R-T-B permanent magnet

Abstract

To provide a permanent magnet having high coercive force.SOLUTION: A permanent magnet 2 contains a rare earth element R (Nd), a transition metal element T (Fe), B, Zr and Cu, the permanent magnet 2 has main phase grains 4 and grain boundary multiple junctions 6 containing Nd, T and B, one grain boundary multiple junction 6 is surrounded by three or more main phase grains 4, a distribution map of elements in a cross section of the permanent magnet 2 shows that the permanent magnet 2 has a plurality of main phase grains 4 and a plurality of grain boundary multiple junctions 6, each of the vertical and the horizontal dimension of the distribution map is 50 μm, each of five grain boundary multiple junctions 6 shown in the distribution map includes a ZrB2 crystal 3 and an R-Cu rich phase 5 containing R and Cu, the concentration of B in each of the five grain boundary multiple junctions 6 is 5 atomic % or more and 20 atomic % or less, the concentration of Cu in each of the five grain boundary multiple junctions 6 is 5 atomic % or more and 25 atomic % or less, and a surface layer portion 4a of the main phase particle 4 includes at least one kind of heavy rare-earth element among Tb and Dy.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an RTB based permanent magnet. [Background technology]

[0002] R-T-B permanent magnets, which contain rare earth elements R (Nd, etc.), transition metal elements T (Fe, etc.), and boron B, are nucleation type permanent magnets. When a magnetic field opposite to the magnetization direction is applied to a nucleation type permanent magnet, nuclei of magnetization reversal tend to occur near the grain boundaries of the many crystal grains (main phase grains) that make up the permanent magnet. Then, as the magnetization reversal of the crystal grains progresses from these nuclei of magnetization reversal, the coercive force of R-T-B permanent magnets tends to be low.

[0003] Heavy rare earth elements such as Dy are added to R-T-B permanent magnets to increase their coercivity. The addition of heavy rare earth elements tends to increase the anisotropic magnetic field, making it difficult for magnetization reversal nuclei to occur near grain boundaries, and increasing the coercivity (HcJ). However, heavy rare earth elements are expensive, so in order to reduce the manufacturing costs of R-T-B permanent magnets, it is desirable to reduce the content of heavy rare earth elements in R-T-B permanent magnets.

[0004] For example, the R-T-B based sintered magnet described in Patent Document 1 listed below comprises a plurality of main phase particles each having a core and a shell covering the core, the shell has a thickness of 500 nm or less, R contains a light rare earth element and a heavy rare earth element, and Zr compounds are present in at least one of the grain boundary phase and the shell. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2011 / 122667 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an RTB based permanent magnet having high coercive force. [Means for solving the problem]

[0007] An R-T-B system permanent magnet according to one aspect of the present invention is an R-T-B system permanent magnet containing a rare earth element R, and transition metal elements T, B, Zr and Cu, wherein the R-T-B system permanent magnet contains at least Nd, and the T-T-B system permanent magnet contains at least Fe, and the R-T-B system permanent magnet comprises a plurality of main phase grains containing Nd, T and B, and a plurality of grain boundary multiple points, one grain boundary multiple point being a grain boundary surrounded by three or more main phase grains, any one of the grain boundary multiple points being ZrB 2 The crystals of ZrB and the R-Cu rich phase containing R and Cu were 2 The concentration of B at one grain boundary multipoint including both the ZrB crystal and the R-Cu rich phase is 5 atomic % or more and 20 atomic % or less, and ZrB 2 The concentration of Cu at one grain boundary multipoint including both the crystal and the R-Cu rich phase is 5 atomic % or more and 25 atomic % or less, and the surface layer portion of the main phase grain contains at least one heavy rare earth element selected from Tb and Dy.

[0008] ZrB 2 The concentration of Zr at one grain boundary multipoint including both the R—Cu rich phase and the R—Cu rich phase may be 1 atomic % or more and 10 atomic % or less.

[0009] ZrB 2 The sum of the concentrations of Nd and Pr at one grain boundary multipoint including both the crystal and the R—Cu rich phase may be 20 atomic % or more and 70 atomic % or less.

[0010] The R-Cu rich phase is ZrB 2 The crystals may be present around the

[0011] The R-Cu rich phase is ZrB 2 The crystals may be present between the crystals of the main phase and the main phase grains.

[0012] Some of the grain boundary multiple points may include a T-rich phase containing T, Cu, and at least one type of R selected from Nd and Pr, and the concentration of T at the grain boundary multiple points including the T-rich phase is higher than the concentration of T at other grain boundary multiple points, and the unit of the concentration of T is atomic %. Effect of the Invention

[0013] According to the present invention, an RTB based permanent magnet having high coercive force is provided. [Brief description of the drawings]

[0014] [Figure 1] (a) in Figure 1 is a schematic perspective view of an R-T-B system permanent magnet according to one embodiment of the present invention, and (b) in Figure 1 is a schematic diagram of a cross section of the R-T-B system permanent magnet shown in (a) in Figure 1 (viewed in the direction of the arrows along line b-b). [Diagram 2] FIG. 2 is an enlarged view of a part (region II) of the cross section shown in (b) of FIG. [Diagram 3] FIG. 3 is a perspective view of the crystal structure of ZrB2. [Figure 4] (a) in FIG. 4 is an image of a grain boundary multiple point containing both ZrB2 crystals and an R-Cu-rich phase, (b) in FIG. 4 is a distribution map of Cu in the region shown in (a) in FIG. 4, (c) in FIG. 4 is a distribution map of Nd in the region shown in (a) in FIG. 4, and (d) in FIG. 4 is a distribution map of Zr in the region shown in (a) in FIG. 4. [Diagram 5] (a) in FIG. 5 is a distribution map of Co in the region shown in (a) in FIG. 4, (b) in FIG. 5 is a distribution map of Fe in the region shown in (a) in FIG. 4, (c) in FIG. 5 is a distribution map of Ga in the region shown in (a) in FIG. 4, and (d) in FIG. 5 is a distribution map of Tb in the region shown in (a) in FIG. 4. [Figure 6]FIG. 6(a) is an image of a ZrB2 crystal, and FIG. 6(b) is an electron beam diffraction pattern of the ZrB2 crystal shown in FIG. 6(a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will be described below 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 embodiments. The "permanent magnet" described below means an R-T-B system permanent magnet. The unit of concentration of each element described below is atomic %.

[0016] (Permanent magnet) The permanent magnet according to the present embodiment contains at least a rare earth element (R), a transition metal element (T), boron (B), zirconium (Zr) and copper (Cu). The permanent magnet according to the present embodiment may be a sintered magnet.

[0017] 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 selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0018] 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.

[0019] FIG. 1(a) is a perspective view of a rectangular parallelepiped permanent magnet 2 according to this embodiment. FIG. 1(b) is a schematic diagram of a cross section 2cs of the permanent magnet 2. 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 rectangle (plate), a polygonal prism, an arc segment, a sector, an annular sector, a sphere, a disk, a cylinder, a tube, a ring, or a capsule. The shape of the cross section 2cs of the permanent magnet 2 may be, for example, a polygon, an arc (circular chord), a bow, an arch, a C-shape, or a circle.

[0020] 2 is an enlarged view of a portion (region II) of the cross section 2cs shown in (b) of FIG. 1. As shown in FIG. 2, the permanent magnet 2 includes a plurality of main phase grains 4. The main phase grains 4 contain at least Nd, T, and B. The main phase grains 4 contain R 2 T 14 The main phase grains 4 may contain crystals (single crystals or polycrystals) of Nd, T and B. The main phase grains 4 may contain other elements in addition to Nd, T and B. For example, R 2 T 14 B is (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 grains 4 may contain heavy rare earth elements such as Tb and Dy as R in addition to the light rare earth elements. The main phase grains 4 may further contain Zr. R 2 T 14 A part of B in B may be substituted with carbon (C). The composition within the main phase particle 4 may be uniform. The composition within the main phase particle 4 may be non-uniform. For example, the concentration distribution of each of R, T and B in the main phase particle 4 may have a gradient.

[0021] The main phase particle 4 is composed of a surface layer 4a and a central portion 4b covered by the surface layer 4a. The surface layer 4a may be referred to as a shell, and the central portion 4b may be referred to as a core. The surface layer 4a of the main phase particle 4 contains at least one heavy rare earth element selected from Tb and Dy. The surface layer 4a 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 4a of a part 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 the surface layer 4a containing a heavy rare earth element, the anisotropic magnetic field is likely to increase locally in the vicinity of the grain boundary, and the nucleus of magnetization reversal is unlikely to occur in the vicinity of the grain boundary. As a result, the coercive force of the permanent magnet 2 at high temperatures is increased. The high temperature may be, for example, 100°C or higher and 200°C or lower. Since the residual magnetic flux density and coercive force of the permanent magnet 2 are easily compatible, the total concentration of the heavy rare earth elements in the surface layer 4a may be higher than the total concentration of the heavy rare earth elements in the central portion 4b.

