JP5293662B2 - Rare earth magnet and rotating machine - Google Patents

Description

  The present invention relates to a rare earth magnet and a rotating machine.

  An RTB-based rare earth magnet containing a transition metal element T such as a rare earth element R, an iron element (Fe), or a cobalt element (Co) and a boron element B has excellent magnetic properties (see Patent Document 1 below). . However, since the rare earth magnet contains a rare earth element that is easily oxidized as a main component, the corrosion resistance tends to be low. Therefore, in order to improve the corrosion resistance of the rare earth magnet, a protective layer made of resin, plating or the like is often provided on the surface of the magnet body.

International Publication No. 2006/112403 Pamphlet

  However, even a rare-earth magnet having a protective layer formed on its surface does not necessarily have complete corrosion resistance. This is because, in a high temperature and high humidity environment, the water vapor permeates the protective layer and reaches the magnet body, thereby causing corrosion of the magnet body.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a rare earth magnet having excellent corrosion resistance. Moreover, an object of this invention is to provide the rotary machine which can maintain the outstanding performance over a long period of time.

  As a result of studying the corrosion mechanism of the magnet body due to water vapor, the present inventors have found that the hydrogen generated by the corrosion reaction is occluded by the R-rich phase existing at the grain boundary in the magnet body, thereby It was discovered that the corrosion progresses rapidly inside the magnet due to the acceleration of the change to hydroxide and the accompanying drop-out of the main phase particles due to volume expansion. The R-rich phase is an alloy phase containing at least the rare earth element R, having a higher R concentration (ratio of the number of atoms) than the crystal particles (main phase) and a lower B concentration than the crystal particles. means. R is, for example, Nd.

  Therefore, the present inventors have intensively studied a method for suppressing hydrogen occlusion by the R-rich phase at the grain boundary, and suppressing hydrogen occlusion by diffusing Al in the R-rich phase near the surface of the magnet body. The inventors have found that the corrosion resistance can be greatly improved, and have reached the following present invention.

The rare earth magnet of the present invention is a rare earth magnet including a crystal particle group of an R—Fe—B alloy containing a rare earth element R, and is included in a grain boundary triple point of crystal grains located on the surface portion of the rare earth magnet. rich phase, R, Cu, there is an alloy containing Co and Al, der sum is 13 atomic% or more content of Cu, Co and Al in the R-rich phase is, of Al in the R-rich phase The content rate is higher than the Al content rate in the crystal particles located in the surface portion . The crystal particle group means a plurality of crystal particles. In the said invention, it is preferable that the total value of the content rate of Co and Cu in the surface part of a rare earth magnet is higher than the total value of the content rate of Co and Cu in the center part of a rare earth magnet. In the present invention, there is an alloy containing R, Cu, Co and Al, and the total content of Cu, Co and Al is 13 atomic% or more, and an R-rich phase existing at a grain boundary triple point. However, it is preferable that it is unevenly distributed only on the surface portion of the rare earth magnet. In the rare earth magnet according to the present invention, after adhering Al alone, an Al alloy or an Al compound to the surface of a magnet body containing rare earth elements R, Fe, B, Cu and Co, the magnet body is 650 ° C. or lower. It is preferable to be manufactured through a heat treatment step.

  According to the present invention, the occlusion of hydrogen by the grain boundary phase of the rare earth magnet is suppressed, and the corrosion resistance of the rare earth magnet is improved.

  In the said invention, it is preferable that the total value of the content rate of Cu and Al in a crystal grain is 2 atomic% or less. By making the total content of Cu and Al not more than the above upper limit, not only corrosion resistance but also sufficient magnetic properties are imparted to the rare earth magnet.

  In the said invention, it is preferable that the ratio of the crystal grain group to the whole rare earth magnet is 85 volume% or more. Thereby, not only corrosion resistance but sufficient magnetic properties are imparted to the rare earth magnet.

  The rotating machine of the present invention includes the rare earth magnet of the present invention. A rotating machine including a rare earth magnet having excellent corrosion resistance can maintain excellent performance for a long period of time even when used in a harsh environment.

