JP2022141577A - Rare earth magnet powder, bonded magnet, compound for bonded magnet, sintered magnet, manufacturing method of rare earth magnet powder, and manufacturing method of rare earth permanent magnet - Google Patents

Abstract

To provide a rare earth magnet powder capable of sufficiently improving bulk density and suitable for manufacturing an anisotropic magnet.SOLUTION: A rare earth magnet powder has an average sphericity P1 defined by the formula (1) of P1=Ls/Ll of 0.65 or more. In the formula (1), Ll is the length of the long side of the circumscribing rectangle having the smallest area with respect to the rare earth magnet powder in a microscope image, and Ls in the formula (1) is the length of the short side of the circumscribing rectangle having the smallest area with respect to the rare earth magnet powder in the microscope image.SELECTED DRAWING: Figure 1A

Description

The present invention relates to rare earth magnet powders, bonded magnets, compounds for bonded magnets, sintered magnets, methods for producing rare earth magnet powders, and methods for producing rare earth permanent magnets.

Rare earth permanent magnets are known to have excellent magnetic properties. Further, RTB system permanent magnets with improved magnetic properties are being developed. When producing a rare earth permanent magnet, the raw material powder to be sintered is refined to an average particle size of about 1 to 10 μm to ensure magnetic properties such as saturation magnetic flux density and coercive force. However, the refinement of the raw material powder becomes a factor that hinders the dimensional accuracy and productivity of the compact.

The raw material powder is press-molded in a magnetic field to form a compact. In molding in this magnetic field, a static magnetic field or a pulse magnetic field is applied to the raw material powder to orient the particles of the raw material powder. During this magnetic field molding, the finer the raw material powder, the poorer the flowability, and the more difficult it is to fill the mold. If the filling property of the powder into the mold is poor, the powder cannot be uniformly filled into the mold. As a result, the density of the molded body varies, and the dimensional accuracy of the molded body cannot be obtained. Alternatively, there is a problem that it takes a long time to fill the mold itself, which hinders productivity. In particular, it is difficult to accurately and efficiently produce thin-walled or complicated-shaped compacts.

For example, Patent Literature 1 proposes a technique of adding a lubricant to coarse powder and then finely pulverizing the powder with an airflow grinder to produce a raw material powder, thereby improving flowability into a mold during molding. However, even if this technique is used, the fluidity is not sufficient, and the bulk density of the molded article cannot be sufficiently improved.

Further, Patent Document 2 discloses an Nd--Fe--B system spherical alloy magnetic powder produced using a thermal plasma method. However, the powder obtained by the method disclosed in this document has a large average particle size, and the intraparticle structure is composed of a fine structure of 1/10 to 1/100 of the spherical particle diameter. Therefore, each magnet powder contains a large number of crystallites inside, and their crystal orientations are random.

Furthermore, Patent Document 3 discloses a technique for obtaining spherical powder having an average grain size of 500 μm or less and a structure having an average grain size of 1 to 30 μm by rapidly solidifying a molten alloy by inert gas atomization. As disclosed in this document, the spherical powder obtained by the gas atomization method tends to be a polycrystalline body in which the internal structure is an aggregation of crystallites smaller than the grain size of the spherical powder. When a large number of crystallites are contained inside individual magnet powders, their crystal orientations become random, which is not suitable for the production of anisotropic magnets.

JP-A-8-111308 JP-A-9-143514 JP-A-8-316016

The present invention has been made in view of such circumstances, and its object is to provide a rare earth magnet powder that can sufficiently improve the bulk density and is suitable for the production of anisotropic magnets, and a molding using the powder. It is an object of the present invention to provide a bonded magnet and a compound for the bonded magnet. It is another object of the present invention to provide a method for producing rare earth magnet powder which can sufficiently improve the bulk density and can easily produce rare earth magnet powder suitable for the production of anisotropic magnets. and a method for manufacturing a rare earth permanent magnet using the manufacturing method.

In order to achieve the above object, the rare earth magnet powder according to the first aspect of the present invention comprises:
The rare earth magnet powder has an average sphericity P1 defined by the formula (1) of P1=Ls/Ll of 0.65 or more. In the formula (1), Ll is the length of the long side of the circumscribing rectangle having the smallest area with respect to the rare earth magnet powder in the microscope image, and Ls in the formula (1) is: It is the length of the short side of the circumscribing rectangle that has the smallest area with respect to the rare earth magnet powder in the microscope image. Furthermore, in the rare earth magnet powder according to the first aspect of the present invention, the number ratio of the single crystal rare earth magnet powder is 65% or more.

Such a magnet powder according to the first aspect can sufficiently improve the bulk density (both the loose bulk density and the hard bulk density). The inventors of the present invention have found that even if the particles are fine, the fluidity does not easily decrease, and the fillability into the mold is improved. As a result of the improved fillability into the mold, the magnet powder can be uniformly filled into the mold, the variation in compact density is reduced, and the deformation of the sintered compact is reduced. In addition, since the friction between powders is reduced, the degree of orientation of the magnetic powder can be increased.

Further, in the magnet powder of the present invention, the degree of orientation of the magnet powder in the compact can be increased. That is, each particle of the magnet powder of the present invention is easily oriented in the direction of the magnetic field, and a rare earth permanent magnet having excellent magnetic properties can be obtained. Furthermore, in the first aspect of the present invention, since the number ratio of the single-crystal rare earth magnet powder is 65% or more, the magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

Preferably, the number ratio of the rare earth magnet powder having a sphericity P1 of 0.9 or more is 30% or more. Even if all the magnet particles do not have a sphericity P1 of 0.9 or more, if the raw material powder for filling the mold contains magnet particles with a specific sphericity P1 above a certain degree, Effective.

In order to achieve the above object, the rare earth magnet powder according to the second aspect of the present invention has an average sphericity P2 defined by the formula (2) of P2=Lt/Lr of 0.70 or more. It is a rare earth magnet powder. In the formula (2), Lr is the peripheral length of the rare earth magnet powder in the microscope image, and Lt in the formula (2) is the image of the rare earth magnet powder from which the peripheral length Lr was calculated. is the perimeter of a perfect circle that has the same area as the area in . Furthermore, in the rare earth magnet powder according to the second aspect of the present invention, the number ratio of the single crystal rare earth magnet powder is 65% or more.

Similar to the first aspect of the present invention, the magnet powder according to the second aspect can sufficiently improve the bulk density. The inventors of the present invention have found that even if the particles are fine, the fluidity does not easily decrease, and the fillability into the mold is improved. As a result of the improved fillability into the mold, the magnet powder can be uniformly filled into the mold, the variation in compact density is reduced, and the deformation of the sintered compact is reduced. Moreover, in the magnet powder according to the second aspect of the present invention, the degree of orientation of the magnet powder in the compact can be increased. Furthermore, in the second aspect of the present invention, magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

Preferably, the number ratio of the rare earth magnet spherical powder having a sphericity P2 of 0.8 or more is 25% or more. Even if all the magnet particles do not have a sphericity P2 of 0.8 or more, if the raw material powder before filling the mold contains magnet particles with a specific sphericity P2 at a certain level or more, Effective.

The average particle size of the rare earth magnet powder is preferably 20 μm or less, more preferably 10 μm or less, preferably 0.5 μm or more, and more preferably 0.5 to 10 μm. If the average particle size of the rare earth magnet powder is too large, gaps are likely to occur between the particles and the bulk density tends to decrease. In addition, if the average particle size of the rare earth magnet powder is too large, there is a tendency for crystal phases different from R2T14B crystals to coexist within a single magnet powder, possibly degrading the magnetic properties after molding. There is On the other hand, if the average particle diameter of the rare earth magnet powder is too small, the particles tend to aggregate frequently, and in this case also the bulk density tends to decrease.

The rare earth magnet powder may include a plurality of coated particles in which at least part of the periphery of individual particles composed of single main phase particles is covered with a coating layer.
Further, preferably, the average of the coverage, which indicates the percentage of the circumference of each of the individual particles covered with the coating layer, is 50% or more. Moreover, preferably, the coated particles include particles whose circumference is covered with a coating rate of 100% (individual particles are covered with a coating layer all around). Preferably, the coating layer is composed of a rare earth-rich component having a rare earth concentration higher than the rare earth concentration contained in the main phase particles.

