WO2015146888A1 - R-t-b系合金粉末およびその製造方法ならびにr-t-b系焼結磁石およびその製造方法 - Google Patents
R-t-b系合金粉末およびその製造方法ならびにr-t-b系焼結磁石およびその製造方法 Download PDFInfo
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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
- H01F41/0266—Moulding; Pressing
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- 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
- H01F41/0273—Imparting anisotropy
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- C22C2202/02—Magnetic
Definitions
- the present invention relates to an RTB-based alloy powder and a manufacturing method thereof, and an RTB-based sintered magnet and a manufacturing method thereof.
- RTB-based sintered magnets (R is a rare earth element including Y, T is a transition element mainly composed of Fe, specifically Fe or Fe and Co, and B is boron) Since it has the highest magnetic energy product among them and its price is relatively low, it is widely used in various electronic devices.
- the RTB-based sintered magnet is produced, for example, by the following process.
- a raw material alloy is manufactured by casting various raw materials by a method such as an ingot method or a strip cast method.
- the obtained raw material alloy is subjected to a pulverization step to obtain an alloy powder having a predetermined particle size.
- This pulverization process usually includes a coarse pulverization process and a fine pulverization process.
- the former uses, for example, a hydrogen embrittlement phenomenon, and the latter uses, for example, an airflow pulverizer (jet mill). Done.
- the powder is subjected to a molding process in a magnetic field in which the powder is molded into a desired shape in a magnetic field.
- An RTB-based sintered magnet is produced by sintering the obtained compact. Further, after sintering, heat treatment is usually performed.
- the easy magnetization direction of each powder particle is aligned with the direction of the applied magnetic field by forming the powder while applying a magnetic field in a predetermined direction.
- Patent Document 1 can obtain a fine powder having an obtuse ridge line by using a counter jet mill in which a vortex generation gas is introduced from a nozzle arranged separately in addition to the main pulverization gas introduced from a pulverization gas nozzle. We disclose what we can do. This fine powder is excellent in slipperiness and can enhance the degree of orientation of the fine powder when pressed while applying a magnetic field during molding.
- Patent Document 2 discloses heat treatment of finely pulverized rare earth alloy powder prior to molding in a magnetic field.
- the heat-treated rare earth alloy powder has a rounded shape due to spheroidization. Thereby, the frictional force and steric hindrance during orientation in a magnetic field are reduced, and the degree of orientation is improved.
- Patent Document 2 includes a process of heat-treating the finely pulverized powder, and thus has a problem that the manufacturing process becomes complicated.
- the present invention has been made in view of the above problems, and an RTB-based alloy powder suitably used for manufacturing an RTB-based sintered magnet with improved magnetic properties and its production It is an object of the present invention to provide a method, an RTB-based sintered magnet using the RTB-based alloy powder, and a manufacturing method thereof.
- the RTB-based alloy powder according to the embodiment of the present invention contains 27.5% by mass or more and 36.0% by mass or less of R (R is at least one of rare earth elements and at least one of Nd and Pr. 1 type is necessarily included), B (boron) of 0.85 mass% or more and 1.05 mass% or less, Element M of 0.1 mass% or more and 2.5 mass% or less (M is Al, Ti, V, At least one selected from the group consisting of Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi), the balance T (T Is a transition element containing Fe as a main component, specifically Fe or Fe and Co), and in a contour shape in which particles are projected two-dimensionally, the ratio from a major axis a and a minor axis b to a / b , The ratio from the circumference L and the equivalent circle diameter d (the diameter of the circle having the same area) When
- the powder satisfying the condition of L / d ⁇ 5.39-1.07 (a / b) is contained in a number ratio of 40% or more.
- An RTB-based sintered magnet according to an embodiment of the present invention can be obtained by orienting and sintering the above RTB-based alloy powder by an external magnetic field.
- the manufacturing method of the RTB-based alloy powder according to the embodiment of the present invention is 27.5% by mass or more and 36.0% by mass or less of R (R is at least one kind of rare earth elements and Nd and Pr 0.85 mass% or more and 1.05 mass% or less B (boron), 0.1 mass% or more and 2.5 mass% or less of element M (M is Al, Ti) , V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi, at least one selected from the group), the remainder
- the pulverizing step is performed so that the pulverized gas has a gauge pressure of 0.75 MPa or more and a residence time of 5 minutes or more.
- An RTB-based sintered magnet manufacturing method includes the steps of obtaining the RTB-based alloy powder, orienting the RTB-based alloy powder with an external magnetic field, Sintering.
- FIG. 2 is a schematic diagram showing a structure of a swirling flow type pulverizer used in an embodiment of the present invention, in which (a) is a side sectional view and (b) is a Z-Z ′ sectional view of (a). It is a figure which shows the relationship between a / b and L / d calculated
- the RTB-based alloy powder according to the embodiment of the present invention has a contour shape obtained by projecting alloy powder particles two-dimensionally, a ratio of a major axis a and a minor axis b to a / b, and a peripheral length L, 20% or more of powders satisfying the condition of L / d ⁇ 5.39-1.07 (a / b) when the ratio is L / d from the equivalent circle diameter d (diameter of circles having the same area) Alloy powder.
