阅读说明：本技术 R－t－b系永久磁铁 (R-T-B permanent magnet ) 是由 三轮将史 三浦晃嗣 坪仓多惠子 于 2020-12-02 设计创作，主要内容包括：本发明提供一种永久磁铁,其含有稀土元素R(Nd等)、过渡金属元素T(Fe等)、B、Zr和Cu,永久磁铁具有含有Nd、T和B的主相颗粒和晶界多重点,一个晶界多重点为由三个以上的主相颗粒包围的晶界,一个晶界多重点包含ZrB-2的结晶和含有R及Cu的富R－Cu相这两者,包含ZrB-2的结晶和富R－Cu相这两者的一个晶界多重点中的B的浓度为5原子％以上20原子％以下,包含ZrB-2的结晶和富R－Cu相这两者的一个晶界多重点中的Cu的浓度为5原子％以上25原子％以下,主相颗粒的表层部含有Tb和Dy中至少一种重稀土元素。(The present invention provides a permanent magnet containing a rare earth element R (Nd, etc.), a transition metal element T (Fe, etc.), B, Zr and Cu, the permanent magnet having main phase particles containing Nd, T and B, and grain boundary multiple points, one grain boundary multiple point being a grain boundary surrounded by three or more main phase particles, and one grain boundary multiple point containing ZrB 2 Both the crystal(s) of (1) and an R-Cu-rich phase containing R and Cu, comprising ZrB 2 Has a concentration of 5 atoms of B in one grain boundary multiple point of both the crystal of (1) and the R-Cu-rich phase% of 20 atom% or more, containing ZrB 2 The concentration of Cu in one grain boundary multiple point of both the crystal of (1) and the R-Cu-rich phase is 5 at% or more and 25 at% or less, and the surface layer portion of the main phase grains contains at least one heavy rare earth element of Tb and Dy.)

1. An R-T-B permanent magnet, characterized in that:

contains rare earth element R, transition metal element T, B, Zr and Cu,

the R-T-B permanent magnet contains at least Nd as R,

the R-T-B permanent magnet contains at least Fe as T,

the R-T-B permanent magnet has 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 particles,

any of the grain boundary multi-focal points contains ZrB₂Both of the crystal of (3) and the R-Cu-rich phase containing R and Cu,

comprises the ZrB₂The concentration of B in one of the grain boundary multiple points of both the crystal of (1) and the R-Cu rich phase is 5 at% or more and 20 at% or less,

comprises the ZrB₂The concentration of Cu in one of the grain boundary multiple points of both the crystal of (1) and the R-Cu-rich phase is 5 at% or more and 25 at% or less,

the surface layer portion of the main phase grains contains at least one heavy rare earth element of Tb and Dy.

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

comprises the ZrB₂The Zr concentration in one of the grain boundary multiple points of both the crystal of (1) and the R — Cu-rich phase is 1 at% or more and 10 at% or less.

3. The R-T-B based permanent magnet according to claim 1, wherein:

comprises the ZrB₂The total of the concentrations of Nd and Pr in the one grain boundary multiple point of both the crystal of (2) and the R — Cu-rich phase is 20 at% or more and 70 at% or less.

4. The R-T-B based permanent magnet according to claim 1, wherein:

the R-Cu-rich phase exists in the ZrB₂Around the crystals of (2).

5. The R-T-B based permanent magnet according to claim 1, wherein:

the R-Cu-rich phase exists in the ZrB₂And the main phase particles.

6. The R-T-B based permanent magnet according to claim 1, wherein:

a part of the grain boundary multiple points include a T-rich phase containing T and Cu and containing at least one R of Nd and Pr,

the concentration of T in the grain boundary multiple points containing the T-rich phase is higher than the concentration of T in the other grain boundary multiple points,

the concentration of T is in atomic%.

Technical Field

The present invention relates to an R-T-B permanent magnet.

Background

An R-T-B-based permanent magnet containing a rare earth element R (Nd, etc.), a transition metal element T (Fe, etc.), and boron B is a nucleation-type permanent magnet. By applying a magnetic field in a direction opposite to the magnetization direction to the nucleation type permanent magnet, nuclei of magnetization reversal are easily generated in the vicinity of the grain boundaries of a plurality of crystal grains (main phase grains) constituting the permanent magnet. Then, since the magnetization of the crystal grains is inverted from the nuclei of this magnetization inversion, the coercive force of the R-T-B permanent magnet tends to be low.

In order to increase the coercive force of an R-T-B permanent magnet, a heavy rare earth element such as Dy is added to the R-T-B permanent magnet. By adding a heavy rare earth element, the anisotropic magnetic field is easily increased, nuclei in which magnetization is inverted are less likely to be generated in the vicinity of the grain boundary, and the coercive force (HcJ) is increased. However, since heavy rare earth elements are expensive, it is desirable to reduce the content of heavy rare earth elements in an R-T-B-based permanent magnet in order to reduce the production cost of the R-T-B-based permanent magnet.

For example, an R-T-B sintered magnet described in international publication No. 2011/122667 has a plurality of main phase particles including a magnetic core and a shell covering the magnetic core, the shell has a thickness of 500nm or less, R includes a light rare earth element and a heavy rare earth element, and a Zr compound is present in at least one of a grain boundary phase and the shell.

Disclosure of Invention

The invention aims to provide an R-T-B permanent magnet with high coercive force.

An R-T-B permanent magnet according to an aspect of the present invention is an R-T-B permanent magnet containing a rare earth element R, a transition metal element T, B, Zr, and Cu, wherein the R-T-B permanent magnet contains at least Nd as R, the R-T-B permanent magnet contains at least Fe as T, the R-T-B permanent magnet has a plurality of main phase particles containing Nd, T, and B, and a plurality of grain boundary multiple points, one grain boundary multiple point is a grain boundary surrounded by three or more main phase particles, and any one grain boundary multiple point includes ZrB₂Both the crystal(s) of (1) and an R-Cu-rich phase containing R and Cu, comprising ZrB₂The concentration of B in one grain boundary multiple point of both the crystal of (1) and the R-Cu-rich phase is 5 at% or more and 20 at% or less, and ZrB is contained₂The concentration of Cu in one grain boundary multiple point of both the crystal of (1) and the R-Cu-rich phase is 5 at% or more and 25 at% or less, and the surface layer portion of the main phase grains contains at least one heavy rare earth element of Tb and Dy.

Comprises ZrB₂The Zr concentration in the one grain boundary multiple point region of both the crystal of (1) and the R — Cu-rich phase may be 1 at% or more and 10 at% or less.

Comprises ZrB₂The total of the concentrations of Nd and Pr in the single grain boundary multiple point of both the crystal of (1) and the R — Cu-rich phase may be 20 at% or more and 70 at% or less.

The R-Cu rich phase may be present in ZrB₂Around the crystals of (2).

The R-Cu rich phase may be present in ZrB₂Between the crystals and the main phase particles.

A part of the grain boundary multiple points may include a T-rich phase containing T and Cu and at least one R of Nd and Pr, and a concentration of T in the grain boundary multiple points including the T-rich phase is higher than a concentration of T in the other grain boundary multiple points, and a unit of the concentration of T is atomic%.

According to the present invention, an R-T-B permanent magnet having a high coercive force can be provided.

Drawings

Fig. 1A is a schematic perspective view of an R-T-B-based permanent magnet according to an embodiment of the present invention, and fig. 1B is a schematic cross-sectional view (a view along line B-B) of the R-T-B-based permanent magnet shown in fig. 1A.

Fig. 2 is an enlarged view of a part (region II) of the cross section shown in fig. 1B.

FIG. 3 is ZrB₂A perspective view of the crystal structure of (2).

FIG. 4A is a schematic diagram including ZrB₂Fig. 4B is a distribution diagram of Cu in the region shown in fig. 4A, fig. 4C is a distribution diagram of Nd in the region shown in fig. 4A, and fig. 4D is a distribution diagram of Zr in the region shown in fig. 4A.

Fig. 5A is a distribution diagram of Co in the region shown in fig. 4A, fig. 5B is a distribution diagram of Fe in the region shown in fig. 4A, fig. 5C is a distribution diagram of Ga in the region shown in fig. 4A, and fig. 5D is a distribution diagram of Tb in the region shown in fig. 4A.

