FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
RARE EARTH SINTERED MAGNET, METHOD OF MANUFACTURING RARE
EARTH SINTERED MAGNET, ROTOR, AND ROTATING MACHINE;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Title of Invention
RARE EARTH SINTERED MAGNET, METHOD OF MANUFACTURING RARE
EARTH SINTERED MAGNET, ROTOR, AND ROTATING MACHINE
5 Technical Field
[0001]
The present disclosure relates to a rare earth sintered magnet, a method of
manufacturing the rare earth sintered magnet, a rotor including the rare earth sintered
magnet, and a rotating machine including the rare earth sintered magnet.
10 Background Technology
[0002]
R-T-B system rare earth sintered magnets are magnets consisting primarily of a
rare earth element R, a transition metal element T such as Fe or Fe partly substituted
with Co, and boron B. The R-T-B system rare earth sintered magnets are used in
15 industrial motors and other applications, and their operating environment temperature
is over 100 deg C. Therefore, conventional R-T-B system rare earth sintered magnets
contain heavy rare earth elements RH such as Dy and Tb for high heat resistance.
However, there are concerns about the supply of the heavy rare earth elements RH
because their resources are unevenly distributed and their production is limited.
20 Means of reducing the use of the heavy rare earth elements RH include a grain boundary
diffusion method. For example, in Patent Document 1, a heavy rare earth element RH
is diffused into a grain boundary of an R-T-B system rare earth sintered magnet in
which neodymium oxyfluoride is dispersed in a grain boundary phase. This allows the
heavy rare earth element RH to diffuse into the grain boundary without being oxidized
25 in the grain boundary phase, thereby reducing the amount of scarce heavy rare earth
element RH used.
Citation List
Patent Document
[0003]
30 Patent Document 1:
Japanese unexamined patent publication 2011-82467
Summary of Invention
Technical Problem
[0004]
35 However, when the neodymium oxyfluoride containing F, which is not beneficial to
the magnetic properties, remains as a compound in the rare earth sintered magnet, the
contents of the rare earth elements R and Fe, which are responsible for the magnetic
properties, relatively decrease, and thus the magnetic properties deteriorate. The low
content of the neodymium oxyfluoride can suppress the deterioration of the magnetic
40 properties but does not allow the heavy rare earth elements RH to diffuse into the inside
of the rare earth sintered magnet. Thus, in the grain boundary diffusion method, it is
3
difficult to diffuse heavy rare earth elements RH into the inside of the rare earth
sintered magnet while suppressing the deterioration of the magnetic properties.
[0005]
The present disclosure is made to solve the above-described problem, and an object
5 thereof is to provide a rare earth sintered magnet that allows a heavy rare earth element
RH to diffuse deeper into the rare earth sintered magnet while suppressing the
deterioration of the magnetic properties, a method of manufacturing the rare earth
sintered magnet, a rotor including the rare earth sintered magnet, and a rotating
machine including the rare earth sintered magnet.
10 Solution to Problem
[0006]
A rare earth sintered magnet according to the present disclosure includes: a
plurality of regions of a main phase each having an R2Fe14B crystal structure containing
at least Nd as a rare earth element R; and a grain boundary phase formed among the
15 plurality of regions of the main phase and having Sm enriched portions in which Sm is
enriched by Sm substitution in a crystalline NdO phase and heavy rare earth element
RH enriched portions in which a heavy rare earth element RH is enriched at least on
part of peripheries of the Sm enriched portions.
[0007]
20 A method of manufacturing a rare earth sintered magnet according to the present
disclosure includes: a pulverization process of pulverizing an R-Fe-B system rare earth
magnet alloy containing Nd and Sm as rare earth elements R; a molding process of
molding a powder of the R-Fe-B system rare earth magnet alloy to produce a compact;
a sintering-and-aging process of sintering the compact at a temperature between 600
25 deg C and 1300 deg C and aging the compact at a temperature equal to or lower than
the sintering temperature to produce a sintered compact; and a grain boundary diffusion
process of adhering a heavy rare earth element RH to the sintered compact and
performing a heat treatment to diffuse the heavy rare earth element RH into a grain
boundary.
30 Advantageous Effects of Invention
[0008]
According to the present disclosure, there is provided the grain boundary phase
including the Sm enriched portions, in which Sm is enriched by the Sm substitution in
the crystalline NdO phase, and the heavy rare earth element RH enriched portions, in
35 which the heavy rare earth element RH is enriched at least on part of the peripheries
of the Sm enriched portions; this allows the heavy rare earth element RH to diffuse
deeper into the rare earth sintered magnet while suppressing the deterioration of the
magnetic properties.
Brief Description of Drawings
40 [0009]
Fig. 1 is a schematic diagram of a part of a rare earth sintered magnet according to
Embodiment 1.
