JP4677942B2 - Method for producing R-Fe-B rare earth sintered magnet - Google Patents

Description

The present invention relates to a method for producing 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 in particular, light rare earth elements RL (of Nd and Pr). At least one kind) as a main rare earth element R, and a part of the light rare earth element RL is substituted by a heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) The present invention relates to a method for producing an R—Fe—B rare earth sintered magnet.

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 outer periphery of the main phase It becomes possible to improve. 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 elements RH are distributed in the main phase shell (near the grain boundary). The crystal magnetic anisotropy of the entire crystal grains is increased, and the nucleation of the reverse magnetic domain is prevented. As a result, the coercive force is improved. 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 2 types or more) is diffused, thereby modifying the damaged part of work-affected damage 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 where 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, the boiling point of Dy is 2560 ° 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-described problems, and the object of the present invention is to efficiently utilize a small amount of heavy rare earth element RH, and to form heavy rare earth element RH in the outer shell portion of the main phase crystal grain. An object of the present invention is to provide a method for producing an R—Fe—B rare earth sintered magnet for diffusing.

  A method for producing an R—Fe—B based rare earth sintered magnet according to the present invention includes a plurality of R—Fe—B based rare earth sintered containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R. A plurality of R—Fe—B rare earth sintered magnet bodies containing at least one heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb). And preparing two R-Fe-B rare earth sintered magnet bodies having different concentrations of the heavy rare earth element RH among the plurality of R-Fe-B rare earth sintered magnet bodies. The step (B) of placing in the processing chamber in a heated state and heating the R—Fe—B rare earth sintered magnet body disposed in the processing chamber results in a relatively high concentration of heavy rare earth element RH. -Fe-B rare earth sintered magnet body Comprising a step (C) the concentration of RH Shigeru Luo rare-earth element to diffuse the heavy rare-earth element RH at a relatively low R-Fe-B rare earth sintered magnet body.

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

  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.

  In a preferred embodiment, among the plurality of R—Fe—B rare earth sintered magnets arranged in the processing chamber in the step (B), the R—Fe—B rare earth having the highest concentration of the heavy rare earth element RH. The sintered magnet body contains a heavy rare earth element RH of 5% by mass or more and 12% by mass or less.

  In the present invention, from the R—Fe—B rare earth sintered magnet having a relatively high concentration of the heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb), R-Fe-B rare earth sintered magnet having a relatively high concentration of heavy rare earth element RH by diffusing heavy rare earth element RH to an R-Fe-B rare earth sintered magnet having a relatively low concentration It is possible to efficiently improve the characteristics of the R—Fe—B based rare earth sintered magnet having a relatively low concentration of the heavy rare earth element RH by utilizing the excess heavy rare earth element RH contained in.

  In the R-Fe-B rare earth sintered magnet to which Dy is added at the stage of melting the raw material alloy, the inventor reduces the coercive force improvement effect when the Dy content is increased from about 5% by mass. Focused on that. The reason why the coercive force does not improve in accordance with the increase in Dy concentration is that not only the main phase outer shell part that causes the coercive force improvement effect but also the inside of the grain boundary phase where Dy added in a large amount does not contribute to the coercive force improvement. This is because it becomes present at a high concentration.

  In the present invention, excessively existing heavy rare earth element RH can be effectively utilized by the following method, and the coercive force can be effectively improved. The heavy rare earth element RH is at least one selected from the group consisting of Dy, Ho, and Tb.

  In the present invention, first, a plurality of R—Fe—B rare earth sintered magnets containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R, of which at least one is A step (A) of preparing a plurality of R—Fe—B rare earth sintered magnet bodies containing the heavy rare earth element RH is performed. The two R-Fe-B rare earth sintered magnet bodies having different concentrations of the heavy rare earth element RH among the plurality of R-Fe-B rare earth sintered magnet bodies are in contact with each other in the processing chamber. Step (B) of arranging is performed. Next, by heating the R—Fe—B rare earth sintered magnet body arranged in the processing chamber, the R—Fe—B rare earth sintered magnet body having a relatively high concentration of the heavy rare earth element RH is heated. A step (C) of diffusing the heavy rare earth element RH into the R—Fe—B rare earth sintered magnet body having a relatively low concentration of the rare earth element RH is performed.

