JP2007258455A - R-Fe-B SYSTEM RARE EARTH SINTERED MAGNET AND ITS METHOD FOR MANUFACTURING - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form efficiently also in the interior of an R-Fe-B system rare earth sintered magnet body, main phase crystal grain particles in which a heavy rare earth element RH is condensed in its contour and to improve the retentivity while suppressing the lowering of residual magnetic flux. <P>SOLUTION: The method for manufacturing an R-Fe-B system rare earth sintered magnet includes a process (A) which prepares at least one R-Fe-B system rare earth sintered magnet body having R<SB>2</SB>Fe<SB>14</SB>B type compound crystal grain particles containing light rare earth element RL (at least one kind of Nd and Pr) as a main rare earth element R as the main phase. After performing the process (A), a process (B) is performed which arranges a foil or powder containing heavy rare earth element RH (at least one kind selected from a group consisting of Dy, Ho, and Tb) in a treatment chamber together with the R-Fe-B system rare earth sintered magnet body, while being contacted to the R-Fe-B system rare earth sintered magnet body. Further, a process (C) is performed which, while supplying heavy rare earth element RH from the foil or the powder to the surface of the sintered magnet body by heating the sintered magnet body, makes it diffuse in the interior of the sintered magnet body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an R—Fe—B rare earth sintered magnet having R ₂ Fe ₁₄ B type compound crystal grains (R is a rare earth element) as a main phase and a method for producing the same, and in particular, to a light rare earth element RL (Nd and Pr). At least one selected from the group consisting of heavy rare earth elements RH (at least one selected from the group consisting of Dy, Ho, and Tb). The present invention relates to a R-Fe-B rare earth sintered magnet and a method for producing the same.

R-Fe-B rare earth sintered magnets with Nd ₂ Fe ₁₄ B type compound as the main phase are known as the most powerful magnets among permanent magnets, and are voice coil motors (VCM) for hard disk drives. In addition, it is used in various motors such as motors for mounting on hybrid vehicles, and home appliances. When R-Fe-B rare earth sintered magnets are used in various devices such as motors, they are required to have excellent heat resistance and high coercive force characteristics in order to cope with high temperature use environments.

As a means for improving the coercive force of an R—Fe—B rare earth sintered magnet, an alloy prepared by melting and melting heavy rare earth element RH as a raw material is used. According to this method, since the rare earth element R in the R ₂ Fe ₁₄ B phase containing the light rare earth element RL as the rare earth element R is replaced with the heavy rare earth element RH, the magnetocrystalline anisotropy of the R ₂ Fe ₁₄ B phase ( The essential physical quantity that determines the coercivity is improved. However, the magnetic moment of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is in the same direction as the magnetic moment of Fe, whereas the magnetic moment of the heavy rare earth element RH is opposite to the magnetic moment of Fe. Therefore, as the light rare earth element RL is replaced with the heavy rare earth element RH, the residual magnetic flux density Br decreases.

  On the other hand, since the heavy rare earth element RH is a rare resource, it is desired to reduce the amount of use thereof. For these reasons, the method of replacing the entire light rare earth element RL with the heavy rare earth element RH is not preferable.

By adding a relatively small amount of heavy rare earth element RH, the effect of improving the coercive force due to heavy rare earth element RH is exhibited, so that powders of alloys / compounds containing a lot of heavy rare earth element RH contain a lot of light rare earth element RL. It has been proposed to add it to the main phase mother alloy powder and form and sinter it. According to this method, since that would heavy rare-earth element RH is distributed more in the vicinity of grain boundaries of the R ₂ Fe ₁₄ B phase, efficiently magnetocrystalline anisotropy of the R ₂ Fe ₁₄ B phase in the main phase outer portion improves It becomes possible to make it. Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type (nucleation type), a large amount of heavy rare earth element RH is distributed in the main phase outer portion (near the grain boundary), so that the crystal The crystal magnetic anisotropy of the whole grain is increased and the nucleation of the reverse magnetic domain is hindered. Further, since the substitution with the heavy rare earth element RH does not occur at the center of the crystal grains that do not contribute to the improvement of the coercive force, it is possible to suppress the decrease in the residual magnetic flux density Br.

  However, when this method is actually carried out, the diffusion rate of the heavy rare earth element RH increases in the sintering process (executed at 1000 ° C. to 1200 ° C. on an industrial scale). As a result, it is difficult to obtain the expected structure.

  Further, as another means for improving the coercive force of the R—Fe—B rare earth sintered magnet, a metal, alloy, compound, or the like containing heavy rare earth element RH is deposited on the magnet surface at the stage of the sintered magnet, and then heat treated and diffused. Thus, it has been studied to recover or improve the coercive force without significantly reducing the residual magnetic flux density (Patent Document 1, Patent Document 2, and Patent Document 3).

