WO2014142137A1 - RFeB系焼結磁石の製造方法及びそれにより製造されるRFeB系焼結磁石 - Google Patents
RFeB系焼結磁石の製造方法及びそれにより製造されるRFeB系焼結磁石 Download PDFInfo
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- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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- B22F9/00—Making metallic powder or suspensions thereof
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
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- B22F9/00—Making metallic powder or suspensions thereof
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- C22C2202/02—Magnetic
Definitions
- the present invention relates to an RFeB system including Nd 2 Fe 14 B (“R” is a rare earth element such as Nd, including Y. Typically represented by R 2 Fe 14 B, R, Fe and B The present invention relates to a method for manufacturing a sintered magnet and an RFeB-based sintered magnet manufactured thereby.
- R is a rare earth element such as Nd, including Y.
- the present invention relates to a method for manufacturing a sintered magnet and an RFeB-based sintered magnet manufactured thereby.
- the RFeB-based sintered magnet is a permanent magnet manufactured by orienting and sintering RFeB-based alloy powder. This RFeB-based sintered magnet was discovered by Sagawa et al. In 1982, but has high magnetic properties far surpassing the permanent magnets used so far, and is relatively abundant in rare earth, iron and boron. It has the feature that it can be manufactured from inexpensive raw materials.
- RFeB-based sintered magnets demand for RFeB-based sintered magnets is expected to increase further in the future, such as permanent magnets for hybrid and electric vehicle motors.
- automobiles must be assumed to be used under severe loads, and their motors must also be guaranteed to operate in a high temperature environment (eg 180 ° C.). Therefore, an RFeB-based sintered magnet having a high coercive force that can suppress a decrease in magnetization (magnetic force) due to an increase in temperature is demanded.
- One way to improve the coercive force of NdFeB sintered magnets without using RH is to use the crystal grains that form the main phase (Nd 2 Fe 14 B) inside the NdFeB sintered magnet (hereinafter referred to as “ There is a method of reducing the particle size of “main phase particles” (non-patent document 1). It is well known that the coercive force of any ferromagnetic material (or ferrimagnetic material) is increased by reducing the grain size of the internal crystal grains.
- the particle size of the alloy powder used as a raw material for the RFeB-based sintered magnet has been reduced.
- the HDDR method As one means for refining crystal grains, the HDDR method is known.
- a lump or coarse powder (hereinafter collectively referred to as “coarse powder”) of RFeB alloy having a diameter of several hundred ⁇ m to 20 mm is heated in a hydrogen atmosphere at 700 to 900 ° C. (Hydrogenation)
- the atmosphere is switched from hydrogen to vacuum, Hydrogen is desorbed from the RH 2 phase, thereby causing a recombination reaction in each phase within each grain of the raw material alloy coarse powder.
- crystal grain refined coarse particles coarse particles in which RFeB-based phases (crystal grains) having an average diameter of 1 ⁇ m or less are formed are obtained.
- the process of forming the crystal grain refined coarse powder grains in this way is referred to as “crystal grain refinement process”.
- Patent Document 1 describes that a sintered magnet is manufactured using a powder obtained by pulverizing crystal grain refined coarse particles after the HDDR treatment with a jet mill using nitrogen gas.
- the crystal grain refined coarse powder becomes a crystal grain aggregate of 100 ⁇ m to several mm in which crystal grains of 1 ⁇ m or less are formed.
- the orientation axis of each crystal grain is not aligned in a normal HDDR process, and is isotropic.
- Anisotropy is also produced by controlling the composition of the raw material alloy and the atmosphere during the HDDR treatment, but the degree of orientation variation is large compared to sintered magnets. For this reason, in the method of pulverizing the alloy coarse powder after the HDDR processing described in Patent Document 1 with a nitrogen gas and sintering, the following problems occur.
- Non-patent Document 2 it has been studied to increase the degree of orientation by solidifying the powder after the HDDR treatment by hot pressing (Non-patent Document 2), but the productivity is poor and the magnetic properties are not as good as the sintered magnet. There are problems such as.
- the problem to be solved by the present invention is to provide a method for producing an RFeB-based sintered magnet having an average particle size of main phase particles of 1 ⁇ m or less and a substantially uniform particle size distribution with a high degree of orientation.
