JP4702522B2 - R-T-B system sintered magnet and manufacturing method thereof - Google Patents

Description

  The present invention relates to an R-T-B sintered magnet (where R is one or more rare earth elements, T is two or more transition metal elements essentially including Fe and Co, and a method for producing the same) In particular, the present invention relates to a technique for controlling the presence position of contained Co.

R-T-B based sintered magnets are made of various materials today because they are made of resource-rich and inexpensive materials and have high magnetic properties compared to Sm-Co based sintered magnets. Used in the field.
In order to improve the temperature characteristics of the RTB-based sintered magnet, it is known to add Co. That is, in the RTB-based sintered magnet, the Curie temperature of the main phase can be improved by substituting part of Fe in the main phase having the Nd ₂ Fe ₁₄ B type crystal structure with Co. . It is also known that the corrosion resistance is improved by replacing part of Fe in the main phase with Co.

However, when the amount of Co added is excessive, the coercive force (HcJ) decreases. According to Japanese Unexamined Patent Publication No. 2002-190404 (Patent Document 1), Co exists in the grain boundary phase in addition to the main phase, and forms an NdCo ₂ compound in the grain boundary phase. Since the NdCo ₂ compound is a ferromagnetic material, it becomes a factor for reducing the coercive force (HcJ) of the RTB-based sintered magnet. Therefore, if the amount of Co is simply increased, the coercive force (HcJ) of the RTB-based sintered magnet is greatly reduced due to the increase in the NdCo ₂ compound.

Therefore, Patent Document 1 provides an RTB-based sintered magnet that exhibits excellent magnetic properties by efficiently incorporating added Co into the main phase. This RTB-based sintered magnet reduces the Co concentration in the grain boundary phase by adding one or more elements of Y, La and Sc having the property of concentrating in the grain boundary phase. Therefore, the formation of the NdCo ₂ compound that is a ferromagnetic substance is suppressed in the grain boundary phase. An Nd ₃ Co compound is produced instead of the NdCo ₂ compound. Patent Document 1 states that this Nd ₃ Co compound is a non-magnetic material and therefore does not cause a decrease in coercive force (HcJ).

JP 2002-190404 A

According to Patent Document 1, the generation of the NdCo ₂ compound, which is a ferromagnetic substance, is suppressed in the grain boundary phase, and the added Co can be efficiently taken into the main phase. However, as is clear from the presence of Co consumed by the Nd ₃ Co compound, which is a nonmagnetic material, Co diffusion still occurs in the grain boundary phase. That is, Patent Document 1 leaves room for efficiently incorporating the added Co into the main phase.
The present invention has been made based on such a technical problem, and an object thereof is to provide an RTB-based sintered magnet in which the added Co is present substantially only in the main phase. Moreover, an object of this invention is to provide the manufacturing method of such a RTB type sintered magnet.

  In order to obtain an RTB-based sintered magnet in which the added Co is substantially present only in the main phase, the present invention employs a mixing method. The mixing method is a method of manufacturing an RTB-based sintered magnet using an alloy for forming a main phase and an alloy for forming a grain boundary phase, and the present invention uses Co as an alloy for forming the main phase. Supply. However, even if the method of supplying Co from the alloy for forming the main phase is adopted, it is difficult to completely prevent Co from diffusing into the grain boundary phase during sintering. Therefore, the diffusion of Co from the main phase to the grain boundary phase is prevented by controlling the sintering conditions. As control of the sintering conditions, the sintering is allowed to proceed to some extent at a temperature lower than the conventional sintering temperature. Sintering at this low temperature can prevent the diffusion of Co from the main phase to the grain boundary phase. Thereafter, sintering is performed at a temperature similar to that of the prior art. Sintering at a temperature similar to the conventional temperature is completed in a short time in order to prevent diffusion of Co into the grain boundary phase.