  Patent Document 1 contains 1.0 atomic% to 50.0 atomic% of at least one of Ti, W, Pt, Au, Cr, Ni, Cu, Co, Al, Ta, and Ag, and the balance R ′ ( R ′ discloses that an alloy thin film layer made of Ce, La, Nd, Pr, Dy, Ho, and Tb is formed on the ground surface of the sintered magnet body.

  Patent Document 2 states that a metal element R (the R is a rare earth element selected from Y and Nd, Dy, Pr, Ho, and Tb) exceeds the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the small magnet. 1 type or two or more types) are diffused, thereby modifying the damaged part of the work and improving (BH) max.

  Patent Document 3 discloses that a chemical vapor deposition film mainly composed of rare earth elements is formed on the surface of a magnet having a thickness of 2 mm or less to recover the magnet characteristics.

Patent Document 4 discloses a rare earth element sorption method in order to recover the coercive force of an R—Fe—B micro sintered magnet or powder. In this method, a sorption metal (a rare earth metal having a relatively low boiling point such as Yb, Eu, Sm) is mixed with an R—Fe—B micro-sintered magnet or powder and then heated uniformly in a vacuum with stirring. A heat treatment is performed. By this heat treatment, the rare earth metal is deposited on the magnet surface and diffuses inside. In an embodiment in which a rare earth metal having a high boiling point (for example, Dy) is sorbed, Dy or the like is selectively heated to a high temperature by a high-frequency heating method. For example, Dy has a boiling point of 2560 ° C. and a boiling point of 1193 ° C. Since Yb is heated to 800 to 850 ° C., Dy is considered to be heated to a temperature exceeding at least 1000 ° C. Furthermore, it is described that it is preferable to keep the R—Fe—B based fine sintered magnet and powder at 700 to 850 ° C.
JP-A-62-192566 JP 2004-304038 A JP 2005-285859 A JP 2004-296773 A

  The conventional techniques disclosed in Patent Document 1, Patent Document 2 and Patent Document 3 are all intended to recover the surface of a sintered magnet that has been deteriorated by processing. Is limited to the vicinity of the surface of the sintered magnet. For this reason, the effect of improving the coercive force is hardly obtained with a magnet having a thickness of 3 mm or more.

  On the other hand, in the prior art disclosed in Patent Document 4, in the embodiment directed to a low-boiling-point rare earth metal such as Yb, the coercivity of individual R—Fe—B-based micromagnets certainly recovers. R-Fe-B magnet and sorption metal are fused during diffusion heat treatment, or it is difficult to separate them from each other after treatment, and unreacted sorption metal (RH) remains on the surface of the sintered magnet body. Virtually inevitable. This not only lowers the magnetic component ratio in the magnet compact and leads to a reduction in magnet properties, but rare earth metals are inherently very active and susceptible to oxidation, so unreacted sorbed metals are likely to be the starting point of corrosion in practical environments. It is not preferable. Moreover, since it is necessary to perform rotation for mixing and stirring and vacuum heat treatment at the same time, a special device incorporating a rotation mechanism is required while maintaining heat resistance and pressure (gas density). There is a problem in terms of stable quality manufacturing. In addition, when powder is used as the sorption raw material, it takes time for safety problems (ignition and harmfulness to human body) and the production process, which increases costs.

  Further, in the embodiment targeting high boiling point rare earth metal containing Dy, both the sorption raw material and the magnet are heated by high frequency, so that only the rare earth metal is heated to a sufficient temperature to keep the magnet at a low temperature. It is not easy, and the magnet is limited to a powder state that is difficult to be induction-heated or a very small magnet.

  In any of the methods disclosed in Patent Documents 1 to 4, a heavy rare earth element RH film (RH film) is formed on the surface of the sintered magnet body and then diffused into the sintered magnet body. In the process of growing the RH film on the sintered magnet body, a large amount of rare earth metal is deposited on portions other than the magnet inside the film forming apparatus (for example, the inner wall of the vacuum chamber). It is against resource saving.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to efficiently utilize a small amount of heavy rare earth element RH, and even if the magnet is relatively thick, the main phase crystal is formed over the entire magnet. An object of the present invention is to provide an R—Fe—B rare earth sintered magnet in which a heavy rare earth element RH is diffused in the outer portion of a grain.

The method for producing an R—Fe—B rare earth sintered magnet of the present invention mainly comprises R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R. Step (A) of preparing at least one R—Fe—B rare earth sintered magnet body having as a phase and heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) (B) arranging the foil or powder to be placed in a processing chamber together with the R-Fe-B rare earth sintered magnet body in a state where the foil or powder is in contact with the R-Fe-B rare earth sintered magnet body; While heating the powder and the R-Fe-B rare earth sintered magnet body, while supplying the heavy rare earth element RH from the foil or powder to the surface of the R-Fe-B rare earth sintered magnet body, Heavy rare earth element R A step (C) of diffusing H into the R-Fe-B rare earth sintered magnet body.

