WO2010082492A1 - R-t-b系焼結磁石の製造方法 - Google Patents
R-t-b系焼結磁石の製造方法 Download PDFInfo
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- WO2010082492A1 WO2010082492A1 PCT/JP2010/000178 JP2010000178W WO2010082492A1 WO 2010082492 A1 WO2010082492 A1 WO 2010082492A1 JP 2010000178 W JP2010000178 W JP 2010000178W WO 2010082492 A1 WO2010082492 A1 WO 2010082492A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- 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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
- C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
- C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C2202/00—Physical properties
- C22C2202/02—Magnetic
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- 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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- 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
- H01F41/0293—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 diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
Definitions
- the present invention relates to a method for producing an RTB-based sintered magnet having a high coercive force and a high residual magnetic flux density, which is particularly suitable for a motor application.
- RTB-based sintered magnet (R is at least one element of rare earth elements, T is Fe or Fe and Co, and B is boron) is a rotary motor, linear motor, voice coil motor (VCM), etc. It is widely used for applications.
- the rare earth elements are a total of 17 elements of Sc (scandium), Y (yttrium), and lanthanoids.
- the RTB-based sintered magnet has a large magnetic flux density, but has a disadvantage that irreversible thermal demagnetization is likely to occur because of its relatively low Curie point.
- Dy and Tb are rare and expensive elements and cannot be added in large quantities from the viewpoint of cost.
- Patent Document 2 two types of R 2 T 14 B-based alloys having different ratios of light rare earth element RL and heavy rare earth element RH in rare earth element R are prepared, mixed, pulverized, and sintered. and the crystal grains in the heavy rare-earth element RH is often R 2 T 14 B phase, a heavy rare-earth element RH is less R 2 T 14 B phase, R 2 T 14 B phase containing the heavy rare-earth element RH in their intermediate amount
- a technique for producing an RTB-based sintered magnet in which is mixed is disclosed.
- Patent Document 3 a first component powder mainly composed of an Nd 2 Fe 14 B intermetallic compound and one of R (Cu 1 ⁇ X T X ) and R (Cu 1 ⁇ X T X ) 2 or A technique is disclosed in which a rare earth sintered magnet is produced by mixing a second component powder containing two kinds of main components and then molding the mixture in a magnetic field and liquid phase sintering the mixture.
- Patent Document 4 a step of obtaining a mixed magnetic powder by mixing a first magnetic powder and a second magnetic powder, a step of obtaining a compact by molding the mixed magnetic powder, and firing the compact.
- a technique for manufacturing a rare earth magnet by a process is disclosed.
- the first magnetic powder is made of a magnetic material containing a rare earth element, a transition element, and boron (B), has an average particle size of 10 ⁇ m or less, and the rare earth element contains Dy.
- the second magnetic powder is composed of a magnetic material containing a rare earth element, a transition element, and boron (B), has an average particle diameter of 10 ⁇ m or less, and is different from the average particle diameter of the first magnetic powder. 2 having an average particle size of 2 and a second Dy content different from the Dy content in the first magnetic powder.
- Patent Document 5 has a core-shell structure including an inner shell portion and an outer shell portion surrounding the inner shell portion, and the concentration of the heavy rare earth element in the inner shell portion is that of the heavy rare earth element in the periphery of the outer shell portion.
- the shortest distance (L) from the periphery of the main phase crystal particle to the inner shell is the equivalent circle diameter (r) of the main phase crystal particle 1
- a technique for producing an RTB-based sintered magnet in which the average value of the ratio (L / r) divided by is in the range of 0.03 to 0.40 is disclosed.
- JP 2000-188213 A JP 2002-356701 A JP-A-6-96928 JP 2006-186216 A International Publication No. 2006/98204
- the sintered magnet includes a portion 3 in which the rare earth element R does not contain much heavy rare earth element RH and a portion in which the rare earth element R contains much heavy rare earth element RH.
- the rare earth element R contains a lot of heavy rare earth elements RH around the portion 4 that contains a lot of heavy rare earth elements RH in the rare earth elements R. It was found that a large number of main phases 5 covered with the non-existing portion 3 existed.
- a first component powder mainly composed of an Nd 2 Fe 1 4 B intermetallic compound, and R (Cu 1 ⁇ X T X ) and R (Cu 1 ⁇ X T X ) 2 are used. Since the powder of the second component powder mainly composed of one or two of the above is mixed and sintered, the densification at the time of sintering is likely to be hindered by the Kirkendall effect or the like. Densification cannot be achieved while maintaining the particle size, and magnetization is reduced due to insufficient density. Also, if the density is increased forcibly, the problem of coercive force decrease due to abnormal grain growth occurs.
- Patent Document 4 among the first and second magnetic powders, when the magnetic powder having a larger average particle diameter has a larger Dy content, the value of the coercive force assumed from each magnetic powder is retained. The value of the residual magnetic flux density can be further improved, but only the manufacturing method described in Patent Document 4 includes a portion containing a large amount of heavy rare earth element RH in rare earth element R as shown in FIG. A large number of main phases 5 covered with a portion 3 that does not contain much heavy rare earth element RH in rare earth element R are present in the sintered magnet, making it difficult to produce a magnet with high coercivity. It was.
