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 于 2020-03-10 设计创作，主要内容包括：本发明的永久磁铁(2)含有Nd、Fe和B,永久磁铁(2)包含多个主相颗粒和位于主相颗粒之间的晶界,主相颗粒含有Nd、Fe和B,至少一部分晶界包含R’-O-C相,R’-O-C相含有稀土元素R’、O和C,R’-O-C相中的R’、O和C各自的浓度比主相颗粒高,永久磁铁(2)具有表层部(21)和中央部(22),表层部(21)位于永久磁铁(2)的表面侧,中央部(22)位于永久磁铁(2)的内侧,表层部(21)的截面中所占的R’-O-C相的面积的比率为S1％,中央部(22)的截面中所占的上述R’-O-C相的面积的比率为S2％,S1比S2高。(The permanent magnet (2) of the present invention contains Nd, Fe, and B, the permanent magnet (2) includes a plurality of main phase particles and grain boundaries located between the main phase particles, the main phase particles contain Nd, Fe, and B, at least a part of the grain boundaries include an R ' -O-C phase, the R ' -O-C phase contains rare earth elements R ', O, and C, the concentrations of R ', O, and C in the R ' -O-C phase are higher than those of the main phase particles, the permanent magnet (2) has a surface layer part (21) and a central part (22), the surface layer part (21) is located on the surface side of the permanent magnet (2), the central part (22) is located inside the permanent magnet (2), the ratio of the area of the R ' -O-C phase occupied in the cross section of the surface layer part (21) is S1%, the ratio of the area of the R ' -O-C phase occupied in the cross section of the central part (22) is S2%, s1 is higher than S2.)

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

contains rare earth element R, transition metal elements T and B,

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 comprises a plurality of main phase grains and grain boundaries between the main phase grains,

the main phase particles contain Nd, T and B,

at least a portion of the grain boundaries comprise an R' -O-C phase,

the R '-O-C phase contains rare earth elements R', O and C,

r' is at least one selected from Nd, Pr, Tb and Dy,

the concentration of each of R', O and C is in atomic%,

the concentration of each of R ', O and C in the R' -O-C phase is higher than that of the main phase particles,

the R-T-B permanent magnet has a surface layer part and a central part,

the surface layer part is positioned on the surface side of the R-T-B series permanent magnet,

the central part is positioned inside the R-T-B series permanent magnet,

the ratio of the area of the R' -O-C phase in the cross section of the surface layer portion is S1%,

the ratio of the area of the R' -O-C phase in the cross section of the central portion is S2%,

s1 is higher than S2.

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

S1-S2 is 1.0-80.

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

s1 is 4.3-80.

4. The R-T-B permanent magnet according to any one of claims 1 to 3,

at least a portion of the R' -O-C phase further comprises N.

Technical Field

The present invention relates to an R-T-B permanent magnet containing at least a rare earth element R, a transition metal element T and boron B.

Background

The R-T-B permanent magnet has excellent magnetic characteristics. However, since rare earth elements, which are main components of the R-T-B-based permanent magnet, are easily oxidized, the R-T-B-based permanent magnet tends to be easily corroded. Therefore, in the conventional production of R-T-B permanent magnets, the corrosion resistance of R-T-B permanent magnets is improved by surface treatment of the magnet matrix. For example, the surface of the magnet body is covered with a resin film or a plating film. On the other hand, measures have been taken to improve the corrosion resistance of the magnet matrix itself. For example, the corrosion resistance of the magnet body itself is improved by the use of the additive element or by changing the internal structure of the magnet body. The corrosion resistance of the magnet matrix itself is extremely important for improving the reliability of the product after the surface treatment. Further, by improving the corrosion resistance of the magnet body itself, the above surface treatment becomes simpler and the manufacturing cost is reduced.

International publication No. 2013/122256 pamphlet discloses that corrosion resistance of a magnet matrix itself is improved by including an R — O — C concentrated portion. The R-O-C concentrated portion is a grain boundary phase in which the respective concentrations of the rare earth elements R, O and C are higher than those of the main phase grains.