4
Fig. 2 is a flowchart showing a procedure of a method of manufacturing a rare earth
sintered magnet according to Embodiment 2.
Fig. 3 is a schematic diagram showing an operation of a raw alloy production process 11
according to Embodiment 2.
5 Fig. 4A to Fig. 4E are diagrams obtained by EPMA analysis of cross sections of rare
earth sintered magnets manufactured by the method of manufacturing the rare earth
sintered magnet according to Embodiment 2.
Fig. 5A to Fig. 5E are diagrams obtained by EPMA analysis of cross sections of rare
earth sintered magnets manufactured by the method of manufacturing the rare earth
10 sintered magnet according to Embodiment 2.
Fig. 6 is a schematic cross-sectional view of a rotor according to Embodiment 3.
Fig. 7 is a schematic cross-sectional view of a rotating machine according to
Embodiment 4.
Description of Embodiments
15 [0010]
Embodiment 1
A rare earth sintered magnet 1 according to Embodiment 1 is an R-Fe-B system rare
earth sintered magnet in which the contained rare earth element R is mainly composed
of a light rare earth element RL and a heavy rare earth element RH. The light rare
20 earth element RL includes at least Nd and Sm. Another light rare earth element RL
may be included. The heavy rare earth element RH includes at least Dy or Tb.
[0011]
A rare earth sintered magnet 1 according to Embodiment 1 is described with
reference to Fig. 1. Fig. 1 is a schematic diagram of a part of the rare earth sintered
25 magnet 1. The rare earth sintered magnet 1 includes a main phase 2 having an
R2Fe14B crystal structure containing at least Nd as the rare earth element R and a grain
boundary phase 3 formed among a plurality of regions of the main phase 2. The grain
boundary phase 3 includes Sm enriched portions 4, in which Sm is enriched by Sm
substitution in a crystalline NdO phase, and heavy rare earth element RH enriched
30 portions 5, in which a heavy rare earth element RH is enriched at least on part of
peripheries of the Sm enriched portions 4.
[0012]
The main phase 2 is made of a crystal grain based on, for example, an Nd2Fe14B
crystal structure. The magnetic properties can be improved with the average crystal
35 grain size of the main phase 2 of, for example, less than 100 m. Another rare earth
element R, including Sm and the heavy rare earth element RH, may make a substitution
at some of Nd sites of the Nd2Fe14B crystal structure of the main phase 2.
[0013]
The grain boundary phase 3 includes the Sm enriched portions 4, in which Sm is
40 enriched by the Sm substitution in the crystalline NdO phase. As shown in Fig. 1, the
Sm enriched portions 4 are partially enriched grain boundary phase 3. The Sm
5
enriched portions 4 are dispersed throughout the grain boundary phase 3, not only in
the surface layer of the rare earth sintered magnet 1, but also in the center of the magnet.
[0014]
The grain boundary phase 3 includes the heavy rare earth element RH enriched
5 portions 5 at least on part of the peripheries of the Sm enriched portions 4. The heavy
rare earth element RH enriched portions 5 are portions of the grain boundary phase 3
in which the heavy rare earth element RH is more enriched than the other portions of
the grain boundary phase 3 including the Sm enriched portions 4, and the main phase
2. The heavy rare earth element RH enriched portion 5 may exist on at least a part of
10 the periphery of a Sm enriched portion 4 as shown in Fig. 1, or may exist so as to
surround the entire periphery of a Sm enriched portion 4.
[0015]
Next, the operation and effect of the present embodiment are described. For
example, in Patent Document 1, F, which is an element not related to magnetic
15 properties, remains as a compound inside the rare earth sintered magnet. As a result,
the contents of the rare earth element R and Fe, which are responsible for magnetic
properties, relatively decrease, which deteriorates the magnetic properties. In
contrast, in the Sm enriched portions 4, Sm, which is a light rare earth element like Nd,
makes a substitution at some of the Nd sites of the crystal structure of the NdO phase
20 in the grain boundary phase 3. Consequently, Sm substitution is made in the
crystalline NdO phase without adding elements not related to the magnetic properties,
and this suppresses the deterioration of the magnetic properties.