[0022] The permanent magnet 2 includes grain boundaries located between main phase grains 4. The permanent magnet 2 includes a plurality of grain boundary multiple points 6 as grain boundaries. The grain boundary multiple points 6 are grain boundaries surrounded by three or more main phase grains 4. The permanent magnet 2 also includes a plurality of two-particle grain boundaries 10 as grain boundaries. The two-particle grain boundaries 10 are grain boundaries located between two adjacent main phase grains 4.

[0023] Any one of the grain boundary multiple points 6 is zirconium boride (ZrB 2 ) crystals 3 and the R-Cu rich phase 5 containing R and Cu. 2 A single grain boundary multiplex 6 including both the Zr-B-R-Cu crystal 3 and the R-Cu rich phase 5 is sometimes referred to as a "Zr-B-R-Cu grain boundary."

[0024] Figure 3 shows ZrB 2 The crystal structure of ZrB 2 The angle between the a-axis and the b-axis is 120°. The a-axis and the b-axis are each perpendicular to the c-axis. 2The crystal structure of ZrB has rotational symmetry with respect to the c-axis and is six-fold symmetric. 2 Crystal 3 of ZrB is hexagonal. 2 The three-dimensional space group of crystal 3 is P6 / mmm.

[0025] The B concentration in one Zr-B-R-Cu grain boundary is 5 atomic % or more and 20 atomic % or less. The B concentration in one Zr-B-R-Cu grain boundary is higher than the average value of the B concentration in the cross section 2cs of the permanent magnet 2.

[0026] The Cu concentration at one Zr-B-R-Cu grain boundary is 5 atomic % or more and 25 atomic % or less. The Cu concentration at one Zr-B-R-Cu grain boundary is higher than the average Cu concentration at the cross section 2cs of the permanent magnet 2.

[0027] A grain boundary multiple point 6 in which the concentrations of B and Cu are within the above ranges is ZrB 2 The B crystal 3 and the R-Cu rich phase 5 are likely to be included. For the same reason, the B concentration in one Zr-B-R-Cu grain boundary may be 6.4 atomic % or more and 15.2 atomic % or less, and the Cu concentration in one Zr-B-R-Cu grain boundary may be 9.2 atomic % or more and 19.6 atomic % or less.

[0028] The sum of the concentrations of Nd and Pr in one Zr-B-R-Cu grain boundary may be higher than the sum of the concentrations of Nd and Pr in the main phase grains 4. The concentration of Cu in one Zr-B-R-Cu grain boundary may be higher than the concentration of Cu in the main phase grains 4. The R-Cu rich phase 5 may be a grain boundary phase included in a grain boundary multiple point 6 in which the sum of the concentrations of Nd and Pr is higher than the sum of the concentrations of Nd and Pr in the main phase grains 4 and the concentration of Cu is higher than the concentration of Cu in the main phase grains 4. The sum of the concentrations of Nd and Pr in the main phase grains 4 may be the average value of the sum of the concentrations of Nd and Pr in all the main phase grains 4 in contact with one Zr-B-R-Cu grain boundary. The concentration of Cu in the main phase grains 4 may be the average value of the concentrations of Cu in all the main phase grains 4 in contact with one Zr-B-R-Cu grain boundary.

[0029] The Zr concentration in one Zr-B-R-Cu grain boundary may be 1 atomic % or more and 10 atomic % or less, or 1.6 atomic % or more and 7.4 atomic % or less. The Zr concentration in one Zr-B-R-Cu grain boundary is higher than the average value of the Zr concentration in the cross section 2cs of the permanent magnet 2.

[0030] The sum of the concentrations of Nd and Pr in one Zr-B-R-Cu grain boundary may be 20 atomic % or more and 70 atomic % or less, or 25.1 atomic % or more and 46.1 atomic % or less.

[0031] The concentrations of Zr, Nd and Pr in one Zr-B-R-Cu grain boundary tend to be within the above range. In other words, one grain boundary multiple point 6 in which the concentrations of Zr, Nd and Pr are within the above range is ZrB 2 The crystals 3 and the R-Cu rich phase 5 tend to be both crystalline and R-Cu rich phases.

[0032] The permanent magnet 2 may include a plurality of Zr-B-R-Cu grain boundaries. Some of the grain boundary multiple points 6 among all the grain boundary multiple points 6 included in the permanent magnet 2 may not be Zr-B-R-Cu grain boundaries. For example, some of the grain boundary multiple points 6 may be ZrB 2 Some of the grain boundary multiple points 6 may include only the R-Cu rich phase 5. Some of the grain boundary multiple points 6 may include only the ZrB 2 The R—Cu rich phase 5 may not be included.

[0033] The Zr-B-R-Cu grain boundaries are formed in the sintering and diffusion steps described below. The diffusion step is carried out after the sintering step. In the sintering step, a compact formed from alloy powder is heated to obtain a magnet base material (sintered body). In the diffusion step, a diffusion material is attached to the surface of the magnet base material, and the magnet base material to which the diffusion material is attached is heated. The diffusion material includes a first component containing at least one R (light rare earth element) selected from Nd and Pr, a second component containing Cu, and a third component containing at least one heavy rare earth element selected from Tb and Dy.

[0034] In the sintering process, the alloy particles that make up the alloy powder are sintered together, and ZrB 2 is generated within the grain boundary multiple points 6. In the sintering process, a grain boundary phase (R phase) with a high concentration of R (light rare earth element such as Nd) is formed at the grain boundary multiple points 6 and the two-particle grain boundary 10. The R in the R phase originates from alloy particles. With the temperature rise in the diffusion process following the sintering process, the R phase present at the grain boundary multiple points 6 and the two-particle grain boundary 10 becomes a liquid phase (R liquid phase). R (light rare earth element such as Nd) and Cu in the diffusion material dissolve into the R liquid phase, and the R and Cu in the diffusion material diffuse from the surface of the magnet base material to the inside of the magnet. As a result, a liquid phase with a high concentration of R (light rare earth element such as Nd) and Cu (R-Cu rich liquid phase) is formed within the grain boundary multiple points 6. ZrB 2 has a high affinity for the R-Cu rich liquid phase. 2 Therefore, in the diffusion process, ZrB 2 is easily dissolved in the R-Cu rich liquid phase. By cooling (quenching) after the diffusion process, ZrB 2 Crystals 3 of the above are redeposited in the R-Cu-rich liquid phase, which then solidifies to become the R-Cu-rich phase 5.

[0035] The heavy rare earth element contained in the surface layer 4a of the main phase particle 4 originates from the heavy rare earth element in the diffusion material used in the diffusion process. 2 Fe 14 B) dissolves in the R-Cu rich liquid phase in the diffusion step. In the process of reprecipitation of the surface layer 4a by cooling (quenching) after the diffusion step, the surface layer 4a takes in the heavy rare earth elements in the R-Cu rich liquid phase, forming the surface layer 4a containing the heavy rare earth elements. As described above, ZrB 2 The increase in the B concentration in the R-Cu-rich liquid phase is due to the dissolution of B into the R-Cu-rich liquid phase. 2 Fe 14 B) is suppressed from dissolving. 2 Fe 14B) is suppressed from dissolving, thereby reducing the thickness of the surface layer 4a that reprecipitates while incorporating the heavy rare earth element. Since the heavy rare earth element is concentrated in the thin surface layer 4a, the concentration of the heavy rare earth element in the surface layer 4a increases. As a result, the coercive force of the permanent magnet 2 increases. The thickness of the surface layer 4a in the direction perpendicular to the surface of the main phase grains 4 may be, for example, 3 nm or more and 50 nm or less.

[0036] For the above reasons, the permanent magnet 2 according to this embodiment can have a high coercive force at high temperatures. A high temperature may be, for example, 100° C. or higher and 200° C. or lower.

[0037] As mentioned above, ZrB dissolved in the R-Cu rich liquid phase 2 is redeposited in the R-Cu rich liquid phase by cooling (quenching) after the diffusion process. In addition, since the R-Cu rich liquid phase has excellent wettability, the R-Cu rich liquid phase easily covers the surfaces of the main phase particles 4 directly in the diffusion process. For these reasons, ZrB 2 The crystal 3 of ZrB is easily formed in the R-Cu rich phase 5. 2 The R-Cu rich phase 5 is easily formed between the ZrB crystals 3 and the main phase particles 4. 2 The R-Cu rich phase 5 may be present around the crystal 3 of ZrB 2 may be present between the crystals 3 and the main phase particles 4. 2 The lattice mismatch between the crystals 3 and the main phase particles 4, or ZrB 2 The lattice defects at the interface between the R-Cu rich phase 5 and the main phase grains 4 are likely to become the starting points of magnetization reversal (nuclei of magnetization reversal). 2 The ZrB 2 The number of places where the crystals 3 of ZrB directly contact the main phase particles 4 is reduced. 2 The starting point of magnetization reversal is unlikely to occur between the crystals 3 and the main phase grains 4, and the coercive force of the permanent magnet 2 is likely to increase.

[0038] ZrB 2 The Zr-B-R-Cu grain boundary may be connected to the two-grain grain boundary 10.2 By including the crystals 3, the permanent magnet 2 tends to have a high coercive force.