Disclosure of Invention

In order to provide excellent corrosion resistance, the R-T-B permanent magnet disclosed in the pamphlet of International publication No. 2013/122256 needs to have a certain amount of concentrated R-O-C portion throughout the entire magnet. However, the coercive force of the R-T-B permanent magnet tends to be lowered because the R-rich phase in the grain boundary tends to decrease as the R-O-C concentrated portion is formed.

The invention aims to: provided is an R-T-B permanent magnet having excellent corrosion resistance and high coercive force.

An R-T-B-based permanent magnet according to an aspect of the present invention is an R-T-B-based permanent magnet containing a rare earth element R, transition metal elements T and B, wherein R is at least Nd in the R-T-B-based permanent magnet, T is at least Fe in the R-T-B-based permanent magnet, the R-T-B-based permanent magnet contains a plurality of main phase particles and grain boundaries between the main phase particles, the main phase particles contain Nd, T and B, at least a part of the grain boundaries contain an R ' -O-C phase, the R ' -O-C phase contains rare earth elements R ', O and C, R ' is at least one selected from Nd, Pr, Tb and Dy, the concentration unit of each of R ', O and C is at atom%, and R ' in the R ' -O-C phase is at least one selected from Nd, Pr, Tb, and Dy, The R-T-B permanent magnet has a surface portion and a central portion, the surface portion is located on the surface side of the R-T-B permanent magnet, the central portion is located on the inner side of the R-T-B permanent magnet, the ratio of the area of the R '-O-C phase in the cross section of the surface portion is S1%, the ratio of the area of the R' -O-C phase in the cross section of the central portion is S2%, and S1 is higher than S2.

S1-S2 may be 1.0 to 80.

S1 may be 4.3 to 80 inclusive.

At least a portion of the R' -O-C phase also contains N.

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

Drawings

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

Fig. 2 is a schematic cross-sectional view (region II) of the surface layer portion of the R-T-B-based permanent magnet shown in B of fig. 1.

FIG. 3 is a distribution diagram of elements in the vicinity of the surface layer portion of the R-T-B permanent magnet of example 1.

Description of the symbols

2 … R-T-B permanent magnet, 2cs … R-T-B permanent magnet cross section, 4 … main phase grain, 3 … R' -O-C phase, 6 … grain boundary multiple point, 10 … two grain boundary, 21 … surface layer part, 22 … central part, part of II1 … surface layer part cross section, part of II2 … central part cross section.

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 magnets" described below are all referred to as "R-T-B-based permanent magnets". The unit of "concentration" of each element in the permanent magnet is atomic%.

(permanent magnet)

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

The permanent magnet contains at least neodymium (Nd) as a rare earth element R. The permanent magnet may contain other rare earth elements R in addition to Nd. The other rare earth element R may be at least one 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. 1 a is a perspective view of a rectangular parallelepiped permanent magnet 2 according to the present embodiment. B in fig. 1 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, for example, a cube, a rectangle (plate), a polygonal column, an arc (arc segment), a fan, a circular sector (annular segment), 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.

As shown in fig. 1B, the permanent magnet 2 has a surface portion 21 and a central portion 22. The surface portion 21 is located on the surface side of the permanent magnet 2. The central portion 22 is located inside the permanent magnet 2. The surface portion 21 may be a region having a depth of 0 μm to 40 μm from the surface of the permanent magnet 2 and including the main phase grains and the R' -O — C phase. Only a part of the surface of the permanent magnet 2 may be the surface layer portion 21. For example, when corrosion resistance is required only for a part of the surface of the permanent magnet 2, only the part requiring corrosion resistance may be the surface portion 21. The entire surface of the permanent magnet 2 may be the surface layer 21. The central portion 22 may be located at the center of the permanent magnet 2 in the thickness direction of the permanent magnet 2. The thickness of the permanent magnet 2 may be, for example, 0.5mm to 50 mm.