  In a preferred embodiment, the heating temperature of the foil or powder and the R—Fe—B rare earth sintered magnet body is set within a range of 700 ° C. or more and 1000 ° C. or less.

  In a preferred embodiment, the R-Fe-B rare earth sintered magnet body is plural, and the plurality of R-Fe-B rare earth sintered magnet bodies sandwich the foil or powder therebetween. Be placed.

  In a preferred embodiment, in the step (C), heat treatment is performed in a state where the processing chamber is filled with a vacuum or an inert atmosphere.

The R—Fe—B rare earth sintered magnet of the present invention has R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R as a main phase. An R—Fe—B rare earth sintered magnet comprising a plurality of laminated sintered magnet portions, each sintered magnet portion having a heavy rare earth element RH (Dy) introduced into the interior by grain boundary diffusion from the surface. , Ho, and Tb).

  In a preferred embodiment, a layer containing the heavy rare earth element RH exists at the boundary between the plurality of sintered magnet portions.

  In the present invention, the heavy rare earth element RH is supplied to a deep position inside the sintered magnet body by performing grain boundary diffusion of the heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb). In addition, the light rare earth element RL can be efficiently replaced with the heavy rare earth element RH in the main phase outer shell. As a result, the coercive force HcJ can be increased while suppressing a decrease in the residual magnetic flux density Br. Further, the heavy rare earth element RH can be diffused into the magnet body extremely efficiently without being wasted.

  The magnet produced by the method for producing an R—Fe—B rare earth sintered magnet of the present invention contains a heavy rare earth element RH introduced into the interior by grain boundary diffusion from the surface of the sintered magnet body. Here, the heavy rare earth element RH is at least one selected from the group consisting of Dy, Ho, and Tb.

  The R—Fe—B based rare earth sintered magnet of the present invention supplies heavy rare earth element RH to the surface of the sintered magnet body from a foil or powder of heavy rare earth element RH (hereinafter referred to as “RH diffusion source”). The heavy rare earth element RH is produced by diffusing from the surface to the inside of the sintered body. In the production method of the present invention, by heating a foil or powder of heavy rare earth element RH which is difficult to vaporize / sublimate to a rare earth sintered magnet body, heating it to an appropriate temperature (preferably 700 ° C. or more and 1000 ° C. or less). The heavy rare earth element RH can be efficiently diffused inside the magnet body.

  The temperature range from 700 ° C. to 1000 ° C. is a temperature at which the vaporization and sublimation of the heavy rare earth element RH hardly occurs, but is also a temperature at which the diffusion of the rare earth element in the R—Fe—B rare earth sintered magnet actively occurs. . When the RH diffusion source is heated to the above temperature in contact with the surface of the magnet body, grain boundary diffusion of the heavy rare earth element RH can proceed from the RH diffusion source to the inside of the magnet body through the surface of the magnet body.

  In the prior art, as described above, a heavy rare earth element RH film (RH film) is formed on the surface of the sintered magnet body and then diffused into the sintered magnet body. However, the RH film is formed on the sintered magnet body. In the process of growth, the deposition material supply source of the heavy rare earth element RH is consumed extremely inefficiently. For example, when an RH film is deposited on a sintered magnet body by a sputtering method, it is necessary to perform sputtering in a state where a target of the heavy rare earth element RH is disposed at a position facing the sintered magnet body. At this time, the heavy rare earth element RH sputtered from the target collides with a portion where the sintered magnet body does not exist in the sputtering apparatus and is deposited there. The same thing occurs when other thin film deposition techniques (such as vapor deposition) are used. That is, according to the conventional thin film deposition technique, there is a problem that a large amount (for example, 80 to 90%) of the heavy rare earth element RH is wasted in the process of depositing the thin film on the sintered magnet body. On the other hand, in the present invention, the heavy rare earth element RH is extremely efficiently diffused into the magnet body by performing heat treatment in a state where the foil or powder of the heavy rare earth element RH is in contact with the sintered magnet body. It becomes possible.

When foil is used as the RH supply source, the thickness of the foil is preferably in the range of 1 to 50 μm. If the thickness of the foil is less than 1 μm, the amount of heavy rare earth element RH (RH amount) diffusing inside the sintered magnet body may be insufficient, and the effect of improving the coercive force may be reduced. On the other hand, if the thickness of the foil exceeds 50 μm, an undiffused RH layer remains in the surface layer portion of the sintered magnet body, and the efficient use of the heavy rare earth element RH is hindered. Further, when all the heavy rare earth elements RH contained in the thick foil are diffused into the sintered magnet body, a large amount of heavy rare earth elements RH diffuses in the main phase R ₂ Fe ₁₄ B type crystal phase, and the magnetization There is also the possibility that the decline will be significant.

