JP6171662B2 - Rare earth magnet, electric motor, and device including electric motor - Google Patents

Description

  The present invention relates to a rare earth magnet, an electric motor, and an apparatus including the electric motor.

An R-T-B rare earth magnet (R is a rare earth element, T is Fe or Fe partially substituted by Co, and B is boron) having a tetragonal R ₂ T ₁₄ B compound as a main phase has excellent magnetic properties. It is known that the invention of 1984 is taken as an arrow (Patent Document 1). Among the R-T-B rare earth magnets that have been improved since then, a neodymium magnet is a high-performance permanent magnet having a maximum energy product at an operating temperature of about 100 ° C.

  R-T-B type rare earth magnets containing at least one of Nd, Pr, Dy, Ho, and Tb as the rare earth element R have a high proportion of anisotropy dependent on crystal magnetic anisotropy, and have a Curie temperature. Is about 300 ° C. Therefore, use in a high temperature environment is limited, and in order to use an R-T-B rare earth magnet for a special purpose, it is necessary to contain Dy or the like, which is a rare element and a rare element among rare earth metals. Not obtained (Patent Document 2). In such a situation, attempts to reduce the amount of Dy used have been actively made (Patent Document 3).

JP 59-46008 A JP 2012-151442 A JP2012-15169A

  However, if the amount of heavy rare earth such as Dy, which has a resource problem, is reduced, and if no heavy rare earth such as Dy is used at all, it is possible to realize a rare earth magnet having stable magnetic properties at high temperatures. It is difficult.

The present invention has been made in view of such problems, and in the fields of transportation equipment and industrial equipment, a heavy rare earth such as Dy, which can contribute to the improvement of the efficiency of an electric motor, particularly in terms of energy consumption. An object is to provide an R-T-B rare earth magnet that is not used.
Specifically, an R-T-B rare earth magnet that can maintain a maximum energy product even after exposure to high temperatures exceeding 150 ° C. and has excellent temperature cycle characteristics that repeats heating and cooling, an electric motor including the rare earth magnet, and It is an object of the present invention to provide an apparatus including the electric motor.

Therefore, the present invention provides an R- containing crystal grains containing a tetragonal R ₂ T ₁₄ B compound (where R is a rare earth element, T is an iron group element, and B is boron) as a main phase. In the TB rare earth magnet, a rare earth magnet in which shape memory alloy nanoparticles are dispersed at least inside crystal grains is provided.

In the RTB-based rare earth magnet according to the present invention, the shape memory alloy nanoparticles are contained in a dispersed state at least inside the crystal particles having a tetragonal R ₂ T ₁₄ B compound as a main phase. Since the shape memory alloy nanoparticles have a fine crystal structure capable of phase transformation without atom transfer, the maximum energy product is obtained after exposure to high temperature exceeding 150 ° C. without adding heavy rare earth such as Dy. An RTB-based rare earth magnet excellent in temperature cycle characteristics that can be maintained and repeats heating and cooling is obtained.

The present inventors speculate as follows about the coercivity maintaining mechanism that contributes to maintaining the shape of the second quadrant of the BH curve necessary for maintaining the maximum energy product after high temperature exposure. Under high temperature, the magnetic domain (corresponding to the whole crystal grain or formed inside the crystal grain) is reconstructed by the domain wall movement (specifically, the movement of the domain wall existing inside the crystal grain or the grain boundary phase). In this case, the shape memory alloy nanoparticles are distorted by a phase transformation that does not involve atom transfer. It is considered that the domain wall movement is suppressed by the stress caused by the distortion of the shape memory alloy nanoparticles, and the decrease in coercive force can be suppressed. In addition to the mechanism to counter such a decrease in coercive force, the distortion of shape memory alloy nanoparticles inside the crystal particles having a tetragonal R ₂ T ₁₄ B compound as a main phase allows the main phase to be dispersed. It acts as a pinning for the movement of atoms constituting the irreversible, it is considered that irreversible demagnetization can be reduced, and excellent temperature cycle characteristics can be obtained.
According to the present invention, there is provided an R-T-B system rare earth magnet that can reduce the amount of heavy rare earth such as Dy, which is a rare metal resource, and achieves the effects described above even if it is not added at all. be able to.

  In the present invention, the shape memory alloy nanoparticles are preferably composed of a Ni-based alloy. The Ni-based alloy has good compatibility with the RTB-based rare earth magnet among the shape memory alloys and is preferably used.