The RTB-based sintered magnet of the present invention based on the above is an R ₂ T ₁₄ B compound (where R is one or more rare earth elements, and T is a transition metal element in which Fe and Co are essential). a main phase consisting of two or more) of a sintered body having a grain boundary phase, Co is substantially free or are only in the main phase in the sintered, sintered, R: 25 -35 wt%, B: 0.5-4 wt%, one or two of Al and Cu are 0.02-0.6 wt%, one or more of Zr, Nb, and Hf are 0.02-1 0.5 wt%, one or two of Bi and Ga being 0.01 to 0.2 wt%, Co: 0.5 to 5 wt%, and the balance being substantially Fe .

The above-described RTB-based sintered magnet according to the present invention includes a main phase forming alloy powder for forming a main phase and a grain boundary phase forming alloy powder for forming a grain boundary phase. A step of producing a body, and holding the molded body at a first stable temperature of 800 to 1000 ° C. (but not including 1000 ° C.) for a predetermined time, and then holding the molded body at a second stable temperature of 1000 to 1100 ° C. for a predetermined time. by a step of sintering comprises, Co and can be obtained by the method for producing the R-T-B-based sintered magnet for supplying an alloy powder for the principal phase formation. This RTB-based sintered magnet is an R ₂ T ₁₄ B compound (where R is one or more rare earth elements, and T is two or more transition metal elements in which Fe and Co are essential). a main phase consisting of a sintered body which example Bei a grain boundary phase, Co is substantially included only in the main phase in the sintered, sintered, R: 25~35wt%, B: 0.5 to 4 wt%, one or two of Al and Cu are 0.02 to 0.6 wt%, one or more of Zr, Nb and Hf are 0.02 to 1.5 wt%, Bi and One or two types of Ga have a composition of 0.01 to 0.2 wt%, Co: 0.5 to 5 wt%, and the balance substantially consisting of Fe.
The sum of the holding time of the first stable temperature and the holding time of the second stable time is preferably 1 to 12 hours, and the holding time of the first stable temperature is preferably 1 to 8 hours. This is to prevent diffusion of Co into the grain boundary phase.

  As described above, according to the present invention, it is possible to provide an RTB-based sintered magnet in which the added Co exists substantially only in the main phase. This RTB-based sintered magnet can exhibit excellent magnetic properties by efficiently making Co present in the main phase.

The RTB-based sintered magnet of the present invention will be described in detail.
The RTB-based sintered magnet of the present invention has a main phase composed of an R ₂ T ₁₄ B compound. This main phase contains Co. The RTB-based sintered magnet of the present invention includes a grain boundary phase in addition to the main phase. The grain boundary phase in the present invention does not substantially contain Co. In addition, since the grain boundary phase of the present invention does not substantially contain Co, it does not contain NdCo ₂ compound as well as Nd ₃ Co compound. This grain boundary phase is composed of R and Fe, and contains more R than the main phase.

  R in the present invention has a concept including Y, and one or two selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu and Y More than a seed element. Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as R is Nd. Further, the inclusion of heavy rare earth elements, particularly Dy and Tb, is effective in improving the coercive force because it increases the anisotropic magnetic field of the main phase. Therefore, it is desirable that R in the main phase includes Dy and / or Tb in addition to Nd. Here, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y can be listed as heavy rare earth elements.

T in the R ₂ T ₁₄ B compound constituting the main phase is Fe and Co. That is, the RTB-based sintered magnet of the present invention uses Co as an essential element. By substituting a part of Fe with Co, various benefits such as improvement of temperature characteristics and improvement of corrosion resistance due to the Curie temperature increase of the R ₂ T ₁₄ B compound can be obtained. Therefore, efficiently incorporating Co into the main phase is important for improving the characteristics of the RTB-based sintered magnet.

Next, a preferable chemical composition of the RTB-based sintered magnet of the present invention will be described. This chemical composition is that of the main phase and the whole grain boundary phase.
R-T-B based sintered magnet of the present invention, 25~35wt% including the R. When the amount of R is less than 25 wt%, the generation of R ₂ T ₁₄ B crystal grains that are the main phase of the R-T-B sintered magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. On the other hand, when the amount of R exceeds 35 wt%, the volume ratio of R ₂ T ₁₄ B crystal grains constituting the main phase is lowered, and the residual magnetic flux density is lowered. On the other hand, when the amount of R exceeds 35 wt%, R reacts with oxygen, and the amount of oxygen contained increases, and as a result, the R-rich phase effective for the generation of coercive force decreases and the coercive force decreases. Therefore, the amount of R is set to 25 to 35 wt%. A desirable amount of R is 26 to 33 wt%, and a more desirable amount of R is 27 to 32 wt%.