- the major axis a represents the maximum diameter of the contour shape
- the minor axis b represents the maximum diameter of the contour shape in the direction orthogonal to the major axis.
- the measuring means for measuring the major axis a, minor axis b, peripheral length L, and equivalent circle diameter d of the contour shape obtained by projecting the particles two-dimensionally is not particularly limited. From the SEM image of the alloy powder, And the contour shape of the extracted particles can be analyzed with commercially available image analysis software.
- the alloy powder satisfying the condition of L / d ⁇ 5.39-1.07 (a / b) is included.
- the composition is 27.5% by mass or more and 36.0% by mass or less R (R is at least one of rare earth elements and always includes at least one of Nd and Pr), 0.85% by mass % To 1.05 mass% B (boron), 0.1 mass% to 2.5 mass% element M (M is Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga) , Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi, and the balance T (T is a transition element mainly composed of Fe) , Specifically Fe or Fe and Co).
- M is preferably at least one selected from the group consisting of Al, Cu, Ga, Zr, and Nb.
- concentration of R is less than 27.5% by mass, it is difficult to generate a liquid phase during the sintering process.
- concentration of R exceeds 36.0% by mass, the magnetization of the RTB-based sintered magnet significantly decreases.
- the concentration of R is preferably 28.5% by mass or more and 33.0% by mass or less.
- concentration of B is less than 0.85% by mass, a soft magnetic phase may be generated and the coercive force of the RTB-based sintered magnet may be reduced.
- concentration of B exceeds 1.05% by mass, a nonmagnetic phase is generated, and the magnetization of the RTB-based sintered magnet is lowered.
- concentration of B is preferably 0.90% by mass or more and 1.05% by mass or less.
- Element M is in the range of 0.1% by mass to 2.5% by mass that does not cause a significant decrease in magnetization.
- the range of the element M is preferably 0.1% by weight or more and 1.5% by weight or less, more preferably 0.25% by weight or more and 0.9% by weight or less.
- T is the balance.
- T is a transition element mainly composed of Fe, and may contain Co.
- T is Fe or Fe and Co, and Fe accounts for 50 atomic% or more of the total of Fe and Co.
- Unavoidable impurities include O, C, N, H, Si, Ca, S, P, and the like. In any case, in order to improve the performance of the magnet, it is preferable to keep the content as small as possible in an industrially possible range.
- RTB-based sintered magnet The RTB-based sintered magnet according to the embodiment of the present invention can be obtained by orienting and sintering the RTB-based alloy powder by an external magnetic field.
- the RTB-based alloy powder according to the embodiment of the present invention is obtained by finely pulverizing alloy powders by grinding while rotating the alloy powder in a pulverizing tank of a pulverizer.
- R 0 mass% or less (R is at least one of rare earth elements and always includes at least one of Nd and Pr), B (boron) of 0.85 mass% to 1.05 mass% 0.1% by mass or more and 2.5% by mass or less of element M (M is Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, And at least one selected from the group consisting of Hf, Ta, W, Pb, and Bi), and the balance T (T is a transition element mainly composed of Fe, specifically Fe or Fe and Co). It is produced by a process of obtaining RTB-based alloy powder.
- M Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, And at least one selected from the group consisting of Hf, Ta, W, Pb, and Bi
- T is a transition element mainly composed of Fe, specifically Fe or Fe and Co). It is produced by a process of
- the alloy powder is retained in the pulverization layer for 8 minutes or more when the pulverization gas introduced into the pulverization tank is 0.65 MPa or more in gauge pressure, and for 5 minutes or more when it is 0.75 MPa or more. .
- the RTB-based alloy powder obtained in the embodiment of the present invention tends to have a shape with few corners.
- the RTB-based alloy powder according to the embodiment of the present invention has a shape with few corners, so that steric hindrance is reduced, and the alloy powder is easily rotated in a forming process in a magnetic field, so that the degree of orientation is low. improves. As a result, the residual magnetic flux density B r of R-T-B based sintered magnet produced by using the alloy powder are improved.
- the mother alloy may be produced by either an ingot method or a strip cast method, but is preferably produced by a strip cast method that is a rapid cooling method. Thereby, ⁇ -Fe does not remain in the cast structure and can be easily pulverized.
- the composition of the mother alloy may be appropriately determined in consideration of the reduction of each element in the intermediate process so that the composition of the obtained RTB-based alloy powder becomes a predetermined composition.
- the pulverization process includes a two-stage pulverization process including a coarse pulverization process and a fine pulverization process.
