JP2024144067A - R-T-B permanent magnet - Google Patents

Abstract

To provide an R-T-B based permanent magnet having both of high residual flux density and high coercive force.SOLUTION: A permanent magnet 2 contains: a rare-earth element R; a transition metal element T; and boron. The permanent magnet 2 includes: a plurality of main phase grains 4; and a plurality of soft magnetic grains 6. The plurality of soft magnetic grains 6 contain Fe. A cross-section 2cs of the permanent magnet 2 includes a plurality of soft magnetic regions sm. The cross-section 2cs of the permanent magnet 2 is parallel to an easy magnetization axis direction C of the permanent magnet 2. Each of the plurality of soft magnetic grains 6 includes the plurality of soft magnetic grains aligned along an AB direction orthogonal to the easy magnetization axis direction C. The plurality of main phase grains 4 and the plurality of soft magnetic regions are alternately disposed in the easy magnetization axis direction. An average value of width S6 of the plurality of soft magnetic grains 6 in the easy magnetization axis direction C ranges from 20nm or more and 5 μm or less.SELECTED DRAWING: Figure 2

Description

This disclosure relates to R-T-B permanent magnets.

In general, the main phase grains in an R-T-B permanent magnet are strongly magnetically coupled to adjacent main phase grains. Therefore, in order to improve the coercive force of an R-T-B permanent magnet, it is necessary to form Nd-enriched grain boundary phases (pinning sites that impede the magnetization reversal process) between the main phase grains by designing a composition that makes it easy to form grain boundaries, or by a grain boundary diffusion process. However, because the grain boundary phase is a non-magnetic phase, the formation of a large amount of grain boundary phase reduces the residual magnetic flux density of the R-T-B permanent magnet.

The permanent magnet described in the following Patent Document 1 aims at high coercivity and high residual magnetic flux density. In the permanent magnet described in the following Patent Document 1, a soft magnetic phase (α-Fe phase, etc.) exhibiting a higher saturation magnetization Ms than the main phase (hard magnetic phase) is mixed with the main phase. In the magnet manufacturing method described in the following Patent Document 1, a ribbon is formed by quenching a molten metal containing a larger amount of Fe than the stoichiometric composition of Nd ₂ Fe ₁₄ B. The permanent magnet described in the following Patent Document 1 is obtained by sintering the ribbon containing a large amount of Fe. The permanent magnet described in the following Patent Documents 1 and 2 and the following Non-Patent Document 1 has a metastable structure formed from an aggregate of fine crystals in which a soft magnetic phase containing Fe and a hard magnetic phase containing Nd ₂ Fe ₁₄ B are mixed, and is called a "nanocomposite magnet" or "exchange spring magnet".

JP 2012-234985 A JP 2005-93730 A

A. M. Gabay et al., Numerical simulation of a magnetostatically coupled composite magnet, JOURNAL OF APPLIEDPHYSICS 101, 09K507 (2007)

The objective of one aspect of the present invention is to provide an R-T-B system permanent magnet that combines high residual magnetic flux density and high coercivity.

For example, as shown in [1] to [6] below, one aspect of the present invention relates to an R-T-B system permanent magnet.

[1] An R-T-B based permanent magnet containing a rare earth element R, a transition metal element T, and boron (B),
The R-T-B system permanent magnet contains at least Nd as a rare earth element R,
The R-T-B system permanent magnet contains at least Fe as a transition metal element T,
The R-T-B based permanent magnet includes a plurality of main phase grains and a plurality of soft magnetic grains,
the plurality of main phase particles contain at least a rare earth element R, a transition metal element T, and boron;
The soft magnetic particles contain at least Fe,
A cross section of the R-T-B system permanent magnet includes a plurality of soft magnetic regions,
the cross section of the R-T-B system permanent magnet is parallel to the easy magnetization axis direction of the R-T-B system permanent magnet,
Each of the soft magnetic regions includes a plurality of soft magnetic grains aligned along a direction perpendicular to the easy axis of magnetization;
A plurality of main phase grains and a plurality of soft magnetic regions are alternately arranged in the direction of the easy axis of magnetization,
The average width of the soft magnetic particles in the direction of easy magnetization is 20 nm or more and 5 μm or less.
R-T-B series permanent magnet.

[2] The average spacing between the soft magnetic regions in the easy axis direction is 4 μm or more and 15 μm or less.
The R-T-B system permanent magnet according to [1].

[3] The area fraction of the soft magnetic particles in the cross section of the R-T-B system permanent magnet is 4% or more and 15% or less.
The R-T-B system permanent magnet according to [1] or [2].

[4] At least a portion of the soft magnetic particles includes an R-T phase containing a rare earth element R and a transition metal element T;
[1] to [3]. An R-T-B system permanent magnet according to any one of [1] to [3].

[5] The content of the rare earth element R is 26% by mass or more and 32% by mass or less,
The boron content is 0.77% by mass or more and 1.15% by mass.
[1] to [4]. An R-T-B system permanent magnet according to any one of [1] to [4].

[6] A plurality of main phase grains observed in the cross section of the R-T-B system permanent magnet are flat.
[1] to [5]. An R-T-B system permanent magnet according to any one of [1] to [5].

[7] A width of the plurality of main phase grains in the direction of the easy axis of magnetization is smaller than a width of the plurality of main phase grains in a direction perpendicular to the easy axis of magnetization;
the average width of the main phase grains in the direction of the easy magnetization axis is 20 nm or more and 200 nm or less;
An R-T-B system permanent magnet according to any one of [1] to [6].

According to one aspect of the present invention, an R-T-B permanent magnet that combines high residual magnetic flux density and high coercivity is provided.

(a) in FIG. 1 is a schematic perspective view of an R-T-B system permanent magnet according to one embodiment of the present invention, (b) in FIG. 1 is a schematic diagram of a cross section of the R-T-B system permanent magnet (a view taken along the arrows in the direction of line b-b in the R-T-B system permanent magnet), and the cross section shown in (b) in FIG. 1 is parallel to the direction of easy magnetization of the R-T-B system permanent magnet. FIG. 2 is an enlarged view of a part (region II) of the cross section shown in (b) of FIG. (a) in FIG. 3 is a backscattered electron image of a cross section of the R-T-B system permanent magnet of Example 1. The cross section shown in (a) in FIG. 3 is parallel to the direction of easy magnetization of the R-T-B system permanent magnet. (b) in FIG. 3 is a backscattered electron image taken at a high magnification of the cross section shown in (a) in FIG. 3. (a) in Figure 4 is a backscattered electron image of a cross section of the R-T-B system permanent magnet of Comparative Example 5. The cross section shown in (a) in Figure 4 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet. (b) in Figure 4 is a backscattered electron image taken at a high magnification of the cross section shown in (a) in Figure 4. (a) in FIG. 5 is a backscattered electron image identical to (a) in FIG. 3, the cross section shown in (a) in FIG. 5 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet, (b) in FIG. 5 is an image obtained by image processing of the backscattered electron image shown in (a) in FIG. 5, and (c) in FIG. 5 is an image obtained by image processing of the image shown in (b) in FIG. 5, and (a) in FIG. 5, (b) in FIG. 5, and (c) in FIG. 5 show identical cross sections. (a) in Figure 6 is an image identical to (b) in Figure 5, the cross section shown in (a) in Figure 6 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet, and (b) in Figure 6 is a graph showing the positions of multiple soft magnetic particles aligned in the easy axis direction of magnetization in the measurement area a1 shown in (a) in Figure 6. (a) in Figure 7 is an image identical to (b) in Figure 5, the cross section shown in (a) in Figure 7 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet, and (b) in Figure 7 is a graph showing the positions of multiple soft magnetic particles aligned in the easy axis direction of magnetization in measurement area a2 shown in (a) in Figure 7. (a) in Figure 8 is an image identical to (b) in Figure 5, the cross section shown in (a) in Figure 8 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet, and (b) in Figure 8 is a graph showing the positions of multiple soft magnetic particles aligned in the easy axis direction of magnetization in measurement area a3 shown in (a) in Figure 8. (a) in Figure 9 is an image identical to (b) in Figure 5, the cross section shown in (a) in Figure 9 is parallel to the easy axis direction of magnetization of the R-T-B system permanent magnet, and (b) in Figure 9 is a graph showing the positions of multiple soft magnetic particles aligned in the easy axis direction of magnetization in measurement area a4 shown in (a) in Figure 9.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In the drawings, equivalent components are given the same reference numerals. The present invention is not limited to the following embodiment. The arrow C and two arrows AB shown in FIG. 1 indicate three coordinate axes perpendicular to each other. The arrow C corresponds to the magnetization easy axis direction C of the R-T-B permanent magnet. Each of the two arrows AB corresponds to the AB direction perpendicular to the magnetization easy axis direction C. The magnetization easy axis direction C and the AB direction are common to all the drawings. For example, the R-T-B permanent magnet may be an R-T-B based hot deformed magnet (R-T-B based hot deformed magnet) or an R-T-B based sintered magnet (R-T-B based sintered magnet). In the following embodiment, the R-T-B permanent magnet is referred to as "permanent magnet" for simplification.

(Permanent magnet)
The permanent magnet according to this embodiment contains at least a rare earth element R, a transition metal element T, and boron (B).

The permanent magnet contains at least neodymium (Nd) as a rare earth element R. The permanent magnet may contain other rare earth elements R in addition to Nd. The other rare earth elements R contained in the permanent magnet may be at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The permanent magnet 2 may not contain a heavy rare earth element (e.g., both Dy and Tb).

The permanent magnet contains at least iron (Fe) as the transition metal element T. The permanent magnet may contain only Fe as the transition metal element T. The permanent magnet may contain both Fe and cobalt (Co) as the transition metal element T.

1A is a perspective view of the permanent magnet 2 according to this embodiment, and FIG. 1B is a schematic diagram of the cross section 2cs of the permanent magnet 2. The cross section 2cs of the permanent magnet 2 is substantially parallel or completely parallel to the magnetization easy axis direction C of the permanent magnet 2. The magnetization easy axis direction C is a direction parallel to a straight line connecting a pair of magnetic poles of the permanent magnet 2. In other words, the magnetization easy axis direction C is a direction from the S pole of the permanent magnet 2 to the N pole of the permanent magnet 2. The magnetization easy axis direction C may be determined based on a measurement of the magnetic flux distribution of the permanent magnet 2. The magnetization easy axis direction C may be determined based on a measurement of the magnetic flux distribution of an analysis sample separated from the permanent magnet 2. As described above, the AB direction is perpendicular to the magnetization easy axis direction C.