[0039] In order to form the Zr-B-R-Cu grain boundary by the above mechanism, the diffusion material must contain a first component containing at least one of R among Nd and Pr, a second component containing Cu, and a third component containing at least one of heavy rare earth elements among Tb and Dy. If the diffusion material does not contain the second component, it is difficult to form a sufficient R-Cu rich liquid phase in the grain boundary multiple points 6 during the diffusion process. As a result, it is difficult to form the Zr-B-R-Cu grain boundary by the above mechanism, and it is also difficult to concentrate the heavy rare earth element in the thin surface layer 4a.

[0040] The technical scope of the present invention is not limited by the above mechanism for the formation of the Zr-B-R-Cu grain boundaries.

[0041] Some of the grain boundary multiple points 6 other than the Zr-B-R-Cu grain boundaries may contain an R-rich phase (rare earth element rich phase). The R-rich phase is a grain boundary phase that contains at least one type of R among Nd and Pr, and is a grain boundary phase included in a grain boundary multiple point where the total concentration of R is higher than other grain boundary multiple points. The total concentration of R at one grain boundary multiple point including an R-rich phase is higher than the average value of the total concentration of R in the cross section 2cs of the permanent magnet 2.

[0042] Some of the grain boundary multiple points 6 other than the Zr-B-R-Cu grain boundary may include an R-O-C phase. The R-O-C phase is a grain boundary phase that contains at least one of R, Nd and Pr, oxygen (O), and C, and is a grain boundary phase that is included in a grain boundary multiple point in which the concentrations of O and C are higher than those of other grain boundary multiple points. The concentration of O at one grain boundary multiple point containing the R-O-C phase is higher than the average concentration of O at the cross section 2cs of the permanent magnet 2. The concentration of C at one grain boundary multiple point containing the R-O-C phase is higher than the average concentration of C at the cross section 2cs of the permanent magnet 2. Water in the atmosphere (e.g., water vapor) oxidizes the R-rich phase in the grain boundary, and the generation and absorption of hydrogen, hydrogenation of the R-rich phase, and oxidation of the hydride of R by water proceed in a chain reaction in the grain boundary. As a result, the permanent magnet 2 is corroded. On the other hand, the R-O-C phase is less likely to be oxidized by water than the R-rich phase. Furthermore, the R-O-C phase is less likely to absorb hydrogen than the R-rich phase. Therefore, when the permanent magnet 2 contains the R-O-C phase, the corrosion resistance of the permanent magnet 2 is improved.

[0043] Some of the grain boundary multiple points 6 other than the Zr-B-R-Cu grain boundaries may include an oxide phase. The oxide phase is a grain boundary phase that contains at least one oxide of R selected from Nd and Pr as a main component and has a different composition from the above-mentioned R-O-C phase.

[0044] A part of the grain boundary multiple points 6 other than the Zr-B-R-Cu grain boundary may contain a T-rich phase (a transition metal element rich phase). The T-rich phase is a grain boundary phase containing T, Cu, and at least one of Nd and Pr, and is a grain boundary phase contained in a grain boundary multiple point where the total concentration of T is higher than that of other grain boundary multiple points. The T contained in the T-rich phase may be only Fe. The T contained in the T-rich phase may be Fe and Co. The total concentration of T in one grain boundary multiple point where the T-rich phase is contained is higher than the total concentration of T in other grain boundary multiple points. Although the concentration of T in the T-rich phase is higher than that of other grain boundary phases, the magnetization of the T-rich phase is relatively low. The magnetic coupling between the main phase grains 4 is easily broken by the presence of the T-rich phase with low magnetization at least in one of the grain boundary multiple points 6 and the two-particle grain boundary 10. As a result, the coercive force of the permanent magnet 2 is easily increased. The T-rich phase may further contain gallium (Ga) in addition to R, T, and Cu.

[0045] One grain boundary multiple point 6 is ZrB 2 The grain boundary 10 may include a plurality of grain boundary phases selected from the group consisting of a ZrB crystal 3, an R-Cu rich phase 5, an R rich phase, an oxide phase, an R-O-C phase, and a T rich phase. 2 The alloy may include a plurality of grain boundary phases selected from the group consisting of a crystal 3, an R-Cu rich phase 5, an R rich phase, an oxide phase, an R-O-C phase, and a T rich phase.

[0046] Some Zr-B-R-Cu grain boundaries are 2 In addition to the crystals 3 and the R-Cu rich phase 5, the grain boundary phase may further include other grain boundary phases as described above. For example, some of the Zr-B-R-Cu grain boundaries may be ZrB 2 The Zr-B-R-Cu grain boundary may further include a T-rich phase in addition to the crystals 3 and the R-Cu rich phase 5. When the Zr-B-R-Cu grain boundary further includes a T-rich phase, the coercive force of the permanent magnet 2 tends to increase.

[0047] ZrB 2The crystals 3, the R-Cu rich phase 5, the main phase grains 4 and other grain boundary phases are clearly distinguished based on differences in composition. The compositions of these components may be identified by analysis of the cross section 2cs of the permanent magnet 2. The cross section 2cs of the permanent magnet 2 may be analyzed by an Electron Probe Micro Analyzer (EPMA) equipped with an Energy Dispersive X-ray Spectroscopy (EDS) device. 2 The Zr-B-R-Cu crystals 3, the R-Cu rich phase 5, the main phase grains 4 and other grain boundary phases can also be identified based on contrast in an image of the cross section 2cs of the permanent magnet 2 taken with a scanning electron microscope (SEM) such as a scanning transmission electron microscope (STEM). The internal structure of the Zr-B-R-Cu grain boundaries may be identified by the contrast of an image obtained, for example, by a High Angle Annular Dark Field-STEM image (HAADF-STEM image). 2 The crystal structure of crystal 3 may be identified based on lattice resolution HAADF-STEM images and electron diffraction patterns.

[0048] According to the EPMA, the distribution maps of Zr, B, and Cu on the cross section 2cs of the permanent magnet 2 are measured. When any one element is expressed as Ex, the bright areas on the distribution map of Ex are areas where the concentration of Ex is higher than the average concentration of Ex on the cross section 2cs of the permanent magnet 2. In other words, the bright areas on the distribution map of Ex are areas where the intensity of the characteristic X-rays of Ex is higher than the average intensity of the characteristic X-rays of Ex on the cross section 2cs of the permanent magnet 2. The areas where the concentration of each element is high on the distribution maps of Zr, B, and Cu overlap on the Zr-B-R-Cu grain boundary. In other words, the position of the Zr-B-R-Cu grain boundary can be identified by overlapping the distribution maps of Zr, B, and Cu. After the position of the Zr-B-R-Cu grain boundary is identified, the concentration of each element on the Zr-B-R-Cu grain boundary can be measured by locally analyzing the Zr-B-R-Cu grain boundary with the EPMA.

[0049] The average particle size or median size (D50) of the main phase particles 4 is not particularly limited, but may be, for example, 1.0 μm or more and 10.0 μm or less, or 1.5 μm or more and 6.0 μm or less. The total volume fraction of the main phase particles 4 in the permanent magnet 2 is not particularly limited, but may be, for example, 80 volume % or more and less than 100 volume %.

[0050] The specific overall composition of the permanent magnet 2 is described below. However, the composition of the permanent magnet 2 is not limited to the composition below. As long as the above-mentioned effects resulting from the Zr-B-R-Cu grain boundaries can be obtained, the content of each element in the permanent magnet 2 may be outside the following range.

[0051] The total content of the rare earth element R in the entire permanent magnet may be 25% by mass or more and 35% by mass or less, or 28% by mass or more and 34% by mass or less. When the content of R is within this range, the residual magnetic flux density and the coercive force tend to increase. When the content of R is too low, the main phase particles (R 2 T 14B) is difficult to form, and the α-Fe phase having soft magnetism is easily formed. As a result, the coercive force tends to decrease. On the other hand, if the content of R is too large, the volume ratio of the main phase particles decreases, and the residual magnetic flux density tends to decrease. Since the residual magnetic flux density and the coercive force tend to increase, the total ratio of Nd and Pr to 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.

[0052] The B content of the entire permanent magnet may be 0.90% by mass or more and 1.05% by mass or less. When the B content is 0.90% by mass or more, the permanent magnet is likely to include Zr-B-R-Cu grain boundaries. When the B content is 0.90% by mass or more, the remanence of the permanent magnet is likely to increase. When the B content is 1.05% by mass or less, the coercive force of the permanent magnet is likely to increase. When the B content is within the above range, the squareness ratio (Hk / HcJ) of the permanent magnet is likely to approach 1.0. Hk is the strength of the demagnetizing field equivalent to 90% of the remanence (Br) in the second quadrant of the magnetization curve.

[0053] The Zr content in the entire permanent magnet may be 0.10% by mass or more and 1.00% by mass or less, preferably 0.25% by mass or more and 1.00% by mass or less. When the Zr content is 0.25% by mass or more, the permanent magnet is likely to include Zr-B-R-Cu grain boundaries. When the Zr content is 0.25% by mass or more, abnormal grain growth of the main phase grains in the sintering process described below is likely to be suppressed, the squareness ratio of the permanent magnet is likely to approach 1.0, and the permanent magnet is likely to be magnetized under a low magnetic field. When the Zr content is 1.00% by mass or less, the residual magnetic flux density of the permanent magnet is likely to increase.