- the RFeB-based sintered magnet manufacturing method according to the present invention made to solve the above problems is as follows. It is obtained from a microscopic image obtained by pulverizing crystal grain refined coarse particles in which RFeB-based crystal grains having an average particle size distribution with an equivalent circle diameter obtained from a microscopic image of 1 ⁇ m or less are formed. Using an RFeB-based alloy powder in which the average value of the particle size distribution due to the equivalent circle diameter is 1 ⁇ m or less and 90% or more of the crystal grains are separated from each other by area ratio, the powder was oriented by a magnetic field. A tangible body is produced and sintered.
- “90% or more in area ratio” means the ratio of the area of the entire single crystal particle to the area of the entire powder composed of single crystal particles and polycrystalline particles.
- “manufacturing a tangible body” means that a product having the same shape as or close to that of the final product (referred to as “tangible body”) is made using RFeB-based alloy powder.
- This tangible body may be a molded body obtained by press-molding RFeB-based alloy powder into the same shape as or close to the final product, or RFeB-based alloy powder in a container (mold) having the same or close shape as the final product. (Without press molding) may be used (see Patent Document 2).
- the “oriented tangible body” means that the RFeB-based alloy powder is oriented after being shaped, oriented after being oriented, and oriented and shaped simultaneously.
- any of what you have done can be. If the tangible body is not press-molded and the mold is filled with RFeB alloy powder, sintering can be performed without applying mechanical pressure to the tangible body (ie, RFeB alloy powder in the mold). It is desirable to do. In this way, RFeB alloy powder having a high coercive force and a small particle size can be easily handled by not applying mechanical pressure to the RFeB alloy powder in the process of producing and sintering the tangible body. Therefore, an RFeB-based sintered magnet having a high maximum energy product can be obtained (see Patent Document 2).
- the crystal grain refined coarse powder after the crystal grain refinement treatment is pulverized to 1 ⁇ m or less, which is the same as the average diameter of the fine crystal grains formed therein, (90% or more by area ratio in the microscopic image) becomes single crystal particles.
- an RFeB sintered magnet having an average particle size of main phase particles of 1 ⁇ m or less and a high degree of orientation can be produced.
- the particle size distribution is sharpened by reducing the number of unmilled polycrystalline particles, liquid phase sintering with high uniformity can be performed.
- the RFeB-based alloy powder having the above characteristics is produced by subjecting the raw material alloy coarse powder to the HDDR method (crystal graining treatment) to produce a crystal grain refined coarse grain, and the crystal grain refined coarse powder is converted to hydrogen. It can be obtained by crushing by a crushing method and then crushing by a jet mill method using helium gas.
- the HDDR method not only refines the grains in the raw material alloy with a uniform grain size distribution, but also disperses the rare earth-rich phase between the refined grains with high uniformity during the recombination reaction. it can. This facilitates crushing of the polycrystalline particles into single crystal particles during hydrogen crushing or jet mill crushing, and a powder having an average particle size of 1 ⁇ m or less and a uniform particle size distribution can be obtained.
- the rare earth-rich phase can be dispersed with high uniformity. Since the rare earth-rich phase exists between the main phase particles, the magnetic coupling between the main phase particles can be weakened. As a result, when a rare earth-rich phase exists between the main phase particles, even if a reverse magnetic field is applied to the entire magnet and some main phase particles are magnetically reversed, propagation of the magnetic field reversal to the adjacent particles is suppressed. The coercive force of the sintered magnet is improved.
- strip cast As raw material alloy coarse powder before processing by HDDR method, coarse powder of alloy produced by strip cast method (“strip cast” alloy) can be used, but alloy produced by melt spinning method (“ It is more desirable to use a coarse powder of “melt melt spinning alloy”.
- the strip casting method rapidly cools the molten metal by pouring the molten material alloy onto the surface of the rotating body such as a roller or a disk, and the melt spinning method ejects such molten metal from the nozzle to the surface of the rotating body. By cooling, it is cooled more rapidly (super rapid cooling) than the strip casting method.
- the strip cast alloy has crystal grains with a grain size of several tens of ⁇ m or more, and lamellar (lamella) -like rare earth-rich phases are formed at intervals of 4 to 5 ⁇ m.
- the alloy has crystal grains having a grain size of 10 nm to several ⁇ m, and the rare earth-rich phase is uniformly dispersed so as to fill the gaps between the crystal grains. Due to the difference in the form of the rare earth-rich phase, when the HDDR treatment is performed on the strip cast alloy, the rare earth-rich phase does not penetrate between the grains of the main phase particles near the middle of the adjacent lamellae. There will be crystal grains surrounded by rich phase and non-enclosed crystal grains, and the dispersion of rare earth rich phase is incomplete.