- the concentration of the heavy rare earth element in the inner shell portion is 10% or more lower than the concentration of the heavy rare earth element in the periphery of the outer shell portion.
- the main phase crystal particles having a shell structure can be used, and the sintered magnet includes a portion 3 and a rare earth element in which the rare earth element R does not contain much heavy rare earth element RH as shown in FIG.
- the main phase 5 in which the portion 4 containing a large amount of the heavy rare earth element RH is present in half and the portion 4 containing the heavy rare earth element RH in the rare earth element R as shown in FIG.
- An object of the present invention is to provide an RTB-based sintered magnet having a structure in which a heavy rare earth element RH is concentrated in an outer shell portion of a main phase.
- the particle size of the alloy having a high RH concentration is relatively reduced.
- the alloy powder having a high RH concentration is first converted into a liquid phase while the alloy powder having a low RH concentration is maintained in a solid phase, and the RH concentration in the liquid phase can be increased.
- crystal grain growth occurs such that the RTB-based alloy powder having a small particle size is taken into the outer peripheral portion of the RTB-based alloy powder having a large particle size (FIG.
- R (R is at least one rare earth element) is 27.3% by mass or more and 31.2% by mass or less, and B is 0.92% by mass or more.
- Alloy powder A, R (R is at least one rare earth element) is 27.3 mass% to 36.0 mass%, B is 0.92 mass% to 1.15 mass%, and T is the balance (
- T is Fe or Fe and Co, and in the case of Fe and Co, an RTB-based alloy powder B represented by a composition in which Co is 20% by mass or less of T) is prepared;
- the particle size D50 of the RTB-based alloy powder B is the particle size of the RTB-based alloy powder A. 1.0 ⁇ m or more smaller than the diameter D50.
- the RTB-based alloy powder A in the mixing step, has a particle size D50 of 3 to 5 ⁇ m.
- the RTB-based alloy powder B in the mixing step, has a particle diameter D50 of 1.5 to 3 ⁇ m.
- the mass of the TB system alloy powder B is adjusted within the range of 60:40 to 90:10.
- an RTB-based sintered magnet having a structure in which a heavy rare earth element RH is concentrated in the outer shell of the main phase is provided, the residual magnetic flux density (B r ) is hardly decreased, and the coercive force (H An RTB -based sintered magnet with significantly improved cJ ) can be obtained.
- FIG. 3 (A) and (b) are schematic views showing powder before sintering and crystal grains after sintering produced by the method for producing an RTB-based sintered magnet according to the present invention.
- (A) And (b) is a schematic diagram showing the crystal grains after sintering produced by the manufacturing method of RTB system sintered magnet according to the prior art.
- 5 is a graph showing the characteristic values shown in Table 2 with the vertical axis representing the residual magnetic flux density B r and the horizontal axis representing the coercive force H cJ . It is the graph which rewritten the unit of FIG. 3 to SI unit.
- 3 is a photograph (reflected electron beam image) showing a cross-sectional configuration of a sintered magnet produced by the method for producing an RTB-based sintered magnet according to the present invention.
- 6 is a photograph (reflected electron beam image) showing a cross-sectional configuration of a sintered magnet produced by a conventional method for producing an RTB-based sintered magnet. It is a graph showing the relationship between the sintering temperature and magnetic properties of the present invention (remanence B r and coercivity H cJ).
- an RTB-based sintered magnet is manufactured from a powder obtained by mixing an RTB-based alloy A powder and an RTB-based alloy B powder.
- R is at least one rare earth element and is contained in an amount of 27.3% to 31.2% by mass of the entire magnet alloy.
- the ratio shown by the mass% is a ratio with respect to the total mass of a magnet alloy in principle.
- the rare earth element R contained in the RTB-based alloy A can contain Dy and Tb, which are heavy rare earth elements RH, alone or both as required. If the ratio of R is less than 27.3 mass%, sintering becomes difficult, and a soft magnetic phase is generated, which may reduce the coercive force of the RTB-based sintered magnet. On the other hand, when the ratio of R exceeds 31.2% by mass, the magnetization of the RTB-based sintered magnet decreases.
- B is included in the range of 0.92% by mass to 1.15% by mass. If the ratio of B is less than 0.92% by mass, a soft magnetic phase may be generated and the coercive force of the RTB-based sintered magnet may be reduced. On the other hand, when the ratio of B exceeds 1.15% by mass, the magnetization of the RTB-based sintered magnet decreases.
- T is the balance and is Fe, or Fe and Co.
- Co is preferably 20% by mass or less of T. If the proportion of Co in the entire magnet exceeds 20% by mass, the magnetization of the RTB-based sintered magnet decreases.
- the RTB-based alloy A may contain a trace additive element M that obtains a known effect.
- the content ratio of M is 0.02% by mass or more and 0.5% by mass or less.
- M is one of Al, Cu, Ti, V, Cr, Mn, Ni, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Au, Pb, and Bi. Species or two or more species are selectively included.
- the magnetic properties such as residual magnetic flux density and coercive force, mechanical properties such as strength, and weather resistance are improved.
- R is a rare earth element containing Y, and is contained in an amount of 27.3 mass% to 36 mass%.