  When Dy and / or Tb is included as R, the sum of Dy and / or Tb and other R is set to 25 to 35 wt%. And in this range, it is preferable that the quantity of Dy and / or Tb shall be 0.1-8 wt%. The amount of Dy and / or Tb is desirably determined within the above range depending on which of the residual magnetic flux density and the coercive force is important. That is, when it is desired to obtain a high residual magnetic flux density, the amount of Dy and / or Tb is set to 0.1 to 3.5 wt%. When a high coercive force is desired to be obtained, the amount of Dy and / or Tb is set to 3.5. It is desirable to set it to -8 wt%.

  The RTB-based sintered magnet of the present invention contains 0.5 to 4 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4 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%.

R-T-B based sintered magnet of the present invention is an essential element of Co, the amount shall be the 0.5 to 5 wt%. Co is effective in improving the Curie temperature and the corrosion resistance. In order to obtain this effect, it is preferably 0.5 wt% or more. Moreover, it has the effect that the aging treatment temperature range from which a high coercive force is obtained is expanded by adding together with Cu. However, excessive addition causes a decrease in coercive force and increases the cost, so the upper limit is made 5 wt%. The desirable Co content is 0.5-3 wt%, and the more desirable Co content is 0.8-2.5 wt%. As described above, the location of Co is specified in the present invention.

R-T-B based sintered magnet of the present invention, one or two of Al and Cu you contain in the range of 0.02~0.6wt%. By including 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 RTB-based sintered magnet. In the case of adding Al, a desirable amount of Al is 0.03 to 0.3 wt%, and a more desirable amount of Al is 0.05 to 0.25 wt%. When Cu is added, the amount of Cu is 0.3 wt% or less (excluding 0), desirably 0.2 wt% or less (excluding 0), and the more desirable amount of Cu is 0 0.03 to 0.15 wt%. One or two kinds of Al and Cu do not adversely affect the effect of the present invention even if they are contained in either the main phase or the grain boundary phase.

R-T-B based sintered magnet of the present invention, Zr, you containing 0.02～1.5Wt% of one or more of Nb and Hf. When reducing the oxygen content in order to improve the magnetic properties of the RTB-based sintered magnet, Zr, Nb and Hf exhibit the effect of suppressing abnormal growth of crystal grains during the sintering process, Make the structure of the sintered body uniform and fine. Therefore, Zr, Nb, and Hf have a remarkable effect when the amount of oxygen is low. A desirable amount of one or more of Zr, Nb and Hf is 0.05 to 1.3 wt%, and a more desirable amount is 0.08 to 1 wt%. One or more of Zr, Nb, and Hf do not adversely affect the effects of the present invention even if they are contained in either the main phase or the grain boundary phase, but are preferably present in the grain boundary phase. .

The RTB-based sintered magnet of the present invention allows the inclusion of other elements. For example, in order to improve the coercive force, one or two of Bi and Ga are set to 0 . It contains in the range of 01~0.2wt%. A more preferable range of one or two of Bi and Ga is 0.03 to 0.15 wt%, and a more preferable range is 0.05 to 0.12 wt%. Even if Bi and Ga are contained in either the main phase or the grain boundary phase, they do not adversely affect the effects of the present invention.

Next, the manufacturing method of the RTB system sintered magnet of this invention is demonstrated.
The RTB-based sintered magnet of the present invention can be manufactured by a mixing method. The present invention uses a main phase forming alloy and a grain boundary phase forming alloy. A method of manufacturing an RTB-based sintered magnet using two types (or two or more types) of alloys having different compositions in this way is called a mixing method. The mixing method has an advantage that a structure ideal or close to that for an RTB-based sintered magnet can be obtained.