  According to the present invention, it is possible to provide a rare earth magnet having excellent corrosion resistance. Moreover, according to this invention, it becomes possible to provide the rotary machine which can maintain the outstanding performance over a long period of time.

FIG. 1 is a perspective view of a rare earth magnet according to an embodiment of the present invention. It is the II-II sectional view taken on the line of the rare earth magnet shown in FIG. It is the schematic diagram which expanded a part of surface part 40 of the rare earth magnet shown in FIG. FIG. 4 is a perspective view schematically showing a rotating machine according to an embodiment of the present invention. FIG. 5A is a distribution diagram of Al in the surface portion of the rare earth magnet of Example 1 created based on an analysis by an electron probe microanalyzer (EPMA), and FIG. FIG. 5C is a distribution diagram of Cu in the surface portion of the rare earth magnet of Example 1 prepared based on the analysis by EPMA, and FIG. 5C is a graph in the surface portion of the rare earth magnet of Example 1 prepared based on the analysis by EPMA. It is a distribution map of Co.

  Hereinafter, a preferred embodiment 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. In the drawings, the same elements are denoted by the same reference numerals, and some of the reference numerals of the same elements are omitted.

(Rare earth magnet)
As shown in FIGS. 1 to 3, the rare earth magnet 100 of the present embodiment includes a plurality of crystal particles 4 (main phase particles). The main phase of the rare earth magnet 100 is composed of crystal particles 4. The crystal particles 4 contain an R—Fe—B alloy as a main component. The R—Fe—B alloy is, for example, an R ₂ Fe ₁₄ B alloy. The rare earth magnet 100 includes a grain boundary phase located between the plurality of crystal grains 4. The grain boundary phase is composed of an R-rich phase, a B-rich phase, an oxide phase, a carbide phase, and the like. The B-rich phase is a phase in which the amount of B element in the phase is larger than the amount contained in the particles constituting the crystal. The oxide phase is a phase containing 20% or more of an oxygen element in the constituent elements of the phase. The carbide phase is a phase in which carbon elements are contained in an element ratio of 20% or more among constituent elements of the phase.

  The dimensions of the rare earth magnet 100 are not particularly limited, but the vertical length is 1 to 200 mm, the horizontal length is 1 to 200 mm, and the height is about 1 to 30 mm. The average particle size of the crystal particles 4 is not particularly limited, but is about 1 to 20 μm. The shape of the rare earth magnet 100 is not particularly limited, and may be a ring shape or a disk shape.

  The rare earth element R may be at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In particular, the rare earth element R is preferably at least one of Nd and Pr. Thereby, the saturation magnetic flux density and the coercive force of the rare earth magnet 100 are remarkably improved.

  The main phase and the grain boundary phase of the rare earth magnet 100 may include other elements such as Co, Cu, Al, Ni, Mn, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si, and Bi as necessary. May further be included.

  Cu, Co and Al are segregated in the R-rich phase contained in the grain boundary triple point 6 located on the surface portion 40 of the rare earth magnet 100, and an alloy containing R, Cu, Co and Al is formed. The grain boundary triple point means a grain boundary phase surrounded by three or more crystal grains 4. A part of Al contained in the R-rich phase at the grain boundary triple point 6 and Fe may form an alloy. That is, the grain boundary triple point 6 may include an alloy phase composed of Fe and Al. Hereinafter, an alloy containing R, Cu, Co, and Al is sometimes referred to as an “R—Cu—Co—Al alloy”.

  Each content of Cu, Co, and Al in the R-rich phase of the grain boundary triple point 6 located on the surface portion 40 of the rare earth magnet 100 is significantly higher than that of the main phase (crystal grain group). The total content of Cu, Co and Al in the R-rich phase at the grain boundary triple point 6 is 13 atomic% or more. In the case where an R-Cu-Co-Al alloy is present and the total content of Cu, Co and Al is 13 atomic% or more and an R-rich phase present at the grain boundary triple point 6 is Will be referred to as "R-Cu-Co-Al phase". In the R—Cu—Co—Al phase, the total content of Cu, Co, and Al is 88 atomic% or less.

