R-t-b based permanent magnet

Abstract

An R-T-B-based permanent magnet contains a rare earth element R, a transition metal element T, and B. 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 contains at least the R, the T, and the B. The plurality of R-rich phases contains at least the R. The plurality of main phase particles is flat when observed in a cross section of the R-T-B-based permanent magnet. The cross section is substantially parallel to an easy magnetization axis direction 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 the easy magnetization axis direction is 5 µm or more and is below a width of the R-T-B-based permanent magnet in the easy magnetization axis direction.

Description

Technical Field

[0001] This disclosure relates to an RTB-based permanent magnet. Background Technology

[0002] RTB-based permanent magnets contain rare earth elements R (such as Nd), transition metal elements T (such as Fe), and boron (B). RTB-based permanent magnets exhibit excellent magnetic properties and are widely used. RTB-based permanent magnets include sintered magnets manufactured by powder metallurgy and hot-worked magnets manufactured by thermoplastic processing. (Refer to Japanese Patent Application Publication Nos. 2017-50396, 2011-42837, 2012-174986, 2015-126213, 2016-46440, and 2016-76549.) Alloy strips used as raw materials for hot-worked magnets can be obtained through a splat cooling process. In this process, molten RTB alloy metal is rapidly cooled on the surface of a cooling roller. As a result, the molten metal solidifies, forming an alloy strip. The alloy ribbons obtained by quenching contain microcrystals (and amorphous alloys). Therefore, the grains (main phase particles) constituting the hot-worked magnet are finer than those of the sintered magnet. As shown in the Kronmuller equation, it is known that the finer the grain size of RTB-based permanent magnets, the greater the coercivity (HcJ). Therefore, hot-worked magnets should have higher coercivity than sintered magnets. However, the coercivity of existing hot-worked magnets is equal to that of sintered magnets with the same composition, and the high coercivity expected from fine grain size cannot be obtained. Summary of the Invention

[0003] Therefore, the inventors investigated and studied why existing RTB-based permanent magnets (e.g., hot-worked magnets) cannot achieve high coercivity corresponding to fine crystal grain size. As a result, the inventors discovered that the distribution of the R-rich phase in the cross-section of an RTB-based permanent magnet, which is approximately parallel to the easy magnetization axis, affects the coercivity. The inventors also discovered a method to obtain an RTB-based permanent magnet with high coercivity by controlling the distribution of the R-rich phase in the aforementioned cross-section.

[0004] One aspect of the present invention is to provide an RTB-based permanent magnet with high coercivity.

[0005] One aspect of the present invention provides an RTB-based permanent magnet containing rare earth element R, transition metal element T, and B, wherein the RTB-based permanent magnet contains at least Nd as R, the RTB-based permanent magnet contains at least Fe as T, the RTB-based permanent magnet comprises 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 main phase particles observed in the cross-section of the RTB-based permanent magnet are flat, the cross-section is substantially parallel to the easy magnetization axis direction of the RTB-based permanent magnet, each of the plurality of R-rich phases is located between the plurality of main phase particles, the average spacing of the plurality of R-rich phases in the easy magnetization axis direction is 5 μm or more and less than the width of the RTB-based permanent magnet in the easy magnetization axis direction.

[0006] The average length of the short axis of the multiple main phase particles observed in the above cross section can also be above 20 nm and below 200 nm.

[0007] The R content in RTB-based permanent magnets can be 28% by mass or more and 33% by mass or less, and the B content in RTB-based permanent magnets can be 0.8% by mass or more and 1.1% by mass or less.

[0008] At least some of the multiple R-rich phases may also contain oxides of R.

[0009] Multiple flat principal phase particles can also be stacked along the easy magnetization axis.

[0010] RTB series permanent magnets can also be heat-processed magnets.

[0011] The concentration of R in at least a portion of multiple R-rich phases can also be higher than the average concentration of R in the aforementioned cross sections, and the unit of R concentration can also be atoms.

[0012] The concentration of R in at least a portion of multiple R-rich phases can also be higher than the concentration of R in multiple main phase particles, and the unit of R concentration can also be atoms.

[0013] According to one aspect of the invention, an RTB-based permanent magnet with high coercivity can be provided. Attached Figure Description

[0014] Figure 1A This is a schematic perspective view of an RTB-based permanent magnet according to one embodiment of the present invention.

[0015] Figure 1B yes Figure 1A The diagram shows a cross-section of an RTB-type permanent magnet (a cross-sectional view along the bb line).

[0016] Figure 2 yes Figure 1B The enlarged view of a portion of the cross section (region II) and the brightness distribution of the backscattered electron image of region II are shown.

[0017] Figure 3 This is a backscattered electron image of the cross-section of the RTB-based permanent magnet in Example 4.

[0018] Figure 4 This is a backscattered electron image of the cross-section of the RTB-based permanent magnet in Comparative Example 1.

[0019] Figure 5 This is a backscattered electron image of the R-rich phase exposed in the cross section of the RTB-based permanent magnet in Example 4.

[0020] [Symbol Explanation]

[0021] 2……RTB series permanent magnet, 2cs……cross section of permanent magnet, 4……main phase particle (primary particle), 4a……secondary particle, 6……R-rich phase, C……direction of easy magnetization axis. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used to denote the same constituent elements. The present invention is not limited to the embodiments described below. The term "permanent magnet" as used below refers to an RTB-based permanent magnet. The concentrations of the elements in the permanent magnets described below are expressed in atomic percentages.

[0023] (Permanent magnet)

[0024] The permanent magnet of this embodiment contains at least rare earth elements (R), transition metal elements (T), and boron (B). The permanent magnet of this embodiment is a heat-worked magnet. However, the permanent magnet of the present invention can also be a sintered magnet.

[0025] Permanent magnets contain at least neodymium (Nd) as a rare earth element R. Permanent magnets may also contain other rare earth elements R besides Nd. These other rare earth elements R may be selected from at least one 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 B crystallization (single crystal or polycrystalline). Main phase particle 4 can also be composed solely of R2T. 14 The crystalline structure of B. R2T 14 Bode (B) can also crystallize into a tetragonal crystal. That is, R²T. 14 The crystallographic axes of B are the a-axis, b-axis, and c-axis, which are orthogonal to each other. R²T 14 The lattice constant of B along the a-axis can be related to R²T. 14 The lattice constants of B along the b-axis are equal, R²T14 The lattice constant of B along the c-axis can also differ from the lattice constants along the a-axis and b-axis. 14 The c-axis direction of B can also be approximately parallel to the easy magnetization axis direction C of the permanent magnet 2.

[0031] The main phase particle 4 may also contain other elements besides Nd, T, and B. For example, R2T, which constitutes the main phase particle 4, 14 B can also be expressed as (Nd) 1-x Pr x )2(Fe 1-y Co y ) 14 B. x can be greater than 0 and less than 1. y can also be greater than 0 and less than 1. The main phase particle 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 be replaced by other elements such as carbon (C). The composition within the main phase particle 4 can also be homogeneous. Alternatively, the composition within the main phase particle 4 can be non-homogeneous. For example, the concentration distributions of R, T, and B in the main phase particle 4 can also exhibit gradients.

[0032] The main phase particle 4 can also be composed of a surface portion and a central portion covered by the surface portion. The surface portion can also be referred to as a shell, and the central portion can also be referred to as a core. The surface portion of the main phase particle 4 can also contain at least one heavy rare earth element selected from Tb and Dy. The surface portion of each of all the main phase particles 4 can also contain at least one heavy rare earth element selected from Tb and Dy. The surface portion of a portion of all the main phase particles 4 can also contain at least one heavy rare earth element selected from Tb and Dy. By containing heavy rare earth elements in the surface portion, the anisotropic magnetic field is more likely to increase locally near the grain boundary, making it difficult to generate a nucleus with magnetization reversal near the grain boundary. As a result, the coercivity of the permanent magnet 2 at high temperatures (e.g., 100–200 °C) increases. The remanent magnetic flux density (Br) and coercivity of the permanent magnet 2 can be balanced, therefore, the total concentration of heavy rare earth elements in the surface portion can be higher than the total concentration of heavy rare earth elements in the central portion.

[0033] 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 besides R. At least a portion of the R-rich phase 6 may also contain oxides of R. 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 the R-rich phase 6. The R-rich phase 6 may also consist solely of oxides of R. The inventors believe that the R-rich phase 6 containing oxides of R is formed by the oxidation of R near the surface of the alloy strip or alloy powder (the precursor of the main phase particles 4) in the manufacturing process of the permanent magnet 2 (especially the conveying processes described later). The R-rich phase 6 may also contain at least one component selected from oxides, metals, alloys, and intermetallic compounds.

[0034] 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.

