Rare-earth permanent magnet and rotating electrical machine including the same

Abstract

To provide a rare earth permanent magnet having improved corrosion resistance on one end face and a rotary electric machine equipped with the rare earth permanent magnet.SOLUTION: A rare earth permanent magnet has a first surface, and when the coercive force of a portion a1 including the center of gravity of the first surface is A1, the coercive force of a portion b1 including the edge of the first surface separated from the portion a1 in the Y direction perpendicular to the normal direction at the center of gravity of the first surface is B1, the coercive force of a portion c1 including the edge of the first surface separated from the portion a1 in the normal direction and the X direction perpendicular to the Y direction at the center of gravity of the first surface is C1, and the coercive force of a portion d1 including the edge of the first surface separated from the portion a1 in the -X direction opposite to the X direction is D1, A1<B1, A1≥C1, and A1≥D1 are satisfied, and a heavy rare earth element is present on the surface layer of the first surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rare earth permanent magnet and a rotating electrical machine including the same.

Background Art

[0002] Conventionally, an R-T-B sintered magnet containing a heavy rare earth element in which the coercive force at the central portion of the main surface is larger than the coercive force at the end portion of the main surface is known by applying the heavy rare earth element only to one main surface or two opposing main surfaces.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Depending on the use of the magnet, it may be desired to improve the corrosion resistance on one end face.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a rare earth permanent magnet having improved corrosion resistance on one end face, and a rotating electrical machine including the same.

Means for Solving the Problems

[0006] The rare earth permanent magnet according to the present invention has a first surface. Let the coercivity of portion a1 including the centroid of the first surface be A1, the coercivity of portion b1 including the end of the first surface that is separated from portion a1 in the Y direction perpendicular to the normal direction at the centroid of the first surface be B1, the coercivity of portion c1 including the end of the first surface that is separated from portion a1 in the X direction perpendicular to the normal direction and the Y direction at the centroid of the first surface be C1, and the coercivity of portion d1 including the end of the first surface that is separated from portion a1 in the -X direction opposite to the X direction be D1. When A1 < B1, A1 ≥ C1, and A1 ≥ D1 are satisfied, a heavy rare earth element is present in the surface layer portion of the first surface.

[0007] According to the present invention, since A1 < B1 is satisfied, it is possible to provide a rare earth permanent magnet with improved corrosion resistance at one end in the Y direction.

[0008] Regarding the mechanism by which corrosion occurs at the end of the rare earth permanent magnet and the reason why the corrosion resistance at the end of the rare earth permanent magnet is improved when the rare earth permanent magnet satisfies A1 < B1, the inventor of the present invention thinks as follows. That is, a phase (R-rich phase) having a higher content of rare earth element R than the main phase, which exists at the grain boundary of the rare earth permanent magnet, is easily oxidized. The R in the R-rich phase existing at the grain boundary is corroded by water derived from water vapor or the like in the use environment and changes into a hydroxide, and hydrogen is generated in the process. This process is represented by the following formula (I).

[0009] 2R + 6H2O → 2R(OH)3 + 3H2 ··· (I)

[0010] The generated hydrogen is occluded in the uncorroded R-rich phase. This process is represented by the following formula (II).

[0011] 2R + xH2 → 2RH x ··· (II)

[0012] By storing hydrogen, the R-rich phase becomes more susceptible to corrosion, and through the corrosion reaction of the hydrogen-stored R-rich phase with water, more hydrogen is generated than the amount stored in the R-rich phase. This process is represented by the following formula (III).

[0013] 2RH x +6H2O→2R(OH)3+(3+x)H2···(III)

[0014] Due to the chain reaction of the above formulas (I) to (III), the corrosion generated at the end of the magnet progresses into the magnet, and the R-rich phase changes to R(OH)3 and RH x As a result of the volume expansion associated with this change, stress accumulates, leading to the detachment of the crystal grains (main phase particles) constituting the main phase of the magnet. Then, due to the detachment of the main phase particles, a new surface of the magnet appears, and the corrosion of the magnet further progresses into the magnet.

[0015] Here, when the magnet satisfies A1 < B1, that is, for example, when the content of heavy rare earth elements increases in the R-rich phase at the end of the magnet, the corrosion potential at the alloy new surface of the R-rich phase is improved. As a result, the generation of hydrogen in the above formula (I) is suppressed, and as a result, the reactions after the above formula (II) are less likely to occur, and the corrosion resistance of the magnet is improved at the end in the +Y direction.

[0016] Also, the above magnet can satisfy B1 - A1 ≥ 10 kA / m.

[0017] Also, the above magnet has a second surface facing the first surface, and heavy rare earth elements are present in the surface layer portion of the second surface. Let the coercive force of the portion including the center of gravity of the second surface be A2, the coercive force of the portion c2 including the end of the second surface separated from the portion a2 including the center of gravity of the second surface in the X direction be C2, and the coercive force of the portion d2 including the end of the second surface separated from the portion a2 including the center of gravity of the second surface in the -X direction be D2. When this is the case, A2 ≥ C2 and A2 ≥ D2 can be satisfied.

[0018] Further, when the magnet has a second surface facing the first surface, a heavy rare earth element is present on the entire second surface, and A2 ≧ C2 and A2 ≧ D2 are satisfied, the magnet can satisfy A2 < B2 when the coercive force of a portion b2 including the end of the second surface away from the portion a2 including the centroid of the second surface in the Y direction is defined as B2.

[0019] Further, when the magnet has a second surface facing the first surface, a heavy rare earth element is present on the entire second surface, and A2 ≧ C2 and A2 ≧ D2 are satisfied, the magnet can satisfy A2 < E2 when the coercive force of a portion e2 including the end of the second surface away from the portion a2 including the centroid of the second surface in the -Y direction opposite to the Y direction is defined as E2.

[0020] Further, the magnet can satisfy A1 < E1 when the coercive force of a portion e1 including the end of the first surface away from the portion including the centroid of the first surface in the -Y direction opposite to the Y direction is defined as E1.

[0021] Further, the Y direction may be the longitudinal direction of the first surface.

[0022] Further, the normal direction at the centroid of the first surface may be parallel to the c-axis of the magnet.

[0023] The rotating electrical machine according to the present invention includes a rotor, a stator, and the magnet provided on the rotor or the stator.

Advantages of the Invention

[0024] According to the present invention, there are provided a rare earth permanent magnet with improved corrosion resistance on one end face and a rotating electrical machine including the same.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, equivalent components are denoted by equivalent reference numerals. The present invention is not limited to the following embodiments.

[0027] <Rare earth permanent magnet> (First Embodiment) FIG. 1 is an external view showing a rare earth permanent magnet 100 (hereinafter also referred to as "magnet 100") according to the first embodiment. As shown in FIG. 1, the magnet 100 according to this embodiment has a rectangular parallelepiped shape. The magnet 100 has a first surface 10 disposed on the XY plane where Z = 0, a second surface 11 disposed parallel to the XY plane and facing the first surface 10, and four side surfaces (end faces) 12 to 15 perpendicular to the XY plane.

[0028] The first surface (main surface) 10 and the second surface (main surface) 11 each have a rectangular shape with the longitudinal direction being the Y direction and the short side direction being the X direction, and are orthogonal to each other in the Z direction and face each other. The side surfaces 13 and 15 are arranged parallel to the ZY plane and face each other, and the side surfaces 12 and 14 are arranged parallel to the XZ plane and face each other.