The main phase forming alloy contains R, Fe, Co, and B as basic constituent elements. The main phase forming alloy includes, in addition to the basic constituent elements, Ru is contained one or two of Cu and Al. Further, Zr, Ru is contained one or more of Nb and Hf. Moreover, the main phase forming alloy, contain one or two of Bi and Ga. Each element in the set configuration of the main phase forming alloy, R: 25~35wt%, B: 0.4~5wt%, 1 species of Al and Cu or two: 0.02~0.6wt%, Zr, One or more of Nb and Hf: 2 wt% or less (including 0), Co: 0.5 to 5 wt%, One or more of Bi and Ga: 0.2 wt% or less (provided that 0 the included) Ru der.

The grain boundary phase forming alloy contains R and Fe as basic constituent elements. The difference between the grain boundary phase forming alloy and the main phase forming alloy is that the main phase forming alloy contains Co and B as basic constituent elements, whereas the grain boundary phase forming alloy contains these two constituent elements. It is not included. This is because even if Co is contained in the grain boundary phase, the improvement of the temperature characteristics, which is the effect of adding Co, cannot be expected. Further, when Co is contained in the grain boundary phase, an NdCo ₂ compound that causes a decrease in magnetic properties, particularly coercive force, is generated, and the effect of Co addition cannot be enjoyed efficiently. This is because B is an element necessary for producing the R ₂ T ₁₄ B compound constituting the main phase, but is not necessary in the grain boundary phase. However, the present invention allows B to exist in the grain boundary phase. In that case, the grain boundary phase forming alloy may contain B.

  The grain boundary phase forming alloy can contain one or two of Cu and Al in addition to the basic constituent elements. In addition, the grain boundary phase forming alloy may contain one or more of Zr, Nb and Hf. Furthermore, the grain boundary phase forming alloy can contain one or two of Bi and Ga. The composition of the alloy for forming the grain boundary phase is not limited, but each element is R: 29 to 50 wt%, B: 0.5 wt% or less (including 0), one or two of Al and Cu: 0 .02 to 4 wt%, one or more of Zr, Nb and Hf: 5 wt% or less (including 0), one or two of Bi and Ga: 3 wt% or less (including 0) It is preferable that In addition, elements other than the basic constituent elements are arbitrarily added elements. In addition, a single grain boundary phase forming alloy is sufficient to produce the RTB-based sintered magnet of the present invention, but the main phase forming alloy may be composed of a plurality of alloys having different compositions. Good.

  In order to manufacture the RTB-based sintered magnet of the present invention, first, an alloy for forming a main phase and an alloy for forming a grain boundary phase are prepared. These alloys can be obtained by strip casting the raw metal in vacuum or in an inert gas, preferably in an Ar atmosphere. In the strip casting method, the molten metal is ejected onto the surface of a rotating roll to rapidly cool and solidify. By rapid solidification, the molten metal becomes a thin plate or a thin piece (scale). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 20 to 30 μm in the minor axis direction and a maximum of 300 μm in the major axis direction. The alloy produced by the strip casting method hardly produces α-Fe, and a refined crystal structure can be obtained. As a raw material metal to be used, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. It goes without saying that the main phase forming alloy and the grain boundary phase forming alloy can be obtained by a casting method other than strip casting.

After producing the main phase forming alloy and the grain boundary phase forming alloy, each of these master alloys is ground separately or together. Hereinafter, an example of the grinding process will be described.
It is desirable that the main phase forming alloy and the grain boundary phase forming alloy (hereinafter sometimes collectively referred to as a raw material alloy) be subjected to a hydrogen occlusion treatment to facilitate subsequent fine pulverization.
Hydrogen storage can be performed by exposing the raw material alloy to a hydrogen-containing atmosphere at room temperature. Since the hydrogen occlusion reaction is an exothermic reaction, means such as cooling the reaction vessel may be applied to prevent the amount of occluded hydrogen from decreasing as the temperature rises. In the raw material alloy stored with hydrogen, cracks occur, for example, along grain boundaries.

