JP2024016680A - neodymium laminated sintered magnet - Google Patents

Abstract

[Problem] To provide a neodymium laminated sintered magnet having high magnetic properties and excellent high electrical resistance. [Solution] A plurality of unit neodymium sintered magnets are laminated, and each unit neodymium sintered magnet is bonded and integrated via a bonding layer, and the bonding layer includes a rare earth-rich region. In addition, the rare earth-rich region has electrical insulating properties. The thickness of this bonding layer is preferably 1.0 μm or more and 200 μm or less. [Selection diagram] None

Description

The present invention relates to a neodymium laminated sintered magnet. In particular, it relates to neodymium laminated sintered magnets used in large motors and generators, such as main motors of electric vehicles.

Neodymium sintered magnets were invented by the present inventors in 1982 (Japanese Patent Publication No. 61-34242), and have magnetic properties that far exceed those of samarium-cobalt magnets, which were the representative high-performance permanent magnet materials up until then. In addition, it is inexpensive because its main ingredients are neodymium (Nd: a type of rare earth element), iron, and boron, which are abundant in resources, and its market has steadily expanded as an ideal permanent magnet material. Its uses include computer HDDs (hard disk drives), magnetic head drive motors (VCM: voice coil motors), high-end speakers, headphones, electrically assisted bicycles, golf carts, and permanent magnet magnetic resonance diagnostic equipment (MRI). A wide variety of things. Furthermore, in recent years, it has been rapidly put into practical use in the main motors of hybrid vehicles (HEVs) and electric vehicles (EVs), energy-saving and low-noise large home appliances (coolers and refrigerators), elevators, and other industrial motors. .

Generally, neodymium sintered magnets have high magnetic properties, but have the disadvantage of poor temperature characteristics. In particular, the temperature characteristics of coercive force are important. When used in home appliances or industrial motors, temperature increases due to coil current cannot be avoided. Further, since a reverse magnetic field acts from the motor armature, irreversible demagnetization occurs in the permanent magnet when the temperature rises and the coercive force decreases. The only way to prevent irreversible demagnetization is to increase the coercive force in advance.

After the discovery of neodymium sintered magnets, additive elements (Patent No. 1606420, etc.), heat treatment (Patent No. 1818977, etc.), and crystal grain size control (Patent No. 1662257, etc.) were developed to improve properties such as coercive force. Although the following effects have been revealed, the most effective method for improving coercive force is the addition of heavy rare earth elements (Dy, Tb) (Patent No. 1802487). If a large amount of heavy rare earth elements is used, the coercive force will surely increase, but the saturation magnetization will decrease and the maximum energy product will decrease. In addition, Dy and Tb are rare and expensive resources, and it is difficult to supply them for HEVs, EVs, and industrial/home motors, which are expected to have a large demand in the future.

Later, in Patent Document 1 listed below, instead of adding Dy/Tb etc. to the alloy composition, a sintered body was prepared and a metal or compound such as Dy/Tb was coated on the outside, and Dy/Tb A method of increasing the coercive force without causing almost any decrease in saturation magnetization or maximum energy product has been discovered using the grain boundary diffusion method, in which heavy rare earth elements are diffused into the grain boundaries inside the sintered body through heat treatment.

On the other hand, neodymium sintered magnets are used as magnets for HEVs and EVs, in order to reduce losses due to eddy current generation during operation, suppress heat generation in the magnet, and reduce temperature rise of the magnet. Suggestions have been made. An example of this proposal is, for example, in Patent Document 2 listed below, Dy fluoride powder is coated on a neodymium sintered magnet with a thickness of 5 mm, and grain boundary diffusion treatment (GBD treatment) is performed by heating at 900°C for 1 hour in Ar. ), and then 18 of these divided magnets were stacked, inserted into the magnet insertion hole of the motor rotor, and hardened with epoxy resin. An IPM motor equipped with a rotor manufactured in this manner has been proposed.

In the future, as the electrification of automobiles continues to progress, the neodymium sintered magnets used in main engine motors will need to be manufactured at the lowest possible cost while maintaining the best magnetic properties. It is desirable to reduce its usage to the limit that is permissible. However, at present, neodymium magnets used in EVs and HEVs contain a certain amount of Dy and Tb, and manufacturing costs cannot be reduced sufficiently. One reason for this is that the above-mentioned neodymium sintered magnets for EVs and HEVs do not have sufficient Dy and Tb savings.

Furthermore, silicon steel plates, which are the iron core material used in motors, are punched and laminated into a predetermined shape with a thickness of 0.5 mm or less in order to reduce overcurrent loss that occurs during motor operation. It would be desirable if the Nd-Fe-B sintered magnet used in the same motor could be punched out into thin pieces and used, as this would reduce eddy current loss to the utmost, but this is not possible. Therefore, the neodymium sintered magnet used in the main motor of an electric vehicle is used as a divided magnet with a thickness of about 5 mm, as in the above-mentioned known example (Patent Document 2). A magnet with a thickness of 5 mm is cut out by machining from a large block of magnet (called a block magnet), which incurs costs due to processing costs and reduced material yield. Moreover, the effect of reducing eddy current loss is insufficient in a laminate having a thickness of about 5 mm. When the thickness of the unit neodymium sintered magnet is set to 5 mm, the eddy current loss is reduced more than that of a block magnet that is not laminated, but the reduction is still not sufficient. It is expected that the eddy current loss generated in the motor can be greatly reduced by using a stacked unit neodymium sintered magnet that is processed to be thinner than half of 5 mm, that is, 2.5 mm or less.

Patent No. 4450239 Japanese Patent Application Publication No. 2011-78268

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a neodymium laminated sintered magnet having high magnetic properties and excellent high electrical resistance.