[0016]
In the conventional grain boundary diffusion method, a difference in the content of
25 the heavy rare earth element RH at the interface between the main phase and the grain
boundary phase serves as a driving force to diffuse the heavy rare earth element RH
into the main phase. This consumes the heavy rare earth element RH that is diffused
in the grain boundary phase. Furthermore, when the substitution by the heavy rare
earth element RH is made in the R2Fe14B crystal structure of the main phase, the
30 residual magnetic flux density decreases due to the antiparallel coupling of the magnetic
moment of the heavy rare earth element RH and that of Fe. In contrast, the rare earth
sintered magnet 1 according to the present embodiment includes the grain boundary
phase 3 having the heavy rare earth element RH enriched portions 5 in which the heavy
rare earth element RH is enriched at least on part of the peripheries of the Sm enriched
35 portions 4. This is considered to be a result of selective diffusion of the heavy rare
earth element RH into at least a part of the grain boundary phase 3 on the peripheries
of the Sm enriched portions 4 in a grain boundary diffusion process 31. Thus, the
selective diffusion of the heavy rare earth element RH into the grain boundary on the
peripheries of the Sm enriched portions 4 suppresses the permeation of the heavy rare
40 earth element RH into the main phase 2. This suppresses the deterioration of the
magnetic properties. Furthermore, the heavy rare earth element RH, which
permeates the main phase to be consumed wastefully in the conventional method,
6
diffuses in the grain boundary phase 3; this allows the heavy rare earth element RH to
diffuse deeper into the rare earth sintered magnet 1 than with the conventional grain
boundary diffusion method.
[0017]
5 The Sm enriched portions 4 are dispersed throughout the grain boundary phase 3,
not only in the surface layer of the rare earth sintered magnet 1, but also in the center
of the magnet. Thus, the heavy rare earth element RH on the peripheries of the Sm
enriched portions 4, which are dispersed from the surface layer to the center of the rare
earth sintered magnet 1, selectively diffuses to the grain boundary. This reduces the
10 heavy rare earth element RH staying in the grain boundary phase 3 including a multiple
grain junction phase, and thus allows the heavy rare earth element RH to diffuse deeper
into the rare earth sintered magnet 1 than with the conventional grain boundary
diffusion method.
[0018]
15 As described above, the rare earth sintered magnet 1 according to the present
embodiment includes the grain boundary phase 3 having the Sm enriched portions 4, in
which Sm is enriched by the Sm substitution in the crystalline NdO phase, and the
heavy rare earth element RH enriched portions 5, in which the heavy rare earth element
RH is enriched at least on part of the peripheries of the Sm enriched portions 4; this
20 allows the heavy rare earth element RH to diffuse deeper into the rare earth sintered
magnet 1 while suppressing the deterioration of the magnetic properties. In addition,
by allowing the heavy rare earth element RH to diffuse deeper into the rare earth
sintered magnet 1, the grain boundary diffusion speed is increased; this shortens the
grain boundary diffusion time, saves the heavy rare earth element RH, and reduces the
25 coercive force difference between the surface layer and center of the rare earth sintered
magnet 1.
[0019]
Note that an excessive Sm content may relatively decrease the content of Nd, which
is an element having a high magnetic anisotropy constant and a high saturated
30 magnetic polarization, and thus deteriorates the magnetic properties. Thus, the
composition ratio of Nd and Sm in the rare earth sintered magnet 1 should be Nd  Sm,
and the Sm content should be higher in the grain boundary phase 3 than in the main
phase 2. This reduces the amount of Sm that makes substitution at the Nd sites of the
Nd2Fe14B crystal structure in the main phase 2, and thus suppresses the deterioration
35 of the magnetic properties of the main phase 2.
[0020]
The heavy rare earth element RH present in the main phase 2 contributes to the
improvement of the coercive force but decreases the residual magnetic flux density
because the magnetic moment of the heavy rare earth element RH and the magnetic
40 moment of Fe are coupled antiparallel to each other. Thus, by making the content of
the heavy rare earth element RH higher in the grain boundary phase 3 than in the main
7
phase 2, the scarce heavy rare earth element RH can be saved while maintaining the
magnetic properties with high residual magnetic flux density and high coercive force.
[0021]
La may be contained as a light rare earth element RL. When the heavy rare earth
5 element RH is diffused into the grain boundary in the rare earth sintered magnet 1
containing La, La in the grain boundary phase 3 is substituted with the heavy rare
earth element RH. This allows the heavy rare earth element RH to diffuse deeper into
the rare earth sintered magnet 1.
[0022]
10 Additive elements that improve magnetic properties may be contained. The
additive elements are, for example, one or more elements selected from Al, Cu, Co, Zr,
Ti, Ga, Pr, Nb, Mn, Gd, and Ho.
[0023]
Embodiment 2
15 The present embodiment relates to a method of manufacturing the rare earth
sintered magnet 1 according to Embodiment 1. The description is made with reference
to Fig. 2 and Fig. 3. Fig. 2 is a flowchart showing a procedure of the method of
manufacturing the rare earth sintered magnet 1 according to the present embodiment.
Fig. 3 is a schematic diagram showing an operation of a raw alloy production process 11.
20 Hereinafter, the raw alloy production process 11, a sintered magnet production process
21, and a grain boundary diffusion process 31 are described separately.