  When the sintered magnet body is plate-shaped, the foil size (planar size) is preferably matched to the area of the surface with which the foil contacts. However, since diffusion occurs three-dimensionally through the grain boundary phase, the heavy rare earth element RH can be diffused throughout the sintered magnet body even if the area of the region where the foil and the sintered magnet body are in contact is small. Is possible. Therefore, it is not necessary to cover the entire surface of the sintered magnet body with the foil. The contact area between the foil and the sintered magnet body may be a plurality of locations. However, it is preferable that the interval between the plurality of contact regions is smaller than the diffusion distance.

  According to the study of the present inventor, the heavy rare earth element RH has a low vapor pressure, is difficult to sublime in the heat treatment step (700 to 1000 ° C.) for diffusion, and can avoid wasteful consumption. In addition, if the surface of the sintered magnet body is brought into contact with the surface of the sintered magnet body in the state of foil or powder as in the present invention, the heavy rare earth element RH diffuses into the magnet body in a short time through the contact surface. As a result, useless sublimation and vaporization of the heavy rare earth element RH can be suppressed. In order to use the heavy rare earth element RH with higher efficiency, it is preferable to perform the heat treatment in a state where a foil or a powder is sandwiched between a plurality of sintered magnet bodies.

  The surface of the foil is preferably smooth, but may have irregularities. There may also be a plurality of holes in the foil. The number of foils brought into contact with one sintered magnet body is not limited to one, and a plurality of foils may be arranged at intervals on the same magnet body.

  The foil may be larger than the contact surface with the sintered magnet body and may protrude from the sintered magnet body. However, in order to reduce the amount of heavy rare earth element RH that is wasted without being used for diffusion by the above-described sublimation, the whole or most of the foil is in contact with the surface of the sintered magnet body. Is preferred.

  When powder is used as the RH supply source, it is preferable to form a powder layer having a thickness of about 1 to 50 μm by bringing the powder having a particle size of 1 to 50 μm into contact with the surface of the sintered magnet body for the same reason as the foil. . In order to increase the contact area with the sintered magnet body and promote diffusion, it is preferable that the individual powder particles have a flat shape. Moreover, in order to expand a contact area, you may press a foil or a powder layer with respect to a sintered magnet body with a pressing member from the outside. The pressing member is preferably made of a metal material such as Nb that hardly reacts with the sintered magnet body during heat treatment for diffusion, or is made of another sintered magnet body.

  As described above, heat treatment may be performed in a state where a foil or powder of heavy rare earth element RH is sandwiched between a plurality of sintered magnet bodies. A heavy rare earth element RH foil or powder sandwiched between adjacent sintered magnet bodies can ensure a sufficiently wide contact area with the magnet body by the pressure generated by its own weight when the sintered magnet bodies are stacked vertically. . On the other hand, when laminating in the horizontal direction, pressure may be applied to the magnet body from both sides.

  When sandwiching a foil or powder with a sintered magnet body, it is preferable to diffuse heavy rare earth elements RH from the exposed surface side of the sintered magnet body located at both ends of the laminated sintered magnet bodies. It is preferable that a foil or a powder of heavy rare earth element RH is also brought into contact with the exposed surfaces (both end surfaces) of the sintered magnet body. In order to sufficiently diffuse the heavy rare earth element RH foil and powder in contact with both end faces into the magnet body, the heavy rare earth element RH foil and powder were brought into contact with the exposed surface of the sintered magnet body. It is preferable to heat the product by wrapping it in a low-reactivity foil such as Nb. Since the heavy rare earth element RH hardly deposits on the surface of the foil such as Nb, it diffuses into the magnet body very efficiently.

  The heat treatment for diffusion may be performed by heating the entire atmosphere of the processing chamber in a state where the R—Fe—B rare earth sintered magnet body in contact with the foil or the powder is left in the processing chamber. Alternatively, the heavy rare earth element RH foil or powder and the sintered magnet body may be directly heated by high-frequency induction heating or the like.

  The heating temperature in the treatment chamber is preferably 700 ° C to 1000 ° C, and more preferably 850 ° C to 950 ° C. In this temperature range, the heavy rare earth element RH diffuses efficiently through the grain boundary phase of the sintered magnet body. During heat treatment, it is preferable to apply a load in order to expand the effective contact area and promote diffusion. The effect by this is remarkable in the case of a small laminated magnet of about 10 mm square. In the case of a laminated magnet larger and heavier than this size, a sufficiently large contact area can be obtained by its own weight.

  An inert atmosphere is preferable in the treatment chamber during the heat treatment. A vacuum or an Ar atmosphere may be used as long as it is an inert atmosphere. The degree of vacuum in the processing chamber does not greatly affect the diffusion amount of RH metal, that is, the degree of improvement in coercive force. When diffusing in the above temperature range, diffusing so as to contain heavy rare earth element RH at a ratio of 0.1% to 1% with respect to the weight of the sintered magnet body by heat treatment for about 30 to 180 minutes. Can do.