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

Figure 2 is an enlarged view of a portion (region II) of cross section 2cs shown in (b) of Figure 1. As shown in Figure 2, permanent magnet 2 includes a plurality of main phase grains 4 and a plurality of soft magnetic grains 6. The plurality of main phase grains 4 are hard magnetic materials. Permanent magnet 2 may further include a plurality of sub-phase grains 8.

The main phase particles 4 contain at least a rare earth element R, a transition metal element T, and B. The main phase particles 4 contain at least Nd as the rare earth element R. The main phase particles 4 contain at least Fe as the transition metal element T. The main phase particles 4 may be referred to as one crystal grain (i.e., a primary particle). The main phase particles 4 contain a crystal (single crystal or polycrystal) of R ₂ T ₁₄ B. R ₂ T ₁₄ B is a ternary intermetallic compound having hard magnetism. The main phase particles 4 may be composed of only R ₂ T ₁₄ B crystals. The R ₂ T ₁₄ B crystals may be tetragonal. That is, the crystal axes of R ₂ T ₁₄ B are the a-axis, b-axis, and c-axis, the a-axis, b-axis, and c-axis being perpendicular to one another, the lattice constant of R ₂ T ₁₄ B in the a-axis direction may be equal to the lattice constant of R ₂ T ₁₄ B in the b-axis direction, and the lattice constant of R ₂ T ₁₄ B in the c-axis direction may be different from the lattice constants in the a-axis and b-axis directions, respectively. The c-axis direction of _{R 2} T ₁₄ B may be approximately parallel or completely parallel to the magnetization easy axis direction C of the permanent magnet 2.

For example, R ₂ T ₁₄ B constituting the main phase particle 4 may be expressed as (Nd _1-x Pr _x ) ₂ (Fe _1-y Co _y ) ₁₄ B. x may be 0 or more and less than 1. y may be 0 or more and less than 1. The main phase particle 4 may contain heavy rare earth elements such as Tb and Dy as R in addition to light rare earth elements. A part of B in _{R 2} T ₁₄ B may be substituted with other elements such as carbon (C). The composition in the main phase particle 4 may be uniform. The composition in the main phase particle 4 may be non-uniform. For example, the concentration distribution of R, T, and B in the main phase particle 4 may have a gradient. The main phase particle 4 may contain other elements in addition to R, T, and B.

As shown in FIG. 2, the multiple main phase particles 4 observed in the cross section 2cs parallel to the easy axis direction C may be flat. In other words, the multiple main phase particles 4 observed in the cross section 2cs may be plate-shaped. The multiple flat main phase particles 4 may be stacked along the easy axis direction C. The permanent magnet 2 may further include secondary particles composed of multiple main phase particles 4 bonded to each other. The permanent magnet 2 may include multiple secondary particles.

The soft magnetic particles 6 contain at least Fe. The soft magnetic particles 6 are ferromagnetic materials. The total content of Fe and Co in the soft magnetic particles 6 may be 70% by mass or more and 100% by mass or less. When the total content of Fe and Co in the soft magnetic particles 6 is 70% by mass or more, the soft magnetic particles 6 tend to have ferromagnetism, the saturation magnetic flux density of the soft magnetic particles 6 tends to be higher than the saturation magnetic flux density of the main phase particles 4, and the residual magnetic flux density of the soft magnetic particles 6 also tends to be higher than the residual magnetic flux density of the main phase particles 4. For example, the saturation magnetic flux density Bs of the α-Fe phase is 2.15 T, and the saturation magnetic flux density Bs of Nd ₂ Fe ₁₄ B is 1.61 T. The soft magnetic particles 6 may further contain elements other than Fe. For example, each of the soft magnetic particles 6 may further contain at least one element selected from the group consisting of R, B, and Co. For example, at least a portion of the soft magnetic particles 6 may contain at least one selected from the group consisting of α-Fe phase, R-T phase, Fe ₃ B phase, and Fe ₂ Co phase. For example, each of the soft magnetic particles 6 may contain at least one selected from the group consisting of α-Fe phase, R-T phase, Fe ₃ B phase, and Fe ₂ Co phase. Each of the soft magnetic particles 6 may consist of at least one selected from the group consisting of α-Fe phase, R-T phase, Fe ₃ B phase, and Fe ₂ Co phase. As long as the soft magnetic particles 6 contain Fe, the permanent magnet 2 may contain multiple types of soft magnetic particles 6 that are different in composition. The composition of the soft magnetic particles 6 may be the same. Each of the soft magnetic particles 6 may be single crystal or polycrystalline.
The R-T phase includes a rare earth element R and a transition metal element T. At least a part of the T included in the R-T phase is Fe. The R-T phase may further include a transition metal element other than Fe (for example, at least one of Co and Cu) as T. At least a part of the R included in the R-T phase may be Nd. The R-T phase may further include one or more other rare earth elements in addition to Nd as R. The R-T phase may further include B. The concentration (unit: atomic %) of all R in one soft magnetic particle 6 may be expressed as [R], the concentration (unit: atomic %) of all T in one soft magnetic particle 6 may be expressed as [T], and the [T]/[R] of the soft magnetic particle 6 including the R-T phase may be 8.4 or more and 8.8 or less. For example, at least a part of the soft magnetic particles 6 may include an R ₂ T ₁₇ phase as the R-T phase. That is, the [T]/[R] of the soft magnetic particles 6 including the R ₂ T ₁₇ phase may be 8.5. The R-T phase may be crystalline. For example, the crystal structure of the R-T phase may be a Th ₂ Zn ₁₇ type structure, a Th ₂ Ni ₁₇ type structure, or a TbCu ₇ type structure. The crystal structure of the R-T phase may be identified by a scanning transmission electron microscope (STEM).

The cross section 2cs parallel to the magnetization easy axis direction C includes a plurality of soft magnetic regions sm. Each of the plurality of soft magnetic regions sm includes a plurality of soft magnetic particles 6 aligned along a direction (AB direction) substantially perpendicular or completely perpendicular to the magnetization easy axis direction C. The angle between the magnetization easy axis direction C and the direction in which the plurality of soft magnetic particles 6 are aligned in each of the plurality of soft magnetic regions sm may be greater than 45° and less than or equal to 90°, preferably 90°. Each of the plurality of soft magnetic regions sm may be composed only of a plurality of soft magnetic particles 6. In the soft magnetic region sm, adjacent soft magnetic particles 6 may be in direct contact with each other. Other particles that do not have soft magnetism may be interposed between the plurality of soft magnetic particles 6 aligned in the soft magnetic region sm. For example, one or more subphase particles 8 may be interposed between the plurality of soft magnetic particles 6 aligned in the soft magnetic region sm. That is, the soft magnetic grains 6 and one or more subphase grains 8 may be aligned along a direction (AB direction) that is substantially or completely perpendicular to the magnetization easy axis direction C in each of the soft magnetic regions sm. The soft magnetic region sm may be referred to as a soft magnetic layer. The width (length) of the soft magnetic region sm in the direction (AB direction) perpendicular to the magnetization easy axis direction C is not limited. For example, the width (length) of the soft magnetic region sm in the direction (AB direction) perpendicular to the magnetization easy axis direction C may be 50 μm or more and 300 μm or less.

A plurality of main phase particles 4 and a plurality of soft magnetic regions sm are arranged alternately in the magnetization easy axis direction C. In other words, one or more main phase particles 4 are sandwiched between a pair of soft magnetic regions sm in the magnetization easy axis direction C. In other words, one or more main phase particles 4 and one or more soft magnetic particles 6 included in the soft magnetic region sm are arranged alternately in the magnetization easy axis direction C. The main phase particles 4 and the soft magnetic region sm (soft magnetic particles 6 in the soft magnetic region sm) may be in direct contact in the magnetization easy axis direction C. A grain boundary phase may be interposed between the main phase particles 4 and the soft magnetic region sm (soft magnetic particles 6 in the soft magnetic region sm) in the magnetization easy axis direction C.

Since one or more main phase grains 4 (hard magnetic phase) having magnetocrystalline anisotropy and a plurality of soft magnetic regions sm (soft magnetic layers) having a saturation magnetization larger than that of the main phase grains 4 are alternately arranged in the magnetization easy axis direction C, a strong exchange interaction is likely to occur between the fine main phase grains 4 and the fine soft magnetic regions sm. Even if the magnetization of the soft magnetic regions sm is reversed, the strong exchange interaction between the main phase grains 4 and the soft magnetic regions sm makes it difficult for the reversed magnetic domains to propagate, and the permanent magnet 2 has excellent hard magnetic properties and a high coercive force. In addition, the inventors speculate that a magnetostatic magnetic exchange interaction occurs between the soft magnetic regions sm and the main phase grains 4 because a plurality of soft magnetic regions sm (soft magnetic layers) are alternately arranged with the main phase grains 4. In conventional exchange spring magnets (nanocomposite magnets), in order to achieve high residual magnetic flux density, a direct magnetic coupling state between the main phase particles and the soft magnetic phase in a short range (e.g., a distance of several nm or less) is required. In contrast, the inventors speculate that in the permanent magnet 2 according to this embodiment, magnetostatic magnetic exchange interaction between the main phase particles 4 and the soft magnetic regions sm in a long range (e.g., a distance of several tens of μm or more) can work. For the above reasons, the permanent magnet 2 can have a high residual magnetic flux density derived from the large saturation magnetization of the multiple soft magnetic regions sm. In conventional exchange spring magnets (nanocomposite magnets), multiple soft magnetic particles are randomly dispersed in the hard magnetic phase without being aligned. Therefore, in conventional exchange spring magnets, the above mechanism resulting from the arrangement of the main phase particles 4 and the soft magnetic regions sm (soft magnetic layers) does not hold, and it is difficult to achieve both high residual magnetic flux density and high coercivity.