[0054] The Cu content of the entire permanent magnet may be 0.04% by mass or more and 0.50% by mass or less. When the Cu content is 0.04% by mass or more, the permanent magnet is likely to include Zr-B-R-Cu grain boundaries. When the Cu content is 0.04% by mass or more, the coercive force of the permanent magnet is likely to increase and the corrosion resistance of the permanent magnet is likely to improve. When the Cu content is 0.50% by mass or less, the coercive force and residual magnetic flux density of the permanent magnet are likely to increase.

[0055] The Ga content of the entire permanent magnet may be 0.03% by mass or more and 0.30% by mass or less. When the Ga content is 0.03% by mass or more, the permanent magnet is likely to include a T-rich phase, and the coercive force of the permanent magnet is likely to increase. When the Ga content is 0.30% by mass or less, the generation of subphases (e.g., phases containing R, T, and Ga) is appropriately suppressed, and the residual magnetic flux density of the permanent magnet is likely to increase.

[0056] The O content of the entire permanent magnet may be 0.03 mass% or more and 0.4 mass% or less, or 0.05 mass% or more and 0.2 mass% or less. If the O content is too low, it is difficult to form the R-O-C phase. If the O content is too high, the coercive force of the permanent magnet is likely to decrease.

[0057] The C content of the entire permanent magnet may be 0.03% by mass or more and 0.3% by mass or less, or 0.05% by mass or more and 0.15% by mass or less. If the C content is too low, it is difficult to form an R-O-C phase. If the C content is too high, the coercive force of the permanent magnet is likely to decrease.

[0058] The Co content of the entire permanent magnet may be 0.30% by mass or more and 3.00% by mass or less. When the Co content is 0.30% by mass or more, the corrosion resistance of the permanent magnet is likely to be improved. When the Co content is more than 3.00% by mass, the effect of improving the corrosion resistance of the permanent magnet reaches a plateau, and there is no benefit that is commensurate with the cost of Co.

[0059] The aluminum (Al) content in the entire permanent magnet may be 0.05% by mass or more and 0.50% by mass or less. When the Al content is 0.05% by mass or more, the coercive force of the permanent magnet is likely to increase. Furthermore, when the Al content is 0.05% by mass or more, the amount of change in the magnetic properties (especially the coercive force) of the permanent magnet associated with the change in temperature of the aging treatment or heat treatment described below tends to be small, and the variation in the magnetic properties of mass-produced permanent magnets tends to be suppressed. When the Al content is 0.50% by mass or less, the residual magnetic flux density of the permanent magnet is likely to increase. Furthermore, when the Al content is 0.50% by mass or less, the change in the coercive force associated with the change in temperature is likely to be suppressed.

[0060] The manganese (Mn) content of the entire permanent magnet may be 0.02% by mass or more and 0.10% by mass or less. If the Mn content is 0.02% by mass or more, the residual magnetic flux density and coercive force of the permanent magnet tend to increase. If the Mn content is 0.10% by mass or less, the coercive force of the permanent magnet tends to increase.

[0061] The total content of Tb and Dy in the entire permanent magnet may be 0.00% by mass or more and 5.00% by mass or less, or 0.20% by mass or more and 5.00% by mass or less. In some cases, the total content of Tb and Dy in the entire permanent magnet may be C Tb+Dy It is written as C of a permanent magnet. Tb+Dy By making the C content 0.20 mass % or more, the magnetic properties (especially the coercive force) of the permanent magnet are easily improved. Tb+Dy When is within the above range, the permanent magnet according to this embodiment has C Tb+Dy In other words, the C of the permanent magnet according to this embodiment is likely to have superior magnetic properties compared to conventional permanent magnets having the same C. Tb+Dy is that of conventional permanent magnets. Tb+Dy Even if the magnetic properties of the permanent magnet according to the present embodiment are less than 100%, the magnetic properties of the permanent magnet according to the present embodiment are superior to those of conventional permanent magnets. Tb+Dy C of conventional permanent magnets Tb+Dy It is possible to reduce the

[0062] The remainder, excluding the above elements from the permanent magnet, may be Fe alone, or Fe and other elements. In order for the permanent magnet to have sufficient magnetic properties, the total content of the elements other than Fe in the remainder may be 5 mass% or less with respect to the total mass of the permanent magnet.

[0063] The permanent magnet may contain, as other elements, at least one element selected from the group consisting of silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), nickel (Ni), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), tin (Sn), calcium (Ca), nitrogen (N), chlorine (Cl), sulfur (S) and fluorine (F).

[0064] The composition of the entire permanent magnet may be analyzed by, for example, X-ray fluorescence (XRF) analysis, high-frequency inductively coupled plasma (ICP) emission analysis, inert gas fusion-non-dispersive infrared absorption (NDIR) method, combustion in oxygen flow-infrared absorption method, inert gas fusion-thermal conductivity method, etc.

[0065] The permanent magnet according to the present embodiment may be applied to motors, generators, actuators, etc. For example, permanent magnets are used in various fields such as hybrid cars, electric cars, hard disk drives, magnetic resonance imaging devices (MRI), smartphones, digital cameras, flat-screen TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators, and wind power generators.

[0066] (Outline of manufacturing method for permanent magnets) The manufacturing method of the permanent magnet according to the present embodiment includes a diffusion step of attaching a diffusion material to the surface of a magnet base material and heating the magnet base material to which the diffusion material is attached. The magnet base material contains R, T, B and Zr. At least a part of the R contained in the magnet base material is Nd. At least a part of the T contained in the magnet base material is Fe. The diffusion material contains a first component, a second component and a third component. The first component is at least one of a Nd hydride and a Pr hydride. The second component is at least one selected from the group consisting of a simple substance of Cu, an alloy containing Cu, and a compound of Cu. The third component is at least one of a Tb hydride and a Dy hydride.

[0067] By using a diffusion material containing both the first component and the second component, the above-mentioned R-Cu rich liquid phase is formed in the grain boundary multiple points in the diffusion process, and the permanent magnet can contain Zr-B-R-Cu grain boundaries. In other words, most of the Cu contained in the Zr-B-R-Cu grain boundaries comes from the second component contained in the diffusion material. If the diffusion material does not contain at least one of the first component and the second component, due to a shortage of Cu or insufficient diffusion of Cu, the above-mentioned R-Cu rich liquid phase is difficult to form in the grain boundary multiple points in the diffusion process, and it is difficult for the permanent magnet to contain Zr-B-R-Cu grain boundaries.

[0068] (Details of each process) Each step of the method for producing a permanent magnet will be described in detail below.

[0069] [Preparation of raw alloy] In the raw alloy preparation step, the raw alloy is prepared from metals (raw metals) containing each element constituting the permanent magnet by a strip casting method or the like. The raw metal may be, for example, 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 so as to match the composition of the desired magnet base material. The content of each element (except Nd, Pr, Cu, Tb, and Dy) in the permanent magnet may be controlled based on the content of each element in the magnet base material (raw alloy). The content of each of Nd, Pr, Cu, Tb, and Dy in the permanent magnet may be controlled based on the content of each of Nd, Pr, Cu, Tb, and Dy in the magnet base material (raw alloy) and the composition and amount of the diffusion material used in the diffusion step. Two or more alloys having different compositions may be used as the raw alloy.

[0070] The raw alloy contains at least R, T, B and Zr. The raw alloy may further contain Cu. The raw alloy does not have to contain Cu.

[0071] At least a part of R contained in the raw alloy is Nd. The raw alloy may further contain at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu as other R. The raw alloy may contain Pr. The raw alloy may not contain Pr. The raw alloy may contain one or both of Tb and Dy. The raw alloy may not contain one or both of Tb and Dy.

[0072] At least a part of T contained in the raw alloy is Fe. All of T contained in the raw alloy may be Fe. T contained in the raw alloy may be Fe and Co. The raw alloy may further contain other transition metal elements other than Fe and Co. T described below means only Fe, or Fe and Co.

[0073] The raw alloy may further contain other elements in addition to R, T, B, and Zr. For example, the raw alloy may contain at least one element selected from the group consisting of Ga, Al, Mn, C, O, N, Si, Ti, V, Cr, Ni, Nb, Mo, Hf, Ta, W, Bi, Sn, Ca, Cl, S, and F as the other elements.

[0074] [Crushing process] In the pulverization step, the raw alloy is pulverized in a non-oxidizing atmosphere to prepare an alloy powder. The raw alloy may be pulverized in two stages, a coarse pulverization step and a fine pulverization step. In the coarse pulverization step, a pulverization method such as a stamp mill, a jaw crusher, or a Braun mill may be used. The coarse pulverization step may be performed in an inert gas atmosphere. After hydrogen is absorbed in the raw alloy, the raw alloy may be pulverized. That is, hydrogen absorption pulverization may be performed as the coarse pulverization step. In the coarse pulverization step, the raw alloy may be pulverized until its particle size is about several hundred μm. In the fine pulverization step following the coarse pulverization step, the raw alloy that has been subjected to the coarse pulverization step may be further pulverized until its average particle size is several μm. In the fine pulverization step, for example, a jet mill may be used. The raw alloy may be pulverized by only one pulverization step. For example, only the fine pulverization step may be performed. When a plurality of raw alloys are used, each raw alloy may be pulverized separately and then mixed. The alloy powder may contain at least one lubricant (grinding aid) selected from the group consisting of fatty acids, fatty acid esters, fatty acid amides, and metal salts of fatty acids (metal soaps). In other words, the raw alloy may be ground together with the grinding aid.