  After the heat treatment, the sintered magnet bodies are joined to each other via the RH foil that has not been consumed for diffusion and the RL layer concentrated at the interface by mutual diffusion. The joined magnet body can be used as a laminated magnet as it is, but may be further separated and processed into a plurality of magnet pieces having a desired shape and size.

  Since the laminated magnet thus produced has a rare earth metal layer (a layer containing heavy rare earth element RH and light rare earth element RL) at the interface, eddy currents that cross these interfaces are less likely to be generated, As a whole, heat generation due to eddy current is suppressed. For this reason, when it mounts and uses for a motor, it becomes possible to exhibit the outstanding magnet characteristic.

  In addition to the heavy rare earth element RH foil and powder layer, a metal foil such as Nb or a thin plate or powder of a material having a high electrical resistance such as a powder or oxide is interposed between the laminated sintered magnet bodies. Also good. Thereby, the eddy current suppression effect is further exhibited.

  According to the present invention, since it is not necessary to sputter or evaporate the RH supply source for film formation, the heavy rare earth element RH can be efficiently diffused into the magnet body, which is a valuable resource. This will greatly contribute to resource saving of the heavy rare earth element RH.

  Furthermore, since the loading efficiency within the same volume is high, the production efficiency is high. In addition, since it is not necessary to manufacture a large-scale apparatus and a general vacuum heat treatment furnace can be used, it is cost-effective and practical.

By the diffusion treatment in the present invention, a part of the light rare earth element RL contained in the R ₂ Fe ₁₄ B main phase crystal grains is replaced with the heavy rare earth element RH that has penetrated into the interior by grain boundary diffusion from the sintered body surface, and R A layer (thickness is, for example, 1 nm) in which the heavy rare earth element RH is relatively concentrated can be formed on the outer portion of the ₂ Fe ₁₄ B main phase.

Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type, when the magnetocrystalline anisotropy in the outer portion of the main phase is increased, the reverse magnetic domain in the vicinity of the grain boundary phase in the main phase is increased. As a result of suppressing the nucleation, the coercive force HcJ of the entire main phase is effectively improved. In the present invention, since the heavy rare earth substitution layer can be formed on the outer shell of the main phase not only in the area close to the surface of the sintered magnet body but also in the area deep from the magnet surface, And the coercive force HcJ of the whole magnet is sufficiently improved. Therefore, according to the present invention, the amount of consumed heavy rare earth element RH can be diffused and penetrated at least into the sintered body, and RH ₂ Fe ₁₄ B can be efficiently produced in the outer portion of the main phase. The coercive force HcJ can be improved while suppressing the decrease in the residual magnetic flux density Br.

The crystal magnetic anisotropy of Tb ₂ Fe ₁₄ B is higher than the crystal magnetic anisotropy of Dy ₂ Fe ₁₄ B, and is about three times as large as that of Nd ₂ Fe ₁₄ B. is doing. For this reason, Tb is more preferable than Dy as the heavy rare earth element RH to be replaced with the light rare earth element RL in the outer portion of the main phase.

  As is clear from the above description, in the present invention, it is not necessary to add the heavy rare earth element RH in the raw material alloy stage. That is, a known R—Fe—B rare earth sintered magnet containing a light rare earth element RL (at least one of Nd and Pr) as a rare earth element R is prepared, and heavy rare earth elements are diffused from the surface into the magnet. . When the conventional heavy rare earth layer is formed on the magnet surface, the heavy rare earth element RH is wasted at that stage, and thus it was difficult to efficiently diffuse the heavy rare earth element inside the magnet. According to the present invention, the heavy rare earth element RH can be efficiently used. Of course, the same effect can be obtained when the present invention is applied to an R—Fe—B based sintered magnet to which some heavy rare earth element RH is added in the raw material alloy stage.

  In addition, the “processing chamber” in the present invention includes a wide space in which the sintered magnet body and the RH supply source are arranged, and may mean a processing chamber of a heat treatment furnace. It may also mean a processing container to be accommodated.

  In the present invention, since the sintered magnet body and the RH supply source come into contact with each other and quickly diffuse, the vaporized RH metal is less likely to adhere to the wall surface in the sintered magnet body processing chamber. Further, if the wall surface in the processing chamber is made of a material that does not react with RH such as a heat-resistant alloy such as Nb or ceramic, the RH metal adhering to the wall surface is vaporized again and finally deposited on the surface of the sintered magnet body. . For this reason, useless consumption of the heavy rare earth element RH which is a valuable resource can be suppressed.

  Furthermore, since the RH supply source and the sintered magnet body are arranged in contact with each other, the amount of the sintered magnet body that can be mounted in the processing chamber having the same volume increases, and the loading efficiency is high. Moreover, since a large-scale apparatus is not required, a general vacuum heat treatment furnace can be used, and an increase in manufacturing cost can be avoided, which is practical.

