JP4438371B2 - NdFeB-based anisotropic exchange spring magnet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a rare earth permanent magnet having anisotropy and a method for producing the same.

  Nd-Fe-B permanent magnets are widely used as magnets used in motors and the like, and are manufactured using a melting method (see Non-Patent Document 1) or a rapid cooling method (see Non-Patent Document 2). . Moreover, HDDR processing (refer nonpatent literature 3) is developed, and it has also become possible to provide anisotropy to magnet powder. With these technological developments, Nd—Fe—B permanent magnets having excellent magnet properties have been put into practical use.

However, Nd—Fe—B permanent magnets are approaching theoretical limit values with respect to magnet characteristics. For this reason, development of a higher performance next-generation magnet is desired. In recent years, exchange spring magnets, also called nanocomposite magnets, have attracted attention as next-generation magnets (see Non-Patent Document 4). The exchange spring magnet has a structure in which a hard phase and a soft phase are finely dispersed on the order of several tens of nm. The exchange spring magnet behaves like a single hard phase as a whole because the magnetization of both phases is linked by exchange interaction and the magnetization of the soft phase is not easily reversed. It has been pointed out that nanocomposite magnets can be very high performance magnets. For example, in the Sm ₂ Fe ₁₇ N ₃ / Fe—Co system, it is theoretically reported that a value of (BH) max = 137MGOe can be obtained if anisotropy can be achieved (see Non-Patent Document 5).

So far, a method for producing an Nd ₂ Fe ₁₄ B / Fe ₃ B exchange spring magnet has been developed (see Non-Patent Document 6). In addition, methods for producing Nd ₂ Fe ₁₄ B / Fe exchange spring magnets have been developed (see Patent Document 1, Patent Document 2, and Non-Patent Document 7).

  However, the melt span method and the mechanical alloying (MA) method used in the above documents cannot obtain the same crystal orientation, so only an isotropic exchange spring magnet can be obtained, and the characteristics of the exchange spring magnet can be fully utilized. Absent.

  As a method for producing an anisotropic exchange spring magnet, a method of heating and crystallizing an Nd—Fe—B amorphous alloy in a strong magnetic field (see Patent Document 3), a rapid cooling in which a hard phase and a soft phase are finely dispersed and precipitated. A method of hot working a ribbon alloy (see Patent Document 4), a method of direct anisotropy in the presence of a liquid phase by warm uniaxial deformation (see Patent Document 5), and the like are disclosed.

However, the anisotropic exchange spring magnet manufactured by the above method has insufficient magnet characteristics. In addition, development of a simpler method for producing an anisotropic exchange spring magnet has been desired.
JP-A-7-173501 JP-A-7-176417 Japanese Patent Laid-Open No. 11-8109 JP-A-11-97222 JP 2000-235909 A M.M. Sagawa et al, Japan Journal of Applied Physics 26 (1987) 785 R. W. Lee, Applied Physics Letter 46 (1985) 790 T. T. Takeshita et al, Proc. 10th Int. Works on Rare Earth Magnets and Ther Applications, Kyoto, (1989) 511 E. F. Kneller and R.M. Hawig, IEEE Transaction Magnetics 27 (1991) 3588 R. Skomski and J.M. M.M. D. Coey, Physical Review B48 (1993) 15812 R. Cohoern et al, Journal de Physique 49 (1988) C8-669. L. Withanawasam et al, Journal of Applied Physics 76 (1994) 7065

  An object of the present invention is to provide an NdFeB-based anisotropic exchange spring magnet having excellent magnet characteristics and a method for producing the same.

  Another object of the present invention is to provide a magnet alloy and magnet powder used in the production of an exchange spring magnet, and a method for producing the magnet powder.

  Another object of the present invention is to provide a motor incorporating an NdFeB-based anisotropic exchange spring magnet.

  The present invention provides an NdFeB rare earth magnet alloy containing a hard phase and a soft phase, wherein the minimum width of the soft phase is substantially 1 μm or less, and the minimum distance between the soft phases is substantially 0.1 μm or more. It is a rare earth magnet alloy. The minimum width of the soft layer is preferably 800 nm or less, and more preferably 400 nm or less.

  When the rare earth magnet alloy of the present invention is used as a raw material, an NdFeB-based anisotropic exchange spring magnet having easy magnetization axes aligned in one direction can be easily manufactured. Since the obtained exchange spring magnet has excellent magnet characteristics, for example, by incorporating the exchange spring magnet of the present invention into a motor, a motor having excellent characteristics can be obtained. In addition, since the amount of rare earth is relatively small, a magnet that is advantageous in terms of cost can be provided.

  The present inventors have found that an NdFeB-based anisotropic exchange spring magnet having excellent magnet characteristics can be obtained by using a rare earth magnet alloy having a hard phase and a hard phase in a predetermined state as a starting material. . Moreover, in manufacture, it discovered that it was suitable to grind | pulverize using a ball mill, and discovered suitable conditions also about manufacturing conditions.