[0075] [Molding process] In the compacting step, the alloy powder is compacted in a magnetic field to obtain a compact containing the alloy powder oriented along the magnetic field. For example, the compact may be obtained by pressing the alloy powder with a die while applying a magnetic field to the alloy powder in the die. The pressure exerted by the die on the alloy powder may be 20 MPa or more and 300 MPa or less. The strength of the magnetic field applied to the alloy powder may be 950 kA / m or more and 1600 kA / m or less. The shape of the compact may be the same as that of a permanent magnet.

[0076] [Sintering process] In the sintering step, the above-mentioned compact is sintered in a vacuum or inert gas atmosphere to obtain a sintered body. The sintering conditions may be appropriately set depending on the composition of the target permanent magnet, the crushing method and particle size of the raw alloy, etc. The sintering temperature may be, for example, 1000°C or higher and 1200°C or lower. The sintering time may be 1 hour or higher and 20 hours or lower.

[0077] [Aging treatment process] An aging treatment step may be performed after the sintering step. However, the aging treatment step is not essential. In the aging treatment step, the sintered body may be heated at a temperature lower than the sintering temperature. In the aging treatment step, the sintered body may be heated in a vacuum or in an inert gas atmosphere. The diffusion step described later may also serve as the aging treatment step. In that case, an aging treatment step other than the diffusion step may not be performed. The aging treatment step may be composed of a first aging treatment and a second aging treatment following the first aging treatment. In the first aging treatment, the sintered body may be heated at a temperature of 700°C or more and 900°C or less. The time for the first aging treatment may be 1 hour or more and 10 hours or less. In the second aging treatment, the sintered body may be heated at a temperature of 500°C or more and 700°C or less. The time for the second aging treatment may be 1 hour or more and 10 hours or less.

[0078] The above steps result in a sintered body. The sintered body is the magnet base material used in the diffusion step described below. The magnet base material (sintered body) comprises a plurality (a large number) of main phase particles (alloy particles) sintered together. However, the composition of each main phase particle contained in the magnet base material is different from the composition of each main phase particle contained in the permanent magnet that has been subjected to the diffusion step described below. The main phase particles contain at least Nd, Fe, B, and Zr. The main phase particles contain R 2 T 14The magnet substrate also has a plurality of grain boundary multiple points. However, the composition of each grain boundary multiple point included in the magnet substrate is different from the composition of each grain boundary multiple point included in the completed permanent magnet. The magnet substrate also has a plurality of two-particle grain boundaries as grain boundaries. However, the composition of each two-particle grain boundary included in the magnet substrate is different from the average composition of each two-particle grain boundary included in the permanent magnet that has been subjected to the diffusion process described below. The concentration of Nd in the grain boundary multiple points may be higher than the concentration of Nd in the main phase grains. In other words, the grain boundary multiple points in the magnet substrate may already include an R-rich phase. As described above, ZrB derived from Zr and B in the main phase grains 2 may be generated within grain boundary multiple points.

[0079] [Diffusion process] In the diffusion process, the diffusion material is attached to the surface of the magnet substrate, and the magnet substrate to which the diffusion material is attached is heated. The diffusion material contains at least a first component, a second component, and a third component. The diffusion material may further contain other components than the first component, the second component, and the third component. For convenience of the following description, one or both of Nd and Pr are represented as RL. One or both of Tb and Dy are represented as RH.

[0080] The first component is at least one of a neodymium hydride and a prussian hydride. The neodymium hydride is, for example, NdH 2 and NdH 3 The hydride of Pr may be, for example, PrH 2 and PrH 3 The Nd hydride and the Pr hydride may be a hydride of an alloy made of Nd and Pr.

[0081] The second component is at least one selected from the group consisting of a simple substance of Cu, an alloy containing Cu, and a compound of Cu. The second component may not contain Nd, Pr, Tb, and Dy. The alloy containing Cu may contain at least one element, excluding Nd, Pr, Tb, and Dy, among the elements that may be contained in a permanent magnet. The compound of copper may be, for example, at least one selected from the group consisting of a hydride and an oxide. The hydride of Cu may be, for example, CuH. The oxide of Cu may be, for example, Cu. 2 It may be at least one of O and CuO.

[0082] The third component is at least one of a hydride of Tb and a hydride of Dy. The hydride of Tb is, for example, TbH 2 and TbH 3 The hydride of Tb may be, for example, a hydride of an alloy of Tb and Fe. The hydride of Dy may be, for example, DyH 2 and DyH 3 The hydride of Dy may be, for example, a hydride of an alloy made of Dy and Fe. The hydride of Tb and the hydride of Dy may be, for example, a hydride of an alloy made of Tb, Dy, and Fe.

[0083] The first component, the second component, and the third component may each be a powder. By the first component, the second component, and the third component each being a powder, RL in the first component, Cu in the second component, and RH in the third component are easily diffused into the inside of the magnet base material. The first component, the second component, and the third component may each be produced by a coarse pulverization process and a fine pulverization process. The method of each of the coarse pulverization process and the fine pulverization process may be the same as the above-mentioned raw alloy pulverization process. The first component, the second component, and the third component may be pulverized together and simultaneously. The particle size of each of the first component, the second component, and the third component may be freely controlled by the coarse pulverization process and the fine pulverization process. For example, after hydrogen is absorbed into a metal element, the metal hydride may be dehydrogenated. As a result, a coarse powder made of a metal hydride is obtained. The coarse hydride powder is further pulverized by a jet mill to obtain a fine powder made of a metal hydride. This fine powder may be used as the first component, the second component, and the third component. The powder of the second component may be prepared by a method separate from the method for preparing the first component and the third component. For example, the powder of the second component may be prepared by a method such as an electrolytic method or an atomization method, and then the powder of the second component may be mixed with the first component and the third component.

[0084] When the magnet base material to which the diffusion material is attached is heated, RL derived from the first component diffuses into the inside of the magnet base material, Cu derived from the second component diffuses into the inside of the magnet base material, and RH derived from the third component diffuses into the inside of the magnet base material. The inventors presume that RL, Cu, and RH diffuse from the surface of the magnet base material into the inside of the magnet base material by the following mechanism. However, the diffusion mechanism is not limited to the following mechanism.

[0085] In the sintering process, a grain boundary phase (R phase) with a high concentration of RL is formed at the grain boundary multiple points 6 and the two-particle grain boundary 10. RL in the R phase originates from alloy particles. With the temperature rise in the diffusion process, the R phase present at the grain boundary multiple points 6 and the two-particle grain boundary 10 becomes a liquid phase (R liquid phase). Then, the diffusion material dissolves in the R liquid phase, and the components of the diffusion material diffuse from the surface of the magnet base material to the inside of the magnet base material. If only the third component (RH hydride) is used as the diffusion material, a dehydrogenation reaction of the RH hydride attached to the surface of the magnet base material occurs with the temperature rise in the diffusion process. The RH generated by the dehydrogenation reaction is likely to rapidly dissolve in the R liquid phase that has seeped out from the inside of the magnet base material to the surface. As a result, the concentration of RH rises rapidly near the surface of the magnet base material, and RH is likely to diffuse into the inside of the main phase particles located near the surface of the magnet base material. In other words, RH is likely to stagnate inside the main phase particles located near the surface of the magnet base material, and is difficult to diffuse into the inside of the magnet base material. Therefore, less RH diffuses inside the magnet, and the increase in the coercive force of the permanent magnet is reduced.

[0086] On the other hand, when the diffusion material includes the first component (RL), the second component (Cu) and the third component (RH), the eutectic temperature of Cu and RL is low, so when the R-liquid phase in the magnet base material seeps out to the surface of the magnet base material, the Cu contained in the diffusion material is likely to dissolve in the R-liquid phase before the RH. In other words, dissolution of Cu into the R-liquid phase occurs first, and the Cu concentration in the R-liquid phase located near the surface of the magnet base material increases. As a result, an R-Cu rich liquid phase is generated near the surface of the magnet base material, and Cu further diffuses into the R-liquid phase inside the magnet base material. On the other hand, the first component RL and the third component RH start to dissolve in the R-Cu rich liquid phase after the dehydrogenation reaction of the hydride occurs. The eutectic temperature of the first component RL and Cu is about 500°C, and the eutectic temperature of the third component RH and Cu is about 700 to 800°C. Therefore, the first component RL dissolves into the R-Cu-rich liquid phase near the surface of the magnet substrate, followed by Cu, and then the third component RH dissolves into the R-Cu-rich liquid phase. The dissolution of the first component RL into the liquid phase followed by Cu promotes the diffusion of Cu into the magnet substrate through the liquid phase, and further generates an R-Cu-rich liquid phase within the grain boundaries of the magnet substrate.