The average value of the width S6 (e.g., maximum width) of the multiple soft magnetic particles 6 in the magnetization easy axis direction C is 20 nm (0.02 μm) or more and 5 μm or less. The average value of the grain diameter of the multiple soft magnetic particles 6 measured in the cross section 2cs parallel to the magnetization easy axis direction C may be regarded as the average value of the width S6 (e.g., maximum width) of the multiple soft magnetic particles 6 in the magnetization easy axis direction C. In other words, the average value of the grain diameter of the multiple soft magnetic particles 6 in the cross section 2cs parallel to the magnetization easy axis direction C may be 20 nm or more and 5 μm or less. The average value of the grain diameter of the multiple soft magnetic particles 6 in the magnetization easy axis direction C may be 50 nm or more and 5 μm or less, or 20 nm or more and 2.11 μm or less. The average value of the widths L6 (e.g., maximum width) of the soft magnetic particles 6 in the AB direction perpendicular to the easy axis direction C may also be 20 nm to 5 μm, 50 nm to 5 μm, or 20 nm to 2.11 μm. At least some of the soft magnetic particles 6 may be flat. In other words, the width S6 of each of the soft magnetic particles 6 in the easy axis direction C may be smaller than the width L6 of each of the soft magnetic particles 6 in the AB direction perpendicular to the easy axis direction C.

Since the average value of the width S6 of the multiple soft magnetic particles 6 is 20 nm or more and 5 μm or less, a high coercive force can be achieved due to the exchange interaction between the main phase particles 4 and the soft magnetic region sm (soft magnetic particles 6) in the magnetization easy axis direction C. In the heat treatment process of the permanent magnet 2 (for example, the hot plastic processing process described later), the grain growth of the soft magnetic particles 6 progresses, so it is difficult to adjust the average value of the width S6 of the multiple soft magnetic particles 6 in the magnetization easy axis direction C to less than 20 nm. If the average value of the width S6 of the multiple soft magnetic particles 6 exceeds 5 μm, magnetization reversal due to a local demagnetizing field occurs, and the coercive force is significantly reduced. In the conventional exchange spring magnet (nanocomposite magnet), it was theoretically predicted that the critical value (upper limit value) of the particle size of each of the main phase particles 4 and the soft magnetic particles 6 is 10 nm in order to achieve high coercive force and high residual magnetic flux density. Contrary to conventional predictions, the inventor's research revealed that high residual magnetic flux density and high coercive force are achieved even though the average width S6 of the multiple soft magnetic particles 6 in the easy axis direction C is 20 nm or more.

In this embodiment, the magnetic coupling between the hard magnetic phase and the soft magnetic phase is formed magnetostatically, so the inventors speculate that the strict constraints on the particle size of each of the main phase particles 4 and the soft magnetic particles 6 are relaxed. Furthermore, in this embodiment, the particle size and distribution of the soft magnetic particles 6 are optimized, so that a high residual magnetic flux density can be achieved while maintaining a high coercive force.

For example, the coercive force (HcJ) of the permanent magnet 2 at 23° C. may be not less than 1103 kA/m and not more than 1473 kA/m.
For example, the residual magnetic flux density (Br) of the permanent magnet 2 at room temperature may be not less than 1447 mT and not more than 1533 mT.
For example, the squareness ratio (Hk/HcJ) of the permanent magnet 2 may be 95.2% or more and 98.8% or less. Hk is the strength of the demagnetizing field corresponding to 90% of the residual magnetic flux density in the second quadrant of the magnetization curve of the permanent magnet 2.

The average value of the spacing i between the multiple soft magnetic regions sm in the magnetization easy axis direction C may be 4 μm or more and 15 μm or less, 4.03 μm or more and 12.17 μm or less, or 4.23 μm or more and 12.17 μm or less. In other words, the average value of the spacing i between the multiple soft magnetic particles 6 contained in the multiple soft magnetic regions sm in the magnetization easy axis direction C may be 4 μm or more and 15 μm or less, 4.03 μm or more and 12.17 μm or less, or 4.23 μm or more and 12.17 μm or less. When the average value of the spacing i between the multiple soft magnetic regions sm is within the above range, it is easy to achieve a high residual magnetic flux density while maintaining a high coercive force. For example, the spacing i between the multiple soft magnetic regions sm in the magnetization easy axis direction C may be the distance between a pair of adjacent soft magnetic particles 6 on an arbitrary reference line Lc parallel to the magnetization easy axis direction C in a cross section 2cs parallel to the magnetization easy axis direction C. For example, the average value of the spacing i between multiple soft magnetic regions sm in the magnetization easy axis direction C may be the average value of all spacings i measured on any 10 reference lines Lc parallel to the magnetization easy axis direction C.

The area fraction (area ratio) of the soft magnetic particles 6 in the cross section 2cs may be 4% or more and 15% or less, or 4.11% or more and 12.10% or less. The average value of the area fraction of the soft magnetic particles 6 in the cross section 2cs may be 4% or more and 15% or less, or 4.11% or more and 12.10% or less. For example, the area of region II (region II shown in FIG. 2), which is an arbitrary part of the cross section 2cs parallel to the magnetization easy axis direction C, may be expressed as Acs, the total area (cross-sectional area) of all the soft magnetic particles 6 present in region II may be expressed as Asm, and the area fraction Ra may be defined as Asm/Acs. In other words, Asm/Acs may be 0.04 or more and 0.15 or less. When the area fraction is 4% or more, the permanent magnet 2 is likely to have a high residual magnetic flux density derived from the soft magnetic particles 6. When the area fraction is 15% or less, magnetization reversal originating from the soft magnetic grains 6 is easily suppressed, and the permanent magnet 2 is likely to have a high coercive force. For example, the area fraction of the multiple main phase grains 4 in the cross section 2cs may be 80% or more and 96% or less, 90% or more and 96% or less, or 95% or more and 96% or less.

For example, the volume ratio of the multiple main phase particles 4 (proportion of the volume of all main phase particles 4 in the permanent magnet 2) may be 80 volume% or more and 96 volume% or less, 90 volume% or more and 96 volume% or less, or 95 volume% or more and 96 volume% or less. For example, the volume ratio of the multiple soft magnetic particles 6 (proportion of the volume of all soft magnetic particles 6 in the permanent magnet 2) may be 4 volume% or more and 15 volume% or less, or 4.11 volume% or more and 12.10 volume% or less.

As described above, the main phase particles 4 observed in the cross section 2cs parallel to the easy axis direction C may be flat. For example, the width S4 of each of the main phase particles 4 (primary particles) in the easy axis direction C may be smaller than the width L4 of each of the main phase particles 4 in the AB direction perpendicular to the easy axis direction C. In other words, the length (S4) of the short axis of each main phase particle 4 may be smaller than the length (L4) of the long axis of each main phase particle 4. For example, the average value of the width S4 of the main phase particles 4 in the easy axis direction C may be 20 nm or more and 200 nm or less, or 67 nm or more and 95 nm or less. For example, the average value of the width L4 of the main phase particles 4 in the AB direction perpendicular to the easy axis direction C may be 100 nm or more and 1000 nm or less. For example, the average value of the aspect ratio L4/S4 of each of the multiple main phase particles 4 may be 2 or more and 10 or less. For example, when the permanent magnet 2 is manufactured by a hot plastic processing process described later, the aspect ratio L4/S4 of 2 or more makes it easy for the c-axis of the main phase particles 4 to be oriented in the magnetization easy axis direction C, and the coercive force is easy to increase. An aspect ratio L4/S4 of 2 or more indicates that anisotropic grain growth of the main phase particles 4 (R ₂ T ₁₄ B crystals) has progressed sufficiently in the hot plastic processing process. Since there is a limit to the anisotropic grain growth of the main phase particles 4 in the hot plastic processing process, the aspect ratio L4/S4 is unlikely to exceed 10.

The shape of the main phase particle 4 in the cross section 2cs is not limited to a rectangle. The shape of the main phase particle 4 in the cross section 2cs may be distorted. The shape of the main phase particle 4 in the cross section 2cs may not be uniform. When the shape of the main phase particle 4 in the cross section 2cs is distorted, the shape of the main phase particle 4 may be approximated by a rectangle with the smallest area among the rectangles circumscribing the main phase particle 4. The rectangle may be a rectangle. The length of the short side of this rectangle may be considered to be the length of the short axis of the main phase particle 4, and the length of the long side of the rectangle may be considered to be the length of the long axis of the main phase particle 4. The average value of the length of the short axis of the main phase particle 4 may be calculated from the measured values of the lengths of the short axes of all the main phase particles 4 present in the backscattered electron image of the cross section 2cs taken with a scanning electron microscope (SEM). The average value of the length of the long axis of the main phase particle 4 may also be calculated from the measured values of the lengths of the long axes of all the main phase particles 4 present in the backscattered electron image. However, the dimensions of the main phase grains 4 that extend beyond the backscattered electron image are excluded from the calculation of the average value. For example, the maximum value of the dimensions of the backscattered electron image used to measure the lengths of the short and long axes of the main phase grains 4 may be 120 μm long × 80 μm wide, or 80 μm long × 120 μm wide. Representative locations within the backscattered electron images taken at these low magnifications may be selected, and the backscattered electron images of each location may be taken at a high magnification. Then, the average values of the long and short axes may be calculated from the lengths of the long and short axes of all the main phase grains 4 measured in the backscattered electron images at the high magnification. Commercially available image analysis software may be used to specify the shape (contour line) of the main phase grains 4 and to measure the dimensions of the main phase grains 4 (rectangles circumscribing the main phase grains 4).

The main phase particles 4 may be composed of a surface layer and a central portion covered by the surface layer. The surface layer may be referred to as a shell, and the central portion may be referred to as a core. The surface layer of the main phase particles 4 may contain at least one heavy rare earth element selected from Tb and Dy. The surface layer of each of all the main phase particles 4 may contain at least one heavy rare earth element selected from Tb and Dy. The surface layer of some of the main phase particles 4 among all the main phase particles 4 may contain at least one heavy rare earth element selected from Tb and Dy. By containing a heavy rare earth element in the surface layer, the anisotropic magnetic field is likely to increase locally near the grain boundaries, and nuclei of magnetization reversal are unlikely to occur near the grain boundaries. As a result, the coercive force of the permanent magnet 2 at high temperatures (e.g., 100 to 200 ° C.) is increased. Since the residual magnetic flux density (Br) and coercive force of the permanent magnet 2 are easily compatible, the total concentration of the heavy rare earth elements in the surface layer may be higher than the total concentration of the heavy rare earth elements in the center.