A sintered magnet obtained by sintering a magnet powder containing such coated particles has improved magnetic properties. For example, a sintered magnet obtained using a rare earth magnet powder containing coating particles has a subphase (coating layer ) is uniformly and thinly distributed on the surface of the main phase (main phase particles), a high coercive force (Hcj) can be obtained. In addition, the segregation of the sub-phase is greatly reduced, and the ratio of the main phase is increased, so that a high residual magnetic flux density (Br) can be obtained.

Preferably, at least a portion of the rare earth magnet powder is composed of RTB permanent magnet powder. This is because the magnetic properties of the RTB system permanent magnet powder are excellent.

A bonded magnet according to one aspect of the present invention preferably contains any one of the rare earth magnet powders described above. The bonded magnet may contain resin. Also, the compound for bonded magnets of the present invention (which may contain a resin or the like) preferably contains any one of the rare earth magnet powders described above. When the above rare earth magnet powder is used as a raw material powder for a bonded magnet (for example, a raw material powder contained in a compound for a bonded magnet), the filling rate is increased and a high degree of orientation is easily obtained, resulting in a high Br bonded magnet. can be realized.

A sintered rare earth magnet according to one aspect of the present invention has a main phase and a subphase observed in its cross section, and the area ratio of the subphase is 2% or less. Also preferably, the main phase is an R2 T14B type crystal. Preferably, in the sintered magnet according to another aspect of the present invention, the degree of orientation obtained by dividing the residual magnetic flux density in the orientation direction by the saturation magnetic flux density is 94% or more.

According to the rare earth sintered magnet according to one aspect of the present invention, the degree of orientation of the main phase is increased and the residual magnetic flux density is increased. In addition, since the secondary phase is distributed on the surface of the main phase, the coercive force of the sintered magnet is increased. Although the sub-phase tends to be unevenly distributed between the main phases, it is possible to reduce the area ratio of the sub-phase, thereby suppressing a decrease in the residual magnetic flux density. In such a sintered magnet, the uneven distribution of subphase components in the sintered body is reduced, so that high residual magnetic flux density and high coercive force can be obtained at the same time.

A method for producing a rare earth magnet powder according to one aspect of the present invention includes a step of pulverizing an alloy having a desired composition to obtain a raw material powder, introducing the raw material powder into a thermal plasma, heating the raw material powder, and then rapidly cooling the raw material powder into a spherical powder. and obtaining By using a thermal plasma method, preferably a high-frequency induction thermal plasma method, the rare earth magnet powder can be spheroidized while suppressing the contamination of impurities. Further, according to the method of the present invention, it is easy to obtain spherical powder having an average particle size of preferably 20 μm or less, more preferably 10 μm or less, and preferably 0.5 μm or more.

Preferably, the raw material powder is introduced into the thermal plasma trailing flame. The temperature of the thermal plasma trailing flame is, for example, 2000 to 5000 K, which is a slightly lower temperature than thermal plasma. It is possible to suppress coarsening due to excessive dissolution and obtain spherical powder having a particle size equivalent to that of the charged raw material powder. Furthermore, according to this manufacturing method, it is easy to obtain a powder having a number ratio of 65% or more of single-crystal rare earth magnet powder, and magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

Further, for example, by putting the raw material powder into the tail flame part of the thermal plasma, heating it, and then rapidly cooling it, the whole or part of each particle of the raw material powder is melted, so that the powder easily becomes spherical. In addition, the components of the subphase are more likely to be uniformly distributed on the powder surface, making it easier to form spherical coated particles. Since the powder is spherical, the bulk density tends to be improved and the degree of orientation tends to be high.

Preferably, the method for producing a rare earth permanent magnet according to one aspect of the present invention comprises the steps of pulverizing an alloy having a desired composition to obtain a raw material powder, and introducing the raw material powder into a thermal plasma trailing flame and heating the raw material powder. A step of quenching to obtain a spherical powder later, and a step of sintering the spherical powder to obtain a sintered body are included. Preferably, the magnet powder containing spherical powder is formed into a predetermined shape by press molding or the like, and then sintered to form a sintered body.

In such a production method, since the powder is spherical, the bulk density tends to be improved and the degree of orientation tends to be high. Therefore, the magnet after sintering tends to have a high residual magnetic flux density. In addition, the components of the subphase are more likely to be uniformly distributed on the powder surface, making it easier to form spherical coated particles. If the components of the subphase are uniformly distributed on the powder surface, the subphase is uniformly distributed (thinly) at the grain boundaries of the two grains during densification even after sintering, so the residual magnetic flux density does not easily decrease. Furthermore, according to this manufacturing method, it is easy to obtain a powder having a number ratio of 65% or more of single-crystal rare earth magnet powder, and magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

FIG. 1A is a micrograph of rare earth magnet powder according to an example of the present invention. FIG. 1B is a micrograph of rare earth magnet powder according to a comparative example of the present invention. FIG. 2A is a schematic diagram for calculating the sphericity of particles. FIG. 2B is a schematic diagram showing a perfect circle having the same cross-sectional area as the cross-sectional area of the particle shown in FIG. 2A. FIG. 3 is a flowchart showing a method for producing rare earth magnet powder according to one embodiment of the present invention. FIG. 4 is a schematic diagram of an apparatus used in the spheronization step shown in FIG. FIG. 5A is a schematic diagram for calculating the coverage of the particles shown in FIG. 1A. FIG. 5B is a schematic explanatory diagram for calculating the coverage of the particles shown in FIG. 1B. FIG. 5C is a cross-sectional photomicrograph of a particle showing a coated particle with a coverage of 100% among the particles shown in FIG. 1A. FIG. 6A is a micrograph of a cross section of a rare earth based sintered magnet according to one embodiment of the present invention. FIG. 6B is a micrograph of a cross section of a rare earth sintered magnet according to a comparative example of the present invention.

An embodiment of the present invention will be described below.

A rare earth magnet powder according to an embodiment of the present invention is, for example, an RTB magnet powder, wherein R represents at least one rare earth element. T represents an iron group element. B represents boron.

Rare earth elements refer to Sc, Y and lanthanoid elements belonging to Group 3 of the long period periodic table. Lanthanide elements include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like. Rare earth elements are classified into light rare earth elements and heavy rare earth elements. In the present application, heavy rare earth elements refer to rare earth elements with atomic numbers of 64 to 71, namely Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and light rare earth elements refer to rare earth elements other than heavy rare earth elements. . In this application, Y is classified as a light rare earth element. Hereinafter, the heavy rare earth element may be referred to as RH. Further, the RTB magnet powder according to this embodiment may contain a heavy rare earth element RH.

T representing an iron group element may be Fe alone, or part of Fe may be substituted with Co. When part of Fe is replaced with Co, temperature characteristics and corrosion resistance can be improved without deteriorating magnetic characteristics.

B represents boron, and part of boron can be substituted with carbon. By substituting part of boron with carbon, that is, by including boron and carbon in the B site, it is easy to form a thick two-particle grain boundary during aging treatment after sintering after molding the powder into a predetermined shape. It has the effect of making it easier to improve the coercive force. When part of boron is replaced with carbon, the amount of replacement may be about 20 at % or less of the total B contained in the R2T14B phase observed after sintering.

The RTB magnet powder may contain other elements. Other elements include, for example, Ti, V, Cr, Mn, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, Al, Ga, Si, Bi, and Sn. The content of R in the RTB magnet powder is arbitrary. The content of R may be 26% by weight or more and 33% by weight or less. The content of B in the RTB magnet powder is arbitrary. The content of boron contained as B may be 0.8% by weight or more and 1.2% by weight or less.

The content of T in the RTB magnet powder is the substantial remainder in the constituent elements of the RTB magnet powder. When Co is contained as T, the content of Co may be 3.0% by weight or less with respect to the sum of the contents of the iron group elements. When Ni is contained as T, the content of Ni may be 1.0% by weight or less with respect to the sum of the contents of the iron group elements.

The amount of oxygen (O) in the RTB magnet powder is arbitrary. For example, it may be 200 ppm or more and 3000 ppm or less. From the viewpoint of improving corrosion resistance, the O content is preferably high, and from the viewpoint of improving magnetic properties, it is preferably low.

The amount of carbon (C) in the RTB magnet powder is arbitrary. For example, it may be 200 ppm or more and 3000 ppm or less. If the amount of C is out of this range, the magnetic properties tend to deteriorate. Further, as described above, the RTB magnet powder may contain carbon, for example, by substituting carbon for part of the boron at the B site in the RTB magnet powder.

The amount of nitrogen (N) in the RTB magnet powder is arbitrary. For example, it may be 200 ppm or more and 1500 ppm or less. If the amount of N is out of this range, the magnetic properties tend to deteriorate.