  The R-Cu-Co-Al phase has a characteristic that it is difficult to occlude hydrogen. Therefore, even if the surface of the rare earth magnet is corroded by water vapor and hydrogen is generated, the R-rich phase inside the rare earth magnet is caused by the R—Cu—Co—Al phase located on the surface portion 40 of the rare earth magnet 100. Invasion and occlusion of hydrogen into the water are suppressed. As a result, the reaction between hydrogen and the R-rich phase is suppressed, and corrosion hardly proceeds from the surface of the rare earth magnet to the inside. The corrosion resistance of the R—Cu—Co—Al phase is believed to be due to the high corrosion potential of the R—Cu—Co—Al alloy. For example, an R—Cu—Co—Al alloy has a higher corrosion potential than Nd alone.

  In addition, when the R—Cu—Co—Al phase is distributed not only in the surface portion 40 of the rare earth magnet 100 but also in the entire interior of the rare earth magnet 100, there is a problem that the magnetic characteristics tend to deteriorate. Therefore, it is preferable that the R—Cu—Co—Al phase is unevenly distributed only on the surface portion 40 of the rare earth magnet 100. Specifically, the R—Cu—Co—Al phase is preferably unevenly distributed only in the region where the depth D from the outer surface of the rare earth magnet 100 is less than 500 μm. More preferably, the R—Cu—Co—Al phase is unevenly distributed only in a region where the depth D from the outer surface of the rare earth magnet 100 is 400 μm or less. This solves the above problem. The depth D corresponds to the thickness of the surface portion 40. In order to achieve both sufficient corrosion resistance and magnetic properties, the thickness D of the surface portion 40 is preferably 100 μm or more, and more preferably 200 μm.

  The total value of the Co and Cu contents in the surface portion 40 of the rare earth magnet 100 is preferably higher than the total value of the Co and Cu contents in the central portion of the rare earth magnet 100. In this case, the corrosion resistance of the rare earth magnet 100 tends to be improved.

  The total content of Cu and Al in the crystal particles 4 is preferably 2 atomic% or less. In other words, the total content of Cu and Al in the main phase of the rare earth magnet 100 is preferably 2 atomic% or less. When the Cu and Al content in the main phase is too high, the saturation magnetic flux density of the rare earth magnet 100 tends to deteriorate. These problems can be suppressed by setting the total content of Cu and Al to the upper limit or less. However, even if the total content of Cu and Al exceeds the above upper limit, the effect of the present invention is achieved.

  The proportion of the main phase composed of the crystal particles 4 is preferably 85% by volume or more with respect to the entire rare earth magnet 100. Thereby, sufficient magnetic properties are imparted to the rare earth magnet.

  The rare earth magnet 100 may further include a protective layer on the surface thereof as necessary. Any protective layer can be used without particular limitation as long as it is usually formed as a layer that protects the surface of the rare earth magnet. Examples of the protective layer include a resin layer formed by painting or vapor deposition polymerization method, a metal layer formed by plating or vapor phase method, an inorganic layer formed by coating method or vapor phase method, an oxide layer, a chemical conversion treatment layer, and the like. It is done.

(Rare earth magnet manufacturing method)
In the production of rare earth magnets, a raw material alloy is first cast to obtain an ingot. As the raw material alloy, an alloy containing rare earth elements R, Fe, B, Cu and Co may be used. The raw material alloy may further contain elements such as Co, Cu, Al, Ni, Mn, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si, and Bi as necessary. The chemical composition of the ingot may be adjusted according to the chemical composition of the main phase and the grain boundary phase of the rare earth magnet to be finally obtained.

  The ingot is roughly pulverized by a disk mill or the like to obtain an alloy powder having a particle size of about 10 to 100 μm. The alloy powder is pulverized by a jet mill or the like to obtain an alloy powder having a particle size of about 0.5 to 5 μm. The alloy powder is pressure-molded in a magnetic field. The strength of the magnetic field applied to the alloy powder during molding is preferably 800 kA / m or more. The pressure applied to the alloy powder during molding is preferably about 10 to 500 MPa. As the molding method, either a uniaxial pressing method or an isotropic pressing method such as CIP may be used. The obtained molded body is fired to form a sintered body. The baking temperature should just be about 1000-1200 degreeC. The firing time may be about 0.1 to 100 hours. You may perform a baking process in multiple times. The firing step is preferably performed in a vacuum or in an inert gas atmosphere such as Ar gas.