FIG. 6A is ZrB₂FIG. 6B is ZrB shown in FIG. 6A₂The electron beam diffraction pattern of the crystal of (1).

[ description of symbols ]

2 … permanent magnet, 2cs … permanent magnet cross section, 3 … ZrB₂4 … main phase grains, 4a … surface layer portion (shell), 4b … center portion (core), 5 … R — Cu rich phase, 6 … grain boundary multiple points, 10 … two grain boundaries.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference numerals. The present invention is not limited to the following embodiments. The "permanent magnet" described below refers to an R-T-B permanent magnet. The unit of the concentration of each element described below is atomic%.

(permanent magnet)

The permanent magnet of 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 of the present embodiment may be a sintered magnet.

The permanent magnet contains at least neodymium (Nd) as a rare earth element R. The permanent magnet may contain other rare earth element R in addition to Nd. The other rare earth element R contained in the permanent magnet may be at least one element selected from 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).

The permanent magnet contains at least iron (Fe) as a 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.

Fig. 1A is a perspective view of a rectangular parallelepiped permanent magnet 2 according to the present embodiment. Fig. 1B is a schematic view 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 column, a circular arc segment, a fan, a circular sector (annular sector), a sphere, a circular plate, a cylinder, a ring, or a capsule. The shape of the cross section 2cs of the permanent magnet 2 may be, for example, a polygon, a circular arc (circular chord), an arch, a C-shape, or a circle.

Fig. 2 is an enlarged view of a part (region II) of the cross section 2cs shown in fig. 1B. As shown in fig. 2, the permanent magnet 2 has a plurality of main phase particles 4. The main phase particles 4 contain at least Nd, T, and B. The main phase particles 4 may contain R₂T₁₄Crystal (single crystal or polycrystal) of B. The main phase particles 4 may also contain other elements in addition to Nd, T, and B. For example, R₂T₁₄B may also be represented by (Nd)_1－xPr_x)₂(Fe_1－yCo_y)₁₄B. 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, as R, heavy rare earth elements such as Tb and Dy in addition to light rare earth elements. The main phase particles 4 may also contain Zr. R₂T₁₄Part of B in B may be replaced with carbon (C). The composition within the main phase particles 4 may be uniform. The composition within the main phase particles 4 may also 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.

The main phase particle 4 is composed of a surface layer 4a and a central portion 4b covered with the surface layer 4 a. The surface portion 4a may be referred to as a shell, and the central portion 4b may be referred to as a magnetic core. The surface layer portion 4a of the main phase grains 4 contains at least one heavy rare earth element of Tb and Dy. The surface layer portion 4a of each of all the main phase grains 4 may contain at least one heavy rare earth element of Tb and Dy. The surface layer portion 4a of a part of the main phase grains 4 out of all the main phase grains 4 may contain at least one heavy rare earth element of Tb and Dy. Since the surface layer portion 4a contains a heavy rare earth element, the anisotropic magnetic field tends to increase locally in the vicinity of the grain boundary, and nuclei for magnetization reversal are less likely to occur in the vicinity of the grain boundary. As a result, the coercive force of the permanent magnet 2 at high temperature increases. The high temperature may be, for example, 100 ℃ to 200 ℃. In order to easily achieve both the residual magnetic flux density and the coercive force of the permanent magnet 2, the total concentration of the heavy rare earth elements in the surface layer portion 4a may be higher than the total concentration of the heavy rare earth elements in the central portion 4 b.

The permanent magnet 2 includes grain boundaries between the main phase grains 4. The permanent magnet 2 includes a plurality of grain boundary stress points 6 as grain boundaries. The grain boundary multiple point 6 is a grain boundary surrounded by three or more main phase grains 4. The permanent magnet 2 further includes a plurality of two-grain boundaries 10 as grain boundaries. The two-particle grain boundary 10 is a grain boundary between two adjacent main phase particles 4.

Any of the grain boundary multiple points 6 contains zirconium boride (ZrB)₂) And an R-Cu rich phase 5 containing R and Cu. Hereinafter, ZrB may be included₂The one grain boundary emphasis point 6 of both the crystal 3 and the R-Cu-rich phase 5 of (A) is described as "Zr-B-R-Cu grain boundary".

FIG. 3 shows ZrB₂Crystal structure of crystal 3 in (a). In FIG. 3, the a-axis, the b-axis and the c-axis are respectively ZrB₂The crystal axis of (1). The angle between the a-axis and the b-axis is 120 °. The a-axis and the b-axis are each perpendicular with respect to the c-axis. ZrB₂The crystal structure of (2) has rotational symmetry about the c-axis and is 6-fold symmetric. That is, ZrB₂Crystal 3 of (b) is a hexagonal system, ZrB₂The three-dimensional space group of crystal 3 in (2) was P6/mmm.

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

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

One grain boundary multiple point 6 in which the concentrations of B and Cu are within the above ranges easily contains ZrB₂Both crystalline 3 and R-Cu rich phase 5. For the same reason, the concentration of B in one Zr-B-R-Cu grain boundary may be 6.4 at% or more and 15.2 at% or less, and the concentration of Cu in one Zr-B-R-Cu grain boundary may be 9.2 at% or more and 19.6 at% or less.

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 particle 4. The concentration of Cu in one Zr-B-R-Cu grain boundary may be higher than that in the main phase particle 4. The R — Cu-rich phase 5 may be a grain boundary phase contained in the grain boundary multiple point 6 in which the total of the concentrations of Nd and Pr is higher than the total of the concentrations of Nd and Pr in the main phase particle 4 and the concentration of Cu is higher than the concentration of Cu in the main phase particle 4. The total of the concentrations of Nd and Pr in the main phase particles 4 may be an average value of the total of the concentrations of Nd and Pr in all the main phase particles 4 in contact with one Zr — B — R — Cu grain boundary. The concentration of Cu in the main phase particles 4 may be an average of the concentrations of Cu in all the main phase particles 4 in contact with one Zr-B-R-Cu grain boundary.

The Zr concentration in one Zr-B-R-Cu grain boundary may be 1 at% or more and 10 at% or less, or 1.6 at% or more and 7.4 at% 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.

The total concentration of Nd and Pr in one Zr-B-R-Cu grain boundary may be 20 at% or more and 70 at% or less, or 25.1 at% or more and 46.1 at% or less.

The respective concentrations of Zr, Nd, and Pr in one Zr-B-R-Cu grain boundary have a tendency to fall within the above-mentioned range. In other words, ZrB is likely to be included in the single grain boundary multiple spot 6 in which the respective concentrations of Zr, Nd, and Pr are within the above ranges₂Both crystalline 3 and R-Cu rich phase 5.

The permanent magnet 2 may contain a plurality of Zr — B — R — Cu grain boundaries. Some of the grain boundary multiple peaks 6 included in the entire grain boundary multiple peaks 6 of the permanent magnet 2 may not be Zr — B — R — Cu grain boundaries. For example, a portion of the grain boundary multiple points 6 may contain only ZrB₂Crystal 3 of (1). A part of the grain boundary multiple spot 6 may contain only the R — Cu rich phase 5. ZrB in a part of the grain boundary multi-focal points 6₂May also be absent from both crystal 3 and R-Cu rich phase 5.

The Zr-B-R-Cu grain boundaries are formed in the sintering step and the diffusion step, which will be described later. The diffusion step is performed after the sintering step. In the sintering step, a compact made of the alloy powder is heated to obtain a magnet base material (sintered compact). In the diffusion step, the 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 comprises: a first component containing at least one R (light rare earth element) of Nd and Pr, a second component containing Cu, and a third component containing at least one heavy rare earth element of Tb and Dy.

In the sintering step, as the alloy particles constituting the alloy powder are sintered to each other, ZrB derived from Zr and B in the alloy particles₂Generated in the grain boundary multiple spot 6. In the sintering step, a grain boundary phase (R phase) in which R (a light rare earth element such as Nd) has a high concentration is formed in the grain boundary emphasis point 6 and the two-grain boundary 10. R in the R phase originates from alloy particles. As the temperature rises in the diffusion step subsequent to the sintering step, the R phase present in the grain boundary multiple point 6 and the two-grain boundary 10 becomes a liquid phase (R liquid phase). R (a light rare earth element such as Nd) and Cu in the diffusion material are dissolved into the R liquid phase, and R and Cu in the diffusion material are diffused from the surface of the magnet base material into the interior of the magnet. As a result, a liquid phase (R — Cu-rich liquid phase) having high concentrations of R (a light rare earth element such as Nd) and Cu is formed in the grain boundary stress point 6. ZrB₂Has excellent affinity for the R-Cu-rich liquid phase. That is, ZrB₂The solubility in the R-Cu rich liquid phase is higher. Thus, in the diffusion step, ZrB₂Readily soluble into the R-Cu rich liquid phase. ZrB by cooling (quenching) after the diffusion step₂The crystal 3 is re-precipitated in the R-Cu-rich liquid phase, and the R-Cu-rich liquid phase is solidified to become an R-Cu-rich phase 5.