- the R of the R—T—B system alloy B always includes the heavy rare earth element RH made of Dy and / or Tb.
- the amount of RH that is, the ratio of Dy + Tb is 4% by mass or more and 36% by mass or less of the entire magnet alloy.
- the ratio of R is less than 27.3 mass%, it is difficult to generate a liquid phase in the sintering process.
- the ratio of R exceeds 36% by mass, the magnetization of the RTB-based sintered magnet decreases. If the ratio of Dy + Tb is less than 4% by mass, the desired structure cannot be obtained after sintering.
- B, T, and trace additive element M are in the same kind and range as RTB-based alloy A, but the amount is not necessarily the same as alloy A.
- the amount of heavy rare earth element RH in the RTB-based alloy A and the amount (mass%) of the heavy rare earth element RH in the RTB-based alloy B are compared,
- the amount of heavy rare earth element RH is larger, and the difference ⁇ RH is set to 4% by mass or more.
- ⁇ RH 4% by mass or more it is possible to generate a structure in which heavy rare earth elements are concentrated in the vicinity of the outer shell portion of the main phase after sintering.
- concentration of heavy rare earth element RH in the vicinity of the main phase outer shell becomes insufficient, and high magnetic properties cannot be obtained.
- ⁇ RH exceeds 16% by mass, depending on the production conditions, there may be many heterogeneous phases other than the concentrated structure of heavy rare earth element RH in the vicinity of the main phase outer shell. Therefore, ⁇ RH is 4% by mass to 16% by mass. The following range is preferable.
- the RTB-based alloy A and the RTB-based alloy B are pulverized to produce powders each having a predetermined powder particle size.
- the particle size D50 of the RTB-based alloy A powder having a relatively small content of the heavy rare earth element RH is set to be 1.0 ⁇ m or more larger than the particle size D50 of the RTB-based alloy B powder. . If this particle size difference is less than 1.0 ⁇ m, the behavior of each powder during sintering cannot be controlled, and a structure in which heavy rare earth elements are concentrated in the vicinity of the main phase outer shell after sintering may be generated. Can not.
- D50 is the value of the powder particle diameter (particle diameter when the cumulative volume is 50% of the total when arranged in order from the smallest particle diameter) obtained by the airflow dispersion type laser diffraction method. It is.
- the raw material alloy can be obtained by an ordinary ingot casting method, strip casting method, direct reduction method or the like.
- the strip cast method has a feature that an ⁇ Fe phase hardly remains in a metal structure and an alloy can be produced at a low cost because a mold is not used. Therefore, it can be suitably used in the present invention.
- the average R-rich interval is preferably 5 ⁇ m or less in the strip casting method. This is because if the average R-rich interval exceeds 5 ⁇ m, an excessive load is applied to the pulverization process, and the amount of impurities in the pulverization process increases remarkably.
- the strip cast method in order to make the average R-rich interval 5 ⁇ m or less, for example, a method of reducing the molten metal feed rate to reduce the thickness of the cast slab, and reducing the surface roughness of the cooling roll to A method of increasing the adhesion degree of the material and increasing the cooling efficiency, a method of making the material of the cooling roll a material having excellent thermal conductivity such as Cu, etc. are carried out singly or in combination, and the average R-rich interval is set to 5 ⁇ m or less. Can do.
- the structure of the alloy can be changed between the RTB type alloy A and the RTB type alloy B. That is, by making the average R-rich interval of the RTB-based alloy B smaller than that of the RTB-based alloy A, the particle size difference of the powder is set to 1 ⁇ m or more in the pulverization step. Becomes easy.
- the raw alloy is preferably crushed by hydrogen embrittlement. This is a method of generating and cracking fine cracks in the alloy by utilizing the embrittlement phenomenon and volume expansion phenomenon of the alloy accompanying hydrogen storage.
- the main phase and the R-rich phase This is because the difference in the amount of hydrogen occlusion, that is, the difference in volume change, causes cracking, so that the probability of cracking at the grain boundary of the main phase increases.
- Hydrogen embrittlement treatment is usually performed by exposing to pressurized hydrogen for a certain period of time. Further, after that, there is a case where the temperature is raised to release excess hydrogen.
- the coarse powder after hydrogen embrittlement treatment is very active because it contains many cracks and the specific surface area is greatly increased, and the amount of oxygen increases significantly when handled in the atmosphere. It is desirable to handle in an inert gas such as nitrogen, Ar. Further, since nitriding may occur at high temperatures, handling in an Ar atmosphere is preferable if the cost permits.
- the amount of oxygen is preferably 0.25% by mass or less. If the amount exceeds 0.25% by mass, the heavy rare earth element RH, which is present in the liquid phase component in the sintering process, has a large affinity for oxygen. This is because the amount of the heavy rare earth element RH concentrated in the main phase outer shell portion is reduced and the target structure cannot be obtained and a large coercive force cannot be obtained. More preferably, it is 0.2 mass% or less.
- dry pulverization using an airflow pulverizer can be used.
- nitrogen gas is generally used as the pulverization gas, but a method using a rare gas such as Ar gas is preferable in order to minimize the mixing of nitrogen.
- He gas when He gas is used, a remarkably large pulverization energy can be obtained, and a finely pulverized powder suitable for the present invention can be easily obtained.
