R-t-b based permanent magnet

Abstract

A permanent magnet contains a rare earth element R, a transition metal element T, and B, contains Nd as R, contains Fe as T, and contains a plurality of main phase grains and a plurality of R-rich phases. The plurality of main phase grains contain R, T, and B, and the plurality of R-rich phases contain R. The plurality of main phase grains observed in a cross section of the permanent magnet are flat, and the cross section is substantially parallel to the direction of an easy magnetization axis of the permanent magnet. The plurality of R-rich phases are each located between the plurality of main phase grains and are substantially perpendicular to the direction of the easy magnetization axis. An average of intervals of the plurality of R-rich phases in a direction substantially perpendicular to the direction of the easy magnetization axis is 30 μm or more and 1000 μm or less. An average of lengths of short axes of the plurality of main phase grains observed in the cross section is 20 nm or more and 200 nm or less.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an R-T-B based permanent magnet. BACKGROUND

[0002] An R-T-B based permanent magnet contains a rare earth element R (Nd, etc.), a transition metal element T (Fe, etc.), and boron (B). The R-T-B based permanent magnet is excellent in magnetic properties and is widely used. Among the R-T-B based permanent magnets, there are sintered magnets manufactured by a powder metallurgy method and hot-worked magnets manufactured by a thermoplastic processing method. (Refer to Japanese Patent Application Publication No. 2016-96203, M. Soderznik et al., Magnetization reversal process of anisotropic hot-deformed magnets observed by magneto-optical Kerr effect microscopy, Journal of Alloys and Compounds 771 (2019) 51-59, LAI Bin et al., Quasi-periodic layer structure of die-upset NdFeB magnets, JOURNAL OF RARE EARTHS, Vol. 31, No. 7, July 2013, P. 679-684.) An alloy ribbon as a raw material of the hot-worked magnet can be obtained by a splat cooling process. In the splat cooling process, a molten metal of an R-T-B based alloy is rapidly cooled on the surface of a cooling roll. As a result, the molten metal solidifies to form an alloy ribbon. The alloy ribbon obtained by the splat cooling process contains crystallites (and amorphous alloy) of the alloy. Therefore, the crystal grains (main phase particles) constituting the hot-worked magnet are finer than those of the sintered magnet. As shown by the Kronmuller formula, it is known that the finer the crystal grain size of the R-T-B based permanent magnet, the higher the coercive force (HcJ) increases. Therefore, the hot-worked magnet should have a higher coercive force than the sintered magnet. However, the coercive force of the conventional hot-worked magnet is equal to that of the sintered magnet having the same composition, and a high coercive force expected from the fine crystal grain size is not obtained. SUMMARY

[0003] Therefore, the present inventors and others investigated and researched the reason why high coercive force corresponding to fine crystal grain diameter is not obtained in the conventional R-T-B based permanent magnet (for example, a hot worked magnet). As a result, the present inventors and others found that the distribution of R-rich phase in the cross section of the R-T-B based permanent magnet approximately parallel to the direction of the easy magnetization axis affects the coercive force. The present inventors and others also found a method of obtaining an R-T-B based permanent magnet having high coercive force by controlling the distribution of R-rich phase in the cross section.

[0004] An aspect of the present application aims to provide an R-T-B based permanent magnet having high coercive force.

[0005] An R-T-B based permanent magnet according to an aspect of the present application contains a rare earth element R, a transition metal element T, and B, wherein the R-T-B based permanent magnet contains at least Nd as R, the R-T-B based permanent magnet contains at least Fe as T, the R-T-B based permanent magnet contains a plurality of main phase particles and a plurality of R-rich phases, the plurality of main phase particles contain at least R, T, and B, the plurality of R-rich phases contain at least R, the plurality of main phase particles observed in a cross section of the R-T-B based permanent magnet are flat, the cross section is approximately parallel to the direction of the easy magnetization axis of the R-T-B based permanent magnet, the plurality of R-rich phases are each located between the plurality of main phase particles, the average of the intervals of the plurality of R-rich phases in a direction approximately perpendicular to the direction of the easy magnetization axis is 30 μm or more and 1000 μm or less, and the average of the lengths of the minor axes of the plurality of main phase particles observed in the cross section is 20 nm or more and 200 nm or less.

[0006] The content of R in the R-T-B based permanent magnet can also be 28 mass% or more and 33 mass% or less, and the content of B in the R-T-B based permanent magnet can also be 0.8 mass% or more and 1.1 mass% or less.

[0007] The plurality of main phase particles that are flat can also be stacked along the direction of the easy magnetization axis.

[0008] The R-T-B based permanent magnet can also be a hot worked magnet.

[0009] The concentration of R in at least a portion of the plurality of R-rich phases can also be higher than the average of the concentration of R in the cross section, and the unit of the concentration of R can also be atom%.

[0010] The concentration of R in at least a portion of the plurality of R-rich phases can also be higher than the concentration of R in the plurality of main phase particles, and the unit of the concentration of R can also be atom%.

[0011] According to an aspect of the present application, an R-T-B based permanent magnet having high coercive force can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1A is a schematic perspective view of an R-T-B based permanent magnet of one embodiment of the present application. Figure 1B is Figure 1A is a schematic view of a cross section (cross-sectional view in the b-b line direction) of the R-T-B based permanent magnet shown in

[0013] Figure 2 is Figure 1B is an enlarged view of a part (Region II) of the cross section, and a brightness distribution of a backscattered electron image of Region II.

[0014] Figure 3 is a backscattered electron image of a cross section of the R-T-B based permanent magnet of Example 2.

[0015] Figure 4 is a backscattered electron image of a cross section of the R-T-B based permanent magnet of Comparative Example 8.

[0016] [Explanation of symbols]

[0017] 2... R-T-B based permanent magnet, 2cs... cross section of the permanent magnet, 4... main phase particle (primary particle), 4a... secondary particle, 6... R-rich phase, C... direction of easy magnetization axis, AB... direction substantially perpendicular to the direction of easy magnetization axis. DETAILED DESCRIPTION

[0018] Hereinafter, a preferred embodiment of the present application will be described with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals. The present application is not limited to the following embodiment. The "permanent magnet" described below refers to an R-T-B based permanent magnet. The unit of the concentration of each element in the permanent magnet described below is atomic %.

[0019] (permanent magnet)

[0020] The permanent magnet of the present embodiment contains at least a rare earth element (R), a transition metal element (T), and boron (B). The permanent magnet of the present embodiment is a hot worked magnet. However, the permanent magnet of the present application can also be a sintered magnet.

[0021] The permanent magnet contains at least neodymium (Nd) as the rare earth element R. The permanent magnet can also contain other rare earth elements R in addition to Nd. The other rare earth element R contained in the permanent magnet can be at least one selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0022] Permanent magnets contain at least iron (Fe) as a transition metal element T. Permanent magnets may also contain only Fe as a transition metal element T. Permanent magnets may also contain both Fe and cobalt (Co) as transition metal elements T.

[0023] Figure 1A This is a perspective view of the permanent magnet 2 in this embodiment. Figure 1B This is a schematic diagram of the cross-section 2cs of the permanent magnet 2, which is approximately parallel to the easy magnetization axis direction C of the permanent magnet 2. The easy magnetization axis direction C is parallel to the straight line connecting the pair of magnetic poles of the permanent magnet 2. That is, the easy magnetization axis direction C is the direction from the S pole of the permanent magnet 2 towards the N pole of the permanent magnet 2. The easy magnetization axis direction C can also be specified based on the measurement of the magnetic flux distribution of the permanent magnet 2. Alternatively, the easy magnetization axis direction C can be specified based on the measurement of the magnetic flux distribution of an analytical sample separated from the permanent magnet 2.

[0024] The permanent magnet 2 in this embodiment is a cuboid (plate). However, the shape of the permanent magnet 2 is not limited to a cuboid. For example, the shape of the permanent magnet 2 may also be a cube, a polygonal prism, an arc segment, an annular sector, a sphere, a circular plate, a cylinder, a tube, or a ring. The shape of the cross-section 2cs of the permanent magnet 2 may also be a polygon, an arc (chord), a bow shape, an arch shape, a C-shape, or a circle.

[0025] Figure 2 yes Figure 1B An enlarged view of a portion (region II) of section 2cs shown. (See diagram below.) Figure 2 As shown, the permanent magnet 2 comprises multiple main phase particles 4 and multiple R-rich phases 6. The R-rich phases 6 are located between the multiple main phase particles 4. The R-rich phases 6 can also be a type of grain boundary phase contained in the grain boundaries between the multiple main phase particles 4. The grain boundaries containing the R-rich phases 6 can be multi-grain boundaries surrounded by three or more main phase particles 4, or they can be two-grain boundaries between two main phase particles 4. The total volume percentage of the main phase particles 4 in the permanent magnet 2 is not particularly limited; for example, it can be 80% or more but less than 100% by volume, 90% or more but less than 100% by volume, or 95% or more but less than 100% by volume.

[0026] The main phase particle 4 contains at least Nd, T, and B. The main phase particle 4 can also be referred to as a single grain (i.e., a primary grain). The main phase particle 4 contains R²T. 14 Crystallization of B (single crystal or polycrystalline). R2T 14 B is a ferromagnetic ternary intermetallic compound. The main phase particle 4 can also consist solely of R2T. 14 The crystalline structure of B. R2T 14 Boron can also crystallize into a tetragonal crystal. That is, R2T14 The crystal axes of B are the a-axis, the b-axis, and the c-axis, which are orthogonal to each other, and R2T 14 The lattice constant in the a-axis direction of B can also be different from the lattice constant in the b-axis direction of R2T 14 The lattice constant in the b-axis direction of B can also be different from the lattice constant in the a-axis direction of R2T 14 The lattice constant in the c-axis direction of B can also be different from the lattice constant in the a-axis direction and the lattice constant in the b-axis direction of R2T 14 The c-axis direction of B can also be substantially parallel to the easy magnetization axis direction C of the permanent magnet 2.

[0027] The main phase particles 4 can also contain other elements in addition to Nd, T, and B. For example, R2T 14 B can also be expressed as (Nd 1-x Pr x )2(Fe 1-y Co y ) 14 B. x can also be 0 or more and less than 1. y can also be 0 or more and less than 1. The main phase particles 4 can also contain heavy rare earth elements such as Tb and Dy in addition to light rare earth elements as R. R2T 14 A portion of B in B can also be substituted with other elements such as carbon (C). The composition in the main phase particles 4 can also be uniform. The composition in the main phase particles 4 can also be non-uniform. For example, the concentration distribution of R, T, and B in the main phase particles 4 can also have a gradient.

[0028] The main phase particles 4 can also be composed of a surface layer portion and a central portion covered with the surface layer portion. The surface layer portion can also be referred to as a shell, and the central portion can also be referred to as a core. The surface layer portion of the main phase particles 4 can also contain at least one heavy rare earth element of Tb and Dy. The surface layer portion of all of the main phase particles 4 can also contain at least one heavy rare earth element of Tb and Dy. The surface layer portion of a portion of the main phase particles 4 among all of the main phase particles 4 can also contain at least one heavy rare earth element of Tb and Dy. By containing a heavy rare earth element in the surface layer portion, the anisotropic magnetic field is easily locally increased near the grain boundary, and a core in which magnetization reversal is difficult to occur near the grain boundary. As a result, the coercive force of the permanent magnet 2 at high temperatures (for example, 100 to 200°C) is increased. The residual flux density (Br) and the coercive force of the permanent magnet 2 are easily balanced, and therefore, the total of the concentration of the heavy rare earth element in the surface layer portion can also be higher than the total of the concentration of the heavy rare earth element in the central portion.