Region II1 shown in fig. 1B and 2 is a part of the cross section of surface layer portion 21. The structure of the cross section of the central portion 22 (region II2) shown in B of fig. 1 may be the same as the structure of the cross section of the surface portion 21 shown in fig. 2, except for the ratio of the area of the R' -O-C phase in the cross section. As shown in fig. 2, the permanent magnet 2 has a plurality of (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 R₂T₁₄And (B) crystallizing. R₂T₁₄B can be represented, for example, 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 contain, as R, heavy rare earth elements such as Tb and Dy in addition to light rare earth elements. R₂T₁₄Part of B in B may be replaced with carbon (C). The main phase particles 4 may contain other elements in addition to Nd, T, and B. 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 R-T-B permanent magnet includes grain boundaries between the main phase grains 4. The permanent magnet 2 may include a grain boundary multiple point 6 as a grain boundary. The grain boundary multiple point 6 is a grain boundary surrounded by three or more main phase grains 4. The permanent magnet 2 may comprise a plurality of (majority of) grain boundary multiple points 6. The permanent magnet 2 may include two grain boundaries 10 as grain boundaries. The two-particle grain boundary 10 is a grain boundary between two adjacent main phase particles 4. The permanent magnet 2 may include a plurality of (a plurality of) two-grain boundaries 10.

At least a portion of the grain boundaries comprise R' -O-C phase 3. The R '-O-C phase 3 contains rare earth elements R', O (oxygen) and C. R' is at least one selected from Nd, Pr, Tb and Dy. The R ', O and C in the R' -O-C phase 3 are each at a higher concentration than the main phase particles 4. That is, the concentration of R ' in the R ' -O-C phase 3 is higher than the concentration of R ' in the main phase particles 4, the concentration of O in the R ' -O-C phase 3 is higher than the concentration of O in the main phase particles 4, and the concentration of C in the R ' -O-C phase 3 is higher than the concentration of C in the main phase particles 4. The concentration of R' is the sum of the concentrations of Nd, Pr, Tb and Dy.

The grain boundary may include a grain boundary phase other than the R' -O-C phase 3. For example, the grain boundaries may comprise an R' rich phase. The R 'rich phase is a phase in which the concentration of R' is higher than that of the other grain boundary phases. The grain boundaries may comprise oxide phases. The oxide phase is a phase that contains an oxide of R 'as a main component and is different in composition from the R' -O-C phase 3. In the case where the permanent magnet 2 contains Ga (gallium), the grain boundary may contain a transition metal-rich phase. The transition metal-rich phase contains T, R' and Ga, and each concentration of T and Ga is higher than that of the other grain boundary phases.

Conventional R-T-B permanent magnets are corroded by the following mechanism. However, the mechanism of corrosion is not limited to the following mechanism.

Water (e.g., water vapor) in the atmosphere oxidizes the R' rich phase in the grain boundary at the surface of the permanent magnet. The oxidation of the R' rich phase by water is represented by the following reaction formula 1. As shown in the following reaction formula 1, the hydroxide of R 'and hydrogen are generated by the oxidation of R' by water. This hydrogen is occluded in the unoxidized R-rich' phase. In other words, R ' in the R ' rich phase is hydrogenated to produce a hydride of R '. The hydrogenation of R 'in the R' -rich phase is represented by the following reaction scheme 2. X in equation 2 is a positive real number that varies according to the hydrogen occlusion amount. The hydride of R' is easily oxidized by water. The oxidation of the hydride by water is represented by the following reaction formula 3. As shown in the following reaction formula 3, hydrogen is generated by oxidation of the hydride of R 'in addition to hydrogen occluded in the R' rich phase (hydride). By these corrosion reactions proceeding in a chain, the permanent magnet expands. As the permanent magnet expands, water easily penetrates into the permanent magnet through the grain boundaries. In addition, as the permanent magnet expands, the main phase particles fall off from the surface of the permanent magnet. The un-corroded R' -rich phase is exposed to the surface of the permanent magnet due to the shedding of the main phase particles. As a result, corrosion proceeds further into the permanent magnet.