  Furthermore, this invention provides the electric motor provided with the said rare earth magnet as a magnetic pole. Since the electric motor according to the present invention includes the rare earth magnet as a magnetic pole, there is little decrease in efficiency during actual operation even when used in a high-temperature environment, and magnetism is caused because it has an effect of recovering magnetic characteristics when stopped. The number of cycles up to can be increased.

  Furthermore, this invention provides an apparatus provided with the said electric motor. Since the apparatus according to the present invention includes the above-described electric motor, it can maintain practicality in a high-temperature environment.

  According to the present invention, even after high temperature exposure exceeding 150 ° C., an R-T-B rare earth magnet that can maintain the maximum energy product and has excellent temperature cycle characteristics that repeats heating and cooling, and an electric motor including the rare earth magnet And a device including the electric motor can be provided.

FIG. 1 is an enlarged cross-sectional view schematically showing an RTB-based rare earth magnet according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

FIG. 1 is an enlarged cross-sectional view schematically showing an RTB-based rare earth magnet according to the present embodiment. The RTB-based rare earth magnet is composed of a plurality of crystal particles 1. The crystal particle 1 has a tetragonal R ₂ T ₁₄ B compound (where R is a rare earth element, T is an iron group element, and B is boron) as a main phase. A grain boundary phase 3 exists between the plurality of crystal grains 1. Shape memory alloy nanoparticles 2 are dispersed inside the crystal particles 1. The shape memory alloy nanoparticles 2 may be present in the grain boundary phase 3.

Regarding the R ₂ T ₁₄ B compound constituting the main phase of the crystal particle 1, R is a rare earth element and is a light rare earth element, a heavy rare earth element, or a combination thereof. Examples of R include Nd and Pr. Nd is preferable from the viewpoint of material cost. T is an iron group element, and Fe or a combination of Fe and Co is preferable. However, R and T are not limited to these specific examples. B is boron. In the rare earth magnet of the present embodiment, the content of each element with respect to the total mass is preferably as follows.

The content of R is preferably 20 to 45% by mass, more preferably 25 to 35% by mass, particularly 29.5 to 33% by mass, based on 100% by mass of the total amount of rare earth magnets. preferable.
The content of B is preferably 0.1 to 2.5% by mass, more preferably 0.5 to 1.5% by mass, based on 100% by mass of the total amount of the rare earth magnet, and 0.7 to It is particularly preferably 0.95% by mass.
The content of the shape memory alloy nanoparticles (however, the content excluding inevitable impurities) is preferably 0.5 to 7.0% by mass with 100% by mass of the rare earth magnet as a whole. It is more preferably 0 to 6.0% by mass, and particularly preferably 2.0 to 4.5% by mass.
T is substantially the remainder excluding the R, B, and shape memory alloy nanoparticles.

  The shape memory alloy nanoparticle 2 is an alloy having a composition known as a shape memory alloy, and an average particle diameter is a nano-order particle. If the average particle size is nano-order, the size distribution is not particularly limited, and the particle size distribution may have a plurality of peaks. The average particle diameter of the shape memory alloy nanoparticles 2 is preferably 10 to 500 nm, more preferably 50 to 400 nm, and still more preferably 100 to 350 nm. The shape memory alloy nanoparticles 2 have a fine crystal structure capable of undergoing phase transformation without atom transfer, and form at least fine crystal parts dispersed inside the crystal particles 2. The fine crystal part can utilize the phase transformation between the austenite phase (phase higher than the transformation temperature) and the martensite phase (phase lower than the transformation temperature).

The maximum energy product after exposure under high temperature can be maintained, and the effect of obtaining excellent temperature cycle characteristics is considered to be due to the following actions. Under high temperature, the magnetic domain (corresponding to the whole crystal particle 1 or formed inside the crystal particle 1) is domain wall moved (specifically, the domain wall existing inside the crystal particle 2 or the grain boundary phase 3). ), The shape memory alloy nanoparticles 2 are distorted by undergoing a phase transformation that does not involve atomic movement as described above, and the coercive force is reduced by the stress caused by the distortion of the shape memory alloy nanoparticles 2. It is considered that the decrease can be suppressed. Further, by dispersing the shape memory alloy nanoparticles 2 with distortion in the crystal particles 1 having a tetragonal R ₂ T ₁₄ B compound as a main phase, pinning can be performed against movement of atoms constituting the main phase. It is considered that irreversible demagnetization can be reduced and excellent temperature cycle characteristics can be obtained.