  It is preferable to apply an aging treatment to the sintered body. In the aging treatment, the sintered body may be heat-treated at about 450 to 950 ° C. In the aging treatment, the sintered body may be heat treated for about 0.1 to 100 hours. The aging treatment may be performed in an inert gas atmosphere. Such an aging treatment further improves the coercivity of the rare earth magnet. The aging treatment may be composed of a multi-step heat treatment process. For example, in the aging treatment comprising two stages of heat treatment, the sintered body may be heated at a temperature of 700 ° C. or higher and lower than the firing temperature for 0.1 to 50 hours in the first stage heat treatment step. In the second heat treatment step, the sintered body may be heated at 450 to 700 ° C. for 0.1 to 100 hours.

  The sintered body obtained by the above steps includes a main phase composed of a crystal particle group of an R—Fe—B based alloy and an R rich phase containing a rare earth element R as a main component. Further, a part of Cu, Co, and Fe also precipitates in the grain boundary phase.

  A magnet body having a desired size is cut out from the sintered body, and Al alone, an Al alloy, or an Al compound is attached to the surface of the magnet body. Examples of the Al adhesion method include a method in which a coating solution in which particles made of Al are dispersed is uniformly applied to the entire surface of the magnet body. The particle size of the Al particles attached to the surface of the magnet body is preferably 50 μm or less. When the particle size of the Al particles is too large, it becomes a problem that Al becomes difficult to diffuse into the magnet body. Note that Al may be attached to the surface of the magnet body by a technique such as plating or vapor phase.

  The magnet body with Al attached to the surface is heat-treated. As a result, Al thermally diffuses from the surface of the magnet body to the R-rich phase of the grain boundary phase of the magnet body, and Cu contained in the grain boundary phase inside the magnet body in a form induced by Al diffusion. Co moves to the surface layer of the magnet body, and an alloy of R, AlCu, and Co is formed. Since the R-Cu-Co-Al alloy has a lower melting point than the main phase, it segregates at the grain boundary triple point in the surface portion. As a result, the rare earth magnet of this embodiment is completed. The magnet body with Al attached to the surface is preferably heat treated at 650 ° C. or lower, more preferably 600 ° C. or lower. Thereby, it becomes easy to form the R—Cu—Co—Al phase only on the surface portion of the rare earth magnet. When the heat treatment temperature of the magnet body with Al deposited on the surface is higher than 650 ° C., the melting point of Al is about 660 ° C., so Al melts and the main phase of the magnet body (R—Fe—B system) May react to form an alloy. Also, if the heat treatment temperature of the magnet body with Al deposited on the surface is too high, Al diffuses not only to the R-rich phase at the grain boundary triple point on the surface of the magnet body but also to the entire magnet body. .

  It is preferable that the magnet body heated in the heat treatment is rapidly cooled at a cooling rate of 30 ° C./min or more. Thereby, it becomes easy to form the R—Cu—Co—Al phase only on the surface portion of the rare earth magnet.

  The diffusion distance D of Al from the surface of the magnet body, the total content of Cu, Co and Al in the R-rich phase at the grain boundary triple point, and the ratio of the main phase to the entire rare earth magnet are Cu, Each content of Co and Al, the amount of Al deposited on the surface of the magnet body, and the heat treatment temperature or heat treatment time of the magnet body with Al deposited on the surface can be appropriately controlled.

  It is preferable to apply the same aging treatment to the rare earth magnet as in the case of the sintered body described above. The coercive force of the rare earth magnet is further improved by the aging treatment. The aging treatment temperature is preferably not more than the heat treatment temperature required for thermal diffusion of Al. It is preferable to rapidly cool the rare earth magnet heated in the aging treatment at a cooling rate of 30 ° C./min or more. Thereby, the magnetic characteristics of the rare earth magnet are easily improved.