Generally known methods can be used to measure the amounts of O, C and N in the RTB magnet powder. The amount of O is measured, for example, by an inert gas fusion-nondispersive infrared absorption method. The amount of C is measured, for example, by combustion in an oxygen stream-infrared absorption method. The amount of N is measured, for example, by an inert gas fusion-thermal conductivity method.

As shown in FIG. 1A, most of the particles in the RTB magnet powder of this embodiment are spherical. That is, the RTB magnet powder of the present embodiment has an average sphericity P1 defined by the formula (1) of P1=Ls/Ll of 0.65 or more, preferably 0.7 or more, More preferably, it is 0.75 or more. In addition, the number ratio of magnet powder having a sphericity P1 of 0.9 or more is preferably 30% or more, more preferably 35% or more, and particularly preferably 40% or more.

In the above formula (1), Ll is the length of the long side of the circumscribing rectangle with the smallest area for each particle 2 of the RTB magnet powder in the microscope image shown in FIG. 2A, for example. In the above formula (1), Ls is the length of the short side of the circumscribing rectangle that has the smallest area for each particle 2 of the RTB magnet powder in the microscope image. be.

The microscopic image is, for example, a cross-sectional SEM image obtained by embedding the RTB magnet powder shown in FIG. 100 magnetic particles are observed in the cross section, and the average of 100 randomly selected particles is obtained. In addition, the number ratio (number density) is obtained by measuring P1 of 100 randomly selected particles and calculating the number ratio of magnetic powder having a sphericity P1 of 0.9 or more among 100 particles. be done.

From another point of view, the RTB magnet powder of the present embodiment preferably has an average sphericity P2 defined by the formula (2) of P2=Lt/Lr of 0.70 or more. is 0.73 or more, more preferably 0.75 or more. In addition, the number ratio of magnet powder having a sphericity P2 of 0.8 or more is preferably 25% or more, more preferably 30% or more, and particularly preferably 35% or more.

In the above formula (2), Lr is the circumference of each particle 2 of the RTB magnet powder in the microscope image shown in FIG. 2A, and Lt in the formula (2) is the circumference. It is the perimeter of a perfect circle 20 shown in FIG. 2B having the same area as the area in the image of each particle 2 for which Lr was calculated. The method for obtaining the microscopic image, the method for calculating the average, the method for calculating the number ratio, and the like are the same as in the case of the formula (1) described above. In addition, the number ratio in the case of the sphericity P2 is obtained by calculating the number ratio of the magnet powder having the sphericity P2 of 0.8 or more.

The average particle size of the RTB magnet powder of the present embodiment is preferably 20 μm or less, more preferably 10 μm or less, preferably 0.5 μm or more, more preferably 0.5 to 10 μm. The average particle size of the RTB magnet powder is calculated by calculating the equivalent circle diameter of each particle from the microscope image as described above, and calculating the average value of at least 100 particles. As a method for measuring the average particle diameter, for example, a light scattering method using a laser diffraction particle size distribution meter is also conceivable.

If the average particle size of the RTB magnet powder is too large, gaps are likely to occur between the particles and the bulk density tends to decrease. In addition, when the average particle size of the rare earth magnet powder is large, there is a tendency for crystal phases different from R2T14B crystals to coexist inside one magnet powder, which may degrade the magnetic properties. For example, when the average grain size is large, different crystal phases tend to coexist, and the larger the grain size, the more difficult it is to obtain a coercive force. On the other hand, if the average particle diameter of the rare earth magnet powder is too small, the particles tend to aggregate frequently, and in this case also the bulk density tends to decrease.

As shown in FIG. 5A, most of the particles 2 of the RTB magnet powder of this embodiment are composed of coated particles 30 having a substantially circular cross section. The coated particles 30 are composed of individual particles 31 mainly composed of single main phase particles 31 a , and at least a portion of the peripheral surface of the individual particles 31 is covered with a coating layer 32 . The main phase grains 31a are composed of single crystals such as R2 T14B crystals.

The number ratio of the main phase particles 31a composed of single crystals contained in the RTB magnet powder of the present embodiment is 65% or more, preferably 70% or more, and more preferably 75% or more. is. Single-crystal grains have a higher degree of orientation than polycrystalline grains, so when these grains are used to produce a bonded magnet or a sintered magnet, the Br of the magnet can be easily improved.

In order to determine whether the particles 2 are single crystals or not, the cross section of the particles is exposed and evaluated using an electron backscatter diffraction (EBSD) analyzer attached to the FE-SEM apparatus. The number ratio is, for example, a number ratio obtained by evaluating 100 randomly selected particles. Specifically, in an image obtained by an EBSD analyzer, the number of grains in which a single crystal plane is observed in each grain is determined, and the ratio is calculated.

As shown in FIG. 5A, at least a portion of the peripheral surface of the main phase particles 31a composed of single crystals contained in the RTB magnet powder of the present embodiment is covered with a coating layer 32. is preferred. The coating layer 32 is composed of a rare earth-rich component having a rare earth concentration higher than that contained in the main phase grains. The thickness of the coating layer 32 is as thin as about 10 to 200 nm, and the average particle size of the coating particles 30 is within the range of the average particle size of the RTB magnet powder described above.

As shown in FIG. 5B, the individual grains 31 may have a plurality of main phase grains 31a connected via the grain boundary phase 33. At least part of the peripheral surface of the particle 31 a is preferably covered with the coating layer 32 .

In addition, in the present embodiment, the average coverage ratio indicating the ratio of the single main phase particle 31a covered with the coating layer 32 is preferably 50% or more, more preferably 60% or more, and particularly preferably 80%. That's it. The higher the average coverage of the main phase grains 31a covered with the coating layer 32 composed of the rare earth-rich component with high magnetic anisotropy, the more difficult the magnetization reversal occurs, and the higher the Hcj.

The average coverage can be obtained as the average coverage of 100 randomly selected particles 2, for example. Calculation of the coverage of the particles 2 can be obtained, for example, as follows. As shown in FIG. 5A, when the individual particle 31 is composed of only a single main phase particle 31a, in the cross section of the particle 2, the circumference of the interface between the outer surface of the main phase particle 31a and the coating layer 32 Directional interface lengths Lb1 and Lb2 are determined by image analysis.

For one particle 2, the exposed circumferential lengths La1 and La2 of the outer surface of the main phase particle 31a not covered with the coating layer 32 are similarly obtained by image analysis. For one particle 2, the sum of the circumferential exposed lengths La1 and La2 and the circumferential interface lengths Lb1 and Lb2 (La1+La2+Lb1+Lb2) is the total circumferential length Lt of the main phase grain 31a (individual grain 31). The coverage for one particle 2 can be expressed as 100×the peripheral interface length (Lb1+Lb2)/the total peripheral length Lt.

When the circumferential interface lengths Lb1 and Lb2 (the circumferential exposed lengths La1 and La2) are one or three or more, the total circumferential interface length ΣLbn (the circumferential exposed length total ΣLan) The number of n (n is an integer of 1 or more) increases or decreases.

In the present embodiment, for example, among 100 particles 2 randomly selected from magnetic powder, at least one or more particles with a coverage rate of 100% all around as shown in FIG. 5C, preferably Ten or more, more preferably thirty or more. The larger the number of particles covered all around, the higher the average coverage, and the higher the Hcj. The “perimeter-coated particles” can also be defined as coated particles in which the entire periphery of individual particles is covered with a coating layer.

In the above example, as shown in FIG. 5A, the calculation of the coverage when the individual particle 31 is a single main phase particle 31a is shown, but as shown in FIG. Calculation of the coverage in the case of an aggregate of main phase particles 31a can be performed in the same manner.

That is, as shown in FIG. 5B , for example, when a plurality of main phase grains 31 a are connected by the grain boundary phase 33 , aggregates of the plurality of main phase grains 31 a are regarded as individual grains 31 . Then, without counting the length of the interface (dotted line portion) between the grain boundary phase 33 and the main phase grain 31a, the circumferential interface length (two-dot chain line portion) Lb1 and Lb2 of the individual grains 31 and the circumferential exposure length The height (solid line portion) La1 and La2 are calculated by image analysis.

The magnet powder of the present embodiment may also contain such individual particles 31 composed of aggregates of a plurality of main phase particles 31a, but it is preferable that the average coverage falls within the above range. . As for the degree of sphericity P1 or P2, it is preferable that the degree of sphericity of each main phase particle 31a falls within the range described above.