- the coarse pulverization of the mother alloy can be performed by a mechanical pulverization method or a hydrogen pulverization method.
- a hydrogen pulverization method using a hydrogen embrittlement phenomenon.
- This method utilizes the embrittlement phenomenon and volume expansion phenomenon of the mother alloy that accompanies hydrogen storage, thereby causing fine cracks in the mother alloy and pulverizing the mother alloy.
- the hydrogen pulverization method is preferable because the probability of cracking at the grain boundary increases. When the probability of cracking at the grain boundary increases, the number of main phase crystals (2-14-1 compound) contained in the grain becomes one, and the easy magnetization direction becomes one direction. Therefore, the magnetic field orientation becomes easy and Br is improved. .
- the hydrogen pulverization method is performed, for example, by exposing to pressurized hydrogen for a certain period of time at room temperature. Next, the temperature is raised to release excess hydrogen and then cooled.
- the alloy powder after hydrogen embrittlement contains a large number of cracks, and the specific surface area is greatly increased. For this reason, it is very active, and the amount of oxygen increases remarkably when handled in the atmosphere. Therefore, it is desirable to handle in an inert gas such as N 2 or Ar.
- the particle size of the alloy powder obtained by the coarse pulverization step is, for example, 500 ⁇ m or less.
- the particle size may be set to a specific range or less using a sieve or the like.
- the coarsely pulverized alloy powders are finely pulverized by grinding while rotating in the pulverization tank of the pulverizer.
- a high-pressure pulverization gas is introduced into a pulverization tank provided in the pulverizer.
- a gas flow swirling at high speed is generated inside the crushing tank, and the alloy powder is swirled in the crushing tank by this gas flow.
- alloy powder with few corners is formed by grinding during swirling.
- the pulverization gas N 2 gas is generally used, but a rare gas such as He or Ar gas may be used.
- the swirl type pulverizer generally refers to a method of pulverizing mainly by a swirl force among airflow pulverizers generally referred to as jet mills, more specifically, those capable of obtaining a grinding effect. Shall be included.
- the residence time is defined as the time from the start of supply from the coarsely pulverized powder supply nozzle until the alloy powder is confirmed in the collection container (not shown).
- the gas pressure introduced into the grinding tank represents the gauge pressure (difference from atmospheric pressure).
- the pressure of the grinding gas is preferably set to 0.75 MPa or more in terms of gauge pressure. More preferably, it is 0.75 MPa or more and 1.5 MPa or less, More preferably, it is 0.75 MPa or more and 0.95 MPa or less.
- the residence time is preferably 5 minutes or more. More preferably, it is 5 minutes or more and 10 minutes or less, More preferably, it is 6 minutes or more and 10 minutes or less.
- a method of reducing the supply amount as compared with the conventional method can be adopted.
- an alloy powder having a generally square shape can be obtained.
- the particle size of the alloy powder recovered after the fine pulverization step is, for example, 1.0 ⁇ m or more and 5.5 ⁇ m or less in D50 (powder particle size obtained by airflow dispersion type laser diffraction method, volume reference central value). .
- the particle diameter is preferably D50 to 2.5 ⁇ m to 5.0 ⁇ m, more preferably 2.51 ⁇ m to 4.63 ⁇ m.
- FIG. 2A is a schematic diagram showing the swirling flow type pulverizer 1.
- FIG. 2B shows a cross section taken along the line ZZ ′ of FIG.
- the swirl type pulverizer 1 includes a pulverization tank 2A that accommodates pulverized gas and pulverized powder that are swirled therein.
- the crushing tank 2 ⁇ / b> A is a space surrounded by the housing 2.
- a plurality of pulverized gas introduction nozzles 5 communicating with the pulverization tank 2 ⁇ / b> A are attached to the housing 2.
- the pulverization gas introduction nozzle 5 is fixedly installed with its injection port directed toward the inside of the pulverization tank 2A (in the direction away from the center).
- one of the pulverized gas introduction nozzles 5 is provided with a coarsely pulverized powder supply port 3 for supplying the coarsely pulverized alloy powder into the pulverization tank. ing. From the coarsely pulverized powder supply port 3, the alloy powder supplied from the hopper-like coarsely pulverized powder supply unit 4 is injected and introduced into the pulverization tank 2A together with the high-speed pulverized gas injected from the pulverized gas introduction nozzle 5. .
- the pulverized gas introduction nozzle 5 is fed with a high-pressure gas (crushed gas) from an unillustrated high-pressure gas supply device via an air supply tube.
- the high-pressure gas supply device is configured so that the pressure of the pulverized gas supplied to the pulverization tank 2A can be 0.75 MPa or more in terms of gauge pressure.
- the alloy powder introduced into the pulverization tank 2A is entrained in the high-speed swirl flow 18 generated by the gas ejected from the plurality of pulverization gas introduction nozzles 5 disposed along the inner wall, and swirls in the pulverization tank 2A. To do. At this time, the alloy powder is pulverized by grinding.