First, an embodiment of a method for producing an anisotropic exchange spring magnet will be outlined. The rare earth magnet alloy of the present invention is obtained by strip casting. FIG. 1-1 is a SEM photograph of a cross section of the rare earth magnet alloy (composition: Nd _9.1 Fe _75.8 Co ₈ B _6.1 V ₁ ) of the present invention. In FIG. 1-1, a whitish foam-like spot and a whitish needle-like spot similar to the foam are the soft phase. Here, the “soft phase” referred to in the claims of the present invention is defined for the sake of accuracy. The “soft phase” in the claims means only the soft phase recognized at the magnification. Specifically, in FIG. 1-1, a soft phase having a size of less than 0.1 μm that cannot be clearly recognized is excluded from the concept of “soft phase” in the claims of the present application. Therefore, in the present application, a blackish portion other than the “soft phase” is the hard phase. The hard phase is a hard phase region that is like a single crystal. In the pulverization process, the hard phase is refined by repeating the cross-slip of crystals. On the other hand, in the pulverization process, cross-slip of the crystal including the soft phase is repeated at the same time. For this reason, the powder obtained by pulverization is in a state of incorporating a fine soft phase.

FIGS. 1-2 and 1-3 show TEM photographs of other rare earth magnet alloys of the present invention. The composition of the rare earth magnet alloy in FIG. 1-2 is Nd ₉ Fe ₇₆ Co ₈ B ₆ V ₁ , and the composition of the rare earth magnet alloy in FIG. 1-3 is Nd ₁₁ Fe ₇₂ Co ₈ B _7.5 V _1.5 . . In the rare earth magnet alloy shown in FIG. 1-2, the minimum width of the crystal grain size of the soft phase is 800 nm or less. In the rare earth magnet alloy shown in FIG. 1-3, the minimum width of the soft phase crystal grain size is 400 nm or less.

  In FIG. 1-2, it is confirmed by EDX that the white part is the soft phase and the other part is the hard phase. That is, in the rare earth magnet alloy of FIG. 1-2, the soft phase is a circular portion having a grain size of about 150 nm and a portion having a minimum width of about 650 nm existing in the grain boundary. Like the rare earth magnet alloy of FIG. 1-2, it is preferable that the minimum width | variety of the crystal grain diameter of a soft phase is 800 nm or less.

  1-3, it is confirmed by EDX that the white part is the soft phase and the other part is the hard phase. In addition, the sample does not exist in the large white areas on the left and right in the figure. In the rare earth magnet alloy of FIGS. 1-3, the soft phase is a circular portion having a grain size of about 150 to 350 nm and a strip-like portion having a minimum width of about 200 nm. As in the rare earth magnet alloy of FIGS. 1-3, it is more preferable that the minimum width of the crystal grain size of the soft phase is 400 nm or less.

  The crystal orientation of the pulverized powder obtained by pulverizing the magnet alloy to the size of the hard phase region or less maintains the original hard phase orientation. The hard phase of the pulverized powder stores the strain generated during pulverization by the ball mill. The pulverized powder is changed into a fine hard phase having a restored magnetic property with a uniform orientation, that is, an easy magnetization axis, by a subsequent heat treatment. As described above, the pulverized powder pulverized by the ball mill also includes a fine soft phase. Therefore, by performing the heat treatment, a more excellent anisotropic rare earth magnet powder (exchange spring magnet powder) in which a soft phase and a hard phase having a uniform orientation are mixed is obtained.

  A method for easily knowing that a rare earth magnet alloy contains a soft phase in addition to a hard phase and that the hard phase region is like a single crystal, that is, has a uniform crystal orientation is described. One of them is a method of actually manufacturing an exchange spring magnet and examining the magnetic characteristics of the obtained exchange spring magnet. That is, a magnetic alloy is pulverized using a ball mill, a green compact is produced by pressing in a magnetic field, and bulked with a discharge plasma apparatus at a temperature of 800 ° C. or lower to obtain a magnet. The degree of anisotropy is examined by comparing the magnetization curve in the direction perpendicular to the magnetic field direction of the press in the magnetic field of the bulking magnet. If there is anisotropy, this is a method for estimating that the hard phase region was in the expected state.

  The other is a simpler method. The produced rare earth alloy ribbon is pulverized to 25 μm or less, mixed with an epoxy resin (adhesive), and solidified in a magnetic field to produce a sample for a vibration type magnetometer (VSM). The magnetization curve in the magnetic field direction and the direction perpendicular thereto is measured by VSM. This is a method of estimating the degree of single crystal-like in the hard phase region from the ratio of magnetization (Js) at 16 kOe which is the maximum magnetic field for measurement. Although it is desirable to pulverize more finely, the reason why the size is 25 μm or less is that the limit size that can be crushed and sieved by hand using a mortar is 25 μm. It is considered that the crystal orientation of the adjacent hard phase regions is not so inclined. That is, it is considered that there is a texture.

  The latter method is very effective in developing rare earth magnet alloys. When an exchange spring magnet was actually produced, an anisotropic exchange spring magnet was produced when a rare earth magnet alloy having a Js ratio (ratio of the magnetic field direction to the direction perpendicular to the magnetic field direction) of 1.3 or more was used as a starting material. Was possible. Note that the Js ratio of the bulk magnet was larger than that.

  The rare earth magnet powder becomes a green compact having anisotropy by molding in a magnetic field under a predetermined magnetic field and pressure conditions. By sintering the green compact at a relatively low temperature so that fine crystals do not grow, an NdFeB-based anisotropic exchange spring magnet having excellent magnet characteristics can be obtained. By such a method, an anisotropic exchange spring magnet having excellent characteristics can be obtained relatively easily.