- a crystal grain refined coarse powder particle in which a rich phase is uniformly and finely dispersed between crystal grains can be obtained. Then, by using an alloy powder obtained by finely pulverizing the crystal grain refined coarse particles as a raw material, it is possible to produce an RFeB-based sintered magnet in which a rare earth-rich phase exists with high uniformity between main phase particles.
- the RFeB-based sintered magnet manufacturing method can manufacture an RFeB-based sintered magnet having an average particle diameter of main phase particles of 1 ⁇ m or less and an orientation degree of 95% or more.
- the crystal grain refined coarse powder particles obtained by subjecting the raw material alloy coarse powder to a crystallizing treatment such as the HDDR method are mutually connected.
- the main phase particles which were not obtained by a combination of conventional crystal graining treatment and nitrogen gas jet mill pulverization, were obtained.
- An RFeB sintered magnet having an average particle diameter of 1 ⁇ m or less, a high degree of orientation, and a nearly uniform particle size distribution can be obtained.
- the graph which shows the particle size distribution of the main phase particle
- the sintered magnet manufacturing method of the present embodiment includes an HDDR process (step S1), a pulverization process (step S2), a filling process (step S3), an orientation process (step S4), and a sintering process (step S4).
- step S5 There are five steps in step S5). Hereinafter, these steps will be described.
- SC alloy coarse powder raw material alloy coarse powder
- SC alloy coarse powder was prepared using a strip cast (SC) alloy lump having the composition shown in Table 1 below.
- FIG. 2 shows an image of the back scattered electron (BSE) image of the SC alloy coarse particles.
- BSE back scattered electron
- the white portion of the three phases is a rare earth-rich phase having a higher rare earth content than the main phase (R 2 Fe 14 B) in the alloy grains.
- the oxygen content of the alloy coarse powder was 88 ⁇ 9 ppm, and the nitrogen content was 25 ⁇ 8 ppm.
- the SC alloy coarse powder of FIG. 2 is exposed to hydrogen gas, and hydrogen atoms are occluded in the SC alloy coarse powder.
- hydrogen atoms are occluded in the main phase, but are mainly occluded in the rare earth-rich phase.
- hydrogen is mainly stored in the rare earth-rich phase, so that the rare earth-rich phase expands in volume and the SC alloy coarse powder becomes brittle.
- FIG. 3 is a graph showing the temperature history and pressure history during the HDR process.
- the above SC alloy coarse powder was heated in a hydrogen atmosphere at 950 ° C. and 100 kPa for 60 minutes, whereby the Nd 2 Fe 14 B compound (main phase) in the SC alloy coarse powder was NdH. Decomposition into three phases of 2 , Fe 2 B and Fe (“HD” in the figure).
- the temperature was lowered to 800 ° C. in a hydrogen atmosphere, and then Ar gas was allowed to flow for 10 minutes while maintaining the temperature at 800 ° C. Then, by maintaining in a vacuum atmosphere at 800 ° C.
- FIG. 4 (a) is a secondary electron image (SEI) image of the crystal grain refined coarse powder obtained by subjecting the SC alloy coarse powder of FIG. 2 to the HDRR process of FIG.
- FIG. 4 (b) shows the outline of each crystal grain extracted from this SEI image, the area value S of the portion surrounded by the outline is obtained for each crystal grain, and the diameter of the circle corresponding to the area value S is obtained.
- D 2 ⁇ (S / ⁇ ) 0.5
- the pulverization step first, an aggregate (powder) of crystal grain refined coarse particles is exposed to hydrogen gas, whereby hydrogen is occluded and embrittled in the crystal grain refined coarse powder particles.
- rough pulverization is performed with a mechanical pulverizer, and an organic lubricant is added and mixed as a pulverization aid.
- the coarse powder thus obtained (hereinafter referred to as “HDDR coarsely pulverized powder”) is used as a helium gas circulation jet pulverization system (manufactured by Nippon Pneumatic Industry Co., Ltd., hereinafter referred to as “He jet mill”). Introduce and grind the coarsely pulverized powder after the HDRD.
- Helium gas provides a high-speed airflow that is about three times faster than nitrogen gas. Therefore, by accelerating the raw material at high speed and repeating the collision, it becomes possible to pulverize to an average particle size of 1 ⁇ m or less, which was impossible with a conventional nitrogen gas jet mill. In this way, after coarsely pulverized powder after HDDR, an organic lubricant is added and mixed. Thereby, the friction between the fine powder particles is reduced, and high-density filling of the mold and magnetic field orientation are facilitated.