As described above, one or more subphase particles 8 may be interposed between the multiple soft magnetic grains 6 aligned in the soft magnetic region sm. For example, the subphase particles 8 may contain at least one of an oxide of a rare earth element R and a metal made of a rare earth element R. The subphase particles 8 may be composed of only at least one of an oxide of a rare earth element R and a metal made of a rare earth element R. For example, the oxide of a rare earth element R contained in the subphase particles 8 may be Nd ₂ O ₃ or NdO. For example, the metal contained in the subphase particles 8 may be a crystal of Nd having a hexagonal close-packed structure. The subphase particles 8 containing the crystal of Nd may have soft magnetism and ferromagnetism. The subphase particles 8 may not have any of hard magnetism, soft magnetism, and ferromagnetism.

The permanent magnet 2 may further include a grain boundary phase. For example, the grain boundary phase may exist at a grain boundary (grain boundary multiple point) surrounded by three or more main phase grains 4. For example, the grain boundary phase may exist at a grain boundary between two main phase grains 4 (two-grain grain boundary). For example, the grain boundary phase may exist between the main phase grain 4 and the soft magnetic region sm (soft magnetic grain 6). For example, the grain boundary phase may exist between the soft magnetic grain 6 and the subphase grain 8.

For example, at least a part of the grain boundary phase may be an R-rich phase. The R-rich phase may be a ferromagnetic material and a soft magnetic material. The R-rich phase contains at least a rare earth element R. For example, the R-rich phase may contain Nd as R. The R-rich phase may further contain one or more other rare earth elements in addition to Nd as R. The R-rich phase may contain one or more heavy rare earth elements in addition to Nd as R. The R-rich phase may further contain one or more elements other than R in addition to R. The R-rich phase may contain at least one selected from the group consisting of a metal element, an alloy, an intermetallic compound, and an oxide. For example, a part or all of the R-rich phase may be composed of only at least one of a metal element, an alloy containing R, and a metal compound containing R. A part or all of the R-rich phase may contain an oxide of R. For example, the oxide of R may be an oxide of Nd. The oxidized surface of the main phase grain 4 may be an oxide of R. A part of the R-rich phase may be composed of only an oxide of R. The concentration of R in the R-rich phase (unit: atomic %) may be higher than the average concentration of R in the main phase grain 4. The concentration of R in the R-rich phase may be higher than the average concentration of R in the cross section 2cs. When the permanent magnet 2 contains multiple types of R, the concentration of R may be the sum of the concentrations of the multiple types of R. The permanent magnet 2 may include a grain boundary phase other than the R-rich phase. For example, the permanent magnet 2 may include at least one grain boundary phase of an R-Fe-Ga-Cu phase and an R-Fe-Co-Cu phase. The R-Fe-Ga-Cu phase is a phase containing R, Fe, Ga, and Cu. The R-Fe-Co-Cu phase is a phase containing R, Fe, Co, and Cu.

For example, the permanent magnet 2 may include a grain boundary phase containing an element introduced into the permanent magnet 2 by the grain boundary diffusion process described below. For example, the element introduced into the permanent magnet 2 by the grain boundary diffusion process may be at least one heavy rare earth element selected from Tb and Dy. The element introduced into the permanent magnet 2 by the grain boundary diffusion process may be a heavy rare earth element and a light rare earth element, and the light rare earth element may be at least one of Nd and Pr. The element introduced into the permanent magnet 2 by the grain boundary diffusion process may be a heavy rare earth element, a light rare earth element, and copper. Eutectic alloys such as Nd-Cu and Nd-Al may be introduced into the permanent magnet 2 by the grain boundary diffusion process.

For example, the dimension of the permanent magnet 2 in the easy axis direction C may be several mm or more and several hundred mm or less, or several tens of mm or more and several hundred mm or less. For example, the dimension of the permanent magnet 2 in the AB direction may be several mm or more and several hundred mm or less, or several tens of mm or more and several hundred mm or less.

The main phase grains 4, the soft magnetic grains 6, the subphase grains 8, and the grain boundary phase can be identified based on the contrast of the reflected electron image of the cross section 2cs of the permanent magnet 2 taken with a scanning electron microscope (SEM). As the atomic weight of the atom increases, the brightness of the atom in the reflected electron image (unit: arbitrary unit) increases. The atomic weight of Fe is smaller than the atomic weight of the rare earth element R. Therefore, the brightness of Fe in the reflected electron image is lower than the brightness of the rare earth element R in the reflected electron image. The concentration of Fe (unit: atomic %) in the soft magnetic grains 6 is higher than the concentration of Fe in the part of the cross section 2cs other than the soft magnetic grains 6. The concentration of the rare earth element R in the soft magnetic grains 6 is lower than the concentration of the rare earth element R (unit: atomic %) in the part of the cross section 2cs other than the soft magnetic grains 6. Therefore, the brightness of the soft magnetic grains 6 in the reflected electron image of the cross section 2cs is lower than the part of the cross section 2cs other than the soft magnetic grains 6. That is, the dark areas (areas with large gray values) in the reflected electron image of the cross section 2cs correspond to the soft magnetic particles 6. The compositions of the main phase particles 4, the soft magnetic particles 6, the subphase particles 8, and the grain boundary phase may be analyzed by an energy dispersive X-ray spectroscopy (EDS) device mounted on the SEM or STEM.

The overall composition of permanent magnet 2 is described below. However, the composition of permanent magnet 2 is not limited to the composition below. The content of each element in permanent magnet 2 may be outside the range below.

For example, the content of the rare earth element R in the permanent magnet 2 may be 26% by mass or more and 32% by mass or less. When the content of R is 26% by mass or more, a liquid phase (R-rich phase) is likely to be generated at the grain boundaries during the manufacturing process of the permanent magnet 2, and the coercive force of the permanent magnet 2 is likely to increase. When the content of R is 26% by mass or more, the formation of an excess of soft magnetic phase (α-Fe phase, etc.) is suppressed, and it is easy to control the maximum width (grain size) of the soft magnetic particles 6 and the spacing of the soft magnetic regions in the easy axis direction within the desired range. On the other hand, when the content of R is 32% by mass or less, the formation of an excess of liquid phase (R-rich phase) is suppressed, and the volume ratio of the main phase is likely to increase. Furthermore, if the R content is 32 mass% or less, the soft magnetic phase, which is the precursor of the soft magnetic particles 6, is likely to precipitate on the surface of the alloy ribbon in the ribbon production process (ultra-rapid solidification method) described below.

Since the residual magnetic flux density and coercive force are likely to increase, the total proportion of Nd and Pr in the total rare earth elements R may be 80 atomic % or more and 100 atomic % or less, or 95 atomic % or more and 100 atomic % or less.

The total content of Tb and Dy in the permanent magnet 2 may be 0.00% by mass or more and 5.00% by mass or less. When the permanent magnet 2 contains at least one heavy rare earth element selected from Tb and Dy, the magnetic properties (particularly the coercive force at high temperatures) of the permanent magnet 2 tend to increase. However, the permanent magnet 2 does not have to contain Tb and Dy.

The content of B in the R-T-B system permanent magnet may be 0.77% by mass or more and 1.15% by mass or less. When the content of B is 0.77% by mass or more, the formation of heterogeneous phases such as _TbCu7 type _{R2Fe17 phase} having in-plane anisotropy is moderately suppressed, and the coercive force is likely to increase. When the content of B is 1.15% by mass or less, the formation of heterogeneous phases such as R1 _{+ εFe4B4} (Boride) is suppressed, and the coercive force is likely to increase. When the content of _B is within the above range, the squareness ratio of the permanent magnet 2 is likely to approach 1.0.

The permanent magnet 2 may contain gallium (Ga). For example, the Ga content may be 0.03 mass% or more and 1.00 mass% or less, or 0.20 mass% or more and 0.80 mass% or less. When the Ga content is within the above range, the generation of subphases (e.g., phases containing R, T and Ga) is appropriately suppressed, and the residual magnetic flux density and coercive force of the permanent magnet 2 tend to increase. However, the permanent magnet 2 does not have to contain Ga.

The permanent magnet 2 may contain aluminum (Al). For example, the Al content in the permanent magnet 2 may be 0.01 mass% or more and 0.2 mass% or less, or 0.04 mass% or more and 0.07 mass% or less. By having the Al content within the above range, the coercive force and corrosion resistance of the permanent magnet are likely to be improved. However, the permanent magnet 2 does not have to contain Al.

The permanent magnet 2 may contain copper (Cu). For example, 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. When the Cu content is within the above range, the permanent magnet 2 is easy to forge, and the coercive force, corrosion resistance, and temperature characteristics of the permanent magnet 2 are easily improved. However, the permanent magnet 2 does not have to contain Cu.

The permanent magnet 2 may contain cobalt (Co). For example, the content of Co in the permanent magnet 2 may be 0.30 mass% or more and 6.00 mass% or less, or 0.30 mass% or more and 4.00 mass% or less. When the permanent magnet 2 contains Co, the Curie temperature of the permanent magnet 2 is likely to be improved. Furthermore, when the permanent magnet 2 contains Co, the corrosion resistance of the permanent magnet 2 is likely to be improved. However, the permanent magnet 2 does not have to contain Co.

The remainder of permanent magnet 2, excluding the above elements, may be Fe only, or Fe and other elements. In order for permanent magnet 2 to have sufficient magnetic properties, the total content of elements other than Fe in the remainder may be 5 mass% or less of the total mass of permanent magnet 2.

The permanent magnet 2 may contain at least one element selected from the group consisting of silicon (Si), titanium (Ti), Mn (manganese), Zr (zirconium), vanadium (V), chromium (Cr), nickel (Ni), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), tin (Sn), calcium (Ca), carbon (C), nitrogen (N), oxygen (O), chlorine (Cl), sulfur (S), and fluorine (F) as other elements (e.g., inevitable impurities). For example, the total content of other elements in the permanent magnet 2 may be 0.001% by mass or more and 0.50% by mass.