- He gas since He gas is expensive, it is preferable to circulate it by incorporating a compressor or the like into the pulverizer. Although the same effect is expected with hydrogen gas, there is a risk of explosion due to the mixing of oxygen gas, etc., which is not industrially preferable.
- a method for reducing the pulverization particle size by the dry pulverization method for example, there are a method for increasing the pulverization gas pressure and a method for increasing the temperature of the pulverization gas, in addition to a method using a gas having a large pulverization capability such as the He gas. , And can be selected as needed.
- a wet pulverization method as another method. Specifically, a ball mill or an attritor can be used. In this case, it is possible to select a grinding medium, a solvent, and an atmosphere so that impurities such as oxygen and carbon are not taken in more than a predetermined amount. For example, a bead mill that stirs at high speed using a very small diameter ball can be miniaturized in a short time, so that the influence of impurities can be reduced, which is preferable for obtaining a fine powder used in the present invention.
- multistage pulverization enables efficient pulverization in a short period of time. Can be suppressed.
- the solvent used in the wet pulverization is selected in consideration of the reactivity with the raw material alloy, the oxidation deterrence, and the ease of removal before sintering.
- organic solvents particularly saturated hydrocarbons such as paraffin are preferred.
- the RTB-based alloy A and the RTB-based alloy B are separately finely pulverized to produce the RTB-based alloy powder A and the RTB-based alloy powder B.
- a particle size difference of about 0.1 to 0.2 ⁇ m may occur at D50.
- the difference in particle size at D50 between the RTB-based alloy powder A and the RTB-based alloy powder B cannot be 1.0 ⁇ m or more.
- the fine grinding conditions are changed to the RTB-based alloy powder A.
- RTB-based alloy powder B must be changed.
- the particle size of the fine powder obtained by the fine pulverization step is preferably finely pulverized with the RTB-based alloy powder A after pulverization so that D50 ⁇ 6 ⁇ m.
- the maximum crystal grain size in the sintered RTB-based sintered magnet is 25 ⁇ m or more in terms of the equivalent circle diameter.
- the coercive force is reduced by the growth of crystal grains.
- the equivalent circle diameter is a diameter of a circle having the same area as an indeterminate crystal grain as seen in the structure observation, and can be easily obtained by image analysis from a structure photograph of the cross section of the magnet.
- the average crystal grain size described later is the diameter of a circle having the same area as “total area of main phase / number of crystal grains” in the cross-sectional structure photograph.
- the RTB-based alloy powder B after pulverization is pulverized so as to be smaller than the particle size of the RTB-based alloy powder A and D50 ⁇ 3.5 ⁇ m.
- the RTB-based alloy powder A is preferably prepared so that the D50 is 3 ⁇ m to 5 ⁇ m.
- the RTB-based alloy powder B is preferably prepared so that the D50 is 1.5 ⁇ m to 3.5 ⁇ m.
- the difference between the D50 of the RTB-based alloy powder A and the D50 of the RTB-based alloy powder B is less than 1.0 ⁇ m, the heavy rare earths close to the main phase outer shell portion. Concentration is insufficient and high magnetic properties cannot be obtained.
- the RTB-based alloy powder A and the RTB-based alloy powder B produced by the pulverization method are added and mixed with an appropriate amount of a lubricant in, for example, a rocking mixer, and lubricated.
- the surface of the alloy powder particles is coated with an agent.
- a known method can be used for the molding method of the present invention. For example, it is a method in which the finely pulverized powder is pressure-molded using a mold in a magnetic field. In order to minimize the uptake of impurities such as oxygen and carbon, it is desirable to minimize the use of lubricants. When the lubricant is used, a highly volatile lubricant that can be degreased before or during the sintering step may be selected from known ones.
- the pressing force at the time of molding is not particularly limited, but is, for example, 9.8 MPa or more, more preferably 19.6 MPa or more.
- the upper limit is 245 MPa or less, more preferably 196 MPa or less.
- the molded body density is set to be, for example, about 3.5 to 4.5 Mg / m 3 .
- the intensity of the applied magnetic field is, for example, 0.8 to 1.5 MA / m.
- the atmosphere in the sintering process is an inert gas atmosphere in vacuum or at atmospheric pressure or lower.
- the inert gas here refers to Ar and / or He gas.
- the method of maintaining an inert gas atmosphere at atmospheric pressure or lower is preferably a method of introducing an inert gas into a sintering furnace while performing evacuation with a vacuum pump.
- the evacuation may be performed intermittently or the inert gas may be introduced intermittently. Both the evacuation and the introduction can be performed intermittently.
- the temperature is 300 ° C. or less, the time is 30 minutes or more and 8 hours or less, in a vacuum or in an inert gas at atmospheric pressure or less. It is preferable to sinter after holding and degreasing.
- the degreasing treatment can be performed independently of the sintering step, but it is preferable to continuously sinter after the degreasing treatment from the viewpoints of processing efficiency, oxidation prevention, and the like.
- the heat processing in a hydrogen atmosphere can also be performed.