- the RTB-based alloy powder with few corners is produced by staying in the pulverization tank 2A of the swirling flow pulverizer 1 for a predetermined time.
- the RTB-based alloy powder obtained by pulverization is taken out from the finely pulverized powder discharge port 6 located above the center of the pulverization tank 2A when the retention amount in the pulverization tank exceeds a certain level.
- the amount of alloy powder that can stay in the crushing tank 2A is determined for each apparatus and for each operating condition.
- the amount of the alloy powder exceeding the amount is introduced into the pulverizing tank 2A, the alloy powder corresponding to the introduced amount is discharged out of the tank. For this reason, the residence time of the powder in a grinding
- RTB-based sintered magnet [Orientation of main phase crystals by external magnetic field]
- the RTB-based alloy powder is oriented by an external magnetic field.
- the orientation by an external magnetic field may be performed by a mold press having a magnetic field application coil, or after the powder container is filled with powder at high density, the RTB-based alloy powder is applied by an external magnetic field.
- the main phase crystals can also be oriented.
- after orienting the magnetic field in the filled container it can be formed by an isostatic press.
- the applied magnetic field may be a static magnetic field or a pulsed magnetic field.
- the density of the compact is set to, for example, 3.7 g / cm 3 or more and 4.7 g / cm 3 or less. When adjusted to this range, it is easy to increase the degree of orientation while maintaining the strength of the compact. When it is less than 3.7 g / cm 3 , the degree of orientation increases, but when molding is performed with a die press, the strength is insufficient and there is a risk of cracking during handling of the molded body. If it exceeds 4.7 g / cm 3 , the strength of the compact is increased, but the movement of particles during magnetic field molding is suppressed, and the degree of orientation may be reduced.
- a lubricant or the like in order to suppress carbon uptake when a molded body of the above RTB system alloy powder is produced by a die press or an isostatic press.
- a highly volatile lubricant is selected in order to enable degreasing.
- the pressure applied during molding is not particularly limited, but for example, 9.8 MPa or more, more preferably 19.6 MPa or more, and 245 MPa or less, more preferably 147 MPa or less. .
- the sintering step is preferably performed in a sintering furnace maintained in a vacuum or an inert gas atmosphere at atmospheric pressure or lower.
- the inert gas here refers to Ar or He gas.
- a method of maintaining an inert gas atmosphere at atmospheric pressure or lower a method of introducing a small amount of inert gas into a sintering furnace while performing evacuation by a vacuum pump is preferable. In this case, evacuation may be performed intermittently or inert gas may be introduced intermittently. Also, both evacuation and introduction can be performed intermittently.
- Sintering is usually performed by holding the compact in a temperature range of 950 ° C. to 1100 ° C. for 30 minutes to 16 hours. Sintering may be performed in multiple steps at the same temperature or different temperatures. Conditions for cooling after sintering can be appropriately combined so that the value of coercive force of the obtained magnet becomes a target value including the following heat treatment.
- any sintering means used in the powder metallurgy method such as hot pressing for heating while applying pressure from the outside, and current sintering for heating the compact by Joule heat, can be applied.
- the sintering temperature and time are not limited to the above.
- the density of the magnet as a sintered body is 7.3 g / cm 3 or more. More preferably, it is 7.5 g / cm 3 or more.
- Heat treatment For the purpose of increasing the coercive force, heat treatment can be performed at a sintering temperature or lower after the end of sintering. Further, this heat treatment may be performed a plurality of times at the same temperature or at different temperatures. Various conditions can be selected as cooling conditions for the heat treatment.
- the magnet obtained as a sintered body may have a shape close to that of the final product, but it may not be the case.
- R after sintering is obtained by machining such as cutting, grinding, and polishing. -Finish the TB sintered magnet into a predetermined shape.
- this process is after sintering, you may perform before or after heat processing, or in the middle of several heat processing.
- the obtained RTB-based sintered magnet is preferably subjected to a surface coating treatment.
- the surface coating treatment include Ni plating, Sn plating, Zn plating, Al deposition, Al alloy deposition, and resin coating.
- Example 1 The main raw material is Nd, electrolytic iron, and low carbon ferroboron alloy with a purity of 99.5% or more.
- the additive elements (Co and M) are added in the form of pure metal or an alloy with Fe, and finally RT—
- the composition of the B-based alloy powder and the sintered magnet is Nd: 30.5, B: 0.94, Co: 0.9, Cu: 0.1, Al: 0.1, Ga: 0.1, Fe:
- the molten alloy melted so that the balance was [mass%] was rapidly cooled by a strip cast method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm.
- the alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of pressurization, and then heated to 600 ° C. in a vacuum and cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 ⁇ m or less.
- the volume of the crushing tank of the apparatus used in this example is 314 cm 3 .