[0024]
[Raw alloy production process 11]
As shown in Fig. 2 and Fig. 3, the raw alloy production process 11 includes: a melting
25 process 12 in which a raw material of a rare earth magnet alloy 47 is heated to a
temperature of 1000 K or higher and melted; a primary cooling process 13 in which the
raw material in a molten state is cooled on a rotator 44 to produce a solidified alloy 45;
and a secondary cooling process 14 in which the solidified alloy 45 is further cooled in a
tray 46.
30 [0025]
In the melting process 12, the raw material of the rare earth magnet alloy 47 is
melted to produce a molten alloy 42. The raw material contains Nd, Fe, B, and Sm.
La, Dy, Tb may be contained, and one or more elements selected from Al, Cu, Co, Zr, Ti,
Ga, Pr, Nb, Mn, Gd, and Ho may be contained as additive elements. As exemplified in
35 Fig. 3, in an atmosphere containing an inert gas such as Ar or in a vacuum, the raw
material of the rare earth magnet alloy 47 is heated to a temperature of 1000 K or higher
in a crucible 41 and melted to produce the molten alloy 42.
[0026]
In the primary cooling process 13, as exemplified in Fig. 3, the molten alloy 42 is
40 poured into a tundish 43 and rapidly cooled on the rotator 44, so that the solidified alloy
45 thinner than an ingot alloy is produced from the molten alloy 42. In Fig. 3, a single
roll is exemplified as the rotator 44; however, twin rolls, a rotary disk, a rotary cast
8
cylinder, etc. may be used for rapid cooling by making contact therewith. For efficient
production of the thin solidified alloy 45, the cooling rate in the primary cooling process
13 should be 10 to 107 deg C/sec, preferably 103 to 104 deg C/sec. The thickness of the
solidified alloy 45 is between 0.03 mm and 10 mm. The molten alloy 42 solidifies from
5 the point where it contacts the rotator 44, and crystals grow in a columnar or needlelike shape in the direction of thickness from the surface of contact with the rotator 44.
[0027]
In the secondary cooling process 14, the solidified alloy 45 is cooled in the tray 46 as
exemplified in Fig. 3. When entering the tray 46, the thin solidified alloy 45 is broken
10 into scale-like pieces of the rare earth magnet alloy 47 and cooled. Although the scalelike pieces of the rare earth magnet alloy 47 are exemplified, ribbon-like pieces of the
rare earth magnet alloy 47 are produced depending on the cooling rate. For producing
the rare earth magnet alloy 47 with the optimum rare earth magnet alloy internal
structure, the cooling rate in the secondary cooling process 14 should be 0.01 to 105 deg
C/sec, preferably 0.1 to 102 15 deg C/sec.
[0028]
Through the above-described raw alloy production process 11, the R-Fe-B system
rare earth magnet alloy 47 containing at least Nd and Sm as rare earth elements R is
produced.
20 [0029]
[Sintered magnet production process 21]
As shown in Fig. 2, the sintered magnet production process 21 includes: a
pulverization process 22 in which the rare earth magnet alloy 47 produced in the abovedescribed raw alloy production process 11 is pulverized; a molding process 23 in which
25 the pulverized rare earth magnet alloy 47 is molded to produce a compact; a sinteringand-aging process 24 in which the compact is sintered and aged.
[0030]
The pulverization process 22 is to pulverize the R-Fe-B system rare earth magnet
alloy 47, which contains Nd and Sm as rare earth elements R and is produced in the
30 above-mentioned raw alloy production process 11, and to produce a powder with a grain
diameter of no more than 200 m, preferably from 0.5 m to 100 m. The rare earth
magnet alloy 47 is pulverized by using, for example, an agate mortar, a stamp mill, a
jaw crusher, a jet mill, or the like. To obtain a powder with a small particle diameter,
the pulverization process 22 should be performed in an atmosphere containing inert gas.
35 The pulverization of the rare earth magnet alloy 47 in an atmosphere containing inert
gas can also prevent oxygen from entering the powder. If the atmosphere in which the
pulverization is performed does not affect the magnetic properties of the magnet, the
pulverization of the rare earth magnet alloy 47 may be performed in the air.
[0031]
40 In the molding process 23, the powder of the rare earth magnet alloy 47 is molded
to produce a compact. For example, in the molding, only the powder of the rare earth
magnet alloy 47 may be press-molded, or a mixture of the powder of the rare earth
9
magnet alloy 47 and an organic binder may be press-molded. The molding may be
performed while applying a magnetic field. The magnetic field to be applied is 2 T, for
example.