  As a result of intensive studies taking into account the characteristics of the anisotropic exchange spring magnet obtained and productivity at the time of manufacture, the inventors have found that the NdFeB rare earth magnet alloy used as a raw material has a hard phase and a soft phase. It has been found that an excellent anisotropic exchange spring magnet can be obtained in the case where the materials are mixed so as to satisfy a predetermined condition. That is, according to the first aspect of the present invention, in a NdFeB rare earth magnet alloy containing a hard phase and a soft phase, the minimum width of the soft phase is substantially 1 μm or less, and the minimum distance between the soft phases is substantially And a rare earth magnet alloy of 0.1 μm or more. A rare earth magnet alloy having a minimum soft phase width of substantially 800 nm or less is preferable, and a rare earth magnet alloy having a minimum soft phase width of substantially 400 nm or less is more preferable.

  Here, the minimum width of the soft phase and the minimum distance between the soft phases will be described with reference to FIG. The soft phase called “soft phase” in the claims of the present application, as already defined, can be recognized at the magnification, specifically, a soft phase having a size of 0.1 μm or more. That is. In the present application, the “minimum width of the soft phase” refers to the minimum value of the width of the soft phase that is confirmed when the rare earth magnet alloy is observed. For the soft phase observed in the form of foam, the length indicated by D1 corresponds to the minimum width in this soft phase. Regarding the soft phase observed in a needle shape, the minimum width (corresponding to D2) at a position other than the needle-like tip portion corresponds to the minimum width in the soft phase. On the other hand, the “minimum distance between soft phases” refers to the distance between a foamy soft phase and the soft phase closest to the soft phase. The length indicated by D3 and D4 corresponds to the minimum distance between the soft phases. The needle-like soft phase is also a value represented by the distance to the closest soft phase.

  In the present application, “the minimum width is substantially 1 μm or less” means that 90% or more of the minimum width of the soft phase is 1 μm or less when the soft phase observed in the SEM photograph or the like is randomly extracted. It means that there is. For example, when ten random samples are extracted, the minimum width of nine or ten soft phases may be 1 μm or less. Preferably, the minimum width of all soft phases is 1 μm or less. Similarly, “the minimum distance is substantially 0.1 μm or more” means that 90% or more of the minimum distance between the soft phases is 0.1 μm when the soft phases observed in SEM photographs are extracted at random. That means that. For example, when 10 places are extracted at random, the minimum distance between the 9 or 10 soft phases may be 0.1 μm or more. Preferably, the minimum distance between all soft phases is 0.1 μm or more. In calculating the minimum width of the soft phase and the minimum distance between the soft phases, a method of observing the cross section of the magnet alloy by SEM can be used. However, the present invention is not limited to this, and alternative means can be used as long as the same calculation is possible. The confirmation of the hard phase can be finally performed by TEM, but as long as there is no particular problem, the above-described deductive inference method may be used.

  When the minimum width of the soft phase and the minimum distance between the soft phases satisfy the above values, the characteristics of the obtained anisotropic exchange spring magnet are improved. The reason is that if the minimum width between the soft phases is too small, that is, if the distance between the soft phases is too short, the hard phase region is too small. For this reason, it is presumed that it is difficult to obtain a magnet powder having a fine hard phase and a uniform magnetization axis of the hard phase, and having a size larger than 0.1 μm. Moreover, it is estimated that when the soft phase is too large, inconveniences such as difficulty in pulverization occur. Considering this, the minimum width of the soft phase is substantially 1 μm or less, preferably 800 nm or less, more preferably 400 nm or less. If the minimum width of the soft phase is large to some extent, it is easy to efficiently pulverize the soft phase and improve the characteristics of the anisotropic exchange spring magnet.

  As a preferable magnet composition for obtaining an exchange spring magnet, the following formula (1):

Is mentioned. The hard phase in this composition was Nd ₂ Fe ₁₄ B, and the soft phase was α-Fe, which could be estimated from X-ray diffraction, measurement of temperature dependence of magnetization, and the like.

The composition of the NdFeCoB rare earth magnet alloy is, for example, Nd _x Fe _85-x Co ₈ B ₆ V ₁ , X = 9 to 11. With this composition, an anisotropic exchange spring magnet having excellent magnet characteristics can be obtained. The hard phase in this composition was Nd ₂ (Fe—Co) ₁₄ B, and the soft phase was α- (Fe—Co), which could be estimated from measurements of temperature dependence of X-ray diffraction and magnetization. However, it is not limited to such a composition. In the formula (1), x, y and z are preferably in the range described below. Further, a predetermined amount may be substituted by the elements exemplified below.

  Preferably x in Formula (1) is 9-11. When the amount of Nd exceeds 11 atom%, the proportion of the soft phase is less than 5%, and it is difficult to expect the characteristics of the exchange spring magnet. On the other hand, when the Nd content is less than 9 atom%, it is difficult to produce a rare earth magnet alloy.

Preferably y in Formula (1) is 5-8. When the amount of B exceeds 8 atom%, other phases other than Nd ₂ Fe ₁₄ B and α-Fe may be generated. On the other hand, when the amount of B is less than 5 atom%, it is difficult to produce a rare earth magnet alloy.

  Preferably z in Formula (1) is 0-2. V is added from the viewpoint of reducing the crystallinity and increasing the coercive force. The addition is not essential and may not be added. However, if it is added too much, it will cause the magnetic properties to deteriorate.

  Nd may be substituted with Pr in the range of 0.01 to 80 atom%. More preferably, it is substituted with Pr in the range of 20 to 60 atom%. When the replacement amount is within this range, the coercive force and the squareness can be improved with almost no decrease in the residual magnetic flux density.

  Nd may be substituted with Dy or Tb in the range of 0.01 to 10 atom%. This is because if the replacement amount is within this range, the coercive force can be improved and the temperature characteristics can be improved without causing a significant decrease in the residual magnetic flux density.