2R’+6H₂O→2R’(OH)₃+3H₂(1)

2R’+xH₂→2R’H_x(2)

2R’H_x+6H₂O→2R’(OH)₃+(3+x)H₂(3)

The R '-O-C phase 3 is less oxidized by water than the R' -rich phase. In addition, the R '-O-C phase 3 is less likely to store hydrogen than the R' -rich phase. Therefore, the R' -O — C phase 3 is contained in the grain boundary of the surface layer portion 21, and thereby generation and occlusion of hydrogen in the grain boundary can be suppressed. In other words, the R '-O — C phase 3 is included in the grain boundary of the surface layer portion 21, whereby oxidation and hydrogenation of the R' -rich phase can be suppressed. As a result, the above-described linkage of the corrosion reaction can be suppressed, and the progress of corrosion into the interior (central portion 22) of the permanent magnet 2 can be suppressed.

The ratio of the area of the R' -O — C phase 3 in the cross section of the surface portion 21 was S1%. The ratio of the area of the R' -O-C phase 3 in the cross section of the central portion 22 was S2%. S1 is higher than S2. In other words, the proportion of the R ' -O-C phase 3 in the surface portion 21 is higher than the proportion of the R ' -O-C phase 3 in the central portion 22, and the R ' -O-C phase 3 is offset from the surface portion 21 of the permanent magnet 2. The corrosion of the permanent magnet 2 progresses gradually from the surface of the permanent magnet 2 to the inside. Therefore, corrosion of the permanent magnet 2 can be effectively suppressed by offsetting the R' -O-C phase 3 from the surface layer portion 21 of the permanent magnet 2. However, the more the R '-O — C phase 3 is, the less the amount of the R' -rich phase in the grain boundary is, and thus the coercivity of the permanent magnet 2 tends to be easily lowered. However, S2 is lower than S1. In other words, the proportion of the R '-O-C phase 3 in the central portion 22 is lower than the proportion of the R' -O-C phase 3 in the surface portion 21. As a result, the decrease in coercive force of the permanent magnet 2 associated with the inclusion of the R' -O-C phase 3 can be suppressed. Therefore, the coercive force of the permanent magnet 2 according to the present embodiment is higher than that of a permanent magnet in which the R' -O-C phase 3 is uniformly distributed.

The larger the S1 to S2 are, the more easily corrosion of the permanent magnet 2 is suppressed in the surface layer portion 21, and the decrease in coercive force of the permanent magnet 2 accompanying the inclusion of the R' -O — C phase 3 is suppressed. For this reason, S1-S2 may be 1.0 to 80, or 2.6 to 38.2.

S1 may be 4.3 to 80, or 5.9 to 41.5. When S1 is equal to or greater than the lower limit value, corrosion of permanent magnet 2 is easily suppressed. When S1 is equal to or less than the above upper limit, the surface layer portion 21 can contain a sufficient R' -rich phase, and the decrease in the coercive force of the permanent magnet 2 can be easily suppressed. However, S1 is not limited to the above range. S2 may be, for example, 0 or more and less than 4.3, or 0 or more and 3.3 or less. The smaller the S2, the more easily the decrease in coercive force of the permanent magnet 2 caused by the inclusion of the R' -O-C phase 3 is suppressed. However, S2 is not limited to the above range as long as it is smaller than S1.

As shown in fig. 1B, the cross section of the surface portion 21 of the measurement S1 and the cross section of the central portion 22 of the measurement S2 may be included in the same cross section 2cs of the permanent magnet 2. The cross section of the surface layer portion 21 of the measurement S1 and the cross section of the central portion 22 of the measurement S2 may not be included in the same cross section 2cs of the permanent magnet 2. The details of the measurement methods of S1 and S2 will be described later.