[0035] 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 R-rich phase 6. At least 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. At least a portion of the R-rich phase can also be dispersed in section 2cs. For example, at least a portion of the R-rich phase 6 can also be dispersed in section 2cs in a direction substantially perpendicular to the easy magnetization axis direction C. At least a portion of the R-rich phase 6 can also be located between multiple flat principal phase particles 4 stacked along the easy magnetization axis direction C.

[0036] The average value i of the R-rich phase 6 spacing along the easy magnetization axis C AVE The width of the permanent magnet 2 in the easy magnetization axis direction C is less than or equal to 5 μm. The average value i of the spacing of the R-rich phase 6 in the easy magnetization axis direction C. AVE It can also be 5μm or larger and 50μm or smaller, 5μm or larger and 10μm or smaller, 5.414μm or larger and 9.217μm or smaller, or 7.9μm or larger and 9.217μm or smaller. The average value i of the intervals of R-rich phase 6 is... AVEWithin 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 along the easy magnetization axis C. AVE It can also be approximately equal to the average value of the combined widths of one or more main phase particles 4 located between a pair of R-rich phases 6 along the easy magnetization axis C. The average value of the spacing of the R-rich phases 6 along the easy magnetization axis C can be determined by the following method.

[0037] 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, 1000x. Figure 2 As shown, a rectangular measurement region A is formed by arbitrarily arranging multiple high-brightness portions (6) along the easy magnetization axis direction C from the backscattered electron image. The width of the measurement region A along the easy magnetization axis direction C can also be larger than the width of the measurement region A in the direction perpendicular to the easy magnetization axis direction C. For example, the width of the measurement region A along the easy magnetization axis direction C can be 80 μm, and the width of the measurement region A in the direction perpendicular to the easy magnetization axis direction C can be 10 μm. By scanning the measurement region A with an electron beam along the easy magnetization axis direction C, the brightness of each measurement point in the measurement region A can be continuously measured along the easy magnetization axis direction C. As a result, the brightness distribution D of the measurement region A along the easy magnetization axis direction C can be obtained. The interval between measurement points can, for example, be less than 1 μm. Brightness is the intensity of the backscattered electron beam at each measurement point ( Figure 2 The term "intenseness" is used. The unit of brightness is arbitrary units (au). The larger the atomic mass of an element, the higher the brightness at the measurement point; the higher the concentration of elements with large atomic mass at the measurement point, the higher the brightness at that point. Among all the elements contained in permanent magnet 2, R has a relatively large atomic mass. Therefore, the peak value of the brightness distribution D suggests the presence of an R-rich phase. The moving average I of brightness is calculated based on the brightness of any measurement point X within measurement area A, the brightness of each of the five measurement points measured before the measurement of the brightness of measurement point X, and the brightness of each of the five measurement points measured immediately after the measurement of the brightness of measurement point X. AVE That is, the moving average I of the brightness is calculated based on the brightness of a total of 11 measurement points, including measurement point X. AVE Subtract I from the brightness at measurement point X AVE The value is I AVE When the brightness at measurement point X is above 5%, it is a phase rich in R phase 6. That is, when the brightness at measurement point X is I... AVE In cases where the brightness of measurement point X is above 105%, the location of the measurement point X (the peak value of the brightness of measurement point X) is... Figure 2The "POSITION" in the figure refers to the position of the R-rich phase 6. The distance between two adjacent R-rich phase 6s along the easy magnetization axis C is the interval of the R-rich phase 6s. Based on the above premises, the average value of the intervals of the R-rich phase 6s within the measurement area A is calculated. For example, in Figure 2 Within the measurement area A shown, there are 4 R-rich phases 6. As the intervals between the R-rich phases 6, i1, i2 and i3 can be measured. Figure 2 The average interval of R-rich phase 6 in the measurement area A shown is (i1+i2+i3) / 3.

[0038] Multiple different measurement regions A are selected within the backscattered electron image, and the average value of the intervals of the R-rich phase 6 in each measurement region A is determined using the method described above. For example, five measurement regions A can be selected from the backscattered electron image. The average value i described above is obtained by further averaging the average values ​​of the intervals of the R-rich phase 6 in each of the multiple measurement regions A. AVE .also, Figure 2 The average line (100% line) of the brightness distribution D in the image can also be a curve.

[0039] The R-rich phase 6 is the cause of the reduced coercivity of the permanent magnet 2. However, the permanent magnet 2 of this embodiment can have a higher coercivity than a conventional permanent magnet with the same composition. In other words, the permanent magnet 2 according to this embodiment can suppress the reduction in coercivity caused by the R-rich phase 6. The mechanism for suppressing the reduction in coercivity caused by the R-rich phase 6 will be described below. However, the technical scope of the present invention is not limited to the mechanism described below.

[0040] The coercivity mechanism of RTB-based permanent magnets is nucleation-type; therefore, the formation of reverse magnetic domains becomes the nucleus for magnetization reversal. That is, the formation of reverse magnetic domains is the cause of reduced coercivity. Reverse magnetic domains are formed from locations with strong local reverse magnetic fields. These locations include pores, the surface of principal phase particles, and heterogeneous phases.

[0041] <Porosity>

[0042] Both sintered magnets and hot-worked magnets are densified to approximately true density, thus making them less prone to porosity.

[0043] <Surface of main phase particles>

[0044] The shape of the main phase particles constituting the sintered magnet reflects the shape of the alloy powder obtained by air jet milling. Therefore, the main phase particles constituting the sintered magnet are irregular (deformed). The surface of the irregularly shaped main phase particles is not smooth, and therefore, they are prone to become the starting point for the generation of reverse magnetic domains.

[0045] On the other hand, the main phase particles constituting hot-worked magnets are plate-shaped crystals formed from extremely fine grains through anisotropic crystal growth. As a result, the main phase particles constituting hot-worked magnets have a more uniform shape, and their surfaces are smoother than those of sintered magnets. Therefore, the local reverse magnetic field is small on the surface of the main phase particles constituting hot-worked magnets, making it difficult to generate reverse magnetic domains. Consequently, hot-worked magnets tend to possess high coercivity.

[0046] <Strange Phenomena>

[0047] Sintered magnets are densified through a sintering process. In this process, a shaped body formed from alloy powder is sintered. During sintering, the surface of the alloy powder becomes a liquid phase, which fills the gaps between the powder particles, forming a grain boundary phase (R-rich phase), thus resulting in a dense sintered body. The two-grain boundary phase is useful for magnetic separation, preventing the movement of magnetic walls between the main phase particles. The remaining grain boundary phase components, other than the two-grain boundary phase, are expelled from the surface of the sintered body, but in very small quantities, mostly segregating at grain boundary multipoints. Grain boundary phases segregated at grain boundary multipoints are useless. This is because these phases become heterogeneous, serving as the starting point for the formation of opposite magnetic domains. However, as mentioned above, a liquid phase is required for densification of sintered magnets; therefore, the segregation of the grain boundary phase (R-rich phase) towards grain boundary multipoints is unavoidable.

[0048] On the other hand, the densification of hot-worked magnets depends on the temperature and pressure of hot pressing and hot-deforming. Therefore, the densification of hot-worked magnets does not require the grain boundary phase found in sintered magnets. Regarding the grain boundary phase as a liquid phase, it is useful for the lubrication (grain boundary slip) of the main phase particles when anisotropically grown plate-like particles are rearranged through hot-deforming. However, the amount of liquid phase required for the lubrication of the main phase particles can be less than that required for the densification of sintered magnets. Therefore, hot-worked magnets exhibit less segregation at multiple points along the R-rich phase grain boundaries than sintered magnets. That is, hot-worked magnets have less of this segregation. Therefore, hot-worked magnets tend to possess high coercivity.

[0049] However, hot-worked magnets inevitably contain a red-rich phase. In this red-rich phase, reverse magnetic domains are easily generated, and the red-rich phase becomes the nucleus for magnetization reversal. Starting from this magnetization reversal nucleus, magnetization reversal occurs in the main phase particles, and the coercivity of the permanent magnet decreases.