A composition in which a part of Fe is substituted with Co may be used, and the substitution amount in that case is preferably 0.01 to 30 atom%, and more preferably 5 to 20 atom%. Within this range, the temperature characteristics are improved without causing a decrease in coercive force and magnetic flux density. In particular, when the substitution amount of Co is 5 to 20 atom%, not only the temperature characteristics but also the magnetic flux density itself can be effectively improved. When a part of Fe is replaced by Co, the hard phase is Nd ₂ (Fe—Co) ₁₄ B, and the soft phase is α- (Fe—Co). It was possible to estimate from the measurement of

  Further, Fe or Co (Co present as Fe—Co) may be substituted with a small amount of one or more of Al, Mo, Zr, Ti, Sn, Cu, Ga, or Nb. By containing these elements, the structure can be made finer and the coercive force can be increased. However, if it is contained too much, it will cause the magnetic properties to deteriorate. From this viewpoint, the amount of element to be substituted is preferably 0.1 to 3 atom% with respect to the total composition.

  In addition, since the magnet according to the present invention is an alloy material, a very small amount of impurities cannot be mixed. However, the smaller the amount of impurities, the more preferable it is 1% by mass or less.

  In the production of the magnet alloy according to the present invention, first, each metal element is adjusted and blended so as to have a desired composition, and a melting ingot is prepared by a known means such as high-frequency induction melting in a vacuum or an argon atmosphere. By subjecting this to a rapid cooling method such as a strip casting method, the rare earth magnet alloy (crystalline alloy ribbon) of the present invention can be obtained relatively easily. The strip casting method can be performed using a known apparatus, and no special improvement is required. However, improvements are not excluded. The manufacturing conditions need to be set as appropriate according to the type of apparatus and alloy used and cannot be uniquely determined. However, when preparing the magnet alloy according to the present invention, it is necessary to pay particular attention to the cooling rate. Even if the cooling rate is too fast (the alloy ribbon becomes thin) or too slow (the alloy ribbon becomes thick), there is a possibility that the crystal size becomes coarse and the uniformity of the alloy ribbon is impaired. The cooling rate is closely related to the thickness of the alloy ribbon obtained by the strip casting method, and it is appropriate to adjust the thickness of the obtained alloy ribbon to be 30 to 300 μm. For example, an alloy ribbon is obtained by rapid cooling at a rate of 1000 ° C./sec or more.

  By grinding the first rare earth magnet alloy of the present invention, rare earth magnet powder is provided. A ball mill is preferably used for grinding the rare earth magnet alloy. That is, the second of the present invention is a rare earth magnet powder obtained by pulverizing the first rare earth magnet alloy of the present invention with a ball mill. The third aspect of the present invention is a method for producing a rare earth magnet powder, characterized in that the first rare earth magnet alloy of the present invention is pulverized by a ball mill using a dispersant in a non-oxidizing atmosphere. .

  The rare earth magnet alloy is preferably pulverized by a ball mill to the size of the hard phase region of the rare earth magnet alloy. For example, when the size of the hard phase region is 0.5 μm, it may be pulverized into particles of 0.5 μm or less. Usually, it is pulverized to the order of 0.1 μm, that is, submicron order. This size is suitable for magnetic field orientation. The lower limit of the size to be pulverized is not particularly limited, but if it is too small, it becomes difficult to align the magnetic field, and there is also a problem that the oxidation resistance is inferior as the powder becomes finer. For this reason, it is preferable that the degree of pulverization is 0.1 μm or more.

  The ball mill may be wet or dry, but is preferably pulverized in a non-oxidizing atmosphere (such as an argon atmosphere or a nitrogen atmosphere) in order to prevent deterioration of magnetic properties due to the oxidation of the magnet powder. In the wet ball mill, cyclohexane or the like can be used for pulverization. Further, a dispersant is used in order to suppress aggregation of the pulverized powder. The dispersant can also have a suitable effect on the magnetic field orientation. As the dispersant, succinic acid may be used in a wet process, and stearic acid may be used in a dry process. In addition, it was estimated from the magnetic measurement, X-ray diffraction, etc. that the powder in the as-milled state seems to be partially amorphous.

  The pulverized powder (magnet powder) obtained by pulverizing the magnet alloy is a more excellent anisotropic rare earth that is mixed with a soft phase and a hard phase with a uniform orientation by further heat treatment. It becomes magnet powder (exchange spring magnet powder). The temperature of the heat treatment is preferably 500 to 800 ° C.

  In the magnetic powder subjected to the heat treatment, the hard phase and the soft phase are finely mixed. In addition, the hard phase easy axis of magnetization has a uniform structure. As already explained, the single crystal-like hard phase is used for fine graining and taking in a fine soft phase in the ball mill process.

Next, a green compact is obtained by orienting the obtained magnetic powder in a magnetic field. The apparatus used for magnetic field orientation and pressing is not particularly limited, and various known means can be used. For example, pressure molding can be performed in a state where the easy axis direction of magnetization is aligned by applying a magnetic field. It is appropriate that the applied pressure is 1 to 5 ton / cm ² and the applied magnetic field is about 15 to 25 kOe. The green compact is produced using the mold of the discharge plasma sintering apparatus described below, and is transported to the apparatus together with the mold as it is in the mold, and the discharge plasma sintering is performed while applying pressure. It is preferable from the viewpoint of ease.