The heavy rare earth element contained in the surface layer portion 4a of the main phase grains 4 is derived from the heavy rare earth element in the diffusion material used in the diffusion step. Surface layer part 4a (R) of main phase particle 4₂Fe₁₄B) Dissolved in the R-Cu rich liquid phase during the diffusion process. In the process of re-precipitating the surface layer portion 4a by cooling (rapid cooling) after the diffusion step, the surface layer portion 4a is doped with the heavy rare earth element in the R — Cu-rich liquid phase, thereby forming the surface layer portion 4a containing the heavy rare earth element. As described above, ZrB is generated by the diffusion process₂Dissolved in the R-Cu-rich liquid phase and the grain boundary multiple points 6 (R-Cu-rich liquid phase)) The concentration of B in (B) increases. The increase in the concentration of B in the R-Cu-rich liquid phase suppresses the surface layer portion 4a (R)₂Fe₁₄B) Dissolution into an R-Cu rich liquid phase. By suppressing the surface part 4a (R)₂Fe₁₄B) The thickness of the surface layer portion 4a, which precipitates again while doping with the heavy rare earth element, becomes thinner. Since the heavy rare earth element is concentrated in the thin surface layer portion 4a, the concentration of the heavy rare earth element in the surface layer portion 4a increases. As a result, the coercive force of the permanent magnet 2 increases. The thickness of the surface layer portion 4a in the direction perpendicular to the surface of the main phase particle 4 may be, for example, 3nm or more and 50nm or less.

For the above reasons, the permanent magnet 2 of the present embodiment can have a high coercive force at a high temperature. The high temperature may be, for example, 100 ℃ to 200 ℃.

ZrB dissolved in R-Cu rich liquid phase as described above₂The R-Cu-rich liquid phase is re-precipitated by cooling (quenching) after the diffusion step. In addition, the R — Cu-rich liquid phase is excellent in wettability, and therefore, the R — Cu-rich liquid phase easily directly covers the surface of the main phase particle 4 in the diffusion step. For these reasons ZrB₂The crystal 3 of (A) is easily formed in the RCu-rich phase 5, and the R-Cu-rich phase 5 is easily formed in ZrB₂Between the crystals 3 and the main phase particles 4. That is, the R-Cu rich phase 5 may exist in ZrB₂Around the crystal 3 of (3), an R-Cu-rich phase 5 may be present in ZrB₂Between the crystals 3 and the main phase particles 4. ZrB₂Crystal 3 and main phase grains 4, or ZrB₂The crystal lattice defect at the interface between the crystal 3 and the main phase particle 4 in (b) is likely to become a starting point of magnetization inversion (a nucleus of magnetization inversion). However, the R-Cu rich phase 5 exists in ZrB₂And the main phase grains 4, thereby, ZrB₂Is reduced where the crystals 3 are in direct contact with the main phase particles 4. As a result, in ZrB₂The starting point of magnetization reversal is hard to occur between the crystal 3 and the main phase grains 4, and the coercive force of the permanent magnet 2 is likely to increase.

ZrB₂The crystals 3 of (2) may be connected to the two-grain boundaries 10. The Zr-B-R-Cu grain boundaries comprise ZrB connected to the two-grain boundaries 10₂Thereby, the permanent magnet 2 is likely to have a high coercive forceForce.

In order to form Zr — B-R-Cu grain boundaries by the above mechanism, the diffusion material needs to contain: a first component containing at least one R of Nd and Pr, a second component containing Cu, and a third component containing at least one heavy rare earth element of Tb and Dy. In the case where 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 in the diffusion step. As a result, it is difficult to form Zr — B — R — Cu grain boundaries by the above mechanism, and it is also difficult to concentrate heavy rare earth elements in the thin surface layer portion 4 a.

The technical scope of the present invention is not limited by the above-described mechanism associated with the formation of the above-described Zr-B-R-Cu grain boundaries.

A part 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 containing at least one R of 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 of the R concentrations in one grain boundary multiple-focal point including the R-rich phase is higher than the average value of the total of the R concentrations in the cross section 2cs of the permanent magnet 2.

A part of the grain boundary multiple points 6 other than the Zr-B-R-Cu grain boundaries may contain an R-O-C phase. The R — O — C phase is a grain boundary phase containing at least one of Nd and Pr, R, oxygen (O), and C, and is a grain boundary phase included in a grain boundary multiple point in which the respective concentrations of O and C are higher than those of other grain boundary multiple points. The concentration of O in one grain boundary multiple spot containing the R-O-C phase is higher than the average value of the concentrations of O in the cross section 2cs of the permanent magnet 2. The concentration of C in one grain boundary multiple spot containing the R-O-C phase is higher than the average value of the concentrations of C in the section 2cs of the permanent magnet 2. The R-rich phase in the grain boundary is oxidized by water (e.g., water vapor) in the atmosphere, and the generation and storage of hydrogen, the hydrogenation of the R-rich phase, and the oxidation of the hydride of R by water are performed in a chain manner in the grain boundary. As a result, the permanent magnet 2 is corroded. On the other hand, the R-O-C phase is less oxidized by water than the R-rich phase. In addition, the R-O-C phase is less likely to store hydrogen than the R-rich phase. Therefore, the corrosion resistance of the permanent magnet 2 is improved by the permanent magnet 2 including the R — O — C phase.

A portion of the grain boundary emphasis points 6 other than the Zr-B-R-Cu grain boundaries may contain an oxide phase. The oxide phase is a grain boundary phase containing an oxide of at least one R of Nd and Pr as a main component and having a composition different from that of the R-O-C phase.

A part of the grain boundary multiple points 6 other than the Zr — B — R — Cu grain boundaries may contain a T-rich phase (transition metal element-rich phase). The T-rich phase is a grain boundary phase containing T and Cu and at least one R of Nd and Pr, and is a grain boundary phase included in a grain boundary multiple point in which the total concentration of T is higher than other grain boundary multiple points. T contained in the T-rich phase may be only Fe. T contained in the T-rich phase may be Fe or Co. The sum of the concentrations of T in one grain boundary multiple focal point including the T-rich phase is higher than the sum of the concentrations of T in the other grain boundary multiple focal points. Although the concentration of T in the T-rich phase is higher than that of the other grain boundary phases, the magnetization of the T-rich phase is also lower. The T-rich phase having a low magnetization exists in at least one of the grain boundary multiple point 6 and the two-particle grain boundary 10, and thus the magnetic coupling between the main phase particles 4 is easily broken. As a result, the coercive force of the permanent magnet 2 is easily increased. The T-rich phase may contain gallium (Ga) in addition to R, T and Cu.

One grain boundary multiple point 6 may comprise ZrB₂A 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. A two-grain boundary 10 may comprise ZrB₂A 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.

A part of Zr-B-R-Cu grain boundary may be other than ZrB₂The crystal 3 and the R-Cu-rich phase 5, and the other grain boundary phases described above. For example, a portion of the Zr-B-R-Cu grain boundaries may be other than ZrB₂Contains a T-rich phase in addition to the crystal 3 and the R-Cu-rich phase 5. In the case where the Zr — B — R — Cu grain boundary further contains a T-rich phase, the coercive force of the permanent magnet 2 is easily increased.