After the hydrogen storage is completed, a dehydrogenation process is performed in which the raw material alloy that has been subjected to hydrogen storage is heated and held. This treatment is performed for the purpose of reducing hydrogen as an impurity as a magnet. The temperature for heating and holding is 200 ° C. or higher, desirably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the alloy, etc., but is at least 30 minutes, preferably 1 hour or more. The dehydrogenation process is performed in a vacuum or Ar gas flow.
By going through the hydrogen storage and dehydrogenation processes described above, the raw material alloy is pulverized to a size of about several mm or less. The above pulverization step is sometimes referred to as coarse pulverization in order to distinguish it from the next pulverization step.

  The coarsely pulverized raw material alloy is then finely pulverized. The fine pulverization can be performed using an airflow pulverizer. The finely pulverized alloy preferably has an average particle size of about 1 to 10 μm, particularly about 2 to 7 μm. The raw material alloy that has been subjected to hydrogen storage and dehydrogenation is in a very high activity state. Therefore, it is required to prevent oxidation after dehydrogenation and before pulverization. When finely pulverizing with an airflow pulverizer, it is effective for preventing oxidation to reduce the amount of oxygen contained in the non-oxidizing gas used for pulverization.

  When the main phase forming alloy and the grain boundary phase forming alloy are separately pulverized in the pulverization process, the finely pulverized main phase forming alloy powder and the grain boundary phase forming alloy powder are mixed in, for example, a nitrogen atmosphere. To do. The mixing ratio of the alloy powder for forming the main phase and the alloy powder for forming the grain boundary phase may be about 80:20 to 97: 3 by weight. The same applies to the mixing ratio when the main phase forming alloy and the grain boundary phase forming alloy are pulverized together. By adding about 0.01 to 0.3 wt% of a grinding aid such as zinc stearate at the time of fine grinding, a fine powder with high orientation can be obtained during subsequent molding in a magnetic field.

  Next, the mixed fine powder is pressure-molded in a state where the crystal axis is oriented by applying a magnetic field. The forming in the magnetic field may be performed at a pressure of 50 to 170 MPa in a magnetic field of 900 to 1400 kA / m.

  After forming in a magnetic field, a compact made of a mixed powder of the main phase forming alloy powder and the grain boundary phase forming alloy powder is sintered in a vacuum or an inert gas atmosphere. The present invention is characterized by this sintering. Sintering is performed by holding at a predetermined temperature (stable temperature) for a predetermined time, and usually, sintering is performed by holding at one stable temperature for a predetermined time. The present invention is characterized in that sintering having a two-stage stable temperature is performed in which a predetermined time is held at the first stable temperature and then held for a predetermined time at a second stable temperature higher than the first stable temperature. have.

  In the present invention, the two-stage stable temperature is employed for the following reason. That is, R-T-B based sintered magnets were generally sintered at a stable temperature of 1000 to 1100 ° C., but when sintered at this temperature, Co from the main phase to the grain boundary phase Some diffusion will occur. Therefore, in the present invention, in order to avoid the diffusion of Co, the sintering is performed at a temperature lower than the general stable temperature, that is, the first stable temperature. However, since a dense sintered body cannot be obtained only by sintering at the first stable temperature, sintering is also performed at a general stable temperature, that is, the second stable temperature. However, if the holding time at the second stable temperature is increased, diffusion of Co into the grain boundary phase occurs, so the holding time at the second stable temperature is changed to the holding time at the first stable temperature. By making the length shorter, the diffusion of Co into the grain boundary phase is suppressed while obtaining a dense sintered body.

The first stable temperature is determined from the above viewpoint, and is set to 800 to 1000 ° C. (however, 1000 ° C. is not included). If it is less than 800 ° C, the progress of the sintering is not sufficient, and if it exceeds 1000 ° C, there is a concern about diffusion of Co. A preferable first stable temperature is 850 to 980 ° C., and a more preferable first stable temperature is 900 to 970 ° C.
The second stable temperature is 1000 to 1100 ° C. When the temperature is lower than 1000 ° C., it is difficult to obtain a dense sintered body. When the temperature exceeds 1100 ° C., the crystal grains become coarse and the magnetic properties are deteriorated. A preferred second stable temperature is 1020 to 1080 ° C, and a more preferred stable temperature is 1030 to 1070 ° C.