[0087] Of the first component (RL), second component (Cu) and third component (RH), the third component is likely to dissolve last in the liquid phase, so RH derived from the third component diffuses into the liquid phase inside the magnet base material following Cu and RL. As a result, a rapid increase in the concentration of RH near the surface of the magnet base material is suppressed compared to the case where the first component and the second component are not present. By suppressing a rapid increase in the concentration of RH near the surface of the magnet base material, excessive diffusion of RH into the inside of the main phase particles located near the surface of the magnet base material is suppressed. As a result, a sufficient amount of RH can diffuse into the inside of the magnet base material, improving the coercivity of the permanent magnet.

[0088] ZrB formed within grain boundary multi-points during sintering process 2 is easily dissolved in the R-Cu rich liquid phase. By cooling (quenching) after the diffusion process, ZrB 2 The crystals of reprecipitate in the R-Cu-rich liquid phase, and the R-Cu-rich liquid phase solidifies to become an R-Cu-rich phase.

[0089] The surface layer of the main phase grains (R 2 Fe 14 B) dissolves in the R-Cu-rich liquid phase formed at the grain boundaries during the diffusion process. During the process in which the surface layer is reprecipitated from the R-Cu-rich liquid phase by cooling (quenching) after the diffusion process, the surface layer takes in the third component (RH) in the R-Cu-rich liquid phase, forming a surface layer containing RH. As described above, ZrB 2 The increase in the B concentration in the R-Cu-rich liquid phase is due to the dissolution of B into the R-Cu-rich liquid phase. 2 Fe 14 B) is suppressed from dissolving. 2 Fe 14 B) The suppression of dissolution reduces the thickness of the surface layer that reprecipitates while absorbing RH. RH is concentrated in the thin surface layer, so the concentration of RH in the surface layer increases. As a result, the anisotropic magnetic field becomes locally large near the grain boundary between two grains, and it becomes difficult for the nucleus of magnetization reversal to occur near the grain boundary between two grains. This increases the coercive force of the permanent magnet.

[0090] As described above, according to this embodiment, the coercive force of the permanent magnet can be increased.

[0091] Since the magnetic properties of the permanent magnet are likely to be improved by the above-mentioned diffusion mechanism, the first component may be at least one of a neodymium hydride and a praseodymium hydride, the second component may be copper as an elemental substance, and the third component may be at least one of a Tb hydride and a Dy hydride.

[0092] In the diffusion step, a slurry containing a first component, a second component, a third component, and a solvent may be attached to the surface of the magnet substrate as a diffusion material. The solvent contained in the slurry may be a solvent other than water. The solvent may be, for example, an organic solvent such as an alcohol, an aldehyde, or a ketone. The diffusion material may further contain a binder so that the diffusion material can easily adhere to the surface of the magnet substrate. The slurry may contain the first component, the second component, the third component, a solvent, and a binder. A paste having a higher viscosity than the slurry may be formed by mixing the first component, the second component, the third component, the binder, and the solvent. This paste may be attached to the surface of the magnet substrate. The paste is a mixture having fluidity and high viscosity. Before the diffusion step, the solvent contained in the slurry or paste may be removed by heating the magnet substrate to which the slurry or paste is attached.

[0093] The diffusion material may be attached to a part or the whole of the surface of the magnet substrate. The method of attaching the diffusion material is not limited. For example, the above-mentioned slurry or paste may be applied to the surface of the magnet substrate. The diffusion material itself or the slurry may be sprayed onto the surface of the magnet substrate. The diffusion material may be evaporated onto the surface of the magnet substrate. The magnet substrate may be immersed in the slurry. The diffusion material may be attached to the magnet substrate via an adhesive (binder) that covers the surface of the magnet substrate. A part or the whole of the surface of the magnet substrate may be covered with a sheet containing the diffusion material.

[0094] The temperature (diffusion temperature) of the magnet base material in the diffusion process may be equal to or higher than the eutectic temperature of RL and Cu, and may be lower than the above-mentioned sintering temperature. For example, the diffusion temperature may be 800°C or higher and 950°C or lower. In the diffusion process, the temperature of the magnet base material may be gradually increased from a temperature lower than the diffusion temperature to the diffusion temperature. The time (diffusion time) during which the temperature of the magnet base material is maintained at the diffusion temperature may be, for example, 1 hour or higher and 50 hours or lower. The atmosphere around the magnet base material in the diffusion process may be a non-oxidizing atmosphere. The non-oxidizing atmosphere may be, for example, a rare gas such as argon. In addition, the pressure of the atmosphere around the magnet base material in the diffusion process may be 1 kPa or lower. By carrying out the diffusion process in such a reduced pressure atmosphere, the dehydrogenation reaction of the hydride (first component and third component) is promoted, and the dissolution of the diffusion material into the liquid phase is easily promoted.

[0095] The total mass of Tb, Dy, Nd, Pr and Cu in the diffusing material is M ELEMENTS The total mass of Tb and Dy in the diffusing material may be expressed as M ELEMENTS % or more, the total mass of Tb and Dy may be 47% by mass or more and 86% by mass or less, 55% by mass or more and 85% by mass or less, 55% by mass or more and 80% by mass or less, or 59% by mass or more and 75% by mass or less. The total mass of Tb and Dy can be said to be the total mass of RH in the diffusion material. When the total mass of RH is 55% by mass or more, the total amount of diffusion material required to increase the coercivity of the permanent magnet is likely to be reduced. When the total mass of RH is 85% by mass or less, less RH stagnates inside the main phase particles located near the surface of the magnet base material, and the coercivity of the permanent magnet is likely to be improved.

[0096] The total mass of Nd and Pr in the diffusing material is M ELEMENTS% or more, it may be 10% by mass or more and 43% by mass or less, 10% by mass or more and 37% by mass or less, 15% by mass or more and 37% by mass or less, or 15% by mass or more and 32% by mass or less. The total mass of Nd and Pr can be said to be the total mass of RL in the diffusion material. When the total mass of RL is 10% by mass or more, the R-Cu rich liquid phase is likely to exist in the interior of the magnet base material in the diffusion process, and the concentration of RH in the surface layer of the main phase particles is likely to be high. When the total mass of RL is 37% by mass or less, the third component (RH) is not too diluted by the first component (RL), and the coercive force of the permanent magnet is likely to increase.

[0097] The Cu content in the diffusion material is M ELEMENTS With respect to the total amount of the magnet base material, the Cu content may be 4% by mass or more and 30% by mass or less, 8% by mass or more and 25% by mass or less, or 8% by mass or more and 20% by mass or less. When the Cu content is 4% by mass or more, an R-Cu rich liquid phase is likely to be generated, and the RH concentration in the surface layer of the main phase particles is likely to increase. When the Cu content is 30% by mass or less, the decrease in the coercive force and residual magnetic flux density of the permanent magnet is likely to be suppressed. When the magnet base material contains Cu, the Cu derived from the magnet base material may exhibit the same effect as that of the Cu derived from the diffusion material. However, it is difficult to obtain the same effect as that of the Cu derived from the diffusion material only by the Cu derived from the magnet base material.

[0098] The particle size of each of the first component, the second component, and the third component may be in the range of 0.3 μm to 32 μm, or 0.3 μm to 90 μm. The particle size of each of the first component, the second component, and the third component may be referred to as the particle size of the diffusion material. As the particle size of the diffusion material increases, the oxygen contained in the diffusion material is reduced, and the diffusion of RH, RL, and Cu is less likely to be inhibited by oxygen. As a result, the coercive force of the permanent magnet is likely to increase. As the particle size of the diffusion material decreases, the time required for dissolving each of the first component, the second component, and the third component is short, and RH, RL, and Cu are likely to diffuse into the interior of the magnet base material. As a result, the coercive force of the permanent magnet is likely to increase. In addition, as the particle size of the diffusion material decreases, the diffusion material is likely to adhere evenly to the surface of the magnet base material, and RH, RL, and Cu are likely to diffuse evenly into the interior of the magnet base material. As a result, the variation in the coercive force of the permanent magnet is suppressed, and the squareness ratio is likely to approach 1.0. The particle size of each of the first component, the second component, and the third component may be the same. The particle size of each of the first component, the second component, and the third component may be different from each other.

[0099] The mass of the magnet base material may be expressed as 100 parts by mass, and the total mass of Tb and Dy in the diffusion material may be 0.0 to 2.0 parts by mass relative to 100 parts by mass of the magnet base material. When the total mass of Tb and Dy relative to the magnet base material is within the above range, the total content of Tb and Dy in the entire permanent magnet is easily controlled to 0.20 to 2.00% by mass, and the magnetic properties of the permanent magnet are easily improved.

[0100] The total content of Nd and Pr in the magnet base material may be 23.0% by mass or more and 32.0% by mass or less. The total content of Tb and Dy in the magnet base material may be 0.0% by mass or more and 5.0% by mass or less. The total content of Fe and Co in the magnet base material may be 63% by mass or more and 72% by mass or less. The content of Cu in the magnet base material may be 0.04% by mass or more and 0.5% by mass or less. When the magnet base material has the above composition, the magnetic properties of the permanent magnet are easily improved.