  The shape memory alloy preferably includes a magnetic metal capable of increasing the residual magnetic flux density as an essential component element, and is made of a Ni-based alloy from the viewpoint of improving compatibility with the R-T-B rare earth magnet. Is more preferable. Specifically, Ni-Ti, Ni-Ti-Co, and Ni-Ti-Cu are mentioned. The composition of these alloys is based on the total amount of the alloy. In Ni—Ti, Ni is 45 to 60 at% and Ti is the balance. In Ni—Ti—Co, Ni is 45 to 60 at% and Co is 0.5. ˜5 at%, Ti is the balance. In Ni—Ti—Cu, Ni is 45-60 at%, Cu is 3-12 at%, and Ti is the balance.

  Next, a preferred embodiment of an electric motor (for example, a motor) including the R-T-B rare earth magnet according to the present invention as a magnetic pole will be described. The electric motor according to this embodiment can be used as a motor for an electric vehicle (permanent magnet type synchronous motor). Specifically, the electric motor according to the present embodiment can be obtained by arranging the RTB-based rare earth magnet according to the present embodiment along the core of the rotor portion. More specifically, a cylindrical rotor and a stator disposed inside the rotor are provided. The rotor includes a cylindrical core and a plurality of R-T-B rare earth magnets provided so that N poles and S poles are alternately arranged along the inner peripheral surface of the cylindrical core. The stator has a plurality of coils provided along the outer peripheral surface. The coil and the R-T-B rare earth magnet are arranged so as to face each other.

  The electric motor according to the present embodiment includes the RTB-based rare earth magnet according to the present invention in the rotor, so that the content of heavy rare earth such as Dy in the magnetic pole is reduced or not contained at all. In use under the environment, it is possible to suppress a decrease in efficiency during actual operation and to increase the number of cycles to reach magnetization because the magnetic characteristics are restored when the vehicle is stopped. Therefore, it can be used for devices such as compressors, electric vehicles, hybrid vehicles, and fuel cell vehicles.

Hereinafter, preferred embodiments of the method for producing an R-T-B rare earth magnet according to the present invention will be described.
Examples of the method for producing the R-T-B rare earth magnet include a sintering method, and examples of the method for producing the raw material alloy include a strip casting method. Here, as an example of a suitable manufacturing method, a case where a raw material alloy is manufactured by a strip casting method will be described below.

  The manufacturing method of the RTB-based rare earth magnet according to the present embodiment includes (a) a raw material production step, (b) a shape memory alloy nanoparticle dispersion step, (c) a pulverization step, (d) a molding step, (e ) A firing step, and (f) a heat treatment step.

(A) Raw material production process The raw material production process includes a raw material 1 production process and a raw material 2 production process. The raw material 1 preparation step is a step of preparing shape memory alloy nanoparticles (raw material 1). The production method may be appropriately selected from electrochemical reduction methods, plasma gas evaporation methods, gas atomization methods, laser ablation methods, sputtering methods, and the like.
The raw material 2 preparation step prepares a molten metal mainly containing Nd, Fe, and B by heating the raw material (raw material 2) of the RTB-based rare earth magnet excluding the shape memory alloy nanoparticles to the melting temperature or higher. It is a process to do.

(B) Shape Memory Alloy Nanoparticle Dispersion Step The shape memory alloy nanoparticle dispersion step uses the raw material 1 and the raw material 2 to crystallize the shape memory alloy nanoparticles as a main phase of at least a tetragonal R ₂ T ₁₄ B compound. It is a step of dispersing inside the particles. In this step, the melting point T ₁ of the shape memory alloy nanoparticles, the heating temperature T ₂ for dissolving the constituent components of the R—T—B rare earth magnet excluding the shape memory alloy nanoparticles, and the cooling roll surface described later by optimizing the temperature T _3, it is possible to obtain a microstructure of the R-T-B rare earth magnet according to the present embodiment. Here, as a method for obtaining the fine structure of the RTB-based rare earth magnet according to the present embodiment by optimizing the relationship between the temperatures of T ₁ , T ₂ , and T ₃ , specifically, the following production method A , B.
(Manufacturing method A)
A melt of the raw material 2 is supplied to the cooling roll surface, in the process of thin strip by the material 2 melt is cooled is formed at temperatures T ₁ or less, and, while the raw material 2 is in a molten state, the shape A water vapor jet containing memory alloy nanoparticles (raw material 1) is sprayed onto the ribbon. As T ₃ the surface temperature of a portion (corresponding to the temperature of the above-mentioned chill roll surface) for blowing steam jet, by optimizing the condition setting of _{T 1, T 2, T 3} , the dispersion of the shape memory alloy nanoparticles To control.
(Manufacturing method B)
T _1> is in the relation of T _2, and, in the molten metal material 1 and material 2 are mixed, the shape memory alloy nanoparticles, T _1, T ₂ in isolated and stabilized are conditions range remains nanoparticles, to optimize the T _3. A desired ribbon can be manufactured by supplying the molten metal in which the raw material 1 and the raw material 2 are mixed to the cooling roll surface.