The holding time at the first stable temperature (first holding time) and the holding time at the second stable temperature (hereinafter referred to as second holding time) are 1 to 12 hours in total. This total time is referred to herein as sintering time.
In the sintering time range, the first holding time is 1 to 8 hours. This is because sintering hardly proceeds when the first holding time is less than 1 hour, and a dense sintered body cannot be obtained unless the second holding time is increased. Further, even if the first holding time exceeds 8 hours, it cannot be expected that the sintering further proceeds. Therefore, in the present invention, the first holding time is 1 to 8 hours. The preferred first holding time is 1.5 to 6 hours.
The second holding time is a time obtained by subtracting the first holding time from the sintering time, but is set to a time shorter than at least the first holding time. This is to prevent the diffusion of Co. Among these, a preferable second holding time is 1 minute to 4 hours, and a more preferable second holding time is 1 minute to 3 hours.

  After sintering, the obtained sintered body can be subjected to an aging treatment. This aging treatment is an important process for controlling the coercive force. When the aging treatment is performed in two stages, for example, holding for a predetermined time at around 900 ° C. and around 500 ° C. is effective. When the heat treatment at around 900 ° 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 500 ° C., when the aging treatment is performed in one stage, the aging treatment at around 500 ° C. is preferably performed. The temperature of this aging treatment should be appropriately changed depending on the composition of the sintered object.

The present invention will be described based on specific examples.
Two types of alloys having the following composition (wt%) were produced by a strip casting method. Alloy A is the main phase forming alloy, and alloy B is the grain boundary phase forming alloy.
Alloy A: 20Nd-9.5Pr-2.5Dy-2Co-0.05Al-1B-bal. Fe
Alloy B: 33Nd-1Dy-2Cu-0.05Al-4Nb-2Ga-bal. Fe

  After blending Alloy A and Alloy B at 95: 5 (weight ratio), fine powder having an average particle size of 4.2 μm is obtained by coarse pulverization by hydrogen pulverization and fine pulverization by an airflow fine pulverizer (jet mill). It was. Prior to fine grinding, 0.1 wt% of zinc stearate was added as a grinding aid. Thereafter, molding was performed in a magnetic field with a transverse magnetic field molding machine (the pressurization direction and the magnetic field application direction were orthogonal) under the conditions of an orientation magnetic field strength of 1274 kA / m and a molding pressure of 100 MPa.

The obtained molded body was heated to 950 ° C. (first stable temperature) at a vacuum degree of about 66.5 Pa (5 × 10 ⁻¹ Torr) and held for 3 hours (first holding time). After holding at 950 ° C. for 3 hours, the temperature was raised to 1050 ° C. (second stable temperature) and held for 0.5 hour (second holding time). Then, it cooled to room temperature.

  The obtained sintered body was held at 900 ° C. for 1 hour in an argon atmosphere, and then a first aging treatment was performed to rapidly cool to room temperature. Next, a second aging treatment was performed in which heating was performed at 500 ° C. for 1 hour in an argon atmosphere and then rapidly cooled to room temperature.

Analysis of the composition (wt%) of the RTB-based sintered magnet (Example) obtained as described above revealed the following. The oxygen content (O), carbon content (C), and nitrogen content (N) contained were O = 5700 ppm, C = 700 ppm, and N = 80 ppm.
Composition: 20.3Nd-2.4Dy-9Pr-1.9Co-0.1Cu-0.05Al-0.16Nb-0.08Ga-1B-bal. Fe
Moreover, the residual magnetic flux density (Br), coercive force (HcJ, Hk), maximum energy product ((BH) max), and squareness ratio (Hk / HcJ) of the obtained RTB-based sintered magnet were obtained. . Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density (Br) in the second quadrant of the magnetic hysteresis loop. Furthermore, the density of the obtained RTB-based sintered magnet was determined. The results are shown in Table 1.