- the gas release is mainly the release of hydrogen gas introduced in the hydrogen embrittlement treatment step. Since the liquid phase is generated only after the hydrogen gas is released, it is preferable to release the hydrogen gas sufficiently, for example, maintaining the temperature in the temperature range of 700 ° C. to 850 ° C. for 30 minutes to 4 hours. preferable.
- the holding temperature during sintering is, for example, 860 ° C. or higher and 1100 ° C. or lower. If it is less than 860 ° C., a sufficient sintered density cannot be obtained.
- the temperature exceeds 1100 ° C. the components of the RTB-based alloy A are also eluted into the liquid phase, and the concentration of the heavy rare earth element RH in the liquid phase decreases, and the RH of the outer shell portion of the main phase after sintering The generation of the concentrated layer becomes insufficient. Moreover, abnormal grain growth is likely to occur, and the coercive force of the resulting magnet is lowered. Abnormal grain growth is not observed in a sintered structure in which the maximum value of crystal grains is a circle equivalent diameter of 25 ⁇ m or less.
- the sintered structure of the magnet of the present invention is not particularly limited, but it is preferable that the crystal grain size of the main phase is small and uniform in order to obtain a large coercive force.
- the crystal grain size is preferably an equivalent circle diameter of 25 ⁇ m or less.
- a more preferable crystal grain size is an equivalent circle diameter of 15 ⁇ m or less.
- the sintering temperature is preferably 1050 ° C. or less.
- the sintering temperature is preferably 1020 ° C. or less. Also, from the viewpoint of not diffusing the heavy rare earth element RH into the main phase, the sintering temperature is desirably low, and the sintering temperature is more preferably 1000 ° C. or less. In the case of a combination of alloys having the same composition, the sintering temperature decreases as the particle size difference increases or the amount of impurities decreases, so that it is difficult to diffuse the heavy rare earth element RH into the main phase.
- the holding time in the sintering temperature range is preferably 2 hours or more and 16 hours or less. If it is less than 2 hours, the progress of densification becomes insufficient, a sufficient sintered density cannot be obtained, and the residual magnetic flux density of the magnet becomes small. On the other hand, if it exceeds 16 hours, the change in density and magnet characteristics is small, but there is a high possibility that a crystal structure having an average crystal grain size exceeding 12 ⁇ m in the sintered body structure will occur. If the crystal structure is formed, the coercive force is lowered.
- sintering at 1000 ° C. or lower it is possible to perform sintering for a longer time. For example, sintering for 48 hours or less may be performed. When sintering at 1000 ° C. or lower, the sintering time is preferably 4 to 16 hours.
- the temperature may be changed from 1000 ° C. to 860 ° C. over 8 hours.
- the RTB alloy powder having a large particle size and relatively few heavy rare earth elements RH. Grain growth that takes in the RTB-based alloy powder having a small particle size and a relatively large amount of heavy rare earth element RH in the outer peripheral portion takes place, so that the heavy rare earth element RH is formed in the main phase outer shell after sintering. As shown in FIGS. 1 (a) and 1 (b), a high-performance magnet enriched with heavy rare earth element RH is formed in the main phase outer shell of the RTB-based sintered magnet as shown in FIGS. Produced.
- the sintering temperature is low. Is preferred. Specifically, the temperature is preferably 1050 ° C. or lower. The sintering temperature is more preferably 1030 ° C, still more preferably 1020 ° C.
- the condition that the holding temperature is slightly lowered is preferable.
- the sintering temperature is first set to 1020 ° C., and after a few tens of minutes to several hours, a liquid phase is formed in the RTB-based alloy compact, and then the sintering temperature is lowered to 960 ° C.
- a condition of sintering until a true density is reached after several tens of minutes to several hours can be considered.
- heat treatment After completion of the sintering process, after cooling to 300 ° C. or less, heat treatment can be performed again in the range of 400 ° C. or more and sintering temperature or less to increase the coercive force. This heat treatment may be performed multiple times at the same temperature or at different temperatures. In particular, in the present invention, by setting the amount of Cu within a predetermined range, the coercive force can be improved more remarkably by heat treatment. For example, heat treatment is performed at 1000 ° C. for 1 hour, followed by rapid cooling, followed by heat treatment at 800 ° C. for 1 hour. Three-stage heat treatment can also be performed, such as post-cooling, heat treatment at 500 ° C. for 1 hour, and rapid cooling.
- the coercive force may be improved by slow cooling after holding at the heat treatment temperature.
- the magnetization does not usually change, so that appropriate conditions for improving the coercive force can be selected for each magnet composition, size, and dimensional shape.
- the RTB-based sintered magnet of the present invention can be subjected to general machining such as cutting and grinding in order to obtain a desired shape and size.
- the RTB-based sintered magnet of the present invention is preferably subjected to a surface coating treatment for rust prevention.
- a surface coating treatment for rust prevention Ni plating, Sn plating, Zn plating, Al vapor deposition film, Al alloy vapor deposition film, resin coating, etc. can be performed.
- the RTB-based sintered magnet of the present invention can be magnetized by a general magnetizing method. For example, a method of applying a pulse magnetic field or a method of applying a static magnetic field can be applied.
- the sintered magnet is usually magnetized by the above-mentioned method after assembling the magnetic circuit.
- the magnet can be magnetized by itself.