[0029] The first surface 10 and the second surface 11 are larger in area than any of the side surfaces 12 to 15. The first surface 10 has short sides 10b, 10e and long sides 10c, 10d. The second surface 11 has short sides 11b, 11e and long sides 11c, 11d.

[0030] Here, a portion including the centroid a1' of the first surface 10 is defined as the central portion a1, a portion including an end away from the central portion a1 in the Y direction is defined as the end portion b1, a portion including an end away from the central portion a1 in the -Y direction is defined as the end portion e1, a portion including an end away from the central portion a1 in the X direction is defined as the end portion c1, and a portion including an end away from the central portion a1 in the -X direction is defined as the end portion d1.

[0031] Similarly, a portion including the centroid a2' of the second surface 11 is defined as the central portion a2, a portion including an end away from the central portion a2 in the Y direction is defined as the end portion b2, a portion including an end away from the central portion a2 in the -Y direction is defined as the end portion e2, a portion including an end away from the central portion a2 in the X direction is defined as the end portion c2, and a portion including an end away from the central portion a2 in the -X direction is defined as the end portion d2.

[0032] In the magnet 100 shown in FIG. 1, the end portion b1 is a portion including the midpoint b1' of the side 10b. The end portion c1 is a portion including the midpoint c1' of the side 10c. The end portion d1 is a portion including the midpoint d1' of the side 10d. The end portion e1 is a portion including the midpoint e1' of the side 10e.

[0033] In the magnet 100 shown in FIG. 1, the end portion b2 is a portion including the midpoint b2' of the side 11b. The end portion c2 is a portion including the midpoint c2' of the side 11c. The end portion d2 is a portion including the midpoint d2' of the side 11d. The end portion e2 is a portion including the midpoint e2' of the side 11e.

[0034] The magnet 100 contains a rare earth element R, a transition metal element T, and boron B, and is an R-T-B system sintered magnet having particles (main phase crystal grains) composed of R2T 14 B crystal and grain boundaries existing between a plurality of adjacent main phase crystal grains. Note that the magnet 100 is not limited to an R-T-B system sintered magnet, and may be, for example, a samarium cobalt magnet, a samarium-iron-nitrogen magnet, or a praseodymium magnet.

[0035] In the magnet 100, R represents at least one of rare earth elements. The rare earth elements refer to Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period type periodic table. The lanthanoid elements include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. The rare earth elements are classified into light rare earths and heavy rare earths. The heavy rare earth elements refer to Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the light rare earth elements are the other rare earth elements.

[0036] In the magnet 100, the content of R is preferably 28.0% by mass or more and 33.0% by mass or less, more preferably 29.0% by mass or more and 32.0% by mass or less. By setting the content of R within the above range, the residual magnetic flux density (Br) and the coercive force (Hcj) are improved.

[0037] In magnet 100, T represents one or more transition metal elements including Fe, or Fe and Co. T may be Fe alone, or a part of Fe may be substituted by Co.

[0038] In magnet 100, the content of Fe is the substantial remainder of the components of magnet 100.

[0039] When magnet 100 contains Co, the content of Co is preferably 0.3 mass% or more and 5 mass% or less, more preferably 0.4 mass% or more and 2.5 mass% or less. By setting the content of Co within the above range, the coercive force and corrosion resistance are improved.

[0040] Examples of transition metal elements other than Fe and Co include Ti, V, Cu, Cr, Mn, Ni, Zr, Nb, Mo, Hf, Ta, W, etc. Further, in addition to transition metal elements, T may further contain at least one element such as Al, Ga, Si, Bi, Sn, etc.

[0041] In magnet 100, a part of B can be substituted by carbon (C). In this case, not only is the manufacturing of the magnet facilitated, but also the manufacturing cost can be reduced. Also, the substitution amount of C should be an amount that does not substantially affect the magnetic properties. Additionally, unavoidably, O, C, Ca, etc. may be mixed in.

[0042] In magnet 100, the content of B is preferably 0.70 mass% or more and 1.10 mass% or less, more preferably 0.75 mass% or more and 1.05 mass% or less, and even more preferably 0.80 mass% or more and 1.00 mass% or less. By setting the content of B within the above range, the residual magnetic flux density and coercive force are improved.

[0043] In magnet 100, the content of C varies depending on other parameters, etc., and is determined as an appropriate amount. Further, magnet 100 may contain Cu, Al, etc. By adding these elements, it becomes possible to increase the coercive force, improve the corrosion resistance, and improve the temperature characteristics.

[0044] In the magnet 100, heavy rare earth elements are present in the surface layer portion of the first surface 10. Specifically, for example, in any of the central portion a1, the end portion b1 away from the central portion a1 in the Y direction, the end portion e1 away from the central portion a1 in the -Y direction, the end portion c1 away from the central portion a1 in the X direction, and the end portion d1 away from the central portion a1 in the -X direction on the first surface 10, and further, at the four corner portions of the first surface 10, heavy rare earth elements are present in the surface layer portion of the first surface 10, particularly at the grain boundaries in the surface layer portion. Note that heavy rare earth elements may or may not be present inside the crystal grains constituting the main phase of the first surface 10. The surface layer portion refers to a region at a depth of up to 0.5 mm from the magnet surface.

[0045] The magnet 100 can be a rare earth permanent magnet in which heavy rare earth elements are diffused into the interior from the first surface 10 along grain boundaries. The magnet 100 in which heavy rare earth elements are diffused along grain boundaries can improve the coercive force with a smaller amount of heavy rare earth elements as compared with the magnet 100 without grain boundary diffusion.

[0046] Regarding grain boundary diffusion, Harrison's diffusion classification model that models the state of diffusion is known. According to Harrison's diffusion classification model, diffusion is classified into type A, type B, and type C. FIGS. 2(A) to (C) are schematic diagrams showing the state in which elements are diffused into the grain boundaries 21 and crystal particles 23 of the magnet 100. FIG. 2(A) is type A, FIG. 2(B) is type B, and FIG. 2(C) is type C. The hatched portions in each figure represent the portions where heavy rare earth elements are diffused. In FIGS. 2(A) to (C), the elements are diffusing from the top to the bottom of the figure.

[0047] As shown in FIG. 2(A), in the case of type A, heavy rare earth elements are diffused not only into the grain boundaries 21 but also into the crystal particles 23. That is, in the case of type A, diffusion into the particles progresses. On the other hand, as shown in FIG. 2(C), in the case of type C, heavy rare earth elements are not diffused into the crystal particles 23, and heavy rare earth elements are diffused only into the grain boundaries 21. As shown in FIG. 2(B), the case of type B is intermediate between the case of type A and the case of type C.

[0048] The concentration of the heavy rare earth element (at least one of Dy and Tb) in the grain boundary 21 is preferably higher than the concentration of the heavy rare earth element in the crystal particle 23, and it is most preferable that the heavy rare earth element diffuses only to the surfaces of the grain boundary 21 and the crystal particle 23. Therefore, it is preferable that diffusion is dominated by type B or type C, and it is particularly preferable that type C is dominated. When the concentration of the heavy rare earth element in the grain boundary 21 is high, it becomes possible to efficiently improve the coercive force with a small amount of the heavy rare earth element. In this specification, the concentration of the heavy rare earth element means the mass concentration of the heavy rare earth element unless otherwise specified.

[0049] In the first embodiment, no heavy rare earth element is present in the grain boundary of the surface layer portion of the second surface 11 of the magnet 100.