For example, the composition of the entire permanent magnet 2 may be analyzed by X-ray fluorescence (XRF) analysis, inductively coupled plasma (ICP) emission spectrometry, inert gas fusion-non-dispersive infrared (NDIR) analysis, oxygen combustion-infrared absorption analysis, and inert gas fusion-thermal conductivity analysis.

The permanent magnet 2 may be applied to motors, generators, actuators, etc. For example, the permanent magnet 2 is used in various fields such as hybrid vehicles, electric vehicles, hard disk drives, magnetic resonance imaging devices (MRIs), smartphones, digital cameras, flat-screen TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators, and wind power generators.

(Manufacturing method of permanent magnets)
The method for producing a permanent magnet according to the present embodiment may include a ribbon preparation step, a hot pressing step, and a hot deforming step. The method for producing a permanent magnet may further include other steps, such as a grain boundary diffusion step, following the hot deforming step. However, the grain boundary diffusion step is not essential.

In order to suppress oxidation of the permanent magnet and its work-in-progress during the manufacturing process, the manufacturing method of the permanent magnet may be carried out under a non-oxidizing atmosphere. For example, the non-oxidizing atmosphere may be an inert gas such as argon (Ar) gas. The non-oxidizing atmosphere may further contain a reducing gas such as hydrogen gas (H ₂ ) in addition to the inert gas.

The ribbon production process is a process of producing an alloy ribbon from raw metal by the rapid solidification method. In the rapid solidification method, the molten metal in a crucible is ejected from a nozzle located at the tip of the container onto the surface of a chill roll. The molten metal comes into contact with the surface of the chill roll, and is instantly thrown off by the chill roll rotating at high speed, becoming a large number of elongated ribbons. The molten metal is rapidly cooled and solidified by contact with the surface of the chill roll. As a result, a large number of elongated alloy ribbons are formed. A container is installed in the direction in which the alloy ribbon is thrown off by the chill roll, and the alloy ribbon is collected in the container. The alloy ribbon may have an amorphous microstructure. The alloy ribbon is crystallized by heating during the hot forming process described later. A soft magnetic phase (e.g., α-Fe phase), which is a precursor of soft magnetic particles in a permanent magnet, precipitates on the surface of the alloy ribbon. The surface of the alloy ribbon on which the soft magnetic phase (e.g., α-Fe phase) is likely to precipitate is the surface opposite to the surface of the alloy ribbon that comes into contact with a cooling roll. Since the process of forming the alloy ribbon by the ultra-rapid solidification method is a thermodynamically non-equilibrium process, even if the molten metal has a composition in which a soft magnetic phase is not formed in an equilibrium phase diagram, a soft magnetic phase (e.g., α-Fe phase and R-T phase) can be formed on the surface of the alloy ribbon.
Among the soft magnetic phases, the R-T phase is a metastable phase, and in the hot plastic working process, the R-T phase reacts with a liquid phase mainly composed of a rare earth element R, and the R-T phase is easily decomposed into a main phase and an α-Fe phase. The higher the content of the rare earth element R in the alloy ribbon, the more easily a liquid phase is generated in the hot plastic working process, the more easily the R-T phase is decomposed by reaction with the liquid phase, and the more easily the proportion of the α-Fe phase in the soft magnetic particles increases. Since the saturation magnetization of the α-Fe phase is higher than that of the R-T phase, the remanence of the permanent magnet is easily increased as the content of the α-Fe phase in the soft magnetic particles increases.

The molten metal is a metal (raw metal) containing each of the elements that make up the permanent magnet. For example, the raw metal may be a rare earth element (metal element), an alloy containing a rare earth element, pure iron, ferroboron, or an alloy containing these. These raw metals are weighed out to match the composition of the desired permanent magnet.

The molten metal may be obtained by heating the raw metal in the container by high-frequency induction heating. For example, the temperature of the molten metal sprayed from the nozzle (spray temperature) may be 1300°C or higher and 1400°C or lower. For example, the rate of temperature rise until the temperature of the raw metal reaches the spray temperature may be about 20 to 100°C/sec.

For example, the nozzle may be made of quartz. For example, the nozzle hole diameter may be 0.6 mm or more and 1.0 mm or less. When the nozzle hole diameter is 0.6 mm or more and 1.0 mm or less, if the nozzle hole diameter is less than 0.6 mm, the average spacing between the multiple soft magnetic regions in the easy axis direction is likely to exceed 15 μm. When the nozzle hole diameter exceeds 1.0 mm, the average spacing between the multiple soft magnetic regions in the easy axis direction is likely to be less than 4 μm, and the average width (grain size) of the multiple soft magnetic particles in the easy axis direction is likely to exceed 5 μm.

In order to suppress oxidation of the molten metal, the atmosphere in the container of the molten metal may be replaced with an inert gas such as argon (Ar) gas. For example, the air pressure in the container of the molten metal may be 100 kPa or more and 240 kPa or less. The cooling roll is installed in the chamber. In order to suppress oxidation of the molten metal and the alloy ribbon (generation of oxides of R), the atmosphere in the chamber may be replaced with an inert gas such as argon (Ar) gas. For the same reason, the atmosphere in the chamber may contain a reducing gas such as hydrogen gas (H ₂ ) in addition to the inert gas. For example, the air pressure in the chamber may be 60 kPa or more and 200 kPa or less.

The air pressure in the container of the molten metal is higher than the air pressure in the chamber. The difference between the air pressure in the container of the molten metal and the air pressure in the chamber is the pressure of the molten metal sprayed from the nozzle (the spray pressure difference). For example, the spray pressure difference may be adjusted to 10 kPa or more and 40 kPa or less, or 20 kPa or more and 40 kPa or less.
As the injection pressure difference increases, the average value of the width (particle size) of the soft magnetic particles in the easy axis direction increases. When the injection pressure difference is 10 kPa or more, the average value of the width (particle size) of the soft magnetic particles in the easy axis direction is likely to be controlled to a value of 2 nm or more. When the injection pressure difference exceeds 40 kPa, the average value of the width (particle size) of the soft magnetic particles in the easy axis direction is likely to exceed 5 μm.
When the injection pressure difference is less than 20 kPa, the average spacing between the soft magnetic regions in the easy axis direction is likely to exceed 15 μm. When the injection pressure difference is more than 40 kPa, the average spacing between the soft magnetic regions in the easy axis direction is likely to be less than 4 μm.

For example, the surface of the chill roll may be made of a metal with high thermal conductivity such as Cu. The temperature of the surface of the chill roll may be controlled by a coolant flowing through the chill roll. For example, the temperature of the surface of the chill roll may be controlled so that the cooling rate of the molten metal on the surface of the chill roll is about 10 ⁵ to 10 ⁶ ° C./sec. When the cooling rate of the molten metal is adjusted to about 10 ⁵ to 10 ⁶ ° C./sec, an alloy ribbon composed of a microstructure in which a nanoscale main phase (R ₂ T ₁₄ B) and a soft magnetic phase (α-Fe phase, etc.) are mixed is easily formed. The higher the cooling rate, the finer the crystal grain size of each of the main phase (R ₂ T ₁₄ B) and the soft magnetic phase (α-Fe phase, etc.) contained in the alloy ribbon is, and the coercive force of the permanent magnet is easily increased. The smaller the amount of molten metal sprayed onto the surface of the chill roll per unit time, the thinner the molten metal attached to the surface of the chill roll becomes, the higher the cooling rate becomes, and the thinner the alloy ribbon becomes. The higher the peripheral speed of the chill roll, the thinner the molten metal adhering to the surface of the chill roll, the higher the cooling rate, and the thinner the alloy ribbon. The thickness of the main phase particles in the direction of easy magnetization (the length of the short axis of the main phase particles) depends on the thickness of the alloy ribbon (as well as the crushing and classification of the alloy ribbon). The thinner the alloy ribbon, the smaller the thickness (particle diameter) of the main phase particles, and the higher the coercive force of the permanent magnet tends to be. For example, the thickness of the alloy ribbon may be 20 μm or more and 60 μm or less, or 30 μm or more and 50 μm or less. For example, the width of the alloy ribbon may be 1.0 mm or more and 5.0 mm or less.

For example, the circumferential speed of the chill roll may be 30 m/sec or more and 60 m/sec or less.
As the circumferential speed of the chill roll decreases, the area fraction of the soft magnetic particles in the cross section of the permanent magnet (cross section parallel to the easy axis of magnetization) increases. When the circumferential speed of the chill roll is less than 40 m/sec, the area fraction of the soft magnetic particles in the cross section of the permanent magnet (cross section parallel to the easy axis of magnetization) is likely to be controlled to a value of 4% or more. When the circumferential speed of the chill roll is less than 30 m/sec, the area fraction of the soft magnetic particles in the cross section of the permanent magnet (cross section parallel to the easy axis of magnetization) is likely to exceed 15%.
As the peripheral speed of the chill roll decreases, the average spacing between the soft magnetic regions in the easy axis direction decreases. When the peripheral speed of the chill roll is less than 20 m/s, the average spacing between the soft magnetic regions in the easy axis direction is likely to become less than 4 μm.
As the circumferential speed of the chill roll decreases, the average width (particle size) of the soft magnetic particles in the direction of the easy axis of magnetization increases. When the circumferential speed of the chill roll is 60 m/s or less, the average width (particle size) of the soft magnetic particles in the direction of the easy axis of magnetization is easily controlled to a value of 2 nm or more. When the circumferential speed of the chill roll is less than 30 m/s, the average width (particle size) of the soft magnetic particles in the direction of the easy axis of magnetization is easily controlled to a value of 5 μm or more.

After the ribbon preparation process, a pulverization/classification process may be performed. The pulverization/classification process is a process in which the alloy ribbon is pulverized using a pulverizer to produce coarse powder, and the coarse powder is classified to recover an alloy powder having a predetermined particle size and aspect ratio. The alloy powder is a precursor of the main phase particles contained in the permanent magnet. The shape of each alloy particle constituting the alloy powder may be plate-like or flake-like. For example, the pulverization method of the alloy ribbon may be at least one of a cutter mill and a propeller mill. The means for classifying the coarse powder is a sieve. For example, the particle size and particle size distribution of the alloy powder obtained by classification may be measured by a laser diffraction scattering method. For example, the particle size of the alloy powder obtained by classification may be 60 μm or more and 2800 μm or less, or 150 μm or more and 2800 μm or less.