[0029] The R-rich phase 6 is a non-ferromagnetic phase. The R-rich phase 6 contains at least R. For example, the R-rich phase 6 may also contain Nd as R. The R-rich phase 6 may also contain one or more other rare earth elements besides Nd as R. The R-rich phase 6 may also contain one or more elements other than R. The R-rich phase 6 may also contain at least one component selected from metals, alloys, intermetallic compounds, and oxides. For example, part or all of the R-rich phase 6 may consist only of at least one component selected from monomers of R, alloys containing R, and metallic compounds containing R. Part or all of the R-rich phase 6 may also contain oxides of R. For example, the oxide of R may also be an oxide of Nd. The oxidized surface of the main phase particles 4 may also be an oxide of R. A portion of the R-rich phase 6 may also consist only of oxides of R. The inventors believe that the R-rich phase 6 containing oxides of R can be formed by oxidation of R near the surface of the alloy strip or alloy powder (the precursor of the main phase particles 4) during the manufacturing process of the permanent magnet 2 (especially the conveying processes described later).

[0030] The concentration of R in the R-rich phase 6 can also be higher than the average concentration of R in the aforementioned cross section 2cs. The concentration of R in the R-rich phase 6 can also be higher than the average concentration of R in the main phase particles 4. In the case where the permanent magnet 2 contains multiple types of R, the concentration of R can also be the sum of the concentrations of all types of R.

[0031] like Figure 2 As shown, the principal phase particles 4 observed in section 2cs are flat. In other words, the principal phase particles 4 observed in section 2cs can also be plate-like. Multiple flat principal phase particles 4 can also be stacked along the easy magnetization axis direction C. The permanent magnet 2 can also further include secondary particles 4a composed of multiple interconnected principal phase particles 4. The permanent magnet 2 can also include multiple secondary particles 4a. At least a portion of the R-rich phase 6 can also be located at the grain boundaries between the multiple secondary particles 4a. The oxidized surface of the secondary particles 4a can also be an oxide of R. Multiple R-rich phases 6 are arranged in a direction substantially perpendicular to the easy magnetization axis direction C. In other words, multiple R-rich phases 6 can also be dispersed in section 2cs in a direction substantially perpendicular to the easy magnetization axis direction C. Each of the multiple R-rich phases 6 arranged in a direction substantially perpendicular to the easy magnetization axis direction C can also be located between at least two principal phase particles 4. A portion of the R-rich phase 6 can also be a layer extending in a direction substantially perpendicular to the easy magnetization axis direction C. A portion of the R-rich phase 6 can also be located between multiple flat main phase particles 4 stacked along the easy magnetization axis C.

[0032] The “AB direction” mentioned below refers to the direction that is approximately perpendicular to the easy magnetization axis direction C.

[0033] The average value i of the R-rich phase 6 interval in the AB direction AVEThe range is between 30 μm and 1000 μm. The average value of the spacing i of the R-rich phase 6 along the AB direction. AVE It can also be 30.42 μm or more and 975.00 μm or less, 34 μm or more and 1000 μm or less, 34.89 μm or more and 975.00 μm or less, 34 μm or more and 38 μm or less, 34.89 μm or more and 37.77 μm or less, 34 μm or more and 36 μm or less, or 34.89 μm or more and 35.82 μm or less. The average value i of the R-rich phase 6 intervals in the AB direction. AVE The lower limit value can also be selected from one of 30 μm, 30.42 μm, 34.89 μm, 35.82 μm, 37.77 μm, 269.87 μm, 446.70 μm, 674.12 μm, 886.36 μm, and 975.00 μm, and the average value i of the R-rich phase 6 intervals in the AB direction. AVE The upper limit can also be selected from one of the following: 30.42 μm, 34.89 μm, 35.82 μm, 37.77 μm, 269.87 μm, 446.70 μm, 674.12 μm, 886.36 μm, 975.00 μm, and 1000 μm. The average value i of the intervals of the R-rich phase 6 is... AVE Within the aforementioned range, the permanent magnet 2 exhibits high coercivity at both room temperature and high temperature. The average value i of the spacing of the R-rich phase 6 in the AB direction. AVE It can also be approximately equal to the average of the combined widths of one or more main phase particles 4 located between a pair of R-rich phase 6 in the AB direction. The average spacing of the R-rich phase 6 in the AB direction can be determined by the following method.

[0034] A backscattered electron image of a portion of the cross-section 2cs (region II) of the permanent magnet 2 was captured by scanning electron microscopy (SEM). The magnification of the backscattered electron image can be, for example, 300x. Figure 2 As shown, a rectangular measurement region A is formed by selecting multiple high-brightness portions (6) from the backscattered electron image and arranging them along the AB direction. The width of the measurement region A along the AB direction is larger than the width of the measurement region A along the easy magnetization axis C. For example, the width of the measurement region A along the AB direction can be 400 μm, and the width of the measurement region A along the easy magnetization axis C can be 15 μm. The measurement region A is scanned along the AB direction with an electron beam, and the brightness of each measurement point within the measurement region A is continuously measured along the AB direction. As a result, the brightness distribution D of the measurement region A along the AB direction is obtained. The interval between measurement points can be, for example, less than 1 μm. Brightness is the intensity of the backscattered electron beam at each measurement point ( Figure 2"intensity" in the above-described equation. The unit of the brightness is arbitrary unit (a.u.). The larger the atomic weight of the element, the higher the brightness of the measurement point where the element exists, and the higher the concentration of the element with a large atomic weight, the higher the brightness of the measurement point. Among the elements contained in the permanent magnet 2, the atomic weight of R is large. Therefore, the peak in the brightness distribution D indicates the presence of the R-rich phase. From the brightness of an arbitrary measurement point X in the measurement region A, the brightness of each of the five measurement points measured immediately before the brightness of the measurement point X is measured, and the brightness of each of the five measurement points measured immediately after the brightness of the measurement point X is measured, the moving average I AVE of the brightness is calculated. AVE That is, the moving average I AVE of the brightness is calculated from the brightness of the measurement point X and the brightness of each of the five measurement points containing the measurement point X. AVE When the value of I AVE is 107% or more of I AVE , the measurement point X is the R-rich phase 6. That is, when the brightness of the measurement point X is 107% or more of I AVE , the position (the "position" in the above-described equation) of the measurement point X (the peak of the brightness at the measurement point X) is the position of the R-rich phase 6. The distance (the distance in the AB direction) between the two adjacent R-rich phases 6 is the interval of the R-rich phases 6 in the AB direction. On the basis of the above-described premise, the average value of the interval of the R-rich phases 6 in the measurement region A is calculated. For example, in the measurement region A shown in FIG. 1, there are four R-rich phases 6, and the intervals i1, i2, and i3 of the R-rich phases 6 are measured. Figure 2 The average value of the intervals of the R-rich phases 6 in the measurement region A shown in FIG. 1 is (i1+i2+i3) / 3. Figure 2

[0035] A plurality of different measurement regions A are selected from the backscattered electron image, and the average value of the intervals of the R-rich phases 6 in each of the measurement regions A is measured by the above-described method. For example, five measurement regions A can be selected from the backscattered electron image. The above-described average value i AVE is obtained by further averaging the average values of the intervals of the R-rich phases 6 in the plurality of measurement regions A. In addition, the average line (the line of 100%) of the brightness distribution D in the above-described equation can be a curved line. Figure 3

[0036] The R-rich phase 6 is a cause of the reduction in the coercive force of the permanent magnet 2. However, the permanent magnet 2 of the present embodiment can have a higher coercive force than a conventional permanent magnet having the same composition. In other words, according to the permanent magnet 2 of the present embodiment, the reduction in the coercive force caused by the R-rich phase 6 can be suppressed. The mechanism of suppressing the reduction in the coercive force caused by the R-rich phase 6 will be described below. However, the technical scope of the present application is not limited by the following mechanism.

[0037] The mechanism of coercivity of the R-T-B based permanent magnet is of nucleation type, and thus, generation of a reverse domain becomes a nucleus of magnetization reversal. That is, the generation of the reverse domain becomes a cause of coercivity reduction. The reverse domain is generated from a position where a local demagnetizing field is large. The position where the local demagnetizing field is large is a pore, a surface of a main phase particle, and a foreign phase.

[0038] < Pore >

[0039] Both the sintered magnet and the hot worked magnet are densified to approximately the true density, and thus, a pore is not easily present.

[0040] < Surface of Main Phase Particle >

[0041] The shape of the main phase particle constituting the sintered magnet reflects the shape of the alloy powder obtained by the jet milling, and thus, the shape of the main phase particle constituting the sintered magnet is irregular (deformed). The surface of the irregular main phase particle is not smooth, and thus, easily becomes a starting point of generation of the reverse domain.

[0042] On the other hand, the main phase particle constituting the hot worked magnet is a plate-like crystal from an extremely fine grain which has undergone anisotropic crystal growth. As a result, the shape of the main phase particle constituting the hot worked magnet is relatively uniform, and the surface of the main phase particle constituting the hot worked magnet is smoother than the surface of the main phase particle constituting the sintered magnet. Thus, on the surface of the main phase particle constituting the hot worked magnet, the local demagnetizing field is small, and the reverse domain is not easily generated. As a result, the hot worked magnet easily has high coercivity.

[0043] < Foreign Phase >

[0044] The sintered magnet is densified by a sintering process. In the sintering process, a molded body formed of the alloy powder is sintered. In the sintering process, the surface of the alloy powder becomes a liquid phase, and the liquid phase fills the gap between the alloy powders to become a grain boundary phase (R-rich phase), and thus, a dense sintered body is obtained. The two-particle grain boundary phase is useful in preventing the magnetic wall between the main phase particles from moving in magnetic separation. The remaining grain boundary phase other than the two-particle grain boundary phase is discharged from the surface of the sintered body, but the amount thereof is extremely small, and is mostly segregated at the grain boundary-rich points. The grain boundary phase segregated at the grain boundary-rich points is useless. This is because the grain boundary phase segregated at the grain boundary-rich points becomes a foreign phase, and becomes a starting point of generation of the reverse domain. However, as described above, a liquid phase is required in the densification of the sintered magnet, and thus, segregation of the grain boundary phase (R-rich phase) to the grain boundary-rich points is unavoidable.

[0045] On the other hand, in the case of the permanent magnet 2 of the present embodiment, the average value i of the interval of the R-rich phase 6 in the AB direction is 30 μm or more, the interval of the R-rich phase 6 in the AB direction is large. Therefore, it is possible to suppress the segregation and agglomeration of the R-rich phase 6 in the AB direction (generation of the nucleus of magnetization reversal), and to reduce the generation frequency of the reverse magnetic domain in the AB direction. As a result, it is possible to suppress the reduction of the coercive force due to the segregation and agglomeration of the R-rich phase 6.