[0050] As a method for measuring various components contained in the magnet 100, a method generally known in the art can be used. For the amounts of various metal elements, measurement may be performed by X-ray fluorescence analysis (XRF). The amount of oxygen may be measured by inert gas fusion-non-dispersive infrared absorption method. The amount of carbon may be measured by combustion-infrared absorption method in an oxygen stream. Inductively coupled plasma atomic emission spectrometry (ICP-AES) may be used when the measurement sample is small or the amount of contained metal elements is trace.

[0051] In one aspect, the magnetization easy axis (c-axis) of the magnet 100 is parallel to the Z direction which is the normal line of the center of gravity a1', that is, perpendicular to the first surface 10. However, in other aspects, it may be perpendicular to the Z direction (for example, parallel to the Y direction or parallel to the X direction), or may be an oblique direction with respect to the Z direction.

[0052] The dimensions of the magnet 100 are not particularly limited and can be appropriately changed according to the application. The length X1 of the magnet 100 in the X direction may be 1 to 100 mm, the length Y1 in the Y direction may be 10 to 300 mm, and the thickness Z1 in the Z direction may be 0.5 to 30 mm, or may be 1 to 15 mm. The magnet 100 may be a cube.

[0053] FIG. 3(A) is a schematic diagram of the coercivity distribution of a cross-section obtained by cutting the magnet 100 shown in the first embodiment along a cutting plane along the ZY plane of x = 0 including the central portions a1, a2, and the end portions b1, e1, b2, e2 in FIG. 1.

[0054] In FIGS. 3 and FIG. 4 described later, the darker (more dots) the black part is, the higher the coercivity, and the lighter (fewer dots) the black part is, the lower the coercivity. Note that the darkness of the black (the number of dots) represents the relative magnitude of the coercivity in a plurality of portions within each drawing. The darkness of the black (the number of dots) does not represent the relative magnitude of the coercivity between different drawings.

[0055] In the present embodiment, in the ZY cross-section, in the first surface 10 and its vicinity, there is a region (inclined structure region) where the coercivity and the concentration of the heavy rare earth element increase toward the first surface 10. From the midpoint e1' (end portion e1) through the centroid a1' (central portion a1) to before the midpoint b1' (end portion b1), in the inclined structure region, the coercivity and the concentration of the heavy rare earth element in the substantially Y direction are constant (the coercivity is within the range of ±9 kA / m, and the concentration of the heavy rare earth element is within the range of ±10%), but the coercivity and the concentration of the heavy rare earth element at the end portion b1 are higher than the constant value, and at the end portion b1, the inclined structure extends deeper in the -Z direction than other portions.

[0056] In other words, when the coercivity of the central portion a1 of the first surface 10 is A1, and the coercivity at the end portion b1 including the end of the first surface separated in the Y direction perpendicular to the normal Z direction of the centroid a1' from the central portion a1 is B1, A1 < B1 is satisfied.

[0057] Since the corrosion resistance at the end portion can be further improved, it is preferable that B1 - A1 is 10 kA / m or more, more preferably 15 kA / m or more, and even more preferably 20 kA / m or more.

[0058] Such a situation is satisfied not only in the ZY cross-section where x = 0 but also in other ZY cross-sections parallel to the ZY cross-section where x = 0. That is, the line u4 on the X-axis connecting the midpoint d1' of side 10d and the midpoint c1' of side 10c in FIG. 1 is divided into n equal parts, and the coercive force of the part including each line segment is A1 n is defined as such, and side 10b of the first surface 10 is divided into n equal parts, and the coercive force B1 n is defined as such. When these are compared at the same X-axis position, even outside the central part a1, at the same position in the X-axis direction of each line segment, A1 n < B1 n is satisfied. The difference preferably satisfies the above formula.

[0059] Corresponding to the fact that the coercive force and the concentration of the heavy rare earth metal element in the part including side 10b such as the end part b1 are higher than the coercive force and the concentration of the heavy rare earth metal element in the part including the X-axis such as the central part a1, from side 10b toward side 11b, for example, up to the center of the Z-direction thickness, the coercive force and the heavy rare earth metal element concentration in each part of the side surface 12 (for example, it can be divided into a grid along the XZ direction) and the coercive force and the heavy rare earth metal element concentration in each part including the ZX cross-section of the central part (y = 0) are compared at corresponding positions separated in the Y direction, the end face 12 side is higher.

[0060] [[ID=1S]] FIG. 4(A) is a schematic diagram of the coercive force distribution of the cross-section obtained by cutting the magnet 100 shown in the first embodiment with the XZ plane where y = 0 including the central parts a1, a2 and the end parts c1, d1, c2, d2 in FIG. 1.

[0061] In this embodiment, in the cross-section, the coercive force of the central part a1 including the centroid a1' of the first surface 10 is equal to or greater than the coercive forces of the end part d1 including the midpoint d1' and the end part c1 including the midpoint c1'. This corresponds to the fact that the concentration of the heavy rare earth element in the end parts c1 and d1 is equal to or less than the concentration of the heavy rare earth element in the central part a1. The coercive force of the central part a1 of the first surface 10 can exceed the coercive forces of both end parts d1 and c1. This corresponds to the fact that the concentration of the heavy rare earth element in the central part a1 is higher than that in the end parts c1 and d1.

[0062] Let the coercive force of the end portion c1 including the end of the first surface 10 that is separated from the central portion a1 in the X direction perpendicular to the normal Z direction and Y direction of the center of gravity a1’ be C1, and the coercive force of the end portion d1 including the end of the first surface 10 that is separated from the central portion a1 in the -X direction opposite to the X direction be D1. When this is the case, the magnet 100 of the present embodiment satisfies A1≧C1 and A1≧D1.

[0063] A1 and C1 may satisfy A1 - C1≧10 kA / m, may satisfy A1 - C1≧20 kA / m, and may satisfy A1 - C1≧30 kA / m.

[0064] A1 and D1 may satisfy A1 - D1≧10 kA / m, may satisfy A1 - D1≧20 kA / m, and may satisfy A1 - D1≧30 kA / m.

[0065] Note that the relationships of A1≧C1 and A1≧D1 are satisfied not only in the ZX cross-section of y = 0 but also in other ZX cross-sections parallel to the ZX cross-section of y = 0.

[0066] Substantially no heavy rare earth metal element exists on the second surface 11, or the concentration is substantially the same in the plane. The coercive forces of the central portion a2 and both end portions b2, e2, c2, d2 are substantially the same (the coercive force is within the range of ±9 kA / m, and the heavy rare earth element concentration is within the range of ±10%), and is equivalent to the coercive force of the central portion a2 in the Z direction (thickness direction).

[0067] In this specification, there is no particular limitation on the size and shape of the portion (sometimes called a chip) of the magnet in which the coercive force or the concentration of the heavy rare earth metal element is defined, such as the center of gravity, end, or corner of the first surface or the second surface.

[0068] The shape of the chip is not particularly limited. For example, as shown in FIG. 5, it may be a rectangular parallelepiped. An example of the thickness Z2 of the chip 30 is 0.5 to 10 mm. The lengths of one side X2 and the other side Y2 can each be 0.5 to 10 mm. An example of the volume can be 1 / 1000 to 1 / 10 of the magnet.

[0069] (Function and Effect) According to the first embodiment, compared with the prior art, the corrosion resistance of the end face 12 can be selectively increased compared to other end faces. Therefore, by arranging the magnet so that the end face 12 is the end face that is most susceptible to corrosion when the magnet is used, the corrosion resistance of the magnet can be increased.