The neodymium laminated sintered magnet of the present invention is one in which a plurality of unit neodymium sintered magnets are stacked, and each unit neodymium sintered magnet is bonded to each other via a bonding layer to form an integrated structure,
The bonding layer of the neodymium laminated sintered magnet includes a rare earth-rich region, and the rare-earth rich region has electrical insulation properties.
In this specification, each thin plate magnet forming a laminated magnet will be referred to as a unit neodymium sintered magnet. Furthermore, bonding does not mean so-called gluing of unit neodymium magnets one by one using an adhesive or the like, but means metallurgically bonding and integrating them by hot pressing or the like. Therefore, in the bonding according to the present invention, no organic substance such as an adhesive is present in the bonding layer.
In addition, in this specification, the term "rare earth rich region" refers to a region in which there is a large content (50% by weight or more) of rare earth elements such as Nd, Pr, Dy, Tb, etc. A bonding region that has electrical insulation properties and is made of compounds such as fluorides and carbides. Here, electrical insulation is defined as a value that is at least two orders of magnitude larger than the specific electrical resistance of the neodymium sintered magnet, which is 1.4×10 ⁻⁶ Ω·m. This is because if the specific resistance differs by two or more orders of magnitude, the value of the current flowing there becomes smaller by two or more orders of magnitude, and eddy current loss can be greatly reduced.
Note that an insulating effect will be obtained if the proportion (volume proportion) of the "rare earth rich region" in the bonding layer of the neodymium laminated magnet of the present invention is 20% or more, but the proportion occupied by this rare earth rich region is preferable. is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and preferably 90% or more. Note that this ratio can be confirmed by elemental analysis of a cross section of the bonding layer using EDS (energy dispersive X-ray spectroscopy).

Further, the present invention is a neodymium laminated sintered magnet having the above-mentioned characteristics, characterized in that the thickness of the bonding layer is 1.0 μm or more and 200 μm or less, and the thickness of the bonding layer is The average thickness is preferably 1.0 μm or more and 100 μm or less, more preferably 1.0 μm or more and 50 μm or less, and particularly preferably 2.0 μm or more and 30 μm or less. The reason why the upper limit of the bonding layer thickness is set to 200 μm is that if it exceeds this, the substantial volume ratio of the sintered magnet portion decreases, and the residual magnetic flux density Br decreases significantly.

Further, the present invention provides a neodymium laminated sintered magnet having the above characteristics, wherein the rare earth-rich region exists continuously and/or intermittently in the bonding layer. It is. That is, the bonding layer of the neodymium laminated sintered magnet of the present invention is a phase containing continuous and/or intermittent rare earth-rich regions.

Further, the present invention provides a neodymium laminated sintered magnet having the above characteristics, in which an Fe-rich metal region containing 50% by weight or more of Fe is present in the bonding layer, and the Fe-rich metal region is The present invention is characterized in that adjacent unit neodymium sintered magnets are connected via the bonding layer.
As used herein, the term "Fe-rich metal region" refers to a phase in which a large amount of Fe (50% by weight or more) is present and compounds of rare earth elements such as Nd, Pr, Dy, and Tb are substantially absent.

In addition, the present invention provides a neodymium laminated sintered magnet having the above-mentioned characteristics, and the weight percent of the total amount (total amount) of rare earth elements in a surface layer region less than 50 μm from the surface of the neodymium laminated sintered magnet, and It is characterized in that the difference from the total amount (total amount) of the rare earth elements in the inner region separated by the above distance is less than 1% by weight. This difference in weight % is preferably 0.8 weight % or less, more preferably 0.5 weight % or less, and particularly preferably 0.3 weight % or less.

Further, the present invention provides a neodymium laminated sintered magnet having the above characteristics, in which at least one of Dy element and Tb element is present as a heavy rare earth element in the rare earth rich region present in the bonding layer. The heavy rare earth elements diffuse from each bonding layer toward the adjacent bonding layer (GBD diffusion) along the grain boundary phase of the Nd ₂ Fe ₁₄ B crystal of each unit neodymium sintered magnet. It is also characterized by

In addition, the present invention provides a neodymium laminated sintered magnet having the above-mentioned characteristics, the sum of the maximum magnetic energy product (BH) max (MGOe) expressed in the CGS unit system and the coercive force iHc (kOe) (hereinafter, this It is also characterized by having magnetic properties with a magic number (sometimes referred to as "MN") of 70 or more.

Furthermore, the present invention provides a neodymium laminated sintered magnet having the above characteristics, wherein the outer surface of the neodymium laminated sintered magnet orthogonal to the bonding layer is at least one pair of opposing outer surfaces or all outer surfaces. It is also characterized by having a flatness of 0.1 mm or less.

The neodymium laminated sintered magnet according to the present invention has high magnetic properties and excellent high electrical resistance, can be manufactured at the same cost as conventional ones, and has the world's best magnetic properties and is suitable for automotive applications. It has sufficient electrical insulation properties and can be applied to magnets for EVs and HEVs, which are expected to grow explosively in the future.

FIG. 3 is a diagram showing a method for manufacturing a neodymium laminated sintered magnet according to the present invention. FIG. 2 is a diagram showing a state in which a stack of unit neodymium sintered magnets is set inside the device together with a mold and a punch. It is a photograph showing the appearance of a cylindrical sample after a deformation test. This is a photograph showing the appearance of the hot press device used in the bonding test. FIG. 3 is a cross-sectional view of the device used in the bonding test. It is a photograph showing the state of a unit neodymium sintered magnet before and after a bonding test. 2 is a SEM photograph of the bonded surface of the neodymium laminated sintered magnet according to Example 1. 1 is an EDS photograph of a portion (rare earth rich region) where rare earth compounds etc. are continuously distributed on the bonding surface of the neodymium laminated sintered magnet according to Example 1. 2 is an EDS photograph of a portion of the bonded surface of the neodymium laminated sintered magnet according to Example 1, where the Fe-rich metal region is distributed across the bonded surface. A jig for applying GBD paste to the surface of unit neodymium sintered magnets (Figure 10a), a state during application of GBD paste (Figure 10b), and a cassette with stacked unit neodymium sintered magnets after applying GBD paste (Figure 10c) This is a photo. 1 is a photograph of neodymium laminated sintered magnets according to Examples 1 and 2. 3 is a photograph of a damaged neodymium laminated sintered magnet according to Comparative Example 1. FIG. 2 is a diagram showing an outline of a C-type yoke for evaluating eddy current loss and a measurement system. This is a photograph of a sample for eddy current evaluation, the surface of which is covered with insulating tape and a search coil is wound around the surface perpendicular to the direction of magnetic field generation. This is a photograph of an evaluation sample set in a C-shaped coil. It is a graph showing the eddy current evaluation results up to a frequency of 200 Hz when excited with a 5 Arms current. It is a graph showing the eddy current evaluation results up to a frequency of 500 Hz when excited with a 2 Arms current. 3 is a photograph showing the appearance of a neodymium laminated sintered magnet produced using a unit neodymium sintered magnet produced by the NPLP method (New-PressLess Process) according to Example 3. 3 is a photograph showing the appearance of a convex lens-shaped neodymium laminated sintered magnet produced in Example 7.