[0050] As described above, in existing sintered magnets and hot-worked magnets, a decrease in coercivity is caused by the R-rich phase. In contrast, in the case of the permanent magnet 2 of this embodiment, the spacing of the R-rich phases 6 in the easy magnetization axis direction C is larger. That is, in the case of the permanent magnet 2 of this embodiment, the average value i of the spacing of the R-rich phases 6 in the easy magnetization axis direction C is larger. AVE The size becomes greater than 5 μm. As a result, the generation frequency of reverse magnetic domains in the easy magnetization axis direction C is reduced, suppressing the decrease in coercivity caused by the R-rich phase 6. The larger the width (or, the thickness of the alloy strip described later) of each main phase particle 4 in the easy magnetization axis direction C, the smaller the specific surface area of ​​each main phase particle 4. The smaller the specific surface area of ​​each main phase particle 4, the easier it is to suppress the oxidation of the surface of each main phase particle 4, and the less likely it is to form the R-rich phase caused by oxidation. As a result, the average value i of the spacing of the R-rich phase 6 in the easy magnetization axis direction C is increased. AVE The coercivity of the permanent magnet 2 is easily increased. On the other hand, the larger the width (or, the thickness of the alloy strip described later) of each main phase particle 4 in the easy magnetization axis direction C, the larger the particle size (crystal grain size) of the main phase particles 4. As the particle size (crystal grain size) of the main phase particles 4 increases, the coercivity of the permanent magnet 2 is easily decreased. However, according to this embodiment, the oxidation of the alloy strip and alloy powder is suppressed in each conveying process described later, and the formation of the R-rich phase is suppressed. Therefore, according to this embodiment, the average value i of the spacing of the R-rich phase 6 can be taken into account. AVE The increase in coercivity is caused by the increase in the size of the main phase particles 4 (crystal size) and the increase in coercivity is caused by the decrease in the size of the main phase particles 4 (crystal size).

[0051] The average length of the minor axis of the principal phase particles 4 (primary particles) observed at the aforementioned cross section 2cs can, for example, be between 20 nm and 200 nm. When the average length of the minor axis of the principal phase particles 4 is within the aforementioned range, it is easier to obtain the average value i of the spacing of the R-rich phase 6 along the easy magnetization axis direction C. AVE The length of the short axis of the main phase particle 4 is controlled within the above range. The larger the average length of the short axis of the main phase particle 4, the larger the average length of the R-rich phase 6 spacing along the easy magnetization axis direction C. AVEThe larger the average length of the short axis of the principal phase particle 4, the higher the coercivity of the permanent magnet 2 tends to be. The average length of the long axis of the principal phase particle 4 (primary particle) observed in the above section 2cs can, for example, be more than 100 nm and less than 1000 nm. The short axis of each principal phase particle 4 observed in section 2cs can also be approximately parallel to the easy magnetization axis direction C. The long axis of each principal phase particle 4 can also be approximately perpendicular to the easy magnetization axis direction C. The shape of the principal phase particle 4 in section 2cs is not limited to a rectangle. The shape of the principal phase particle 4 in section 2cs can also be deformed. The shape of the principal phase particle 4 in section 2cs can also be different. In the case of a deformed shape of the principal phase particle 4 in section 2cs, the shape of the principal phase particle 4 can also be approximated by the quadrilateral with the smallest area among the quadrilaterals circumscribed by the principal phase particle 4. The quadrilateral can also be a rectangle. The length of the short side of the quadrilateral can also be regarded as the length of the short axis of the principal phase particle 4, and the length of the long side of the quadrilateral can also be regarded as the length of the long axis of the principal phase particle 4. The average length of the minor axis of the principal phase particles 4 can also be calculated based on the measured lengths of the minor axes of all principal phase particles 4 present in a backscattered electron image of cross section 2cs taken by a scanning electron microscope (SEM). The average length of the major axis of the principal phase particles 4 can also be calculated based on the measured lengths of the major axes of all principal phase particles 4 present in the aforementioned backscattered electron images. However, the size of the principal phase particles 4 that spills out of the backscattered electron images is excluded from the calculation of the average value. The maximum size of the backscattered electron images used to measure the lengths of the minor and major axes of the principal phase particles 4 can be, for example, 120 μm × 80 μm or 88 μm × 126 μm. Alternatively, representative locations within these backscattered electron images taken at low magnification can be selected, and backscattered electron images of each location can be taken at high magnification. Furthermore, the average lengths of the major and minor axes can be calculated based on the lengths of the major and minor axes of all principal phase particles 4 measured in the high-magnification backscattered electron images. Commercially available image analysis software can also be used to determine the shape (outline) of the main phase particle 4 and the size of the main phase particle 4 (the quadrilateral circumscribed with the main phase particle 4).

[0052] The width of each R-rich phase 6 along the easy magnetization axis C can, for example, be 100 nm or more and 1000 nm or less. When the width of the R-rich phase 6 along the easy magnetization axis C is within the above range, it is easy to suppress the magnetization reversal of the main phase particle 4, and the permanent magnet 2 easily has high coercivity. The width of the R-rich phase 6 along the easy magnetization axis C can also be smaller than the length of the minor axis of the main phase particle 4 (primary particle). The width of the R-rich phase 6 along the easy magnetization axis C can also be smaller than the length of the minor axis of the secondary particle 4a.

[0053] The width of the permanent magnet 2 along the easy magnetization axis C is greater than the average value of the spacing of the R-rich phase 6 along the easy magnetization axis C. AVE The lower limit is much larger. The width of the permanent magnet 2 in the direction of the easy magnetization axis C can, for example, be more than a few mm and less than several hundred mm, or more than tens of mm and less than several hundred mm. The longitudinal width of the permanent magnet 2 in the direction perpendicular to the easy magnetization axis C can, for example, be more than a few mm and less than several hundred mm, or more than tens of mm and less than several hundred mm. The transverse width of the permanent magnet 2 in the direction perpendicular to the easy magnetization axis C can, for example, be more than a few mm and less than several hundred mm, or more than tens of mm and less than several hundred mm.

[0054] Grain boundary phases other than R-rich phase 6 may also be included within the grain boundaries. For example, grain boundaries may also contain grain boundary phases containing elements introduced into the permanent magnet 2 through the grain boundary diffusion process described later. The elements introduced into the permanent magnet 2 through the grain boundary diffusion process may also be at least one heavy rare earth element selected from Tb and Dy. The elements introduced into the permanent magnet 2 through the grain boundary diffusion process may be heavy rare earth elements and light rare earth elements, and the light rare earth elements may also be at least one selected from Nd and Pr. The elements introduced into the permanent magnet 2 through the grain boundary diffusion process may also be heavy rare earth elements, light rare earth elements, and copper.

[0055] The main phase particles 4 and the R-rich phase 6 can each be identified based on the contrast of images of the cross-section 2cs of the permanent magnet 2 taken by scanning electron microscopy (SEM) or scanning transmission electron microscopy (STEM). The composition of the main phase particles 4 and the R-rich phase 6 can also be analyzed by an electron probe microanalyzer (EPMA) equipped with energy-dispersive X-ray spectroscopy (EDS).

[0056] The overall composition of permanent magnet 2 is described below. However, the composition of permanent magnet 2 is not limited to the composition described below. The content of each element in permanent magnet 2 may also deviate from the ranges described below.

[0057] 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. 14B 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.

[0058] 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.

[0059] 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 B content is 0.70% by mass or more, the remanent magnetic flux density tends to increase. When the B content is 1.10% by mass or less, the coercivity of the permanent magnet 2 tends to increase. When the B content is within the above range, the rectangularity ratio (Hk / HcJ) of the permanent magnet 2 tends to approach 1.0. Hk is the strength of the demagnetizing field, which corresponds to 90% of the remanent magnetic flux density, in the second quadrant of the magnetization curve.

[0060] 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 high. 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 towards the stress direction, the grain filling rate in permanent magnet 2 tends to increase, and the coercivity and remanent flux density of permanent magnet 2 tend to increase.

[0061] The permanent magnet 2 may also contain gallium (Ga). The Ga content may be 0.03% by mass or more and 1.00% by mass or less, or 0.20% by mass or more and 0.80% by mass or less. When the Ga content is within the above range, by appropriately suppressing the formation of secondary phases (e.g., phases containing R, T, and Ga), the remanent magnetic flux density and coercivity of the permanent magnet 2 can be easily increased. However, the permanent magnet 2 may also not contain Ga.

[0062] The permanent magnet 2 may also contain aluminum (Al). The Al content in the permanent magnet 2 may be 0.01% by mass or more and 0.2% by mass or 0.04% by mass or more and 0.07% by mass. When the Al content is within the above range, the coercivity and corrosion resistance of the permanent magnet are easily improved. However, the permanent magnet 2 may also not contain Al.

[0063] The permanent magnet 2 may also contain copper (Cu). The Cu content in the permanent magnet 2 may be 0.01% by mass or more and 1.50% by mass or less, or 0.04% by mass or more and 0.50% by mass or less. By keeping the Cu content within the above range, the coercivity, corrosion resistance, and temperature characteristics of the permanent magnet 2 are easily improved. However, the permanent magnet 2 may also not contain Cu.

[0064] The permanent magnet 2 may also contain cobalt (Co). The Co content in the permanent magnet may be 0.30% by mass or more and 6.00% by mass or more and 4.00% by mass or less. By containing Co, the Curie temperature of the permanent magnet 2 is easily increased. Furthermore, by containing Co, the corrosion resistance of the permanent magnet 2 is easily improved. However, the permanent magnet 2 may also not contain Co.