- the pulverized gas is N 2 gas whose oxygen concentration is controlled to 8000 ppm or less.
- the pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.
- Supplied amount is the amount of alloy powder charged into the grinding tank per minute.
- the residence time is defined as the time required from the start of supply from the coarsely pulverized powder supply nozzle to the presence of the alloy powder in the recovery container (not shown) through a cyclone (not shown). Even if it is a small amount, it can be recovered after 4 minutes, and when it is recovered after 4 minutes and 4 minutes, it is 6 minutes.
- FIG. 1 (a) A photograph (SEM image) of the alloy powder of Sample 1 (Example) in which the pressure of the pulverization gas was 0.75 MPa and the residence time was 6 minutes is shown in FIG. As shown in FIG. 1 (a), the surface of the alloy powder of Sample 1 had a rounded shape with few corners.
- Table 2 shows a / b and L / d of the alloy powder arbitrarily extracted from the alloy powder.
- the alloy powder of sample 1 (particles a to m), which is an example, has a contour shape obtained by two-dimensionally projecting each particle from an SEM image, and the conditional expression is L / d ⁇ 5.39-1.07 (a / b) Was met.
- the distribution graph (scattering chart) corresponding to the measurement results in Table 2 is shown in FIG. From this graph, it can be seen that the alloy powder of the example is in the lower left region of FIG. 3 where a / b and L / d satisfy the conditional expression of the present invention.
- the alloy powder of sample 2 (particles n to v) of the comparative example does not satisfy the conditional expression, L / d ⁇ 5.39-1.07 (a / b), and is included in the lower left region of FIG. You can see that it is not.
- Samples 1 and 2 were sintered in a reduced pressure Ar gas atmosphere at 1080 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.
- the degree of orientation of the RTB-based sintered magnet is such that the easy magnetization direction of the obtained RTB-based sintered magnet is the X-axis direction, the residual magnetic flux density in the X-axis direction is B rx , and the orientation magnetic field direction
- the residual magnetic flux densities in two directions orthogonal to the direction Bry and B rz are the three-direction orientation degree (B rx / (B rx ) which is the ratio of B rx to (B rx 2 + B ry 2 + B rz 2 ) 1/2 . 2 + B ry 2 + B rz 2 ) 1/2 ).
- the compact density and sintered density in the table are values calculated from the measurement results of dimensions and mass.
- Sample 1 (Example) has the same composition as Sample 2 (Comparative Example) and a high density of the compact, but the residual magnetic flux density B r , coercive force H cJ, and orientation The degree value has been improved.
- sample 1 is a powder having no corners, particles are likely to move during molding in a magnetic field, resulting in a high degree of orientation and an improvement in Br .
- Example 2 Nd, electrolytic iron, and low carbon ferroboron alloy with a purity of 99.5% or more are used as main raw materials, and additive elements (Co and M) are added as pure metals or alloys with Fe, and finally the RTB system
- the composition of the alloy powder and the sintered magnet is Nd: 29.1, B: 0.94, Co: 0.9, Cu: 0.1, Al: 0.1, Ga: 0.1, Fe: balance [ The molten alloy melted to a mass%] was quenched by a strip casting method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm.
- the alloy was held in a hydrogen pressure atmosphere using a heat treatment furnace capable of pressurization, and then heated to 600 ° C. in a vacuum and cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 ⁇ m or less.
- the volume of the crushing tank of the apparatus used in this example is 314 cm 3 .
- the pulverization gas is nitrogen gas.
- the pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.
- Table 4 shows the pulverization conditions and the particle size (D50) of the powder obtained by changing the supply amount and the residence time using the swirl type pulverizer 1 shown in FIGS. 2 (a) and 2 (b). Show.
- Sample 5 contained 20% of alloy powder satisfying the conditional expression
- Sample 13 contained 40% of alloy powder satisfying the conditional expression.
- the “ratio of the alloy powder that satisfies the condition” is determined by the number of powders that satisfy the condition (that is, the number ratio) with respect to the total number of measured powders.
- Samples 7 to 9, 11, and 14 contained 100% of alloy powder satisfying the conditional expression.
- samples 3 to 14 were sintered in a reduced pressure Ar gas atmosphere at 1080 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.
- sample 11 having a residence time of 6 minutes has a residual magnetic flux density B r and a coercive force H cJ of sample 11 having a residence time of 6 minutes. And the degree of orientation was excellent.
- Example 3 Nd, Pr, Dy, Tb having a purity of 99.5% or more, electrolytic iron, and a low-carbon ferroboron alloy are used as main raw materials, and additive element M is added as a pure metal or an alloy with Fe.
- the composition of the B-based alloy powder and the sintered magnet is Nd: 22.8, Pr: 7.6, Dy: 1.0, Tb: 1.0, B: 1.05, Cu: 0.1, Al: The molten alloy melted to have 0.3, Nb: 0.5, Fe: balance [mass%] was quenched by a strip cast method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm. .