ZrB₂The crystal 3, the R — Cu-rich phase 5, the main phase grains 4, and other grain boundary phases of (a) are each clearly identified based on the difference in composition. The composition of these compositions can be determined by analyzing the cross section 2cs of the permanent magnet 2To be determined. The cross section 2cs of the permanent magnet 2 can be analyzed by an Electron beam Probe microanalyzer (EPMA) equipped with an Energy Dispersive X-ray Spectroscopy (EDS) device. ZrB₂The crystal 3, the R-Cu-rich phase 5, the main phase grains 4, and the other grain boundary phases of (A) can be identified based on the contrast in an image of the cross section 2cs of the permanent magnet 2 taken by a Scanning Electron Microscope (SEM) such as a Scanning Transmission Electron Microscope (STEM). The internal structure of the Zr-B-R-Cu grain boundary can be determined by the contrast of an image obtained from a High Angle Annular Dark Field-STEM image (HAADF-STEM image) or the like, for example. ZrB₂The crystal structure of crystal 3 of (a) can be determined based on the HAADF-STEM image of lattice resolution and the electron beam diffraction pattern.

By using EPMA, distribution patterns of Zr, B, and Cu in the cross section 2cs of the permanent magnet 2 were measured. When any element is denoted as Ex, the bright place in the Ex distribution diagram is a place where the concentration of Ex is higher than the average value of the concentration of Ex in the cross section 2cs of the permanent magnet 2. In other words, the bright place in the Ex distribution map is a place where the intensity of the Ex characteristic X-ray is higher than the average value of the intensities of the Ex characteristic X-rays in the cross section 2cs of the permanent magnet 2. The Zr-B-R-Cu grain boundaries overlap where the concentration of each element in the distribution diagram of Zr, B and Cu is high. That is, the position of the Zr-B-R-Cu grain boundary can be determined by the coincidence of the respective distribution patterns of Zr, B and Cu. After the position of the Zr-B-R-Cu grain boundary was determined, the Zr-B-R-Cu grain boundary was locally analyzed by EPMA, whereby the concentration of each element in the Zr-B-R-Cu grain boundary could be measured.

The average particle diameter or the median particle diameter (D50) of the main phase particles 4 is not particularly limited, and 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 of the volume ratios of the main phase particles 4 in the permanent magnet 2 is not particularly limited, and may be 80 vol% or more and less than 100 vol%, for example.

The specific composition of the entire permanent magnet 2 is described below. However, the composition of the permanent magnet 2 is not limited to the following composition. The content of each element in the permanent magnet 2 may be out of the following range as long as the above-described effects by the Zr — B — R — Cu grain boundaries are obtained.

The total content of the rare earth elements R in the entire permanent magnet may be 25 mass% to 35 mass%, or 28 mass% to 34 mass%. When the content of R is in this range, the residual magnetic flux density and the coercive force tend to increase. When the content of R is too small, it is difficult to form main phase particles (R)₂T₁₄B) An α -Fe phase having soft magnetism is easily formed. As a result, the coercivity tends to decrease. On the other hand, when the content of R is too large, the volume ratio of the main phase particles is low, and the residual magnetic flux density tends to decrease. From the viewpoint of easy increase in residual magnetic flux density and coercive force, the total proportion of Nd and Pr in all rare earth elements R may be 80 at% to 100 at%, or 95 at% to 100 at%.

The content of B in the entire permanent magnet may be 0.90 mass% or more and 1.05 mass% or less. When the content of B is 0.90 mass% or more, the permanent magnet easily contains Zr — B — R — Cu grain boundaries. When the content of B is 0.90 mass% or more, the residual magnetic flux density of the permanent magnet tends to increase. When the content of B is 1.05 mass% or less, the coercive force of the permanent magnet tends to increase. When the content of B 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 corresponding to 90% of the remanent flux density (Br) in the second quadrant of the magnetization curve.

The Zr content in the entire permanent magnet may be 0.10 mass% or more and 1.00 mass% or less, and preferably 0.25 mass% or more and 1.00 mass% or less. When the Zr content is 0.25 mass% or more, the permanent magnet easily contains Zr-B-R-Cu grain boundaries. When the Zr content is 0.25 mass% or more, abnormal grain growth of the main phase grains in the sintering step described later is easily suppressed, the squareness ratio of the permanent magnet is easily close to 1.0, and the permanent magnet is easily magnetized in a low magnetic field. When the Zr content is 1.00 mass% or less, the residual magnetic flux density of the permanent magnet tends to increase.

The Cu content in the entire permanent magnet may be 0.04 mass% or more and 0.50 mass% or less. When the Cu content is 0.04 mass% or more, the permanent magnet easily contains Zr-B-R-Cu grain boundaries. When the Cu content is 0.04 mass% or more, the coercive force of the permanent magnet tends to increase, and the corrosion resistance of the permanent magnet tends to improve. When the Cu content is 0.50 mass% or less, the coercive force and residual magnetic flux density of the permanent magnet tend to increase.

The Ga content in the entire permanent magnet may be 0.03 mass% or more and 0.30 mass% or less. When the Ga content is 0.03 mass% or more, the permanent magnet easily contains a T-rich phase, and the coercive force of the permanent magnet easily increases. When the Ga content is 0.30 mass% or less, the formation of a secondary phase (for example, a phase containing R, T and Ga) can be appropriately suppressed, and the residual magnetic flux density of the permanent magnet is likely to increase.

The content of O in the entire permanent magnet may be 0.03 mass% to 0.4 mass%, or 0.05 mass% to 0.2 mass%. When the content of O is too small, it is difficult to form an R-O-C phase. When the content of O is too large, the coercive force of the permanent magnet tends to be lowered.

The content of C in the entire permanent magnet may be 0.03 mass% to 0.3 mass%, or 0.05 mass% to 0.15 mass%. When the content of C is too small, it is difficult to form an R-O-C phase. When the content of C is too large, the coercive force of the permanent magnet tends to be lowered.

The content of Co in the entire permanent magnet may be 0.30 mass% or more and 3.00 mass% or less. When the Co content is 0.30 mass% or more, the corrosion resistance of the permanent magnet is easily improved. When the content of Co is more than 3.00 mass%, the effect of improving the corrosion resistance of the permanent magnet is limited, and there is no advantage commensurate with the cost of Co.

The content of aluminum (Al) in the entire permanent magnet may be 0.05 mass% or more and 0.50 mass% or less. When the Al content is 0.05 mass% or more, the coercive force of the permanent magnet tends to increase. When the Al content is 0.05 mass% or more, the amount of change in the magnetic properties (particularly, the coercive force) of the permanent magnet due to a temperature change in aging treatment or heat treatment described later tends to be small, and the variation in the magnetic properties of the permanent magnet in mass production tends to be suppressed. When the Al content is 0.50 mass% or less, the residual magnetic flux density of the permanent magnet tends to increase. In addition, when the Al content is 0.50 mass% or less, the change in coercive force accompanying the temperature change is easily suppressed.

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

The total content of Tb and Dy in the entire permanent magnet may be 0.00 mass% or more and 5.00 mass% or less, or 0.20 mass% or more and 5.00 mass% or less. In some cases, the total content of Tb and Dy in the entire permanent magnet is represented by C_Tb+Dy. C by permanent magnets_Tb+DyWhen the amount is 0.20% by mass or more, the magnetic properties (particularly, coercive force) of the permanent magnet are likely to increase. In addition, in C of the permanent magnet_Tb+DyIn the case of being within the above range, with C_Tb+DyThe permanent magnet of the present embodiment is likely to have superior magnetic characteristics compared to conventional permanent magnets. In other words, the permanent magnet of the present embodiment is also C_Tb+DyC being a conventional permanent magnet_Tb+DyIn the following cases, the permanent magnet according to the present embodiment can also have magnetic properties superior to those of conventional permanent magnets. That is, according to the permanent magnet of the present embodiment, C can be made without impairing the magnetic characteristics_Tb+DyC of the conventional permanent magnet_Tb+DyAnd decreases.

The remaining part of the permanent magnet excluding the above elements may be only Fe, or Fe and other elements. In order that the permanent magnet has sufficient magnetic properties, the total content of elements other than Fe in the remainder may be 5 mass% or less with respect to the total mass of the permanent magnet.

The permanent magnet may contain, as another element, at least one 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).

The composition of the entire permanent magnet can be analyzed by, for example, a fluorescent X-ray (XRF) analysis method, a high-frequency Inductively Coupled Plasma (ICP) emission analysis method, an inert gas melting-non-dispersive infrared absorption (NDIR) method, a combustion-infrared absorption method in an oxygen gas flow, an inert gas melting-heat conduction method, and the like.

