Pr as light rare earth elements,
Forming an RTB alloy powder mainly composed of an R ₂ T ₁₄ B compound and an RT alloy powder mainly composed of R and T in a magnetic field;
And sintering the molded body obtained by molding in the magnetic field,
Tb is supplied from the RT alloy powder,
Dy is supplied from the RTB alloy powder,
In the case where Nd is selected as the light rare earth element, Nd is supplied only from the R-T-B alloy powder. Dy is supplied also from the said RT alloy powder, The manufacturing method of the RTB type | system | group sintered magnet of Claim 4 characterized by the above-mentioned.

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