[0070] Even if the R-T-B magnet of the prior art has a structure as shown in Fig. 4(B) in the XZ cut surface, it becomes as shown in Fig. 3(E) in the ZY cut surface, and A1 < B1 is not satisfied.

[0071] (Second Embodiment) The magnet according to this embodiment has a difference in the distribution of the coercive force, that is, the distribution of the heavy rare earth elements, compared with the first embodiment.

[0072] Fig. 3(B) is a schematic diagram of the coercive force distribution of the cross-section obtained by cutting the magnet 100 shown in the second embodiment with the ZY plane of x = 0 including the central portions a1, a2 and the end portions b1, e1, b2, e2 of Fig. 1.

[0073] In this embodiment, on the cut surface, the inclined structure such as the coercive force on the side of the first surface 10 is the same as that of the first embodiment.

[0074] In the ZY cross-section, in the second surface 11 and its vicinity, there is further a region (inclined structure region) where the coercive force and the concentration of the heavy rare earth element increase toward the second surface 11. From the midpoint b2' (end portion b2) through the centroid a2' (central portion a2) to before the midpoint e2' (end portion e2), in the inclined structure region, the coercive force and the concentration of the heavy rare earth element in the substantially Y direction are constant (the coercive force is within the range of ±9 kA / m, and the concentration of the heavy rare earth element is within the range of ±10%), but the coercive force and the concentration of the heavy rare earth element at the end portion e2 are higher than the constant value, and at the end portion e2, the inclined structure extends deeper in the +Z direction than other portions.

[0075] In other words, when the coercive force of the central portion a2 of the second surface 11 is A2 and the coercive force at the end portion e2 of the second surface separated from the central portion a2 in the -Y direction is E2, A2 < E2 is satisfied.

[0076] It is preferable that E2 - A2 is 10 kA / m or more, more preferably 15 kA / m or more, and even more preferably 20 kA / m or more.

[0077] Such a situation is satisfied not only in the ZY cross-section where x = 0 but also in other ZY cross-sections parallel to the ZY cross-section where x = 0. That is, a line u2 parallel to the X-axis connecting the midpoint d2' of the side 11d and the midpoint c2' of the side 11c is divided into n equal parts (for example, 10 equal parts), and the coercive force of the portion including each line segment is taken as A2 n and the side 11e of the end face 14 is divided into n equal parts, and the coercive force of the portion including each line segment is taken as E2 n When these are compared at the same X-axis position, even outside the central portion a2, at the same position in the X-axis direction of each line segment, A1 n < E2 n is satisfied. The difference preferably satisfies the above formula.

[0078] Corresponding to the fact that the coercive force and the concentration of the heavy rare earth metal element of the portion including the side 11e such as the end portion e2 are higher than the coercive force and the concentration of the heavy rare earth metal element of the portion including the line u2 parallel to the X-axis such as the central portion a2, when comparing the coercive force and the concentration of the heavy rare earth metal element of each portion of the end face 14 and the coercive force and the concentration of the heavy rare earth metal element of each portion including the ZX cross-section of the central portion (y = 0) from the side 11e toward the side 10e, for example, up to the center of the Z-direction thickness, at corresponding positions separated in the Y-direction, the end face 14 side is higher.

[0079] FIG. 4(B) is a schematic diagram of the coercive force distribution of the cross-section obtained by cutting the magnet 100 shown in the second embodiment in the XZ plane where y = 0 including the central portions a1, a2 and the end portions c1, d1, c2, d2 of FIG. 1.

[0080] In this embodiment, the distribution of the coercive force and the heavy rare earth element on the first surface 10 side is the same as that in the first embodiment.

[0081] In this embodiment, on the cut surface, the coercive force of the central portion a2 of the second surface 11 is equal to or greater than the coercive forces of both end portions d2 and c2. This corresponds to the fact that the concentration of the heavy rare earth element at the end portions c2 and d2 is equal to or lower than the concentration of the heavy rare earth element at the central portion a2. The coercive force of the central portion a2 of the second surface 11 can exceed the coercive forces of both end portions d2 and c2. This corresponds to the fact that the concentration of the heavy rare earth element at the central portion a2 is higher than that at the end portions c2 and d2.

[0082] When the coercive force of the end portion c2 of the second surface 11, which is separated from the central portion a2 in the X direction perpendicular to the normal Z direction and the Y direction of the center of gravity a2', is defined as C2, and the coercive force of the end portion d2 including the end of the second surface separated from the central portion a2 in the -X direction opposite to the X direction is defined as D2, the magnet 100 of this embodiment satisfies A2≥C2 and A2≥D2.

[0083] A2 and C2 may satisfy A2 - C2≥10 kA / m, may satisfy A2 - C2≥20 kA / m, and may satisfy A2 - C2≥30 kA / m.

[0084] A2 and D2 may satisfy A2 - D2≥10 kA / m, may satisfy A2 - D2≥20 kA / m, and may satisfy A2 - D2≥30 kA / m.

[0085] Note that the relationship of A2≥C2 and A2≥D2 is satisfied not only in the ZX cross-section of y = 0 but also in other ZX cross-sections parallel to the ZX cross-section of y = 0.

[0086] In the magnet 100 of the second embodiment, heavy rare earth elements are present in the surface layer portion of the second surface 11, particularly at the grain boundaries of the surface layer portion. Specifically, for example, in any of the central portion a2, the end portion b2 in the Y direction, the end portion e2 in the -Y direction, the end portion c2 in the X direction, and the end portion d2 in the -X direction, and further, at the four corner portions of the second surface, heavy rare earth elements are present at the grain boundaries of the surface layer portion of the second surface 11. Note that heavy rare earth elements may or may not be present inside the crystal grains constituting the main phase of the second surface 11. The magnet 100 can be a rare earth permanent magnet in which heavy rare earth elements are diffused from the second surface 11 toward the inside along the grain boundaries.

[0087] According to the present embodiment, the corrosion resistance at the end faces 12 and 14 can be selectively increased. Therefore, by orienting the faces that are most susceptible to corrosion during the use of the magnet toward the end faces 12 and / or 14, the durability of the magnet can be increased.

[0088] (Third Embodiment) The magnet according to the present embodiment is different from the second embodiment in the distribution of the coercive force on the second surface 11 side, that is, the distribution of heavy rare earth elements.

[0089] FIG. 3(C) is a schematic diagram of the coercive force distribution of a cross section obtained by cutting the magnet 100 shown in the third embodiment along the ZY plane of x = 0 including the central portions a1, a2 and the end portions b1, e1, b2, e2 of FIG. 1.

[0090] In this embodiment, the gradient structure of the coercivity and the like on the first surface 10 side of the cut surface is the same as in the first and second embodiments. Furthermore, the second surface 11 and its vicinity further have a gradient structure region in which the coercivity and the concentration of the heavy rare earth element increase toward the second surface 11. Here, in the gradient structure region from the midpoint e2' (end e2) through the center of gravity a2' (central portion a2) to just before the midpoint b2' (end b2), the coercivity and the concentration of the heavy rare earth element in the Y direction are substantially constant (the coercivity is within ±9 kA / m, and the heavy rare earth element concentration is within ±10%), but the coercivity and the concentration of the heavy rare earth element at end b2 are higher than the constant values, and the gradient structure at end b2 extends deeper in the +Z direction than other portions.