In order to obtain a neodymium layered sintered magnet having high magnetic properties and excellent electrical resistance, the present inventors first considered the ideal method for manufacturing a neodymium layered sintered magnet. The study model is shown in Figure 1.
First, a stack of unit neodymium sintered magnets made of neodymium sintered bodies is prepared. Here, methods for producing unit neodymium sintered magnets include a method of cutting out a larger sintered body and a method of producing the unit neodymium sintered magnet so that the appearance itself after sintering is in the shape of a unit neodymium sintered magnet. This laminate is placed inside a mold that has a space with a limited volume, specifically a space that matches the shape of the product, and is heated to a high temperature while applying pressure to bond the unit neodymium sintered magnets together. At the same time, the laminate is deformed (deformed) in the pressing direction and in two directions orthogonal to the pressing direction up to the inner wall of the mold. This allows the neodymium laminated sintered magnet to occupy virtually 100% of the space limited by the product shape, so there is no remaining space and the magnetic properties of this neodymium laminated sintered magnet are the same as those of the normal shape. The same high residual magnetic flux density as an integrated magnet can be achieved. The feasibility of this study model is determined by whether or not it can be deformed, whether it can be joined, and whether the low melting point Nd-rich phase elutes and welds with the mold. We have established a new method and have made it possible to bring to the world a completely net-shaped, no-processing, low-cost product that has the best magnetic properties according to performance evaluations.

The first point to consider is whether the unit neodymium sintered magnet can be deformed under high temperature and pressure. The reason for this is that the size of the main phase crystal grains constituting a unit neodymium sintered magnet is generally less than 10 μm, with an average of around 5 μm, and their abundance ratio in the magnet structure is 90% or more. This is because since it is a tetragonal Nd ₂ Fe ₁₄ B type intermetallic compound, the main phase itself is hardly expected to undergo plastic deformation. However, although there is a possibility of crystal sliding of the main phase via the low melting point Nd-rich phase that is the second phase, there is no report yet that plastic deformation is possible when the crystal grain size is 1 μm or more. Figure 2 shows the details of an experiment conducted to determine this. Table 1 shows the components of the unit neodymium sintered magnets used.

Here, the unit neodymium sintered magnet was prepared as follows. First, an SC alloy having the components shown in Table 1 was prepared, and after hydrogen cracking, jet mill pulverization was performed in a high-pressure nitrogen gas atmosphere of 0.6 MPa. It is possible to adjust the average particle size (D50) by adjusting the raw material supply rate to the jet mill pulverizer and changing the classification conditions of the fine powder after crushing, and in this experiment, the raw material with an average particle size of 3 μm was used. Powder was used. This powder was filled into a carbon mold at a packing density of 3.6 g/cc, and after aligning the c-axis direction of the powder crystal grains in one direction by applying a 4T pulsed magnetic field, the powder was placed in a sintering furnace. Sintering was performed at a temperature of 985° C. for 4 hours in a vacuum atmosphere of 10 ⁻⁴ Pa or less to obtain a block-shaped magnet with a size of about 50 mm x about 70 mm x thickness 20 mm (direction of orientation). The sintered body thus obtained was processed into a cubic shape of 7 mm x 7 mm x 7 mm (orientation direction), and its magnetic properties were evaluated.

As a result, Br=14.1 kG, iHc=16.1 kOe, (BH)max=47.7 MGOe, and degree of magnetic orientation Br/4πMs=0.965. From this block magnet, a cylindrical neodymium sintered magnet with a diameter of 15 mm and a thickness of 6 mm (in the orientation direction) was prepared by processing. This was placed inside a carbon cylindrical mold with an inner diameter of φ20 mm, carbon punches slightly smaller than the inside size of the mold were attached to the top and bottom, and the whole was placed in a Spark Plasma Sintering (hereinafter referred to as SPS) device LABOX-325R manufactured by Sinterland Co., Ltd. (maximum pressing force 30 kN, maximum pulse current output 2.5 kA). A carbon sheet approximately 0.2 mm thick was sandwiched between the inner wall of the mold and the contact surface between the punch and the sample. Here, the atmosphere during the SPS treatment was a vacuum of about 20 Pa that could be reached by a rotary pump. In an SPS machine, a large current is passed through the mold and workpiece through the upper and lower punches, and the mold and workpiece are heated by the generated Joule heat while processing is performed by applying pressure through the upper and lower punches. In this experiment, a thermocouple was inserted into the hole made in the upper punch to measure the temperature at the top of the sample and control the temperature.

Table 2 shows the experimental conditions and the results obtained, and FIG. 3 shows a photograph of the sample after the experiment. In this experiment, the temperature increase rate from room temperature to the SPS processing temperature was fixed at 25°C/min, and the pressurizing force was changed in the sample thickness direction ( The amount of displacement in the pressure application direction) was measured. In addition, the presence or absence of elution of the low melting point Nd-rich phase from the side surface of the sample after the end of the experiment was also shown. As can be seen from FIG. 3, no defects such as cracks or cracks were observed in the sintered body itself in any of the cases in this experiment.