  After heat-treating the magnet body with Al attached to the surface, Al remaining on the surface of the rare earth magnet may be removed by polishing or etching. A protective layer may be formed on the surface of the rare earth magnet. Any protective layer can be used without particular limitation as long as it is usually formed as a layer that protects the surface of the rare earth magnet. Examples of the protective layer include a resin layer formed by painting or vapor deposition polymerization method, a metal layer formed by plating or vapor phase method, an inorganic layer formed by coating method or vapor phase method, an oxide layer, a chemical conversion treatment layer, and the like. It is done.

(Rotating machine)
FIG. 4 is an explanatory diagram showing the internal structure of the rotating machine (permanent magnet rotating machine) of the present embodiment. The rotating machine 200 of this embodiment is a permanent magnet synchronous rotating machine (SPM rotating machine), and includes a cylindrical rotor 50 and a stator 30 disposed inside the rotor 50. The rotor 50 is provided with a plurality of rare earth magnets 100 so that N poles and S poles are alternated along the inner circumferential surface of the cylindrical core 52 and the cylindrical core 52. The stator 30 has a plurality of coils 32 provided along the inner peripheral surface. The coil 32 and the rare earth magnet 100 are arranged to face each other.

  The rotating machine 200 includes the rare earth magnet 100 according to the above embodiment in the rotor 50. Since the rare earth magnet 100 is excellent in corrosion resistance, it is possible to sufficiently suppress a decrease in magnetic characteristics over time. Therefore, the rotating machine 200 can maintain excellent performance for a long time. The rotating machine 200 can be manufactured by a normal method using normal rotating machine parts for parts other than the rare earth magnet 100.

  The rotating machine 200 may be an electric motor (motor) that converts electrical energy into mechanical energy by the interaction between the field by the electromagnet generated by energizing the coil 32 and the field by the permanent magnet 100. Further, the rotating machine 200 may be a generator that converts mechanical energy into electrical energy by electromagnetic induction interaction between the field by the permanent magnet 100 and the coil 32.

  Examples of the rotating machine 200 that functions as an electric motor (motor) include a permanent magnet DC motor, a linear synchronous motor, a permanent magnet synchronous motor (SPM motor), a permanent magnet synchronous motor (IPM motor), and a reciprocating motor. Examples of the motor that functions as a reciprocating motor include a voice coil motor and a vibration motor. Examples of the rotating machine 200 that functions as a generator include a permanent magnet synchronous generator, a permanent magnet commutator generator, and a permanent magnet AC generator.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

Example 1
According to the powder metallurgy method, the composition is 22.5 wt% Nd-5.2 wt% Pr-2.7 wt% Dy-0.5 wt% Co-0.3 wt% Al-0.07 wt% Cu-1 An ingot with 0.0 wt% B-balance Fe was prepared. The coarse powder obtained by coarsely pulverizing the ingot was pulverized by a jet mill in an inert gas to obtain a fine powder having an average particle diameter of about 3.5 μm. The fine powder was filled into a mold and pressure molded in a magnetic field to obtain a molded body. After the molded body was fired in vacuum, an aging treatment was performed to obtain a sintered body. The sintered body was cut out and a magnet body having a size of 10 mm × 8 mm × 1 mm was produced.

  The surface of the magnet body was degreased and etched. A coating solution in which Al particles having an average particle diameter of 3 μm were dispersed was prepared. The coating solution was applied to the surface of the magnet body after etching by dip coating to form a coating film having a thickness of about 8 μm on the entire surface of the magnet body. This coating film was dried at 120 ° C. for 20 minutes.

  The magnet body having a coating film was heat-treated at 600 ° C. for 1 hour in an Ar atmosphere, and then rapidly cooled at 50 ° C./min to diffuse Al in the coating film into the magnet body. The magnet body after the heat treatment was aged at 540 ° C. for 1 hour in an Ar atmosphere, and then rapidly cooled at 50 ° C./min. The reaction product remaining on the surface of the magnet body after the aging treatment was removed by polishing, and the surface of the magnet body was etched to obtain the rare earth magnet of Example 1.