(C) Crushing step In this step, the ribbon obtained in the step (b) is crushed. Specifically, the ribbon obtained by the step (b) is pulverized in an inert gas atmosphere or in a hydrogen atmosphere as necessary while suppressing the progress of oxidation, or occluded with hydrogen (hydrogen embrittlement). The powder is then pulverized to obtain a fine powder (hereinafter referred to as “raw material fine powder”). This step includes a coarse pulverization step and a fine pulverization step. The two stages in which the fine pulverization process is performed after the coarse pulverization process are preferable, but may be one stage. The coarse pulverization step can be performed using, for example, a stamp mill, a jaw crusher, a brown mill, or the like. In the coarse pulverization step, the raw material alloy is pulverized until the average particle size is about several hundred μm to several mm.

  In the fine pulverization step, the coarse powder obtained in the coarse pulverization step is finely pulverized to produce a raw material fine powder having an average particle diameter of about several μm. The average particle diameter of the raw material fine powder may be set in consideration of the degree of growth of crystal grains after sintering. The fine pulverization can be performed using, for example, a jet mill.

(D) Molding step This step is a step of forming a molded body by molding the raw material fine powder obtained in the above step (c) in a magnetic field. Specifically, after forming the raw material fine powder into a mold arranged in an electromagnet, molding is performed by applying a magnetic field with an electromagnet and pressing the raw material fine powder while orienting the crystal axis of the raw material fine powder. I do. The molding in the magnetic field may be performed at a pressure of about 30 to 300 MPa in a magnetic field of 1000 to 1600 kA / m, for example.

(E) Firing step This step is a step of firing the molded body obtained in the step (d) to obtain a sintered body. After molding in a magnetic field, the compact can be fired in a vacuum or an inert gas atmosphere to obtain a sintered compact. Firing conditions are preferably set as appropriate according to conditions such as the composition of the molded body, the method of pulverizing the raw material fine powder, and the particle size, but may be performed at 1000 to 1100 ° C. for about 1 to 10 hours, for example.

(F) Heat treatment step This step is a step of aging treatment of the sintered body obtained in the step (e). Through this step, the width of the grain boundary phase formed between adjacent crystal grains and the composition thereof are determined. However, these fine structures are not controlled only by this process, but are determined by taking into consideration the various conditions of the above (e) sintering process and the state of the raw material fine powder. Therefore, the conditions such as the heat treatment temperature and time in this step may be set in consideration of the state of the microstructure of the sintered body obtained in the step (e). The heat treatment may be usually performed in a temperature range of 450 ° C. to 900 ° C., but after heat treatment at 700 to 900 ° C., preferably 750 to 850 ° C., 450 to 650 ° C., preferably 500 to 600 ° C. The heat treatment may be performed in two stages.

  The R-T-B rare earth magnet obtained by the step (e) is completely commercialized through the steps of processing, surface treatment, and magnetization depending on the application.

  As mentioned above, although this invention was demonstrated based on the said embodiment, embodiment is an illustration and various deformation | transformation and change are possible.

  Hereinafter, although the content of the present invention is explained in detail using an example and a comparative example, the present invention is not limited to the following examples.