The hot compacting step is a step of forming a compact by pressing an alloy strip (alloy powder) while heating it. For example, the alloy powder may be compressed in a die while heating the alloy powder in the die. Pressurizing the alloy powder reduces the gaps between the alloy powder, resulting in a dense compact. Heating the alloy powder with pressurization crystallizes the alloy strip. Furthermore, heating the alloy powder with pressurization forms a liquid phase (R-rich phase such as Nd-rich phase) from the surface of the alloy powder, and the liquid phase fills the gaps (grain boundaries) between the alloy powder, and the liquid phase lubricates the alloy powder, resulting in a dense compact. A cold compacting step may be performed before the hot compacting step. In the cold compacting step, a compact may be formed by pressing the alloy powder at room temperature (room temperature). The compact obtained by the cold compacting step may be densified by pressing the compact obtained by the cold compacting step while heating it in the hot compacting step. For example, the temperature of the alloy powder in the hot compacting step (hot compacting temperature) may be 550°C or more and 800°C or less. If the hot compacting temperature is too low, a sufficient liquid phase is not formed from the surface of the alloy powder, and the compact is difficult to densify. If the hot compacting temperature is too high, the grain growth of the crystals ( _R2T14B ) constituting the alloy powder proceeds excessively, and the coercive force of the permanent magnet is likely to decrease. For example, the pressure applied to the alloy powder in the hot _compacting step (hot compacting pressure) may be 50 MPa or more and 300 MPa or less. For example, the time (hot compacting time) during which the combined hot compacting temperature and hot compacting pressure are maintained in the above range may be several tens of seconds or more and several hundreds of seconds or less.

After the hot compaction step, a hot plastic working step is performed. The hot plastic working step is a step of obtaining a magnet base material including a plurality of main phase grains (R ₂ T ₁₄ B crystal grains) whose c-axes (axis of easy magnetization) are oriented in a predetermined direction by heating and pressurizing the compact obtained by the hot compaction step. For example, die upset forging may be performed as the hot plastic working step. For example, hot extrusion may be performed as the hot plastic working step.

Heating during the hot plastic processing process liquefies the grain boundary phase in the compact, generating a liquid phase (R-rich phase). Pressurization during the hot plastic processing process applies stress to the compact in a specific direction, distorting each alloy particle (alloy ribbon) that constitutes the compact. As the liquid phase is generated and the alloy particles are distorted, anisotropic growth of the crystal grains progresses in a direction perpendicular to the c-axis of the crystal grains. The liquid phase also lubricates each crystal grain, and a force acts on each crystal grain in response to the stress. As a result, the crystal grains rotate due to grain boundary sliding, and the c-axis of each crystal grain (main phase particle) is oriented parallel to the stress direction. In other words, multiple flat main phase particles extending in a direction perpendicular to the c-axis are stacked along the stress direction. The magnetization easy axis direction of the magnet base material is approximately or completely parallel to the stress direction. As each crystal grain (main phase particle) is oriented, the surface on which the soft magnetic phase (such as the α-Fe phase) precipitated in the alloy ribbon from which the main phase particles originated becomes approximately or completely perpendicular to the direction of the easy magnetization axis (stress direction). The soft magnetic phase precipitated on the surface of the alloy ribbon becomes multiple soft magnetic particles aligned in a direction approximately or completely perpendicular to the direction of the easy magnetization axis. As a result, multiple soft magnetic regions (soft magnetic layers) are formed that are alternately arranged with one or more main phase particles in the direction of the easy magnetization axis.

For example, the temperature of the formed body in the hot plastic working step (hot plastic working temperature) may be 700°C or higher and lower than 900°C, or 700°C or higher and 850°C or lower.
If the hot plastic working temperature is too low, liquid phases (R-rich phases such as Nd-rich phases) are unlikely to form at the grain boundaries in the compact, crystal grains are unlikely to grow, and crystal grain rotation due to grain boundary sliding is unlikely to occur. As a result, the average length of the minor axis of the main phase grains is likely to be less than 20 nm, and the c-axes of each main phase grain (crystal grain) are unlikely to be oriented parallel to the stress direction.
When the hot plastic processing temperature is too high (for example, when the hot plastic processing temperature is 900° C. or higher), the liquid phase (R-rich phase) seeps out excessively from each alloy particle and segregates to the surface of each alloy particle and the interface between the alloy particles, and most of the liquid phase is consumed in the grain growth of the crystal grains. Since most of the liquid phase is consumed in the grain growth of the crystal grains, the grain growth of the main phase particles (crystal grains) progresses abnormally, and coarse main phase particles are likely to be formed, and the average length of the minor axis of the main phase particles is likely to exceed 200 nm. The coarse main phase particles are difficult to orient in the direction of the easy axis of magnetization.
For example, the pressure applied to the formed body in the hot plastic working step (hot plastic working pressure) may be 50 MPa or more and 200 MPa or less. For example, the time during which the hot plastic working temperature and the hot plastic working pressure are maintained within the above ranges (hot plastic working time) may be several tens of seconds.

The magnet base material obtained by the above process may be a finished permanent magnet. The magnet base material that has undergone the grain boundary diffusion process described below may be a finished permanent magnet.

After the cooling process, the grain boundary diffusion process described below may be carried out.

For example, in the grain boundary diffusion process, a diffusing material containing a heavy rare earth element may be attached to the surface of the magnet base material, and the diffusing material and the magnet base material may be heated. By heating the magnet base material to which the diffusing material is attached, the heavy rare earth element in the diffusing material diffuses from the surface of the magnet base material to the inside of the magnet base material. Inside the magnet base material, the heavy rare earth element diffuses through the grain boundaries to the vicinity of the surface of the main phase particles. In the vicinity of the surface of the main phase particles, some of the light rare earth elements (Nd, etc.) are replaced with the heavy rare earth element. By localizing the heavy rare earth element near the surface and at the grain boundaries of the main phase particles, the anisotropic magnetic field becomes locally large near the grain boundaries, and it becomes difficult for nuclei of magnetization reversal to occur near the grain boundaries. As a result, a permanent magnet with high coercivity is obtained.

For example, the temperature (diffusion temperature) of the diffusion material containing a heavy rare earth element and the magnet base material may be 550°C or more and 900°C or less. For example, the time (diffusion time) during which the diffusion temperature is maintained in the above range may be 1 minute or more and 1,440 minutes or less.

The diffusion material may contain at least one heavy rare earth element selected from Tb and Dy. The diffusion material may further contain at least one light rare earth element selected from Nd and Pr in addition to the heavy rare earth element. The diffusion material may further contain Cu in addition to the heavy rare earth element and the light rare earth element. For example, the diffusion material may be a metal consisting of one of the above elements, a hydride of one of the above elements, an alloy containing multiple types of the above elements, or a hydride of the alloy. The diffusion material may be a powder. In the grain boundary diffusion process, a slurry containing the diffusion material and an organic solvent may be applied to the surface of the magnet substrate. In the grain boundary diffusion process, the surface of the magnet substrate may be covered with a sheet containing the diffusion material and a binder. In the grain boundary diffusion process, the surface of the magnet substrate may be covered with an alloy foil (ribbon) composed of the diffusion material.

A eutectic alloy (such as Nd-Cu and Nd-Al) containing a rare earth element R may be introduced into the magnet base material by a grain boundary diffusion process. For example, a diffusion material containing a eutectic alloy may be attached to the surface of the magnet base material, and the diffusion material and magnet base material may be heated. For example, the diffusion material containing a eutectic alloy may be a fine ribbon made of a eutectic alloy. The melting point of the eutectic alloy is lower than the melting point of the magnet base material itself. Therefore, by heating the diffusion material containing a eutectic alloy and the magnet base material at a temperature equal to or higher than the melting point of the eutectic alloy and lower than the melting point of the magnet base material, the molten eutectic alloy penetrates and diffuses from the surface of the magnet base material to the grain boundaries in the magnet base material. As a result, a permanent magnet with high coercivity is easily obtained.

The surface of the magnet base material may be polished before the grain boundary diffusion process to promote diffusion of the diffusion material. The surface of the magnet base material may be polished after the grain boundary diffusion process to remove the diffusion material remaining on the surface of the magnet base material after the grain boundary diffusion process.

The dimensions and shape of the magnet substrate may be adjusted by cutting and polishing the magnet substrate. A passive layer may be formed on the surface of the magnet substrate by oxidation or chemical treatment of the surface of the magnet substrate. The surface of the magnet substrate may be covered with a protective film such as a resin film. The passive layer or protective film improves the corrosion resistance of the permanent magnet.

The present invention is not necessarily limited to the above-described embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the present invention.

The present invention will be described in detail with reference to the following examples and comparative examples. The present invention is not limited to the following examples.

Example 1
Each step of Example 1 below was carried out in a non-oxidizing atmosphere (Ar gas).

In the ribbon production step, an alloy ribbon was produced from the raw alloy by the above-mentioned ultra-rapid solidification method. The raw alloy metals (molten metal) used in the ribbon production step were composed of Nd, Fe, Co, Ga, Al and B.
The Nd content in the raw material metal was 29.00 mass %.
The Fe content in the raw material metal was 64.52 mass %.
The Co content in the raw material metal was 5.02 mass %.
The Ga content in the raw material metal was 0.53 mass %.
The Al content in the raw material metal was 0.03 mass %.
The B content in the raw material metal was 0.90 mass %.

The temperature of the molten metal sprayed from the quartz nozzle (spray temperature) was 1300° C. The cooling rate of the molten metal on the surface of the copper chill roll was about 10 ⁵ ° C./sec. The gas (atmosphere) in the chamber in which the chill roll was placed was Ar. The atmospheric pressure in the chamber was 50 kPa.

The gas supplied into the molten metal container was Ar. The injection pressure difference (unit: kPa), which is the difference between the air pressure inside the molten metal container and the air pressure inside the chamber, was the value shown in Table 1 below. The nozzle hole diameter (unit: mm) was the value shown in Table 1 below. The peripheral speed of the chill roll (unit: m/sec) was the value shown in Table 1 below.