  The obtained green compact is subjected to pressure sintering with a discharge plasma sintering apparatus to obtain a bulked anisotropic exchange spring magnet. By using discharge plasma pressure sintering, sintering at a relatively low temperature can suppress the coarsening of the crystalline size, and the properties of the obtained magnet can be made excellent. The discharge plasma pressure sintering can be performed using a commercially available apparatus such as Model SPS-2040 manufactured by Izumi Tech Co., Ltd., and may be appropriately improved according to the magnet to be manufactured and the production line.

If the holding temperature of the discharge plasma pressure sintering is too high, the crystalline size becomes coarse, the coercive force of the magnet is lowered, and the exchange coupling may be weakened. For this reason, it is preferable to carry out at 800 degrees C or less, and 700 degrees C or less is more preferable. On the other hand, if the temperature is too low, the densification may be insufficient. The pressure sintering is preferably performed under reduced pressure using a rotary pump or the like, and the heating rate up to the holding temperature is suitably about 15 to 25 K / min. The holding time needs to be appropriately changed according to the apparatus used, the temperature, the size of the green compact, etc. and cannot be uniquely defined, but is generally about 0 to 10 minutes. After holding at the holding temperature, cool the furnace. A temperature drop rate of about 10 to 30 K / min is appropriate. A pressure of about 1 to 10 ton / cm ² is appropriate. However, the discharge plasma pressure sintering may deviate from the above conditions as long as the crystal size becomes coarse and the characteristics of the anisotropic exchange spring magnet do not deteriorate. In addition, when the discharge plasma pressure sintering is used, a bulk magnet having a low oxygen concentration can be manufactured, and the magnet characteristics can be improved.

  The size of exchange coupling can be recognized by the size of the springback. In the anisotropic exchange spring magnet finally obtained, it is a matter of course that the spring back can be confirmed, but the magnet powder subjected to heat treatment also showed the spring back phenomenon. In addition, as expected from the description of the present application, a springback phenomenon was observed in the second and third quadrants of the magnetization curve even when the material was pulverized by ball milling.

The present invention provides a method of manufacturing an NdFeB-based anisotropic exchange spring magnet by the method described above. That is, the fourth of the present invention is a step of obtaining a green compact by molding the second rare earth magnet powder of the present invention in a magnetic field at a pressure of 1 to 5 ton / cm ² in a magnetic field of 15 to 25 kOe. And an NdFeB anisotropic exchange spring comprising a step of pressure-sintering the green compact at a temperature of 600 to 800 ° C. and a pressure of 1 to 10 ton / cm ^{2 in} a discharge plasma apparatus to obtain a bulk magnet. It is a manufacturing method of a magnet.

  According to the fourth aspect of the present invention, an NdFeB-based anisotropic exchange spring magnet is provided. The exchange spring magnet of the present invention is preferably 95% or more of the true density of the rare earth magnet alloy used as a raw material. If the density of the exchange spring magnet is 95% or more, the exchange spring magnet has a large energy product. That is, the fifth of the present invention is the NdFeB-based anisotropic exchange spring magnet obtained by the fourth of the present invention, wherein the density of the magnet is 95% or more of the true density of the rare earth magnet alloy having the same composition. A certain NdFeB-based anisotropic exchange spring magnet.

  The anisotropic exchange spring magnet of the present invention is very useful when used in various applications that require high magnetic properties. For example, the bulk anisotropic exchange spring magnet of the present invention can be applied to a motor. In that case, compared with the conventional Nd-Fe-B sintered magnet, since the magnet of the present invention has a large magnet flux, it can be reduced in size. Moreover, the magnet of the present invention has excellent temperature characteristics. For these reasons, it is advantageous to drive motors for electric vehicles, HEVs, and FCVs. The reason why the magnet flux is larger than that of the sintered magnet is that the exchange spring magnet contains a soft phase. A possible reason for the excellent temperature characteristics is that the coercive force mechanism is different. It seems that the crystal grain size of the hard phase is small and the coercive force mechanism is close to that of the pinning type. (Sintered magnets are a new creation type coercive force mechanism.) Therefore, it seems that temperature stability is increased.

  Next, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.

Example 1
The composition of the alloy ingot was Nd _9.1 Fe _75.8 Co ₈ B _6.1 V _1, and an alloy ribbon as a rare earth magnet alloy was prepared by strip casting. The condition of the strip casting method was that the cooling rate to about 900 ° C., which is the solidification temperature, was about 2300 ° C./sec. When the cut surface of the obtained alloy ribbon was observed by SEM, a soft phase and a hard phase were mixed. The minimum width of the soft phase was substantially 1 μm or less, and the minimum distance between the soft phases was substantially 0.1 μm or more. The alloy ribbon had a finer structure on the roll surface side in the strip cast method. The SEM photograph about the center of the cut surface of the obtained alloy ribbon is shown in FIG. As described above, the whitish particles and the needle-like portion are precipitates of α-Fe (more strictly, α- (Fe—Co)). The other part is the hard phase region.

  The alloy ribbon was pulverized in a mortar to 25 μm or less to prepare a VSM sample. The VSM sample was prepared by a method in which the powder was fixed with an epoxy adhesive in a magnetic field of 10 kOe. With a VSM with a maximum applied magnetic field of 16 kOe, the magnetization curve in the direction perpendicular to the direction parallel to the magnetic field was measured, and the Js ratio at 16 kOe was evaluated (the ratio of parallel to vertical). The magnitude of this value reflects that the hard phase region is large and that the hard phase region forms a texture. FIG. 2 shows an example of the measurement result. In this case, the Js ratio is 1.7.