In the individual grains 31 made up of aggregates of a plurality of main phase grains 31a, the grain boundary phase 33, like the coating layer 32, is composed of a component containing more rare earth elements than the main phase grains 31a. and are of similar composition, but not necessarily identical. The grain boundary phase 33 exists between the main phase grains 31a and the main phase grains 31a, and the coating layer 32 covers the outer surface of the main phase grains 31a without contacting other main phase grains 31a. Defined as the part where the outer surface is exposed.

The RTB magnet powder according to the present embodiment can sufficiently improve the bulk density (both loose bulk density and hard bulk density), and when pressure-molded in a magnetic field, Even if the magnet powder is fine, the flowability does not easily decrease, and the mold filling property is improved. As a result of the improved fillability into the mold, the magnet powder can be uniformly filled into the mold, the variation in compact density is reduced, and the deformation of the sintered compact is reduced.

Further, in the RTB magnet powder of the present embodiment, the degree of orientation of the magnet powder in the compact can be increased. That is, each particle of the magnet powder of the present invention is easily oriented in the direction of the magnetic field, and an RTB magnet having excellent magnetic properties can be obtained. In addition, since the friction between powders is reduced, the degree of orientation of the magnetic powder can be increased. Furthermore, in the present embodiment, since the number ratio of the single-crystal rare earth magnet powder is 65% or more, the magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

A sintered magnet is preferable as the RTB permanent magnet from the viewpoint of high magnetic properties and heat resistance. The sintered magnet is preferably a sintered magnet having a sintered body obtained by sintering a compact obtained by compacting the above-described rare earth magnet powder in a magnetic field. As shown in FIG. 6A, preferably, a main phase and a subphase are observed in the cross section of the sintered body, and the area ratio of the subphase is 2% or less. Preferably, the main phase is R2 T14B type crystals. Preferably, the sintered magnet has a degree of orientation of 94% or more, more preferably 95% or more, obtained by dividing the residual magnetic flux density in the orientation direction by the saturation magnetic flux density.

According to the sintered magnet according to this embodiment, the degree of orientation of the main phase is increased, and the residual magnetic flux density is increased. In addition, since the secondary phase is uniformly distributed on the surface of the main phase, the coercive force of the sintered magnet is increased. Although the sub-phase tends to be unevenly distributed between the main phases, it is possible to reduce the area ratio of the sub-phase, thereby suppressing a decrease in the residual magnetic flux density. In such a sintered magnet, the uneven distribution of subphase components in the sintered body is reduced, so that high residual magnetic flux density and high coercive force can be obtained at the same time.

The area ratio of the subphase can be calculated from a backscattered electron image obtained using, for example, FE-SEM (Field Emission Scanning Electron Microscope). When using FE-SEM, first, a sample for FE-SEM is prepared. Specifically, an RTB permanent magnet is embedded in an epoxy or phenol resin and polished so that a cross section parallel to the orientation direction of the RTB permanent magnet can be observed. Specifically, polishing is performed by rough polishing by a normal method, and then finish polishing. Final polishing is performed so that the cross section is glossy. There is no particular limitation on the method of final polishing.

It is preferable to perform finish polishing by dry polishing without using a polishing liquid such as water. When a polishing liquid such as water is used, it may become impossible to perform an appropriate analysis due to corrosion of the grain boundary phase. Next, the cross section of the RTB permanent magnet obtained by polishing is subjected to ion milling treatment to remove oxide films, nitride films, and the like.

Next, a cross section of the obtained RTB permanent magnet is observed with an FE-SEM to obtain a backscattered electron image with a size of 50 μm square to 100 μm square at a magnification of 1000 times or more and 3000 times or less. From the contrast of the backscattered electron image, it can be confirmed that the RTB system permanent magnet consists of a plurality of phases. By comparing the result of point analysis by an EDS (energy dispersive X-ray spectrometer) attached to the FE-SEM with the contrast of the backscattered electron image, the main phase crystal grains (main phase) composed of R2 T14B, R It can be classified into phases (subphases) such as the rich phase. From the measurement result by EDS, it can be determined whether the main phase crystal grains (main phase) or not.

In order to calculate the area ratio of the subphase, the backscattered electron image is subjected to image processing and binarized. In this embodiment, in the backscattered electron image of the RTB system permanent magnet, a region having a brighter contrast than that of the main phase crystal grains by a predetermined level or more is extracted and defined as a subphase region. For example, the reflected electron image of the RTB system permanent magnet shown in FIG. 6A or 6B is subjected to image processing and binarized. By dividing the area of the subphase detected by binarization by the area of the RTB system permanent magnet, the area ratio of the subphase (area ratio of the subphase) can be calculated.

The secondary phase such as the R-rich phase generally has a higher content of the rare earth element R than the main phase crystal grains. Here, the rare earth element R is an element having a particularly large atomic number among the elements normally contained in RTB system permanent magnets. It is known that the signal intensity of a backscattered electron image increases as the content of an element with a large atomic number increases, and the image appears brighter. In this embodiment, the volume ratio can also be calculated by assuming that the area ratio and the volume ratio are equal.

The permanent magnet of this embodiment may be a bonded magnet in which the RTB magnet powder described above is kneaded into a resin, or a bonded magnet compound (for example, in the form of pellets). When the rare earth magnet powder of the present embodiment is used as a raw material powder for a bonded magnet (for example, a raw material powder contained in a compound for a bonded magnet), the filling rate is increased and a high degree of orientation is easily obtained, resulting in a high Br. A bonded magnet can be realized.

A method for manufacturing an RTB system sintered magnet (hereinafter also referred to as an RTB system permanent magnet) will be described in detail below.

<Method for Producing RTB Permanent Magnet>
A method for manufacturing an RTB permanent magnet according to this embodiment includes the following steps.
(a) an alloy preparation step of preparing a raw material alloy (b) a pulverizing step of pulverizing a raw material alloy (c) a step of spheroidizing the pulverized raw material alloy powder (d) a forming step of forming the spheroidized raw material powder (e) A sintering step of sintering the molded body to obtain an RTB permanent magnet substrate (f) a processing step of processing the RTB permanent magnet substrate

[Alloy preparation process]
A raw material alloy for the RTB permanent magnet according to this embodiment is prepared. A material metal corresponding to the composition of the RTB permanent magnet according to the present embodiment is melted in a vacuum or an inert gas atmosphere such as Ar gas, and then cast using the melted material metal. A raw material alloy having a desired composition is produced. In this embodiment, the case of the one-alloy method will be described, but a two-alloy method in which the main phase alloy and the grain boundary alloy are produced separately may also be used.

Examples of raw metals that can be used include rare earth metals, rare earth alloys, pure iron, ferroboron, and alloys and compounds thereof. Casting methods for casting raw metals include, for example, an ingot casting method, a strip casting method, a book mold method, and a centrifugal casting method. The raw material alloy obtained is subjected to a homogenization treatment as necessary when there is solidification segregation.

[Pulverization process]
After the raw material alloy is produced, the raw material alloy is pulverized.

The pulverization step includes a coarse pulverization step (step S1 shown in FIG. 3) for pulverizing until the particle size is about several hundred μm to several mm, and a fine pulverization step for finely pulverizing until the particle size is about several μm (FIG. 3 can be performed in two stages, ie, step S3) shown in FIG.

(Coarse pulverization process)
The raw material alloy is coarsely pulverized until the grain size is about several hundred μm to several mm (step S1 shown in FIG. 3). As a result, a coarsely pulverized powder of the raw material alloy is obtained. Coarse pulverization involves causing the raw material alloy to absorb hydrogen, then releasing hydrogen based on the difference in the amount of hydrogen absorbed between different phases, and dehydrogenating the alloy to cause self-collapsing pulverization (hydrogen absorption pulverization). by In addition, the coarse pulverization step may not use hydrogen absorption pulverization as described above, for example, it may be performed using a coarse pulverizer such as a stamp mill, jaw crusher, or Brown mill in an inert gas atmosphere. good.

In addition, in order to obtain high magnetic properties, the atmosphere in each step from the pulverization step to the sintering step, which will be described later, preferably has a low oxygen concentration. The oxygen concentration is adjusted by controlling the atmosphere in each manufacturing process. If the oxygen concentration in each manufacturing process is high, the rare earth element in the powder of the raw material alloy is oxidized to form R-oxide, which is not reduced during sintering and is precipitated at the grain boundary as it is in the form of R-oxide. The residual magnetic flux density Br of the obtained RTB system permanent magnet is lowered. Therefore, for example, it is preferable to set the concentration of oxygen in each step to 100 ppm or less.