[0065] The remainder after removing the aforementioned elements from the permanent magnet 2 may consist only of Fe, or Fe and other elements. For the permanent magnet 2 to possess sufficient magnetic properties, the total content of elements other than Fe in the remainder may be less than 5% by mass relative to the total mass of the permanent magnet 2.

[0066] As other elements (e.g., unavoidable impurities), the permanent magnet 2 may contain at least one selected from silicon (Si), titanium (Ti), manganese (Mn), zirconium (Zr), 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 content of other elements in the permanent magnet 2 may also be 0.001% by mass or more and 0.50% by mass.

[0067] The overall composition of the permanent magnet 2 can also be analyzed by methods such as fluorescence X-ray (XRF) analysis, high-frequency inductively coupled plasma (ICP) luminescence analysis, inert gas melting-nondispersive infrared absorption (NDIR) method, combustion in oxygen flow-infrared absorption method, and inert gas melting-thermal conductivity method.

[0068] Permanent magnet 2 can also be used in electric motors, generators, or actuators. For example, permanent magnet 2 can be used in a wide variety of fields such as hybrid vehicles, electric vehicles, hard disk drives, magnetic resonance imaging (MRI) devices, smartphones, digital cameras, slim TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators, and wind turbines.

[0069] (Manufacturing method of permanent magnets)

[0070] The method for manufacturing a permanent magnet according to this embodiment includes at least: a strip fabrication step, a first conveying step, a crushing / grading step, a second conveying step, a thermoforming step, a third conveying step, and a thermoplastic processing step. The method for manufacturing a permanent magnet may also include other steps such as a grain boundary diffusion step following the thermoplastic processing step. However, the grain boundary diffusion step is not mandatory.

[0071] The inventors believe that the R-rich phase is formed by the oxidation of R contained in the vicinity of the surface of alloy strips or alloy powders during the manufacturing process of permanent magnets. To suppress the formation of the R-rich phase, the following steps can be performed in a non-oxidizing atmosphere. However, if each step is performed only in a non-oxidizing atmosphere, it is difficult to achieve an average value i of the R-rich phase spacing along the easy magnetization axis. AVE The value is controlled to be greater than 5 μm. This is to increase the average value of the R-rich phase spacing along the easy magnetization axis. AVE To achieve a value of 5μm or higher, the oxygen concentration in the atmosphere of each conveying process must be controlled below a specified value. Details of each process are described below.

[0072] The ribbon fabrication process involves creating alloy ribbons from raw material alloys using a rapid cooling method. In this method, molten metal in a container is sprayed from a nozzle located at the front of the container onto the surface of a cooling roller. Upon contact with the surface of the cooling roller, the molten metal is instantly ejected by the high-speed rotating roller, forming multiple thin, ribbon-like strands. Through contact with the surface of the cooling roller, the molten metal is rapidly cooled and solidified, resulting in multiple thin alloy ribbons. A container is positioned in the direction in which the alloy ribbons are ejected by the cooling roller, and the alloy ribbons are collected into the container.

[0073] Molten metal is a metal containing the elements that constitute a permanent magnet (raw material metal). Raw material metals can be, for example, monomers of rare earth elements (metal monomers), alloys containing rare earth elements, pure iron, ferroborone alloys, or alloys containing them. These raw material metals are weighed in a manner consistent with the composition of the desired permanent magnet.

[0074] Molten metal can also be obtained by heating the raw material metal in the container using high-frequency induction heating. The temperature of the molten metal ejected from the nozzle (ejection temperature) can be, for example, about 1400°C. The heating rate of the raw material metal to reach the injection temperature can be, for example, about 20 to 100°C / second.

[0075] The surface of the cooling roller can also be made of a metal with high thermal conductivity, such as Cu. The temperature of the cooling roller surface can also be controlled by the refrigerant circulating within the cooling roller. For example, the cooling rate of the molten metal on the surface of the cooling roller can be set to approximately 10. 5 ~10 6 The surface temperature of the cooling roller is controlled in °C / second. A higher cooling rate results in a higher crystal density (R2T) in the alloy strip. 14 The finer the particle size of B), the higher the coercivity of the permanent magnet. The less molten metal is sprayed onto the surface of the cooling roller per unit time, the thinner the molten metal adhering to the surface of the cooling roller, the higher the cooling rate, and the thinner the alloy strip. The higher the circumferential speed of the cooling roller, the thinner the molten metal adhering to the surface of the cooling roller, the higher the cooling rate, and the thinner the alloy strip. The thickness of the main phase particles (the length of the minor axis of the main phase particles) in the direction of the easy magnetization axis depends on the thickness of the alloy strip (and the crushing and classification of the alloy strip). The thinner the alloy strip, the smaller the thickness (particle size) of the main phase particles, and the higher the coercivity of the permanent magnet tends to be. However, one reason for R-phase richness is the oxidation of the alloy strip surface; the thinner the alloy strip, the easier it is for thin, oxidized main phase particles to be included in the permanent magnet, and the spacing of R-phase richness in the direction of the easy magnetization axis tends to be smaller. To balance the high coercivity of the permanent magnets with the large spacing of the R-phase, the thickness of the alloy 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 strip can also be, for example, 1.0 mm or more and 5.0 mm or less.

[0076] To suppress the oxidation of molten metal, the atmosphere inside the container of molten metal can be replaced by an inert gas such as argon (Ar). The gas pressure inside the container of molten metal can be, for example, above 100 kPa and above 240 kPa.

[0077] Cooling rollers are disposed within the chamber. One reason for the presence of the R-rich phase is the preferential oxidation of R present near the surface of the alloy strip. To suppress the formation of the R-rich phase caused by the oxidation of the molten metal and alloy strip, the atmosphere within the chamber can be replaced with an inert gas such as argon (Ar). For the same reason, the atmosphere within the chamber can also contain a reducing gas such as hydrogen (H2) in addition to the inert gas. The concentration of hydrogen in the atmosphere within the chamber can, for example, be between 0.1% by mass and 0.5% by mass. The reducing properties of hydrogen in the atmosphere within the chamber further suppress the oxidation of the molten metal and alloy strip (formation of the R-rich phase). Therefore, by containing hydrogen in the atmosphere within the chamber, the spacing of the R-rich phases along the easy magnetization axis is more likely to be larger, and the average value of the R-rich phase spacing i AVE It is easy to achieve a spacing of 5 μm or more. With increasing hydrogen concentration in the chamber atmosphere, the spacing of the R-rich phase along the easy magnetization axis tends to increase, and the average spacing of the R-rich phase, i... AVE It is easy to achieve a thickness of 5 μm or more. The pressure inside the chamber can be, for example, 60 kPa or more and 200 kPa or less. The molten metal does not immediately cool to room temperature on the surface of the cooling roller. The temperature of the alloy strip immediately after solidification is still high, and the alloy strip continues to cool through heat conduction to the frame of the quenching device and the atmosphere inside the chamber. When the pressure inside the chamber is low (for example, when the pressure inside the chamber is 20 kPa), the heat conduction from the alloy strip to the atmosphere inside the chamber is small, and the cooling rate of the alloy strip slows down. With a slow cooling rate, relative to R2T 14 The stoichiometry of B results in an excess of R being discharged from the interior of the alloy ribbon to the surface. As a result, near the surface of the alloy ribbon, R becomes excessive, and oxides of R are easily formed on the surface of the alloy ribbon. The spacing of the R-rich phase in the direction of the easy magnetization axis is easily less than 5 μm.

[0078] The pressure inside the container of molten metal is higher than the pressure inside the chamber. The pressure difference between the container and the chamber is the pressure of the molten metal ejected from the nozzle (ejection differential pressure).

[0079] Following the strip fabrication process, a first conveying process is performed. This first conveying process involves transporting the alloy strip, fabricated by the quenching method, to the crushing / grading apparatus used in the crushing / grading process. The atmosphere in the first conveying process is a non-oxidizing atmosphere. That is, the alloy strip is maintained in a non-oxidizing atmosphere from the moment it is formed until it arrives at the crushing / grading apparatus. For example, the atmosphere in the conveying path connecting the quenching apparatus (a chamber equipped with cooling rollers) to the crushing / grading apparatus can also be a non-oxidizing atmosphere, and the alloy strip can be conveyed within this conveying path. Alternatively, the alloy strip contained in a container filled with a non-oxidizing atmosphere can be conveyed from the chamber to the crushing / grading apparatus. The atmosphere (non-oxidizing atmosphere) in the first conveying process can, for example, be an inert gas such as Ar. The oxygen concentration in the atmosphere of the first conveying process is between 0 ppm and 20 ppm by mass. The lower the oxygen concentration in the atmosphere of the first conveying process, the less likely the surface of the alloy strip is to be oxidized in the first conveying process, and the less likely multiple R-rich phases originating from the oxidized surface of the alloy strip are to be contained in the permanent magnet. As a result, the spacing of the R-rich phases along the easy magnetization axis tends to increase, and the average value of the R-rich phase spacing, i, increases. AVE It is easy to become 5μm or larger. On the other hand, when the oxygen concentration in the atmosphere of the first conveying process is higher than 20 ppm by mass, the spacing of the R-rich phase in the direction of the easy magnetization axis tends to become smaller, and the average value of the R-rich phase spacing i AVE It is easy to be below 5μm.