This experiment revealed the following: First, neodymium sintered bodies can be deformed without causing cracks or chips. When the maximum temperature is 800° C., a displacement of more than 7% can be achieved even at a pressure of 10 MPa. On the other hand, at 700°C, which is 100°C lower, only 3.81% displacement is obtained even if a pressure of 20 MPa is applied, and as the pressure is further increased to 30 MPa and 40 MPa, the displacement increases to 4.54% and 5.13%. However, it cannot reach a displacement of more than 7% at 800° C. and 10 MPa. In other words, it was found that the magnitude of displacement was more strongly influenced by the temperature factor than by the pressure. Also, regarding the elution status of the low melting point Nd-rich phase from the side of the sample, Experiment No. 1 and no. In No. 2, the liquid phase was eluted (see Fig. 3), but in No. 2, the temperature was the same as 700°C and the pressure was 30 MPa or more. 3.No. 4, no elution was observed. That is, the presence or absence of elution of the low melting point Nd-rich phase is determined not only by temperature but also by pressure conditions, and it was found that the higher the pressure, the less elution of the liquid phase occurs. Generally, it is thought that the higher the pressure, the easier the liquid phase components are to escape, so this result was unexpected, and we are currently working to elucidate the mechanism. In any case, the fact that the elution of the low melting point Nd-rich phase does not occur during deformation of the sintered body means that when the sintered body reaches the inner wall of the mold due to deforming, the eluted low melting point Nd rich liquid phase and the mold This means that the risk of reacting and damaging the sample and mold can be reduced. From the above, we have discovered the possibility of deforming a neodymium sintered body without causing the elution of the low melting point Nd-rich phase from the sintered body by appropriately selecting the temperature and pressure conditions.

Next, we investigated whether or not the unit sintered magnet stack could be joined, which is the second point to check. FIG. 4 is a photograph showing the appearance of the hot press experimental apparatus used, and FIG. 5 is a diagram showing a cross-sectional view of the structure of the apparatus. The sample space provided in the center of the apparatus shown in FIG. 5 has a diameter of 15 mm and a length of 10 mm.
The unit neodymium sintered magnet used in this experiment was cut into a size of φ15 mm x thickness 1.5 mm (in the orientation direction) from the same sintered block as the sintered body used in the previous experiment. Eight sheets were laminated and whether or not they could be bonded was examined. An experiment was conducted in an Ar atmosphere, heated to a temperature of 850° C. before applying pressure, and applied up to 40 MPa using a hydraulic press (FIG. 6). As a result of this experiment, a stack of eight unit neodymium sintered magnets was firmly joined and integrated. When the bonding strength was evaluated, it was found to be comparable to that of block-shaped neodymium sintered magnets.

From these experimental results, we were able to clear both the first and second points, and we are now on track to realize the originally envisioned non-processing neodymium laminated sintered magnet.
The present inventors completed the present invention based on the knowledge obtained from the above experiments, and were able to manufacture the neodymium laminated sintered magnet of the present invention.

Hereinafter, a neodymium laminated sintered magnet of the present invention in which a plurality of unit neodymium sintered magnets are laminated, joined together and deformed at a high temperature (for example, 700 to 950° C.) will be described.
First, a unit neodymium sintered magnet is prepared. It is produced by coarsely pulverizing, finely pulverizing, forming, orienting, and sintering an SC alloy prepared to have a predetermined composition according to a conventional method. A method of forming a neodymium sintered magnet body into a predetermined shape and size by processing such as cutting, or more preferably a unit neodymium sintered magnet of the shape and size by the NPLP method (Patent No. 6280137) made by the inventors of the present application. It is possible to adopt both methods of obtaining the sintered material in an as-sintered state. Various thicknesses can be selected for the unit neodymium sintered magnet, and the thinner it is, the more effective it is in reducing eddy current loss, but from the viewpoint of productivity and cost, material loss and processing cost are required when processing. In relation to this, in the case of the NPLP method, from the viewpoint of powder filling performance and productivity, the thickness of the unit neodymium sintered magnet is preferably 0.5 mm or more and 3 mm or less, and more preferably 1 mm or more and 2.5 mm or less. It is desirable to do so. This is because if the thickness is less than 0.5 mm, it will be difficult to manufacture, and if the thickness exceeds 3 mm, the insulation will be insufficient. Also, when a unit neodymium sintered magnet is obtained by cutting or other processing from a block-shaped neodymium sintered magnet, it is preferable to have the same thickness as above.

The average particle diameter (D50) of the fine powder is preferably 10 μm or less from the viewpoint of coercive force characteristics, and 1 μm or more from the viewpoint of crushability, but more preferably 5 μm or less and 2 μm or more. By applying a magnetic field after powder compaction, the c-axis orientation of the fine powder, which is mainly composed of tetragonal Nd ₂ Fe ₁₄ B type crystals, is aligned and the magnetic properties of the sintered body are improved, but the degree of c-axis crystal orientation is 90% or more. Must. This is because if it is less than 90%, the magnetic properties, particularly the residual magnetic flux density Br, will decrease, making it impossible to supply sufficient magnetic force when applied to an EV motor or the like. Further, the crystal orientation direction must be parallel to the main surface of the unit neodymium sintered magnet, that is, the plane perpendicular to the lamination direction of the neodymium laminated sintered magnet and in one direction. As a result, the eddy current generated in the direction across the laminated surfaces of the neodymium laminated sintered magnet is shredded by the high electrical resistance layer made of electrically insulating compounds (oxides, fluorides, carbides, etc.) formed on the laminated surfaces. This is because eddy current loss can be significantly reduced.

Next, a laminate is constructed by stacking a plurality of unit neodymium sintered magnets prepared in this way. The number of layers in the laminate is determined based on the thickness of the unit neodymium sintered magnet and the final product dimensions. For example, if the thickness of the unit neodymium sintered magnet is 2 mm and the size of the final product in the stacking direction is 30 mm, it is necessary to stack at least 15 unit neodymium sintered magnets by simple calculation, but it is perpendicular to the pressing direction. Considering the deformation in two directions, 16 or 17 or more layers are required. Determination of the number of laminated layers can be found by dividing the product volume calculated from the final product shape by the volume of a unit neodymium sintered magnet.

When stacking a predetermined number of unit neodymium sintered magnets, adhesives such as silicone grease, fluorides, oxides and carbides containing heavy rare earth elements such as Dy and Tb, LiF and CaF may be applied between the stacks as necessary. Inserting fluorides, oxides such as SiO ₂ and Al ₂ O ₃ , carbonates such as CaCO ₃ , hydroxides such as Ca(OH) ₂ , porcelain powder such as BaTiO ₃ , etc. can improve production efficiency and Effective in improving electrical insulation. In particular, the insertion of a compound containing heavy rare earth elements such as Dy and Tb is extremely effective for improving the magnetic properties of the neodymium laminated sintered magnet, especially the coercive force.