  The inside of the treatment chamber during the heat treatment is preferably an inert atmosphere. The “inert atmosphere” in this specification includes a state filled with a vacuum or an inert gas. Further, the “inert gas” is a rare gas such as argon (Ar), for example, but if it is a gas that does not chemically react between the RH bulk body and the sintered magnet body, the “inert gas” is designated as “inert gas”. May be included. The pressure of the inert gas is reduced to show a value lower than the atmospheric pressure.

RH contained in the RH supply source diffuses in the grain boundary phase toward the inside of the magnet by using the difference in RH concentration at the magnet interface as a driving force. At this time, a part of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is replaced by the heavy rare earth element RH diffused and penetrated from the magnet surface. As a result, a layer enriched with heavy rare earth elements RH is formed in the outer portion of the R ₂ Fe ₁₄ B phase.

By forming such an RH enriched layer, the magnetocrystalline anisotropy of the main phase outline is increased, and the coercive force HcJ is improved. That is, by using a small amount of RH metal, the rare earth element RH is diffused and penetrated deep inside the magnet, and only the outer portion of the main phase is efficiently converted to RH ₂ Fe ₁₄ B, so that the residual magnetic flux density Br is reduced. It is possible to improve the coercive force HcJ over the entire magnet while suppressing it.

  According to the experiment, it was found that the light rare earth element RL diffuses from the inside of the sintered magnet body to the surface as the heavy rare earth element RH diffuses and penetrates, thereby forming an RL concentrated layer on the surface of the magnet body. For this reason, the total amount of rare earth elements inside the sintered magnet body (volume ratio of the main phase) hardly changes, and a decrease in residual magnetic flux density is suppressed.

As described above, since the R—Fe—B based sintered magnet has a coercive force generation mechanism by nucleation, the crystal magnetic anisotropy in the outer portion of the main phase is increased, so that the grains of the main phase are increased. Nucleation of reverse magnetic domains in the vicinity of the field phase is suppressed, and the coercive force HcJ is increased. Since the magnetocrystalline anisotropy of Tb ₂ Fe ₁₄ B is about three times the magnetocrystalline anisotropy of Nd ₂ Fe ₁₄ B, the coercivity is improved when Tb is used as the rare earth element RH rather than Dy. It is possible to increase the effect.

  Moreover, it is preferable to set the content of RH to diffuse in the range of 0.1% to 1.5% by weight ratio of the whole magnet. If it exceeds 1.5%, the decrease in the residual magnetic flux density Br may not be suppressed, and if it is less than 0.1%, the effect of improving the coercive force HcJ is insufficient. A diffusion amount of 0.1% to 1% can be achieved by heat treatment in the above temperature range for 30 to 180 minutes.

  The surface state of the sintered magnet is preferably closer to the metal state so that RH can easily diffuse and penetrate, and it is better to perform an activation treatment such as acid cleaning or blasting in advance. However, in the present invention, when the heavy rare earth element RH is vaporized and deposited on the surface of the sintered magnet body in an active state, it diffuses into the sintered magnet body at a faster rate than the formation of a solid layer. Go. For this reason, the surface of the sintered magnet body may be in a state in which oxidation after the cutting process is completed, for example.

  According to the present invention, since the heavy rare earth element RH can be diffused mainly through the grain boundary phase, the heavy rare earth element RH is efficiently diffused to a deeper position inside the magnet by adjusting the processing time. It is possible.

  The RH supply source may be a metal or an alloy as long as it contains at least one heavy rare earth element RH.

  According to the present invention, even for a thick magnet having a thickness of 3 mm or more, for example, a small amount of heavy rare earth element RH is used to increase both the residual magnetic flux density Br and the coercive force HcJ, and the magnetic characteristics deteriorate even at high temperatures. High performance magnets can be provided. Such a high-performance magnet greatly contributes to the realization of an ultra-small and high-power motor. The effect of the present invention using the grain boundary diffusion is particularly remarkable in a magnet having a thickness of 10 mm or less. Also, if a plurality of sintered magnet bodies are laminated with RH foil or the like sandwiched between them and heat treatment is performed, even if the overall thickness is increased to the same level as that of the block magnet, heavy rare earth elements RH are contained therein. An efficiently diffused magnet can be obtained.

  Hereinafter, a preferred embodiment of a method for producing an R—Fe—B rare earth sintered magnet according to the present invention will be described.

[Raw material alloy]
First, an alloy containing a light rare earth element RL of 25% by mass or more and 40% by mass or less, B (boron) of 0.6% by mass to 1.6% by mass, the remainder Fe and inevitable impurities is prepared. . A part of B may be substituted by C (carbon), and a part of Fe (50 atomic% or less) may be substituted by another transition metal element (for example, Co or Ni). This alloy is suitable for a variety of purposes, including Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and About 0.01 to 1.0% by mass of at least one additive element M selected from the group consisting of Bi may be contained.

  The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy by a strip casting method will be described.