(Fine pulverization process)
After coarsely pulverizing the raw material alloy, the obtained coarsely pulverized powder of the raw material alloy is finely pulverized to an average particle size of about several μm (step S3 shown in FIG. 3). As a result, a finely pulverized powder of the raw material alloy is obtained. By further finely pulverizing the coarsely pulverized powder, it is possible to obtain finely pulverized powder having particles of preferably 1 μm or more and 10 μm or less, more preferably 3 μm or more and 5 μm or less.

Fine pulverization is carried out by further pulverizing the coarsely pulverized powder using a fine pulverizer such as a jet mill, ball mill, vibrating mill, wet attritor, etc., while appropriately adjusting conditions such as pulverization time. In the jet mill, a high-pressure inert gas (for example, _N2 gas) is released from a narrow nozzle to generate a high-speed gas flow. This is a method of pulverizing by causing collisions between coarsely pulverized powders and collisions with a target or a container wall.

When the coarsely pulverized powder of the raw material alloy is finely pulverized, by adding a pulverizing aid such as zinc stearate or oleic acid amide (lubricant addition step in step S2 shown in FIG. A ground powder can be obtained. An example of the RTB magnet powder obtained in the pulverization process of step S3 is shown in FIG. 1(B). The RTB magnet powder obtained in the pulverization step of step S3 has an average sphericity P1 defined by the above-described formula (1) of less than 0.65, preferably 0.60 or less. is. Moreover, the average value of the sphericity P2 defined by the above-described formula (2) is less than 0.70, preferably 0.68 or less.

[Spheroidization step]
Next, in the present embodiment, a spheroidizing step shown in step S4 shown in FIG. 3 is performed. In the spheroidization step, the finely pulverized powder finely pulverized in the pulverization step is spheroidized using, for example, the apparatus shown in FIG.

The apparatus 10 shown in FIG. 4 can generate a high-frequency induction thermal plasma 12 inside a plasma generation chamber 13 provided in the upper central portion of the chamber 11 . The high-frequency induction thermal plasma 12 is formed by locally concentrating high-frequency power in an atmosphere of atmospheric pressure or a reduced pressure close to atmospheric pressure, and by electromagnetic induction, transforming various gases into an ultra-high temperature plasma state of approximately 10,000 degrees. be done. Raw materials (powder, gas, liquid) are introduced into this plasma 12, and through vaporization, melting, decomposition, chemical reactions, etc., synthesis and reaction of nanoparticles, modification and spheroidization of fine powder, film formation, harmful gas can be disassembled.

The plasma generation chamber 13 communicates with the chamber 11 disposed below, and the raw material powder supply unit 14 is connected in the vicinity of the connecting portion between the plasma generation chamber 13 and the chamber 11. From there, the fine raw material powder is introduced (sprayed) toward the tail flame portion 12 a of the thermal plasma 12 .

A high-frequency coil is arranged around the plasma generation chamber 13, and high-frequency induction heating is performed inside the plasma generation chamber 13 to generate a flame of the thermal plasma 12. As shown in FIG. The high frequency (frequency) and voltage (or power) of the high frequency voltage applied to the high frequency coil are not particularly limited, and may be appropriately selected according to properties such as the temperature of the thermal plasma.

In this embodiment, the fine raw material powder obtained in the fine pulverization step is heated by thermal plasma to be spherical. A gas for plasma is turned into a thermal plasma of about 10,000°C by high-frequency induction, and fine raw material powder is introduced into the plasma. The spheroidized raw material powder after the thermal plasma treatment may be classified by a cyclone or the like. By this high-frequency induction thermal plasma method, it is possible to produce a spheroidized raw material powder that is close to a true sphere. It should be noted that not all of the fine raw material powder may be processed into a spherical shape by the thermal plasma method.

In this embodiment, it is more preferable to spray the fine raw material powder obtained in step S3 shown in FIG. 3 toward the tail flame portion 12a of the thermal plasma 12 of the apparatus 10 shown in FIG. This suppresses excessive evaporation and melting of the fine raw material powder, and as a result, the fine raw material powder (RTB magnet powder of the present embodiment) having an average particle size of about 0.5 to 20 μm is spherical. easy to obtain.

The particle size and particle size distribution of the spherical raw material powder can be controlled by controlling the particle size of the fine raw material powder, the spray amount of the fine raw material powder to the thermal plasma 12 per unit time, the flow rate of the carrier gas, and the like. The trailing flame portion 12a of the thermal plasma 12 is near the tip of the flame of the thermal plasma 12 (lower end in the drawing), and the temperature of the trailing flame portion 12a is about 2000-5000K.

The temperature of the tail flame portion 12a is rather low as a thermal plasma. can be suppressed. When the raw material powder is introduced from above the thermal plasma (upstream side of the tail flame), a large amount of nano-powder is likely to be generated, and the nano-powder tends to agglomerate, resulting in a decrease in bulk density.

The raw material powder introduced into the trailing flame portion 12a is exposed to a high temperature in the trailing flame portion 12a of the thermal plasma 12, and then quenched by the quenching gas 15 in the upper part of the chamber 11 to be spheroidized. The atmosphere of the quench gas 15 in the upper interior of the chamber 11 is, for example, an inert atmosphere of argon or a reducing atmosphere of argon containing hydrogen.

The plasma gas ejected from the gas ejection port 16 provided in the upper part of the plasma generation chamber 13 is a mixture of hydrogen gas and argon gas, and the internal pressure of the plasma generation chamber 13 is the same as that of the chamber 11. Similarly to , the atmosphere is preferably a reduced pressure atmosphere of 700 Torr or less, more preferably 75 to 675 Torr. In place of argon gas, or together with argon gas, an inert gas such as helium gas or nitrogen gas may be used. Hydrogen gas does not necessarily have to be contained, but is preferably contained. Hydrocarbon gas such as oxygen, methane, ethane, propane, butane, acetylene, ethylene, propylene and butene may be used instead of hydrogen gas depending on the purpose.

The spheroidized powder inside the chamber 11 is collected and recovered in a box-shaped powder recovery section 17 provided below the chamber 11 . The spheroidized powder (RTB magnet powder of the present embodiment) collected by the powder collecting unit 17 is classified as necessary, and subjected to the orientation molding step (step S5) shown in FIG. transferred to a device for

[Orientation molding process]
Next, the RTB magnet powder of this embodiment as shown in FIG. 1A is formed into a desired shape. A compact is thus obtained. In the molding step, magnet powder is filled in a mold placed between electromagnets and pressed to form an arbitrary shape (step S5 shown in FIG. 3). At this time, by applying pressure while applying a magnetic field, the spheroidized powder is oriented in a predetermined manner, and compacted in the magnetic field with the crystal axis oriented. Since the molded body obtained is oriented in a specific direction, an RTB permanent magnet base material having stronger magnetic anisotropy can be obtained.

[Sintering process]
Next, the compact obtained by molding into the desired shape in step S5 shown in FIG. 3 is sintered in a vacuum or an inert gas atmosphere (step S6) to produce an RTB permanent magnet. obtain. The sintering temperature needs to be adjusted according to various conditions such as the composition, pulverization method, and difference in particle size and particle size distribution. C. or less for 1 hour or more and 10 hours or less to sinter. As a result, the spheroidized powder undergoes liquid phase sintering, and an RTB permanent magnet base material with an improved volume ratio of the main phase is obtained. In addition, it is preferable to rapidly cool the sintered RTB permanent magnet substrate from the viewpoint of improving production efficiency.

If the magnetic properties are to be measured at this point, aging treatment is performed. Specifically, after sintering, the obtained RTB permanent magnet base material is maintained at a temperature lower than that during sintering, so that the RTB permanent magnet base material is subjected to aging treatment. apply. The aging treatment is, for example, two-stage heating at a temperature of 700° C. or higher and 900° C. or lower for 1 hour to 3 hours and further at a temperature of 500° C. to 700° C. for 1 hour to 3 hours, or a temperature of about 600° C. for 1 hour. The treatment conditions are appropriately adjusted according to the number of times the aging treatment is performed, such as one-step heating for 3 hours. Such aging treatment can improve the magnetic properties of the RTB permanent magnet substrate. Also, the aging treatment may be performed after the processing step.