The R '-O-C phase 3 may contain other elements in addition to R', O and C. For example, at least a portion of the R' -O-C phase 3 may also contain N (nitrogen). When the permanent magnet 2 contains N, the R' -O-C phase 3 easily contains N. When the R' -O-C phase 3 contains N, the generation and occlusion of hydrogen in the grain boundary can be easily suppressed. Only a part of the R' -O-C phase 3 included in the permanent magnet 2 may contain N. All of the R' -O-C phases 3 included in the permanent magnet 2 may contain N. All of the R' -O-C phases 3 included in the permanent magnet 2 may not contain N. The R '-O-C-N phase described below refers to the N-containing R' -O-C phase 3.

The concentration of R 'in the R' -O-C phase 3 may be, for example, 30 at% to 55 at%. The concentration of O in the R' -O-C phase 3 may be, for example, 10 atomic% or more and 50 atomic% or less. The concentration of C in the R' -O-C phase 3 may be, for example, 5 at% to 30 at%. The concentration of N in the R' -O-C phase 3 may be, for example, 0 atomic% or more and 30 atomic% or less. The concentration of R ' in the R ' -O-C phase 3 can be expressed as [ R ' ] atomic%. The concentration of O in the R' -O-C phase 3 can be expressed as [ O ] atom%. The concentration of N in the R' -O-C phase 3 can be expressed as [ N ] atom%. [ O ]/[ R' ] can be greater than 0 and less than 1.0, greater than 0.4 and less than 0.7, or greater than 0.5 and less than 0.7. When [ O ]/[ R ' ] is within the above range, oxidation and hydrogenation of the R ' -rich phase are easily suppressed, and a decrease in the coercive force of the permanent magnet 2 accompanying the inclusion of the R ' -O — C phase 3 is easily suppressed. For the same reason, [ N ]/[ R' ] can be greater than 0 and less than 1.0. At least a portion of the R' -O-C phase 3 may be cubic. Since the R' -O — C phase 3 is a cubic crystal, generation and occlusion of hydrogen in the grain boundary can be easily suppressed.

The average particle diameter or D50 of the main phase particles 4 is not particularly limited, and may be, for example, 1.0 μm to 10.0 μm or less, or 1.5 μm to 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 respective compositions of the main phase grains 4 and the grain boundary phase can be specified by the respective analyses of the main phase grains 4 and the grain boundary phase exposed to the cross section 2cs of the permanent magnet 2. The main phase particles 4 and the grain boundary phase exposed to the cross section 2cs of the permanent magnet 2 can be easily recognized based on the signal intensity of a reflected electron image taken by an electron beam probe microanalyzer (EPMA). The respective compositions of the main phase particles 4 and the grain boundary phase can be analyzed by an electron beam probe microanalyzer (EPMA) or energy dispersive X-ray spectroscopy (EDS).

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 effect of the present invention by the R' -O-C phase 3 described above can be obtained.

The content of O in the 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, the R' -O-C phase is difficult to form. 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 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, the R' -O-C phase is difficult to form. When the content of C is too large, the coercive force of the permanent magnet tends to be lowered.

The content of N in the permanent magnet may be 0 mass% to 0.15 mass%, or 0.03 mass% to 0.10 mass%. When the content of N is too small, the R' -O-C phase tends to be difficult to form. When the content of N is too large, the coercive force of the permanent magnet tends to be lowered. The permanent magnet may not contain N.

The content of R in the permanent magnet may be 25 to 35 mass% or 29 to 34 mass%. When the permanent magnet contains a heavy rare earth element as R, the total content of all rare earth elements including the heavy rare earth element may be 25 to 35 mass% or 29 to 34 mass%. By the content of R being in this range, there are residual magnetic flux densities andthe coercivity tends to increase. When the content of R is too small, it is difficult to form main phase particles (R)₂T₁₄B) On the other hand, when the content of R is too large, the volume ratio of the main phase particles tends to be low, and the residual magnetic flux density tends to be low, and the total ratio of Nd and Pr to the total rare earth element R may be 80 to 100 atomic% or 95 to 100 atomic% in terms of the ease of increasing the residual magnetic flux density and the coercive force.