  In the manufacturing method of the present invention, a process of depositing a metal layer of heavy rare earth element RH on the surface of the rare earth sintered magnet body is unnecessary, and the heavy rare earth element RH is consumed wastefully during such deposition process. Can solve the problem.

  Further, in the present invention, the heavy rare earth element RH that has not been used to replace the outer shell of the main phase is contained inside the R—Fe—B rare earth sintered magnet body containing the heavy rare earth element RH at a relatively high concentration. R-Fe-B rare earth sintered magnet body that is recycled efficiently and contains heavy rare earth element RH at a relatively low concentration, or R-Fe-B rare earth sintered magnet body that does not contain heavy rare earth element RH In order to increase the coercive force, it is possible to efficiently improve the magnet characteristics with a small amount of heavy rare earth element RH.

  In the R—Fe—B rare earth sintered magnet body containing the heavy rare earth element RH, a part of the heavy rare earth element RH is replaced with the light rare earth element RL in the outer shell of the main phase. The rare earth element RH exists in the grain boundary phase and the main phase and does not contribute to the improvement of the coercive force. Of the heavy rare earth elements RH that are not useful for improving the magnet properties, the heavy rare earth elements RH located in the grain boundary phase can be diffused into other R—Fe—B rare earth sintered magnet bodies by heat treatment. Thus, without degrading the characteristics of the sintered magnet body (relatively high rare earth element RH) serving as a diffusion source, other sintered magnet bodies (relatively low heavy rare earth element RH) can be used. The magnet characteristics can be effectively improved.

  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, it is possible to diffuse the heavy rare earth element RH extremely efficiently into the magnet body by performing the heat treatment in a state where the sintered magnet bodies are in contact with each other. .

  The R—Fe—B based sintered magnet body having a relatively high concentration of heavy rare earth element RH preferably contains 5 to 12% by mass of heavy rare earth element RH. On the other hand, the R—Fe—B based sintered magnet body having a relatively low concentration of heavy rare earth element RH contains heavy rare earth element RH at a low concentration of 5 mass% or less, or contains heavy rare earth element RH. It is preferable not to contain.

  A plurality of sintered magnet bodies having different concentrations of the heavy rare earth element RH may be laminated as they are, but in order to obtain various effects, a low melting point metal such as Al, Zn, Sn or the like is interposed between the magnet bodies. A foil may be sandwiched or a film of these metals may be formed on the surface of the magnet body. Among these metals, Al works favorably because it promotes the effect of improving the coercive force by the heavy rare earth element RH. The contact surface of the sintered magnet body preferably has high smoothness from the viewpoint of increasing the effective contact area. Moreover, it is preferable that there is no layer (thick oxide layer) that hinders diffusion on the contact surface of the sintered magnet body. For this reason, it is preferable to perform a pretreatment such as acid cleaning using nitric acid or the like on the surface of each magnet body before the stacked arrangement.

  The number of laminated sintered magnet bodies having different heavy rare earth element RH contents is not limited to two, and may be three or more. When laminating three or more layers of sintered magnet bodies, the content (concentration) of heavy rare earth element RH in these sintered magnet bodies is not limited to two types, and may be three or more types.

  The heat treatment for diffusion performed on the laminated sintered magnet body may be performed by a method of heating the entire atmosphere of the processing chamber. The sintered magnet body may be directly heated by a method such as high frequency induction heating. The heating temperature in the treatment chamber is preferably set in the range of 700 ° C. or higher and 1000 ° C. or lower, and more preferably set in the range of 850 ° C. or higher and 950 ° C. or lower. If set within such a temperature range, a sintered magnet body having a relatively high concentration of heavy rare earth element RH to a sintered magnet body having a relatively low concentration of heavy rare earth element RH via a grain boundary phase. The heavy rare earth element RH can be diffused efficiently. During this diffusion, the light rare earth element RL diffuses from a sintered magnet body having a relatively low concentration of heavy rare earth element RH to a sintered magnet body having a relatively high concentration of heavy rare earth element RH (interdiffusion). ).

  The inside of the treatment chamber during the heat treatment is preferably an inert atmosphere. As long as it is an inert atmosphere, a vacuum or an Ar atmosphere may be used. The degree of vacuum in the processing chamber does not greatly affect the diffusion amount of the heavy rare earth element RH, that is, the degree of improvement in coercive force.