The unit neodymium sintered magnet laminate thus prepared is set in a mold whose interior is designed to match the shape and size of the product. The material of the mold can be selected from carbon, heat-resistant alloy, etc., and coating the surface with a material for preventing welding such as BN is also effective in improving the life of the mold. The atmosphere of the laminate, mold, and punch that applies pressure to the laminate from above and below can be controlled using a hot press (HP) device or Spark Plasma Sintering (SPS) device, which applies high pressure while heating to a high temperature of about 1000°C. Set it in a device that can apply voltage. Although the present invention was mainly studied using an SPS device, it goes without saying that the essence of the obtained results is the same for an HP device. The optimal bonding and deforming conditions need to be adjusted depending on the raw material alloy composition, but the heating temperature is preferably 700° C. or higher and the sintering temperature of the sintered body or lower, and the pressing force is preferably 25 MPa or more and less than 100 MPa. If the temperature is lower than 700° C., the deformation rate of the sintered body is slow and cracks occur in the joined body, resulting in poor productivity. Moreover, above the sintering temperature, the low melting point Nd-rich phase is noticeably eluted, the laminate and the mold are significantly welded together, the laminate and the mold are severely worn out, and the magnet components change significantly, deteriorating the magnetic properties. If the pressure is less than 25 MPa, the low melting point Nd-rich phase that was revealed in the above feasibility verification stage will elute and weld with the mold, and if it is 100 MPa or more, a device that can apply such a large pressure will be required. This is because they are so large that they are not suitable for mass production.

In the neodymium laminated sintered magnet produced in this way, an oxide film, a fluoride film, etc. are formed on the bonding surface to block the flow of current across the bonding layer. When fluorides or oxides made of heavy rare earth elements such as Dy or Tb are sandwiched, additional heat treatment is performed after the bonding and deforming process to cause grain boundary diffusion (hereinafter referred to as GBD) and improve coercive force characteristics. can be significantly improved. Similar to the process of performing GBD from the surface of a normal sintered body to its interior, as is generally well known, the GBD processing temperature is 800°C or higher and lower than 950°C, and the GBD processing time is 5 to 20 hours. It is. The atmosphere during GBD processing may be a vacuum. Here, when the GBD treatment temperature is less than 800°C, the coercive force is not sufficiently improved, and when it is 950°C or more, Br decreases. Furthermore, if the heat treatment time is less than 5 hours, the improvement in coercive force will be insufficient, and if it exceeds 20 hours, productivity will deteriorate.

The neodymium laminated sintered magnet according to the present invention has a characteristic structure resulting from its special process. Here, we conducted the following tests to clarify its organizational characteristics. First, a sintered body having the components listed in Table 1 was prepared, and from it a circular sintered body with a diameter of 14.5 mm and a thickness of 1.3 mm (in the orientation direction) was prepared. Four sets of 3.9 mm laminates were constructed. A mixed paste of oxides and fluorides shown in Table 3 was divided into two equal parts and applied between the two layers of the laminate. At that time, an appropriate amount of liquid paraffin was mixed with these powders to make it easier to apply between the layers, and the powder was applied in the form of a slurry. The coating amount was set so that the amount of Tb was 0.5 wt% relative to the sintered weight. In Test 3, the element ratio was set to Tb:Nd=1:1, and in Test 4, the amount of Tb from TbF ₃ and Tb ₄ O ₇ was equal and the total amount was 0.5 wt%. It was weighed as follows.

This three-layer laminate was loaded into a cylindrical mold shown in FIG. 2, and bonded and deformed using the same SPS device LABOX-325R as above at a maximum temperature of 700° C. and a pressure of 50 MPa. The three laminates were completely bonded, no elution of the Nd-rich phase from the surroundings was observed, and the thickness direction dimension was reduced from 3.9 mm to 3.6 mm or 3.7 mm, with a deformation rate of about 6%. It was a deforming process. This laminated integrated sintered body was subjected to GBD heat treatment at 890° C. for 20 hours in a vacuum, and then cut perpendicularly to the sample thickness direction to observe the cross-sectional structure including the bonding surface (cross section of the bonding layer). The measurement devices used were a HITACHI SU3500 scanning electron microscope (SEM) and a HORIBA EMAX ENERGY EX-250 energy dispersive X-ray spectrometer (EDS).

FIG. 7 shows SEM composition images taken at magnifications of 100x, 500x, 1000x, and 2000x. Here, regions where there are many elements with heavy atomic numbers are white, and regions where there are many light elements are black, so it can be seen that whitish regions are regions that contain many rare earth elements, and dark regions are regions that contain relatively few rare earth elements. . In FIG. 7, it can be seen that a whitish region is formed along the bonding surface, and it can be seen that many rare earth elements are present in this region. Table 3 above shows the average value of the thickness measured at 5 visual fields and 3 points in each visual field, for a total of 15 points. As shown in Table 3, the average value of the bonding surface (bonding layer) thickness is the thinnest for fluoride coating materials such as DyF ₃ and TbF ₃ , just under 4 μm, and for the oxides of Tb ₄ O ₇ and Nd ₂ O ₃ The thickness of the mixed material was 18.5 μm.

Next, FIGS. 8 and 9 show the elemental mapping results obtained by performing EDS measurement at a magnification of 1000 times on the cut surface of the neodymium laminated sintered magnet produced in Test 4. As shown in FIG. 8, in most regions of the joint surface (rare earth rich region), Nd, Pr, O, and F exist continuously along the joint surface, and Fe is not present here. On the other hand, in the region shown in FIG. 9 (Fe-rich metal region existing in a part of the bonding surface), a large amount of Fe exists, and almost no Nd, Pr, O, and F exist. In other words, although the bonding surface appears to have a continuous structure with a thickness of 8.60 μm, it actually consists of a region made of rare earth oxides and rare earth fluorides (rare earth rich region) and an Fe rich region. It was found that it consists of.
The above observation results were similarly observed not only in Test 4 but also in Tests 1 to 3, and are a structure unique to neodymium laminated sintered magnets. In other words, rare earth oxides and fluorides have high electrical resistance, so they improve the total electrical resistivity of the bonding surface, and at the same time, they are used so that the Fe-rich region straddles between adjacent unit neodymium sintered magnets via the bonding layer. It can be considered that the neodymium sintered magnets are strongly connected in a bridge shape and play a role in ensuring the high strength of the neodymium laminated sintered magnet.