After subjecting the RTB permanent magnet substrate to aging treatment, the RTB permanent magnet substrate is rapidly cooled in an Ar gas atmosphere. As a result, the RTB permanent magnet base material according to the present embodiment can be obtained. The cooling rate is not particularly limited, and is preferably 30° C./min or higher.

The obtained RTB permanent magnet base material may be processed into a desired shape if necessary (step S7 shown in FIG. 3). Processing methods include shape processing such as cutting and grinding, and chamfering such as barrel polishing. However, in the present embodiment, since the powder that has been spheroidized by the spheroidizing process (RTB magnet powder according to the present embodiment) is used for molding, it has excellent fluidity. In the orientation molding process of step S5 shown in FIG. 3, it is also possible to mold using a mold having a shape close to the final product. In other words, in the present embodiment, since it is possible to form a thin molded product, which has been difficult to achieve in the past, it is also possible to produce a product without cutting the sintered magnet base material in the processing process. is. After the processing step, the following diffusion step may be performed as required.

[Diffusion process]
The heavy rare earth element RH may be diffused into the grain boundaries of the RTB permanent magnet base material. As a pretreatment for grain boundary diffusion, it is preferable to subject the magnet base material to an etching treatment. Specifically, a mixed solution of 100% by mass of ethanol and 3% by mass of nitric acid is prepared, and the magnet substrate is immersed in the mixed solution for 3 minutes for etching, and then immersed for 1 minute in ethanol for cleaning.

Diffusion is carried out by attaching a compound containing a heavy rare earth element to the surface of an RTB permanent magnet base material and then subjecting it to heat treatment, or by performing RTB in an atmosphere containing vapor of the heavy rare earth element. It can be carried out by a method such as a method of heat-treating the permanent magnet base material.

There is no particular limitation on the method of depositing the heavy rare earth element RH. For example, there are methods using vapor deposition, sputtering, electrodeposition, spray coating, brush coating, jet dispenser, nozzle, screen printing, squeegee printing, sheet construction method, and the like.

The type of heavy rare earth element RH is arbitrary, but Dy or Tb is preferred, and Tb is particularly preferred. Further, for example, when Tb is diffused as the heavy rare earth element RH, the effect of diffusion can be made more favorable by appropriately controlling the adhesion amount of Tb, the diffusion temperature and the diffusion time.

When the heavy rare earth element RH is applied by coating, it is common to apply a paint comprising a heavy rare earth compound containing the heavy rare earth element RH and a solvent. There are no particular restrictions on the form of the paint. Also, the type of the heavy rare earth compound is arbitrary. Examples include alloys, oxides, halides, hydroxides, hydrides and the like. It is particularly preferred to use hydrides.

When a Tb compound is deposited, for example, Tb hydride (TbH2), Tb oxide (Tb2O3, Tb4O7) or Tb fluoride (TbF3) may be deposited.

The heavy rare earth compound is preferably particulate. Also, the average particle diameter is preferably 100 nm to 50 μm, more preferably 1 μm to 20 μm.

As a solvent to be used for the paint, a solvent capable of uniformly dispersing the heavy rare earth compound without dissolving it is preferable. Examples thereof include alcohols, aldehydes, ketones, etc. Among them, ethanol is preferred.

There are no particular restrictions on the content of the heavy rare earth compound in the paint. For example, it may be from 50% to 90% by weight. The paint may further contain components other than the heavy rare earth compound, if necessary. For example, the paint may contain a dispersant for preventing agglomeration of the heavy rare earth compound particles, powders of transition metals or base metals, powders mainly composed of light rare earth elements, and the like.

In the diffusion step of the present embodiment, there is no particular limitation on the number of surfaces of the RTB permanent magnet substrate to which the paint containing the heavy rare earth compound is attached. For example, it may be attached to all surfaces, or may be attached only to two surfaces, the largest surface and the surface opposite to this surface. Moreover, a mask may be applied to a surface other than the surface to be adhered, if necessary. Moreover, it is preferable that the surface on which the paint containing the heavy rare earth element is adhered is the magnetic pole surface.

The adhesion amount of Tb can be, for example, 0.2% by weight or more and 3.0% by weight or less when the whole RTB system permanent magnet is 100% by weight. Moreover, the heat treatment temperature at the time of diffusion can be 800° C. or more and 950° C. or less. The heat treatment time during diffusion is preferably 1 hour or more and 30 hours or less. Although the atmosphere during the diffusion process is arbitrary, it is preferable to use an Ar atmosphere.

[Aging treatment process]
After the diffusion step, the RTB permanent magnet may be aged. After the diffusion step, the obtained RTB permanent magnet is subjected to an aging treatment, such as by holding the obtained RTB permanent magnet at a temperature lower than that during diffusion. The aging treatment is performed, for example, at a temperature of 450° C. or higher and 700° C. or lower for 0.5 hours or more and 4 hours or less, and the number of times of aging treatment is appropriately adjusted. Aging treatment can improve the magnetic properties of RTB permanent magnets. The atmosphere during the aging treatment is arbitrary, but an Ar atmosphere is preferable.

[Cooling process]
After subjecting the RTB system permanent magnet to aging treatment, the RTB system permanent magnet is cooled in an Ar gas atmosphere. As a result, the RTB system permanent magnet according to this embodiment can be obtained. Although the cooling rate is arbitrary, it is, for example, 30° C./min or more and 300° C./min or less.

[Surface treatment process]
The RTB permanent magnet obtained by the above steps may be subjected to surface treatment such as plating, resin coating, oxidation treatment, chemical conversion treatment, etc., depending on the intended use and desired properties. Also, the surface treatment step may be omitted.

A magnet product can be obtained by magnetizing the RTB system permanent magnet according to the present embodiment according to a conventional method.

According to the method of the present embodiment, in the spheroidization step, it is possible to obtain spherical powder having a particle diameter equivalent to that of the raw material powder fed. Furthermore, according to this manufacturing method, it is easy to obtain a powder having a number ratio of 65% or more of single-crystal rare earth magnet powder, and magnetic properties such as the coercive force (Hcj) of the magnet can be improved.

Further, for example, by putting the raw material powder into the tail flame part of the thermal plasma, heating it, and then rapidly cooling it, the whole or part of each particle of the raw material powder is melted, so that the powder easily becomes spherical. In addition, the components of the subphase are more likely to be uniformly distributed on the powder surface, making it easier to form spherical coated particles. Since the powder is spherical, the bulk density tends to be improved and the degree of orientation tends to be high.

In such a production method, since the powder is spherical, the bulk density tends to be improved and the degree of orientation tends to be high. Therefore, the magnet after sintering tends to have a high residual magnetic flux density. In addition, the components of the subphase are more likely to be uniformly distributed on the powder surface, making it easier to form spherical coated particles. If the components of the subphase are uniformly distributed on the powder surface, the subphase is uniformly distributed (thinly) at the grain boundaries of the two grains during densification even after sintering, so the residual magnetic flux density does not easily decrease. Furthermore, according to this manufacturing method, it is easy to obtain a powder having a number ratio of 65% or more of rare earth magnet powder composed of single crystals, and the magnetic properties such as the coercive force of the magnet can be improved.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

For example, the rare earth magnet powder of the present invention may be further supplied to a microstructure refinement step by the HDDR method. By further subjecting the rare earth magnet powder of the present invention to the HDDR method, it is possible to reduce the crystallite size while substantially maintaining the particle shape, particle size, and magnetic anisotropy. Permanent magnets can be obtained.

Moreover, the RTB system permanent magnets of the above-described embodiments can be modified in various ways and combined in various ways, and can be similarly applied to other rare earth system magnets. For example, RTB system permanent magnets are not limited to RTB system sintered magnets manufactured by sintering as described above. It may be an RTB system permanent magnet manufactured by performing hot forming and hot working instead of sintering.

When the cold compact obtained by compacting the raw material powder at room temperature is subjected to hot compaction in which pressure is applied while being heated, the pores remaining in the cold compact disappear and are not sintered. It can be densified. Furthermore, by subjecting the molded body obtained by hot molding to hot extrusion as hot working, an RTB permanent magnet having a desired shape and magnetic anisotropy is obtained. can be obtained.

Further, the use of the RTB system permanent magnet according to this embodiment is arbitrary. Examples include motors for electric vehicles and wind power generation.

Further, as applications of the rare earth magnet powder of the present invention, magnetic refrigeration, magnetic fluid, magnetic sheets, magnetic recording, etc. can be exemplified as applications other than magnet molding.