[0046] However, the hot-worked magnet inevitably contains the R-rich phase. The R-rich phase such as the two-particle grain boundary phase covers the surface of each main phase particle, the adjacent main phase particles are magnetically separated from each other, and the coercive force of the permanent magnet increases. On the other hand, the R-rich phase which is segregated and agglomerated toward the grain boundary tends to generate the reverse magnetic domain. That is, the R-rich phase which is segregated and agglomerated toward the grain boundary becomes the nucleus of magnetization reversal. The magnetization reversal of the main phase particle is performed from the nucleus of magnetization reversal, and the coercive force of the permanent magnet decreases.

[0047] As described above, in the conventional sintered magnet and the hot-worked magnet, the reduction of the coercive force due to the R-rich phase which is segregated and agglomerated toward the grain boundary occurs.

[0048] On the other hand, in the case of the permanent magnet 2 of the present embodiment, the average value i of the interval of the R-rich phase 6 in the AB direction is 30 μm or more, the interval of the R-rich phase 6 in the AB direction is large. Therefore, it is possible to suppress the segregation and agglomeration of the R-rich phase 6 in the AB direction (generation of the nucleus of magnetization reversal), and to reduce the generation frequency of the reverse magnetic domain in the AB direction. As a result, it is possible to suppress the reduction of the coercive force due to the segregation and agglomeration of the R-rich phase 6. AVE 30 μm or more, the interval of the R-rich phase 6 in the AB direction is large. Therefore, it is possible to suppress the segregation and agglomeration of the R-rich phase 6 in the AB direction (generation of the nucleus of magnetization reversal), and to reduce the generation frequency of the reverse magnetic domain in the AB direction. As a result, it is possible to suppress the reduction of the coercive force due to the segregation and agglomeration of the R-rich phase 6.

[0049] In the case where the average value i of the interval of the R-rich phase 6 in the AB direction is 30 μm or more, the R-rich phase 6 which is segregated and agglomerated toward the grain boundary is small, and the R-rich phase 6 easily uniformly surrounds each main phase particle 4. As a result, the adjacent main phase particles are magnetically separated from each other, and the coercive force of the permanent magnet 2 increases. AVE

[0050] However, as the average value i of the interval of the R-rich phase 6 in the AB direction increases, the width of each main phase particle 4 which is located between a pair of R-rich phases 6 in the AB direction tends to increase. That is, as the average value i of the interval of the R-rich phase 6 in the AB direction increases, the width of each main phase particle 4 in the AB direction tends to increase. AVE AVE ​​The particle diameter (crystal grain diameter) of the main phase particles 4 located between a pair of R-rich phases 6 in the AB direction tends to increase. Due to the increase in the particle diameter (crystal grain diameter) of the main phase particles 4, the coercive force of the permanent magnet 2 easily decreases, the coercive force easily decreases as the temperature rises, the rectangularity ratio (Hk / HcJ) of the permanent magnet 2 easily decreases. (Hk is the strength of the demagnetizing field corresponding to 90% of the residual magnetic flux density in the second quadrant of the magnetization curve.) In addition, the coarse main phase particles 4 are difficult to rotate in thermoplastic processing, are difficult to orient in the easy magnetization axis direction C, and thus become one cause of the decrease in the residual magnetic flux density.

[0051] However, according to the present embodiment, the average value i of the interval of the R-rich phases 6 in the AB direction is 1000 μm or less, and thus the main phase particles 4 whose particle diameter (crystal grain diameter) is excessively large are difficult to be included in the permanent magnet 2. As a result, the decrease in the coercive force caused by the increase in the particle diameter (crystal grain diameter) of the main phase particles 4 is suppressed, the decrease in the coercive force accompanying the temperature rise is suppressed, the decrease in the rectangularity ratio is suppressed, and the decrease in the residual magnetic flux density is suppressed. AVE The average value i of the interval of the R-rich phases 6 in the AB direction is 1000 μm or less, and thus the main phase particles 4 whose particle diameter (crystal grain diameter) is excessively large are difficult to be included in the permanent magnet 2. As a result, the decrease in the coercive force caused by the increase in the particle diameter (crystal grain diameter) of the main phase particles 4 is suppressed, the decrease in the coercive force accompanying the temperature rise is suppressed, the decrease in the rectangularity ratio is suppressed, and the decrease in the residual magnetic flux density is suppressed.

[0052] The average value of the length of the short axis of the main phase particles 4 (primary particles) observed on the aforementioned cross section 2cs is, for example, 20 nm or more and 200 nm or less. In the case where the average value of the length of the short axis of the main phase particles 4 is less than 20 nm, each main phase particle 4 (R2T 14 The anisotropic growth of the crystal of B is insufficient, each main phase particle 4 is difficult to orient in the easy magnetization axis direction C, and the coercive force, the rectangularity ratio, and the residual magnetic flux density easily decrease. In the case where the average value of the length of the short axis of the main phase particles 4 is greater than 200 nm, the particle diameter (crystal grain diameter) of the main phase particles 4 is excessively large, the main phase particles 4 are difficult to orient in the easy magnetization axis direction C, and the coercive force, the rectangularity ratio, and the residual magnetic flux density easily decrease. The decrease in the coercive force, the rectangularity ratio, and the residual magnetic flux density is easily suppressed, and thus the average value of the length of the short axis of the main phase particles 4 observed on the aforementioned cross section 2cs can also be 22 nm or more and 187 nm or less. For the same reason, the lower limit value of the average value of the length of the short axis of the main phase particles 4 observed on the aforementioned cross section 2cs can also be one value selected from 20 nm, 22.00 nm, 86.00 nm, 92.00 nm, 122.00 nm, 157.00 nm, 164.00 nm, 172.00 nm, 187.00 nm, and 198.00 nm, and the upper limit value of the average value of the length of the short axis of the main phase particles 4 observed on the aforementioned cross section 2cs can also be one value selected from 22.00 nm, 88.00 nm, 92.00 nm, 122.00 nm, 157.00 nm, 164.00 nm, 172.00 nm, 187.00 nm, 198.00 nm, and 200 nm.

[0053] The average value of the length of the long axis of the main phase particles 4 (primary particles) observed on the aforementioned cross section 2cs can also be, for example, 100 nm or more and 1000 nm or less. In the case where the average value of the length of the long axis of the main phase particles 4 is within the aforementioned range, the average value i of the interval of the R-rich phase 6 in the AB direction is easily controlled AVE The average value of the length of the long axis of the main phase particles 4 is controlled within the aforementioned range. The greater the average value of the length of the long axis of the main phase particles 4, the greater the average value i of the interval of the R-rich phase 6 in the AB direction is controlled. AVE The average value of the length of the long axis of the main phase particles 4 is controlled within the aforementioned range. The greater the average value of the length of the long axis of the main phase particles 4, the greater the average value i of the interval of the R-rich phase 6 in the AB direction is controlled.

[0054] The short axis of each main phase particle 4 observed on the cross section 2cs can also be substantially parallel to the easy axis direction C. The long axis of each main phase particle 4 can also be substantially perpendicular to the easy axis direction C. The shape of the main phase particles 4 in the cross section 2cs is not limited to a rectangular shape. The shape of the main phase particles 4 in the cross section 2cs can also be deformed. The shape of the main phase particles 4 in the cross section 2cs can also not be the same. In the case where the shape of the main phase particles 4 in the cross section 2cs is deformed, the shape of the main phase particles 4 can also be approximated by the smallest quadrangle among the quadrangles circumscribing the main phase particles 4. The quadrangle can also be a rectangle. The length of the short side of the quadrangle can also be regarded as the length of the short axis of the main phase particles 4, and the length of the long side of the aforementioned quadrangle can also be regarded as the length of the long axis of the main phase particles 4. The average value of the length of the short axis of the main phase particles 4 can also be calculated from the measured values of the lengths of the short axes of all the main phase particles 4 present in the backscattered electron image of the cross section 2cs taken by a scanning electron microscope (SEM). The average value of the length of the long axis of the main phase particles 4 can also be calculated from the measured values of the lengths of the long axes of all the main phase particles 4 present in the aforementioned backscattered electron image. However, the sizes of the main phase particles 4 overflowing from the backscattered electron image are excluded from the calculation of the average values. The maximum value of the size of the backscattered electron image used in the measurement of the lengths of the short and long axes of the main phase particles 4 can also be, for example, 120 μm in the vertical direction x 80 μm in the horizontal direction, or 80 μm in the vertical direction x 120 μm in the horizontal direction. Representative portions in the backscattered electron image taken at a low magnification can also be selected, and a backscattered electron image of each portion can also be taken at a high magnification. Furthermore, the average values of the lengths of the long and short axes can also be calculated from the lengths of the long and short axes of all the main phase particles 4 measured in the backscattered electron image at a high magnification. Commercially available image analysis software can also be used in the aforementioned specification of the shape (outline) of the main phase particles 4, and the measurement of the size of the main phase particles 4 (the quadrangle circumscribing the main phase particles 4).

[0055] The width of each R-rich phase 6 in the easy magnetization axis direction C can be, for example, 100 nm or more and 20,000 nm or less. The width of each R-rich phase 6 in the AB direction can be, for example, 100 nm or more and 20,000 nm or less. In a case where the width of the R-rich phase 6 is within the above range, the magnetization reversal of the main phase particles 4 caused by the R-rich phase 6 is easily suppressed, and the permanent magnet 2 easily has high coercivity. The width of the R-rich phase 6 in the easy magnetization axis direction C can be shorter than the length of the minor axis of the main phase particles 4 (primary particles). The width of the R-rich phase 6 in the easy magnetization axis direction C can be shorter than the length of the minor axis of the secondary particles 4a. The width of the R-rich phase 6 in the AB direction can be shorter than the length of the major axis of the main phase particles 4 (primary particles). The width of the R-rich phase 6 in the AB direction can be shorter than the length of the major axis of the secondary particles 4a.

[0056] The width of the permanent magnet 2 in the AB direction can be much larger than the lower limit value and the upper limit value of the average value i of the interval of the R-rich phases 6 in the AB direction. AVE The width of the permanent magnet 2 in the AB direction can be, for example, several mm or more and several hundred mm or less, or several tens of mm or more and several hundred mm or less. The longitudinal width of the permanent magnet 2 in a direction perpendicular to the AB direction can be, for example, several mm or more and several hundred mm or less, or several tens of mm or more and several hundred mm or less. The lateral width of the permanent magnet 2 in a direction perpendicular to the AB direction can be, for example, several mm or more and several hundred mm or less, or several tens of mm or more and several hundred mm or less.

[0057] A grain boundary phase other than the R-rich phase 6 can be included in the grain boundary. For example, the grain boundary can include a grain boundary phase including an element introduced into the permanent magnet 2 by a grain boundary diffusion process described later. The element introduced into the permanent magnet 2 by the grain boundary diffusion process can be at least one heavy rare earth element of Tb and Dy. The element introduced into the permanent magnet 2 by the grain boundary diffusion process can be a heavy rare earth element and a light rare earth element, and the light rare earth element can be at least one of Nd and Pr. The element introduced into the permanent magnet 2 by the grain boundary diffusion process can be a heavy rare earth element, a light rare earth element, and copper.