[0032]
5 The sintering-and-aging process 24 includes a sintering process and an aging
process. In the sintering process, the compact is heat-treated. The sintering process
is performed at a temperature of 600 deg C to 1300 deg C, for 0.1 hours to 100 hours,
preferably 1 hour to 20 hours. Hot working may be added to provide magnetic
anisotropy and improve coercive force. In the aging process, the compact is heat10 treated at a temperature lower than that of the sintering process to produce a sintered
compact. The aging process is performed at a temperature lower than that of the
sintering process, for example, 300 deg C to 1000 deg C, for 0.1 hours to 100 hours,
preferably 1 hour to 20 hours. The aging process may be divided into two stages, for
example, a primary aging process and a secondary aging process. In this case, the
15 temperature of the primary aging process is lower than the sintering temperature,
preferably from 300 deg C to 1000 deg C. The time is from 0.1 hours to 100 hours,
preferably from 1 hour to 20 hours. The secondary aging process is performed at a
temperature lower than that of the primary aging process for 0.1 hours to 100 hours,
preferably 1 hour to 20 hours. The sintering-and-aging process 24 should be performed
20 in an atmosphere containing inert gas or in a vacuum to suppress oxidation. This
process may be performed while applying a magnetic field.
[0033]
The sintering-and-aging process 24 enables to produce the sintered compact
provided with the plurality of regions of the main phase 2 each having the R2Fe14B
25 crystal structure containing at least Nd as the rare earth element R, and the grain
boundary phase 3 having the Sm enriched portions 4 in which Sm is enriched by Sm
substitution in the crystalline NdO phase.
[0034]
[Grain boundary diffusion process 31]
30 As shown in Fig. 2, the grain boundary diffusion process 31 includes an adhesion
process 32 for adhering the heavy rare earth element RH to the sintered compact
produced in the sintered magnet production process 21 to produce a diffusion precursor,
and a diffusion process 33 for heat-treating the diffusion precursor to diffuse the heavy
rare earth element RH into the grain boundary. In the diffusion process 33, the heavy
35 rare earth element RH is selectively diffused into at least a part of the grain boundary
phase 3 on the peripheries of the Sm enriched portions 4. In the grain boundary
diffusion process 31, a known grain boundary diffusion method may be used. Various
techniques have been proposed for the grain boundary diffusion method depending on
the form of supply of the heavy rare earth element RH; typical examples thereof include
40 a coating diffusion method, a sputtering diffusion method, and a vapor diffusion method.
The grain boundary diffusion process 31 may be performed simultaneously with the
sintering-and-aging process 24.
10
[0035]
The grain boundary diffusion process 31 using the coating diffusion method is
described. In the adhesion process 32, a slurry prepared by mixing a powdery heavy
rare earth element RH compound with water or an organic solvent is adhered to the
5 surface of the sintered compact to produce a diffusion precursor. The adhesion is
performed by spraying, dip coating, spin coating, screen printing, electrodeposition, or
the like. In the diffusion process 33, the heavy rare earth element RH is diffused into
the inside of the diffusion precursor by heat-treating the diffusion precursor at a
temperature equal to or lower than that of the sintering process. The heat treatment
10 is performed at a temperature lower than that of the sintering process, for example, 300
deg C to 1000 deg C, for 0.1 hours to 100 hours, preferably 1 hour to 20 hours.
[0036]
The grain boundary diffusion process 31 using the sputtering diffusion method is
described. In the adhesion process 32, a thin film of an elemental metal or alloy
15 composition of the heavy rare earth element RH is formed on the surface of the sintered
compact in a dry environment to produce the diffusion precursor. In the diffusion
process 33, the heavy rare earth element RH is diffused into the inside of the diffusion
precursor by heat-treating the diffusion precursor at a temperature equal to or lower
than that of the sintering process. The heat treatment is performed at a temperature
20 lower than that of the sintering process, for example, 300 deg C to 1000 deg C, for 0.1
hours to 100 hours, preferably 1 hour to 20 hours.
[0037]
The grain boundary diffusion process 31 using the vapor diffusion method is
described. In the adhesion process 32, the sintered compact and a supply source of the
25 heavy rare earth element RH are placed in a vacuum furnace. In the diffusion process
33, the heavy rare earth element RH is diffused into the inside of the diffusion precursor
by heat-treating the diffusion precursor at a temperature equal to or lower than that of
the sintering process. In the heat treatment, the heavy rare earth element RH is
supplied to the diffusion precursor through a gas phase by vacuum heating. The heat
30 treatment is performed at a temperature lower than that of the sintering process, for
example, 600 deg C to 900 deg C, for 0.1 hours to 100 hours, preferably 1 hour to 20
hours. The vapor diffusion method can shorten the time of the grain boundary
diffusion process 31 because the adhesion process 32 and the diffusion process 33 of the
heavy rare earth element RH can be performed at the same time.