The content of B in the permanent magnet may be 0.5 to 1.5 mass%, or 0.75 to 0.98 mass%. When the content of B is too small, R₂T₁₇The compatibility is liable to be precipitated, and the coercive force tends to be lowered. On the other hand, if the content of B is too large, the residual magnetic flux density of the permanent magnet tends to decrease.

The permanent magnet may contain Co. The content of Co in the permanent magnet may be 0.1 to 4.0 mass%, or 0.3 to 2.5 mass%. The curie temperature of the permanent magnet is easily increased by the permanent magnet containing Co. Further, since the permanent magnet contains Co, the corrosion resistance of the grain boundary phase is easily improved, and the corrosion resistance of the entire permanent magnet is easily improved.

The permanent magnet may contain aluminum (Al). The content of Al in the permanent magnet may be 0.03 to 0.6 mass%, or 0.1 to 0.4 mass%. When the Al content is in the above range, the coercive force and corrosion resistance of the permanent magnet can be easily improved.

The permanent magnet may contain copper (Cu). The Cu content in the permanent magnet may be 0.03 to 1.5 mass%, or 0.05 to 0.6 mass%. When the Cu content is in the above range, the coercive force, corrosion resistance and temperature characteristics of the permanent magnet are easily improved.

The remaining part of the permanent magnet from which the above-mentioned elements have been removed may be Fe alone or Fe and other elements. In order that the permanent magnet has sufficient magnetic properties, the total content of the elements other than Fe in the remainder may be 0 to 5 mass% based on the total mass of the permanent magnet.

The permanent magnet may contain, as another element, at least one element selected from the group consisting of zirconium (Zr), silicon (Si), gallium (Ga), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), tin (Sn), calcium (Ca), 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-thermal conductivity method, and the like.

The permanent magnet according to the present embodiment can be applied to an engine, a generator, an actuator, and 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.

(method for producing permanent magnet)

The following describes a method of manufacturing the permanent magnet.

A raw material alloy is made of a metal (raw material metal) containing each element constituting the above permanent magnet. The raw material alloy may be produced by a strip casting method, a stack casting method or a centrifugal casting method. The raw material metal may be, for example, a simple substance (metal simple substance) of a rare earth element, pure iron, ferroboron, or an alloy containing them. These raw metals are weighed in a manner substantially in accordance with the composition of the desired permanent magnet. One or more kinds of raw material alloys may be used. The raw alloy is preferably not mixed with oxides. When a mixture of a raw material alloy and an oxide is used as a raw material for a permanent magnet, an excessive amount of R' -O — C phase is easily formed in the central portion of the permanent magnet, S2 is easily increased, and it is difficult to manufacture a permanent magnet having S1 higher than S2. For the same reason, it is preferable that the raw material alloy is not mixed with carbon or carbide, and it is preferable that the raw material alloy is not mixed with nitride.

By pulverizing the above-described raw material alloys, alloy powder can be obtained. The raw material alloy may be pulverized in two stages of a coarse pulverization step and a fine pulverization step. The following steps may be performed in a non-oxidizing atmosphere having an oxygen concentration of less than 100 ppm.

In the coarse pulverization step, the raw material alloy is pulverized until the particle diameter of the raw material alloy becomes about several hundred μm or several mm. As the rough pulverization step, hydrogen storage pulverization may be performed. In the hydrogen occlusion pulverization, hydrogen is occluded in the raw material alloy. After hydrogen occlusion, hydrogen is desorbed from the raw material alloy by heating the raw material alloy. The raw material alloy can be pulverized by the desorption of hydrogen from the raw material alloy. In the rough grinding step, the raw material alloy having occluded hydrogen may be heated in an atmosphere containing nitrogen. The R' -O-C-N phase is easily formed in the permanent magnet by heating the raw material alloy having occluded hydrogen in an atmosphere containing nitrogen. The nitrogen concentration in the atmosphere may be, for example, 200 vol ppm or more and 1000 vol ppm or less. When the nitrogen content is within the above range, the R' -O-C-N phase is easily formed. In the coarse pulverization step, the raw material alloy may be pulverized by a mechanical method. The mechanical method may be, for example, a disc mill, a jaw crusher, a brown mill or a triturator.