  The heat treatment time is determined depending on the thickness of the magnet body to be diffused. For example, when using a magnet body having an individual thickness of 1 mm to 5 mm, the heat treatment time is preferably set within a range of about 30 minutes to 5 hours. If the heat treatment time is less than 30 minutes, the heavy rare earth element RH does not diffuse sufficiently. In addition, in the case of a magnet body having a thickness of 5 mm, since the diffusion is completed within 5 hours, the coercive force is not significantly improved even if the heat treatment is continued for 5 hours or more. In the case of a magnet body having a thickness of about 1 mm, the heavy rare earth element RH can be diffused throughout the magnet body by a heat treatment for about 3 hours.

  During heat treatment, it is preferable to apply a load to the magnet body in order to increase the effective contact area at the interface of the magnet body. In particular, in the case of a small laminated magnet of about 10 mm square, application of such a load is particularly preferable, but in the case of a laminated magnet larger than that, a sufficiently large contact area can be secured by its own weight.

  In the laminated sintered magnet body after the heat treatment, a layer of heavy rare earth element RH and light rare earth element RL is formed at the interface, thereby joining the magnet bodies. The magnet bodies coupled by joining may be used as laminated magnets as they are, or may be individually separated or processed into magnet pieces having a desired shape and size.

  Since the laminated magnet manufactured in this way has a rare earth metal layer (a layer containing heavy rare earth element RH and light rare earth element RL) at the magnet body interface, eddy currents that cross these interfaces are unlikely to occur. Thus, heat generation due to eddy current is suppressed as a whole. For this reason, when it mounts and uses for a motor, it becomes possible to exhibit the outstanding magnet characteristic.

  The magnet of the present invention has a higher coercive force than the sintered magnet obtained when the same amount of the heavy rare earth element RH contained in the laminated magnet of the present invention is blended in the alloy melting stage. The improvement effect can be obtained. That is, the total amount of heavy rare earth elements RH necessary to obtain a magnet having the same coercive force can be reduced by the present invention, and resource saving of heavy rare earth elements RH, which is a valuable resource, can be realized.

  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, there is a cost merit and it is practical.

According to the diffusion treatment in the present invention, in the magnet body having a relatively low RH concentration, a part of the light rare earth element RL of the R ₂ Fe ₁₄ B main phase crystal grains is substituted with the heavy rare earth element RH, and R ₂ Fe A layer (thickness is, for example, 1 nm) in which heavy rare earth element RH is relatively concentrated can be formed in the outer shell of the ₁₄ B main phase.

Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type, if the magnetocrystalline anisotropy in the outer shell of the main phase is increased, a reverse magnetic domain is formed in the vicinity of the grain boundary phase in the main phase. As a result, the coercive force H _{cJ 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, The coercive force H _{cJ 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 can be efficiently produced in the outer shell portion of the main phase. by forming the B, it is possible to improve the coercive force H _cJ while suppressing the decrease in remanence B _r.

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 preferable to Dy as the heavy rare earth element RH to be replaced with the light rare earth element RL in the main phase outer shell.

  As is apparent from the above description, in the present invention, when producing a sintered magnet body having a relatively low concentration of heavy rare earth element RH, it is not necessary to add rare earth element RH at the stage of the raw material alloy. On the other hand, when producing a sintered magnet body having a relatively high concentration of heavy rare earth element RH, the addition method and timing of addition of heavy rare earth element RH are arbitrary, and rare earth element RH is added to the raw material alloy. Also good.

  Since the heavy rare earth element RH located inside the main phase is difficult to be used for diffusion into the sintered magnet body having a low RH concentration, the heavy rare earth element RH is biased to the grain boundary phase in the sintered magnet body having a high RH concentration. Preferably present. In order to make the heavy rare earth element RH mainly exist in the grain boundary phase, after the sintered magnet body is produced without adding the heavy rare earth element RH at the stage of the raw material alloy, the heavy rare earth element RH is diffused in the sintered magnet body. May be. In addition, as a method for efficiently introducing the heavy rare earth element RH into the sintered magnet body, the inventor of the present application arranges a bulk body of the heavy rare earth element RH in the vicinity of the sintered magnet body, The invention in which heavy rare earth elements RH are diffused into the sintered magnet body by heat treatment while the powder is in contact with the sintered magnet body is completed, and disclosed in Japanese Patent Application Nos. 2006-58555 and 2006-81066. is doing. A sintered magnet body having a high concentration of heavy rare earth element RH may be produced by such a method.