  The obtained RTB-based sintered magnet was subjected to element mapping by EPMA (Electron Probe Micro Analyzer). The result is shown in FIG. FIG. 1 also shows a reflected electron beam image of the region where element mapping has been performed. It can be seen from the elemental mapping and reflected electron beam image regarding Nd and Fe that the white region of the reflected electron beam image is the grain boundary phase. Further, Nd is rich in the grain boundary phase. It can be confirmed that Co is not substantially present in the grain boundary phase.

  An R-T-B system sintered magnet (comparative example) was prepared under the same conditions as in the above example except that alloy a and alloy b having the following composition (wt%) were used, and the magnetic properties and the like were measured. did. The results are shown in Table 1. Further, element mapping by EPMA was also performed on this RTB-based sintered magnet. The result is shown in FIG. FIG. 2 also shows a reflected electron beam image of the region where element mapping has been performed. It can be seen that the white region of the reflected electron beam image is the grain boundary phase. Although Co was present in the main phase, it was confirmed that it was also present in the grain boundary phase. In addition, the compounding composition of the alloy a and the alloy b corresponds with an Example.

Alloy a: 20Nd-9.5Pr-2.5Dy-0.05Al-1B-bal. Fe
Alloy b: 33Nd-1Dy-40Co-2Cu-0.05Al-4Nb-2Ga-bal. Fe

As shown in Table 1, it can be seen that the RTB-based sintered magnets according to the examples have better magnetic properties than the RTB-based sintered magnets according to the comparative examples.
From FIG. 1, the RTB-based sintered magnet according to the example cannot confirm the presence of Co in the grain boundary phase. That is, Co is substantially contained only in the main phase. From FIG. 2, the R-T-B sintered magnet according to the comparative example can confirm the presence of Co in the grain boundary phase. Thus, in the RTB-based sintered magnet according to the example, substantially all of the added Co is contained in the main phase, and since it has such a structure, as shown in Table 1. It is understood that high magnetic properties were obtained.

  Next, R- having a different Co content as in Example 1 except that the Co content of the alloy A (main phase forming alloy) and the Co content of the alloy b (grain boundary phase forming alloy) were changed. TB sintered magnets (Examples and Comparative Examples) were produced. The Co content was set to 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% and 8 wt% after sintering. The coercive force (HcJ) of the obtained RTB-based sintered magnet was determined. The results are shown in Table 2. The RTB-based sintered magnet obtained by adding Co to Alloy A (main phase forming alloy) and obtained by sintering according to the present invention has a coercive force due to Co addition. It can be seen that the decrease in (HcJ) is suppressed.

Two types of alloys having the following composition (wt%) were produced by a strip casting method. Alloy C is the main phase forming alloy, and alloy D is the grain boundary phase forming alloy.
Alloy C: 20Nd-9.5Pr-2.5Dy-2Co-0.05Al-1.6Zr-1B-bal. Fe
Alloy D: 33Nd-1Dy-2Cu-0.05Al-1Bi-bal. Fe

  After blending Alloy C and Alloy D at 95: 5 (weight ratio), fine powder having an average particle size of 4.2 μm is obtained by coarse pulverization by hydrogen pulverization and fine pulverization by an airflow fine pulverizer (jet mill). It was. Prior to fine grinding, 0.1 wt% of zinc stearate was added as a grinding aid. Thereafter, molding was performed in a magnetic field with a transverse magnetic field molding machine (the pressurization direction and the magnetic field application direction were orthogonal) under the conditions of an orientation magnetic field strength of 1274 kA / m and a molding pressure of 100 MPa. In order to obtain high magnetic properties, the atmosphere in each step from the collection of coarse pulverization to the sintering (put into the sintering furnace) was suppressed to an oxygen concentration of 100 ppm or less.

The obtained molded body was heated to 950 ° C. (first stable temperature) at a vacuum degree of about 66.5 Pa (5 × 10 ⁻¹ Torr) and held for 3 hours (first holding time). After holding at 950 ° C. for 3 hours, the temperature was raised to 1050 ° C. (second stable temperature) and held for 0.5 hour (second holding time). Then, it cooled to room temperature.