In the hot forming process, the alloy powder was compressed in a die while the alloy powder in the die was heated, to produce a compact. The compact was cylindrical. The diameter of the end face (circle) of the cylinder (i.e., the thickness of the cylinder) was 10 mm. The height of the cylinder was 10 mm. The hot forming temperature was 700°C. The hot forming pressure was 300 MPa. The hot forming time was 180 seconds.

In the hot plastic processing process, a permanent magnet was produced from the compact by die upset forging. In die upset forging, pressure perpendicular to the end face of the compact (cylinder) was applied to the compact while the compact was heated at 800°C. In other words, a disk-shaped permanent magnet was produced by crushing the compact in a direction perpendicular to the end face of the compact. The thickness direction of the permanent magnet was the easy axis direction C of the permanent magnet. In other words, the direction perpendicular to the circular surface of the permanent magnet was the easy axis direction C of the magnet. The height of the permanent magnet (disc thickness) is expressed as hf (unit: mm). The height of the compact (cylinder) before pressure is expressed as hi (unit: mm). As mentioned above, hi is 10 mm. The time required for hi to decrease to hf is expressed as T (unit: seconds). T can be rephrased as the time required to pressurize the compact. The draft is defined as (hi-hf)/hi x 100. The unit of the draft is %. The draft was 78%. That is, hf was 2.2 mm. The press speed is defined as (hi-hf)/T. The unit of the draft is mm/sec. The draft was 0.1 mm/sec. That is, T was 78 seconds.

(Examples 2 to 7 and Comparative Examples 1 to 4)
The jet differential pressure of each of Examples 2 to 7 and Comparative Examples 1 to 4 was the value shown in the following Table 1. The nozzle hole diameter of each of Examples 2 to 7 and Comparative Examples 1 to 4 was the value shown in the following Table 1. The peripheral speed of the chill roll of each of Examples 2 to 7 and Comparative Examples 1 to 4 was the value shown in the following Table 1.

The permanent magnets of Examples 2 to 7 and Comparative Examples 1 to 4 were produced in the same manner as Example 1, except for the above points.

(Comparative Example 5)
The raw material metal (molten metal) used in the ribbon production process of Comparative Example 5 was composed of Nd, Tb, Fe, Co, Ga, Al, and B. The composition of the raw material metal of Comparative Example 5 was approximately or completely consistent with the stoichiometric composition of R ₂ T ₁₄ B.
The Nd content in the raw metal of Comparative Example 5 was 25.62 mass %.
The Tb content in the raw metal of Comparative Example 5 was 0.06 mass %.
The Fe content in the raw material metal of Comparative Example 5 was 70.46 mass %.
The Co content in the raw material metal of Comparative Example 5 was 2.53 mass %.
The Ga content in the raw material metal of Comparative Example 5 was 0.20 mass %.
The Al content in the raw metal of Comparative Example 5 was 0.18 mass %.
The B content in the raw metal of Comparative Example 5 was 0.95 mass %.

The injection differential pressure in Comparative Example 5 was the value shown in Table 1 below. The nozzle hole diameter in Comparative Example 5 was the value shown in Table 1 below. The peripheral speed of the cooling roll in Comparative Example 5 was the value shown in Table 1 below.

The permanent magnet of Comparative Example 5 was produced in the same manner as in Example 1, except for the above points.

(Examples 8 to 11)
The raw metals (molten metal) used in the ribbon production process in each of Examples 8 to 11 were composed of Nd, Fe, Co, Ga, Al and B.

The Nd content in the raw material metal of Example 8 was 29.82 mass %.
The Fe content in the raw material metal of Example 8 was 65.15 mass %.
The Co content in the raw material metal of Example 8 was 3.59 mass %.
The Ga content in the raw material metal of Example 8 was 0.53 mass %.
The Al content in the raw metal of Example 8 was 0.02 mass %.
The B content in the raw metal of Example 8 was 0.89 mass %.

The Nd content in the raw metal of Example 9 was 29.66 mass %.
The Fe content in the raw material metal of Example 9 was 65.24 mass %.
The Co content in the raw metal of Example 9 was 3.57 mass %.
The Ga content in the raw material metal of Example 9 was 0.53 mass %.
The Al content in the raw metal of Example 9 was 0.02 mass %.
The B content in the raw metal of Example 9 was 0.98 mass %.

The Nd content in the raw metal of Example 10 was 29.54 mass %.
The Fe content in the raw material metal of Example 10 was 65.31 mass %.
The Co content in the raw material metal of Example 10 was 3.56 mass %.
The Ga content in the raw material metal of Example 10 was 0.53 mass %.
The Al content in the raw metal of Example 10 was 0.02 mass %.
The B content in the raw metal of Example 10 was 1.04 mass %.

The Nd content in the raw metal of Example 11 was 29.42 mass %.
The Fe content in the raw material metal of Example 11 was 65.39 mass %.
The Co content in the raw material metal of Example 11 was 3.55 mass %.
The Ga content in the raw material metal of Example 11 was 0.52 mass %.
The Al content in the raw metal of Example 11 was 0.02 mass %.
The B content in the raw material metal of Example 11 was 1.10 mass %.

The permanent magnets of Examples 8 to 11 were produced in the same manner as Example 1, except for the above points.

<Analysis of Permanent Magnets>
(Permanent Magnet Composition and Microstructure)
A backscattered electron image of the cross section of each of the permanent magnets of Examples 1 to 11 and Comparative Examples 1 to 5 was taken by a scanning electron microscope (SEM). The cross section of each permanent magnet was parallel to the magnetization easy axis direction C of each permanent magnet. The composition of the cross section of each permanent magnet was analyzed by an energy dispersive X-ray spectroscopy (EDS) device mounted on the scanning electron microscope. Backscattered electron images of a portion of the cross section of Example 1 are shown in (a) and (b) of FIG. 3. Backscattered electron images of a portion of the cross section of Comparative Example 5 are shown in (a) and (b) of FIG. 4.

In all cases of Examples 1 to 11 and Comparative Examples 1 to 5, the permanent magnets had the following characteristics.
The overall composition of the permanent magnets matched that of the source metals.
The permanent magnet contained numerous primary phase grains (R ₂ T ₁₄ B grains).
Each of the main phase grains contained at least Nd as R and at least Fe as T.
Each main phase grain observed in cross section was flat.
The minor axis of each main phase grain was approximately parallel or completely parallel to the direction C of easy axis of magnetization.
The major axis of each main phase grain was approximately perpendicular or completely perpendicular to the direction C of easy axis of magnetization.
A large number of flat main phase grains were stacked along the direction of easy axis C of magnetization.
The permanent magnet included a plurality of soft magnetic particles.
Each soft magnetic particle was identified as the darkest part in the cross-sectional backscattered electron image (see FIG. 3(a)).
The total content of Fe and Co in each soft magnetic particle was 70 mass % or more. Soft magnetic particles containing an α-Fe phase, soft magnetic particles containing an Fe ₃ B phase, and soft magnetic particles containing an Fe ₂ Co phase were detected.

The permanent magnets of all the examples had the following characteristics. The permanent magnets of all the comparative examples except for Comparative Example 5 also had the following characteristics.
The cross section of the permanent magnet included a plurality of soft magnetic regions.
Each of the soft magnetic regions included a plurality of soft magnetic grains aligned along an AB direction perpendicular to the easy axis C of magnetization.
In the direction of easy axis C, a plurality of main phase grains and a plurality of soft magnetic regions were arranged alternately.

As shown in FIG. 4(b), multiple soft magnetic particles were randomly distributed in the cross section of the permanent magnet of Comparative Example 5. In other words, the cross section of the permanent magnet of Comparative Example 5 did not include a soft magnetic region containing multiple soft magnetic particles aligned along the AB direction perpendicular to the magnetization easy axis direction C.

(Measurements on soft magnetic particles)
The backscattered electron image of the cross section of the permanent magnet of Example 1 shown in (a) of Figure 5 is identical to (a) of Figure 3. In other words, the backscattered electron image in (a) of Figure 5 is parallel to the magnetization easy axis direction C. The dimensions of the backscattered electron image in (a) of Figure 5 are 63.5 μm vertical × 47.6 μm horizontal.

The backscattered electron image of (a) in FIG. 5 was converted into the monochrome image of (b) in FIG. 5 by threshold processing (binarization processing) based on the RGB color model (Red-Green-Blue color model). Each of the multiple black parts in the monochrome image of (b) in FIG. 5 corresponds to a soft magnetic particle. The area of each soft magnetic particle in the monochrome image of (b) in FIG. 5 was measured. Based on the measured area of each soft magnetic particle, the area fraction of the multiple soft magnetic particles in the cross section of the permanent magnet (the monochrome image in (b) in FIG. 5) was calculated.
Using the same method as above, the area fractions of the soft magnetic particles in a total of 10 regions in the cross section of the permanent magnet of Example 1 were calculated. The average area fraction Ra_avg was calculated from the area fractions of the 10 regions. The average area fraction Ra_avg of the soft magnetic particles of Example 1 is shown in Table 1 below.

The outline of each soft magnetic particle in the monochrome image of FIG. 5(b) was extracted by image processing of the monochrome image of FIG. 5(b). Each of the multiple closed curves (ellipses) included in the image shown in FIG. 5(c) corresponds to the outline of each soft magnetic particle in the monochrome image of FIG. 5(b). In other words, the image of FIG. 5(c) was obtained by approximating the outline of each soft magnetic particle in the monochrome image of FIG. 5(b) with an ellipse (including a perfect circle). The approximation of the outline of each soft magnetic particle with an ellipse was performed by fitting based on the least squares method. Parts of the black parts in the monochrome image that were less than or equal to (10 nm long x 10 nm wide) were removed from the image as noise. In the image processing of the monochrome image of FIG. 5(b), the soft magnetic particles that were interrupted at the edge of the image were removed from the image.