- FIG. 5 (a) is an SEI image of the alloy powder obtained by introducing this coarsely pulverized powder after HDDR into a He jet mill having a pulverization pressure of 0.7 MPa after sufficient hydrogen storage treatment at room temperature. Comparing FIG. 4 (a) and FIG. 5 (a), the crystal grains are not separated in FIG. 4 (a), but in FIG. 5 (a) they are separated from each other.
- FIG. 5 (b) is a graph showing the equivalent circle diameter of each particle in the SEI image of FIG. 5 (a) as a particle size distribution (the same applies to the particle size distributions of FIGS. 6 to 9 described later). The average value and standard deviation of the particle size distribution in FIG. 5 (b) are 0.57 ⁇ m and 0.21 ⁇ m.
- the ratio of unground polycrystalline particles that were not pulverized to single crystal particles despite the treatment in the pulverization step was 10% in area ratio.
- the alloy powder of FIG. 5 is referred to as the alloy powder of “Example 1”.
- Fig. 6 (a) shows the SEI image of the alloy powder obtained by inserting the coarsely pulverized post-HDDR in Fig. 4 into a He jet mill with a pulverization pressure of 0.7 MPa after hydrogen storage at 200 ° C for 5 hours.
- 6 (b) is the particle size distribution, and the average value and standard deviation are 0.56 ⁇ m and 0.19 ⁇ m. Further, the proportion of unground polycrystalline particles in this alloy powder was 3% in area ratio.
- the alloy powder of FIG. 6 is referred to as the alloy powder of “Example 2”. It can be seen that the alloy powder of Example 2 has a smaller proportion of particles of 0.8 ⁇ m or more than the alloy powder of Example 1, and is further finely pulverized. That is, by storing hydrogen at 200 ° C., the grindability was improved as compared with Example 1 in which the hydrogen storage treatment was performed at room temperature.
- FIG. 8 (a) shows the SEI image of this alloy powder
- FIG. 8 (b) shows the particle size distribution.
- the average value and standard deviation of the particle size distribution are 0.70 ⁇ m and 0.33 ⁇ m.
- FIG. 9 shows the results when an alloy powder is produced only by hydrogen storage and a He jet mill without performing the HDDR process.
- This alloy powder is obtained by storing hydrogen in an SC alloy coarse powder at room temperature, coarsely pulverizing it to produce a coarse powder having an average particle size of several hundreds of ⁇ m, and then using a He jet mill with a pulverization pressure of 0.7 MPa. And it was obtained by pulverizing under the same conditions as in the second example.
- FIG. 9 (a) is an SEI image of this alloy powder
- FIG. 9 (b) is its particle size distribution. The average value and standard deviation of this particle size distribution are 0.95 ⁇ m and 0.63 ⁇ m.
- This alloy powder is referred to as “Comparative Example 2” alloy powder.
- the particle size distribution becomes very broad as shown in FIG. 9 (b). That is, the alloy powder is a mixture of alloy powder particles having a large particle size and alloy powder particles having a small particle size (FIG. 9 (a)).
- FIG. 10 is a comparison of SEI images of the alloy powders of Examples 1 and 2 and Comparative Examples 1 and 2. As can be seen by directly comparing the respective SEI images, the alloy powders of Examples 1 and 2 have particles having a smaller particle diameter than the alloy powders of Comparative Examples 1 and 2 almost uniformly.
- NdFeB-based sintered magnets were produced from the alloy powders of Example 1, Example 2 and Comparative Example 1 prepared from the coarsely pulverized powder after HDDR by the following procedure.
- an organic lubricant is mixed in each alloy powder, each alloy powder is filled into a cavity of a predetermined mold at a filling density of 3.6 g / cm 3 (filling process), and mechanical pressure is applied to the alloy powder in the cavity.
- an AC pulse magnetic field of about 5T was applied twice and a DC pulse magnetic field was applied once (alignment process).
- the oriented alloy powder was placed in a sintering furnace together with the mold, and then sintered by vacuum heating at 880 ° C. for 2 hours without applying mechanical pressure to the alloy powder (sintering process). .
- the sintered body thus obtained was machined to produce a cylindrical sintered magnet having a diameter of 9.8 mm and a length of 6.5 mm.