35 [0038]
The grain boundary diffusion process 31 enables the production of the rare earth
sintered magnet 1 including the grain boundary phase 3 having the heavy rare earth
element RH enriched portions 5 in which the heavy rare earth element RH is enriched
at least on part of the peripheries of the Sm enriched portions 4. In addition, in a 10
40 mm thick rare earth sintered magnet 1 produced by the manufacturing method
according to the present embodiment, the coercive force difference between the surface
layer and the center of the rare earth sintered magnet 1 was 20% or less. This is
11
thought to be the result of the diffusion of the heavy rare earth element RH into the
inside of the rare earth sintered magnet 1, resulting in a smaller coercive force
difference between the surface layer and the center of the rare earth sintered magnet 1.
[0039]
5 As described above, in the manufacturing method of the rare earth sintered magnet
1 according to the present embodiment, the R-Fe-B system rare earth magnet alloy 47
containing Nd and Sm as the rare earth elements R is pulverized, and then, through
the sintering-and-aging process 24, the compact of the powder of the R-Fe-B system rare
earth magnet alloy 47 is made into the sintered compact including the Sm enriched
10 portions 4, in which Sm is enriched in a part of the grain boundary phase 3, and the
heavy rare earth element RH is diffused into the sintered compact at the grain boundary.
This enables the production of the rare earth sintered magnet 1 including the grain
boundary phase 3 having the heavy rare earth element RH enriched portions 5, in which
the heavy rare earth element RH is enriched at least on part of the peripheries of the
15 Sm enriched portions 4. This allows the heavy rare earth element RH to diffuse deeper
into the rare earth sintered magnet 1 while suppressing the deterioration of the
magnetic properties.
[0040]
When a fluoride powder is mixed with the rare earth magnet alloy, as in Patent
20 Document 1, for example, the rare earth magnet alloy and the fluoride powder may not
be mixed uniformly. In contrast, in the manufacturing method of the rare earth
sintered magnet 1 according to the present embodiment, the raw material of the rare
earth magnet alloy 47 containing Sm is melted to produce the molten alloy 42 in the
melting process 12 of the raw alloy production process 11. Thus, elements such as Nd,
25 Fe, and B are uniformly mixed with Sm. This enables the production of the rare earth
sintered magnet 1 in which the Sm enriched portions 4 are uniformly dispersed
throughout the grain boundary phase 3, not only in the surface layer of the rare earth
sintered magnet 1, but also in the center of the magnet.
[0041]
30 The manufacturing method of the rare earth sintered magnet 1 according to the
present embodiment does not form a new compound such as neodymium oxyfluoride in
the grain boundary phase, but forms the Sm enriched portions 4, in which Sm, which is
a light rare earth element like Nd, is enriched and makes substitution at some of the
Nd sites of the crystal structure of the NdO phase of the grain boundary phase 3
35 generated in the process of the sintered magnet production process 21 described above.
This suppresses the deterioration of the magnetic properties.
[0042]
In the molding process 23, the press-molding is exemplified to produce the compact,
but a heat-molding of a mixture of powder of the rare earth magnet alloy 47 and a resin
40 may be used. The resin may be a thermosetting resin such as an epoxy resin, or a
thermoplastic resin such as a polyphenylene sulfide resin.
[0043]
12
The sintered compact described above may be produced by a one-alloy method or a
two-alloy method, and the rare earth sintered magnet 1 may be produced by diffusing
the heavy rare earth element RH into the grain boundary of the sintered compact.
[0044]
5 The addition of La to the raw material of the rare earth magnet alloy 47 produces a
sintered compact with a higher content of La in the grain boundary phase 3 than in the
main phase 2. When the heavy rare earth element RH is diffused into the grain
boundary of this sintered compact, the grain boundary diffusion is promoted because La
is substituted with the heavy rare earth element RH. This allows the heavy rare earth
10 element RH to diffuse deeper into the rare earth sintered magnet 1 while suppressing
the deterioration of the magnetic properties.
[0045]
Next, the evaluation results of the magnetic properties of the rare earth sintered
magnet 1 produced by the manufacturing method according to the present embodiment
15 are described with reference to Table 1. Table 1 summarizes the results of evaluating
the magnetic properties of the samples of Examples 1 to 12 and Comparative Examples
1 to 8, which are rare earth sintered magnets 1 having different contents of Sm, La, Dy,
and Tb (Dy and Tb being the heavy rare earth elements RH) and having different
thicknesses. The coercive force difference in Fig. 4 is a value obtained by subtracting
20 the coercive force of a 7 mm thick magnet from the coercive force of a 1.75 mm thick
magnet.
[0046]
Table 1: Evaluation results of magnetic properties of rare earth sintered magnets 1
25
30
35
[0047]
40 The magnetic properties were evaluated by measuring the residual magnetic flux
density and coercive force of each sample using a pulse excitation type B-H curve tracer.