[0058] The main phase particles 4 and the R-rich phases 6 can each be identified based on the contrast of an image of the cross section 2cs of the permanent magnet 2 taken by a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM). The composition of each of the main phase particles 4 and the R-rich phases 6 can be analyzed by an electron probe micro-analyzer (EPMA) equipped with an energy dispersive X-ray spectroscopy (EDS) device.

[0059] The overall composition of the permanent magnet 2 will be described below. However, the composition of the permanent magnet 2 is not limited to the composition described below. The content of each element in the permanent magnet 2 can deviate from the range described below.

[0060] The total content of rare earth element R in the permanent magnet 2 can be 25.00% by mass or more and 35.00% by mass or less, or 28.00% by mass or more and 33.00% by mass or less. When the R content is within the above range, the remanent magnetic flux density and coercivity of the permanent magnet 2 are easily increased. If the R content is too low, it is difficult to form R2T that constitutes the main phase particles 4. 14 B readily forms the soft magnetic α-Fe phase. As a result, coercivity tends to decrease. On the other hand, with excessive R content, the volume ratio of the main phase particles (4) decreases, and the remanent magnetic flux density tends to decrease. Remanent magnetic flux density and coercivity tend to increase. Therefore, the combined proportion of Nd and Pr in all rare earth element R can be 80 atomic% or more and 100 atomic% or less, or 95 atomic% or more and 100 atomic% or less.

[0061] The combined content of Tb and Dy in the permanent magnet 2 can also be 0.20% by mass or more and 5.00% by mass or less. By including at least one heavy rare earth element, Tb or Dy, the magnetic properties (especially the coercivity at high temperatures) of the permanent magnet 2 are easily increased. However, the permanent magnet 2 may also not contain Tb and Dy.

[0062] The content of boron (B) in the permanent magnet 2 can be 0.70% by mass or more and 1.10% by mass or less, or 0.80% by mass or more and 1.10% by mass or less. When the content of B is 0.70% by mass or more, the remanent magnetic flux density tends to increase. When the content of B is 1.10% by mass or less, the coercivity of the permanent magnet 2 tends to increase. When the content of B is within the above-mentioned range, the rectangularity of the permanent magnet 2 tends to approach 1.0.

[0063] When the total content of rare earth element R in permanent magnet 2 is 28.00% by mass or more and 33.00% by mass or less, and the content of B in permanent magnet 2 is 0.80% by mass or more and 1.10% by mass or less, the content of rare earth element R in permanent magnet 2 relative to R2T 14 The stoichiometry of B is relatively large. As a result, during the thermoplastic processing described later, a liquid phase is easily generated at the grain boundaries. The liquid phase at the grain boundaries promotes grain growth (R2T). 14 B) Anisotropic growth, grain boundary slip, and grain rotation. As a result, the c-axis of the grains tends to align in the stress direction, the grain filling rate in permanent magnet 2 tends to increase (in other words, the volume ratio of the main phase tends to increase), and the coercivity and remanent flux density of permanent magnet 2 tend to increase.

[0064] The permanent magnet 2 can also contain gallium (Ga). The content of Ga can also be 0.03 mass% or more and 1.00 mass% or less, or 0.20 mass% or more and 0.80 mass% or less. In the case where the content of Ga is within the above range, generation of a side phase (for example, a phase containing R, T, and Ga) is appropriately suppressed, and the residual flux density and the coercive force of the permanent magnet 2 easily increase. However, the permanent magnet 2 can also not contain Ga.

[0065] The permanent magnet 2 can also contain aluminum (Al). The content of Al in the permanent magnet 2 can also be 0.01 mass% or more and 0.2 mass% or less, or 0.04 mass% or more and 0.07 mass% or less. By the content of Al being within the above range, the coercive force and the corrosion resistance of the permanent magnet easily improve. However, the permanent magnet 2 can also not contain Al.

[0066] The permanent magnet 2 can also contain copper (Cu). The content of Cu in the permanent magnet 2 can also be 0.01 mass% or more and 1.50 mass% or less, or 0.04 mass% or more and 0.50 mass% or less. By the content of Cu being within the above range, the coercive force, the corrosion resistance, and the temperature characteristics of the permanent magnet 2 easily improve. However, the permanent magnet 2 can also not contain Cu.

[0067] The permanent magnet 2 can also contain cobalt (Co). The content of Co in the permanent magnet can also be 0.30 mass% or more and 6.00 mass% or less, or 0.30 mass% or more and 4.00 mass% or less. By the permanent magnet 2 containing Co, the Curie temperature of the permanent magnet 2 easily improves. In addition, by the permanent magnet 2 containing Co, the corrosion resistance of the permanent magnet 2 easily improves. However, the permanent magnet 2 can also not contain Co.

[0068] The balance of the above-described elements can also be only Fe, or Fe and other elements. In order for the permanent magnet 2 to have sufficient magnetic characteristics, the total of the contents of the elements other than Fe in the balance can also be 5 mass% or less with respect to the total mass of the permanent magnet 2.

[0069] As other elements (for example, unavoidable impurities), the permanent magnet 2 can also contain at least one selected from silicon (Si), titanium (Ti), Mn (manganese), Zr (zirconium), vanadium (V), chromium (Cr), nickel (Ni), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), tin (Sn), calcium (Ca), carbon (C), nitrogen (N), oxygen (O), chlorine (Cl), sulfur (S), and fluorine (F). The total of the contents of the other elements in the permanent magnet 2 can also be 0.001 mass% or more and 0.50 mass% or less.

[0070] The composition of the permanent magnet 2 as a whole can also be analyzed by, for example, fluorescent X-ray (XRF) analysis, high-frequency inductively coupled plasma (ICP) emission analysis, inert gas fusion-non-dispersive infrared absorption (NDIR) analysis, combustion in an oxygen stream-infrared absorption analysis, and inert gas fusion-thermal conductivity analysis.

[0071] The permanent magnet 2 can also be applied to motors, generators, or actuators, and the like. For example, the permanent magnet 2 can be utilized in a wide variety of fields such as hybrid cars, electric cars, hard disk drives, magnetic resonance imaging apparatuses (MRI), smartphones, digital cameras, thin TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washing and drying machines, elevators, and wind power generators.

[0072] (Method for manufacturing permanent magnet)

[0073] The method for manufacturing the permanent magnet of the present embodiment includes at least a thin strip production step, a first conveyance step, a pulverization / classification step, a second conveyance step, a hot forming step, a third conveyance step, and a thermoplastic working step. The method for manufacturing the permanent magnet can also include other steps such as a grain boundary diffusion step in succession to the thermoplastic working step. However, the grain boundary diffusion step is not essential.

[0074] The thin strip production step is a step of producing an alloy thin strip from a raw alloy by a rapid cooling method. In the rapid cooling method, molten metal in a container is sprayed from a nozzle located at the front end of the container toward the surface of a cooling roll. The molten metal is instantaneously bounced off by the cooling roll rotating at high speed by contacting the surface of the cooling roll, and becomes a plurality of elongated ribbon-like strips. The molten metal is rapidly cooled and solidified by contacting the surface of the cooling roll. As a result, a plurality of elongated alloy thin strips are formed. A container is provided in the direction in which the alloy thin strips are bounced off by the cooling roll, and the alloy thin strips are recovered into the container.

[0075] The aperture of the nozzle can be, for example, 0.2 mm or more and 1.0 mm or less. In the case where the aperture of the nozzle is 0.2 mm or more and 1.0 mm or less, in the pulverization / classification step, it is easy to recover alloy powder having an average value of the aspect ratio of 1 or more and 2 or less.

[0076] The molten metal is a metal (raw metal) containing each element constituting the permanent magnet. The raw metal can be, for example, a single body of a rare earth element (metal single body), an alloy containing a rare earth element, pure iron, a boron-iron alloy, or an alloy containing the same. These raw metals are weighed in a manner consistent with the composition of the desired permanent magnet.

[0077] The molten metal can also be obtained by heating the raw material metal in the container by high-frequency induction heating. The temperature of the molten metal ejected from the nozzle (ejection temperature) can be, for example, about 1400°C. The temperature increase rate of the raw material metal to reach the ejection temperature can also be, for example, about 20 to 100°C / sec.

[0078] The surface of the cooling roll can also be composed of a metal having a high thermal conductivity such as Cu. The temperature of the surface of the cooling roll can also be controlled by a refrigerant flowing through the cooling roll. For example, the temperature of the surface of the cooling roll can be controlled in such a manner that the cooling speed of the molten metal on the surface of the cooling roll becomes about 10 5 ~10 6 °C / sec. The higher the cooling speed, the more easily the particle size of the crystal (R2T 14 B) contained in the alloy thin strip becomes fine, and the coercive force of the permanent magnet becomes higher. The less the amount of the molten metal ejected per unit time to the surface of the cooling roll, the thinner the molten metal adhered to the surface of the cooling roll, the higher the cooling speed, and the thinner the alloy thin strip. The higher the circumferential speed of the cooling roll, the thinner the molten metal adhered to the surface of the cooling roll, the higher the cooling speed, and the thinner the alloy thin strip. The thickness of the main phase particles in the easy magnetization axis direction (the length of the minor axis of the main phase particles) depends on the thickness of the alloy thin strip (as well as the pulverization and classification of the alloy thin strip). The thinner the alloy thin strip, the smaller the thickness (particle size) of the main phase particles, and the coercive force of the permanent magnet tends to be higher. However, one of the reasons for the R-rich phase is the oxidation of the surface of the alloy thin strip, and the thinner the alloy thin strip, the more easily the thin main phase particles whose surface is oxidized are contained in the permanent magnet, and the average value i AVE of the interval of the R-rich phase tends to be smaller. The thickness of the alloy thin strip can be, for example, 20 μm or more and 60 μm or less, or 30 μm or more and 50 μm or less. The width of the alloy thin strip can be, for example, 1.0 mm or more and 5.0 mm or less. In the case where the alloy thin strip has the above-described dimensions, in the pulverization / classification process, it is easy to recover the alloy powder whose average value of the aspect ratio is 1 or more and 2 or less.

[0079] In order to suppress the oxidation of the molten metal, the atmosphere in the container of the molten metal can be replaced with an inert gas such as argon (Ar) gas. The gas pressure in the container of the molten metal can be, for example, 100 kPa or more and 240 kPa or more.

[0080] A cooling roll is provided in the chamber. One cause of the R-rich phase is preferential oxidation of R contained near the surface of the alloy ribbon. In order to suppress generation of the R-rich phase due to oxidation of the molten metal and the alloy ribbon, the atmosphere in the chamber can also be replaced with an inert gas such as argon (Ar) gas. For the same reason, the atmosphere in the chamber can also contain a reducing gas such as hydrogen (H2) gas in addition to the inert gas. The concentration of hydrogen in the atmosphere in the chamber can be, for example, 0.1 mass% or more and 0.5 mass% or less. By the reducing action of hydrogen in the atmosphere in the chamber, oxidation of the molten metal and the alloy ribbon (generation of the R-rich phase) is further suppressed. Therefore, by the atmosphere in the chamber containing hydrogen, the interval of the R-rich phase more easily becomes large, and the average value i AVE easily becomes 30 μm or more. As the concentration of hydrogen in the atmosphere in the chamber increases, the interval of the R-rich phase more easily becomes large, and the average value i AVE easily becomes 30 μm or more. The gas pressure in the chamber can be, for example, 60 kPa or more and 200 kPa or less. The molten metal is not necessarily cooled to room temperature immediately on the surface of the cooling roll. The temperature of the alloy ribbon immediately after solidification is still high, and cooling of the alloy ribbon continues through heat conduction to the frame of the quenching device and the atmosphere in the chamber. In the case where the gas pressure in the chamber is low (for example, in the case where the gas pressure in the chamber is 20 kPa), heat conduction from the alloy ribbon to the atmosphere in the chamber is small, and the cooling speed of the alloy ribbon becomes slow. In the case where the cooling speed is slow, R2T 14 B is in excess, R is discharged from the inside of the alloy ribbon to the surface. As a result, near the surface of the alloy ribbon, R is in excess, and an oxide of R is easily formed on the surface of the alloy ribbon, and the average value i AVE easily becomes less than 30 μm.