The permanent magnet of the present embodiment can be applied to a motor, a generator, an actuator, or the like. For example, permanent magnets are used in various fields such as hybrid cars, electric cars, hard disk drives, magnetic resonance imaging devices (MRI), smart phones, digital cameras, thin TVs, scanners, air conditioners, heat pumps, refrigerators, dust collectors, laundry dryers, elevators, and wind power generators.

(outline of method for producing permanent magnet)

The method for manufacturing a permanent magnet according to the present embodiment includes a diffusion step of attaching a diffusion material to a surface of a magnet base material and heating the magnet base material to which the diffusion material is attached. The magnet base material contained R, T, B and Zr. At least a part of R contained in the magnet base material is Nd. At least a part of 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 hydride of Nd and a hydride of Pr. 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 hydride of Tb and a hydride of Dy.

By using a diffusion material containing both the first component and the second component, the R — Cu-rich liquid phase is formed in the grain boundary-rich region in the diffusion step, and the permanent magnet can contain Zr — B — R — Cu grain boundaries. That is, most of the Cu contained in the Zr-B-R-Cu grain boundaries is derived from the second component contained in the diffusion material. In the case where the diffusion material does not contain at least one of the first component and the second component, it is difficult to form the above-mentioned R — Cu-rich liquid phase in the grain boundary multiple points in the diffusion step due to the deficiency of Cu or the insufficient diffusion of Cu, and the permanent magnet is difficult to contain the Zr — B-R-Cu grain boundary.

(details of the respective steps)

The following describes details of each step of the method for manufacturing a permanent magnet.

[ preparation Process of raw Material alloy ]

In the raw material alloy preparation step, a raw material alloy is produced by a strip casting method or the like using a metal (raw material metal) containing each element constituting the permanent magnet. The raw material metal may be, for example, a simple substance of a rare earth element (metal simple substance), an alloy containing a rare earth element, pure iron, a ferroboron alloy, or an alloy containing them. These raw metals are weighed in a manner consistent with the desired composition of the magnet substrate. The content of each element (except for Nd, Pr, Cu, Tb, and Dy.) in the above permanent magnet may be controlled based on the content of each element in the magnet base material (raw material alloy). The content of each of Nd, Pr, Cu, Tb, and Dy in the permanent magnet can be controlled based on the content of each of Nd, Pr, Cu, Tb, and Dy in the magnet base material (raw material alloy) and the composition and usage amount of the diffusion material used in the diffusion process. As the raw material alloy, two or more alloys having different compositions may be used.

The raw material alloy contains at least R, T, B and Zr. The raw material alloy may further contain Cu. The raw material alloy may not contain Cu.

At least a part of R contained in the raw material alloy is Nd. The raw material alloy may further contain at least one selected from Sc, Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu as the other R. The raw alloy may contain Pr. The raw alloy may also be Pr-free. The raw material alloy may contain one or both of Tb and Dy. The raw material alloy may contain neither Tb nor Dy.

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

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

[ grinding Process ]

In the pulverization step, the raw material alloy is pulverized in a non-oxidizing atmosphere to prepare an alloy powder. The raw material alloy can be pulverized in two stages of a coarse pulverization step and a fine pulverization step. In the coarse pulverization step, for example, a pulverization method such as a masher, a jaw crusher, or a brown mill may be used. The coarse pulverization step may be performed in an inert gas atmosphere. The raw material alloy may be pulverized after hydrogen is occluded in the raw material alloy. That is, hydrogen storage pulverization may be performed as the rough pulverization step. In the rough grinding step, the raw material alloy may be ground to a particle size of several hundred μm. In the fine pulverization step subsequent to the coarse pulverization step, the raw material alloy subjected to the coarse pulverization step can be further pulverized so that the average particle diameter thereof becomes several μm. In the fine grinding step, for example, a jet mill may be used. The raw material alloy may be pulverized by only one stage of pulverization process. For example, only the fine pulverization step may be performed. In the case of using a plurality of raw material alloys, the raw material alloys may be mixed after being pulverized separately. 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 also be comminuted with the grinding aid.

[ Molding Process ]

In the molding step, the alloy powder is molded in a magnetic field, thereby obtaining a molded body containing the alloy powder oriented along the magnetic field. For example, the alloy powder in the die may be pressurized by the die while applying a magnetic field to the alloy powder to obtain a molded body. The pressure applied by the die to the alloy powder may be 20MPa to 300 MPa. The strength of the magnetic field applied to the alloy powder may be 950kA/m or more and 1600kA/m or less. The shape of the molded body may be the same as that of the permanent magnet.

[ sintering Process ]

In the sintering step, the molded body 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 method of pulverizing the raw material alloy, the particle size, and the like. The sintering temperature may be, for example, 1000 ℃ to 1200 ℃. The sintering time may be 1 hour to 20 hours.

[ aging treatment Process ]

The aging treatment step may be performed after the sintering step. However, the aging process 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 an inert gas atmosphere. The diffusion step described later may also serve as the aging treatment step. In this case, the aging treatment step may not be performed separately from the diffusion step. The aging treatment step may be composed of a first aging treatment and a second aging treatment subsequent to the first aging treatment. In the first aging treatment, the sintered body may be heated at a temperature of 700 ℃ to 900 ℃. The time of the first effect treatment may be 1 hour to 10 hours. In the second aging treatment, the sintered body may be heated at a temperature of 500 ℃ to 700 ℃. The time of the second aging treatment may be 1 hour to 10 hours.

Through the above steps, a sintered body was obtained. The sintered body is a magnet base material used in the following diffusion step. The magnet base material (sintered body) has a plurality of (many) main phase particles (alloy particles) sintered to each other. 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 having undergone the diffusion step described later. The main phase particles at least compriseNd, Fe, B and Zr. The main phase particles may comprise R₂T₁₄And (B) crystallizing. The magnet base material also has a plurality of grain boundary multiple points. However, the composition of each grain boundary multiple point included in the magnet base material is different from the composition of each grain boundary multiple point included in the finished permanent magnet. The magnet base material also has a plurality of two-grain boundaries as grain boundaries. However, the composition of each of the two-grain boundaries included in the magnet base material is different from the average composition of each of the two-grain boundaries included in the permanent magnet having undergone the diffusion step described later. The concentration of Nd in the grain boundary multiple points may be higher than the concentration of Nd in the primary phase particles. That is, the grain boundary multiple points in the magnet base material may already contain the R-rich phase. In addition, as described above, ZrB derived from Zr and B in the main phase grains₂And may be generated in a grain boundary multiple point region.

[ diffusion Process ]

In the diffusion step, the 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 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 is referred to as RL. One or both of Tb and Dy is described as RH.

The first component is at least one of a hydride of Nd and a hydride of Pr. The hydride of Nd may be, for example, NdH₂And NdH₃At least any one of. The hydride of Pr may be, for example, PrH₂And PrH₃At least any one of. The hydride of Nd and the hydride of Pr may be a hydride of an alloy composed of Nd and Pr.

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 or Dy. The Cu-containing alloy may contain at least one element other than Nd, Pr, Tb, and Dy among elements that may be contained in the permanent magnet. The compound of copper may be, for example, at least one selected from hydrides and oxides. The hydride of Cu may be CuH, for example. The oxide of Cu may be, for example, Cu₂O and CuO toAny one of them is omitted.

The third component is at least one of a hydride of Tb and a hydride of Dy. The hydride of Tb may be, for example, TbH₂And TbH₃At least any one of. The hydride of Tb may be, for example, a hydride of an alloy composed of Tb and Fe. The hydride of Dy may be, for example, DyH₂And DyH₃At least any one of. The hydride of Dy may be, for example, a hydride of an alloy composed of Dy and Fe. The hydride of Tb and the hydride of Dy may be, for example, a hydride of an alloy composed of Tb, Dy, and Fe.

The first, second and third components may each be a powder. Since the first component, the second component, and the third component are each powder, RL in the first component, Cu in the second component, and RH in the third component easily diffuse into the magnet base material. The first component, the second component, and the third component can be produced by a coarse grinding step and a fine grinding step, respectively. The respective methods of the rough grinding step and the fine grinding step may be the same as those of the grinding step of the raw material alloy. The first component, the second component and the third component may be pulverized at once. The particle diameters of the first component, the second component, and the third component can be freely controlled by the coarse grinding step and the fine grinding step. For example, after hydrogen is absorbed in a simple metal, a hydride of the metal may be dehydrogenated. As a result, coarse powder made of metal hydride is obtained. The coarse powder of the hydride is further pulverized by a jet mill, whereby a fine powder composed of a metal hydride is obtained. The fine powder can 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 different 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 electrolysis or atomization, and then the powder of the second component may be mixed with the first component and the third component.