[0101] [Heat treatment process] The magnet base material that has undergone the diffusion process may be used as a finished permanent magnet. Alternatively, a heat treatment process may be carried out after the diffusion process. In the heat treatment process, the magnet base material may be heated to 450°C or more and 600°C or less. In the heat treatment process, the magnet base material may be heated at the above temperature for 1 hour or more and 10 hours or less. The heat treatment process tends to improve the magnetic properties (especially the coercive force) of the permanent magnet.

[0102] The size and shape of the magnet substrate after the diffusion step or heat treatment step may be adjusted by processing methods such as cutting and polishing.

[0103] In this manner, a permanent magnet is completed.

[0104] The present invention is not limited to the above embodiment. For example, the magnet base material used in the diffusion process may be a hot deformed magnet instead of a sintered body. EXAMPLES

[0105] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0106] Example 1 <Magnetic substrate preparation> A raw alloy was produced from the raw metals by strip casting. The raw alloy composition was adjusted by weighing the raw metals so that the composition of the raw alloy after sintering would match the composition of the magnet base material in Table 1 below.

[0107] After hydrogen was absorbed into the raw alloy at room temperature, the raw alloy was heated at 600°C for 1 hour in an Ar atmosphere to remove hydrogen, thereby obtaining raw alloy powder. In other words, hydrogen pulverization was performed.

[0108] Oleic acid amide was added as a grinding aid to the raw alloy powder, and these were mixed in a conical mixer. The content of oleic acid amide in the raw alloy powder was adjusted to 0.1 mass%. In the subsequent fine grinding process, the average particle size of the raw alloy powder was adjusted to 3.5 μm using a jet mill. In the subsequent compacting process, the raw alloy powder was filled into a die. A magnetic field of 1200 kA / m was applied to the raw powder in the die, while the raw powder was pressed at 120 MPa to obtain a compact.

[0109] In the sintering step, the compact was heated in a vacuum at 1060° C. for 4 hours and then rapidly cooled to obtain a sintered body.

[0110] A magnet base material was obtained by the above method. The contents of each element in the magnet base material are shown in Table 1 below.

[0111] <Preparation of Diffusion Material A> An elemental Tb (elemental metal) was used as the raw material of the diffusion material A. The purity of the elemental Tb was 99.9 mass %.

[0112] Hydrogen was absorbed into the Tb element by supplying a flow of hydrogen gas to the Tb element. After the hydrogen absorption, the Tb element was heated in an Ar atmosphere at 600°C for 1 hour to dehydrogenate it, and a powder of Tb hydride was obtained. In other words, a hydrogen crushing process was performed.

[0113] Zinc stearate was added as a grinding aid to the Tb hydride powder, and they were mixed in a cone mixer. The content of zinc stearate in the Tb hydride powder was adjusted to 0.05 mass%. In the subsequent fine grinding process, the Tb hydride powder was further ground in a non-oxidizing atmosphere with an oxygen content of 3000 ppm. A jet mill was used for the fine grinding process. The average particle size of the Tb hydride powder was adjusted to about 10.0 μm.

[0114] By the above method, Tb hydride (TbH 2 ) was obtained as a fine powder (third component).

[0115] From the elemental form of Nd, Nd hydride (NdH 2 The purity of the Nd element was 99.9 mass%. The average particle size of the fine powder consisting of Nd hydride was about 10.0 μm. The preparation method of the first component was the same as that of the third component, except that Nd element was used as the raw material.

[0116] A paste-like diffusion material A was produced by kneading a fine powder (first component) made of Nd hydride, a fine powder (second component) made of a simple Cu, a fine powder (third component) made of Tb hydride, alcohol (solvent), and an acrylic resin (binder). The mass ratio of the first component in the diffusion material A was 17.0 parts by mass. The mass ratio of the second component in the diffusion material A was 11.2 parts by mass. The mass ratio of the third component in the diffusion material A was 46.8 parts by mass. The mass ratio of the solvent in the diffusion material A was 23.0 parts by mass. The mass ratio of the binder in the diffusion material A was 2.0 parts by mass.

[0117] <Making permanent magnets> The magnet substrate was mechanically processed to adjust its dimensions to 14 mm length x 10 mm width x 3.7 mm thickness. After the dimensions of the magnet substrate were adjusted, an etching process was carried out on the magnet substrate. In the etching process, the entire surface of the magnet substrate was washed with an aqueous solution of nitric acid. Then, the entire surface of the magnet substrate was washed with pure water. After washing, the magnet substrate was dried. The concentration of the aqueous solution of nitric acid was 0.3 mass%. After the etching process, the following diffusion process was carried out.

[0118] In the diffusion process, the diffusion material A was applied to all surfaces of the magnet base material. The mass of the diffusion material A applied to the magnet base material was adjusted so that the mass of Tb contained in the diffusion material A was 0.8 parts by mass per 100 parts by mass of the magnet base material. The magnet base material to which the diffusion material A was applied was placed in an oven, and the magnet base material was heated at 160°C to remove the solvent in the diffusion material A. After removing the solvent, the magnet base material to which the diffusion material A was applied was heated at 900°C for 12 hours in Ar gas.

[0119] In the heat treatment step following the diffusion step, the magnet substrate was heated at 540° C. for 2 hours in Ar gas.

[0120] By the above method, a permanent magnet of Example 1 was produced. The contents of each element in the permanent magnet of Example 1 are shown in Table 1 below.

[0121] <Measurement of magnetic properties of permanent magnets> The surface of the permanent magnet was ground to remove a portion of the permanent magnet that was 0.1 mm or less deep from the surface. The residual magnetic flux density Br and coercive force HcJ of the permanent magnet were then measured using a BH tracer. Br (unit: mT) was measured at room temperature. HcJ (unit: kA / m) was measured at 160°C. The Br and HcJ of Example 1 are shown in Table 1 below.

[0122] <Cross-section analysis of a permanent magnet> After cutting the permanent magnet to expose its cross section, the permanent magnet was embedded in hot mounting resin. Pоlyfast (trade name) manufactured by Struers ApS was used as the hot mounting resin. Pоlyfast is a black Bakelite (phenolic resin) containing carbon filler. The cross section of the permanent magnet embedded in the hot mounting resin was polished by ethanol-based wet polishing. After polishing the cross section of the permanent magnet, the distribution map of each element in the cross section of the permanent magnet was measured by EPMA. JXA8500F (trade name) manufactured by JEOL Ltd. was used as the EPMA. The size of the distribution map was 50 μm long x 50 μm wide.

[0123] The distribution maps of each element showed that the permanent magnet had multiple main phase particles including Nd, Fe, Co, and B, and multiple grain boundary multiple points. In each of the distribution maps of Zr, B, and Cu, points (high concentration points) where the characteristic X-ray intensity of each element was higher than the average characteristic X-ray intensity of each element in each distribution map were identified. The high concentration points of Zr, B, and Cu overlapped at multiple grain boundary multiple points. A grain boundary multiple point where the high concentration points of Zr, B, and Cu overlap is denoted as a "Zr-B-Cu grain boundary."

[0124] The composition of each of five Zr-B-Cu grain boundaries randomly selected from the cross section of the permanent magnet was analyzed by EPMA. The composition of the Zr-B-Cu grain boundaries was analyzed under the following conditions. The analysis results are shown in Table 2 below. The composition of each of the grain boundary phases 4-1, 4-2, 4-3, 4-4, and 4-5 in Table 2 below corresponds to one Zr-B-Cu grain boundary. Accelerating voltage: 10kV Irradiation current: 0.1μA Measurement time (peak / background): 40sec / 10sec

[0125] The composition of the main phase grains was analyzed in the same manner as for the Zr-B-Cu grain boundary. The analysis results are shown in Table 2 below. Three grain boundary multiple points other than the Zr-B-Cu grain boundary were randomly selected from the cross section of the permanent magnet. The composition of each of the three grain boundary multiple points other than the Zr-B-Cu grain boundary was analyzed in the same manner as for the Zr-B-Cu grain boundary. The analysis results are shown in Table 2 below. The composition of each of grain boundary phase 1, grain boundary phase 2, and grain boundary phase 3 in Table 2 below corresponds to one grain boundary multiple point other than the Zr-B-Cu grain boundary. Grain boundary phase 1 was the R-rich phase described above. Grain boundary phase 2 was the R-O-C phase described above. Grain boundary phase 3 was the T-rich phase described above.