- Table 2 shows the magnetic properties of NdFeB-based sintered magnets produced from the above three types of alloy powders. This magnetic property was measured by a pulse BH tracer (manufactured by Nippon Electromagnetic Sokki Co., Ltd.).
- H cj is the coercive force
- B r / J s is the degree of orientation
- H K is the absolute value of the magnetic field when the magnetization is reduced by 10% from the residual magnetization
- SQ is the squareness ratio
- H K is H cj (Value divided by). The larger these values are, the better magnet characteristics are obtained.
- the graph of the 1st quadrant of the magnetization curve (JH curve) measured by the pulse BH tracer is shown in FIG.
- the sintered magnets of Examples 1 and 2 obtained a high degree of orientation B r / J s of 95% or more.
- the sintered magnet manufactured from the alloy powder of Comparative Example 1 (hereinafter referred to as “sintered magnet of Comparative Example 1”) had an orientation degree B r / J s of less than 95%. This is because many unmilled polycrystalline particles remained (more than 10%), and reducing the area ratio (ratio) occupied by the unmilled polycrystalline particles gives a high degree of orientation B r / J s It turned out to be necessary.
- Example 2 when Example 1 and Example 2 were compared, a higher squareness ratio SQ was obtained in Example 2. This is considered to be because the hydrogen occlusion process in the pulverization process was performed while heating, not at room temperature.
- the heating temperature is less than 100 ° C.
- hydrogen is occluded in both the main phase and the rare earth-rich phase, and thus both expand greatly.
- the heating temperature exceeds 300 ° C.
- the rare earth-rich phase has a structure of RH 2 and the hydrogen storage amount decreases. For this reason, it is considered that the strain between the main phase and the rare earth-rich phase is reduced.
- the heating time is less than 1 hour, the influence is small, and if it exceeds 10 hours, it is not preferable for production.
- the heating temperature in the hydrogen storage step is 100 to 300 ° C. and the heating time is 1 to 10 hours.
- FIG. 12 is a BSE image of a cross-section including the orientation axes of these three types of sintered magnets and the sintered magnet manufactured from the alloy powder of Comparative Example 2, and FIG. 13 is the magnetic pole surface of these four types of sintered magnets ( FIG. 14 shows the particle size distribution of the equivalent-circle diameter of the main phase particles in the sintered magnet obtained by image processing from the SEI image of the fracture surface. It is a graph to show.
- the white part in FIG. 12 is a rare earth (Nd) rich phase.
- the main phase particles in this example have a feature of low flatness as described below.
- Flatness is expressed by the ratio (b / a) between the longest axis (a) of the cross section of the crystal grain including the orientation axis and the length (b) of the axis perpendicular to it. Means. If the grain size is the same, a b / a value closer to 1 means that the specific surface area is smaller and the crystal grain boundary is smaller, so that there is an advantage that the required rare earth-rich phase can be reduced.
- heavy rare earth elements Dy, Tb
- are also diffused into the grain boundaries of the sintered magnet see, for example, Patent Document 3
- the b / a value obtained from FIG. 12 was 0.65 ⁇ 0.17 (0.48 to 0.82) in Example 1, and 0.62 ⁇ 0.17 (0.45 to 0.79) in Example 2.
- the b / a value estimated from FIG. 9 of the same document is 0.23 ⁇ 0.08.
- the difference is that in the hot plastic working magnet, the main phase particles are deformed flat with respect to the orientation axis by applying stress to the crystal grains in order to improve the degree of orientation. This is because the addition of stress is unnecessary.
- an NdFeB magnet having a flatness lower than that of a hot plastic working magnet can be obtained.
- the HDDR process and pulverization are performed in the same manner as in the case of the SC alloy ingot described above.
- the results of an experiment (Example 3) in which an alloy powder was produced by performing the steps and an NdFeB-based sintered magnet was produced from the obtained alloy powder by the same method as in Examples 1 and 2 described above.
- FIG. 15 shows a reflected electron image on the fracture surface of the MS alloy ingot used in this example.
- the average grain size of the crystal grains in this MS alloy ingot determined from the backscattered electron image is 20 nm.
- Example 3 an electron micrograph of a fracture surface obtained by fracture of a mass (HDDR post-mass) obtained by subjecting an MS alloy mass to HDDR treatment is shown in FIG. 16 (a), and the particle size distribution of the particles in the HDDR post-mass is shown.