[0081] The gas pressure in the container of the molten metal is higher than the gas pressure in the chamber. The difference between the gas pressure in the container of the molten metal and the gas pressure in the chamber is the pressure of the molten metal ejected from the nozzle (ejection differential pressure).

[0082] After the thin strip production step, a first conveying step is performed. The first conveying step is a step of conveying the alloy thin strip produced by the quenching method to a pulverizing / classifying device used in the pulverizing / classifying step. The atmosphere of the first conveying step is a non-oxidizing atmosphere. That is, the alloy thin strip is maintained in a non-oxidizing atmosphere during the period from the time when the alloy thin strip is formed to the time when the alloy thin strip reaches the pulverizing / classifying device. For example, the atmosphere in a conveying path from the quenching device (chamber provided with a cooling roll) to the pulverizing / classifying device can also be a non-oxidizing atmosphere, and the alloy thin strip can be conveyed in the conveying path. The alloy thin strip housed in a container filled with a non-oxidizing atmosphere can also be conveyed from the chamber to the pulverizing / classifying device. The atmosphere of the first conveying step (non-oxidizing atmosphere) can also be, for example, an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the first conveying step is 0 mass ppm or more and 20 mass ppm or less. The lower the concentration of oxygen in the atmosphere of the first conveying step, the less likely the surface of the alloy thin strip is oxidized in the first conveying step, and the less likely the R-rich phase derived from the oxidized surface of the alloy thin strip is contained in the permanent magnet. As a result, the interval of the R-rich phase is likely to become larger, and the average value i AVE of the interval of the R-rich phase is likely to be 30 μm or more. On the other hand, in the case where the concentration of oxygen in the atmosphere of the first conveying step is higher than 20 mass ppm, the interval of the R-rich phase is likely to become smaller, and the average value i AVE of the interval of the R-rich phase is likely to be less than 30 μm.

[0083] After the first conveying step, the pulverizing / classifying step is performed. The pulverizing / classifying step is a step of pulverizing the alloy thin strip using a pulverizing device, producing a coarse powder, classifying the coarse powder, and thereby recovering an alloy powder having a prescribed particle diameter and aspect ratio. The alloy powder is a precursor of the permanent magnet. The shape of each alloy particle constituting the alloy powder can also be plate-like or flake-like. The method of pulverizing the alloy thin strip can also be, for example, at least one of a cutting-type pulverizer and a propeller mill. The mechanism of classifying the coarse powder is a sieve. The particle diameter and particle size distribution of the alloy powder obtained by the classification can also be measured, for example, by a laser diffraction scattering method. The particle diameter of the alloy powder obtained by the classification can also be, for example, 60 μm or more and 2800 μm or less, or 150 μm or more and 2800 μm or less.

[0084] The average value of the aspect ratio of the alloy powder recovered in the pulverizing / classifying step is 1 or more and 2 or less. The smaller the average value of the aspect ratio of the alloy powder, the better, and the average value of the aspect ratio of the alloy powder is most preferably 1. In the case where the average value of the aspect ratio of the alloy powder is 1 or more and 2 or less, the segregation and agglomeration of the R-rich phase are suppressed in the hot forming step and the thermoplastic working step, and it is easy to obtain the average value i AVE30 μm or more. In other words, as the average value of the aspect ratio of the alloy powder decreases, segregation and coagulation of the R-rich phase are suppressed in the thermoplastic working step, and the average value i of the interval of the R-rich phase AVE For the same reason, it is preferable that the standard deviation σ of the aspect ratio of the alloy powder be as small as possible. For example, the standard deviation σ of the aspect ratio of the alloy powder can also be 0 or more and 2 or less.

[0085] In the case where the average value of the aspect ratio of the alloy powder is too large, the shape of each alloy particle deforms, and thus, in the hot forming step and the thermoplastic working step, the force acting on each alloy particle is not uniform, and each alloy particle is easily broken. The liquid phase (R-rich phase) exuded from each alloy particle easily coagulates in the grain boundary where the cross section of each alloy particle is present. As a result, a plurality of R-rich phases are easily formed in the permanent magnet, and the average value i of the interval of the R-rich phase AVE easily decreases to 30 μm or less. In addition, abnormal growth of each alloy particle easily occurs due to the coagulated liquid phase (R-rich phase), and coarse main phase particles are easily formed. Due to the dispersion of stress in the molded body accompanying the coagulation of the liquid phase and the coarsening of the main phase particles, the main phase particles are difficult to rotate, and the main phase particles are difficult to orient in the easy magnetization axis direction. In addition, in the case where the average value of the aspect ratio of the alloy powder is too large, the shape of each alloy particle deforms, and thus, in the hot forming step and the thermoplastic working step, each alloy particle is difficult to densely fill in the molded body, and a gap is easily generated in the molded body. As a result, the residual flux density easily decreases.

[0086] The average value of the aspect ratio of the alloy powder is controlled by the aperture of the nozzle and the sieve used in the classification of the coarse powder as follows.

[0087] The length of the long axis of the flat alloy particle constituting the coarse powder is denoted by I (lowercase letter L). The length of the short axis of the alloy particle is denoted by w. The thickness of the alloy particle is denoted by t. I, w, and t satisfy t < w ≤ I. The aspect ratio AR of the alloy particle is denoted by I / w. AR is a real number of 1 or more. I can also be referred to as the major axis of the alloy particle in a direction substantially perpendicular to the thickness direction of the alloy particle. W can also be referred to as the minor axis of the alloy particle in a direction substantially perpendicular to the thickness direction of the alloy particle. The thickness direction of the alloy particle can correspond to the direction of the short axis of the main phase particle in the cross section of the permanent magnet parallel to the easy magnetization axis direction. The thickness t of the alloy particle can also be substantially the same as the thickness of the alloy thin strip, and for example, can be 20 μm or more and 60 μm or less, or 30 μm or more and 50 μm or less. The length w of the short axis of the alloy particle can also be substantially the same as the width of the alloy thin strip, and for example, can be 1.0 mm or more and 5.0 mm or less.

[0088] In the classification of the coarse powder, a first sieve and a second sieve having a mesh inner diameter (pore diameter) smaller than that of the first sieve are used. The mesh inner diameter of the first sieve is denoted as Dl. In other words, the mesh of the first sieve is square, and the length of one side of the square is Dl. The mesh inner diameter of the second sieve is denoted as D2. In other words, the mesh of the second sieve is square, and the length of one side of the square is D2. D2 is smaller than Dl. In the coarse powder obtained by pulverizing the alloy thin strip, alloy powder that does not pass through the second sieve after passing through the first sieve is recovered and used as a material for a permanent magnet. In other words, alloy particles having a length l of the long axis of Dl or less and greater than D2 are easily recovered from between the first sieve and the second sieve. Therefore, each of the alloy particles that constitute the alloy powder recovered from between the first sieve and the second sieve tends to satisfy the following Inequality 1. The length l of the long axis of the alloy particle is denoted as w x AR, and therefore, the following Inequality 1 is equivalent to the following Inequality 2. The following Inequality 3 is derived from the following Inequality 2. In the case where the mesh inner diameter Dl of the first sieve is constant, the following Inequality 3 exhibits a tendency that the aspect ratio of the alloy particle increases as the length w of the short axis of the alloy particle decreases. In the case where the length w of the short axis of the alloy particle is constant, the following Inequality 3 exhibits a tendency that the aspect ratio of the alloy particle increases as the mesh inner diameter Dl of the first sieve increases. In addition, the following Inequality 3 exhibits a tendency that the range of the aspect ratio of the alloy particle narrows and the standard deviation σ of the aspect ratio decreases as the difference (Dl - D2) between Dl and D2 decreases.

[0089] D2 < l ≤ Dl (1)

[0090] D2 < w x AR ≤ Dl (2)

[0091] (D2 / w) < AR ≤ (Dl / w) (3)

[0092] The length w of the short axis of the alloy particle and the aspect ratio (l / w) of the alloy particle depend on the pore diameter of the nozzle used in the above-described rapid cooling method for the following reasons.

[0093] The size of the molten metal (droplet) ejected from the nozzle is approximately equal to the pore diameter of the nozzle. Also, the molten metal (droplet) ejected from the nozzle toward the surface of the cooling roll is instantaneously flattened and spread on the surface of the cooling roll. As a result, a flat and elongated alloy thin strip is formed. Therefore, the width of the alloy thin strip tends to be larger than the pore diameter (size of the droplet) of the nozzle, and the length w of the short axis of the alloy particle formed by pulverizing the alloy thin strip also tends to be larger than the pore diameter (size of the droplet) of the nozzle. Also, as the pore diameter of the nozzle decreases, the droplet becomes smaller, the alloy thin strip formed from the droplet becomes elongated, and the length w of the short axis of the alloy particle formed by pulverizing the alloy thin strip tends to decrease. Therefore, the length w of the short axis of the alloy particle and the aspect ratio (l / w) of the alloy particle can be controlled in accordance with the pore diameter of the nozzle.

[0094] The length l of the long axis of the alloy particles is difficult to depend on the aperture of the nozzle, as is the length w of the short axis of the alloy particles. The length l of the long axis of the alloy particles is easily controlled within a desired range depending on the method and conditions of the pulverization of the alloy thin strip.

[0095] As described above, the aspect ratio of the alloy powder recovered by the classification is controlled based on the relationship among the aperture of the nozzle, the length w of the short axis of the alloy particles, the length l of the long axis of the alloy particles, and the inner diameter of the mesh of each sieve (D1 and D2).

[0096] The alloy powder that does not pass through the first sieve can also be reused. For example, the coarse powder that does not pass through the first sieve can also be recovered and repulverized together with the alloy thin strip. The alloy powder that passes through the second sieve can also be reused. For example, the alloy powder that passes through the second sieve can also be recovered and used as a raw material for molten metal. The alloy powder that passes through the second sieve can also be discarded.