[0080] Following the first conveying process, a crushing / grading process is performed. This crushing / grading process involves crushing the alloy ribbon using a crushing device to produce coarse powder, grading the coarse powder, and thereby recovering alloy powder with a specified particle size. The alloy powder is a precursor to permanent magnets. The shape of each alloy particle constituting the alloy powder can also be plate-shaped or sheet-shaped. The crushing method for the alloy ribbon can be, for example, at least one of a cutting mill and a propeller mill. The grading mechanism for the coarse powder can be, for example, a sieve. The particle size and particle size distribution of the alloy powder obtained through grading can be determined, for example, by laser diffraction scattering. The particle size of the alloy powder obtained through grading can be, for example, 50 μm or more and 300 μm or less, preferably 50 μm or more and 200 μm or less. In other words, the inner diameter of the mesh of the sieve used for grading can be 50 μm or more and 300 μm or less, preferably 50 μm or more and 200 μm or less.

[0081] The specific surface area of ​​alloy powder is larger than that of alloy ribbon, therefore, alloy powder is more easily oxidized than alloy ribbon. (The specific surface area of ​​alloy ribbon is larger than that of a molded body formed from alloy powder, therefore, alloy ribbon is more easily oxidized than a molded body.) Furthermore, the smaller the particle size of the alloy powder, the larger its specific surface area, and the easier its surface is to oxidize. Through the oxidation of the alloy powder, multiple R-rich phases originating from the oxidized surface of the alloy powder are easily contained in the permanent magnet. Therefore, the smaller the particle size of the alloy powder, the smaller the spacing of the R-rich phases along the easy magnetization axis, and the greater the average value i of the R-rich phase spacing. AVE It is easy to find particle sizes below 5 μm. In other words, the larger the particle size of the alloy powder, the smaller the specific surface area of ​​the alloy powder, and the more it inhibits the oxidation of the alloy powder surface. By inhibiting the oxidation of the alloy powder, the number of R-rich phases contained in the permanent magnet is reduced. Therefore, the larger the particle size of the alloy powder, the easier it is for the spacing of R-rich phases in the direction of the easy magnetization axis to become larger, and the average value of the R-rich phase spacing i AVE It is easier to become 5μm or larger.

[0082] The atmosphere for the pulverizing / classifying process is a non-oxidizing atmosphere. By performing the pulverizing / classifying process in a non-oxidizing atmosphere, oxidation of alloy ribbons, coarse powder, and alloy powder during the pulverizing / classifying process is suppressed. As a result, the spacing of the R-rich phase in the direction of the easy magnetization axis tends to increase, and the average value i of the R-rich phase spacing increases. AVE It is easy to achieve a size greater than 5 μm. The atmosphere (non-oxidizing atmosphere) in the pulverizing / classifying process can be, for example, an inert gas such as Ar. The oxygen concentration in the atmosphere of the pulverizing / classifying process is between 0 ppm and 20 ppm by mass. The lower the oxygen concentration in the atmosphere of the pulverizing / classifying process, the easier it is for the spacing of the R-rich phase in the direction of the easy magnetization axis to increase, and the average value of the R-rich phase spacing i AVE The more easily it becomes 5μm or larger. On the other hand, when the oxygen concentration in the atmosphere of the pulverizing / classifying process is higher than 20 ppm by mass, the spacing of the R-rich phase in the direction of the easy magnetization axis tends to become smaller, and the average value of the R-rich phase spacing i AVE It is easy to be below 5μm.

[0083] After the crushing / classification process, a second conveying process can be performed. This second conveying process involves transporting the alloy powder obtained from the crushing / classification process to a forming apparatus used in the thermoforming process. The atmosphere in the second conveying process is a non-oxidizing atmosphere. That is, the alloy powder is maintained in a non-oxidizing atmosphere from the moment it is formed until it arrives at the forming apparatus. For example, the atmosphere in the conveying path connecting the crushing / classification apparatus to the forming apparatus can also be a non-oxidizing atmosphere, and the alloy powder can be conveyed within this conveying path. Alternatively, an alloy strip contained in a container filled with a non-oxidizing atmosphere can be conveyed from the crushing / classification apparatus to the forming apparatus. The atmosphere (non-oxidizing atmosphere) in the second conveying process can, for example, be an inert gas such as Ar. The oxygen concentration in the atmosphere of the second conveying process is between 0 ppm by mass and 20 ppm by mass. The lower the oxygen concentration in the atmosphere of the second conveying process, the less likely the surface of the alloy powder is to be oxidized in the second conveying process, and the less likely multiple R-rich phases originating from the oxidized surface of the alloy powder are to be contained in the permanent magnet. As a result, the spacing of the R-rich phases along the easy magnetization axis tends to increase, and the average value of the R-rich phase spacing, i, increases. AVE It is easy to become 5μm or larger. On the other hand, when the oxygen concentration in the atmosphere of the second conveying process is higher than 20 ppm by mass, the spacing of the R-rich phase in the direction of easy magnetization axis tends to become smaller, and the average value of the R-rich phase spacing i AVE It is easy to be below 5μm.

[0084] After the second conveying process, a thermoforming process can be performed. The thermoforming process involves heating alloy powder while applying pressure to form a molded body. For example, the alloy powder can be heated within a mold while being compressed through the mold. By pressurizing the alloy powder, the voids between the powder particles are reduced, resulting in a dense molded body. Furthermore, by heating the alloy powder while it is being pressurized, a liquid phase forms from the surface of the alloy powder. This liquid phase fills the voids (grain boundaries) between the powder particles, and the powder becomes lubricated by the liquid phase, thus obtaining a dense molded body. A cold forming process can also be performed before the thermoforming process. In the cold forming process, the alloy powder can be pressurized at room temperature to form a molded body. The molded body obtained through the cold forming process is then heated and pressurized in the thermoforming process, thereby densifying the molded body. The temperature of the alloy powder in the thermoforming process (thermoforming temperature) can, for example, be 700°C or higher and 800°C or lower. If the thermoforming temperature is too low, a sufficient liquid phase does not form from the surface of the alloy powder, making it difficult to densify the molded body. When the hot forming temperature is too high, the crystallization of the alloy powder (R2T) occurs. 14If particle growth in B) is excessive, the coercivity of the permanent magnet is easily reduced. The pressure applied to the alloy powder during the thermoforming process (thermoforming pressure) can be 50 MPa or more and 200 MPa or less. The time for which the thermoforming temperature and thermoforming pressure are maintained within the above range (thermoforming time) can be, for example, tens of seconds or more and hundreds of seconds or less.

[0085] The grain boundary phases formed during the thermoforming process are distributed relatively uniformly near the surface of each grain. Furthermore, the grain boundaries formed during the thermoforming process are finer than the R-rich phases induced by oxidation, making them difficult to detect in the measurement of R-rich phase spacing. Therefore, the grain boundary phases formed during the thermoforming process do not significantly affect the spacing of the R-rich phases induced by oxidation.

[0086] To suppress oxidation of the alloy powder and the molded body during the hot forming process, the hot forming process can also be carried out in a non-oxidizing atmosphere. The atmosphere (non-oxidizing atmosphere) for the hot forming process can be, for example, an inert gas such as Ar. The oxygen concentration in the atmosphere for the hot forming process can be, for example, 0 ppm by mass or more and 20 ppm by mass or less.

[0087] After the thermoforming process, a third conveying process is performed. This third conveying process involves transporting the molded body obtained from the thermoforming process to the molding apparatus used in the thermoplastic processing process. To suppress oxidation of the molded body, the atmosphere in the third conveying process can also be a non-oxidizing atmosphere. That is, from the moment the molded body is formed until it arrives at the molding apparatus for thermoplastic processing, the molded body can be maintained in a non-oxidizing atmosphere. For example, the atmosphere in the conveying path connecting the thermoforming molding apparatus to the thermoplastic processing molding apparatus can also be a non-oxidizing atmosphere, and the molded body can be conveyed within this conveying path. Alternatively, the molded body contained in a container filled with a non-oxidizing atmosphere can be conveyed from the thermoforming molding apparatus to the thermoplastic processing molding apparatus. The atmosphere in the third conveying process can be, for example, an inert gas such as Ar. The specific surface area of ​​the molded body formed from alloy powder is significantly smaller than that of the alloy powder and alloy strip, therefore, the molded body (especially the interior of the molded body) is less prone to oxidation than the alloy powder and alloy strip. Therefore, even when the oxygen concentration in the atmosphere of the third conveying process is higher than the oxygen concentration in the atmospheres of the first and second conveying processes, the average value i of the R-rich phase interval can still be achieved. AVE The size is controlled to be 5μm or larger. For example, when the atmosphere in the third conveying process is air, by reducing the oxygen concentration in the atmospheres of the first and second conveying processes, the average value i of the R-rich phase interval can be increased. AVEThe concentration of oxygen in the atmosphere of the third conveying process can be 0 ppm or more and 200,000 ppm or less by mass, preferably 0 ppm or more and 2,000 ppm or less by mass, and more preferably 0 ppm or more and 20 ppm or less by mass.