In the fine grinding step subsequent to the coarse grinding step, the raw material alloy is further ground until the average particle diameter of the raw material alloy becomes 0.1 to 10.0 μm. In the fine pulverization step, for example, a pulverization device such as a jet mill or a bead mill may be used. In the fine pulverization step, a pulverization aid (lubricant) may be added to the raw material alloy. By adding the pulverization aid, the coagulation of the raw material alloy and the adhesion of the raw material alloy to the pulverization apparatus can be suppressed. The pulverization aid may be, for example, at least one organic compound selected from the group consisting of fatty acid esters, amine carboxylates, fatty amines, fatty acids, and fatty acid amides. It may be carried out by means of a jet mill in an atmosphere containing nitrogen. In the case where the atmosphere of the jet mill contains nitrogen, an R' -O-C-N phase is easily formed in the permanent magnet.

In the molding step, the alloy powder is molded in a magnetic field to obtain a molded body. For example, a compact can be obtained by applying a magnetic field to the raw alloy powder in a die while pressing the alloy powder with the die. The pressure applied by the die to the alloy powder may be 30MPa 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. A mixture (slurry) of the alloy powder and the organic solvent may be formed. That is, the molded body can be formed by wet molding.

In the sintering step, the molded body is sintered in a sintering furnace to obtain a sintered body. The atmosphere in the sintering furnace may be vacuum or inert gas. The conditions of the sintering step may be appropriately set according to the composition of the intended permanent magnet, the method of pulverizing the raw material alloy, the particle size, and the like.

The sintering process comprises a temperature rise process and a sintering process. In the temperature raising process, the temperature in the sintering furnace is raised from room temperature to the sintering temperature Ts. During sintering, the shaped body is continuously heated with Ts. The sintering temperature Ts may be higher than 900 ℃ and 1200 ℃ or lower. The duration of the sintering process may be, for example, 1 hour to 30 hours. During the temperature rise, carbon monoxide (CO) gas is introduced into the sintering furnace at a time when the temperature in the sintering furnace is 800 ℃ to 900 ℃. A mixed gas of CO and argon (Ar) may be introduced into the sintering furnace. In the temperature range of 800 ℃ to 900 ℃ inclusive, the compact is not yet densified, and therefore, a large number of voids are formed in the compact. Therefore, the CO gas can enter the molded body from the surface of the molded body to a certain depth via the void. Further, the R '-O-C phase is generated from the surface of the molded body to a certain depth by the reaction of CO with the rare earth element R' in the molded body. The R '-O-C phase is easily formed in a region close to the surface of the molded article, and the R' -O-C phase is hardly formed in a region distant from the surface of the molded article. That is, the R '-O-C phase is easily formed in the surface layer portion of the molded article, and the R' -O-C phase is hardly formed in the central portion of the molded article. In the case of shaped bodies containing oxygen, carbon or nitrogen as impurities, these elements are also incorporated into the R' -O-C phase. When the temperature in the sintering furnace is increased to the sintering temperature Ts, the compact is densified, and a grain boundary including an R' -O-C phase can be formed. Through the above process, a surface layer portion containing a large amount of R' -O — C phase is formed on a part or the entire region of the surface of the permanent magnet (sintered body). After the alloy powders are sintered to each other to densify the compact, the CO gas is less likely to penetrate into the compact, and the surface layer portion including a large amount of the R' -O — C phase is less likely to be formed. After the compact is densified, the CO gas reacts with a liquid phase (for example, a liquid phase of R') exuded from the inside of the sintered compact, and a coating film is formed on the surface of the compact.

In the temperature rise process in the sintering step, the temperature in the sintering furnace may be continuously raised from room temperature to the sintering temperature Ts. The temperature in the sintering furnace can be maintained at a specific temperature of 800 ℃ to 900 ℃ for a certain period of time as the CO gas is introduced into the sintering furnace. During the temperature rise, nitrogen gas may be introduced into the sintering furnace together with CO gas. The nitrogen may be incorporated into the R' -O-C phase.