[0097] The average of the aspect ratio of the alloy powder recovered in the pulverization / classification process can also be measured by the following method. Each alloy particle constituting the alloy powder is placed on a flat surface in a manner not to overlap each other. The flat surface can also have adhesiveness in order to fix each alloy particle. The plurality of alloy particles placed on the flat surface can be observed by a scanning electron microscope (SEM). The size of the field of view observed by the SEM can be, for example, 1 mm in length x 1 mm in width. The number of the alloy particles observed within the field of view observed by the SEM can be, for example, about 100 or more and 1000 or less. Each alloy particle is plate-like or sheet-like, and the thickness t of each alloy particle is smaller than the length l of the long axis and the length w of the short axis of each alloy particle. Therefore, each alloy particle placed on the flat surface is observed as a two-dimensional shape including the long axis and the short axis of each alloy particle. The shape of each alloy particle can be approximated by the quadrangle having the smallest area among the quadrangles circumscribed around each alloy particle. The quadrangle is a rectangle or a square. The length of the short side of the quadrangle is regarded as the length w of the short axis of the alloy particle. The length of the long side of the quadrangle is regarded as the length l of the long axis of the alloy particle. Based on the above premise, the length l of the long axis and the length w of the short axis of each alloy particle are measured, and the aspect ratio (l / w) of each alloy particle is calculated. The average of the aspect ratio of the alloy powder and the standard deviation of the aspect ratio are calculated from the aspect ratios of all the alloy particles present within the field of view observed by the SEM. A commercially available image analysis software can also be used in the specification of the shape (contour line) of each alloy particle and the measurement of the size of the quadrangle circumscribed around each alloy particle.

[0098] The specific surface area of the alloy powder is larger than that of the alloy thin strip, and therefore, the alloy powder is more easily oxidized than the alloy thin strip. (The specific surface area of the alloy thin strip is larger than that of the shaped body formed of the alloy powder, and therefore, the alloy thin strip is more easily oxidized than the shaped body.) In addition, the smaller the particle diameter of the alloy powder, the larger the specific surface area of the alloy powder, and the more easily the surface of the alloy powder is oxidized. By oxidation of the alloy powder, a plurality of R-rich phases originating from the oxidized surface of the alloy powder is easily contained in the permanent magnet. Therefore, the smaller the particle diameter of the alloy powder, the more easily the interval of the R-rich phases becomes small, and the average value of the interval of the R-rich phases i AVE is easily below 30 μm. In other words, the larger the particle diameter of the alloy powder, the smaller the specific surface area of the alloy powder, and the more the oxidation of the surface of the alloy powder is suppressed. By suppression of the oxidation of the alloy powder, the number of the R-rich phases contained in the permanent magnet is reduced. Therefore, the larger the particle diameter of the alloy powder, the more easily the interval of the R-rich phases becomes large, and the average value of the interval of the R-rich phases i AVE is easily 30 μm or more.

[0099] The atmosphere of the pulverization / classification process is a non-oxidizing atmosphere. By conducting the pulverization / classification process in a non-oxidizing atmosphere, oxidation of the alloy thin strip, the coarse powder, and the alloy powder in the pulverization / classification process is suppressed. As a result, the interval of the R-rich phases easily becomes large, and the average value of the interval of the R-rich phases i AVE is easily 30 μm or more. The atmosphere of the pulverization / classification process (the non-oxidizing atmosphere) may, for example, be an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the pulverization / classification process is 0 mass ppm or more and 20 mass ppm or less. The lower the concentration of oxygen in the atmosphere of the pulverization / classification process, the more easily the interval of the R-rich phases becomes large, and the average value of the interval of the R-rich phases i AVE is easily 30 μm or more. On the other hand, in a case where the concentration of oxygen in the atmosphere of the pulverization / classification process is higher than 20 mass ppm, the interval of the R-rich phases easily becomes small, and the average value of the interval of the R-rich phases i AVE is easily below 30 μm.

[0100] After the pulverization / classification process, a second conveyance process is performed. The second conveyance process is a process of conveying the alloy powder obtained by the pulverization / classification process to a molding device used in the hot molding process. The atmosphere of the second conveyance process is a non-oxidizing atmosphere. That is, from the time when the alloy powder is formed to the time when the alloy powder reaches the molding device, the alloy powder is maintained in a non-oxidizing atmosphere. For example, the atmosphere in a conveyance path from the pulverization / classification device to the molding device can also be a non-oxidizing atmosphere, and the alloy powder can be conveyed in the conveyance path. The alloy powder contained in a container filled with a non-oxidizing atmosphere can also be conveyed from the pulverization / classification device to the molding device. The atmosphere of the second conveyance process (the non-oxidizing atmosphere) can also be, for example, an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the second conveyance process is 0 mass ppm or more and 20 mass ppm or less. The lower the concentration of oxygen in the atmosphere of the second conveyance process, the more difficult it is for the surface of the alloy powder to be oxidized in the second conveyance process, and the more difficult it is for the R-rich phase derived from the oxidized surface of the alloy powder to be contained in the permanent magnet. As a result, the interval of the R-rich phase is likely to become 30 μm or more. On the other hand, in a case where the concentration of oxygen in the atmosphere of the second conveyance process is higher than 20 mass ppm, the interval of the R-rich phase is likely to become smaller, and the average value i AVE of the interval of the R-rich phase is likely to be lower than 30 μm. AVE

[0101] After the second conveyance process, the hot molding process is performed. The hot molding process is a process of forming a molded body by performing pressurization while heating the alloy powder. For example, the alloy powder in a mold can be compressed by the mold while being heated. By the pressurization of the alloy powder, the voids between the alloy powders are reduced, and a dense molded body is obtained. In addition, by the heating of the alloy powder along with the pressurization, a liquid phase (an R-rich phase such as a Nd-rich phase) is formed from the surface of the alloy powder, the liquid phase fills the voids (grain boundaries) between the alloy powders, and the alloy powders become lubricated by the liquid phase, whereby a dense molded body is obtained. The cold molding process can be performed before the hot molding process. In the cold molding process, a molded body can be formed by pressurizing the alloy powder at ordinary temperature (room temperature). The molded body obtained by the cold molding process can be densified by being pressurized while being heated in the hot molding process. The temperature of the alloy powder in the hot molding process (hot molding temperature) can also be, for example, 700°C or more and 800°C or less. In a case where the hot molding temperature is too low, a sufficient liquid phase is not formed from the surface of the alloy powder, and the molded body is difficult to be densified. In a case where the hot molding temperature is too high, the crystal (R2T 14 ​B) is excessively progressed, and the coercive force of the permanent magnet is likely to be reduced. The pressure applied to the alloy powder in the hot molding step (hot molding pressure) can also be 50 MPa or more and 200 MPa or less. The time for which the hot molding temperature and the hot molding pressure are maintained in the above range (hot molding time) can also be, for example, several tens of seconds or more and several hundred seconds or less.

[0102] In order to suppress oxidation of the alloy powder and the molded body in the hot molding step, the hot molding step can also be performed in a non-oxidizing atmosphere. The atmosphere of the hot molding step (non-oxidizing atmosphere) can also be, for example, an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the hot molding step can also be, for example, 0 mass ppm or more and 20 mass ppm or less.

[0103] After the hot molding step, a third transport step is performed. The third transport step is a step of transporting the molded body obtained by the hot molding step to a molding device used in the thermoplastic working step. In order to suppress oxidation of the molded body, the atmosphere of the third transport step can also be a non-oxidizing atmosphere. That is, the molded body can also be maintained in a non-oxidizing atmosphere from the time when the molded body is formed to the time when the molded body reaches the molding device for thermoplastic working. For example, the atmosphere in a transport path that communicates from the molding device for hot molding to the molding device for thermoplastic working can also be a non-oxidizing atmosphere, and the molded body can also be transported in this transport path. The molded body housed in a container filled with a non-oxidizing atmosphere can also be transported from the molding device for hot molding to the molding device for thermoplastic working. The atmosphere of the third transport step can also be, for example, an inert gas such as Ar gas. The specific surface area of the molded body formed from the alloy powder is significantly smaller than the specific surface area of each of the alloy powder and the alloy thin strip, and thus the molded body (particularly the inside of the molded body) is less likely to be oxidized than the alloy powder and the alloy thin strip. Therefore, even in the case where the concentration of oxygen in the atmosphere of the third transport step is higher than the concentration of oxygen in each of the atmospheres of the first transport step and the second transport step, it is possible to control the average value i AVE to be 30 μm or more. For example, in the case where the atmosphere of the third transport step is air, by reducing the concentration of oxygen in each of the atmospheres of the first transport step and the second transport step, it is possible to control the average value i AVE to be 30 μm or more. The concentration of oxygen in the atmosphere of the third transport step can also be 0 mass ppm or more and 200,000 mass ppm or less, preferably 0 mass ppm or more and 2,000 mass ppm or less, and more preferably 0 mass ppm or more and 20 mass ppm or less.

[0104] After the third transporting step, a thermoplastic processing step is performed. The thermoplastic processing step is a step in which a molded body obtained by the hot forming step is subjected to hot extrusion forming, and a magnet base material including a plurality of main phase particles (R2T 14 B) whose c-axes (easy magnetization axes) are oriented in a prescribed direction is obtained. For example, in the thermoplastic processing step, the molded body is heated while being extruded from a mold. In the mold, the grain boundary phase in the heated molded body is liquefied to generate a liquid phase (R-rich phase), and stress is applied to the molded body in a prescribed direction, and each alloy particle constituting the molded body is deformed. With the generation of the liquid phase and the deformation of the alloy particles, anisotropic growth of the grains in a direction perpendicular to the c-axes of the grains is performed. In addition, the liquid phase lubricates each grain, and force is applied to each grain according to the stress. As a result, the grains are rotated by grain boundary sliding, and the c-axes of each grain (main phase particle) are oriented approximately in parallel with the stress direction. In other words, a plurality of flat main phase particles extending in a direction approximately perpendicular to the c-axes are stacked along the stress direction.

[0105] The temperature of the molded body in the thermoplastic processing step (thermoplastic processing temperature) can be, for example, 700°C or higher and lower than 900°C, or 700°C or higher and 850°C or lower.

[0106] In a case where the thermoplastic processing temperature is excessively low, it is difficult for the liquid phase (R-rich phase or the like) to be generated at the grain boundaries in the molded body, and the grains are difficult to grow, and rotation of the grains caused by grain boundary sliding is difficult to occur. As a result, the average value of the lengths of the short axes of the main phase particles is likely to be lower than 20 nm, and the c-axes of each main phase particle (grain) are difficult to be oriented approximately in parallel with the stress direction.

[0107] In a case where the thermoplastic processing temperature is excessively high (for example, in a case where the thermoplastic processing temperature is 900°C or higher), the liquid phase (R-rich phase) excessively exudes from each alloy particle, and is segregated to the surface of each alloy particle and the interface between the alloy particles, and most of the liquid phase is consumed in the grain growth of the grains. As a result, the frequency of generation of the R-rich phase in the AB direction decreases, and the average value of the intervals of the R-rich phases i AVE is likely to exceed 1000 μm. In addition, most of the liquid phase is consumed in the grain growth of the grains, and thus the grain growth of the main phase particles (grains) is abnormally performed, and a coarse main phase particle is likely to be formed, and the average value of the lengths of the short axes of the main phase particles is likely to exceed 200 nm. The coarse main phase particle is difficult to be oriented in the easy magnetization axis direction.