- Example 1 Nd with a purity of 99.5% by mass or more, Tb, Dy, electrolytic iron, low carbon ferroboron alloy with a purity of 99.9% by mass or more, and other target elements are added in the form of an alloy with pure metal or Fe.
- the alloy having the composition was melted and cast by a strip casting method to obtain a plate-like alloy having a thickness of 0.3 mm to 0.4 mm.
- the alloy was hydrogen embrittled in a hydrogen-pressurized atmosphere, and then heated and cooled in vacuum to 600 ° C. to obtain a coarse alloy powder. 0.05% zinc stearate by mass ratio was added to and mixed with the coarse powder.
- the particle diameter D50 is a value obtained by a laser diffraction method using an airflow dispersion method.
- the particle size D50 shown in Table 1 has the target composition.
- RTB-based alloy powder B having the following characteristics was prepared.
- Table 1 shows the composition and D50 particle size of RTB-based alloy powder A, and the composition and D50 particle size of RTB-based alloy powder B in unit mass% and ⁇ m. Note that.
- the analysis was ICP emission spectroscopic analysis.
- the analytical values of oxygen, nitrogen, and carbon in Table 1 are the results of analysis with a gas analyzer and are expressed in mass%.
- the target composition is obtained by performing bead mill pulverization for a predetermined time using beads having a diameter of 0.8 mm as a medium and n-paraffin as a solvent.
- An RTB-based alloy powder B having a predetermined particle diameter D50 having the following characteristics was prepared.
- the powder A and the powder B were mixed at a ratio (mixing ratio) shown in Table 1. An appropriate amount of lubricant was added during mixing.
- the mixed powder thus produced was molded in a magnetic field to produce a molded body.
- the magnetic field at this time was a static magnetic field of about 0.8 MA / m, and the applied pressure was 5 MPa.
- the magnetic field application direction and the pressing direction are orthogonal to each other.
- this compact was sintered in a vacuum at a temperature range of 960 ° C. to 1020 ° C. for 2 hours.
- sintering temperature differs depending on the composition, in each case, sintering was performed by selecting a low temperature in the range where the density after sintering was 7.5 Mg / m 3 .
- this sintered magnet was mechanically processed to obtain an RTB-based sintered magnet sample having a thickness of 3 mm ⁇ length of 10 mm ⁇ width of 10 mm.
- the obtained sintered magnet was heat-treated at various temperatures for 1 hour in an Ar atmosphere and cooled.
- the heat treatment is performed under various temperature conditions depending on the composition, and the heat treatment is performed up to three times at different temperatures.
- the sample having the largest coercive force HcJ at room temperature was used as the evaluation target.
- Table 3 shows values obtained by converting the numerical values indicating the magnet characteristics in Table 2 into SI units.
- No. 1 to No. No. 25, which is within the scope of the present invention, is compared with those within the scope of the present invention. 2 to No. 4, no. 6, no. 7, no. 9, no. 10, no. 13, no. 15, no. 19 to No. 21, no. 24, no. 25 shows that the residual magnetic flux density (Br) is small and the coercive force (HcJ) is improved.
- the alloy powder B was manufactured by wet pulverization using a bead mill. 4, no. The same effect was obtained for No. 7, and no influence due to the difference in the grinding method was observed.
- the characteristic values shown in Table 2 are shown in a graph in which the vertical axis represents the residual magnetic flux density B r and the horizontal axis represents the coercive force H cJ (FIG. 3).
- the sintered magnets within the scope of the present invention are divided into examples (R 29.6% by mass) and examples (R 31.2% by mass) for each of the same total rare earth element amount R.
- Sintered magnets outside the scope of the present invention are divided into comparative examples (R 29.6% by mass) and comparative examples (R 31.2% by mass) with the same total rare earth element amount R.
- a graph in which the units in FIG. 3 are replaced with SI units is shown in FIG.
- the RTB-based alloy powder having a small particle size is taken into the outer peripheral portion of the RTB-based alloy powder having a large particle size in the sintered structure. Grain growth occurs.
- the heavy rare earth element RH is concentrated on a part or the entire surface of the outer shell of the phase crystal particle.
- the sintered magnet includes a portion 3 in which the rare earth element R does not contain much heavy rare earth element RH and a rare earth element R in the rare earth element R.
- the main phase 5 in which the portion 4 containing a large amount of the heavy rare earth element RH exists in half was confirmed.
- the main phase 5 in which the periphery of the portion 4 containing the heavy rare earth element RH in the rare earth element R is covered with the portion 3 not containing the heavy rare earth element RH in the rare earth element R. was also confirmed.
- Table 2 No. 1 to No. When the sintered body structure of 25 sintered magnets was observed, the average crystal grain size was 3.5 to 5.5 ⁇ m in terms of equivalent circle diameter.
- Example 2 As in Example 1, RTB-based alloy powder A and RTB-based alloy powder B having the composition and particle size D50 shown in Table 4 were produced by dry pulverization.
- the powder A and the powder B were mixed at a ratio (mixing ratio) shown in Table 4. An appropriate amount of lubricant was added during mixing.
- An RTB-based sintered magnet sample having a thickness of 3 mm, a length of 10 mm, and a width of 10 mm was obtained from the mixed powder thus produced under the same production conditions as in Example 1.