By heating the magnet base material to which the diffusion material is attached, RL derived from the first component diffuses into the interior of the magnet base material, Cu derived from the second component diffuses into the interior of the magnet base material, and RH derived from the third component diffuses into the interior of the magnet base material. The present inventors speculate that RL, Cu, and RH diffuse from the surface of the magnet base material into the interior of the magnet base material by the following mechanism. However, the mechanism of diffusion is not limited to the following mechanism.

In the sintering step, a grain boundary phase (R phase) having a high RL concentration is formed in the grain boundary multiple point 6 and the two-grain boundary 10. The RL in the R phase originates from alloy grains. As the temperature rises in the diffusion step, the R phase present in the grain boundary multiple point 6 and the two-grain boundary 10 becomes a liquid phase (R liquid phase). Then, the diffusion material is dissolved in the R liquid phase, and the component of the diffusion material diffuses from the surface of the magnet base material into the interior of the magnet base material. It is assumed that, when only the third component (hydride of RH) is used as the diffusion material, dehydrogenation reaction of the hydride of RH adhering to the surface of the magnet base material occurs as the temperature rises in the diffusion step. RH generated by the dehydrogenation reaction is easily and rapidly dissolved in the R liquid phase exuded from the inside of the magnet base material to the surface. As a result, the concentration of RH rapidly increases near the surface of the magnet base material, and diffusion of RH into the main phase particles located near the surface of the magnet base material is likely to occur. That is, RH tends to stay in the main phase grains located in the vicinity of the surface of the magnet base material, and is difficult to diffuse into the magnet base material. Therefore, RH diffused into the magnet is reduced, and the coercivity of the permanent magnet is reduced.

On the other hand, when the diffusion material contains the first component (RL), the second component (Cu), and the third component (RH), the eutectic temperature of Cu and RL is low, and therefore, when the R liquid phase in the magnet base material bleeds out to the surface of the magnet base material, Cu contained in the diffusion material is likely to dissolve into the R liquid phase before RH. That is, first, dissolution of Cu in the R liquid phase occurs, and the Cu concentration in the R liquid phase located in the vicinity of 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 is more difficult to diffuse into the R liquid phase inside the magnet base material. On the other hand, RL of the first component and RH of the third component start to dissolve into the R — Cu-rich liquid phase after the dehydrogenation reaction of the hydride occurs. The eutectic temperature of RL and Cu of the first component is about 500 ℃, and the eutectic temperature of RH and Cu of the third component is about 700-800 ℃. Therefore, after Cu, RL of the first component dissolves in the R-Cu rich liquid phase near the surface of the magnet base material, and then RH of the third component dissolves in the R-Cu rich liquid phase. After Cu, RL of the first component is dissolved into the liquid phase, thereby promoting diffusion of Cu into the magnet base material through the liquid phase, and further generating an R — Cu-rich liquid phase in the grain boundary of the magnet base material.

Since the third component (RH) of the first component (RL), the second component (Cu), and the third component (RH) is likely to be finally dissolved in the liquid phase, RH derived from the third component is unlikely to diffuse into the liquid phase inside the magnet base material after Cu and RL. As a result, the rapid increase in the concentration of RH in the vicinity of the surface of the magnet base material can be suppressed as compared with the case where the first component and the second component are not present. By suppressing the rapid increase in the concentration of RH in the vicinity of the surface of the magnet base material, it is possible to suppress excessive diffusion of RH into the interior of the main phase grains located in the vicinity of the surface of the magnet base material. As a result, RH can be diffused in a sufficient amount into the magnet base material, and the coercive force of the permanent magnet can be improved.

ZrB formed in grain boundary multiple points in sintering process₂Is easily dissolved in the R-Cu rich liquid phase. ZrB by cooling (quenching) after the diffusion step₂The crystal (2) is re-precipitated in the R-Cu-rich liquid phase, and the R-Cu-rich liquid phase is solidified to become an RCu-rich phase.

Surface layer part (R) of main phase particle₂Fe₁₄B) In the diffusion step, the particles are dissolved in an R-Cu-rich liquid phase formed at the grain boundary. In the process of re-precipitating the surface layer portion from the R — Cu-rich liquid phase by cooling (rapid cooling) after the diffusion step, the third component (RH) in the R — Cu-rich liquid phase is incorporated into the surface layer portion, thereby forming the surface layer portion containing RH. As described above, ZrB in the diffusion process₂Dissolved in the R-Cu-rich liquid phase, whereby the concentration of B in the grain boundary (R-Cu-rich liquid phase) increases. Suppression of increase in B concentration in R-Cu-rich liquid phase in surface layer portion (R)₂Fe₁₄B) Dissolution into an R-Cu rich liquid phase. By suppressing the surface layer part (R)₂Fe₁₄B) The thickness of the surface layer portion, which precipitates again while doping with RH, becomes thinner. Since RH is concentrated in the thin surface layer portion, the RH concentration in the surface layer portion increases. As a result, the anisotropic magnetic field is locally changed in the vicinity of the grain boundary of the two grainsLarge, it is difficult to generate nuclei for magnetization reversal in the vicinity of the grain boundaries of the two particles. Further, the coercive force of the permanent magnet increases.

As described above, according to the present embodiment, the coercive force of the permanent magnet can be increased.

In view of the fact that the magnetic properties of the permanent magnet are easily improved by the diffusion mechanism described above, the first component may be at least one of a hydride of neodymium and a hydride of praseodymium, the second component may be a simple substance of copper, and the third component may be at least one of a hydride of Tb and a hydride of Dy.

In the diffusion step, a slurry containing the first component, the second component, the third component, and a solvent may be attached to the surface of the magnet base material 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 alcohol, aldehyde or ketone. The diffusion material may further contain a binder in order to facilitate adhesion of the diffusion material to the surface of the magnet base material. The slurry may also contain a first component, a second component, a third component, a solvent, and a binder. By mixing the first component, the second component, the third component, the binder and the solvent, a paste having a higher viscosity than the slurry can be formed. The paste may be attached to the surface of the magnet base material. Pastes are mixtures with fluidity and higher viscosity. The solvent contained in the slurry or paste can be removed by heating the magnet base to which the slurry or paste has adhered before the diffusion step.

The diffusion material may be attached to a part or the whole of the surface of the magnet base material. 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 base material. The diffusion material itself or the slurry may be sprayed (spray) onto the surface of the magnet base material. The diffusion material may be evaporated on the surface of the magnet base material. The magnet base material may be immersed in the slurry. The diffusion material may be attached to the magnet base material via an adhesive (adhesive agent) covering the surface of the magnet base material. A part or the whole of the surface of the magnet base material may be covered with a sheet containing a diffusion material.

The temperature of the magnet base material in the diffusion step (diffusion temperature) may be equal to or higher than the eutectic temperature of RL and Cu, or may be lower than the sintering temperature. For example, the diffusion temperature may be 800 ℃ to 950 ℃. In the diffusion step, 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 for maintaining the temperature of the magnet base material at the diffusion temperature (diffusion time) may be, for example, 1 hour to 50 hours. The atmosphere around the magnet base material in the diffusion step may be a non-oxidizing atmosphere. The non-oxidizing atmosphere may be a rare gas such as argon. The pressure of the atmosphere around the magnet base material in the diffusion step may be 1kPa or less. By performing the diffusion step in such a reduced-pressure atmosphere, the dehydrogenation reaction of the hydride (the first component and the third component) can be promoted, and the diffusion material can be easily dissolved in the liquid phase.

The total mass of Tb, Dy, Nd, Pr and Cu in the diffusion material can be expressed as M_ELEMENTS. The total mass of Tb and Dy in the diffusion material is equal to M_ELEMENTSThe content may be 47 mass% to 86 mass%, 55 mass% to 85 mass%, 55 mass% to 80 mass%, or 59 mass% to 75 mass%. The total value of the masses of Tb and Dy is also referred to as the total value of the masses of RH in the diffusion material. When the total mass of RH is 55 mass% or more, the total amount of the diffusion material required for increasing the coercive force of the permanent magnet is easily reduced. When the total RH mass is 85 mass% or less, RH staying in the main phase grains located in the vicinity of the surface of the magnet base material is reduced, and the coercive force of the permanent magnet is easily increased.