[0088] Following the third conveying process, a thermoplastic processing step is performed. The thermoplastic processing step involves hot extrusion molding of the molded body obtained through the thermoforming process to obtain multiple main phase particles (R2T) oriented in a specified direction along the c-axis (easily magnetized axis). 14 A magnet substrate (with grains of B). For example, in a thermoplastic processing step, the molded body is heated while being extruded from a mold. Inside the mold, the grain boundary phase in the heated molded body liquefies to form a liquid phase, which exerts stress on the molded body in a predetermined direction. With the formation of the liquid phase, anisotropic growth of grains occurs in the direction perpendicular to the c-axis of the grains. In addition, the liquid phase lubricates each grain, corresponding to the stress acting on each grain. As a result, the grains rotate by grain boundary slip, and the c-axis of each grain (main phase particle) is oriented approximately parallel to the stress direction. In other words, multiple flat main phase particles extending in a direction approximately perpendicular to the c-axis are stacked along the stress direction. The temperature of the molded body in the thermoplastic processing step (thermoplastic processing temperature) can, for example, be 700°C or higher and 800°C or lower. If the thermoplastic processing temperature is too low, it is difficult for the liquid phase to form in the grain boundaries of the molded body, anisotropic growth of grains is difficult to occur, and it is difficult to generate grain rotation caused by grain boundary slip. As a result, the c-axis of each grain is difficult to align approximately parallel to the stress direction, and the coercivity and remanent flux density of the magnet substrate tend to decrease. When the thermoplastic processing temperature is too high, excessive grain growth occurs, and the coercivity of the magnet substrate tends to decrease. The pressure applied to the molded body during the thermoplastic processing step (thermoplastic processing pressure) can be 50 MPa or more and 200 MPa or less. The time for which the thermoplastic processing temperature and thermoplastic processing pressure are maintained within the above range (thermoplastic processing time) can, for example, be tens of seconds.

[0089] The grain boundary phases formed during the thermoplastic processing are generally uniformly distributed near the surface of each grain. Furthermore, the grain boundaries formed during the thermoplastic processing are finer than the R-rich phases induced by oxidation, making them difficult to detect in the measurement of R-rich phase spacing. Therefore, the grain boundary phases formed during the thermoplastic processing have little effect on the spacing of the R-rich phases induced by oxidation.

[0090] To suppress oxidation of the molded body and the magnet substrate during the thermoplastic processing, the thermoplastic processing can be carried out in a non-oxidizing atmosphere. The atmosphere (non-oxidizing atmosphere) for the thermoplastic processing can be, for example, an inert gas such as Ar. The oxygen concentration in the atmosphere for the thermoplastic processing can be, for example, 0 ppm by mass or more and 20 ppm by mass or less.

[0091] The magnet substrate obtained through the above processes can also be a finished product of a permanent magnet. The magnet substrate obtained through the following grain boundary diffusion process can also be a finished product of a permanent magnet.

[0092] The following grain boundary diffusion process can also be performed after the thermoplastic processing step. The grain boundary diffusion process involves attaching a diffusion material containing heavy rare earth elements to the surface of a magnet substrate and heating both the diffusion material and the magnet substrate. Through heating the magnet substrate with the attached diffusion material, the heavy rare earth elements in the diffusion material diffuse from the surface of the magnet substrate into its interior. Inside the magnet substrate, the heavy rare earth elements diffuse through grain boundaries to the vicinity of the surface of the main phase particles. Near the surface of the main phase particles, some light rare earth elements (such as Nd) are replaced by heavy rare earth elements. Because the heavy rare earth elements are locally present near the surface of the main phase particles and at the grain boundaries, the anisotropic magnetic field locally increases near the grain boundaries, making it difficult to generate nuclei with magnetization reversal near the grain boundaries. As a result, a permanent magnet with high coercivity is obtained.

[0093] In the grain boundary diffusion process, the elements contained in the diffusion material diffuse approximately uniformly into the grain boundaries and grain surfaces within the magnetic substrate. Furthermore, the grain boundaries formed by the elements originating from the diffusion material are finer than the R-rich phase caused by oxidation, making them difficult to detect in the measurement of the R-rich phase spacing. Therefore, the elements originating from the diffusion material have little effect on the spacing of the R-rich phase caused by oxidation.

[0094] To suppress oxidation of the magnet substrate during the grain boundary diffusion process, the grain boundary diffusion process can be performed in a non-oxidizing atmosphere. The atmosphere (non-oxidizing atmosphere) for the grain boundary diffusion process can be, for example, an inert gas such as Ar. The oxygen concentration in the atmosphere for the grain boundary diffusion process can be, for example, 0 ppm by mass or more and 20 ppm by mass or less. The gas pressure in the atmosphere for the grain boundary diffusion process can be, for example, 50 kPa or more and 120 kPa or less. The temperature of the diffusion material and the magnet substrate in the grain boundary diffusion process (diffusion temperature) can be, for example, 550°C or more and 900°C or less. The time for which the diffusion temperature is maintained within the above range (diffusion time) can be, for example, 1 minute or more and 1440 minutes or less.

[0095] The diffusion material may also contain at least one heavy rare earth element selected from Tb and Dy. In addition to heavy rare earth elements, the diffusion material may also contain at least one light rare earth element selected from Nd and Pr. In addition to heavy and light rare earth elements, the diffusion material may also contain Cu. The diffusion material may, for example, be a metal composed of one of the above elements, a hydride of one of the above elements, an alloy containing multiple of the above elements, or a hydride of the alloy. The diffusion material may also be a powder. In the grain boundary diffusion process, a slurry containing the diffusion material and an organic solvent may be coated onto the surface of the magnet substrate. In the grain boundary diffusion process, a sheet containing the diffusion material and an adhesive may also be used to cover the surface of the magnet substrate. In the grain boundary diffusion process, an alloy foil (ribbon) composed of the diffusion material may also be used to cover the surface of the magnet substrate.

[0096] To promote the diffusion of the diffusion material, the surface of the magnetic substrate can be ground before the grain boundary diffusion process. To remove the diffusion material remaining on the surface of the magnetic substrate after the grain boundary diffusion process, the surface of the magnetic substrate can also be ground after the grain boundary diffusion process.

[0097] The size and shape of the magnet substrate can also be adjusted by cutting and grinding. A passivation layer can be formed on the surface of the magnet substrate through oxidation or chemical treatment. A protective film, such as a resin film, can also be used to cover the surface of the magnet substrate. Through passivation layers or protective films, the corrosion resistance of permanent magnets is improved.

[0098] This invention is not necessarily limited to the embodiments described above. Various modifications can be made to this invention without departing from its spirit, and these modifications are also included in this invention.

[0099] [Example]

[0100] The present invention will be described in detail through the following embodiments and comparative examples. The present invention is not limited to the following embodiments.

[0101] <Making of Permanent Magnets>

[0102] (Example 1)

[0103] In the strip fabrication process, alloy strips are produced from raw material alloys using a rapid cooling method. The raw material metals (molten metals) used in the strip fabrication process contain Nd, Fe, Co, Ga, Al, and B.

[0104] The Nd content in the raw metal was 30.17% by mass.

[0105] The Co content in the raw metal is 3.96% by mass.

[0106] The Ga content in the raw material metal is 0.59% by mass.

[0107] The Al content in the raw metal is 0.04% by mass.

[0108] The boron content in the raw metal is 0.97% by mass.

[0109] The balance of raw material metals other than Nd, Co, Ga, Al and B is Fe.

[0110] The temperature of the molten metal ejected from the nozzle (ejection temperature) is 1400°C. The heating rate until the raw material metal reaches the injection temperature is 100°C / second. The cooling rate of the molten metal on the surface of the cooling roller is controlled at approximately 10°C / second. 5 °C / sec. Nozzle orifice diameter is 0.6 mm. Circumferential speed of cooling roller is 40 m / sec.

[0111] The gas inside the nozzle (the atmosphere inside the container of molten metal) is Ar. The pressure inside the nozzle (the gas pressure inside the container of molten metal) is 100 kPa.