  In addition, the “processing chamber” in the present specification includes a wide space in which a plurality of sintered magnet bodies that are in contact 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, the sintered magnet bodies are in contact with each other and the heavy rare earth element RH diffuses between them, so that the vaporized RH metal does not adhere to the wall surface in the sintered magnet body processing chamber. For this reason, useless consumption of the heavy rare earth element RH which is a valuable resource can be suppressed.

  Furthermore, since no special diffusion source or vapor deposition source is required in addition to the sintered magnet body, 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.

The RH contained in the sintered magnet body having a high RH concentration diffuses in the grain boundary phase toward the inside of the low-concentration magnet body using the difference in the RH concentration at the magnet body 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 shell of the R ₂ Fe ₁₄ B phase. By forming such an RH enriched layer, the magnetocrystalline anisotropy of the outer shell portion of the main phase is increased and the coercive force H _cJ is improved. That is, by using a small amount of RH metal, the heavy rare earth element RH is diffused and penetrated deep inside the magnet, and only the main phase outer shell portion is efficiently converted to RH ₂ Fe ₁₄ B. Therefore, the residual magnetic flux density _Br The coercive force H _cJ can be improved over the entire magnet while suppressing the decrease.

  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 main phase outer shell is increased, so that the main phase Nucleation of reverse magnetic domains in the vicinity of the grain boundary phase is suppressed, and the coercive force H _cJ 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. Exceeds 1.5%, may not be able to suppress a decrease in remanence B _r, is less than 0.1%, is because insufficient effect of improving the coercivity H _cJ. A diffusion amount of 0.1% to 1.5% 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 a metallic 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.

  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.

According to the present invention, for example, even for a thickness of 3mm or more thick material magnet, increasing both the remanence B _r and coercivity H _cJ with the heavy rare-earth element RH in small amounts, the magnetic properties at high temperatures It is possible to provide a high performance magnet that does not deteriorate. 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 prominent when the thickness of each magnet body is 10 mm or less.

  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]
In this embodiment, in order to produce a plurality of sintered magnet bodies having different Dy concentrations, an alloy having different Dy concentrations is prepared, and each alloy is pulverized and sintered.

  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. On the other hand, an alloy to which Dy is added as the heavy rare earth element RH is also prepared.

  Part of B in the above alloy may be substituted by C (carbon), and part of Fe (50 atomic% or less) is substituted by another transition metal element (for example, Co or Ni). May be. 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 holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy ingot having a thickness of about 0.3 mm. 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.

  Thus, a plurality of sintered magnet bodies having different concentrations of the heavy rare earth element RH can be obtained.

[Diffusion process]
Next, the sintered magnet bodies having different concentrations of the heavy rare earth element RH are arranged in the processing chamber in contact with each other, and the heavy rare earth element RH is diffused from one to the other sintered magnet body by heating.

  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.

Example 1
First, an alloy ingot blended to have a composition of Nd: 31.8, B: 1.0, Co: 0.9, Cu: 0.1, Al: 0.2, balance: Fe (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 cubic shape of 15 mm square, the sintered body block is mechanically processed to obtain a sintered magnet having a thickness (magnetization direction size) of 1 mm × length of 7 mm × width of 7 mm. And a plurality of sintered magnet bodies having a thickness (magnetization direction size) of 3 mm × length of 7 mm × width of 7 mm were produced (sintered magnet body 1, Dy concentration: 0 mass%).

  By the same process as the sintered magnet body 1, Nd: 29.6, Dy: 2.5, B: 1.0, Co: 0.9, Cu: 0.1, Al: 0.2, balance: Fe A sintered magnet body produced from an alloy ingot having a composition of (mass%) was produced (sintered magnet body 2, Dy concentration: 2.5 mass%). Moreover, Nd: 26.8, Dy: 5.0, B: 1.0, Co: 0.9, Cu: 0.1, Al: 0.2, the remainder by the process similar to the sintered magnet body 1 A sintered magnet body produced from an alloy ingot having a composition of Fe (mass%) was produced (sintered magnet body 3, Dy concentration: 5.0 mass%).