Hereinafter, specific embodiments of the neodymium laminated sintered magnet of the present invention will be described in detail with reference to Examples and Comparative Examples, but the content of the present invention is not limited thereto.
[Example 1 and Example 2]

SC alloys having the compositions shown in Table 4 below were produced. After crushing with hydrogen, 0.05 wt % of methyl caprylate was mixed therein, and the mixture was kneaded and coarsely pulverized using a Piccolo stirrer. The raw material after coarse pulverization was jet milled in a nitrogen atmosphere using a jet mill device MJT-LAB manufactured by Hosokawa Micron Corporation. The crushing pressure was 0.6 MPa, and the average particle diameter D50 was set at around 3 μm by adjusting the rotation speed of the classification rotor. The thus obtained fine powder raw material was mixed with 0.07 wt % of methyl laurate and kneaded using a Piccolo stirrer to obtain a pre-sintering raw material. After filling this into a carbon container at a packing density of 3.6 g/cc, a pulsed magnetic field of a maximum of 4 T was applied multiple times to orient the powder particles. This oriented body was put into a sintering furnace together with the carbon mold, and sintered in vacuum at 1030° C. for 4 hours to obtain a block-shaped sintered body. Using a 7 mm cube-shaped evaluation sample cut out from this sample, evaluation was performed using a pulse BH tracer PBH-1000 manufactured by Nippon Denji Sokki Co., Ltd. As a result, the residual magnetic flux density Br = 13.8 kG and the coercive force iHc = 19.9 kOe. Ta.

Further, a predetermined number of unit neodymium sintered magnets with a target size of 15.24 mm x 4.24 mm (orientation direction) x 1.8 mm were prepared from the block-shaped sintered body by processing. Separately, materials to be applied between the layers were prepared. The components are Test 1 and Test 4 shown in Table 3. This time, the number of laminated layers of the unit neodymium laminated sintered magnet was set to 24. The inner shape of the mold into which this laminate is loaded is set to the target product size, specifically, 15.5 (±0.1) mm x 5.0 (±0.05) mm (orientation direction), and pressure is applied. The direction size was ensured to be longer than the target product size so that the upper and lower punches could be set.

Thereafter, the coating materials for Test 1 and Test 4 were applied between the layers to produce two types of 24-sheet laminates. These are referred to as Example 1 and Example 2, respectively. An outline of the manufacturing method is shown in FIG. First, a coating jig shown in 10a) is prepared. This jig has a through hole that is slightly smaller than the size of the unit neodymium sintered magnet. The thickness of this through-hole is designed so that a predetermined amount of coating can be achieved if the hole is evenly filled with the coating material. As shown in 10b), the coating material is filled along the through hole and the upper surface is scraped off with a spatula to adjust the coating amount to the calculated value. After that, this jig is removed, and the unit neodymium sintered magnets coated with the coating material are taken out and stacked. At that time, if a laminate holding jig as shown in 10c) is prepared, the laminate can be transported. It is convenient for Of course, the application jig is not limited to this. In short, any material that can be coated with a predetermined amount of coating material and that can be easily taken out and laminated will suffice.

Next, a set of 24 laminates of each of Example 1 and Example 2 prepared in this way was set in a carbon mold for SPS manufactured according to the above product dimensions. The mold had a split structure to facilitate sample removal after SPS treatment. The laminate was set in this split mold while aligning the upper and lower punches. Since a split mold is used, a so-called die is also required to hold the split mold. The unit neodymium sintered magnet laminate, upper and lower punches, split molds, and die assembled in this way were set in an SPS device (LABOX-325R) manufactured by Sinterland Co., Ltd., and the upper punch was equipped with a K thermocouple for temperature measurement. I installed it. After evacuating the inside of the SPS device to a degree of vacuum of about 20 Pa using a rotary pump, the device was heated until the thermocouple reading reached 850° C. while passing a large current of several hundred A through upper and lower punches. After the temperature reached 850° C., a pressure of 65 MPa was applied to the unit neodymium sintered magnet laminate using upper and lower punches to perform a bonding and deforming process. In this experiment, laminates were subjected to SPS treatment using different coating materials in Example 1 and Example 2, but the SPS heating and pressing conditions were the same. The results are shown in FIG. 11, and the final dimensions are shown in Table 5.

As described above, these two neodymium laminated sintered magnets have almost the same size and shape, and are completely indistinguishable from each other in appearance. The flatness of two pairs of opposing outer surfaces parallel to the pressurizing direction (i.e., two pairs of outer surfaces where the laminated state can be visually recognized) was evaluated using a surface roughness meter with a sensor head diameter of 0.05 mm. It was confirmed that the value was within a range of plus or minus 0.05 mm around the center value. This is because the lamination misalignment that inevitably occurs during the lamination stage is corrected by the SPS process in which each unit neodymium sintered magnet is deformed and pressed against the inner surface of the mold. Therefore, in the present invention, the outer surface is flat even without mechanical processing such as polishing or grinding. As a result, the size of the neodymium laminated sintered magnet becomes the same as the dimension defined by the inner surface of the mold, and its density can be estimated to be approximately 100%. This allows the above-mentioned high Br characteristics to be obtained.

The neodymium laminated sintered magnet after this SPS process was subjected to GBD treatment at 890° C. for 20 hours in a vacuum as a post-process. Table 6 shows the results of evaluating the magnetic properties of the resulting neodymium laminated sintered magnets according to Examples 1 and 2 without processing and using the same size.
The measuring device used at this time was a highly sensitive vibrating sample magnetometer TM-VSM70100-SMS device manufactured by Tamagawa Seisakusho Co., Ltd., and the characteristics were evaluated by applying a maximum magnetic field of 8 T using a superconducting magnet coil.

From the above results, the neodymium laminated sintered magnet according to this example has very high magnetic properties.Although the type of Tb compound laminated between the layers is different between Example 1 and Example 2, the Tb content is It was also found that the same coercive force can be obtained if the same adjustment is made.