[0091] In other words, when the coercive force of the central portion a2 of the second surface 11 is A2 and the coercive force of the end portion b2 of the second surface 11 away from the central portion a2 in the Y direction is B2, A2 <B2を満たす。

[0092] Since this allows for further improvement in corrosion resistance at the ends, B2-A2 is preferably 10 kA / m or more, more preferably 15 kA / m or more, and even more preferably 20 kA / m or more.

[0093] This situation is satisfied not only in the ZY cross section at x = 0, but also in other ZY cross sections parallel to the ZY cross section at x = 0. That is, if the line u2 that is parallel to the X axis and connects the midpoint d2' of the side 11d and the midpoint c2' of the side 11c is divided into n equal parts, and the coercive force of the part including each line segment is A2 n Divide the side 11b of the end face 12 into n equal parts, and the coercive force B2 of the part including each line segment is n When comparing these at the same X-axis position, A2 is also found at the same X-axis position of each line segment, except for the central part a2. n <B2 n The difference preferably satisfies the above formula.

[0094] Corresponding to the fact that the coercive force and the concentration of the heavy rare earth metal element in the portion including the side 11b such as the end portion b2 are higher than the coercive force and the concentration of the heavy rare earth metal element in the portion including the line u2 parallel to the X-axis such as the central portion a2, when comparing the coercive force and the heavy rare earth metal element concentration in each part of the end face 12 from the side 11b toward the side 10b, for example, up to the center of the Z-direction thickness, with the coercive force and the heavy rare earth metal element concentration in each part including the ZX cross-section of the central portion (y = 0) at corresponding positions separated in the Y-direction, the side of the end face 12 is higher.

[0095] In the magnet 100 shown in the third embodiment, the distribution of the coercive force of the cut surface along the XZ plane of y = 0 including the central portions a1, a2, and the end portions c1, d1, c2, d2 in FIG. 1 is shown in FIG. 4(B), which is the same as that of the second embodiment.

[0096] According to the present embodiment, the corrosion resistance on the end face 12 can be selectively made higher. Therefore, by orienting the surface that is most susceptible to corrosion during the use of the magnet toward the end face 12, the durability of the magnet can be made higher.

[0097] (Fourth Embodiment) The magnet according to the present embodiment is different from the third embodiment in the distribution of the coercive force at the end portion on the -Y side, that is, the distribution of the heavy rare earth element.

[0098] FIG. 3(D) is a schematic diagram of the distribution of the coercive force of the cross-section obtained by cutting the magnet 100 shown in the fourth embodiment with the ZY plane of x = 0 including the central portions a1, a2, and the end portions b1, e1, b2, e2 in FIG. 1.

[0099] In the present embodiment, the gradient distribution of the coercive force and the heavy rare earth element on the +Y side of the magnet is the same as that of the third embodiment.

[0100] Furthermore, in the present embodiment, the gradient distribution of the coercive force and the heavy rare earth element on the -Y side of the magnet is also the same as that on the +Y side of the third embodiment.

[0101] According to the present embodiment, the corrosion resistance on the end faces 12 and 14 can be selectively increased compared to other end faces. Therefore, by orienting the faces that are most susceptible to corrosion during the use of the magnet towards the end faces 12 and / or 14, the durability of the magnet can be enhanced.

[0102] (Modification) The magnet according to the present invention is not limited to the above embodiment, and various modifications are possible.

[0103] In the above embodiment, for the magnet 100 shown in FIG. 1, the X direction was the short side direction of the first surface 10 and the second surface 11, and the Y direction was the long side direction of the first surface 10 and the second surface 11. However, the X direction and the Y direction can be arbitrarily defined. For example, for the magnet 100, the X direction may be the long side direction of the first surface 10 and the second surface 11, and the Y direction may be the short side direction of the first surface 10 and the second surface 11.

[0104] Also, the first surface may not be the main surface 10, and the side surfaces (end faces) 12, 14, or the side surfaces 13, 15 may be the main surfaces. In any case, the portion where corrosion resistance is required should be the surface that is exposed in the Y direction.

[0105] Also, the shape of the magnet does not have to be a rectangular parallelepiped.

[0106] For example, among the side surfaces 12 to 15, any two opposing side surfaces may be parallel to each other or may not be parallel to each other. Specifically, as shown in FIG. 6(A), the magnet may be a disc (cylinder). The thickness Z1 of the cylinder in the Z direction may be 1.5 to 9 mm, or may be 2 to 7 mm. The diameter H1 of the first surface 10 and the second surface 11 may be 10 to 100 mm.

[0107] Even in this case, a central portion a1 is provided in the portion including the centroid a1' of the first surface 10, a central portion a2 is provided in the portion including the centroid a2' of the second surface 11, a coordinate system with the normal line of the centroid a1' as the Z direction is given, and any directions are set as the X and Y directions. The end portions b1 to e1 and the end portions b2 to e2 can be defined as shown in FIG. 6(A), similar to the case of a rectangular parallelepiped.

[0108] In such a case, the portion and size can be appropriately set as described above, and can be appropriately deformed according to the shape of the edge of the chip including the end.

[0109] Also, the first surface 10 and the second surface 11 may be parallel to each other or may not be parallel to each other. Further, the first surface 10 and / or the second surface 11 may be a curved surface.

[0110] For example, (B) in FIG. 6 is a shape obtained by cutting a part of a cylinder with a predetermined thickness by two planes along the axial direction. The outer peripheral surface of the cylinder is disposed on the first surface 10, and the inner peripheral surface of the cylinder is disposed on the second surface 11, and it is also called a C shape or an arch shape.

[0111] Even when the first surface 10 is a curved surface, a central portion a1 is provided in a portion including the center of gravity a1' of the curved surface. Even when the second surface 11 is a curved surface, a central portion a2 is provided in a portion including the center of gravity a2' of the second surface 11. A coordinate system with the normal line of the center of gravity a1' as the Z direction is given, and an arbitrary direction is set as the X and Y directions, and the end portions b1 to e1 and the end portions b2 to e2 can be determined.

[0112] (C) in FIG. 6 is a view in which the second surface 11 is a plane in (B) of FIG. 6, and similarly, the central portions a1, a2, the end portions b1 to e1, and the end portions b2 to e2 can be determined.

[0113] When the magnet has a curved surface, the shape of the chip can also be correspondingly a shape having a curved surface.

[0114] <Method for manufacturing rare earth permanent magnet> Hereinafter, a method for manufacturing the magnet 100 according to the present embodiment (hereinafter, also referred to as "the manufacturing method of the present embodiment") will be described. In the following, a magnet 100 manufactured by the powder metallurgy method and in which a heavy rare earth element is grain boundary diffused will be described as an example, but the manufacturing method of the present embodiment is not particularly limited, and other methods can also be used.

[0115] The manufacturing method of this embodiment includes a molding step of molding raw material powder to obtain a molded body, a sintering step of sintering the molded body to obtain a sintered body, and a grain boundary diffusion step of causing a heavy rare earth element to diffuse into the grain boundaries of the sintered body.

[0116] [Preparation Step of Raw Material Powder] The raw material powder can be produced by a known method. In the manufacturing method of this embodiment, the case of the single alloy method using a single alloy will be described, but a so-called two-alloy method in which a first alloy and a second alloy are mixed to produce the raw material powder may also be used.