The total mass of Nd and Pr in the diffusion material relative to M_ELEMENTSThe content may be 10 mass% to 43 mass%, 10 mass% to 37 mass%, 15 mass% to 37 mass%, or 15 mass% to 32 mass%. The sum of the masses of Nd and Pr is also referred to as the sum of the masses of RL in the diffusion material. When the total mass of RL is 10 mass% or more, the R — Cu-rich liquid phase is likely to be present inside the magnet base material in the diffusion step, and the RH concentration in the surface layer portion of the main phase grains is likely to be higherIt becomes easy to become high. When the total mass of RL is 37 mass% or less, the third component (RH) is not diluted too much by the first component (RL), and the coercive force of the permanent magnet is likely to increase.

Cu content in diffusion material relative to M_ELEMENTSThe content may be 4 to 30 mass%, 8 to 25 mass%, or 8 to 20 mass%. When the Cu content is 4 mass% or more, an R — Cu-rich liquid phase is easily generated, and the RH concentration in the surface layer portion of the main phase particle is easily increased. When the Cu content is 30 mass% or less, the decrease in the coercive force and residual magnetic flux density of the permanent magnet is easily suppressed. When the magnet base material contains Cu, the same effects as those of Cu derived from the diffusion material can be exhibited by Cu derived from the magnet base material. However, it is difficult to obtain the same effect as that of Cu derived from a diffusion material only by Cu derived from the magnet base material.

The particle size of each of the first component, the second component and the third component may be in the range of 0.3 to 32 μm, or 0.3 to 90 μm. The respective diameters of the first component, the second component, and the third component may also be referred to as the particle diameters of the diffusion material. As the particle diameter of the diffusion material increases, the oxygen contained in the diffusion material decreases, and diffusion of RH, RL, and Cu is less likely to be hindered by oxygen. As a result, the coercive force of the permanent magnet is easily increased. As the particle size of the diffusion material decreases, the time required for dissolution of each of the first component, the second component, and the third component becomes shorter, and RH, RL, and Cu easily diffuse into the magnet base material. As a result, the coercive force of the permanent magnet is easily increased. Further, as the particle diameter of the diffusion material decreases, the diffusion material easily and uniformly adheres to the surface of the magnet base material, and RH, RL, and Cu easily and uniformly diffuse into the interior of the magnet base material. As a result, the coercivity of the permanent magnet can be suppressed from varying, and the squareness ratio can be easily approximated to 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.

The mass of the magnet base material may be represented by 100 parts by mass, and the total mass of Tb and Dy in the diffusion material may be 0.0 part by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the magnet base material. When the total value of the mass of Tb and Dy is within the above range with respect to the magnet base material, the total value of the content of Tb and Dy in the entire permanent magnet is easily controlled to be 0.20 mass% or more and 2.00 mass% or less, and the magnetic properties of the permanent magnet are easily improved.

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

[ Heat treatment Process ]

The magnet base material subjected to the diffusion process can also be used as a finished product of a permanent magnet. Alternatively, the diffusion step may be followed by a heat treatment step. In the heat treatment step, the magnet base material may be heated at 450 ℃ to 600 ℃. In the heat treatment step, the magnet base material may be heated at the above-described temperature for a period of 1 hour to 10 hours. The magnetic properties (particularly, coercive force) of the permanent magnet are easily improved by the heat treatment step.

The size and shape of the magnet base material subjected to the diffusion step or the heat treatment step may be adjusted by a machining method such as cutting or polishing.

By the above method, the permanent magnet is completed.

The present invention is not limited to the above-described embodiments. For example, the magnet base material used in the diffusion step may be a hot-worked magnet (hot deformed magnet) instead of the sintered body.

[ examples ]

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

(example 1)

< production of magnet base Material >

The raw material alloy is produced from the raw material metal by a strip casting method. The composition of the raw material alloy was adjusted by weighing the raw material metal so that the composition of the raw material alloy after sintering was consistent with the composition of the magnet base material in table 1 below.

After hydrogen was stored in the raw material alloy at room temperature, the raw material alloy was heated at 600 ℃ for 1 hour in an Ar atmosphere to be dehydrogenated, thereby obtaining a raw material alloy powder. Namely, the hydrogen pulverization treatment is carried out.

Oleamide as a grinding aid was added to the raw alloy powder, and they were mixed by a conical mixer. The content of oleamide in the raw material alloy powder was adjusted to 0.1 mass%. Next, in the fine pulverization step, the average particle diameter of the raw alloy powder was adjusted to 3.5 μm using a jet mill. Next, in the molding step, the raw alloy powder is filled into the mold. The raw material powder in the mold was pressurized at 120MPa while applying a magnetic field of 1200kA/m, thereby obtaining a molded article.

In the sintering step, the molded body was heated at 1060 ℃ for 4 hours in vacuum and then quenched to obtain a sintered body.

The magnet base material was obtained by the above method. The contents of the respective elements in the magnet base material are shown in table 1 below.

< preparation of diffusion Material A >

As a raw material of the diffusion material a, a simple substance of Tb (simple metal substance) is used. The purity of Tb simple substance was 99.9 mass%.

By supplying a hydrogen gas flow to the element of Tb, hydrogen is occluded in the element of Tb. After storing hydrogen, the Tb simple substance was heated at 600 ℃ for 1 hour in an Ar atmosphere to dehydrogenate, thereby obtaining a powder composed of a Tb hydride. That is, the hydrogen pulverization treatment was performed.

To the powder of the hydride of Tb, zinc stearate as a grinding aid was added, and they were mixed by means of a conical mixer. The content of zinc stearate in the Tb hydride powder was adjusted to 0.05 mass%. Next, in the fine pulverization step, Tb hydride powder was further pulverized in a non-oxidizing atmosphere having an oxygen content of 3000 ppm. A jet mill is used in the micro-pulverization process. The average particle diameter of the powder composed of the hydride of Tb was adjusted to about 10.0 μm.

By the above method, a hydride of Tb (TbH) is obtained₂) And fine powder (third component) of the composition.

Using the simple substance of Nd, a hydride of Nd (NdH) was produced₂) The fine powder (first component) thus formed. The purity of Nd as a simple substance was 99.9 mass%. The average particle size of the fine powder composed of the hydride of Nd was about 10.0. mu.m. The method for producing the first component is the same as that for the third component, except that the simple substance of Nd is used as the raw material.

The paste-like diffusion material a was prepared by kneading a fine powder (first component) composed of a hydride of Nd, a fine powder (second component) composed of a simple substance of Cu, a fine powder (third component) composed of a hydride of Tb, an alcohol (solvent), and an acrylic resin (binder). The proportion of the mass of the first component in the diffusion material a was 17.0 parts by mass. The ratio of the mass of the second component in the diffusion material a was 11.2 parts by mass. The ratio of the mass of the third component in the diffusion material a was 46.8 parts by mass. The ratio of the mass 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.

< manufacture of permanent magnet >

The dimensions of the magnet base material were adjusted to 14mm in length, 10mm in width and 3.7mm in thickness by machining the magnet base material. After the dimensions of the magnet base material were adjusted, the magnet base material was etched. In the etching treatment, the entire surface of the magnet base material was cleaned with an aqueous solution of nitric acid. Next, the entire surface of the magnet base material was cleaned with pure water. The cleaned magnet base material was dried. The concentration of the aqueous solution of nitric acid was 0.3 mass%. After the etching treatment, the following diffusion step was performed.

In the diffusion step, the diffusion material a is applied to the entire surface 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 became 0.8 parts by mass with respect to 100 parts by mass of the magnet base material. The magnet base material coated with the diffusion material a was placed in an oven, and the magnet base material was heated at 160 ℃. After the solvent was removed, the magnet base material coated with the diffusion material a was heated at 900 ℃ for 12 hours in Ar gas.

In the heat treatment step subsequent to the diffusion step, the magnet base material was heated at 540 ℃ for 2 hours in Ar gas.

The permanent magnet of example 1 was produced by the above method. The contents of the respective elements in the permanent magnet of example 1 are shown in table 1 below.