  For the obtained alloy ribbon, a VSM sample was separately prepared in the same manner as described above, and the magnetization curve in the parallel direction was measured (FIGS. 3 and 4). FIG. 4 is a magnetization curve measured by enlarging the horizontal axis of FIG. 3 10 times. As can be confirmed from FIG. 3 and FIG. 4, the springback phenomenon was also exhibited in the alloy ribbon. In the second and third quadrants of the magnetization curve in the parallel direction, when the measurement magnetic field is reversed halfway, the magnetization returns as shown in the figure, and the return method rebounds. This is the springback phenomenon. Normally, the magnetization does not increase when the measuring magnetic field is reversed. Such a springback is evidence that the soft phase and the hard phase are close to each other and the interaction is working strongly.

  One feature of the rare earth magnet alloy of the present invention is that it is crystalline. When differential thermal analysis (DTA) was performed to confirm this, no clear exothermic peak was observed.

  The obtained alloy ribbon was separately pulverized using a wet ball mill (in an Ar atmosphere, using cyclohexane). When pulverizing with a ball mill, polybutenyl succinimide tetraethylenepentamine (molecular weight 1300) was used as a dispersant. This dispersant contained some mineral oil. SEM observation was performed on the pulverized powder (rare earth magnet powder) obtained as a result of the pulverization. FIG. 5 is an SEM photograph of the pulverized powder. The particle size of the powder was 1 μm or less, and particles of 1 μm or more could not be confirmed.

  As for the powder in the as-milled state, a VSM sample was prepared in the same manner as described above, and the magnetization curve was measured. FIG. 6 shows the measurement results. The Js ratio in FIG. 6 is 1.5. That is, the pulverized powder also showed anisotropy. Since the coercive force is increased compared to FIG. 2, it can be seen that the hard phase is miniaturized. FIG. 7 confirms the springback phenomenon in the parallel direction of FIG.

  The magnet powder obtained by pulverization was heat-treated at 612 ° C. Thereafter, the magnetization curve for the VSM sample was measured in the same manner. FIG. 8 shows the measurement results. The magnet powder subjected to the heat treatment was anisotropic. The Js ratio is about 1.4, but this value is a reference value. This is because the heat-treated powder is agglomerated and is not a sufficiently magnetically oriented VSM sample. In addition, the improvement of Js ratio was able to be confirmed by grind | pulverizing the heat-processed powder with a mortar, releasing agglomeration a little, and producing and measuring a VSM sample. Further, the coercive force was significantly increased (6.4 kOe) as compared with FIG. Moreover, when the structure was observed, it was a mixed structure of a finely dispersed hard phase and soft phase.

  For reference, FIG. 9 shows X-ray diffraction results of the powder (a) in an as-milled state and the powder (b) obtained by heat-treating the powder at 612 ° C. It can be seen that the diffraction peak becomes sharper after heat treatment. A considerable amount of distortion may have been applied in the as-milled state. It is also conceivable that an amorphous phase is included.

(Example 2)
An alloy ribbon was prepared as a rare earth magnet alloy by the same procedure as in Example 1 using the strip casting method with the composition of the alloy ingot being Nd ₁₀ Fe ₇₅ Co ₈ B ₆ V ₁ . When the cut surface of the obtained alloy ribbon was observed by SEM, a soft phase and a hard phase were mixed. The minimum width of the soft phase was substantially 1 μm or less, and the minimum distance between the soft phases was substantially 0.2 μm or more. The alloy ribbon was pulverized in a mortar to 25 μm or less to prepare a VSM sample, and the Js ratio obtained was 1.8.

(Example 3)
The composition of the alloy ingot was Nd ₁₁ Fe ₇₄ Co ₈ B ₆ V ₁ and an alloy ribbon as a rare earth magnet alloy was prepared by the same procedure as in Example 1 using the strip casting method. When the cut surface of the obtained alloy ribbon was observed by SEM, a soft phase and a hard phase were mixed. Further, the minimum width of the soft phase was substantially 1 μm or less, and the minimum distance between the soft phases was substantially 0.5 μm or more. The alloy ribbon was pulverized in a mortar to 25 μm or less to prepare a VSM sample, and the Js ratio obtained was 1.8.

(Comparative Example 1)
The composition of the alloy ingot was Nd ₈ Fe ₇₇ Co ₈ B ₆ V ₁ and an alloy ribbon as a rare earth magnet alloy was prepared by the same procedure as in Example 1 using the strip casting method. When the cut surface of the obtained alloy ribbon was observed by SEM, a soft phase and a hard phase were mixed. Further, many soft phases having a minimum width of more than 1 μm could be confirmed, and the minimum width was not substantially less than 1 μm. In many cases, the minimum distance between the soft phases was also less than 0.1 μm. The alloy ribbon was pulverized in a mortar to 25 μm or less to prepare a VSM sample, and the Js ratio obtained was 1.2.

Example 4
The composition of the alloy ingot was Nd ₁₁ Fe ₇₂ Co ₈ B _7.5 V _1.5, and an alloy ribbon as a rare earth magnet alloy was prepared by the same procedure as in Example 1 using the strip casting method. In Example 4, the condition of the strip casting method was that the cooling rate to about 900 ° C., which is the solidification temperature, was about 2000 ° C./sec. When the cut surface of the obtained alloy ribbon was observed by SEM, a soft phase and a hard phase were mixed. Further, the minimum width of the soft phase was substantially 1 μm or less, and the minimum distance between the soft phases was substantially 1 μm or more. The SEM photograph about the center of the cut surface of the obtained alloy ribbon is shown in FIG. The black striped pattern that can be confirmed from the upper left to the lower right is the soft phase (α- (Fe—Co)). The other area is the hard phase. That is, the hard layer is isolated by the belt-like soft phase.