[0117] First, after melting the raw material metals corresponding to the composition of the magnet 100 by a known method, an alloy having a desired composition is produced by casting.

[0118] After producing the alloy, the produced alloy is pulverized (pulverization step). The pulverization step may be carried out in two stages or in one stage. The method of pulverization is not particularly limited. For example, it is carried out by a method using various pulverizers.

[0119] [Molding Step] In the molding step, the pulverized powder obtained by the pulverization step is molded into a predetermined shape. The molding method is not particularly limited, but in this embodiment, the pulverized powder is filled into a mold and pressurized in a magnetic field.

[0120] The pressurization during molding is preferably carried out at 20 MPa to 300 MPa. The applied magnetic field is preferably 950 kA / m to 1600 kA / m. The shape of the molded body obtained by molding the pulverized powder is not particularly limited, and can be an arbitrary shape according to the desired shape of the magnet 100, such as a rectangular parallelepiped, a flat plate shape, a columnar shape, and an arch shape.

[0121] [Sintering Step] The sintering process is a process of sintering a green compact in a vacuum or an inert gas atmosphere to obtain a sintered body. The sintering temperature needs to be adjusted according to various conditions such as composition, grinding method, differences in particle size and particle size distribution, etc. For the green compact, for example, in a vacuum or in the presence of an inert gas, it is fired by performing a heating treatment at 1000 °C or higher and 1200 °C or lower for 1 hour or longer and 20 hours or shorter. Thereby, a high-density sintered body can be obtained. At this time, it is preferable that there is a substantially uniform coercive force distribution throughout the sintered body.

[0122] [Grain boundary diffusion process] In this process, a paint containing a heavy rare earth element is applied to the sintered body obtained in the sintering process, and then heat-treated to cause the heavy rare earth element to diffuse into the magnet interior along the grain boundaries from the paint.

[0123] Here, an example of applying the paint to a rectangular parallelepiped sintered body 50 having a first surface 60, a second surface 61, and end faces 62 to 65 corresponding to the first surface 10, the second surface 11, and the end faces 12 to 15 of the magnet that is the final product will be described with reference to FIGS. 7 and 8.

[0124] In order to give a coercive force distribution as in the first embodiment ((A) of FIG. 3 and (A) of FIG. 4), the paint 40 is applied to the entire surface of the first surface 60 from the -Y side toward the +Y side or from the +Y side toward the -Y side in FIGS. 7 and 8(A). Then, the paint is applied twice only at the end portion M1 on the +Y side, and the thickness of the paint 40 at the end portion M1 on the +Y side is made thicker than the thickness of the other portions of the first surface 60.

[0125] As shown in FIG. 8(A), when viewed from the X direction, the amount per unit area of the paint 40 is large at the end portion M1 on the +Y side, so the amount of heavy rare earth elements diffusing from the end portion M1 is large, and a coercive force distribution as in FIG. 3(A) can be realized. Further, by applying the paint in the +Y direction or the -Y direction, when viewed from the Y direction, the amount of paint per unit area at both ends on the ±X sides is equal to or less than that at the central portion, so a coercive force distribution as in FIG. 4 can be obtained.

[0126] There is no need to apply paint to the end faces 62 to 65.

[0127] To provide a coercive force distribution as in the second embodiment ((B) of FIG. 3 and (B) of FIG. 4), as shown in (B) of FIG. 8, after applying paint to the entire first surface 60 of the sintered body 50, paint may also be applied to the entire second surface 61. At this time, the paint 40 containing a diffusion material is applied to the entire second surface 61 from the -Y side to the +Y side or from the +Y side to the -Y side of FIG. 7. Then, on the second surface 61, the paint 40 is applied twice only at the end portion M3 on the -Y side, and the thickness of the paint 40 at the end portion M3 on the -Y side is made thick. Regarding the first surface 60, as described in the first embodiment, the paint is applied twice only at the end portion M1 on the +Y side, and the thickness of the paint 40 at the end portion M1 on the +Y side is made thicker than the thickness of the other portions of the first surface 60, so that a coercive force distribution as in the second embodiment ((B) of FIG. 3 and (B) of FIG. 4) is provided.

[0128] Also, to provide a coercive force distribution as in the third embodiment ((C) of FIG. 3 and (B) of FIG. 4), after applying paint to the entire first surface 60 of the sintered body 50, as shown in (C) of FIG. 8, on the second surface 61, the paint is applied twice only at the end portion M4 on the +Y side, and the thickness of the paint only at the end portion M4 on the +Y side is made thick. Regarding the first surface 60, as described in the first embodiment, the paint is applied twice only at the end portion M1 on the +Y side, and the thickness of the paint 40 at the end portion M1 on the +Y side is made thicker than the thickness of the other portions of the first surface 60, so that a coercive force distribution as in the third embodiment ((C) of FIG. 3 and (B) of FIG. 4) is provided.

[0129] Furthermore, to provide a coercive force distribution as in the fourth embodiment ((D) of FIG. 3 and (B) of FIG. 4), as shown in (D) of FIG. 8, after applying paint to each of the entire first surface 60 and the entire second surface 61, at each surface, the end portions M1 to M4 at the +Y side and the -Y side are applied twice and the thickness is made thick.

[0130] Note that, as shown in (E) of FIG. 8, on the first surface 60 and the second surface 61, if only one coating is applied, the coercive force distribution as shown in (E) of FIG. 3 and (B) of FIG. 4 will be obtained. That is, in this case, the obtained magnet 100 does not satisfy A1 < B1, A2 < B2, A1 < E1, and A2 < E2.

[0131] The length in the Y direction of the end where the paint is applied twice can be adjusted as appropriate. For example, it can be set to 1 to 15 mm.

[0132] The heavy rare earth element contained in the paint is not particularly limited, but Dy or Tb is preferable, and Tb is more preferable.

[0133] The heavy rare earth element may be contained in the paint as a heavy rare earth compound. Examples of such heavy rare earth compounds include alloys, oxides, halides, hydroxides, and hydrides, but it is preferable to use hydrides. Examples of the hydrides of heavy rare earth elements include DyH2, TbH2, hydrides of Dy-Fe, or hydrides of Tb-Fe. In particular, DyH2 or TbH2 is preferable.

[0134] The heavy rare earth compound is preferably in particulate form. Also, the average particle size is preferably 100 nm to 100 μm, and more preferably 1 μm to 50 μm.

[0135] As the solvent used in the paint, those that can uniformly disperse without dissolving the heavy rare earth compound are preferable. For example, alcohols, aldehydes, and ketones can be mentioned, and ethanol is particularly preferable.

[0136] There is no particular limitation on the content of the heavy rare earth compound in the paint. For example, it may be 10 to 90% by mass. The paint may further contain components other than the heavy rare earth compound as necessary. For example, a dispersant for preventing aggregation of heavy rare earth compound particles can be mentioned.

[0137] In the case of double-sided coating, the coating amount (or density) of the heavy rare earth element on the first surface 60 and the coating amount (or density) of the heavy rare earth element on the second surface 61 may be changed.

[0138] There is no particular limitation on the method of applying the heavy rare earth element. For example, there are methods using vapor deposition, sputtering, electroplating, spray coating, brush coating, jet dispenser, nozzle, screen printing, squeegee printing, sheet method, etc. Further, in order to apply the heavy rare earth element only to the surface, masking may be performed on the surfaces other than the surface as necessary.