<Production of R-T-B rare earth magnet>
(A) Raw material preparation step and (b) shape memory alloy nanoparticle dispersion step (production method A)
Raw material 1: A raw material composed of shape memory alloy nanoparticles having an average particle diameter of 240 nm and a raw material 2: an alloy containing Nd, Fe and B were weighed in predetermined amounts, respectively. The raw material 2 was heated and melted at a heating temperature (T ₂ ) shown in Table 1 in an electron beam heating and melting furnace to obtain a molten alloy. The obtained molten alloy was supplied along the cooling roll surface through a tundish. Crystallization progressed while the molten alloy was fed along the cooling roll surface, and an alloy ribbon was formed. The ribbon thickness and the surface temperature of the molten alloy supplied to the cooling roll surface were measured optically in a non-contact manner, and the position where the shape memory alloy nanoparticles were added was determined. A fluid consisting of shape memory alloy nanoparticles dispersed in an ultrapure aqueous solution is passed through a heating pipe, and a water vapor jet containing shape memory alloy nanoparticles of 0.3 to 0.8 MPa, 150 to 200 ° C. is used as described above. The shape memory alloy nanoparticles were dispersed in the ribbon by irradiation toward the determined position.

(Manufacturing method B)
Raw material 1: A raw material composed of shape memory alloy nanoparticles having an average particle diameter of 240 nm and a raw material 2: an alloy containing Nd, Fe and B were weighed in predetermined amounts, respectively. The raw material 2 was heated and melted at a heating temperature (T ₂ ) shown in Table 1 in an electron beam heating and melting furnace to obtain a molten alloy. The raw material 1 was mixed with the obtained molten alloy, supplied through a tundish along the cooling roll surface. Crystallization progressed while the molten alloy was fed along the cooling roll surface, and an alloy ribbon was formed. Shape memory alloy nanoparticles were dispersed in the ribbon.

(C) Grinding process (coarse grinding process)
Next, hydrogen embrittlement treatment was performed in which the obtained alloy ribbon was occluded with hydrogen, and the mixture was left in an Ar atmosphere at 600 ° C. for 1 hour, and then pulverized. Thereafter, the obtained pulverized product was cooled to room temperature under an Ar atmosphere.
(Fine grinding process)
Oleic acid amide was added as a pulverization aid to the obtained pulverized product, mixed, and then finely pulverized using a jet mill to obtain a raw material fine powder having an average particle diameter of about 2 to 3 μm.

(D) Molding Step The obtained raw material fine powder was molded under the conditions of an orientation magnetic field of 1200 kA / m and a molding pressure of 120 MPa in a low oxygen atmosphere to obtain a molded body.

(E) Firing step The obtained molded body was fired in vacuum at 1030 to 1050 ° C. for 3 hours, and then rapidly cooled to obtain a sintered body.

(F) Heat treatment process The obtained sintered body was subjected to two-stage heat treatment at 800 ° C and 500 ° C. The first stage of heat treatment at 800 ° C. (aging 1) is maintained at a constant temperature for 1 hour, and after heat release to 500 ° C., the second stage of heat treatment at 500 ° C. (aging 2) is maintained at a constant temperature for 3 hours. And heated.

From the R-T-B rare earth magnet obtained through the steps (a) to (f), a piece having a thickness of 1 mm, a length of 36 mm, and a width of 4 mm is cut out by the following method, and the maximum energy product (MOe) and The cycle demagnetization rate (%) at 140 ° C. and 170 ° C. was evaluated.
In addition, since preliminary examination was performed on the effect of adding shape memory alloy nanoparticles, and almost no size dependency was observed in the range of the average particle size of 100 to 350 nm, the shape memory alloy nanoparticles having an average particle size of 240 nm were used. Was used.

<Characteristic evaluation of R-T-B rare earth magnet>
A method for evaluating the maximum energy product and the cycle demagnetization rate of the R-T-B rare earth magnet will be described.
(Measurement of maximum energy product)
A small piece produced by the above method was used as an evaluation sample, and a BH curve was first recorded with a BH curve tracer at room temperature (25 ° C.). The maximum energy product (BH _max ) was calculated, and this was _defined as BH _max0 .
(Measurement of cycle demagnetization factor)
Next, the sample for evaluation was heated at 140 ° C. for 2 hours and returned to room temperature (one cycle). After this cycle was repeated 60 times, when the temperature of the sample for evaluation returned to room temperature, the residual magnetic flux was measured, and the measured value was BH _max1 . Similarly, the measured value of high temperature exposure at 170 ° C. was defined as BH _max2 . Cycle demagnetization _{D 170} in cycle demagnetization _{D 140} and 170 ° C. at 140 ° C., the following formulas (1) was calculated by (2).
_{D 140 = (BH max1 -BH max0} ) / BH max0 * 100 (%) ... (1)
_{D 170 = (BH max2 -BH max0} ) / BH max0 * 100 (%) ... (2)