  For the powder in the as-milled state, a VSM sample was prepared in the same manner as in Example 1, and the magnetization curve was measured. FIG. 11 shows the measurement results. The Js ratio was a little over 1.5. The ball milling in this case is also estimated to follow the same process as in the first embodiment. FIG. 12 is a magnetization curve of the powder heat-treated at 610 ° C. The coercive force is 9.0 kOe, which is increased compared to FIG. The Js ratio, which is the degree of anisotropy, is small for the same reason as described above. In other words, since the magnet powder after heat treatment is agglomerated, even if a VSM sample is produced, it does not become a fully oriented sample. FIG. 13 is a magnetization curve for investigating the springback phenomenon for the sample prepared in the same manner as in FIG. A springback phenomenon was observed for the magnet powder after the heat treatment.

  In addition, the following experiment was conducted in order to find suitable conditions for spark plasma sintering.

(Reference Example 1)
By the same procedure as in Example 1, the alloy ribbon as a rare earth magnet alloy was pulverized using a wet ball mill to obtain a rare earth magnet powder. The rare earth magnet powder was oriented in a magnetic field of 20 kOe and molded in a magnetic field at a pressure of 2 ton / cm ² to produce a green compact. A non-magnetic WC type was used as the type. The shape of the obtained bulk body was about 10 mm × 10 mm × 7 mm.

An NdFeB-based anisotropic exchange spring magnet was obtained by bulking the green compact with a discharge plasma sintering apparatus under the conditions of 650 ° C., 3 minutes, and applied pressure of 9 ton / cm ² . The density of the exchange spring magnet reached the true density.

  The obtained exchange spring magnet was observed by SEM and TEM. The soft phase and the hard phase were mixed, and the grain size was 15-40 nm. From the diffraction pattern of the electron beam (TEM observation), it was confirmed that the directions of the hard phase were aligned.

(Reference Example 2)
An NdFeB-based anisotropic exchange spring magnet was obtained in the same manner as in Reference Example 1 except that the applied pressure in the discharge plasma sintering was 8 ton / cm ² . The density of the exchange spring magnet was 95% of the true density.

(Reference Example 3)
An NdFeB-based anisotropic exchange spring magnet was obtained in the same manner as in Reference Example 1 except that the applied pressure in the discharge plasma sintering was 7 ton / cm ² . The density of the exchange spring magnet was 90% of the true density.

(Reference Example 4)
An NdFeB-based anisotropic exchange spring magnet was obtained in the same manner as in Reference Example 1 except that the temperature in the discharge plasma sintering was 810 ° C. The density of the exchange spring magnet reached the true density.

  The magnetization curves of the obtained exchange spring magnets of Reference Examples 1 to 4 were measured with a (direct current) BH tracer having a maximum applied magnetic field of 20 kOe. The ratio of magnetization at 20 kOe in the direction perpendicular to the magnetic field orientation was evaluated (Js ratio 2 in Table 1 is that). The Js ratio 2 of the magnet of Reference Example 1 was 1.8, which was larger than the Js ratio (1.7) of Example 1. Table 1 also shows the energy product (BHmax) obtained from the magnetization curve of the magnet. Regarding the coercive force, Reference Examples 1 to 3 had a value of about 7.0 kOe, but Reference Example 4 was as low as 5.0 kOe. As shown in Table 1, it was found that the density of the magnet is desirably 95% or more of the true density, and the sintering temperature in the discharge plasma apparatus is desirably 800 ° C. or less.

(Example 5)
The replacement spring magnet of Reference Example 1 was applied to a surface magnet type motor (12 stator poles, 8 rotor poles). FIG. 14 is a quarter sectional view of a concentrated winding surface magnet type motor to which an exchange spring magnet is applied. The outer side is an aluminum case 11, the inner side is a stator (inner diameter 52 mm, outer diameter 108 mm) 12, 1-2 is a u phase, 3-4 is a v phase, and 5-6 is a w phase winding. The stator 12 was a laminated body of electromagnetic steel sheets. On the rotor iron 14, a magnet 13 having a shape as shown in the figure was arranged. The outermost diameter of the rotor was 50.7 mm, and the thickness of the stator and rotor was 79.8 mm.

  The performance of the motor was a maximum rating of 2 kW and a heat resistance limit of 160 ° C. The coercive force of this magnet was 7.2 kOe. On the other hand, when a conventional NdFeB sintered magnet is used, it is necessary to use a magnet having a coercive force of about 19.8 kOe or more in order to ensure equivalent heat resistance. That is, when the magnet of the present invention is applied to a motor, it has been shown that excellent characteristics are exhibited in thermal design.