The maximum applied magnetic field by the B-H curve tracer is 5 T or higher, at which
13
the sample is completely magnetized. Instead of the pulse excitation type B-H curve
tracer, a DC recording magnetic flux meter, which is called a direct current type B-H
curve tracer, a vibrating sample magnetometer (VSM), a magnetic property
measurement system (MPMS), a physical property measurement system (PPMS), etc.
5 may be used if they can generate a maximum applied magnetic field of 5 T or more.
The measurements were performed in an atmosphere containing an inert gas such as
nitrogen, and evaluation was performed at room temperature. With respect to the
shape of each sample, the 7 mm thick magnet sample has a cube shape, and its length,
width, and height are all 7 mm. The 1.75 mm thick magnet sample is a magnet
10 processed to 7 mm in length, 7 mm in width, and 1.75 mm in height; four samples were
stacked to form a 7 mm cube and measured.
The measurement error was +/-1%.
[0048]
Comparative Example 1 and Comparative Example 2 are samples produced
15 according to the above-described manufacturing method using Nd, Fe, and B as the raw
materials of the rare earth magnet alloy so that the general formula will be Nd-Fe-B;
the grain boundary diffusion process 31 was not performed. The magnet thickness of
Comparative Example 1 is 1.75 mm, and that of Comparative Example 2 is 7 mm. The
magnetic properties of these samples were evaluated by the methods described above.
20 The residual magnetic flux densities of Comparative Examples 1 and Comparative
Example 2 were 1.39 T. The coercive forces were 1500 kA/m and 1502 kA/m,
respectively. The coercive force difference was -2 kA/m, which is a level of
measurement error. Since the grain boundary diffusion process 31 was not performed
for Comparative Example 1 and Comparative Example 2, there is little difference in
25 coercive force depending on magnet thickness.
[0049]
Comparative Example 3 and Comparative Example 4 are samples produced
according to the above-described manufacturing method using Nd, Sm, La, Fe, and B as
the raw materials of the rare earth magnet alloy so that the general formula will be (Nd,
30 Sm, La)-Fe-B; the grain boundary diffusion process 31 was not performed. The magnet
thickness of Comparative Example 3 is 1.75 mm, and that of Comparative Example 4 is
7 mm. The magnetic properties of these samples were evaluated by the methods
described above. The residual magnetic flux density of Comparative Example 3 was
1.36 T, and that of Comparative Example 4 was 1.37 T. The coercive forces were 1428
35 kA/m and 1425 kA/m, respectively. The coercive force difference was 3 kA/m, which is
a level of measurement error. Since the grain boundary diffusion process 31 was not
performed for Comparative Example 3 and Comparative Example 4, there is little
difference in coercive force due to magnet thickness.
[0050]
40 Comparative Example 5 and Comparative Example 6 are samples in which Dy was
diffused into the grain boundaries according to the above-described manufacturing
method using Nd, Fe, and B as the raw materials of the rare earth magnet alloy so that
14
the general formula will be (Nd, Dy)-Fe-B. The magnet thickness of Comparative
Example 5 is 1.75 mm, and that of Comparative Example 6 is 7 mm. The magnetic
properties of these samples were evaluated by the methods described above. The
residual magnetic flux density of Comparative Example 5 was 1.34 T, and that of
5 Comparative Example 6 was 1.33 T. Comparisons of these results with those of
Comparative Example 1 and Comparative Example 2 show that the addition of Dy
reduced the residual magnetic flux density. The coercive forces were 1941 kA/m and
1720 kA/m, respectively. The coercive force difference was 221 kA/m. These results
suggest that Dy was not sufficiently diffused into the center of the magnet in
10 Comparative Example 6, which is a 7 mm thick magnet, resulting in a difference in
coercive force compared to Comparative Example 5, which is a 1.75 mm thick magnet.
Compared to Comparative Example 1 and Comparative Example 2, the coercive forces
were improved but the residual magnetic flux densities were reduced. This is because
the diffusion of Dy into the grain boundaries improved the coercive forces, but the
15 permeation of Dy into the main phase 2 lowered the residual magnetic flux densities.