- the alloy was kept in a hydrogen pressurized atmosphere using a heat treatment furnace capable of being pressurized, and then heated to 660 ° C. in a vacuum and cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 ⁇ m or less.
- the volume of the crushing tank of the apparatus used in this example is 314 cm 3 .
- the pulverization gas is nitrogen gas whose oxygen concentration is controlled to 8000 ppm or less.
- the pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.
- Table 6 shows the pulverization conditions and the particle size of the powder obtained by changing the supply amount and the residence time using the swirling flow pulverizer 1 shown in FIGS.
- the sample 16 contained 100% of alloy powder satisfying the conditional expression.
- Sample 15 did not contain alloy powder that satisfies the conditional expression.
- Samples 15 and 16 were sintered in a reduced pressure Ar gas atmosphere at 1080 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.
- the sample 16 as an example has the same composition. Compared to 15, the residual magnetic flux density B r , the coercive force H cJ and the degree of orientation were improved.
- Example 4 Nd, Pr, electrolytic iron and low carbon ferroboron alloy with a purity of 99.5% or more are used as main raw materials, and additive elements (Co and M) are added as pure metal or an alloy with Fe, and finally RT—
- the composition of the B-based alloy powder and the sintered magnet is Nd: 21.9, Pr: 7.3, B: 0.94, Co: 2.0, Cu: 0.1, Al: 0.05, Ga:
- the molten alloy melted so as to be 0.1, Fe: balance [mass%] was quenched by a strip casting method to obtain a plate-like alloy having a thickness of 0.1 to 0.3 mm.
- the alloy was held in a hydrogen-pressurized atmosphere using a heat treatment furnace capable of being pressurized, and then heated in vacuum to 580 ° C. and cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 ⁇ m or less.
- the volume of the grinding tank of the apparatus used in this example is 628 cm 3 .
- the grinding gas is helium gas.
- the pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.
- Table 8 shows the pulverization conditions and the particle size of the powder obtained by changing the supply amount and the residence time using the swirl type pulverizer 1 shown in FIGS.
- Sample 18 contained 100% of alloy powder satisfying the conditional expression.
- the sample 17 did not contain alloy powder satisfying the conditional expression.
- Samples 17 and 18 were sintered in a reduced pressure Ar gas atmosphere at 1040 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.
- the sample 18 as an example is a sample having the same composition. Compared to 17, the residual magnetic flux density B r , the coercive force H cJ and the degree of orientation were improved.
- Nd, Pr, Dy, Tb, purity 99.5% or more of Nd, Pr, Tb, electrolytic iron, and low carbon ferroboron alloy are used as main raw materials, and additive elements (Co and M) are added as pure metal or an alloy with Fe.
- the composition of the RTB-based alloy powder and the sintered magnet is Nd: 22.5, Pr: 7.5, Dy: 0.1, Tb: 0.1, B: 0.90, Co: 0.00. 9, Cu: 0.15, Al: 0.1, Ga: 0.5, Zr: 0.1, Fe: The molten alloy melted so as to be the remaining [mass%] was quenched by a strip cast method, A plate-like alloy having a thickness of 0.1 to 0.3 mm was obtained.
- the alloy was held in a hydrogen-pressurized atmosphere using a heat treatment furnace capable of pressurization, and then heated in vacuum to 550 ° C. and cooled. After taking out from the furnace, the particle size was adjusted with a sieve to obtain an alloy powder having a particle size of 425 ⁇ m or less.
- the volume of the crushing tank of the apparatus used in this example is 314 cm 3 .
- the grinding gas is argon gas.
- the pulverization gas pressure is a value representing the pressure of the pulverization gas introduced into the pulverization tank by a gauge pressure.
- Table 10 shows the pulverization conditions and the particle sizes obtained by pulverizing using the swirling flow pulverizer 1 shown in FIGS.
- Sample 20 contained 100% of alloy powder satisfying the conditional expression.
- the sample 19 did not contain alloy powder satisfying the conditional expression.
- Samples 19 and 20 were sintered in a reduced pressure Ar gas atmosphere at 1060 ° C. for 4 hours. Further, the obtained RTB-based sintered magnet was heat-treated at 500 ° C. for 2 hours in a vacuum atmosphere, and then cooled.
- the sample 20 as an example is a sample having the same composition. Compared to 19, the residual magnetic flux density B r , the coercive force H cJ and the degree of orientation were improved.
- the volume of the grinding chamber was given two of 314cm 3, 628cm 3
- the supply amount as the residence time of the alloy powder is in the range of the present invention depending on the size of the volume Is appropriately adjusted, and is not limited to the size of the volume.
- the RTB-based alloy powder according to the embodiment of the present invention is suitably used for producing an RTB-based sintered magnet.