- Table 4 No. 26 to No. 38 sintering temperatures are listed.
- the obtained sintered magnet was heat-treated at various temperatures for 1 hour in an Ar atmosphere in the same manner as in Example 1, cooled, and the results of evaluating the magnet properties are shown in Table 5.
- the crystal grain size in Table 5 is the equivalent circle diameter of the largest one among the crystal grains confirmed when the sintered body structure is observed. It was confirmed that no abnormal grain growth occurred in any sample.
- Table 6 shows values obtained by converting the numerical values indicating the magnet characteristics in Table 5 into SI units.
- Example 3 In the same manner as in Example 1, RTB-based alloy powder A and RTB-based alloy powder B having the composition and particle size D50 shown in Table 7 were produced by dry pulverization.
- the powder A and the powder B were mixed at a ratio (mixing ratio) shown in Table 7.
- 0.4 mass% of methyl caprylate was added as a lubricant during mixing.
- An RTB-based sintered magnet sample having a thickness of 3 mm, a length of 10 mm, and a width of 10 mm was obtained from the mixed powder thus produced under the same production conditions as in Example 1.
- Table 7 no. 39 to No. The sintering temperature of 41 is indicated.
- the obtained sintered magnet was heat-treated at various temperatures for 1 hour in an Ar atmosphere in the same manner as in Example 1, cooled, and the results of evaluating the magnet properties are shown in Table 8.
- the magnetic characteristics shown in Table 8 are the magnetic characteristics when the upper numerical value is 23 ° C., and the numerical values displayed in italics in the lower are the magnetic characteristics at 140 ° C.
- No. corresponding to the present invention No. 39, which is a comparative example.
- No. 40 it was examined how the magnetic characteristics changed when the sintering temperature was changed in the range of 985 ° C. to 1020 ° C. The result is shown in FIG. In FIG. 7, the residual magnetic flux density (B r ) is shown on the left vertical axis, and the coercive force (H cJ ) is shown on the right vertical axis. From FIG. 7, in the embodiment of the present invention (No. 39), even if the sintering temperature region is 1030 ° C. or lower where abnormal growth of crystal grains does not occur, the allowance for improving the coercive force increases as the sintering temperature increases. A small thing was confirmed. This is presumed to be due to the fact that the Dy distribution state in the sintered body approaches uniformly as the temperature rises, and the effect of the present invention is considered to be more prominent in low temperature sintering.
- the RTB -based sintered magnet according to the present invention produces a rare-earth sintered magnet with substantially no reduction in residual magnetic flux density (B r ) and greatly improved coercive force (H cJ ).
- rare earth element heavy rare-earth element RH into the R is a relatively large heavy rare-earth element RH in a relatively small R 2 T 14 B alloy powder 2 rare earth element R R 2 T 14 B alloy powder 3 rare earth element R Region in which heavy rare earth element RH is relatively small in 4 Region in which rare earth element R is relatively rich in heavy rare earth element RH 5 R 2 T 14 B main phase crystal particle of RTB-based sintered magnet