- the result obtained by the above-described image analysis is shown in FIG. From these results, in this post-HDDR lump, the average particle size (equivalent circle diameter) is 0.53 ⁇ m, which is smaller than the above-mentioned SC alloy example (0.60 ⁇ m).
- FIGS. 17 (a) and 17 (b) two photographs taken at different magnifications are shown in FIGS. 17 (a) and 17 (b) for the reflected electron images in the polished cross section of the HDDR post lump using the MS alloy lump as the raw material alloy lump.
- FIG. 17C shows a photograph of the reflected electron image in the polished cross section of the post-HDDR lump using the SC alloy lump described above as the raw material alloy lump.
- the rare earth-rich phase lamellar structure shown in white remains corresponding to the structure of the raw material alloy lump shown in Fig.
- the rare earth-rich phase is highly uniform around the main phase crystal particles by using the coarsely ground post-HDDR powder obtained by grinding the post-HDDR lump in which the rare earth-rich phase is uniformly dispersed around each crystal grain.
- RFeB-based sintered magnets can be manufactured.
- FIG. 18 (a) An electron micrograph of the post-HDDR coarsely pulverized powder obtained by pulverizing the post-HDDR ingot using the MS alloy ingot as the raw material alloy ingot by the hydrogen crushing method and the jet mill method is shown in FIG. 18 (a), and the particle size distribution graph is shown in FIG. 18 (b). Respectively. From FIG. 18 (a), it can be seen that coarsely pulverized powder after HDDR having almost no uncrushed polycrystalline particles is obtained. The average particle size of the alloy powder was 0.73 ⁇ m.
- the NdFeB-based sintered magnet was produced from the coarsely pulverized powder after HDDR by the same method as the NdFeB-based sintered magnet produced from the post-HDDR coarsely pulverized powder using SC alloy as a raw material alloy lump.
- FIG. 19 shows an electron micrograph of a fracture surface of the obtained NdFeB-based sintered magnet
- FIG. 20 shows an electron micrograph of a polished cross-section. In both FIG. 19 and FIG. 20, the lower figure is taken at a magnification twice as large as the upper figure.
- FIG. 21 (b) shows the particle size distribution obtained by image analysis based on an electron micrograph at the fractured surface (FIG. 21 (a), where the position on the fractured surface taken is different from FIG. 19). .
- the average particle size of the main phase particles in the manufactured NdFeB-based sintered magnet was 0.80 ⁇ m. From the micrograph of the polished cross section, it can be said that the white image showing the rare earth-rich phase is distributed in the form of dots, and the rare earth-rich phase is dispersed with high uniformity even in the NdFeB-based sintered magnet.
- the alloy powder of the present embodiment is not limited to the manufacturing method in which the powder is filled in the mold cavity as described above, and then the orientation and sintering are performed without applying mechanical pressure. After the powder filled in is oriented, it can also be used in a production method in which the powder is compression molded by a press and the compression molded body is sintered.
- the main phase alloy powder mainly composed of the R 2 Fe 14 B alloy and the rare earth content than the main phase alloy are included.
- a light rare earth element R L composed of Nd and / or Pr is used for the rare earth element R contained in the main phase alloy powder, and Tb, Dy and Ry are contained in the rare earth element contained in the grain boundary phase alloy powder.
- a heavy rare earth element R H composed of one or more of Ho By using a heavy rare earth element R H composed of one or more of Ho, a structure in which R H is concentrated can be formed around the main phase particles. As a result, high magnetization can be obtained as compared with an RFeB-based sintered magnet made of one alloy and having the same composition.
- the rare-earth rich phase can be uniformly dispersed between the main phase alloy powders. The coercive force can be improved.