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Abstract
Description
本発明の実施形態にかかるR-T-B系合金粉末は、合金粉末の粒子を2次元に投影した輪郭形状において、長径a、短径bからその比をa/bとし、周囲長L、円相当径d(同じ面積を有する円の直径)からその比をL/dとしたとき、L/d≦5.39-1.07(a/b)の条件を満たす粉末が20%以上含まれている合金粉末である。
本発明の実施形態によるR-T-B系焼結磁石は、前記R-T-B系合金粉末を外部磁界により配向し、焼結することで得られる。
本発明の実施形態によるR-T-B系合金粉末は、合金粉末を粉砕装置の粉砕槽内にて旋回させつつ、合金粉末同士を磨砕により微粉砕し、27.5質量%以上36.0質量%以下のR(Rは希土類元素のうちの少なくとも1種でありNdおよびPrのうちの少なくとも1種を必ず含む)、0.85質量%以上1.05質量%以下のB(ホウ素)、0.1質量%以上2.5質量%以下の元素M(Mは、Al、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Zr、Nb、Mo、Ag、In、Sn、Hf、Ta、W、Pb、およびBiからなる群から選択された少なくとも1種)、残部T(TはFeを主成分とする遷移元素であり、具体的にはFeまたはFeとCo)を含むR-T-B系合金粉末を得る工程により作製される。上記の微粉砕する工程において、粉砕槽に導入する粉砕ガスがゲージ圧で0.65MPa以上のときには8分以上、また、0.75MPa以上のときには5分以上、合金粉末を粉砕層内に滞留させる。
母合金はインゴット法、ストリップキャスト法のいずれによって作製されてもよいが、急冷法であるストリップキャスト法にて作製することが好ましい。これにより、鋳造組織にα-Feが残存せず、容易に粉砕することができる。母合金の組成は、得られるR-T-B系合金粉末の組成が所定の組成となるよう途中工程における各元素の減少分を考慮して適宜決めればよい。
粉砕工程には、粗粉砕工程と微粉砕工程との2段階の粉砕工程が含まれる。
[外部磁界による主相結晶の配向]
前記R-T-B系合金粉末を外部磁界により配向する。
金型プレスを用いる場合、成形体の密度は例えば3.7g/cm3以上4.7g/cm3以下に設定される。この範囲に調整すると、成形体の強度を保ちつつ、配向度を高くしやすい。3.7g/cm3未満であると、配向度が高まるが、金型プレスにて成形を行った場合、強度が不足し、成形体取扱い時に割れてしまう恐れがある。4.7g/cm3を超えると、成形体強度は高くなるが、磁界成形時の粒子の動きが抑えられ、配向度が低下することがある。
焼結工程は、真空中または大気圧以下の不活性ガス雰囲気に保たれた焼結炉内で行うのが好ましい。ここでの不活性ガスとは、ArまたはHeガスを指す。大気圧以下の不活性ガス雰囲気を保持する方法は、真空ポンプによる真空排気を行いつつ、不活性ガスを少量焼結炉内に導入する方法が好ましい。この場合、真空排気を間歇的に行ってもよく、不活性ガスの導入を間歇的に行ってもよい。また真空排気と導入の双方とも間歇的に行うこともできる。
保磁力を高めることを目的に、焼結終了後、焼結温度以下で熱処理を行うことができる。また、この熱処理を、同じ温度または温度を変えて複数回行ってもよい。熱処理の際の冷却条件として、種々の条件を選択できる。
焼結体として得られた磁石が最終製品に近い形状を有している場合もあるが、そうでない場合もあり、一般的には切断、研削、研磨等の機械加工により、焼結後のR-T-B系焼結磁石を所定形状に仕上げる。なお、この加工は、焼結後であれば、熱処理の前でも後でも、または複数回の熱処理の中間に行ってもよい。
防錆のため、得られたR-T-B系焼結磁石に表面コーティング処理を施すのが好ましい。表面コーティング処理の例としては、Niめっき、Snめっき、Znめっき、Al蒸着、Al合金蒸着、樹脂塗装などがある。
純度99.5%以上のNd、電解鉄、低炭素フェロボロン合金を主原料とし、添加元素(CoおよびM)は純金属またはFeとの合金の形で添加して、最終的にR-T-B系合金粉末および焼結磁石の組成が、Nd:30.5、B:0.94、Co:0.9、Cu:0.1、Al:0.1、Ga:0.1、Fe:残部[質量%]となるように溶解した合金溶湯をストリップキャスト法で急冷し、厚さ0.1~0.3mmの板状の合金を得た。
純度99.5%以上のNd、電解鉄、低炭素フェロボロン合金を主原料とし、添加元素(CoおよびM)を純金属またはFeとの合金として添加して、最終的にR-T-B系合金粉末および焼結磁石の組成が、Nd:29.1、B:0.94、Co:0.9、Cu:0.1、Al:0.1、Ga:0.1、Fe:残部[質量%]となるように溶解した合金溶湯をストリップキャスト法で急冷し、厚さ0.1~0.3mmの板状の合金を得た。