  The obtained sintered body was held at 900 ° C. for 1 hour in an argon atmosphere, and then a first aging treatment was performed to rapidly cool to room temperature. Next, a second aging treatment was performed in which heating was performed at 500 ° C. for 1 hour in an argon atmosphere and then rapidly cooled to room temperature.

Analysis of the composition (wt%) of the RTB-based sintered magnet (Example) obtained as described above revealed the following. The oxygen content (O), carbon content (C), and nitrogen content (N) contained were O = 560 ppm, C = 680 ppm, and N = 90 ppm.
Composition: 20.2Nd-2.5Dy-8.9Pr-1.9Co-0.1Cu-0.05Al-0.15Zr-0.05Bi-1B-bal. Fe
Moreover, the residual magnetic flux density (Br), coercive force (HcJ, Hk), maximum energy product ((BH) max), and squareness ratio (Hk / HcJ) of the obtained RTB-based sintered magnet were obtained. . Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density (Br) in the second quadrant of the magnetic hysteresis loop. Furthermore, the density of the obtained RTB-based sintered magnet was determined. The results are shown in Table 3.
Moreover, element mapping was performed by EPMA about the obtained RTB-based sintered magnet. As a result, it was confirmed that Co was not substantially present in the grain boundary phase.

An R-T-B system sintered magnet (comparative example) was produced under the same conditions as in the above example except that the alloy c and the alloy d having the following composition (wt%) were used, and the magnetic characteristics and the like were measured. did. The results are shown in Table 3. Moreover, when element mapping by EPMA was performed also about this RTB type sintered magnet, it was confirmed that Co was present in both the main phase and the grain boundary phase. In addition, the compounding composition of the alloy c and the alloy d corresponds with an Example.
Alloy c: 20Nd-9.5Pr-2.5Dy-0.05Al-1.6Zr-1B-bal. Fe
Alloy d: 33Nd-1Dy-40Co-2Cu-0.05Al-1Bi-bal. Fe

  As shown in Table 3, it can be seen that the RTB-based sintered magnets according to the examples have better magnetic properties than the RTB-based sintered magnets according to the comparative examples.

It is a figure which shows the observation result by EPMA of the sintered magnet by an Example. It is a figure which shows the observation result by EPMA of the sintered magnet by a comparative example.

Claims (3)

A main phase composed of an R ₂ T ₁₄ B compound (where R is one or more rare earth elements, T is two or more transition metal elements essential to Fe and Co), and a grain boundary phase Made of sintered body,
Co is free or is only in the main phase in substantially the sintered body,
The sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu, 0.02 to 0.6 wt%, one of Zr, Nb and Hf, or A composition comprising 0.02 to 1.5 wt% of two or more, 0.01 to 0.2 wt% of one or two of Bi and Ga, Co: 0.5 to 5 wt%, and the balance substantially consisting of Fe. An RTB-based sintered magnet comprising: A main phase composed of an R ₂ T ₁₄ B compound (where R is one or more rare earth elements and T is two or more transition metal elements essential for Fe and Co) and a grain boundary phase Made of a sintered body,
Co is substantially contained only in the main phase in the sintered body,
The sintered body is R: 25 to 35 wt%, B: 0.5 to 4 wt%, one or two of Al and Cu, 0.02 to 0.6 wt%, one of Zr, Nb and Hf, or A composition comprising 0.02 to 1.5 wt% of two or more, 0.01 to 0.2 wt% of one or two of Bi and Ga, Co: 0.5 to 5 wt%, and the balance substantially consisting of Fe. A method for producing an RTB-based sintered magnet having:
Producing a molded body including a main phase forming alloy powder for forming the main phase and a grain boundary phase forming alloy powder for forming the grain boundary phase;
A step of sintering the molded body by holding it at a first stable temperature of 800 to 1000 ° C. (but not including 1000 ° C.) for a predetermined time and then holding it at a second stable temperature of 1000 to 1100 ° C. for a predetermined time ; With
Co is supplied from the main phase forming alloy powder. A method for producing an RTB-based sintered magnet. Claim 2, wherein said first stable temperature retention time and total 12-hour retention time in the second stabilization time, and the retention time of the first stable temperature is 1-8 hours method for producing R-T-B based sintered magnet according to.

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