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Abstract
Description
(1) 平均粒径3μm以下の粉砕が困難であるため、単結晶にまでは粉砕されていない、結晶粒集合体である粒径数μmの多結晶粒子が多く混入する。これにより、粒度分布がブロードになるため、低温で焼結する細かい粒子と、高温で焼結する荒い粒子が存在するために、最適な焼結温度での均一な液相焼結ができない。
(2) 混入した多結晶粒子が等方性であるため、磁界中配向処理を行っても、多結晶粒子内の各結晶粒の配向軸を揃えることができない。異方性原料を用いた場合であっても、HDDR処理を行うことなくジェットミル粉砕を行った粉末で作製した従来の焼結磁石と比較して配向にばらつきがある。
(3) 微細な単一結晶粒子(単結晶から成る粒)とそれよりも粒径が大きい多結晶粒子が混在することによって、液相焼結に寄与する希土類リッチ相の組織が不均一になる。このため、液相焼結が不均一となって、焼結密度が低下したり、異常粒成長が生じるといった問題が生じる。また、焼結磁石中の希土類リッチ相の分散が悪くなると保磁力が低下する。
顕微鏡画像から求められた円相当径による粒度分布の平均値が1μm以下であるRFeB系の結晶粒が内部に形成された結晶粒微細化粗粉粒を粉砕して得られる、顕微鏡画像から求められた円相当径による粒度分布の平均値が1μm以下の粉末であって、面積比で前記結晶粒の90%以上が互いに分離された状態にあるRFeB系合金粉末を用いて、磁場によって配向させた有形体を作製し、焼結することを特徴とする。
また、「有形体を作製する」とは、RFeB系合金粉末を用いて、最終製品と同じ又は近い形状を有するもの(これを「有形体」という)を作製することである。この有形体は、RFeB系合金粉末を最終製品と同じ又は近い形状にプレス成形した成形体であっても良いし、最終製品と同じ又は近い形状のキャビティを有する容器(モールド)にRFeB系合金粉末を充填した(プレス成形を行わない)ものであっても良い(特許文献2参照)。
また、有形体がプレス成形による成形体の場合には、「配向させた有形体」は、RFeB系合金粉末を成形した後に配向させたもの、配向させた後に成形したもの、配向と成形を同時に行ったもののいずれであっても良い。
有形体がプレス成形を行わずにモールドにRFeB系合金粉末を充填したものである場合には、有形体(すなわち、モールド内のRFeB系合金粉末)に機械的圧力を印加することなく焼結を行うことが望ましい。このように、有形体の作製及び焼結の過程においてRFeB系合金粉末に機械的圧力を印加しないことにより、保磁力が高く、且つ、粒径の小さいRFeB系合金粉末を容易に取り扱うことができるため最大エネルギー積が高いRFeB系焼結磁石を得ることができる(特許文献2参照)。
HDDR法では、原料合金内の結晶粒を均一な粒度分布で微細化するだけでなく、再結合反応の際に、微細化された結晶粒間に希土類リッチ相を高い均一性で分散させることができる。これにより、水素解砕やジェットミル粉砕の際に、多結晶粒子を単結晶粒子に粉砕し易くなり平均粒径が1μm以下且つ粒度分布が均一な粉末を得ることができる。また、結晶粒微細化粗粉粒及びそれを粉砕したRFeB系合金粉末において希土類リッチ相を高い均一性で分散させることができ、該RFeB系合金粉末から作製される焼結磁石においても主相粒子間に希土類リッチ相を高い均一性で分散させることができる。希土類リッチ相は、主相粒子間に存在することで、主相粒子間の磁気的結合性を弱めることができる。これにより、希土類リッチ相が主相粒子間に存在すると、磁石全体に逆磁場がかかって一部の主相粒子が磁場反転しても、隣の粒子へ磁場反転の伝搬が抑制されるため、焼結磁石の保磁力が向上する。
また、この合金粗粉の酸素含有量は88±9ppm、窒素含有量は25±8ppmであった。
加熱温度が100℃未満では、主相と希土類リッチ相の両方に水素が吸蔵されるため、どちらも膨張が大きい。このため、主相と希土類リッチ相間の歪が入りにくく、クラックが入りにくい。一方、加熱温度が300℃を超えると、希土類リッチ相は、RH2という構造になり、水素吸蔵量が低下する。このため、主相と希土類リッチ相間の歪が小さくなると考えられる。また、加熱時間が1時間未満では、影響が小さく、10時間を超えると生産上好ましくない。以上の理由により、水素吸蔵工程における加熱温度は100~300℃、加熱時間は1~10時間とすることが望ましい。
扁平性は、配向軸を含む結晶粒の断面の最長軸(a)と、それに垂直な軸の長さ(b)の比(b/a)で表され、この値が小さいほど扁平であることを意味する。仮に同一粒径の場合であれば、b/a値が1に近いほうが、比表面積が小さく、結晶粒界が小さいことを意味するため、必要な希土類リッチ相が少なくて済むメリットがある。また、保磁力を向上させるために、重希土類元素(Dy, Tb)を焼結磁石の粒界に拡散させる(例えば特許文献3参照)際にも、拡散経路が短くなるというメリットがある。
Claims (9)
- 顕微鏡画像から求められた円相当径による粒度分布の平均値が1μm以下であるRFeB系の結晶粒が内部に形成された結晶粒微細化粗粉粒を粉砕して得られる、顕微鏡画像から求められた円相当径による粒度分布の平均値が1μm以下の粉末であって、面積比で前記結晶粒の90%以上が互いに分離された状態にあるRFeB系合金粉末を用いて、磁場によって配向させた有形体を作製し、焼結することを特徴とするRFeB系焼結磁石の製造方法。