In the aging treatment step, the sintered body may be further heated. The magnetic properties of the sintered body are improved by the aging treatment step. The atmosphere of the aging treatment process may be vacuum or inert gas. In the aging treatment step, the sintered body may be heated at about 600 ℃ for 1 to 3 hours. The aging treatment process can be performed in a plurality of stages. For example, in the first aging treatment, the sintered body may be heated at 700 to 950 ℃ for 1 to 3 hours, and in the second aging treatment subsequent to the first aging treatment, the sintered body may be heated at 450 to 700 ℃ for 1 to 3 hours. The aging treatment step may be performed continuously with the sintering step.

The sintered body can be rapidly cooled by the cooling step subsequent to the aging treatment step. The sintered body may be quenched in an inert gas such as Ar gas. The cooling rate of the sintered body may be, for example, 5 ℃/min to 100 ℃/min.

In the machining step, the size and shape of the sintered body can be adjusted by cutting, grinding, or the like. The sintered body (base material) obtained by the above method may not contain a heavy rare earth element. That is, the sintered body before the diffusion step may not contain a heavy rare earth element. The sintered body before the diffusion step may already contain a heavy rare earth element. The following diffusion step may be performed regardless of the presence or absence of the heavy rare earth element in the sintered body. However, the diffusion process is not essential.

In the case of manufacturing a permanent magnet containing a heavy rare earth element, a diffusion step may be performed. In the diffusion step, the heavy rare earth element or a compound thereof may be attached to the surface of the sintered body, and then the sintered body may be heated. For example, a compound such as a fluoride, an oxide, or a hydride of a heavy rare earth element may be attached to the surface of the sintered body. The sintered body may be heated in a vapor containing a heavy rare earth element. In the diffusion step, the heavy rare earth element diffuses from the surface of the sintered body to the inside, and the heavy rare earth element further diffuses to the surface of the main phase grains via the grain boundary.

A coating containing a heavy rare earth element may be applied to the surface of the sintered body. The composition of the coating material is not limited as long as the coating material contains a heavy rare earth element. The coating material may contain, for example, a simple substance of a heavy rare earth element, an alloy containing a heavy rare earth element, a fluoride, an oxide, or a hydride compound. The solvent (dispersion medium) contained in the dope may be a solvent other than water. For example, the solvent may be an organic solvent such as alcohol, aldehyde or ketone. The concentration of the heavy rare earth element in the dope is not limited.

The diffusion treatment temperature in the diffusion step may be 800 ℃ to 950 ℃. The diffusion treatment time may be 1 hour to 50 hours. When the diffusion treatment temperature and the diffusion treatment time are within the above ranges, the concentration distribution of the heavy rare earth element can be easily controlled, and the manufacturing cost of the permanent magnet can be reduced. The diffusion step may be performed as the aging treatment step described above.

After the diffusion step, the permanent magnet may be further subjected to a heat treatment. The heat treatment temperature after the diffusion step may be 450 ℃ to 600 ℃. The heat treatment time may be 1 hour to 10 hours. The magnetic properties (particularly, coercive force) of the finally obtained permanent magnet are easily improved by the heat treatment after the diffusion step.

The size and shape of the sintered body may be adjusted by cutting, grinding, or the like after the diffusion step.

The order of the heat treatment step, the processing step, and the diffusion step is not limited.

A part of the surface layer portion can be removed from the surface of the sintered body by etching. That is, the thickness of the surface layer portion can be adjusted by etching. A passive layer may be formed on the surface of the sintered body by oxidation or chemical surface treatment (chemical treatment) of the surface of the sintered body. The surface of the sintered body may be covered with a resin film. The corrosion resistance of the permanent magnet is further improved by forming a passive layer or a resin film.

The permanent magnet according to the present embodiment can be obtained by the above method.

The present invention is not limited to the above embodiments. For example, the R-T-B permanent magnet may be a hot-worked magnet.