< measurement of magnetic Property of permanent magnet >

The surface of the permanent magnet is ground to remove a portion having a depth of 0.1mm or less from the surface. Next, the residual magnetic flux density Br and coercive force HcJ of the permanent magnet were measured by a BH tracer. Br (unit: mT) was measured at room temperature. HcJ (unit: kA/m) was measured at 160 ℃. Br and HcJ of example 1 are shown in table 1 below.

< analysis of the Cross section of permanent magnet >

After the permanent magnet is cut to expose the cross section of the permanent magnet, the permanent magnet is embedded (embedded) in a hot-setting resin (hot-setting resin). As the thermal insert resin, Polyfast (trade name) manufactured by Struers corporation (Struers ApS) was used. Polyfast is a black Bakelite (phenolic resin) containing carbon filler material. The cross section of the permanent magnet embedded in the thermal insert resin was polished by ethanol-based wet polishing. After polishing the cross section of the permanent magnet, the distribution pattern of each element in the cross section of the permanent magnet was measured by EPMA. As the EPMA, JXA8500F (trade name) manufactured by japan electronics corporation (JEOL Ltd.) was used. The size of the distribution plots was 50 μm long by 50 μm wide.

The distribution pattern of each element shows that the permanent magnet has a plurality of main phase particles containing Nd, Fe, Co, and B and a plurality of grain boundary multiple points. In the distribution maps of Zr, B, and Cu, a portion (high concentration portion) where the intensity of the characteristic X-ray of each element is higher than the average value of the intensities of the characteristic X-rays of each element in each distribution map is specified. The high concentration portions of Zr, B, and Cu overlap each other at a plurality of grain boundaries. One grain boundary where the high concentration portions of Zr, B, and Cu overlap is often referred to as "Zr — B — Cu grain boundary".

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 respective conditions. The analysis results are shown in table 2 below. The compositions of grain boundary phase 4-1, grain boundary phase 4-2, grain boundary phase 4-3, grain boundary phase 4-4, and grain boundary phase 4-5 in the following Table 2 each correspond to one Zr-B-Cu grain boundary.

Acceleration voltage: 10kV

Irradiation current: 0.1 μ A

Determination time (peak/background): 40sec/10sec

The composition of the main phase particles was analyzed by the same method as in 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 are 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 by the same method as the Zr-B-Cu grain boundary. The analysis results are shown in table 2 below. The compositions of grain boundary phase 1, grain boundary phase 2, and grain boundary phase 3 in table 2 below correspond to one grain boundary multiple point except for the Zr — B — Cu grain boundary. The grain boundary phase 1 is the above-mentioned R-rich phase. The grain boundary phase 2 is the above-mentioned R-O-C phase. The grain boundary phase 3 is the above-mentioned T-rich phase.

The permanent magnet was subjected to planar sampling using a Focused Ion Beam (FIB), and then the permanent magnet was thinned, thereby preparing a sample containing the grain boundary phase 4-1 (Zr-B-Cu grain boundary) described above. An HAADF-STEM image of the Zr-B-Cu grain boundary including the grain boundary phase 4-1 was taken. The HAADF-STEM image of the Zr-B-Cu grain boundaries including the grain boundary phase 4-1 is shown in FIG. 4A. Titan-G2 (trade name) manufactured by FEI was used as STEM. The distribution map of each element in the region shown in fig. 4A was measured by STEM-EDS.

The distribution of Cu in the region of fig. 4A is shown in fig. 4B.

The profile of Nd in the region of fig. 4A is shown in fig. 4C.

The distribution of Zr in the region of fig. 4A is shown in fig. 4D.

The distribution of Co in the region of fig. 4A is shown in fig. 5A.

The distribution of Fe in the region of fig. 4A is shown in fig. 5B.

The distribution of Ga in the region of fig. 4A is shown in fig. 5C.

The distribution of Tb in the region of fig. 4A is shown in fig. 5D.

In the element distribution map using STEM-EDS, the energy region of the characteristic X-ray of Zr and the energy region of the characteristic X-ray of B overlap each other, and the detection sensitivity of B is insufficient, so that it is difficult to detect B.

The results of the above analysis show that the permanent magnet of example 1 has the following characteristics.

As shown in FIG. 4A, the grain boundary phase 4-1 is composed of the plate-like crystal 3 and the R-Cu-rich phase 5 containing Nd, Pr, and Cu. The region of the Zr distribution substantially completely coincides with the position of the plate-like crystal 3. The R-Cu-rich phase 5 exists around the plate-like crystals 3. The R — Cu rich phase 5 exists between the plate-like crystals 3 and the main phase particles 4. The plate-like crystals 3 are connected to the two-particle grain boundaries. The total of the concentrations of Nd and Pr in one Zr — B — Cu grain boundary containing both the plate-like crystal 3 and the R — Cu-rich phase 5 is higher than the total of the concentrations of Nd and Pr in the main phase particle 4. The concentration of Cu in one Zr — B — Cu grain boundary containing both the plate-like crystals 3 and the R — Cu-rich phase 5 is higher than that in the main phase particles 4. The surface layer portion of the main phase particles 4 contains Tb.

An HAADF-STEM image of the plate-like crystal 3 contained in the grain boundary phase 4-1 is shown in FIG. 6A. In a region 3x in the plate-like crystal 3 shown in fig. 6A, an electron beam diffraction pattern was measured. The measured electron beam diffraction pattern is shown in fig. 6B. Lattice constant and symmetry of plate-like crystal 3 determined from electron beam diffraction pattern and ZrB of hexagonal system₂Are consistent with the symmetry and lattice constant of the crystal. One Zr-B-Cu grain boundary containing grain boundary phase 4-1 contains ZrB₂Both crystalline and R-Cu rich phases.

As with the sample containing the grain boundary phase 4-1, a sample containing a grain boundary phase 4-2, a grain boundary phase 4-3, and a grain boundary phaseFour samples of phase 4-4 and grain boundary phase 4-5. Each of these samples was analyzed by the same method as that for the sample containing the grain boundary phase 4-1. The analysis results thereof showed that each of grain boundary phase 4-2, grain boundary phase 4-3, grain boundary phase 4-4 and grain boundary phase 4-5 had the same characteristics as grain boundary phase 4-1. That is, intergranular phase 4-2, intergranular phase 4-3, intergranular phase 4-4, and intergranular phase 4-5 each contain ZrB₂Both crystalline and R-Cu rich phases.

Comparative example 1

In comparative example 1, a diffusion material B produced by the following method was used instead of the diffusion material a.

The fine powder (third component) composed of Tb hydride, alcohol (solvent), and acrylic resin (binder) were kneaded to prepare a paste-like diffusion material B. That is, the diffusion material B does not contain a fine powder (first component) composed of a hydride of Nd and a fine powder (second component) composed of a simple substance of Cu. The ratio of the mass of the third component in the diffusion material B was 75.0 parts by mass. The ratio of the mass of the solvent in the diffusion material B was 23.0 parts by mass. The mass ratio of the binder in the diffusion material B was 2.0 parts by mass.

A permanent magnet of comparative example 1 was produced in the same manner as in example 1, except that the diffusion material B was used. The contents of the respective elements in the permanent magnet of comparative example 1 are shown in table 1 below.

Br and HcJ of the permanent magnet of comparative example 1 were measured by the same method as in example 1. Br and HcJ of comparative example 1 are shown in Table 1 below. It was confirmed that the coercive force of the permanent magnet of example 1 at 160 ℃ was higher than that of the permanent magnet of comparative example 1 at 160 ℃.

The cross section of the permanent magnet of comparative example 1 was analyzed by the same method as in example 1. The analysis results of comparative example 1 are shown in table 3 below. The compositions of 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 has a plurality of main phase grains containing Nd, Fe, Co, and B, and a plurality of grain boundary-rich spots. In the permanent magnet of comparative example 1, grain boundary multiple points (grain boundary phase 4-1) were detected in which high concentration portions of Zr and B overlapped. However, in the permanent magnet of comparative example 1, a grain boundary-rich point (Zr — B — Cu grain boundary) where high concentration portions of Zr, B, and Cu overlap was not detected. That is, in the case of comparative example 1, the concentration of Cu in the grain boundary multiple points where the high concentration portions of Zr and B overlap is not higher than the concentration of Cu in the other grain boundary multiple points.

[ Table 1]

[ Table 2]

[ Table 3]

[ industrial applicability ]

The R-T-B permanent magnet of the present invention is suitable for a material mounted on a motor of a hybrid vehicle or an electric vehicle, for example.