Next, after laminating sintered magnet bodies having different Dy concentrations as shown in FIG. 1, heat treatment (diffusion treatment) was performed at 900 to 950 ° C. for 30 to 180 minutes in a vacuum heat treatment furnace. The pressure in the vacuum heat treatment furnace was set to 1.0 × 10 ⁻² Pa. Thereafter, an aging treatment at 500 ° C. for 60 minutes was performed under a pressure of 2 Pa. “A” to “F” shown in FIG. 1 schematically show the stacked structures of the samples A to F, respectively.

The characteristics (residual magnetic flux density: B _r , coercive force: H _cJ ) of the samples A to F thus obtained were measured with a BH tracer. The diffusion state of Dy was evaluated by EPMA (EPM-810 manufactured by Shimadzu Corporation). FIG. 2 is a graph showing measurement results of magnet characteristics.

As can be seen from FIG. 2, the coercive force H _cJ as a whole of the plurality of sintered magnet bodies is improved by superposing the plurality of sintered magnet bodies having different Dy concentrations and performing the heat treatment. 2 shows, as a comparative example, the sintered magnet body 1, the sintered magnet bodies 2, for each of the sintered magnet body 3, the residual magnetic flux density B _r of case without diffusion treatment, is also shown the coercive force H _cJ ing.

  In the combination (samples B, C, E, and F) including the sintered magnet body 3 (Dy concentration: 5.0%), the coercive force improving effect was particularly remarkable. This is because the Dy concentration is 5.0%. Since excess Dy is present in the grain boundary phase of the sintered magnet body at a high concentration, the Dy concentration gradient becomes large at the interface contacting the sintered magnet body having a low Dy concentration, and this gradient is used as the driving force for the Dy concentration. This is presumably because Dy rapidly diffused into the grain boundary phase of the sintered magnet body having a low thickness.

  FIG. 3 shows a cross-sectional EPMA analysis result after heat treatment (900 ° C., 30 minutes and 500 ° C., 60 minutes) of Sample D as an example. In sample D, it was confirmed that Dy diffused from the sintered magnet body 2 to the sintered magnet body 1.

(Example 2)
As shown in FIG. 4, samples D, E, and F on which sintered magnet bodies were laminated were prepared. However, in this example, between the sintered magnet bodies, Al foil (99% made by Nilaco, 7 mm × 7 mm × 0.002 mm), Cu foil (99.9% made by Nilaco, 7 mm × 7 mm × 0.002 mm), Or after sandwiching Au foil (99.9% made by Nilaco, 7 mm x 7 mm x 0.0025 mm), in a vacuum heat treatment furnace at 900-1000 ° C, 30-180 minutes, 1.0 x 10 ^-2 Pa Heat treatment was performed. Thereafter, an aging treatment was performed under the conditions of 500 ° C., 60 minutes and 2 Pa.

The magnetic properties (residual magnetic flux density: B _r , coercive force: H _cJ ) of the sample were measured using a BH tracer. The measurement results are shown in FIG.

  Also in this example, it was confirmed that the coercive force was improved by stacking samples having a difference in Dy concentration and performing heat treatment. In particular, the effect was remarkable in the samples E and F containing the sintered magnet body 3 (Dy 5.0%). The reason is as described for the first embodiment.

FIG. 6 is a graph showing the relationship between the average Dy concentration and the magnet characteristics in each sample. The coercive force is further improved by performing heat treatment with an Al foil sandwiched between the sintered magnet bodies. For this reason, when the average Dy concentration as a whole is 3.75% (sample E), a coercive force substantially equal to the coercive force of the sintered magnet body 3 having a Dy concentration of 5.0% can be obtained. Since the residual magnetic flux density (B _r ) is higher than that of the sintered magnet body 3, it can be said that a magnet having better magnetic properties than the sintered magnet body 3 was obtained.

(Example 3)
Samples D, E, and F on which sintered magnet bodies were laminated as shown in FIG. 7 were prepared. However, in this example, after applying Al coating on the surfaces of the sintered magnet bodies 1 to 3 under the conditions of 10 kV, 1.6 A and 30 minutes by the EB (electron beam heating vapor deposition) method, as shown in FIG. Laminated. Samples D, E, and F were heat-treated in a vacuum heat treatment furnace at 900 to 950 ° C. for 30 to 180 minutes and 1.0 × 10 ⁻² Pa, and then at 500 ° C. for 60 minutes and 2 Pa. An aging treatment was performed.