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Abstract
Description
本発明では、R-T-B系合金Aの粉末とR-T-B系合金Bの粉末とを混合した粉末からR-T-B系焼結磁石を製造する。
本発明では、前記R-T-B系合金Aと、前記R-T-B系合金Bとを、粉砕することにより、それぞれ、所定の粉末粒径を有する粉末を作製する。相対的に重希土類元素RHの含有量の少ないR-T-B系合金Aの粉末の粒径D50は、R-T-B系合金Bの粉末の粒径D50よりも1.0μm以上大きくする。この粒径差が1.0μm未満であると、焼結時の各粉末の挙動を制御できず、焼結後の主相外殻部近傍に重希土類元素が濃化した組織を生成することができない。なお、D50とは、気流分散型レーザー回折法により得られる粉末粒径(粒径の小さいものから順に並べていったときに累積の体積が全体の50%になったときの粒子の直径)の値である。
原料合金は、通常のインゴット鋳造法、ストリップキャスト法、直接還元法などの方法で得ることができる。
本発明の磁石を得るための製造方法の一例として、粗粉砕と微粉砕の2段階の粉砕を行う場合を以下に示す。以下の記載は、他の製造方法を排除するものではない。
本実施形態では、前記粉砕方法で作製されたR-T-B系合金粉末AとR-T-B系合金粉末Bとを、例えばロッキングミキサー内で、潤滑剤を適量添加・混合し、潤滑剤で合金粉末粒子の表面を被覆する。R-T-B系合金粉末AとR-T-B系合金粉末Bは、質量比でR-T-B系合金粉末A:R-T-B系合金粉末B=60:40から90:10になるように混合する。
本発明の成形方法は、既知の方法を用いることができる。例えば、磁界中で前記微粉砕粉を、金型を用いて加圧成形する方法である。酸素や炭素などの不純物の取り込みを最小限とするため、潤滑剤等の使用は最小限にとどめることが望ましい。潤滑剤を用いる際は、焼結工程、またはその前に脱脂可能な、揮発性の高い潤滑剤を、公知のものから選択して用いてもよい。
焼結過程における雰囲気は、真空中または大気圧以下の不活性ガス雰囲気とする。ここでの不活性ガスとは、Ar及びまたはHeガスを指す。
焼結工程終了後、一旦300℃以下にまで冷却した後、再度400℃以上、焼結温度以下の範囲で熱処理を行い、保磁力を高めることができる。この熱処理は、同一温度、または温度を変えて複数回行ってもよい。特に、本発明においては、Cu量を所定範囲とすることで、より顕著に熱処理による保磁力向上を図ることができ、例えば1000℃で1時間熱処理後急冷し、続いて800℃で1時間熱処理後急冷、500℃で1時間熱処理後急冷というように、3段階の熱処理を行うこともできる。また、熱処理温度で保持後、徐冷することで保磁力が向上する場合もある。焼結後の熱処理では、通常は磁化が変化することはないので、磁石組成、大きさ、寸法形状毎に、保磁力向上のために適正な条件を選択することができる。
本発明のR-T-B系焼結磁石には、所望の形状、寸法を得るため、一般的な切断、研削等の機械加工を施すことができる。
本発明のR-T-B系焼結磁石には、好ましくは防錆のための表面コーティング処理を施す。例えば、Niめっき、Snめっき、Znめっき、Al蒸着膜、Al系合金蒸着膜、樹脂塗装などを行うことができる。
本発明のR-T-B系焼結磁石には、一般的な着磁方法で着磁することができる。例えば、パルス磁界を印加する方法や、静的な磁界を印加する方法が適用できる。なお、焼結磁石の着磁は、取り扱い上の容易さを考慮して、通常は磁気回路を組み立てた後、前記方法で着磁するが、もちろん磁石単体で着磁することもできる。
純度99.5質量%以上のNd、純度99.9質量%以上のTb、Dy、電解鉄、低炭素フェロボロン合金を主として、その他目的元素を純金属またはFeとの合金の形で添加して目的組成の合金を溶解し、ストリップキャスト法で鋳造し、厚さ0.3mmから0.4mmの板状合金を得た。
実施例1と同様に乾式粉砕にて表4に示す組成と粒径D50を有する、R-T-B系合金粉末AとR-T-B系合金粉末Bとを作製した。
実施例1と同様に乾式粉砕にて、表7に示す組成と粒径D50を有する、R-T-B系合金粉末AとR-T-B系合金粉末Bとを作製した。
2 希土類元素R中に重希土類元素RHが相対的に多いR2T14B系合金粉末
3 希土類元素R中に重希土類元素RHが相対的に少ない領域
4 希土類元素R中に重希土類元素RHが相対的に多い領域
5 R-T-B系焼結磁石のR2T14B主相結晶粒子
Claims (4)
- R(Rは、希土類元素の少なくとも1種)が27.3質量%以上31.2質量%以下、Bが0.92質量%以上1.15質量%以下、Tが残部(ここでTはFeまたはFeとCoであり、FeとCoの場合CoはTのうち20質量%以下)である組成で表されるR-T-B系合金粉末Aと
R(Rは希土類元素の少なくとも1種)が27.3質量%以上36.0質量%以下、Bが0.92質量%以上1.15質量%以下、Tが残部(ここでTはFeまたはFeとCoであり、FeとCoの場合におけるCoはTのうち20質量%以下)である組成で表されるR-T-B系合金粉末Bと、
を準備する工程と、
前記R-T-B系合金粉末Aと前記R-T-B系合金粉末Bとを混合する工程と、
前記混合したR-T-B系合金粉末を所定形状の成形体に成形する工程と、
前記成形体を焼結する工程と、
を包含し、
前記R-T-B系合金粉末Bに含まれるRは、DyおよびTbの少なくとも1種からなる重希土類元素RHを4質量%以上、36質量%以下含み、前記R-T-B系合金粉末Bに含まれる重希土類元素RHの含有量は、前記R-T-B系合金粉末Aに含まれる重希土類元素RHの含有量より4質量%以上多く、
前記R-T-B系合金粉末Bの粒径D50は、前記R-T-B系合金粉末Aの粒径D50より1.0μm以上小さい、R-T-B系焼結磁石の製造方法。 - 前記混合工程において、R-T-B系合金粉末Aは粒径D50で3~6μmである請求項1に記載のR-T-B系焼結磁石の製造方法。
- 前記混合工程において、R-T-B系合金粉末Bは粒径D50で1.5~3μmである請求項1に記載のR-T-B系焼結磁石の製造方法。
- 前記R-T-B系合金粉末Aと前記R-T-B系合金粉末Bとを混合する工程では、R-T-B系合金粉末Aの質量:R-T-B系合金粉末Bの質量が60:40から90:10の範囲内に調整される請求項1から3のいずれかに記載のR-T-B系焼結磁石の製造方法。
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JPWO2010082492A1 (ja) | 2012-07-05 |
EP2388350B1 (en) | 2018-09-19 |
EP2388350A4 (en) | 2016-12-14 |
CN102282279A (zh) | 2011-12-14 |
US8287661B2 (en) | 2012-10-16 |
JP5561170B2 (ja) | 2014-07-30 |
US20110262297A1 (en) | 2011-10-27 |
EP2388350A1 (en) | 2011-11-23 |
CN102282279B (zh) | 2013-10-02 |
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