The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

Example 1
First, the composition of Nd: 30.5, Al: 0.23, Co: 0.5, Cu: 0.06, Zr: 0.15, B: 1.01, Fe: balance (unit: wt%) In order to obtain an RTB magnet powder having

Next, after allowing the material alloy to absorb hydrogen at room temperature, dehydrogenation treatment was performed at 600° C. for 1 hour, and the material alloy was hydrogen pulverized (coarsely pulverized) to obtain a coarsely pulverized powder. Each step (pulverizing and molding) from hydrogen pulverization to sintering was performed in an atmosphere with an oxygen concentration of less than 50 ppm.

Next, 0.2% by weight of oleic acid amide was added as a grinding aid to the coarsely ground powder of the raw material alloy, and mixed using a Nauta mixer. After that, fine pulverization was performed using high-pressure N ₂ gas using a jet mill to obtain a finely pulverized powder having an average particle size of 4.0 μm (fine pulverization step).

Next, the finely pulverized powder thus obtained was spheroidized as described below (spheronization step). Specifically, the finely pulverized powder was passed through the raw material powder supply section 14 of the device 10 shown in FIG. As the device 10, a modified TP-40020NPS device manufactured by JEOL Ltd. was used. The powder was supplied to the apparatus 10 using a JEOL Ltd. TP-99010FDR apparatus as a powder feeder, feeding the powder at various feeding speeds and feeding the powder into the generated thermal plasma.

A high frequency voltage of about 4 MHz and about 6 kV is applied to the high frequency transmission coil for generating the thermal plasma 12, and the plasma gas ejected from the gas ejection port 16 contains 100 liters/minute of argon and 10 liters of hydrogen. /min of mixed gas was used. At this time, the atmosphere of the thermal plasma 12 formed in the plasma generation chamber 13 was a reduced pressure atmosphere of about 375 Torr.

Further, the fine raw material powder was loaded into the tail flame portion 12a of the thermal plasma 12 while being supported by 5 liters/minute of argon as a carrier gas. The dosing rate was 15.0 g/min. The temperature of the tail flame portion 12a was about 2000-5000K. The quench gas 15 in the upper interior of the chamber 11 was a reducing gas consisting of argon with hydrogen.

The average particle size and sphericity P1 and P2 of the spherical powder (magnet powder) obtained in the powder recovery unit 17 were obtained by the methods described above. Results are shown in Table 1A. Further, the number ratio of the main phase particles composed of single crystals contained in the magnet powder (single crystal magnet powder content) was obtained by the method described above. Results are shown in Table 1A. Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained by the method described above. Results are shown in Table 1B.

Whether or not it was a single crystal was determined using an EBSD analyzer. EBSD analyzers can image designated crystal planes in each grain. That is, when a single crystal face is observed in each particle in the image obtained by the EBSD analyzer, such a particle is presumed to be a single crystal, and each particle has multiple crystal planes. If crystal faces of are observed, such grains can be judged to be polycrystalline.

Furthermore, the bulk density of the magnet powder was obtained by the following method. That is, the bulk density was measured using a powder property measuring machine (manufactured by Hosokawa Micron) to measure the firm bulk density (g/cm ³ ) and loose bulk density (g/cm ³ ). The mesh size of the sieve used was 710 μm, and the metal funnel used had an inner diameter of 0.8 cm. VIBRATION was performed at 2.0 (power supply: AC 100 V, 50 Hz). Results are shown in Table 1B.

A micrograph of the magnet powder obtained in Example 1 is shown in FIG. 1A. Furthermore, the average coverage of the coated particles contained in the magnet powder was determined by the method described above. Results are shown in Table 1B. Also, the presence or absence of magnet powder with a coverage of 100% was determined by the method described above. Results are shown in Table 1B.

Comparative example 1
Magnet powder was obtained in the same manner as in Example 1, except that the spheroidizing step was not performed. That is, finely pulverized powder immediately after finely pulverizing with high-pressure N ₂ gas using a jet mill (pulverizing step) was used as magnet powder. In the same manner as in Example 1, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. A micrograph of the magnet powder obtained in Comparative Example 1 is shown in FIG. 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Example 2
Magnet powder was obtained in the same manner as in Example 1, except that the finely pulverized powder having an average particle size of 10.0 μm was obtained by changing the conditions of the pulverizing step performed before the spheroidizing step. That is, the finely pulverized powder after finely pulverizing with high-pressure N ₂ gas using a jet mill (pulverizing step) is charged into the tail flame portion 12a of the thermal plasma 12 in the same manner as in Example 1. The spheroidized powder was used as magnet powder. In the same manner as in Example 1, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Comparative example 2
Magnet powder was obtained in the same manner as in Example 2, except that the spheroidizing step was not performed. That is, finely pulverized powder immediately after finely pulverizing with high-pressure N2 gas using a jet mill (pulverizing step) was used as magnet powder. In the same manner as in Example 2, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 2. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Comparative example 3
Magnet powder was obtained in the same manner as in Example 1, except that the finely pulverized powder after the pulverizing step was put into the upper portion 12b (see FIG. 4) of the thermal plasma 12 in the spheroidizing step. The temperature of the central portion of the thermal plasma 12 was 10000K or higher. In the same manner as in Example 1, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Comparative example 4
Magnetic powder was obtained in the same manner as in Example 2, except that the finely pulverized powder after the pulverizing step was charged into the upper portion 12b (see FIG. 4) of the thermal plasma 12 in the spheroidizing step. The temperature of the central portion of the thermal plasma 12 was 10000K or higher. In the same manner as in Example 2, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 2. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was determined in the same manner as in Example 2. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Comparative example 5
Magnet powder having the same composition as in Example 1 was formed by a gas atomization method without using the strip casting (SC) method, and the magnetic powder was formed in the same manner as in Example 1 except that the spheroidization treatment by thermal plasma was not performed. A magnet powder was obtained. In the same manner as in Example 1, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 1. Results are shown in Table 1B. Further, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Examples 3-5
Magnet powder was obtained in the same manner as in Example 1, except that the atmospheric pressure of the thermal plasma formed in the plasma generation chamber 13 was changed to 675 Torr, 300 Torr, and 75 Torr in the spheroidization step. In the same manner as in Example 1, the average particle diameter, sphericity P1 and P2, and single crystal magnet powder content were determined. Results are shown in Table 1A.

Further, the number ratio of magnet powder having a sphericity P1 of 0.9 or more and the number ratio of magnet powder having a sphericity P2 of 0.8 or more were obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, the bulk density of the magnet powder was obtained in the same manner as in Example 1. Results are shown in Table 1B. Furthermore, Table 1B shows the average coverage of the coated particles contained in the magnet powder and the presence or absence of magnet powder with a coverage of 100%.

Rating 1
As shown in Tables 1A and 1B, in Examples 1 to 5, compared with Comparative Examples 1 to 4, both the sphericity P1 and P2 were improved, the bulk density was improved, and the sphericity P1 was 0.00. It was confirmed that the number ratio of magnet powder having a sphericity P2 of 9 or more was improved, and the number ratio of magnet powder having a sphericity P2 of 0.8 or more was also improved. It was also found that the average particle size of the magnet powder can be controlled within a preferable range. Furthermore, by controlling the particle size of the fine raw material powder, the spray amount (input amount) of the fine raw material powder to the thermal plasma per unit time, the flow rate of the carrier gas, the internal pressure of the plasma generation chamber, etc., the spherical raw material powder ( It has also been confirmed that the particle size and particle size distribution of the magnet powder) can be controlled, and the single-crystal magnet powder content and average coverage can be controlled.

Further, as shown in Tables 1A and 1B, in Examples 1 to 5, compared with Comparative Examples 1 to 5, the average coverage (average coverage) of each particle constituting the magnet powder was improved. , magnet powder with a coverage of 100% was confirmed. It has been confirmed that the improved coverage improves the magnetic properties of the magnet, as will be described later.

In Comparative Example 3, the reason why the average particle diameter was small is considered as follows. When particles with a small particle size are introduced from the upper portion 12b of the thermal plasma 12, the particles pass through the plasma at several tens of thousands of degrees and are excessively heat-transferred to completely evaporate the particles. When it re-solidifies, nano-powder is generated. In addition, since particles with a small particle size tend to aggregate, the generated nanopowder aggregates and the particle shape becomes distorted. In addition, it is thought that a large number of irregularly shaped particles are generated during re-solidification, resulting in poor sphericity.