[0108] The extrusion speed of the hot extrusion forming can be, for example, 10 -2mm / sec or more and 9.9 mm / sec or less. In a case where the extrusion speed is excessively high (for example, in a case where the extrusion speed is 10 mm / sec or more), anisotropic growth of the main phase particles (grains) in the molded body does not sufficiently proceed, and thus the average value of the length of the short axis of the main phase particles (primary particles) tends to be less than 20 nm. That is, in a case where the extrusion speed is excessively high, the molded body is extruded from the mold before anisotropic growth of the grains in the molded body sufficiently proceeds. As a result, it is difficult for the c-axes of the respective main phase particles (grains) to be oriented substantially in parallel with the stress direction.

[0109] The pressure (thermoplastic working pressure) applied to the molded body in the thermoplastic working process can also be 50 MPa or more and 200 MPa or less. The time (thermoplastic working time) for which the thermoplastic working temperature and the thermoplastic working pressure are maintained in the above range can also be, for example, several tens of seconds.

[0110] In order to suppress oxidation of the molded body and the magnet base material in the thermoplastic working process, the thermoplastic working process can also be performed in a non-oxidizing atmosphere. The atmosphere (non-oxidizing atmosphere) of the thermoplastic working process can also be, for example, an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the thermoplastic working process can also be, for example, 0 mass ppm or more and 20 mass ppm or less.

[0111] The magnet base material obtained through the above process can also be a finished product of a permanent magnet. The magnet base material via the following grain boundary diffusion process can also be a finished product of a permanent magnet.

[0112] The following grain boundary diffusion process can also be performed after the thermoplastic working process. The grain boundary diffusion process is a process of attaching a diffusion material containing a heavy rare earth element to the surface of the magnet base material, and heating the diffusion material and the magnet base material. By heating the magnet base material to which the diffusion material is attached, the heavy rare earth element in the diffusion material diffuses from the surface of the magnet base material to the inside of the magnet base material. In the inside of the magnet base material, the heavy rare earth element diffuses to the vicinity of the surface of the main phase particles via the grain boundaries. In the vicinity of the surface of the main phase particles, a part of the light rare earth elements (Nd, etc.) is replaced by the heavy rare earth element. By the heavy rare earth element locally existing in the vicinity of the surface of the main phase particles and the grain boundaries, the anisotropic magnetic field locally becomes large in the vicinity of the grain boundaries, and it is difficult to generate a nucleus of magnetization reversal in the vicinity of the grain boundaries. As a result, a permanent magnet having high coercive force can be obtained.

[0113] In the grain boundary diffusion process, each element contained in the diffusion material diffuses substantially uniformly to each grain boundary and the surface of each grain in the magnet base material. In addition, the grain boundary formed of each element derived from the diffusion material is finer than the R-rich phase caused by oxidation, and is difficult to be detected in the measurement of the interval of the R-rich phase. Therefore, each element derived from the diffusion material is difficult to affect the interval of the R-rich phase.

[0114] In order to suppress oxidation of the magnet base material in the grain boundary diffusion process, the grain boundary diffusion process can also be performed in a non-oxidizing atmosphere. The atmosphere of the grain boundary diffusion process (non-oxidizing atmosphere) can also be, for example, an inert gas such as Ar gas. The concentration of oxygen in the atmosphere of the grain boundary diffusion process can also be, for example, 0 mass ppm or more and 20 mass ppm or less. The gas pressure of the atmosphere of the grain boundary diffusion process can also be, for example, 50 kPa or more and 120 kPa or less. The temperature of the diffusion material and the magnet base material in the grain boundary diffusion process (diffusion temperature) can also be, for example, 550°C or more and 900°C or less. The time for which the diffusion temperature is maintained (diffusion time) can also be, for example, 1 minute or more and 1440 minutes or less.

[0115] The diffusion material can also contain at least one heavy rare earth element among Tb and Dy. The diffusion material can also contain at least one light rare earth element among Nd and Pr in addition to the heavy rare earth element. The diffusion material can also contain Cu in addition to the heavy rare earth element and the light rare earth element. The diffusion material can be, for example, a metal composed of one of the above-described elements, a hydride of one of the above-described elements, an alloy containing a plurality of the above-described elements, or a hydride of the alloy. The diffusion material can also be a powder. In the grain boundary diffusion process, a slurry containing the diffusion material and an organic solvent can also be applied to the surface of the magnet base material. In the grain boundary diffusion process, a sheet containing the diffusion material and a binder can also cover the surface of the magnet base material. In the grain boundary diffusion process, an alloy foil (ribbon) composed of the diffusion material can also cover the surface of the magnet base material.

[0116] In order to promote diffusion of the diffusion material, the surface of the magnet base material can also be polished before the grain boundary diffusion process. In order to remove the diffusion material remaining on the surface of the magnet base material after the grain boundary diffusion process, the surface of the magnet base material after the grain boundary diffusion process can also be polished.

[0117] The size and shape of the magnet base material can also be adjusted by cutting and polishing of the magnet base material or the like. A passive layer can also be formed on the surface of the magnet base material by oxidation or chemical treatment of the surface of the magnet base material. The surface of the magnet base material can also be covered by a protective film such as a resin film or the like. The corrosion resistance of the permanent magnet is improved by the passive layer or the protective film.

[0118] The present application is not necessarily limited to the above-described embodiments. Various modifications of the present application can be made within the scope of the present application, and these modifications are also included in the present application.

[0119] [Examples]

[0120] The present application will be described in detail by the following examples and comparative examples. The present application is not limited by the following examples.

[0121] Manufacture of Permanent Magnet

[0122] (Example 1)

[0123] In the thin strip production step, an alloy thin strip was produced from a raw material alloy by a rapid solidification method. The raw material metal (molten metal) used in the thin strip production step contained Nd, Fe, Co, Ga, Al, and B.

[0124] The content of Nd in the raw material metal was 30.17 mass%.

[0125] The content of Co in the raw material metal was 3.96 mass%.

[0126] The content of Ga in the raw material metal was 0.59 mass%.

[0127] The content of Al in the raw material metal was 0.04 mass%.

[0128] The content of B in the raw material metal was 0.97 mass%.

[0129] The balance of the raw material metal other than Nd, Co, Ga, Al, and B was Fe.

[0130] The temperature of the molten metal ejected from the nozzle (ejection temperature) was 1400°C. The temperature increase rate until the temperature of the raw material metal reached the ejection temperature was 100°C / sec. The cooling rate of the molten metal on the surface of the cooling roll was controlled to about 10 5 °C / sec. The peripheral speed of the cooling roll was 40 m / sec. The aperture of the nozzle was the value shown in Table 1 below.

[0131] The gas in the nozzle (atmosphere in the container of the molten metal) was Ar. The pressure of the nozzle (gas pressure in the container of the molten metal) was 100 kPa.

[0132] The gas (atmosphere) in the chamber provided with the cooling roll was Ar. The concentration of hydrogen in the atmosphere in the chamber was 0.00 mass%. The pressure of the chamber (gas pressure in the chamber) was 60 kPa. The ejection differential pressure was 40 kPa.

[0133] In the first conveyance step after the thin strip production step, the alloy thin strip was conveyed from the rapid solidification device to the pulverization / classification device. The gas (atmosphere) of the first conveyance step was Ar. The concentration of oxygen in the atmosphere of the first conveyance step was 20 mass ppm.

[0134] In the pulverization / classification step after the first conveyance step, alloy powder having a prescribed aspect ratio was recovered by pulverization and classification of the alloy thin strip. The inside diameter D1 of the mesh of the first sieve used in the classification was the value shown in Table 1 below. The inside diameter D2 of the mesh of the second sieve used in the classification was the value shown in Table 1 below. The average value AR of the aspect ratio of the recovered alloy powder was measured by the above-described method.AVE The average value AR of the aspect ratio of the recovered alloy powder AVE The standard deviation σ of the aspect ratio of the alloy powder was the value shown in Table 1 below.

[0135] The gas (atmosphere) of the pulverization / classification process was Ar. The concentration of oxygen in the atmosphere of the pulverization / classification process was 20 mass ppm.

[0136] In the second conveyance process after the pulverization / classification process, the alloy powder was conveyed from the pulverization / classification device to the molding device. The gas (atmosphere) of the second conveyance process was Ar. The concentration of oxygen in the atmosphere of the second conveyance process was 20 mass ppm.

[0137] In the hot molding process after the second conveyance process, the alloy powder in the mold was heated while the alloy powder was compressed through the mold, whereby a molded body was produced. The molded body was a thin plate. The length of the molded body was 80 mm, the width of the molded body was 22 mm, and the thickness of the molded body was 11 mm. The hot molding temperature was 750°C. The hot molding pressure was 100 MPa. The hot molding time was 300 seconds. The gas (atmosphere) of the hot molding process was Ar. The concentration of oxygen in the atmosphere of the hot molding process was 20 mass ppm.

[0138] In the third conveyance process after the hot molding process, the molded body was conveyed from the molding device for hot molding to the molding device for thermoplastic processing. The gas (atmosphere) of the third conveyance process was Ar. The concentration of oxygen in the atmosphere of the third conveyance process was 20 mass ppm.

[0139] After the third conveyance process, the thermoplastic processing process was performed. The mold used in the thermoplastic processing process (hot extrusion molding of the molded body) was a cylindrical shape. That is, the cavity of the mold passed through the mold from the end face (the starting end face) of the mold, which was open to the inlet for the molded body, to the end face (the terminal end face) of the mold, which was open to the extrusion outlet for the molded body. The starting end face and the terminal end face were parallel planes to each other. The direction from the starting end face to the terminal end face was the extrusion direction of the molded body, and the extrusion direction was perpendicular to the starting end face and the terminal end face. The opening area of the extrusion outlet for the molded body was smaller than the opening area of the inlet for the molded body.

[0140] The cavity was divided into an inlet side region, an intermediate region, and an extrusion outlet side region along the extrusion direction. The inlet side region was open on the starting end face. The extrusion outlet side region was open on the terminal end face. The intermediate region was located between the inlet side region and the extrusion outlet side region in the extrusion direction.

[0141] The shape of the cavity on the cross section of the mold perpendicular to the extrusion direction (the cross section of the mold parallel to the starting end face and the terminal end face) was a quadrangle with all four angles being right angles. One pair of opposite sides in the quadrangle was denoted as the first side, and the other pair of opposite sides in the quadrangle was denoted as the second side.

[0142] The length of the first side and the second side in the entry-side region is constant. That is, the opening area of the entry-side region in the cross section perpendicular to the extrusion direction is constant. In the intermediate region, the length of the first side gradually decreases along the extrusion direction, and eventually coincides with the length of the first side in the exit-side region. Therefore, the first side in the exit-side region is shorter than the first side in the entry-side region. Further, in the intermediate region, the length of the second side gradually increases along the extrusion direction, and eventually coincides with the length of the second side in the exit-side region. Therefore, the second side in the exit-side region is longer than the second side in the entry-side region. Further, the opening area of the intermediate region in the cross section perpendicular to the extrusion direction gradually decreases along the extrusion direction, and eventually coincides with the opening area of the exit-side region in the cross section perpendicular to the extrusion direction. Therefore, the opening area of the exit-side region in the cross section perpendicular to the extrusion direction is smaller than the opening area of the entry-side region in the cross section perpendicular to the extrusion direction. The length of the first side and the second side in the exit-side region is constant. That is, the opening area of the exit-side region in the cross section perpendicular to the extrusion direction is constant.