The characteristics (residual magnetic flux density: B _r , coercive force: H _cJ ) of the samples D to F thus obtained were measured with a BH tracer. FIG. 8 is a graph showing measurement results of magnet characteristics.

  As can be seen from FIG. 8, the coercive force of the entire magnet is improved by performing heat treatment by superposing samples having a difference in Dy concentration in an Al-coated state. In particular, in the combination (samples E and F) in which the sintered magnet body 3 (Dy: 5.0%) is included, the reason why the effect is remarkable is as described above.

FIG. 9 shows the magnet characteristics with the total Dy concentration on the horizontal axis. By applying Al coating and heat treatment, the degree of improvement in coercive force is further increased, and is equivalent to the coercive force of sintered magnet body 3 (Dy concentration 5.0%) at a total Dy concentration of 3.75% (sample E). It became clear that the above coercive force level was reached. Since the residual magnetic flux density (B _r ) is higher than that of the sintered magnet body 3, the magnetic characteristics as a whole are improved.

  FIG. 9 is a graph showing the relationship between the average Dy concentration and the magnet characteristics in each sample. Even when the heat treatment was performed with the Al coating layer sandwiched between the sintered magnet bodies, the same effect as when the Al foil was sandwiched was obtained.

  According to the present invention, the heavy rare earth element RH is efficiently diffused widely into the grain boundary phase inside the sintered magnet body without wastefully consuming the heavy rare earth element RH, and the heavy rare earth element RH is formed in the outer shell portion of the main phase crystal grain. Since it can be concentrated, a high-performance magnet having both a high residual magnetic flux density and a high coercive force can be provided.

It is a schematic cross section which shows the arrangement | positioning relationship of the some sintered magnet body laminated | stacked about sample AF. It is a graph which shows the magnet characteristic obtained about sample AF in Example 1 of this invention, and a comparative example. 2 is a photograph showing a cross-sectional EPMA analysis result obtained for Sample D in Example 1. FIG. It is a schematic cross section which shows the arrangement | positioning relationship of the some sintered magnet body laminated | stacked about the samples DF in Example 2. FIG. It is a graph which shows the magnet characteristic acquired about samples DF and the comparative example in Example 2 of this invention. It is a graph which shows the Dy amount dependence of the magnet characteristic obtained about sample DF and the comparative example in Example 2 of this invention. It is a schematic cross section which shows the arrangement | positioning relationship of the some sintered magnet body laminated | stacked about the samples DF in Example 3 of this invention. It is a graph which shows the magnet characteristic acquired about samples DF and the comparative example in Example 3 of this invention. It is a graph which shows the Dy amount dependence of the magnet characteristic obtained about the samples DF in Example 3 of this invention, and a comparative example.

Claims (4)

A plurality of R—Fe—B rare earth sintered magnets containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R, at least one of which is a heavy rare earth element RH (Dy A step (A) of preparing a plurality of R—Fe—B rare earth sintered magnet bodies containing at least one selected from the group consisting of H, Tb, and Tb;
A step of arranging two R-Fe-B rare earth sintered magnet bodies having different concentrations of heavy rare earth elements RH among the plurality of R-Fe-B rare earth sintered magnet bodies in a state where they are in contact with each other. (B) and
By heating the R—Fe—B rare earth sintered magnet body disposed in the processing chamber, the R—Fe—B rare earth sintered magnet body having a relatively high concentration of the heavy rare earth element RH is converted into a heavy rare earth element. A step (C) of diffusing a heavy rare earth element RH into an R—Fe—B rare earth sintered magnet having a relatively low concentration of RH;
Method of R-Fe-B rare earth sintered magnet including   2. The R—Fe—B based rare earth sintering according to claim 1, wherein in the step (C), the heating temperature of the R—Fe—B based rare earth sintered magnet body is set within a range of 700 ° C. or more and 1000 ° C. or less. A manufacturing method of a magnet.   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.   Among the plurality of R—Fe—B rare earth sintered magnet bodies arranged in the processing chamber in the step (B), the R—Fe—B rare earth sintered magnet body having the highest concentration of the heavy rare earth element RH is The manufacturing method of the R-Fe-B type rare earth sintered magnet of Claim 1 containing 5 to 12 mass% of heavy rare earth elements RH.