[0139] After applying the paint containing the heavy rare earth element, the paint is dried and then the heavy rare earth element is diffused into the sintered body. There is no particular limitation on the diffusion treatment method, but usually the diffusion treatment is carried out by heating in a vacuum or an inert gas. In the above example, the application is described as an example, but the same applies when the heavy rare earth element is attached by a method other than application.

[0140] Among the above-described A-type, B-type, and C-type diffusions, which diffusion becomes dominant depends on the diffusion treatment temperature, the base material composition, and the structure. The higher the diffusion treatment temperature, the more likely the A-type becomes dominant, and the lower the diffusion treatment temperature, the more likely the C-type becomes dominant. As described above, it is preferable that the C-type becomes dominant. Also, although the lower the diffusion treatment temperature, the more likely the C-type becomes dominant, the lower the diffusion treatment temperature, the lower the diffusion rate, and longer heating may be required, which may cause a decrease in manufacturing efficiency.

[0141] The preferable diffusion treatment temperature according to this embodiment depends on the composition of the magnet 100, but is 700 to 1000°C. By setting it to 700°C or higher, the diffusion rate is likely to be sufficiently high. Also, by setting it to 1000°C or lower, the C-type diffusion is likely to become dominant.

[0142] Also, when the coating amounts of the heavy rare earth elements are the same, the coercive force when grain boundary diffusion occurs at a temperature at which C-type diffusion is dominant tends to be higher than that when grain boundary diffusion occurs at a temperature at which A-type diffusion or B-type diffusion is dominant.

[0143] [Processing step (after grain boundary diffusion)] After the diffusion treatment step, a treatment for removing the residual film on the surface may be performed as necessary. There is no particular limitation on the type of processing performed in the processing step after the diffusion treatment. For example, chemical removal methods, shape processing such as physical cutting and grinding, and chamfering processing such as barrel polishing may be performed after the diffusion treatment.

[0144] The magnet 100 obtained through the above steps may be subjected to surface treatments such as plating, resin coating, oxidation treatment, and chemical conversion treatment. This can further improve the corrosion resistance.

[0145] Furthermore, magnets obtained by cutting and dividing the magnet 100 can be used. Also, the magnet 100 may be used alone, or two or more magnets 100 may be combined and used as necessary. There is no particular limitation on the bonding method. For example, there are methods of mechanically bonding and methods of bonding with a resin mold.

[0146] Specifically, the magnet 100 is suitably used for applications such as compressors, magnetic sensors, speakers, and rotating electrical machines described later.

[0147] Examples of the rotating electrical machine include a small motor, a large motor, a generator, and an IPM motor described later. Examples of the generator include a wind power generator, a hydraulic power generator, and a thermal power generator. In applications that particularly require large rare earth permanent magnets such as large motors, wind power generators, and IPM motors, large magnets 100 manufactured by combining two or more magnets 100 can be used.

[0148] <Rotating Electrical Machine> As shown in FIG. 9, the magnet 100 may be used in the motor 110. The motor 110 shown in FIG. 9 is an IPM motor (Interior Permanent Magnet Motor). The motor 110 includes a cylindrical rotor 70 (rotor) and a stator 80 (stator) disposed outside the rotor 70 so as to surround the rotor 70. FIG. 9 shows the internal structure of the motor 110 in the rotational axis direction (Z direction) of the rotor 70. The rotor 70 has a cylindrical rotor core 72 and a plurality of magnets 100. A plurality of accommodation holes 74 are formed at predetermined intervals along the outer peripheral surface of the rotor core 72, and the magnets 100 are accommodated in the respective accommodation holes 74. That is, each magnet 100 is arranged along the circumferential surface of the rotor core 72. The magnet 100 is fixed in the accommodation hole 74 by resin molding. In resin molding, a high pressure is applied to the magnet 100.

[0149] As shown in FIG. 9, the magnets 100 adjacent to each other along the circumferential direction of the rotor 70 may be accommodated in the accommodation holes 74 such that the positions of the N poles and the S poles are opposite to each other. That is, the magnets 100 adjacent to each other along the circumferential direction generate magnetic force lines in opposite directions along the radial direction of the rotor 70. Although the rotor 70 shown in FIG. 9 has six magnets 100, the number (number of poles) of the magnets 100 included in the rotor 70 is not limited.

[0150] Preferably, the Y direction in the magnet 100 coincides with the rotational axis direction of the rotor 70. In particular, in the first embodiment, it is preferable that the end face 12 on the high coercivity end b1 side (+Y side) of the magnet 100 is exposed from the accommodation hole 74, and in the second to fourth embodiments, it is preferable that the end face 12 on the high coercivity end b1 side (+Y side) or the end face 14 on the end e1 side (-Y side) of the magnet is exposed from the accommodation hole 74. In the magnet 100 fixed in the accommodation hole 74, the exposed surface not surrounded by the inner wall of the accommodation hole 74 is easily corroded by water. Therefore, when the magnet 100 is accommodated in such an orientation, the surface not surrounded by the inner wall of the accommodation hole 74 becomes the side face 12 of the magnet 100 with high corrosion resistance, and the corrosion resistance of the motor is improved.

[0151] The stator 80 has a plurality of coil portions 82 provided at predetermined intervals along the outer peripheral surface of the rotor 70. The coil portions 82 and the magnet 100 are arranged to face each other. The stator 80 applies torque to the rotor 70 by electromagnetic action, and the rotor 70 rotates in the circumferential direction. The stator 80 shown in FIG. 9 has eight coil portions 82, but the number of coil portions 82 (number of slots) of the stator 80 is not limited. In this embodiment, magnets are accommodated in the rotor, but magnets may be accommodated in the stator.

Example

[0152] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0153] (Example 1) [Sintering process] A raw material alloy was prepared by the strip casting method so as to obtain a sintered body satisfying 26 mass% Nd - 4 mass% Pr - 0.4 mass% Al - 0.8 mass% Co - 0.5 mass% Cu - 0.35 mass% Zr - 0.1 mass% Ga - 0.90 mass% B - bal.Fe.

[0154] Next, after hydrogen was occluded in the raw material alloy at room temperature, a hydrogen pulverization treatment (coarse pulverization) of dehydrogenation at 600°C for 1 hour was performed in an Ar gas atmosphere.

[0155] Next, 0.1 mass% of oleic acid amide was added to the raw material alloy as a pulverization aid to the coarse pulverized powder before fine pulverization, and it was mixed using a Nauta mixer. Then, fine pulverization was performed using a jet mill using N2 gas to obtain a fine pulverized powder having an average particle size of about 4.0 μm.

[0156] The obtained fine pulverized powder was filled into a mold disposed in an electromagnet, and magnetic field molding was performed by applying a pressure of 50 MPa while applying a magnetic field of 1200 kA / m to obtain a molded body.

[0157] The obtained formed body was sintered at 1060 °C for 12 hours to obtain a sintered body. Then, the obtained sintered body was surface polished, cut, washed, and dried to finally obtain a sintered body with a size of 20.2×100.2×6.2 mm.

[0158] The residual magnetic flux density of the entire sintered body was 1390 mT, and the coercive force of the entire sintered body was 1281 kA / m.

[0159] [Diffusion treatment process] For the obtained sintered body, pretreatment of the diffusion treatment process was carried out by immersing it in a mixed solution of nitric acid and ethanol for 3 minutes and then in ethanol for 1 minute twice. After pretreatment, the sintered body was washed and dried.