[Comparative example 1]
FIG. 12 shows the results of SPS treatment performed under the same conditions as in Example 1, except that the temperature conditions were changed to 945° C. and the pressure was changed to 30 MPa. The liquid phase was eluted and a reaction with the split mold was observed, and cracks spanning the joint surface were generated on the top and center of the sample. This is because the low melting point Nd-rich phase was eluted and came into contact with the split mold, reacting with it, and cracking occurred during cooling because the temperature exceeded the appropriate temperature range and the applied pressure was low.

In Comparative Example 1, the heating temperature and pressurizing pressure conditions were not appropriate, and the elution of the low melting point Nd-rich grain boundary phase was significant, so the magnet components may have changed. Since this elution occurs from the inside of the neodymium laminated sintered magnet toward the inner wall of the mold, there is a possibility that the components differ depending on the part of the neodymium laminated sintered magnet. Therefore, to determine whether there is a difference in composition between the surface layer region less than 50 μm from the magnet surface near the inner wall and the magnet center (region more than 50 μm from the surface), the magnification of SEM-EDX was set at a low magnification of about 50 times. investigated. Table 7 lists the results regarding the main elements in comparison with the case of Example 1.

From this result, in the case of Comparative Example 1, the total amount of rare earth elements near the surface layer is about 34 wt%, while the inside is about 30 wt%, a difference of about 4 wt%. I understand. As a precaution, a similar analysis was conducted for Example 1, but no large difference in the total amount of rare earth elements was observed between the surface layer and the interior as in Comparative Example 1 (the difference was 0.11 wt%). This can be said to be a feature of the neodymium laminated sintered magnet according to the present invention in which the elution of the Nd-rich grain boundary phase is controlled.

Regarding the neodymium laminated sintered magnet according to Comparative Example 1, a sample of the maximum removable size (15.5 mm x 5.0 mm x 20.0 mm) was subjected to additional heat treatment in vacuum at 890° C. for 20 hours to obtain magnetic properties. The results are shown in Table 8.

From Table 6, very high magnetic properties are obtained in the neodymium laminated sintered magnet according to the example, and the sum of the coercive force iHc and the maximum magnetic energy product (BH) max is Magic Number (hereinafter referred to as MN). The world's highest performance was achieved with a score of 77 or higher. On the other hand, in the sample of Comparative Example 1, which was damaged due to the elution of the low melting point Nd-rich phase, although the Br properties were high, the iHc properties and squareness deteriorated, which is thought to be due to the decrease in the rare earth element content. Therefore, the MN was a little less than 69 (Table 8), and the magnetic properties remained mediocre that could be obtained by ordinary methods.

[Example 3 and Example 4]
A laminate of unit neodymium sintered magnets was prepared using the SC raw material with composition A shown in Table 1 and the coating materials of Test 1 and Test 4 in Table 3 so that the Tb amount was 0.5 wt%. A neodymium laminated sintered magnet was produced under the same conditions as in Example 1 and Example 3, except that the SPS conditions were a heating temperature of 700° C. and an SPS pressure of 65 MPa. Its magnetic properties are shown in Table 9.

Similar to Examples 1 and 2, very high magnetic properties were exhibited. As a result of cross-sectional observation of the bonding surfaces, the characteristics of the bonding surfaces shown in FIGS. 8 and 9, namely, the average thickness of the bonding layer in Example 3 was 3.71 μm, and in Example 4 was 8.60 μm, and In both Examples, the Fe-rich metal phase region shown in FIG. 9 and the rare earth oxide and rare earth fluoride phases shown in FIGS. 8 and 9 were observed. As a result of elemental analysis by EDS of the cross section of the bonding layer, the volume ratio of the rare earth-rich region in the bonding layer in the neodymium laminated sintered magnet of Example 3 was approximately 20%, and that of the neodymium laminated sintered magnet of Example 4. The volume ratio of the rare earth-rich region in the bonding layer was approximately 80%.
Eddy current loss was measured for the neodymium laminated sintered magnets of Examples 3 and 4 having these different rare earth compound layers. In this case, as shown in Table 10, a continuum neodymium sintered magnet fabricated from a block magnet to have almost the same shape and a unit neodymium sintered magnet are laminated by resin bonding to create a resin-bonded magnet fabricated in substantially the same shape. were also measured at the same time. As a result, the degree of eddy current loss of the neodymium laminated sintered magnet according to the present invention was compared between the case where the neodymium layer was not laminated and the case where the magnet was completely insulated and bonded with resin.

The measurement system used in this measurement is shown in FIG. First, a C-shaped yoke made of a laminated iron core having a circular cross section was prepared, and a 9 mm gap was provided in the yoke to set the laminated sample. A coil that excites this C-shaped yoke is attached around the yoke on the opposite side to the gap, and a search coil with 50 turns is attached to the sample to be measured, as shown in Figure 14, in the direction of the magnetic field generated by the C-shaped yoke, that is, in the orientation direction. They were set so that they were perpendicular to each other. In order to pass a large alternating current through the C-type yoke, it was fixed as shown in FIG. 15 and measurements were taken. The measurement results are shown in FIGS. 16 and 17.
FIG. 16 shows the frequency dependence of eddy current loss up to a frequency of 200 Hz when the current value is 5 A. From this, the obvious result was that the resin-bonded sample had the smallest eddy current loss, and the continuum sample had the largest. On top of that, the eddy current loss when the average thickness of the high electrical resistance film of the bonding layer is 3.71 μm is almost equivalent to the eddy current loss of the continuum, while when the average thickness is 8.60 μm, the loss level is It was found to be equivalent to the resin bonded sample.
On the other hand, Figure 17 shows the results for a lower current value of 2 A and a higher frequency of 500 Hz, where the overall trend is the same as in Figure 16, but even with an average thickness of 3.71 μm, the continuum sample It can be seen that there is a decrease in loss compared to the above. Generally, as the frequency increases, the distance into which the magnetic field penetrates, the so-called skin depth, decreases, so even if the high-resistance film thickness is small, it is expected that the magnetic field separation effect will increase and the reduction in eddy current loss will become apparent. That is, it is considered that as the excitation frequency becomes higher, even a high electrical resistance film thickness of 3.71 μm becomes effective in reducing eddy current loss.