[0126] A sample containing the above grain boundary phase 4-1 (Zr-B-Cu grain boundary) was prepared by planar sampling of the permanent magnet using a focused ion beam (FIB) and then slicing the permanent magnet. HAADF-STEM images of the Zr-B-Cu grain boundary containing grain boundary phase 4-1 were taken. The HAADF-STEM image of the Zr-B-Cu grain boundary containing grain boundary phase 4-1 is shown in Figure 4(a). Titan-G2 (product name) manufactured by FEI was used as the STEM. The distribution map of each element in the area shown in Figure 4(a) was measured by STEM-EDS. The distribution map of Cu in the region (a) in FIG. 4 is shown in (b) in FIG. The distribution map of Nd in the region of (a) in FIG. 4 is shown in (c) in FIG. The distribution map of Zr in the region (a) in FIG. 4 is shown in (d) in FIG. The distribution map of Co in the region (a) in FIG. 4 is shown in (a) in FIG. The distribution map of Fe in the region (a) in FIG. 4 is shown in (b) in FIG. The distribution map of Ga in the region (a) in FIG. 4 is shown in (c) in FIG. The distribution map of Tb in the region (a) in FIG. 4 is shown in (d) in FIG. In mapping using STEM-EDS, it was difficult to detect B because the energy range of the characteristic X-rays of Zr and that of B overlapped, and the detection sensitivity of B was insufficient.

[0127] The results of the above analysis showed that the permanent magnet of Example 1 had the following characteristics.

[0128] As shown in FIG. 4(a), the grain boundary phase 4-1 was composed of the plate-like crystals 3 and the R-Cu-rich phase 5 containing Nd, Pr, and Cu. The region in which Zr was distributed almost completely coincided with the position of the plate-like crystals 3. The R-Cu-rich phase 5 was present around the plate-like crystals 3. The R-Cu-rich phase 5 was present between the plate-like crystals 3 and the main phase grains 4. The plate-like crystals 3 were connected to the two-grain grain boundary. The sum of the concentrations of Nd and Pr in one Zr-B-Cu grain boundary including both the plate-like crystals 3 and the R-Cu-rich phase 5 was higher than the sum of the concentrations of Nd and Pr in the main phase grains 4. The concentration of Cu in one Zr-B-Cu grain boundary including both the plate-like crystals 3 and the R-Cu-rich phase 5 was higher than the concentration of Cu in the main phase grains 4. The surface layer of the main phase grains 4 contained Tb.

[0129] The HAADF-STEM image of the plate crystal 3 contained in the grain boundary phase 4-1 is shown in FIG. 6(a). An electron diffraction pattern was measured in the region 3x in the plate crystal 3 shown in FIG. 6(a). The measured electron diffraction pattern is shown in FIG. 6(b). The lattice constant and symmetry of the plate crystal 3 identified from the electron diffraction pattern are those of hexagonal ZrB 2 The lattice constant and symmetry of the grain boundary phase 4-1 are consistent with those of the Zr-B-Cu grain boundary. 2 The crystals contained both R-Cu-rich phase and R-Cu-rich phase.

[0130] Similarly to the sample containing the grain boundary phase 4-1, four samples containing the grain boundary phase 4-2, grain boundary phase 4-3, grain boundary phase 4-4 and grain boundary phase 4-5 were prepared. Each of these samples was analyzed in the same manner as the sample containing the grain boundary phase 4-1. The analysis results showed that each of the grain boundary phases 4-2, grain boundary phase 4-3, grain boundary phase 4-4 and grain boundary phase 4-5 had the same characteristics as the grain boundary phase 4-1. That is, each of the grain boundary phases 4-2, grain boundary phase 4-3, grain boundary phase 4-4 and grain boundary phase 4-5 was composed of ZrB 2 The crystals contained both R-Cu-rich phase and R-Cu-rich phase.

[0131] Comparative Example 1 In Comparative Example 1, diffusing material B prepared by the following method was used instead of diffusing material A.

[0132] A paste-like diffusion material B was produced by kneading a fine powder (third component) made of Tb hydride, alcohol (solvent), and acrylic resin (binder). In other words, diffusion material B did not contain a fine powder (first component) made of Nd hydride, or a fine powder (second component) made of simple Cu. The mass ratio of the third component in diffusion material B was 75.0 parts by mass. The mass ratio of the solvent in diffusion material B was 23.0 parts by mass. The mass ratio of the binder in diffusion material B was 2.0 parts by mass.

[0133] A permanent magnet of Comparative Example 1 was produced in the same manner as in Example 1, except for using diffusion material B. The contents of each element in the permanent magnet of Comparative Example 1 are shown in Table 1 below.

[0134] The Br and HcJ of the permanent magnet of Comparative Example 1 were measured in the same manner as in Example 1. The Br and HcJ of Comparative Example 1 are shown in the following Table 1. It was confirmed that the coercive force of the permanent magnet of Example 1 at 160°C was higher than the coercive force of the permanent magnet of Comparative Example 1 at 160°C.

[0135] The cross section of the permanent magnet of Comparative Example 1 was analyzed in the same manner as in Example 1. The analysis results of Comparative Example 1 are shown in Table 3 below. The compositions of the grain boundary phase 1, grain boundary phase 2, grain boundary phase 3, and grain boundary phase 4-1 shown in Table 3 below correspond to one grain boundary multiple point. The permanent magnet of Comparative Example 1 had a plurality of main phase particles containing Nd, Fe, Co, and B, and a plurality of grain boundary multiple points. A grain boundary multiple point (grain boundary phase 4-1) where high concentration areas of Zr and B overlap was detected in the permanent magnet of Comparative Example 1. However, a grain boundary multiple point (Zr-B-Cu grain boundary) where high concentration areas of Zr, B, and Cu overlap was not detected in the permanent magnet of Comparative Example 1. That is, in the case of Comparative Example 1, the concentration of Cu at the grain boundary multiple point where high concentration areas of Zr and B overlap was not higher than the concentration of Cu at other grain boundary multiple points.

[0136] [Table 1]

[0137] [Table 2]

[0138] [Table 3] [Industrial Applicability]

[0139] The RTB permanent magnet according to the present invention is suitable as a material for motors mounted on hybrid or electric vehicles, for example. [Explanation of symbols]

[0140] 2...Permanent magnet, 2cs...Cross section of permanent magnet, 3...ZrB 2 crystal, 4...main phase particle, 4a...surface layer (shell), 4b...center (core), 5...R-Cu rich phase, 6...grain boundary multiple points, 10...two-particle grain boundary.

Claims

1. An R-T-B system permanent magnet containing a rare earth element R, transition metal elements T, B, Zr and Cu, The R-T-B system permanent magnet contains at least Nd as R, The R-T-B system permanent magnet contains at least Fe as T, The R-T-B system permanent magnet comprises a plurality of main phase grains containing Nd, T, and B, and a plurality of grain boundary multiple points, One of the grain boundary multiple points is a grain boundary surrounded by three or more of the main phase grains, a distribution map of elements in a cross section of the R-T-B system permanent magnet showing that the R-T-B system permanent magnet comprises the plurality of main phase grains and the plurality of grain boundary multiple points; The size of the distribution map is 50 μm long by 50 μm wide. The five grain boundary multiple points shown in the distribution map are ZrB ２ and an R-Cu rich phase containing R and Cu, The ZrB ２ the concentration of B at each of the five grain boundary multiple points including both the R—Cu-rich phase and the R—Cu-rich phase is 5 atomic % or more and 20 atomic % or less; The ZrB ２ the concentration of Cu at each of the five grain boundary multiple points including both the R-Cu rich phase and the R-Cu rich phase is 5 atomic % or more and 25 atomic % or less; The surface layer portion of the main phase grain contains at least one heavy rare earth element selected from the group consisting of Tb and Dy. R-T-B series permanent magnet.

2. The ZrB ２ The concentration of Zr at each of the five grain boundary multiple points including both the R-Cu rich phase and the R-Cu rich phase is 1 atomic % or more and 10 atomic % or less. The R-T-B system permanent magnet according to claim 1 .

3. The ZrB ２ the sum of the concentrations of Nd and Pr at each of the five grain boundary multiple points including both the R-Cu rich phase and the R-Cu rich phase is 20 atomic % or more and 70 atomic % or less; The R-T-B system permanent magnet according to claim 1 or 2.

4. The R-Cu rich phase is ２ are present around the crystals of The R-T-B system permanent magnet according to any one of claims 1 to 3.

5. The R-Cu rich phase is ２ and the main phase grains, The R-T-B system permanent magnet according to any one of claims 1 to 4.

6. A portion of the grain boundary multiple points includes a T-rich phase containing T, Cu, and at least one R selected from Nd and Pr, the concentration of T at the grain boundary multiple points including the T-rich phase is higher than the concentration of T at other grain boundary multiple points; The unit of the concentration of T is atomic %. The R-T-B system permanent magnet according to any one of claims 1 to 5.

7. The distribution map is measured by an electron probe microanalyzer. The R-T-B system permanent magnet according to any one of claims 1 to 6.

8. The five grain boundary multiple points are randomly selected from the cross section. The R-T-B system permanent magnet according to any one of claims 1 to 7.

9. The distribution maps of Zr, B and Cu in the cross section of the R-T-B system permanent magnet are measured, In the distribution maps of Zr, B and Cu, high concentration locations are identified where the intensity of characteristic X-rays of each element is higher than the average value of the intensity of characteristic X-rays of each element in each distribution map; The high concentration points of Zr, B and Cu overlap at the five grain boundary multiple points. The R-T-B system permanent magnet according to any one of claims 1 to 8.

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