- 前記RFeB系合金粉末をモールドのキャビティに充填し、該RFeB系合金粉末に機械的圧力を印加することなく磁場によって配向させることにより前記有形体を作製し、該有形体に機械的圧力を印加することなく該有形体を焼結することを特徴とする請求項1に記載のRFeB系焼結磁石の製造方法。
- 前記RFeB系合金粉末が、原料合金の粗粉にHDDR法を施すことにより前記結晶粒微細化粗粉粒を作製するものであることを特徴とする請求項1又は2に記載のRFeB系焼結磁石の製造方法。
- 前記原料合金がメルトスピニング法により作製された合金であることを特徴とする請求項3に記載のRFeB系焼結磁石の製造方法。
- 前記結晶粒微細化粗粉粒を水素解砕法により解砕した後、ヘリウムガスを用いたジェットミル法で粉砕することを特徴とする請求項1~3のいずれかに記載のRFeB系焼結磁石の製造方法。
- 前記水素解砕法による処理を、100~300℃で1~10時間行うことを特徴とする請求項5に記載のRFeB系焼結磁石の製造方法。
- 前記RFeB系合金粉末に、該RFeB系合金粉末よりも希土類の含有率が高い材料から成る粉末を混合することを特徴とする請求項1~6のいずれかに記載のRFeB系焼結磁石の製造方法。
- 主相となるR2Fe14Bの粒子の平均粒径が1μm以下、配向度が95%以上であることを特徴とするRFeB系焼結磁石。
- RFeB系焼結磁石の配向軸を含む断面BSE画像から求められる、結晶粒の最長軸の長さaに対するそれに垂直な軸の長さbの比b/aが0.45以上であることを特徴とする請求項8に記載のRFeB系焼結磁石。
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2014
- 2014-03-12 EP EP14762415.9A patent/EP2975619A4/en not_active Withdrawn
- 2014-03-12 WO PCT/JP2014/056396 patent/WO2014142137A1/ja active Application Filing
- 2014-03-12 US US14/773,877 patent/US20160027564A1/en not_active Abandoned
- 2014-03-12 CN CN201480014387.4A patent/CN105190802A/zh active Pending
- 2014-03-12 KR KR1020157028398A patent/KR101780884B1/ko active IP Right Grant
- 2014-03-12 JP JP2015505499A patent/JP6177877B2/ja active Active
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2016027791A1 (ja) * | 2014-08-18 | 2016-02-25 | インターメタリックス株式会社 | RFeB系焼結磁石 |
CN107112125A (zh) * | 2015-01-09 | 2017-08-29 | 因太金属株式会社 | RFeB系烧结磁体的制造方法 |
EP3330978A4 (en) * | 2015-07-31 | 2019-04-10 | Nitto Denko Corporation | SINTER BODY FOR THE PRODUCTION OF A RARE-DAMAGED AND SINTERED RARE-EDGE MAGNET |
JP2017157834A (ja) * | 2016-02-26 | 2017-09-07 | Tdk株式会社 | R−t−b系永久磁石 |
WO2021111921A1 (ja) | 2019-12-03 | 2021-06-10 | 信越化学工業株式会社 | 希土類焼結磁石 |
WO2021117672A1 (ja) | 2019-12-13 | 2021-06-17 | 信越化学工業株式会社 | 希土類焼結磁石 |
EP3913644A1 (en) | 2020-05-19 | 2021-11-24 | Shin-Etsu Chemical Co., Ltd. | Rare earth sintered magnet and making method |
Also Published As
Publication number | Publication date |
---|---|
EP2975619A1 (en) | 2016-01-20 |
EP2975619A4 (en) | 2016-03-09 |
KR101780884B1 (ko) | 2017-09-21 |
KR20150128931A (ko) | 2015-11-18 |
US20160027564A1 (en) | 2016-01-28 |
CN105190802A (zh) | 2015-12-23 |
JP6177877B2 (ja) | 2017-08-09 |
JPWO2014142137A1 (ja) | 2017-02-16 |
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