純度99.5%以上のNd、Pr、Dy、Tb、電解鉄、低炭素フェロボロン合金を主原料とし、添加元素Mを純金属またはFeとの合金として添加して、最終的にR-T-B系合金粉末および焼結磁石の組成が、Nd:22.8、Pr:7.6、Dy:1.0、Tb:1.0、B:1.05、Cu:0.1、Al:0.3、Nb:0.5、Fe:残部[質量%]となるように溶解した合金溶湯をストリップキャスト法で急冷し、厚さ0.1~0.3mmの板状の合金を得た。
純度99.5%以上のNd、Pr、電解鉄、低炭素フェロボロン合金を主原料とし、添加元素(CoおよびM)を純金属またはFeとの合金として添加して、最終的にR-T-B系合金粉末および焼結磁石の組成が、Nd:21.9、Pr:7.3、B:0.94、Co:2.0、Cu:0.1、Al:0.05、Ga:0.1、Fe:残部[質量%]となるように溶解した合金溶湯をストリップキャスト法で急冷し、厚さ0.1~0.3mmの板状の合金を得た。
純度99.5%以上のNd、Pr、Dy、Tb、電解鉄、低炭素フェロボロン合金を主原料とし、添加元素(CoおよびM)を純金属またはFeとの合金として添加して、最終的にR-T-B系合金粉末および焼結磁石の組成が、Nd:22.5、Pr:7.5、Dy:0.1、Tb:0.1、B:0.90、Co:0.9、Cu:0.15、Al:0.1、Ga:0.5、Zr:0.1、Fe:残部[質量%]となるように溶解した合金溶湯をストリップキャスト法で急冷し、厚さ0.1~0.3mmの板状の合金を得た。
2 ハウジング
2A 粉砕槽
3 粗粉砕粉供給口
4 粗粉砕粉供給部
5 粉砕ガス導入ノズル
6 微粉砕粉排出口
18 高速旋回流
Claims (6)
- 27.5質量%以上36.0質量%以下のR(Rは希土類元素のうちの少なくとも1種でありNdおよびPrのうちの少なくとも1種を必ず含む)、0.85質量%以上1.05質量%以下のB(ホウ素)、0.1質量%以上2.5質量%以下の元素M(Mは、Al、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Zr、Nb、Mo、Ag、In、Sn、Hf、Ta、W、Pb、およびBiからなる群から選択された少なくとも1種)、残部T(TはFeまたはFeとCo)を含み、
かつ、粒子を2次元に投影した輪郭形状において、長径a、短径bからその比をa/bとし、周囲長L、円相当径d(同じ面積を有する円の直径)からその比をL/dとしたとき、L/d≦5.39-1.07(a/b)の条件を満たす粉末が個数比率で20%以上含まれているR-T-B系合金粉末。 - 前記L/d≦5.39-1.07(a/b)の条件を満たす粉末が個数比率で40%以上含まれている、請求項1に記載のR-T-B系合金粉末。
- 請求項1または2に記載のR-T-B系合金粉末を外部磁界により配向し、焼結することで得られるR-T-B系焼結磁石。
- 27.5質量%以上36.0質量%以下のR(Rは希土類元素のうちの少なくとも1種でありNdおよびPrのうちの少なくとも1種を必ず含む)、0.85質量%以上1.05質量%以下のB(ホウ素)、0.1質量%以上2.5質量%以下の元素M(Mは、Al、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Zr、Nb、Mo、Ag、In、Sn、Hf、Ta、W、Pb、およびBiからなる群から選択された少なくとも1種)、残部T(TはFeまたはFeとCo)を含む合金粉末を用意する工程と、
前記合金粉末と粉砕ガスとを粉砕槽に導入して前記合金粉末を粉砕する工程であって、前記粉砕槽内で前記粉砕ガスの流れによって前記合金粉末を旋回させて磨砕することによって粉砕する工程と
を包含し、
前記粉砕する工程は、前記粉砕槽に導入する前記粉砕ガスのゲージ圧が0.65MPa以上かつ前記粉砕槽内における前記合金粉末の滞留時間が8分以上の条件を満たすか、または、前記粉砕ガスのゲージ圧が0.75MPa以上かつ前記滞留時間が5分以上の条件を満たすように行われる、R-T-B系合金粉末の製造方法。 - 前記粉砕する工程は、前記粉砕ガスのゲージ圧が0.75MPa以上かつ前記滞留時間が5分以上の条件を満たすように行われる、請求項4に記載の製造方法。
- 請求項4または5のいずれかに記載の方法によってR-T-B系合金粉末を得る工程と、
前記R-T-B系合金粉末を外部磁界により配向し、焼結する工程と
を包含する、R-T-B系焼結磁石の製造方法。
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