  First, a raw material alloy having the above composition is melted by high frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after this molten metal is kept at about 1350 ° C., it is rapidly cooled by a single roll method to obtain a flaky alloy ingot having a thickness of about 0.3 mm, for example. The alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm, for example, before the next hydrogen pulverization. In addition, the manufacturing method of the raw material alloy by a strip cast method is disclosed by US Patent 5,383,978 specification, for example.

[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement process (hereinafter sometimes referred to as “hydrogen pulverization process”) is performed inside the hydrogen furnace. When the coarsely pulverized alloy powder after hydrogen pulverization is taken out from the hydrogen furnace, it is preferable to perform the take-out operation in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. This is because the coarsely pulverized powder is prevented from oxidizing and generating heat, and the magnetic properties of the magnet are improved.

  By the hydrogen pulverization, the rare earth alloy is pulverized to a size of about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After the hydrogen pulverization, the embrittled raw material alloy is preferably crushed more finely and cooled. In the case where the raw material is taken out in a relatively high temperature state, the cooling process time may be relatively long.

[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. Thus, a fine powder of about 0.1 to 20 μm (typically 3 to 5 μm) can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.

[Press molding]
In this embodiment, for example, 0.3 wt% of a lubricant is added to and mixed with the magnetic powder produced by the above method in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. Next, the magnetic powder produced by the above-described method is molded in an orientation magnetic field using a known press machine. The intensity of the applied magnetic field is, for example, 1.5 to 1.7 Tesla (T). The molding pressure is set so that the green density of the molded body is, for example, about 4 to 4.5 g / cm ³ .

[Sintering process]
With respect to said powder molded object, the process hold | maintained for 10 to 240 minutes at the temperature within the range of 650-1000 degreeC, and sintering further by the temperature (for example, 1000-1200 degreeC) higher than said holding temperature after that. It is preferable to sequentially perform the proceeding steps. During sintering, particularly when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Then, sintering progresses and a sintered magnet body is formed. After sintering, an aging treatment (500 to 1000 ° C.) is performed as necessary.

[Diffusion process]
Next, the rare earth element RH is efficiently diffused and infiltrated into the sintered magnet body thus manufactured to improve the coercive force HcJ. Specifically, a heavy rare earth element RH foil or powder is placed in the processing chamber in contact with the sintered magnet body, and the heavy rare earth element RH is supplied from the foil or powder to the surface of the sintered magnet body by heating. However, it is diffused inside the sintered magnet body.

  In the diffusion step in the present embodiment, it is preferable to set the temperature of the sintered magnet body within a range of 700 ° C. or higher and 1000 ° C. or lower. The diffusion process in this embodiment is not sensitive to the surface condition of the sintered magnet body, and a film made of Zn, Sn, or the like may be formed on the surface of the sintered magnet body before the diffusion process. This is because Zn and Sn are low melting point metals, and if they are in a small amount, they do not deteriorate the magnetic properties and do not hinder the diffusion described above. An element such as Zn or Sn is contained in a heavy rare earth element RH foil or powder, or a foil or powder such as Zn or Sn is overlapped with or mixed with a heavy rare earth element RH foil or powder. You can go.

  First, an ingot of an alloy blended so as to have a composition of Nd: 31.8, B: 0.97, Co: 0.92, Cu: 0.1, Al: 0.24, and the balance: Fe (% by mass) Was melted by a strip casting apparatus and solidified by cooling. Thus, alloy flakes having a thickness of 0.2 to 0.3 mm were produced.

  Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with a hydrogen gas atmosphere at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.

  After adding 0.05 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the hydrogen treatment described above and mixing, a pulverization step using a jet mill device is performed, so that the powder particle size is about 3 μm. Powder was produced.

  The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus and subjected to a sintering process at 1020 ° C. for 4 hours in a vacuum furnace. Thus, after producing a sintered body block having a 15 mm square cube shape, the sintered body block is mechanically processed to obtain a sintered magnet having a thickness (magnetization direction size) of 1 mm × length of 10 mm × width of 10 mm. Several bodies were made.

  These sintered magnet bodies were pickled with a 0.3% nitric acid aqueous solution, dried, and then placed in a processing vessel. At this time, Samples 1 to 6 were prepared with three sintered magnet bodies as one set and a Dy foil (manufactured by Niraco: Dy purity 99.9) sandwiched between them. In each sample 1-6, Dy foil shown in Table 1 below was sandwiched between sintered magnet bodies.

  FIGS. 1A to 1F schematically show the positional relationship between the sintered magnet body 1 and the Dy foil 2 for Samples 1 to 6, respectively. The left side of FIG. 1 shows a cross-sectional configuration, and the right side shows a planar configuration.

Samples 1 to 6 were heat-treated in a vacuum heat treatment furnace under the conditions of 900 ° C., 60 min, and 1.0 × 10 ⁻² Pa, and then subjected to aging treatment at 500 ° C., 60 min, and 2 Pa. Thereafter, magnet characteristics (residual magnetic flux density: Br, coercive force: HcJ) were measured using a BH tracer. The measurement results are shown in Table 2 below.