(Example 2)
The magnet body having the above-mentioned coating film was heat-treated at 570 ° C. for 1 hour in an Ar atmosphere, and Al in the coating film was diffused into the magnet body in the same manner as in Example 1 except that A rare earth magnet was produced.

(Example 3)
In Example 3, the magnet body having the above coating film was heat-treated at 540 ° C. for 1 hour in an Ar atmosphere to diffuse Al in the coating film into the magnet body. In Example 3, since this one heat treatment also serves as an aging treatment, unlike Example 1, no separate aging treatment was performed after the heat treatment. Except for these matters, the rare earth magnet of Example 3 was produced in the same manner as in Example 1.

(Comparative Example 1)
A rare earth magnet of Comparative Example 1 was produced in the same manner as in Example 1 except that the steps after the etching of the surface of the magnet body were not performed. That is, the rare earth magnet of Comparative Example 1 was produced without using Al.

[Analysis of composition]
Each rare earth magnet of Examples 1 to 3 and Comparative Example 1 was cut, and the element distribution on the polished cut surface was confirmed by EPMA. As an EPMA apparatus, JXA-8800 manufactured by JEOL was used. In EPMA, mapping of elements existing in a region (hereinafter referred to as “surface portion A”) in which the depth from the outer surface of the rare earth magnet is 0 to 100 μm and the width in the direction parallel to the outer surface is 100 μm. The R-rich phase was identified and the range of the 1 μm diameter spot of the phase was analyzed. The area of the surface portion A is 100 μm × 100 μm. Table 1 shows the content (atomic%) of each element in the main phase existing in the surface portion A of each rare earth magnet. Table 1 shows the content (atomic%) of each element in the R-rich phase contained in the grain boundary triple point existing in the surface portion A of each rare earth magnet. The content of each element in the main phase is an average value of the content of each element measured by any three main phase particles (crystal particles) in the surface portion A. The content of each element in the R-rich phase in the grain boundary triple point is an average value of the content of each element measured in each R-rich phase in any three grain boundary triple points in the surface portion A. In addition, since the composition of the main phase of the rare earth magnet of each Example was the same, Table 1 shows the composition of the main phase common to all Examples.

  A distribution diagram of Al in the surface portion A of Example 1 is shown in FIG. A white portion in FIG. 5A is a portion where Al is present. A distribution diagram of Cu in the surface portion A of Example 1 is shown in FIG. A white portion in FIG. 5B is a portion where Cu exists. A distribution diagram of Co in the surface portion A of Example 1 is shown in FIG. A white portion in FIG. 5C is a portion where Co exists.

  As a result of the analysis by EPMA, in each of the rare earth magnets of Examples 1 to 3, the ratio of the main phase composed of crystal particles of the R—T—B system alloy was 91% by volume with respect to the whole rare earth magnet. It was confirmed that there was. It was confirmed that a large amount of Al diffused in the R-rich phase at the grain boundary triple point at the surface portion of each rare earth magnet of Examples 1 to 3. Further, it was confirmed that Al at each grain boundary in Examples 1 to 3 hardly diffused into the main phase. In the surface portion of each rare earth magnet of Examples 1 to 3, it was confirmed that a larger amount of Cu and Co was present in the R-rich phase at the grain boundary triple point than in Comparative Example 1. As apparent from the comparison between FIG. 5A, FIG. 5B, and FIG. 5C, the portions where Al, Cu, and Co are present in the surface portion A coincide with each other. In the R-rich phase at each grain boundary triple point in A, it was confirmed that an alloy containing R, Al, Cu and Co was formed. It was found that Nd, Pr, and Fe were present in any of the R-rich phases at the grain boundary triple points of Examples 1 to 3. On the other hand, it was confirmed that Al did not diffuse into the R-rich phase at the grain boundary triple point at the surface portion of each rare earth magnet of Comparative Example 1.