[0112] The gas (atmosphere) in the chamber equipped with the cooling roller is Ar. The hydrogen concentration in the atmosphere within the chamber is 0.00% by mass. The pressure within the chamber (gas pressure) is 60 kPa. The injection differential pressure is 40 kPa.

[0113] In the first conveying step after the strip fabrication process, the alloy strip is conveyed from the quenching unit to the crushing / grading unit. The gas (atmosphere) in the first conveying step is Ar. The oxygen concentration in the atmosphere of the first conveying step is 20 ppm by mass.

[0114] In the crushing / grading process following the first conveying step, alloy powder with a specified particle size is produced by crushing and grading the alloy strip. The lower limit of the inner diameter of the mesh of the sieve used for grading is 50 μm. The upper limit of the inner diameter of the mesh of the sieve used for grading is 200 μm. Therefore, the particle size of the alloy powder is in the range of 50 μm or more and 200 μm or less.

[0115] The gas (atmosphere) for the pulverizing / classifying process is Ar. The oxygen concentration in the atmosphere for the pulverizing / classifying process is 20 ppm by mass.

[0116] In the second conveying step following the crushing / grading process, the alloy powder is conveyed from the crushing / grading device to the forming device. The gas (atmosphere) in the second conveying step is Ar. The oxygen concentration in the atmosphere of the second conveying step is 20 ppm by mass.

[0117] In the thermoforming process following the second conveying step, alloy powder inside the mold is heated while being compressed through the mold to create a molded body. The molded body is a thin sheet. The length of the molded body is 80 mm, the width is 22 mm, and the thickness is 11 mm. The thermoforming temperature is 750℃. The thermoforming pressure is 100 MPa. The thermoforming time is 300 seconds. The gas (atmosphere) in the thermoforming process is Ar. The oxygen concentration in the atmosphere of the thermoforming process is 20 ppm by mass.

[0118] In the third conveying step after the thermoforming process, the molded part is conveyed from the thermoforming molding apparatus to the thermoplastic processing molding apparatus. The gas (atmosphere) in the third conveying step is Ar. The oxygen concentration in the atmosphere of the third conveying step is 20 ppm by mass.

[0119] Following the third conveying process, a thermoplastic processing step is performed. The thermoplastic processing step (thermal extrusion molding of the molded body) uses a cylindrical mold. That is, the mold cavity extends from the end face of the mold (starting end face) opening at the inlet for the molded body to the end face of the mold (ending end face) opening at the extrusion port for the molded body. The starting and ending end faces are parallel planes. The direction from the starting end face to the ending end face is the extrusion direction of the molded body, and the extrusion direction is perpendicular to both the starting and ending end faces. The opening area of ​​the extrusion port is smaller than the opening area of ​​the inlet for the molded body.

[0120] The chamber is divided into an inlet-side region, an intermediate region, and an extrusion port-side region along the extrusion direction. The inlet-side region opens on the starting end face. The extrusion port-side region opens on the ending end face. The intermediate region is located between the inlet-side region and the extrusion port-side region along the extrusion direction.

[0121] The cavity shape on the cross-section of the die perpendicular to the extrusion direction (the cross-section of the die parallel to the starting end face and the ending end face) is a quadrilateral with all four corners being right angles. The pair of sides facing each other in this quadrilateral is referred to as the first side, and the other pair of sides facing each other in the quadrilateral is referred to as the second side.

[0122] The lengths of the first and second sides in the inlet-side region are constant. That is, the opening area of ​​the inlet-side region in a cross-section perpendicular to the extrusion direction is constant. In the middle region, the length of the first side gradually decreases along the extrusion direction, eventually matching the length of the first side in the extrusion outlet-side region. Therefore, the first side in the extrusion outlet-side region is shorter than the first side in the inlet-side region. Furthermore, in the middle region, the length of the second side gradually increases along the extrusion direction, eventually matching the length of the second side in the extrusion outlet-side region. Therefore, the second side in the extrusion outlet-side region is longer than the second side in the inlet-side region. Additionally, the opening area of ​​the middle region in a cross-section perpendicular to the extrusion direction gradually decreases along the extrusion direction, eventually matching the opening area of ​​the extrusion outlet-side region in a cross-section perpendicular to the extrusion direction. Therefore, the opening area of ​​the extrusion outlet-side region in a cross-section perpendicular to the extrusion direction is smaller than the opening area of ​​the inlet-side region in a cross-section perpendicular to the extrusion direction. The lengths of the first and second sides in the extrusion outlet-side region are constant. That is, the opening area of ​​the extrusion outlet-side region in a cross-section perpendicular to the extrusion direction is constant.

[0123] The length of the first side of the inlet-side region (starting end face) is 22 mm, and the length of the second side of the inlet-side region (starting end face) is 11 mm. The length of the first side of the extrusion outlet-side region (ending face) is 7 mm, and the length of the second side of the extrusion outlet-side region (ending face) is 30 mm. The length of the inlet-side region in the extrusion direction is 80 mm. The length of the intermediate region in the extrusion direction is 20 mm. The length of the extrusion outlet-side region in the extrusion direction is 20 mm.

[0124] As described above, the opening area of ​​the extrusion port side region in the cross-section perpendicular to the extrusion direction is smaller than the opening area of ​​the inlet side region in the cross-section perpendicular to the extrusion direction, and the first side of the extrusion port side region (terminal surface) is shorter than the second side of the extrusion port side region (terminal surface). Therefore, in the extrusion port side region, a stress approximately parallel to the first side acts on the molded body, resulting in grain boundary slip and rotation of the main phase particles. As a result, the c-axis of the main phase particles is oriented along the stress direction (the direction of the first side). That is, the easy magnetization axis direction of the magnet substrate obtained by thermo-extrusion molding is the direction of the first side in the extrusion port side region (terminal surface).

[0125] In the thermoplastic processing step, the magnet substrate is manufactured by hot extrusion molding of the molded body using the aforementioned mold. The temperature at the mold inlet is 750°C. The temperature at the extrusion outlet is also 750°C. The thermoplastic processing pressure is 100 MPa. The extrusion speed of the hot extrusion molding is 1 mm / s.

[0126] The gas (atmosphere) for the thermoplastic processing step is Ar. The oxygen concentration in the atmosphere for the thermoplastic processing step is 20 ppm by mass.

[0127] In the grain boundary diffusion process following the thermoplastic processing, the magnet substrate with the diffusion material attached is heated. The diffusion material is a powder of a hydride of a eutectic alloy composed of Nd, Tb, and Cu. In the grain boundary diffusion process, a slurry, which is a mixture of the diffusion material and an organic solvent, is applied to the entire surface of the magnet substrate. The Nd content in the diffusion material is 66% by mass. The Tb content in the diffusion material is 24% by mass. The Cu content in the diffusion material is 10% by mass. The mass of the diffusion material attached to the magnet substrate is adjusted so that the Tb content in the permanent magnet (the magnet substrate after the grain boundary diffusion process) is consistent with 2% by mass.

[0128] The gas (atmosphere) for the grain boundary diffusion process is Ar. The pressure (atmosphere pressure) for the grain boundary diffusion process is 100 kPa. The diffusion temperature is 650℃. The diffusion time is 300 minutes.

[0129] The permanent magnet of Example 1 was produced using the methods described above.

[0130] (Example 2, Comparative Examples 1-6)

[0131] The gases (atmospheres) in the first conveying process of Examples 2 and Comparative Examples 1-6 are shown in Table 1 below. The oxygen concentration in the atmosphere of the first conveying process of Examples 2 and Comparative Examples 1-6 is shown in Table 1 below.

[0132] The gases (atmospheres) in the second conveying process of Examples 2 and Comparative Examples 1-6 are shown in Table 1 below. The oxygen concentrations in the atmospheres of the second conveying processes of Examples 2 and Comparative Examples 1-6 are shown in Table 1 below.

[0133] The gases (atmospheres) in the third conveying process of Examples 2 and Comparative Examples 1-6 are shown in Table 1 below. The oxygen concentration in the atmosphere of the third conveying process of Examples 2 and Comparative Examples 1-6 is shown in Table 1 below.

[0134] Permanent magnets for Examples 2 and Comparative Examples 1 to 6 were produced using the same methods as in Example 1, except for the matters described above.

[0135] (Comparative Example 7)

[0136] The oxygen concentration in the atmosphere of the first conveying step of Comparative Example 7 is shown in Table 2 below. The permanent magnet of Comparative Example 7 was manufactured by the same method as in Example 1, except for the oxygen concentration in the atmosphere of the first conveying step.

[0137] (Comparative Example 8)

[0138] The oxygen concentration in the atmosphere of the second conveying step of Comparative Example 8 is shown in Table 3 below. The permanent magnet of Comparative Example 8 was manufactured by the same method as in Example 1, except for the oxygen concentration in the atmosphere of the second conveying step.