[Example 5 and Example 6]
In this example, 10 unit neodymium sintered magnets having the composition C shown in Table 11 below were manufactured using the NPLP method (New-PressLess Process, Patent No. 6280137, WO2016/047593) previously devised by the present inventors. Then, a bonding/deforming test was conducted using an SPS device. Table 12 shows the weight, size, etc. of unit neodymium sintered magnets produced by the NPLP method.

The weight and size of each unit neodymium sintered magnet are not the same, and there are variations in weight and size. However, by laminating the coating material of Table 3 Test 2 between the layers and applying SPS treatment at a heating temperature of 850°C and a pressing force of 60 MPa, the width was 15.91 mm, the orientation direction was 7.61 mm, and the pressing direction was 15.91 mm. A rectangular parallelepiped neodymium laminated sintered magnet with a thickness of 17.05 mm was prepared, and then subjected to GBD treatment in vacuum at 875° C. for 16 hours to evaluate its magnetic properties (Example 5). FIG. 18 shows a photograph of the neodymium laminated sintered magnet according to Example 5, and Table 13 shows the magnetic properties obtained. Table 13 also shows the magnetic properties when the coating material of Test 5 in Table 3 was used to stack 10 unit sintered magnets with the same weight and size variations as in Table 12. Example 6). The flatness of the opposing surface pressed against the mold in each example was evaluated using the same measurement method as above, and was found to be at most 0.1 mm, which is almost the same as when a unit neodymium laminated magnet was prepared by cutting. .

In this way, regardless of whether a Tb compound or a Dy compound is used as the coating material, it has high Br, coercive force of about 20 kOe or more, and MN of 77.8 and 74.0, which are the world's best magnetic properties. A neodymium laminated sintered magnet having the following properties was obtained. As a result, unit neodymium sintered magnets can be manufactured using any cost-effective method, whether it is the NPLP method or processing, and the magnetic properties themselves can be determined by appropriately selecting the GBD coating material sandwiched between the layers. I understand that.

In the examples so far, it has been shown that a high coercive force can be obtained by performing GBD processing after SPS processing, and the reason is as follows. That is, although the GBD coating material is sandwiched between layers when stacking unit neodymium sintered magnets, no disadvantages to the GBD treatment process due to the subsequent SPS treatment have been observed. On the contrary, the diffusion distance of heavy rare earth elements such as Dy and Tb due to GBD treatment is short at maximum, about 2.5 mm, that is, about the thickness of a unit neodymium sintered magnet, and uniform magnetic properties can be obtained regardless of the product shape. This is because it will be done.

[Example 7]
A neodymium laminated sintered magnet obtained by preparing a lens-shaped unit neodymium sintered body having a thickness of 2 mm and having the above-mentioned composition B, laminating 22 sheets, applying the coating material of Test 3 between the laminated layers, and performing an SPS test. A photograph is shown in Figure 19.
The neodymium laminated sintered magnet produced in this way had a flatness of plus or minus 0.34 mm on the upper and lower convex long surfaces of the lens shape, and a flatness of plus or minus 0.09 mm on the left and right short surfaces of the lens. In other words, it is thought that the left and right short surfaces (thinner end portions of the lens) deformed first and hit the inside of the mold, and the deformation stopped there. When we measured the characteristics of this neodymium laminated sintered magnet, we confirmed that even with a product with a complicated lens shape, we could obtain a neodymium laminated magnet with no problems in other dimensions, including magnetic properties.

In addition, in the present invention, when a laminate of unit neodymium sintered magnets (a laminate before being pressurized) is placed in a space inside a mold, a gap is formed around the laminate, that is, a gap between the laminate and the inner wall of the mold. By manufacturing unit neodymium sintered magnets by considering the deformation rate in each direction so that when the laminate is deformed by pressure, the entire surface of the laminate comes into contact with the inner wall of the mold at the same time. It is effective to manufacture neodymium laminated sintered magnets using a mold having an internal space of the same size and shape.

The neodymium laminated sintered magnet of the present invention has high magnetic properties and excellent electrical resistance, and can be used in motors for various home appliances, industrial motors, and especially EVs (electric vehicles) and HEVs (hybrid vehicles). ) can be used as a magnet.

Claims (8)

A neodymium laminated sintered magnet in which a plurality of unit neodymium sintered magnets are stacked, and the unit neodymium sintered magnets are joined together via a bonding layer to be integrated,
A neodymium laminated sintered magnet, wherein the bonding layer of the neodymium laminated sintered magnet includes a rare earth-rich region, and the rare earth-rich region has electrical insulation properties. The neodymium laminated sintered magnet according to claim 1, wherein the thickness of the bonding layer is 1.0 μm or more and 200 μm or less. The neodymium laminated sintered magnet according to claim 1 or 2, wherein the rare earth-rich region exists continuously and/or intermittently in the bonding layer. An Fe-rich metal region containing 50% by weight or more of Fe is present in the bonding layer, and the Fe-rich metal region connects adjacent unit neodymium sintered magnets via the bonding layer. The neodymium laminated sintered magnet according to claim 1 or 2, characterized in that: The difference between the weight percent of the total amount of rare earth elements in the surface layer region less than 50 μm from the surface of the neodymium laminated sintered magnet and the weight percent of the total amount of rare earth elements in the inner region 50 μm or more away from the surface is less than 1 weight percent. The neodymium laminated sintered magnet according to claim 1 or 2, characterized in that: In the rare earth rich region existing in the bonding layer, at least one of Dy element and Tb element is present as a heavy rare earth element, and the heavy rare earth element is Nd ₂ Fe ₁₄ of each unit neodymium sintered magnet. The neodymium laminated sintered magnet according to claim 1 or 2, wherein the neodymium layered sintered magnet diffuses from each bonding layer toward the adjacent bonding layer along the grain boundary phase of the B crystal. The neodymium according to claim 1 or 2, characterized in that the neodymium has magnetic properties in which the sum of the maximum magnetic energy product (BH) max (MGOe) expressed in the CGS unit system and the coercive force iHc (kOe) is 70 or more. Laminated sintered magnet. According to claim 1 or 2, the outer surfaces of the neodymium laminated sintered magnet orthogonal to the bonding layer have a flatness of 0.1 mm or less on at least one pair of opposing outer surfaces or all outer surfaces. neodymium laminated sintered magnet.

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