[0160] In addition, a Tb-containing paint to be applied to the sintered body was prepared. The TbH2 raw material was finely pulverized using a jet mill using N2 gas to prepare TbH2 fine powder. Then, the obtained TbH2 fine powder was mixed with an alcohol solvent and dispersed in the alcohol solvent to be made into a paint, and a Tb-containing paint was obtained.

[0161] For the entire two main surfaces of the sintered body, the Tb-containing paint was applied by brush coating in the +Y direction on the first surface 60 and in the -Y direction on the second surface 61. Then, at the end on the +Y side of one first surface 60 of the sintered body (end M1 in FIG. 7) and the end on the other second surface 61 (end M3 in FIG. 7), the paint was applied again. At this time, at the ends M1 and M3 in FIG. 7 where the paint was applied twice, the adhesion density of Tb was 30 mg / cm 2 The paint was applied so that it would be. In the regions of both main surfaces where the paint was applied once, the paint was applied so that the adhesion density of Tb was 20 mg / cm 2 The amount of Tb adhered to the entire substrate at this time was 1.0 mass% with respect to 100 mass% of the substrate weight.

[0162] After applying the Tb-containing paint to the sintered body, diffusion treatment was carried out after drying. The diffusion temperature was 850 °C and the diffusion time was 6 hours. Then, the sintered body subjected to the diffusion treatment was subjected to aging treatment at 500 °C.

[0163] Cutting and polishing with a thickness of 0.1 mm were performed on all six surfaces of the sintered body after the diffusion treatment process. As a result, the size of the sintered body became 20 mm in the X direction, 100 mm in the Y direction, and 6 mm in the Z direction. The sintered body after polishing was washed and dried to obtain a sample (magnet).

[0164] (Example 2) In the end portions M1 and M3 of FIG. 7 where the paint was applied twice, the paint was applied so that the adhesion density of Tb was 31 mg / cm 2 In the regions of both main surfaces where the paint was applied once, the paint was applied so that the adhesion density of Tb was 22 mg / cm 2 A sample (magnet) was obtained in the same manner as in Example 1, except that the paint was applied as described above.

[0165] (Comparative Example 1) In the diffusion treatment process, after applying the Tb-containing paint by brushing on the entire surfaces of the two main surfaces of the sintered body, a sample (magnet) was obtained in the same manner as in Example 1, except that the paint was not reapplied to the end portion (end portion M1 in FIG. 7) on one main surface and the end portion (end portion M3 in FIG. 7) on the other main surface of the sintered body.

[0166] The evaluation methods for the respective characteristics will be described below.

[0167] [Coercivity of a part] First, chips including the side surface 12 in the magnet 100 shown in FIG. 1 were cut out from the magnet at the respective positions shown by hatching in FIG. 10(A). In the present embodiment, the shape of the chip was a rectangular parallelepiped with X2 = 1 mm, Y2 = 5 mm, and Z2 = 1 mm shown in FIG. 5. The chips were arranged at equal intervals in the X direction and the Z direction. The positions of the chips are represented by combinations of the coordinates α1 to α8 and b1' in the Z direction and the coordinates β1 to β5 in the Z direction.

[0168] Also, chips of the same size as described above were cut out from the magnet at each position illustrated by hatching in Fig. 10(B), including the XZ plane where Y = 0 in the magnet 100 shown in Fig. 1. The chips are arranged at equal intervals in the X and Z directions. The positions of the chips are represented by combinations of the coordinates γ1 to γ8 and a1' in the Z direction and the coordinates ε1 to ε5 in the Z direction.

[0169] The coercivity of the cut-out chips was measured using a pulse excitation type magnetic property measuring device. The results are shown in Table 1.

[0170] [Corrosion resistance] The +Y side end and the central part in the Y direction of the magnet were cut off with a Y-axis length of 5 mm, and a pressure cooker test (PCT test) was conducted. Specifically, the samples obtained under the environment of a temperature of 120 °C, a humidity of 100% RH, a pressure of 2 atm, and a saturated PCT mode were left, and the weight per unit surface area was measured at regular test times. The weight was measured using an electronic balance. The weight change (mg / cm 2 ) from the weight before the start of the test (test time 0 hours) is shown in Table 2. Also, a graph with the test time on the horizontal axis and the weight change (mg / cm 2 ) from the weight before the start of the test (test time 0 hours) on the vertical axis is shown in Fig. 11.

[0171]

Table 1

[0172]

Table 2

Explanation of symbols

[0173] 10…First surface, 11…Second surface, 12 - 16…Side surfaces (end faces), 21…Grain boundary, 23…Matrix crystal particles, 30…Sample, 70…Rotor, 80…Stator, 100…R-T-B system sintered magnet, 110…Motor.

Claims

1. A rare earth permanent magnet having a first surface, wherein the coercivity of a portion a1 including the centroid of the first surface is A1, the coercivity of a portion b1 including the end of the first surface separated in the Y direction perpendicular to the normal direction at the centroid of the first surface from the portion a1 is B1, the coercivity of a portion c1 including the end of the first surface separated in the X direction perpendicular to the normal direction and the Y direction at the centroid of the first surface from the portion a1 is C1, when the coercivity of a portion d1 including the end of the first surface separated in the -X direction opposite to the X direction from the portion a1 is D1, A1 < B1, A1 ≥ C1, and A1 ≥ D1 are satisfied, a heavy rare earth element is present in the surface layer portion of the first surface, in the surface layer portion of the first surface, the heavy rare earth element is present in the portion a1, the portion b1, the portion c1, and the portion d1, a rare earth permanent magnet in which the coercivity and the concentration of the heavy rare earth element increase toward the first surface in the portion a1.

2. The rare earth permanent magnet according to claim 1, wherein B1 - A1 ≥ 10 kA / m.

3. having a second surface facing the first surface, a heavy rare earth element is present in the surface layer portion of the second surface, the coercivity of a portion a2 including the centroid of the second surface is A2, the coercivity of a portion c2 including the end of the second surface separated in the X direction from the portion a2 including the centroid of the second surface is C2, when the coercivity of a portion d2 including the end of the second surface separated in the -X direction from the portion a2 including the centroid of the second surface is D2, the rare earth permanent magnet according to claim 1 or 2, wherein A2 ≥ C2 and A2 ≥ D2 are satisfied.

4. when the coercivity of a portion b2 including the end of the second surface separated in the Y direction from the portion a2 including the centroid of the second surface is B2, The rare earth permanent magnet according to claim 3, wherein A2 < B2 is satisfied.

5. when the coercivity of a portion e2 including the end of the second surface separated in the -Y direction opposite to the Y direction from the portion a2 including the centroid of the second surface is E2, The rare earth permanent magnet according to claim 3 or 4, wherein A2 < E2 is satisfied.

6. when the coercivity of a portion e1 including the end of the first surface separated in the -Y direction opposite to the Y direction from the portion a1 including the centroid of the first surface is E1, The rare earth permanent magnet according to any one of claims 1 to 5, wherein A1 < E1 is satisfied.

7. The rare earth permanent magnet according to any one of claims 1 to 6, wherein the Y direction is the longitudinal direction of the first surface. **Claim 8** The rare earth permanent magnet according to any one of claims 1 to 7, wherein the normal direction at the center of gravity of the first surface is parallel to the c-axis of the rare earth permanent magnet. **Claim 9** A rotating electrical machine comprising a rotor, a stator, and the rare earth permanent magnet according to any one of claims 1 to 8 provided on the rotor or the stator. ​

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