[0139] (Example 3)

[0140] The oxygen concentration in the atmosphere of the third conveying step in Example 3 is shown in Table 4 below. The permanent magnet of Example 3 was manufactured by the same method as in Example 1, except for the oxygen concentration in the atmosphere of the third conveying step.

[0141] (Examples 4-6)

[0142] The concentrations of hydrogen in the atmosphere within the chambers of Examples 4 through 6 are shown in Table 5 below. The permanent magnets of Examples 4 through 6 were fabricated using the same method as in Example 1, except for the concentration of hydrogen in the atmosphere within the chambers.

[0143] (Examples 7, 8 and Comparative Example 10)

[0144] The pressure of the nozzles (gas pressure inside the container of molten metal) in Examples 7, 8, and Comparative Example 10 is shown in Table 6 below. The pressure of the chambers (gas pressure inside the chambers) in Examples 7, 8, and Comparative Example 10 is shown in Table 6 below. The permanent magnets of Examples 7, 8, and Comparative Example 10 were manufactured by the same method as in Example 4, except for these matters.

[0145] (Comparative Examples 11 and 12)

[0146] The gases (atmospheres) of the first conveying process in Comparative Examples 11 and 12 are shown in Table 7 below. The oxygen concentrations in the atmospheres of the first conveying processes in Comparative Examples 11 and 12 are also shown in Table 7 below. Permanent magnets for Comparative Examples 11 and 12 were manufactured using the same method as in Example 4, except for these aspects.

[0147] (Compare Examples 13 and 14)

[0148] The gases (atmospheres) of the second conveying process in Comparative Examples 13 and 14 are shown in Table 8 below. The oxygen concentration in the atmosphere of the second conveying process in Comparative Examples 13 and 14 is shown in Table 8 below. Apart from these matters, the permanent magnets of Comparative Examples 13 and 14 were manufactured by the same method as in Example 4.

[0149] (Examples 9 and 10)

[0150] The gases (atmospheres) in the third conveying process of Examples 9 and 10 are shown in Table 9 below. The oxygen concentrations in the atmospheres of the third conveying processes of Examples 9 and 10 are also shown in Table 9 below. The permanent magnets of Examples 9 and 10 were manufactured using the same method as in Example 4, except for these aspects.

[0151] (Example 11)

[0152] The composition of the raw material alloy (molten metal) of Example 11 is shown in Table 10 below. The permanent magnet of Example 11 was produced by the same method as in Example 4, except for the composition of the raw material alloy (molten metal).

[0153] (Example 12)

[0154] The composition of the diffusion material in Example 12 is shown in Table 11 below. The permanent magnet of Example 12 was produced by the same method as in Example 4, except for the composition of the diffusion material.

[0155] <Analysis of Permanent Magnets>

[0156] (Composition and microstructure of permanent magnets)

[0157] 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 direction 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).

[0158] In all embodiments and comparative examples, the permanent magnet comprises multiple main phase particles (Nd2Fe). 14 The main phases (B 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 stacked along the easy magnetization axis. In all embodiments and comparative examples, at least a portion of the R-rich phase contains Nd oxide.

[0159] Figure 3 and Figure 5 The image shows a portion of the backscattered electron image of the cross-section of the permanent magnet in Example 4. 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.

[0160] Figure 3 In each of the measurement regions A(a), A(b), A(c), A(d), and A(e), the luminance distribution was measured along the easy magnetization axis C. The width of each measurement region along the easy magnetization axis C was 80 μm. The width of each measurement region perpendicular to the easy magnetization axis C was 10 μm. In each measurement region, the average value of the R-rich phase spacing along the easy magnetization axis C was measured based on the luminance distribution. By further averaging the average values ​​of the R-rich phase spacing in each of the five measurement regions, the average value i of the R-rich phase spacing along the easy magnetization axis C was obtained. AVE Details of the method for measuring brightness distribution and the interval of R-rich phases are as described in the above embodiments. Figure 5 The brighter portion (the part with higher brightness) is an example of an R-rich phase.

[0161] Figure 4 The image shows a portion of the backscattered electron image of the cross-section of the permanent magnet in Comparative Example 1. Figure 4 The five backscattered electron images are identical. Backscattered electron images were acquired using SEM. The cross-section of the acquired backscattered electron images is parallel to the easy magnetization axis. Figure 4 In each of the measurement regions A'(a), A'(b), A'(c), A'(d), and A'(e), the brightness distribution along the easy magnetization axis direction C was measured. Furthermore, using the same method as in Example 4, the average value i of the R-rich phase intervals of Comparative Example 1 was obtained. AVE .

[0162] Using the same method as in Example 4, the average value i of the R-rich phase intervals for all examples and comparative examples was obtained. AVE .

[0163] (Size of the main phase particles)

[0164] Backscattered electron images (SSEs) of the cross-section of the permanent magnet of Example 1 were captured using SEM. The cross-section of the captured SSEs was parallel to the easy magnetization axis. The dimensions of the SSEs were 88 μm x 126 μm. Representative locations within the SSEs were selected, and SSEs of each location were captured at high magnification. The lengths of the major and minor axes of the principal phase particles present in the high-magnification SSEs were measured. The shape of each principal phase particle was approximated by the rectangle with the smallest area among the rectangles circumscribed by the principal phase particle. The length of the long side of this rectangle was considered the length of the major axis of the principal phase particle, and the length of the short side was considered the length of the minor axis. The average length of the major axes of all principal phase particles present in the high-magnification SSEs was calculated. The average length of the minor axes of all principal phase particles present in the high-magnification SSEs was also calculated. The average length of the major axes of the principal phase particles in Example 1 was 243 nm. The average length of the minor axis of the main phase particles in Example 1 is 67.3 nm.

[0165] The lengths of the major and minor axes of the main phase particles in Comparative Example 1 were measured using the same method as in Example 1. The average length of the major axis of the main phase particles in Comparative Example 1 was 261 nm. The average length of the minor axis of the main phase particles in Comparative Example 1 was 69.2 nm.

[0166] Using the same method as in Example 1, the lengths of the major and minor axes of the main phase particles in all examples and comparative examples were measured. The minimum average length of the major axis of the main phase particles in each example was approximately 100 nm. The maximum average length of the major axis of the main phase particles in each example was approximately 1000 nm. The maximum average length of the minor axis of the main phase particles in each example was approximately 200 nm. The minimum average length of the minor axis of the main phase particles in each example was approximately 20 nm.

[0167] (Magnetic properties of permanent magnets)

[0168] The remanent magnetic flux density (Br), coercivity (HcJ), and rectangularity ratio (Hk / HcJ) of the permanent magnets in all examples and comparative examples were measured. The remanent magnetic flux density, coercivity, and rectangularity ratio were measured using a BH tracer. Coercivity was measured at 23°C and 150°C. Br was measured at room temperature. The rectangularity ratio was measured at 23°C. The temperature coefficient β of the coercivity for all examples and comparative examples was calculated. The temperature coefficient β was defined according to Equation 1 below. HcJ in Equation 1 below... 150 The coercivity is at 150℃. HcJ in Equation 1 below... 23 Coercivity at 23℃.

[0169] β=100×(HcJ 150 -HcJ23 ) / HcJ 23 (150-23) (1)

[0170] The analytical results of the permanent magnets are presented in the table below.

[0171]

[0172] [Table 2]

[0173]

[0174] [Table 3]

[0175]

[0176] [Table 4]

[0177]

[0178]

[0179]

[0180] [Table 7]

[0181]

[0182] [Table 8]

[0183]

[0184] [Table 9]

[0185]

[0186]

[0187] [Table 11]

[0188]

[0189] [Industry availability]

[0190] The RTB-based permanent magnet of one aspect of the present invention is suitable for materials such as those used in electric motors of electric vehicles or hybrid vehicles.

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 has a plurality of main phase particles and a plurality of R-rich phases, the plurality of main phase particles contains at least the R, the T, and the B, the plurality of R-rich phases contains at least the R, the plurality of main phase particles observed in a cross section of the R-T-B based permanent magnet is flat, the cross section is substantially parallel to an easy magnetization axis direction 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 value of intervals of the plurality of R-rich phases in the easy magnetization axis direction is 5 pm or more and 10 pm or less.

2. The R-T-B based permanent magnet according to claim 1, wherein an average value 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.

3. The R-T-B based permanent magnet according to claim 1 or 2, 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.

4. The R-T-B based permanent magnet according to claim 1 or 2, wherein at least a part of the plurality of R-rich phases contains an oxide of the R.

5. 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 easy magnetization axis direction.

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

7. 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 value of a concentration of the R in the cross section, a unit of the concentration of the R is atom%.

8. 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 atom%.

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