  Each rare earth magnet was analyzed by laser irradiation type inductively coupled plasma mass spectrometry (LA-ICP-MS). In the analysis by LA-ICP-MS, mapping measurement was performed on the cross section of the rare earth magnet at a pitch of 20 μm, and the diffusion distance of Al from the magnet surface was measured. As a result of LA-ICP-MS, in Example 1, Al diffuses into a region where the depth from the outer surface of the rare earth magnet is 0 to 400 μm, and the concentrations of Cu, Co, and Al in that region are high. It was confirmed. In Example 2, it was confirmed that Al diffused into a region where the depth from the outer surface of the rare earth magnet was 0 to 200 μm, and the concentrations of Cu, Co, and Al were high in that region. In Example 3, it was confirmed that Al diffused into a region where the depth from the outer surface of the rare earth magnet was 0 to 100 μm, and the concentrations of Cu, Co, and Al were high in that region.

[Evaluation of corrosion resistance]
Corrosion resistance of each of the rare earth magnets of Examples 1 to 3 and Comparative Example 1 was evaluated by a pressure cooker test (PCT). In PCT, the amount of decrease in the weight of each rare earth magnet was measured after 300 hours from the installation of each rare earth magnet in an environment of 2 atm, temperature of 120 ° C., and humidity of 100% RH. Table 2 shows the weight loss (unit: mg / cm ² ) per unit surface area of each rare earth magnet.

  It was confirmed that each of the rare earth magnets of Examples 1 to 3 was excellent in corrosion resistance as compared with Comparative Example 1.

  Each rare earth magnet of Example 1 and Comparative Example 1 was tested in a hydrogen atmosphere at 100 ° C. and 0.1 MPa. In Comparative Example 1, the hydrogen partial pressure began to decrease after the rare earth magnet occluded hydrogen after 100 seconds. On the other hand, in Example 1, the rare earth magnet did not absorb hydrogen after 300 seconds, and the hydrogen partial pressure did not decrease.

[Evaluation of magnetic properties]
The residual magnetic flux density (Br) and coercive force (HcJ) of each of the rare earth magnets of Examples 1 to 3 and Comparative Example 1 were measured. Table 3 shows Br (unit: T) and HcJ (unit: kA / m) of each rare earth magnet.

  It was confirmed that each of the rare earth magnets of Examples 1 to 3 has a coercive force superior to that of Comparative Example 1.

  4 ... Crystal grain, 6 ... Grain boundary triple point, 30 ... Stator, 32 ... Coil, 40, A ... Surface part, 50 ... Rotor, 52 ... Core, 100 ... Rare earth magnet, 200 ... Rotating machine, D ... Surface thickness (Al diffusion distance).

Claims (7)

A rare earth magnet comprising a crystal particle group of an R—Fe—B alloy containing a rare earth element R,
An alloy containing R, Cu, Co and Al is present in the R-rich phase contained in the grain boundary triple point of the crystal grain located on the surface portion of the rare earth magnet,
Wherein Ri der Cu, the sum of the content of Co and Al 13 atomic% or more in the R-rich phase,
The content of Al in the R-rich phase is higher than the content of Al in the crystal particles located in the surface portion ;
Rare earth magnet. The total content of Cu and Al in the crystal particles is 2 atomic% or less,
The rare earth magnet according to claim 1. The proportion of the crystal particle group in the entire rare earth magnet is 85% by volume or more,
The rare earth magnet according to claim 1 or 2. The total content of Co and Cu in the surface portion of the rare earth magnet is higher than the total content of Co and Cu in the center of the rare earth magnet.
The rare earth magnet as described in any one of Claims 1-3. The alloy containing R, Cu, Co and Al is present, and the total content of Cu, Co and Al is 13 atomic% or more, and the R rich phase present at the grain boundary triple point is: Unevenly distributed only on the surface of the rare earth magnet,
The rare earth magnet according to any one of claims 1 to 4. Manufactured through a process of attaching Al alone, an Al alloy or an Al compound to the surface of a magnet body containing rare earth elements R, Fe, B, Cu and Co and then heat-treating the magnet body at 650 ° C. or lower. The
The rare earth magnet according to any one of claims 1 to 5. A rotating machine comprising the rare earth magnet according to any one of claims 1 to 6 .

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