[0143] The length of the first side in the entry-side region (the starting end surface) was 22 mm, and the length of the second side in the entry-side region (the starting end surface) was 11 mm. The length of the first side in the exit-side region (the terminal end surface) was 7 mm, and the length of the second side in the exit-side region (the terminal end surface) was 30 mm. The length of the entry-side region in the extrusion direction was 80 mm. The length of the intermediate region in the extrusion direction was 20 mm. The length of the exit-side region in the extrusion direction was 20 mm.

[0144] As described above, the opening area of the exit-side region in the cross section perpendicular to the extrusion direction is smaller than the opening area of the entry-side region in the cross section perpendicular to the extrusion direction, and the first side in the exit-side region (the terminal end surface) is shorter than the second side in the exit-side region (the terminal end surface). Therefore, in the exit-side region, a stress approximately parallel to the first side acts on the molded body, and grain boundary sliding and rotation of the main phase particles occur. As a result, the c-axes of the main phase particles are oriented along the stress direction (the direction of the first side). That is, the easy magnetization axis direction of the magnet substrate obtained by the hot extrusion molding is the direction of the first side in the exit-side region (the terminal end surface).

[0145] In the thermoplastic working step, a magnet substrate was produced by hot extrusion molding of a molded body using the above-described mold. The temperature of the entry of the mold was the value shown in Table 1 below. The temperature of the exit (the exit) of the mold was the value shown in Table 1 below. The thermoplastic working pressure was 100 MPa. The extrusion speed of the hot extrusion molding was the value shown in Table 1 below.

[0146] The gas (atmosphere) of the thermoplastic processing step was Ar. The concentration of oxygen in the atmosphere of the thermoplastic processing step was 20 mass ppm.

[0147] In the grain boundary diffusion step after the thermoplastic processing step, the magnet substrate to which the diffusion material was attached was heated. The diffusion material was a powder of a hydride of a eutectic alloy composed of Nd, Tb, and Cu. In the grain boundary diffusion step, a slurry of a mixture of the diffusion material and an organic solvent was applied to the entire surface of the magnet substrate. The content of Nd in the diffusion material was 60 mass%. The content of Tb in the diffusion material was 20 mass%. The content of Cu in the diffusion material was 20 mass%. The mass of the diffusion material attached to the magnet substrate was adjusted so that the content of Tb in the permanent magnet (magnet substrate after the grain boundary diffusion step) would coincide with 2 mass%.

[0148] The gas (atmosphere) of the grain boundary diffusion step was Ar. The pressure of the grain boundary diffusion step (gas pressure of the atmosphere of the grain boundary diffusion step) was 100 kPa. The diffusion temperature was 700°C. The diffusion time was 300 minutes.

[0149] By the above method, the permanent magnet of Example 1 was produced.

[0150] (Examples 2 to 9 and Comparative Examples 1 to 12)

[0151] The aperture of the nozzle of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0152] The inner diameter D1 of the mesh of the first sieve of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0153] The inner diameter D2 of the mesh of the second sieve of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0154] The average value AR of the aspect ratio of the alloy powder of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below. AVE

[0155] The standard deviation σ of the aspect ratio of the alloy powder of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0156] The temperature of the inlet of the mold in the thermoplastic processing step of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0157] The temperature of the extrusion outlet (outlet) of the mold in the thermoplastic processing step of each of Examples 2 to 9 and Comparative Examples 1 to 12 was the value shown in Tables 1 to 5 below.

[0158] ​The extrusion speeds for the thermal extrusion molding of Examples 2-9 and Comparative Examples 1-12 are the values ​​shown in Tables 1-5 below.

[0159] Except for the manufacturing conditions shown in Tables 1 to 5 below, permanent magnets for Examples 2 to 9 and Comparative Examples 1 to 12 were manufactured using the same method as in Example 1.

[0160] <Analysis of Permanent Magnets>

[0161] (Composition and microstructure of permanent magnets)

[0162] The cross-sections of the permanent magnets in all embodiments and comparative examples were observed using a scanning electron microscope (SEM). The observed cross-sections of each permanent magnet were parallel to the easy magnetization axis of each permanent magnet. Furthermore, the composition of the cross-sections of each permanent magnet was analyzed using an electron probe microanalyzer (EPMA) and energy-dispersive X-ray spectroscopy (EDS).

[0163] In all embodiments and comparative examples, the permanent magnet comprises multiple main phase particles (Nd2Fe). 14 The main phases (B-type grains) and multiple R-rich phases (Nd-rich phases) are present. In all embodiments and comparative examples, the main phase particles observed in cross-section are flat, and the multiple flat main phase particles are stacked along the easy magnetization axis. In all embodiments and comparative examples, each R-rich phase is located between the multiple main phase particles. At least a portion of the R-rich phase is located between the multiple main phase particles arranged along the AB direction. In all embodiments and comparative examples, a portion of the R-rich phase contains Nd oxide.

[0164] Figure 3 The image shows a portion of the backscattered electron image of a cross-section of the permanent magnet in Example 2. Figure 3 The five backscattered electron images are identical. Backscattered electron images were acquired using SEM. The cross-section of the captured backscattered electron images is parallel to the easy magnetization axis.

[0165] exist Figure 4 In each of the measurement regions A(a), A(b), A(c), A(d), and A(e), the luminance distribution along the AB direction was measured. The width of each measurement region along the AB direction was 400 μm. The width of each measurement region along the easy magnetization axis C was 15 μm. In each measurement region, the average value of the R-rich phase intervals along the AB direction was measured based on the luminance distribution. By further averaging the average values ​​of the R-rich phase intervals in each of the five measurement regions, the average value i of the R-rich phase intervals along the AB direction was obtained. AVE Details of the method for measuring brightness distribution and the interval of R-rich phases are described in the embodiments above.

[0166] Figure 4FIG. 5 is a backscattered electron image of a part of a cross section of the permanent magnet of Comparative Example 8. Figure 4 The five backscattered electron images in FIG. 5 are the same. The backscattered electron images were taken by SEM. The cross section from which the backscattered electron images were taken was parallel to the direction of the easy magnetization axis. In ​ In each of the measurement regions A'(a), A'(b), A'(c), A'(d), and A'(e) in FIG. 5, the intensity distribution was measured along the AB direction. Moreover, by the same method as in Example 2, the average value i of the interval of the R-rich phase of Comparative Example 8 was obtained. AVE .

[0167] By the same method as in Example 2, the average value i of the interval of the R-rich phase of each of all of the examples and comparative examples was obtained. AVE The average value i of the interval of the R-rich phase of each of Examples 1 to 9 and Comparative Examples 11 to 12 is shown in Tables 1 to 5 below. AVE

[0168] (Size of main phase particles)

[0169] A backscattered electron image of a cross section of the permanent magnet of Example 2 was taken by SEM. The cross section from which the backscattered electron image was taken was parallel to the direction of the easy magnetization axis. The size of the backscattered electron image was 88 μm in the vertical direction x 126 μm in the horizontal direction. Representative multiple sites within the backscattered electron image were selected, and a backscattered electron image of each site was taken at a high magnification. The length of the long axis and the length of the short axis of a main phase particle (primary particle) present in the backscattered electron image at the high magnification were measured. The shape of each main phase particle was approximated by a rectangle having the smallest area among rectangles circumscribing the main phase particle. The length of the long side of the rectangle was taken as the length of the long axis of the main phase particle, and the length of the short side of the rectangle was taken as the length of the short axis of the main phase particle. The average value Labof the length of the long axis of all of the main phase particles present in the backscattered electron image at the high magnification was calculated. The average value Lcof the length of the short axis of all of the main phase particles present in the backscattered electron image at the high magnification was calculated.

[0170] By the same method as in Example 2, the length of the long axis and the length of the short axis of a main phase particle of each of all of the examples and comparative examples were measured. The average value Lcof the length of the short axis of a main phase particle (primary particle) of each of Examples 1 to 9 and Comparative Examples 11 to 12 is shown in Tables 1 to 5 below.

[0171] The minimum value of the average value Labof the length of the long axis of a main phase particle (primary particle) of each example was about 100 nm. The maximum value of the average value Labof the length of the long axis of a main phase particle (primary particle) of each example was about 1000 nm.

[0172] (Magnetic properties of permanent magnet)

[0173] ​The residual magnetic flux density (Br), the coercive force (HcJ), and the rectangular ratio (Hk / HcJ) of each of all the examples and comparative examples were measured. The residual magnetic flux density, the coercive force, and the rectangular ratio were measured by a BH tracer. The coercive force was measured at 23°C and 150°C. The Br was measured at room temperature. The rectangular ratio was measured at 23°C. The temperature coefficient β of the coercive force of each of all the examples and comparative examples was calculated. The temperature coefficient β was defined according to the following mathematical expression 4. HcJ 150 in the following mathematical expression 4 is the coercive force at 150°C. HcJ 23 in the following mathematical expression 4 is the coercive force at 23°C.

[0174] β = 100 x (HcJ 150 - HcJ 23 ) / HcJ 23 (150 - 23) (4)

[0175] The measured values of the magnetic properties of the permanent magnets described above are shown in Tables 1 to 5 below.

[0176]

[0177]

[0178]

[0179] [Industrial Applicability]

[0180] The R-T-B based permanent magnet of one aspect of the present application is suitable as a material for, for example, an electric motor mounted on an electric automobile or a hybrid automobile.

Claims

1. An R-T-B based permanent magnet, wherein a rare earth element R, a transition metal element T, and B are contained, the R-T-B based permanent magnet contains at least Nd as the R, the R-T-B based permanent magnet contains at least Fe as the T, the R-T-B based permanent magnet includes a plurality of main phase particles and a plurality of R-rich phases, the plurality of main phase particles contain at least the R, the T, and the B, the plurality of R-rich phases contain at least the R, the plurality of main phase particles observed in a cross section of the R-T-B based permanent magnet are flat, the cross section is substantially parallel to a direction of an easy magnetization axis of the R-T-B based permanent magnet, each of the plurality of R-rich phases is located between the plurality of main phase particles, an average of intervals of the plurality of R-rich phases in a direction substantially perpendicular to the direction of the easy magnetization axis is 30 pm or more and 1000 pm or less, an average of lengths of short axes of the plurality of main phase particles observed in the cross section is 20 nm or more and 200 nm or less.

2. The R-T-B based permanent magnet according to claim 1, wherein a content of the R is 28 mass% or more and 33 mass% or less, a content of the B is 0.8 mass% or more and 1.1 mass% or less.

3. The R-T-B based permanent magnet according to claim 1 or 2, wherein the plurality of flat main phase particles are stacked along the direction of the easy magnetization axis.

4. The R-T-B based permanent magnet according to claim 1 or 2, which is a hot worked magnet.

5. The R-T-B based permanent magnet according to claim 1 or 2, wherein a concentration of the R in at least a part of the plurality of R-rich phases is higher than an average of concentrations of the R in the cross section, a unit of the concentration of the R is at%.

6. The R-T-B based permanent magnet according to claim 1 or 2, wherein a concentration of the R in at least a part of the plurality of R-rich phases is higher than a concentration of the R in the plurality of main phase particles, a unit of the concentration of the R is at%.

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