It is a SEM photograph about the cross section of the rare earth magnet alloy of Example 1 (composition: Nd _9.1 Fe _75.8 Co ₈ B _6.1 V ₁ ). Other rare earth magnet alloy _{(composition: Nd 9 Fe 76 Co 8 B} 6 V 1) is a TEM photograph of. Still other rare earth magnet alloy _{(composition: Nd 11 Fe 72 Co 8 B} 7.5 V 1.5) is a TEM photograph of. 2 is a magnetization curve for a VSM sample produced from an alloy ribbon as a rare earth magnet alloy of Example 1. It is the magnetization curve measured in order to confirm a spring back about the alloy ribbon of Example 1. FIG. 4 is a magnetization curve measured by enlarging the horizontal axis 10 times in the magnetization curve of FIG. 3. 2 is a SEM photograph of the pulverized powder (rare earth magnet powder) of Example 1. 2 is a magnetization curve of a VSM sample produced from an as-milled magnet powder obtained in Example 1. It is the magnetization curve measured in order to confirm the spring back phenomenon in the parallel direction of FIG. 2 is a magnetization curve of a VSM sample produced from the heat-treated magnet powder obtained in Example 1. It is the result of X-ray diffraction about the powder (a) of the state of as-milled obtained in Example 1, and the powder (b) which heat-processed it at 612 degreeC. It is a SEM photograph about the cross section of the rare earth magnet alloy of Example 4 (composition: Nd ₁₁ Fe ₇₂ Co ₈ B _7.5 V _1.5 ). 6 is a magnetization curve for a VSM sample produced from the as-milled magnet powder obtained in Example 4. 6 is a magnetization curve of a VSM sample produced from the heat-treated magnet powder obtained in Example 4. It is the magnetization curve measured in order to confirm the springback phenomenon about the magnet powder after the heat processing obtained in Example 4. FIG. FIG. 4 is a quarter cross-sectional view of a concentrated winding surface magnet type motor to which an exchange spring magnet is applied.

Explanation of symbols

  1-2 ... u phase winding, 3-4 ... v phase winding, 5-6 ... w phase winding, 11 ... aluminum case, 12 ... stator, 13 ... magnet, 14 ... rotor iron, 15 ... shaft.

Claims (15)

1) The hard phase contains a soft phase of 0.1 μm or more in the crystal grains of the hard phase and in the grain boundary, the minimum width of the soft phase is substantially 1 μm or less, and the minimum distance between the soft phases is Obtaining a crystalline NdFeB-based rare earth magnet alloy ribbon which is substantially 0.1 μm or more by a strip casting method;
2) obtaining a rare earth magnet powder by grinding with a ball mill to a size below the hard phase region of the NdFeB rare earth magnet alloy ribbon ;
3) the rare earth magnet powder and magnetic Banaka molded, and obtaining a green compact,
4) a step of obtaining a bulk magnet by pressure sintering the powder compact made,
The composition of the crystalline NdFeB-based rare earth magnet alloy has the following formula (1):
(Wherein x = 9 to 11, y = 5 to 8, z = 0 to 2)
A method for producing an NdFeB-based bulk anisotropic exchange spring magnet, characterized in that:   The method for producing an NdFeB-based bulk anisotropic exchange spring magnet according to claim 1, wherein 0.01 to 80 atom% of Nd in the formula (1) is substituted with Pr.   The method for producing a NdFeB-based bulk anisotropic exchange spring magnet according to claim 1 or 2, wherein 0.01 to 10 atom% of Nd in the formula (1) is substituted with Dy or Tb.   The production of an NdFeB-based bulk anisotropic exchange spring magnet according to any one of claims 1 to 3, wherein 0.01-30 atom% of Fe in the formula (1) is substituted with Co. Method. Fe or Co of the formula (1) is substituted with at least one of Al, Mo, Zr, Ti, Sn, Cu, Ga, or Nb in an amount of 0.1 to 3 atom% based on the total composition. The manufacturing method of the NdFeB type | system | group bulk anisotropic exchange spring magnet of any one of Claims 1-4. Wherein 1) the thickness of the alloy strip stages, NdFeB-based bulk anisotropic exchange spring manufacturing method of a magnet according to any one of claims 1 to 5, characterized in that a 30 to 300 [mu] m. The method for producing an NdFeB-based bulk anisotropic exchange spring magnet according to any one of claims 1 to 6 , wherein the minimum width of the soft phase is substantially 800 nm or less. The method for producing an NdFeB-based bulk anisotropic exchange spring magnet according to claim 7 , wherein the minimum width of the soft phase is substantially 400 nm or less. The NdFeB system according to any one of claims 1 to 8 , wherein in the step ( 2 ) of obtaining the rare earth magnet powder, a heat treatment at a temperature of 500 to 800 ° C is further applied to the magnet powder. Manufacturing method of bulk anisotropic exchange spring magnet. At the stage of the two), the rare-earth magnet alloy ribbon by using a dispersing agent, in a non-oxidizing atmosphere, according to any one of claims 1 to 9, characterized in that grinding by a ball mill A method for producing a NdFeB-based bulk anisotropic exchange spring magnet. The method for producing an NdFeB-based bulk anisotropic exchange spring magnet according to claim 10 , wherein the ball mill is wet. The method for producing an NdFeB-based bulk anisotropic exchange spring magnet according to claim 10 , wherein the ball mill is a dry type. In the step 3), the rare earth magnet powder is 1 to 5 ton / cm in a magnetic field of 15 to 25 kOe. ² In a magnetic field at a pressure of
In step 4), the green compact is discharged into a discharge plasma apparatus at a temperature of 600 to 800 ° C. and 1 to 10 ton / cm. ² The method for producing an NdFeB-based anisotropic exchange spring magnet according to any one of claims 1 to 12, wherein the bulk magnet is obtained by pressure sintering at a pressure of 1 to 12.   An NdFeB-based anisotropic exchange spring magnet obtained by the production method according to claim 1, wherein the density of the magnet is 95% or more of the true density of a rare earth magnet alloy having the same composition. NdFeB bulk anisotropic exchange spring magnet.   A motor incorporating the NdFeB-based bulk anisotropic exchange spring magnet according to claim 14.