  FIGS. 2A and 2B are graphs showing the results of Table 2. FIG. Data on the left end of each graph (data described as “As” in the graph) indicates the magnet characteristics before Dy diffusion.

  As is clear from the above results, the coercive force HcJ was improved while suppressing a decrease in the residual magnetic flux density regardless of the shape and area ratio of the Dy foil.

  On the other hand, the diffusion state of Dy into the magnet body was evaluated by EPMA (EPM-1610 manufactured by Shimadzu Corporation). FIG. 3 is a photograph showing the analysis result of the sample 2 by cross-sectional EPMA. FIG. 3A is a diagram showing a partial cross-sectional configuration of sample 2, a SEM photograph, and a graph showing a Dy concentration distribution. FIG. 3B is a photograph showing the analysis result at the center of the uppermost surface of the sintered magnet body, and FIG. 3C shows the analysis result at a depth of about 200 μm from the uppermost surface of the sintered magnet body. It is a photograph. FIG. 4 is a photograph showing an analysis result by cross-sectional EPMA of sample 2, and FIG. 4 (a) is the same as FIG. 3 (a). FIG. 4B is a photograph showing the analysis result in the vicinity of the interface between the two sintered magnet bodies, and FIG. 4C is a photograph showing the analysis result in a depth of about 200 μm from the vicinity of the interface.

  It was confirmed that Dy diffused from the interface with the Dy foil into the magnet material by the heat treatment.

  According to the present invention, the heavy rare earth element RH can be efficiently diffused into the sintered magnet body without wasting wastefully, and the heavy rare earth element RH can be concentrated in the outer portion of the main phase crystal grains. A high-performance magnet having both a high residual magnetic flux density and a high coercive force can be provided.

(A)-(f) is a schematic diagram which shows the arrangement | positioning relationship between the sintered magnet body 1 and Dy foil 2, about the samples 1-6, respectively. It is a graph which shows the magnet characteristic obtained about samples 1-6 which are the examples of the present invention, (a) is a graph which shows residual magnetic flux density Br, and (b) is a graph which shows coercive force HcJ. It is a photograph which shows the cross-sectional EPMA analysis result obtained about the sample 2 which is an Example of this invention, (a) is a graph etc. which show Dy density | concentration profile of a depth direction, (b) is a sintered magnet. It is a photograph which shows the analysis result in the upper surface center part of a body, (c) is a photograph which shows the analysis result in the depth of about 200 micrometers from the upper surface of a sintered magnet body. It is the photograph which shows the cross-sectional EPMA analysis result obtained about the said sample 2, (a) is a graph etc. which show Dy density | concentration profile of a depth direction, (b) is the interface vicinity of two sintered magnet bodies (C) is a photograph which shows the analysis result in the depth of about 200 micrometers from the interface of a sintered magnet body.

Claims (6)

At least one R—Fe—B rare earth sintered magnet body having R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R as a main phase. Step (A) to be prepared,
The R-Fe-B rare earth sintered magnet body is contacted with a foil or powder containing a heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb). A step (B) of arranging in the processing chamber together with the Fe-B rare earth sintered magnet body;
By heating the foil or powder and the R-Fe-B rare earth sintered magnet body, the heavy rare earth element RH is supplied from the foil or powder to the surface of the R-Fe-B rare earth sintered magnet body. Meanwhile, the step (C) of diffusing the heavy rare earth element RH into the R-Fe-B rare earth sintered magnet body;
Method of R-Fe-B rare earth sintered magnet including   2. The R—Fe according to claim 1, wherein in the step (C), a heating temperature of the foil or powder and the R—Fe—B rare earth sintered magnet body is set in a range of 700 ° C. or more and 1000 ° C. or less. -Manufacturing method of B type rare earth sintered magnet.   The R-Fe-B rare earth sintered magnet body is plural, and the plurality of R-Fe-B rare earth sintered magnet bodies are arranged so as to sandwich the foil or powder therebetween. Item 2. A method for producing an R-Fe-B rare earth sintered magnet according to Item 1.   The said process (C) is a manufacturing method of the R-Fe-B type rare earth sintered magnet of Claim 1 which heat-processes in the state with which the said process chamber was satisfy | filled with the vacuum or the inert atmosphere. An R—Fe—B rare earth sintered magnet having R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R as a main phase,
It has a plurality of laminated sintered magnet parts,
Each sintered magnet portion contains an R—Fe—B system containing a heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) introduced into the interior by grain boundary diffusion from the surface. Rare earth sintered magnet.   6. The R—Fe—B based rare earth sintered magnet according to claim 5, wherein a layer containing the heavy rare earth element RH exists at a boundary portion between the plurality of sintered magnet portions.