Further, in Comparative Example 4, when particles having a large particle size are introduced from the upper portion 12b of the thermal plasma 12, they pass through the plasma at several tens of thousands of degrees and are heated to become a liquid. The liquid particles coalesce to form enlarged particles. As a result, it is considered that the average particle size of the powder after the spheroidizing process is as large as 25.6 μm. In addition, it is thought that the re-solidification of the bloated liquid particles takes time compared to particles with a small particle size, and during this time the particles aggregate to form particles with poor sphericity.

In addition, in Comparative Example 4, the particles aggregated during re-solidification, so that the internal structure of the particles constituting the powder differed from those in Examples 1 to 5, and the particles consisted of two or more crystallites (for example, It tends to be individual particles 31) shown in 5B. In Examples 1-5, the particles that make up the powder are considered to be single single crystals (eg, individual particles 31 shown in FIG. 5A), preferably having an average particle size of 1-10 μm (more preferably 3-10 μm). ) is preferably a single crystal main phase grain 31a.

Further, in Comparative Example 5, the sphericity is slightly inferior to that of Examples 1-5, but the single-crystal magnet powder content is extremely lower than that of Examples 1-5. Further, the average particle size of the magnet powder of Comparative Example 5 is larger than those of Examples 1-5. Furthermore, compared with Examples 1 to 5, the average coverage of the magnet powder in Comparative Example 5 was lower, and the magnet powder with a coverage of 100% could not be observed. Therefore, as will be described later, when a permanent magnet is produced using the magnet powder of Comparative Example 5, the magnetic properties are inferior to those of Examples 1-5.

Examples 11-14, Comparative Examples 11 and 12
Using the magnet powders of Examples 1 and 3 to 5 and Comparative Examples 1 and 5, the orientation forming step and the sintering step in the above embodiment were carried out to obtain samples of permanent magnets made of sintered bodies. made. The area ratio of the subphase was determined for each magnet sample obtained. Table 2 shows the results. Also, residual magnetic flux density Br, coercive force Hcj, and degree of orientation Br/Js were determined. Table 2 shows the results. These magnetic properties were measured using a BH tracer and an X-ray diffractometer (XRD). FIG. 6A shows an FE-SEM micrograph of the cross section of the sintered magnet sample obtained in Example 11, and FIG. 6B shows the FE-SEM micrograph of the cross section of the sintered magnet sample obtained in Comparative Example 11. .

Evaluation 2
Compared to Comparative Examples 11 and 12, in Examples 11 to 14, the existence ratio (area ratio) of the subphase is reduced, and the residual magnetic flux density Br, the coercive force Hcj, and the degree of orientation Br/Js are improved. It could be confirmed. It is considered that the remanence Br was improved as a result of the improvement of the filling rate and the degree of orientation by using magnet powder with a high degree of sphericity. In addition, it is thought that since the main phase grains made of single crystals coated with a coating layer made of an R-rich phase with high magnetic anisotropy are used, magnetization reversal is less likely to occur, and the coercive force Hcj is improved. be done. In addition, since the coating layer of the main phase particles in the examples is very thin and uniform, it does not contribute to an increase in the area ratio of the subphase in the cross section of the sintered body after firing. The area ratio of the subphase is preferably 2% or less, more preferably 1% or less.

Also, in the alloy from which the magnetic powder is produced by the strip casting method as in Comparative Example 1 (Comparative Example 11), dendrites composed of an R-rich phase are generated, and the composition may be uneven within the particles. By sintering and densifying these particles, for example, as shown in FIG. 6B, the R-rich phase that is unevenly distributed within the particles is affected, and many subphases (three grain points) of the sintered magnet structure are generated.

On the other hand, regarding magnetic particles that have been subjected to plasma treatment, such as in Example 1 (Example 11), since the magnetic particles are put into high-temperature plasma, the magnetic particles are melted, and there is no texture unevenness, and the texture of the magnetic particles is uniform. spherical powder) can be obtained. As a result, after sintering, as shown in FIG. 6A, the occurrence of secondary phases (three grain points) composed of the R-rich phase is suppressed, and it is possible to obtain a sintered magnet with a high main phase ratio.

Examples 21, 22 and Comparative Examples 21, 22
Each of the magnet powders obtained in Examples 4 and 5 and Comparative Examples 1 and 5 shown in Table 3 was kneaded into polyphenylene sulfide resin to prepare a bond magnet compound. A sample of each bond magnet was produced using a compound in which each of these magnet powders was kneaded. The residual magnetic flux density Br and the coercive force Hcj of each bonded magnet sample obtained were determined in the same manner as in Examples 11-14. Table 3 shows the results.

Evaluation 3
Compared with Comparative Examples 21 and 22, Examples 21 and 22 were confirmed to have improved residual magnetic flux density Br and coercive force Hcj. It is considered that the remanence Br was improved as a result of the improvement of the filling rate by using magnet powder with a high degree of sphericity. In addition, it is thought that since the main phase grains made of single crystals coated with a coating layer made of an R-rich phase with high magnetic anisotropy are used, magnetization reversal is less likely to occur, and the coercive force Hcj is improved. be done.

2 Particles of RTB magnet powder (rare earth magnet powder) 10 Apparatus 11 Chamber 12 Thermal plasma 12a Tail flame portion 12b Upper portion 13 Plasma generation chamber 14 Raw material powder supply portion 15 Rapid cooling Gas 16... Gas ejection port 17... Powder recovery part 20... Perfect circles 30, 30a... Coated particles 31... Individual particles 31a... Main phase particles 32... Coating layer 33... Grain boundary phase

Claims (14)

A rare earth magnet powder having an average sphericity P1 defined by the formula (1) of P1=Ls/Ll of 0.65 or more,
In the above formula (1), Ll is the length of the long side of a circumscribing rectangle that has the smallest area with respect to the rare earth magnet powder in the microscope image,
In the formula (1), Ls is the length of the short side of the circumscribing rectangle that has the smallest area with respect to the rare earth magnet powder in the microscope image,
Rare earth magnet powder in which the number ratio of rare earth magnet powder composed of single crystals is 65% or more. 2. The rare earth magnet powder according to claim 1, wherein the number ratio of the rare earth magnet powder having a sphericity P1 of 0.9 or more is 30% or more. A rare earth magnet powder having an average sphericity P2 defined by the formula (2) of P2=Lt/Lr of 0.70 or more,
In the formula (2), Lr is the circumference of the rare earth magnet powder in the microscope image,
In the formula (2), Lt is the circumference of a perfect circle having the same area as the area in the image of the rare earth magnet powder for which the circumference Lr was calculated,
Rare earth magnet powder in which the number ratio of rare earth magnet powder composed of single crystals is 65% or more. 4. The rare earth magnet powder according to claim 3, wherein the number ratio of the rare earth magnet powder having a sphericity P2 of 0.8 or more is 25% or more. The rare earth magnet powder according to any one of claims 1 to 4,
Rare earth magnet powder having an average particle size of 20 μm or less. The rare earth magnet powder according to any one of claims 1 to 5,
A rare earth magnet powder comprising a plurality of coated particles in which at least part of the periphery of individual particles composed of a single main phase particle is covered with a coating layer. The rare earth magnet powder according to claim 6,
The coated particles are rare earth magnet powders containing all-around-coated particles in which the individual particles are entirely covered with the coating layer. The rare earth magnet powder according to claim 6 or 7,
Rare earth magnet powder having an average coverage ratio of 50% or more, which indicates the percentage of the circumference of each of the individual particles covered with the coating layer. The rare earth magnet powder according to any one of claims 1 to 8,
A rare earth magnet powder, wherein the rare earth magnet powder includes RTB magnet powder. A bonded magnet containing the rare earth magnet powder according to any one of claims 1 to 9. A compound for bonded magnets containing the rare earth magnet powder according to any one of claims 1 to 9. A rare earth sintered magnet,
A main phase and a subphase are observed in a cross section of the rare earth sintered magnet, and the area ratio of the subphase is 2% or less,
The main phase is an R2 T14B type crystal,
A rare earth sintered magnet having a degree of orientation of 94% or more obtained by dividing the residual magnetic flux density in the orientation direction by the saturation magnetic flux density. a step of pulverizing an alloy having a desired composition to obtain raw material powder;
A method for producing a rare earth magnet powder, comprising a step of putting the raw material powder into a thermal plasma trailing flame, heating it, and then quenching it to obtain a spherical powder. a step of pulverizing an alloy having a desired composition to obtain raw material powder;
a step of putting the raw material powder into a thermal plasma tail flame, heating it, and then quenching it to obtain a spherical powder;
and a step of sintering the spherical powder to obtain a sintered body.

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