(Examples 1 to 14 and Comparative Examples 1 to 8)
A Ni based shape memory alloy nanoparticles of the melting point T _1, using the components of the R-T-B rare earth magnet as a raw material except the shape memory alloy nanoparticles by the method A and the process B, the table in the following Table 1 An RTB-based rare earth magnet having the composition described above was produced. In Process B of Example 9-14 and Comparative Examples 1-5, the temperature of the cooling roll surface was _{T 3.} In addition, about content of each element shown in Table 1, R (Nd, Dy), T (Fe), and the constituent element (Ni, Ti, Co, Cu) of a shape memory alloy nanoparticle, a fluorescent X ray analysis And B was measured by ICP emission spectroscopy.

Table 1 shows the obtained maximum energy product value (BH _max0 ), the cycle demagnetization factor D _{140 at} 140 ° C., and the cycle demagnetization factor D ₁₇₀ at 170 ° C. for Examples 1 to 14 and Comparative Examples 1 to 8. Comparative Examples 1 to 5 are examples in which Ni and Ti do not have a shape memory alloy composition, Comparative Example 6 is an example that does not include raw material 1, and Comparative Examples 7 and 8 are replaced with raw material 1. This is an example including Dy.

For Examples 1 to 14, the maximum energy product obtained is almost equivalent to the value and Dy5% addition of Comparative Example 7, 170 ° C. cycle demagnetization D ₁₇₀ was superior I prefer the present Example product. The phase transformation between the austenite phase and the martensite phase has a pinning effect on the domain wall motion in the heating and cooling temperature cycle, and this phase transformation is reversible. It can be seen that the fine adjustment is based on a different effect. Looking at the results of Comparative Examples 1 to 5 in which Ni and Ti are not in the shape memory alloy nanoparticle composition, the results are different from the conventional composition optimization approaches, and the phase transformation of the shape memory alloy nanoparticles is effective. It is clear that it works. It should be noted that a typical Ni-Ti shape memory alloy has a function that enables the use of Dy addition effect and high temperature comparable to those known so far. Although two types of production methods for obtaining the microstructure of the present invention have been shown, there is no significant difference between the production methods.

<Evaluation of an electric motor including an R-T-B rare earth magnet as a magnetic pole>
Next, the R-T-B rare earth magnets of Example 1 and Comparative Examples 6 to 8 shown in Table 1 are incorporated into a permanent magnet type synchronous motor, and the change in efficiency at 10% load of the prototype motor is shown. evaluated. Assuming actual use in an electric vehicle, the evaluation was repeated for 50 cycles of an operation at an ambient temperature of 120 ° C. for 10 hours and then a 2-hour stop, and the efficiency was compared with the initial efficiency at 25 ° C. As a result, the reduction in efficiency was 8% when the rare earth magnet of Example 1 was incorporated, 15.2% for Comparative Example 6, 10.7% for Comparative Example 7, and 7.2% for Comparative Example 8. . As described above, even in an electric motor, the use amount of heavy rare earth such as Dy is reduced, and further, practicality in use under a high temperature environment can be expected without using it at all.

  In Examples 1 to 14, Dy is not actively used, but it is presumed that the same or higher effect can be obtained when Dy is added. Since the mechanism that exerts the effect of the present invention and the role played by the addition of Dy have different aspects and are considered to be largely independent, a higher performance magnet can be obtained even for a system to which Dy is added. Usefulness is high from the viewpoint.

DESCRIPTION OF SYMBOLS 1 ... Crystal particle, 2 ... Shape memory alloy nanoparticle, 3 ... Grain boundary phase

Claims (4)

R—T—B-based rare earth including crystal grains having a main phase of a tetragonal R ₂ T ₁₄ B compound (where R is a rare earth element, T is an iron group element, and B is boron) A rare earth magnet in which shape memory alloy nanoparticles are dispersed at least inside the crystal particles.   The rare earth magnet according to claim 1, wherein the shape memory alloy nanoparticles are made of a Ni-based alloy.   An electric motor comprising the rare earth magnet according to claim 1 as a magnetic pole.   An apparatus comprising the electric motor according to claim 3.

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