The length of the major axis of the ellipse approximating the contour of each soft magnetic particle in the image (c) in FIG. 5 was measured. That is, the Feret's diameter of the ellipse approximating the contour of each soft magnetic particle in the image (c) in FIG. 5 was measured. Furthermore, the average value of the length of the major axis of the ellipse approximating the contour of each soft magnetic particle in the image (c) in FIG. 5 was calculated. The width of each of the soft magnetic particles in the easy axis direction is equal to or less than the length of the major axis of the ellipse approximating the contour of each soft magnetic particle. Therefore, the length of the major axis of the ellipse approximating the contour of each soft magnetic particle is regarded as the maximum width of the particle diameter of each soft magnetic particle, and is regarded as the width (maximum width) of each soft magnetic particle in the easy axis direction. The average value of the width of each soft magnetic particle in the image (c) in FIG. 5 was calculated.
A total of 10 reflected electron images were taken in the cross section of the permanent magnet at the same magnification as the reflected electron image in (a) in FIG. 5. One of the total 10 locations is the portion shown in (a) in FIG. 5. Furthermore, the average value of the width (ferret diameter) of each soft magnetic particle in each reflected electron image was calculated by the same image processing as above. That is, 10 average values were calculated as the average value of the width of the soft magnetic particles. The average value Ws_avg of the width (maximum width) of the multiple soft magnetic particles in the magnetization easy axis direction was calculated by dividing the sum of the 10 average values by 10. The average value Ws_avg of the width of the multiple soft magnetic particles in Example 1 is shown in Table 1 below.

The monochrome images shown in (b) of FIG. 5, (a) of FIG. 6, (a) of FIG. 7, (a) of FIG. 8, and (a) of FIG. 9 are identical.
FIG. 6B is a distribution diagram of gray values obtained by a line scan along the scanning direction dc in the measurement area a1 shown in FIG. 6A.
FIG. 7B is a distribution diagram of gray values obtained by line scanning along the scanning direction dc in the measurement area a2 shown in FIG.
FIG. 8B is a distribution diagram of gray values obtained by line scanning along the scanning direction dc in the measurement area a3 shown in FIG. 8A.
FIG. 9B is a distribution diagram of gray values obtained by line scanning along the scanning direction dc in the measurement area a4 shown in FIG. 9A.
The scanning direction dc is parallel to the magnetization easy axis direction C. The origin of the horizontal axis in each of Fig. 6(b), Fig. 7(b), Fig. 8(b), and Fig. 9(b) is the point where the line scan starts. The horizontal axis in each of Fig. 6(b), Fig. 7(b), Fig. 8(b), and Fig. 9(b) indicates the distance (unit: μm) in the magnetization easy axis direction.
The gray value is a relative value that depends on the method of binarization processing, and the unit of the gray value is an arbitrary unit. The apex of the peak with a gray value of 50 or more is considered to be the position of the soft magnetic particle. Therefore, the distance between the apexes of a pair of adjacent peaks is considered to be the interval between a pair of adjacent soft magnetic particles in the direction of the easy magnetization axis. In other words, the distance between the apexes of a pair of adjacent peaks is considered to be the interval between a pair of adjacent soft magnetic regions in the direction of the easy magnetization axis.
In each of the above-mentioned measurement regions a2, a2, a2, and a4, the intervals between the soft magnetic regions in the direction of the easy axis of magnetization (scanning direction dc) were measured. Furthermore, in each of six measurement regions other than the measurement regions a2, a2, a2, and a4, the intervals between the soft magnetic regions in the direction of the easy axis of magnetization (scanning direction dc) were calculated.
Each of the 10 measurement regions described above was randomly selected from a portion of the image of the mochrome in FIG. 5B where a plurality of main phase grains and a plurality of soft magnetic regions are alternately arranged in the direction of the easy axis of magnetization. The intervals between the plurality of soft magnetic regions measured in the 10 measurement regions were averaged to obtain an average value Int_avg of the intervals between the plurality of soft magnetic regions in the direction of the easy axis of magnetization (scanning direction dc). The average value Int_avg of the intervals between the plurality of soft magnetic regions in Example 1 is shown in Table 1 below.

The measurements on the soft magnetic particles described above were performed using ImageJ, a public domain image processing software.

In the same manner as in Example 1, the average value Ra_avg of the area fraction of the plurality of soft magnetic particles in each of Examples 2 to 11 and Comparative Examples 1 to 5 was calculated.
In the same manner as in Example 1, the average value Ws_avg of the widths of the multiple soft magnetic particles in each of Examples 2 to 11 and Comparative Examples 1 to 5 was calculated.
In the same manner as in Example 1, the average value Int_avg of the spacing between the multiple soft magnetic regions was calculated for each of Examples 2 to 11 and Comparative Examples 1 to 5.
The Ra_avg, Ws_avg, and Int_avg of each of Examples 2 to 11 and Comparative Examples 1 to 5 are shown in Tables 1 and 2 below.

A flake was obtained by polishing the permanent magnet of Example 1 with a focused ion beam (FIB). The thickness of the flake was 100 nm. The composition of each of the three soft magnetic particles (particles 1 to 3) contained in the flake was analyzed. Particles 1 to 3 were aligned along the AB direction perpendicular to the magnetization easy axis direction C in one soft magnetic region. The composition of each of particles 1 to 3 was analyzed by STEM-EDS. The concentration (unit: atomic %) of each element in each of particles 1 to 3 is shown in Table 3 below. The [T]/[R] of each of particles 1 to 3 is also shown in Table 3 below. The inventors speculate that the Cu detected in each soft magnetic particle is an impurity derived from the cooling roll. Soft magnetic particles with [T]/[R] of 8.4 to 8.8 were considered to be soft magnetic particles containing an R-T phase. The definition of [T]/[R] is as described above. Soft magnetic particles with a [T]/[R] of 99.0 or more were considered to be soft magnetic particles containing the α-Fe phase. Particles 1 and 2 in Example 1 were soft magnetic particles containing the R-T phase. Particle 3 in Example 1 was a soft magnetic particle containing the α-Fe phase.

In the same manner as in Example 1, the composition of the soft magnetic particles in each of Examples 2 to 11 and Comparative Examples 1 to 5 was analyzed.
In all of Examples 2 to 7 and Comparative Examples 1 to 5, both soft magnetic particles containing an RT phase and soft magnetic particles containing an α-Fe phase were detected.
On the other hand, in all of Examples 8 to 11, soft magnetic particles containing an α-Fe phase were detected, but soft magnetic particles containing an RT phase were not detected.

(Measurements on main phase particles)
A backscattered electron image of the cross section of each of the permanent magnets of Examples 1 to 11 and Comparative Examples 1 to 5 was taken by SEM. The cross section on which the backscattered electron image was taken was parallel to the magnetization easy axis direction C. The size of the backscattered electron image was 63.5 μm in length × 47.6 μm in width. Ten representative locations in the backscattered electron image were selected, and the backscattered electron image of each location was taken at a high magnification. The minor axis diameter (length of the minor axis) of the main phase particles (primary particles) present in the high magnification backscattered electron image was measured. The shape of each main phase particle was approximated by a rectangle with the smallest area among the rectangles circumscribing the main phase particle. The length of the short side of the rectangle was considered to be the minor axis diameter of the main phase particle. ImageJ, which is a public domain image processing software, was used to approximate the shape of each main phase particle. The average value Dm_avg of the minor axis diameters of all the main phase particles present in the high magnification backscattered electron image was calculated. The Dm_avg of each of Examples 1 to 11 and Comparative Examples 1 to 5 is shown in Tables 1 and 2 below.

(Measurement of magnetic properties of permanent magnets)
The coercive force (HcJ), residual magnetic flux density (Br), and squareness ratio (Hk/HcJ) of each of the permanent magnets of Examples 1 to 11 and Comparative Examples 1 to 5 were measured. The coercive force, residual magnetic flux density, and squareness ratio were measured using a BH tracer. The coercive force was measured at 23°C. The residual magnetic flux density was measured at room temperature. The squareness ratio was measured at 23°C. The measured values are shown in Tables 1 and 2 below.

For example, the R-T-B permanent magnet according to one aspect of the present invention may be used as a material for the motor installed in an electric vehicle or hybrid vehicle.

2... R-T-B system permanent magnet, 2cs... Cross section of R-T-B system permanent magnet (cross section parallel to the axis of easy magnetization), 4... Main phase particle, 6... Soft magnetic particle, 8... Subphase Particle, sm...soft magnetic region.

Claims (7)

An R-T-B system permanent magnet containing a rare earth element R, a transition metal element T, and boron,
The R-T-B system permanent magnet contains at least Nd as the rare earth element R,
The R-T-B system permanent magnet contains at least Fe as the transition metal element T,
the R-T-B based permanent magnet includes a plurality of main phase particles and a plurality of soft magnetic particles,
a plurality of the main phase particles contain at least the rare earth element R, the transition metal element T, and the boron;
The soft magnetic particles contain at least Fe,
A cross section of the R-T-B system permanent magnet includes a plurality of soft magnetic regions,
the cross section of the R-T-B system permanent magnet is parallel to the magnetization easy axis direction of the R-T-B system permanent magnet,
Each of the soft magnetic regions includes a plurality of the soft magnetic grains aligned along a direction perpendicular to the easy axis direction,
a plurality of the main phase grains and a plurality of the soft magnetic regions are alternately arranged in the direction of the easy magnetization axis,
an average value of widths of the soft magnetic particles in the direction of the easy axis of magnetization is 20 nm or more and 5 μm or less;
R-T-B series permanent magnet. an average value of intervals between the soft magnetic regions in the easy axis direction is 4 μm or more and 15 μm or less;
The R-T-B system permanent magnet according to claim 1 . the area fraction of the soft magnetic particles in the cross section of the R-T-B system permanent magnet is 4% or more and 15% or less;
The R-T-B system permanent magnet according to claim 1 . At least a portion of the soft magnetic particles includes an R-T phase including the rare earth element R and the transition metal element T.
The R-T-B system permanent magnet according to claim 1 . The content of the rare earth element R is 26% by mass or more and 32% by mass or less,
The boron content is 0.77% by mass or more and 1.15% by mass.
The R-T-B system permanent magnet according to claim 1 . a plurality of the main phase grains observed in the cross section of the R-T-B system permanent magnet are flat;
The R-T-B system permanent magnet according to claim 1 . a width of the main phase grains in the direction of the easy axis of magnetization is smaller than a width of the main phase grains in a direction perpendicular to the easy axis direction,
an average width of the plurality of main phase grains in the direction of the easy axis of magnetization is 20 nm or more and 200 nm or less;
The R-T-B system permanent magnet according to claim 1 .

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