[0051]
Comparative Example 7 and Comparative Example 8 are samples in which Tb was
diffused into the grain boundaries according to the above-described manufacturing
method using Nd, Fe, and B as the raw materials of the rare earth magnet alloy so that
20 the general formula will be (Nd, Tb)-Fe-B. The magnet thickness of Comparative
Example 7 is 1.75 mm, and that of Comparative Example 8 is 7 mm. The magnetic
properties of these samples were evaluated by the methods described above. The
residual magnetic flux density of Comparative Example 7 was 1.33 T, and that of
Comparative Example 8 was 1.34 T. Comparisons of these results with those of
25 Comparative Example 1 and Comparative Example 2 show that the addition of Tb
reduced the residual magnetic flux density. The coercive forces were 2013 kA/m and
1821 kA/m, respectively. The coercive force difference was 92 kA/m. These results
suggest that Tb was not sufficiently diffused to the center of the magnet in Comparative
Example 8, which is a 7 mm thick magnet, resulting in a difference in coercive force
30 compared to Comparative Example 7, which is a 1.75 mm thick magnet. Compared to
Comparative Example 1 and Comparative Example 2, the coercive forces were improved
but the residual magnetic flux densities were reduced. This is because the diffusion of
Tb into the grain boundaries improved the coercive force, but the permeation of Tb into
the main phase 2 lowered the residual magnetic flux densities.
35 [0052]
Examples 1 to 6 are samples in which Dy was diffused into the grain boundaries
according to the above-described manufacturing method using Nd, Sm, La, Fe, and B as
the raw materials of the rare earth magnet alloy 47 so that the general formula will be
(Nd, Sm, La, Dy)-Fe-B. The magnetic properties of these samples were evaluated by
40 the methods described above. The results show that the residual magnetic flux density
of each of Examples 1 to 6 was higher than those of Comparative Example 5 and
Comparative Example 6. This reflects the result of the selective grain boundary
15
diffusion of Dy into at least part of the peripheries of the Sm enriched portions 4, which
suppressed the permeation of Dy into the main phase 2. Compared to Comparative
Example 5 and Comparative Example 6, the coercive force difference was small. Also,
the coercive force difference decreased as the contents of Sm and La increased. This
5 reflects the result of the selective grain boundary diffusion of Dy into the peripheries of
the Sm enriched portions 4 that are dispersed from the surface to the center of the
sintered rare earth magnet 1, thereby diffusing Dy deeper into the sintered rare earth
magnet 1 than with the conventional grain boundary diffusion method. La is present
in grain boundary phase 3 and promotes the permeation of Dy into the grain boundary.
10 [0053]
Examples 7 to 12 are samples in which Tb was diffused into the grain boundaries
according to the above-described manufacturing method using Nd, Sm, La, Fe, and B as
the raw materials of the rare earth magnet alloy 47 so that the general formula will be
(Nd, Sm, La, Tb)-Fe-B. The magnetic properties of these samples were evaluated by
15 the methods described above. The results show that each residual magnetic flux
density was higher than those of Comparative Example 7 and Comparative Example 8.
This reflects the result of the selective grain boundary diffusion of Tb into at least part
of the peripheries of the Sm enriched portions 4, which suppressed the permeation of
Tb into the main phase 2. Compared to Comparative Example 7 and Comparative
20 Example 8, the coercive force difference was small. This reflects the result of the
selective grain boundary diffusion of Tb into the peripheries of the Sm enriched portions
4 that are dispersed from the surface to the center of the sintered rare earth magnet 1,
thereby diffusing Tb deeper into the sintered rare earth magnet 1 than by using the
conventional grain boundary diffusion method. La is present in grain boundary phase
25 3 and promotes the permeation of Dy into the grain boundary. Furthermore, the
coercive force differences of Examples 7 to 12 are smaller than those of Examples 1 to 6.
This shows that Tb is more effective than Dy as the heavy rare earth element RH.
[0054]
Next, the evaluation results of the magnet internal structures of the rare earth
30 sintered magnets 1 produced by the manufacturing method according to the present
embodiment are described.
[0055]
The magnet internal structures were evaluated by elemental analysis using a
scanning electron microscope (SEM) and an electron probe micro analyzer (EPMA).
35 Here, a field emission type electron probe microanalyzer (JXA-8530F manufactured by
JEOL Ltd.) was used as the SEM and EPMA, and the elemental analysis was performed
under evaluation conditions of an acceleration voltage of 15.0 kV, an irradiation current
of 3.05e-007A, an irradiation time of 10 ms, the number of pixels of 256 x 256 pixels, a
magnification of 5000 times, and the number of integration times of 5.
40 [0056]
Fig. 4 shows cross sections of the rare earth sintered magnet 1 of Example 1
evaluated under the above-described evaluation conditions, in which Fig. 4A is a
16
compositional image in backscattered electron mode, Fig. 4B is a mapping diagram of
Nd, Fig. 4C is a mapping diagram of Sm, Fig. 4D is a mapping diagram of Dy, and Fig.
4E is a mapping diagram of La. Fig. 5 shows cross sections of the rare earth sintered
magnet 1 of Example 7 evaluated under the above-described evaluation conditions, in
5 which Fig. 5A is a compositional image in backscattered electron mode, Fig. 5B is a
mapping diagram of Nd, Fig. 5C is a mapping diagram of Sm, Fig. 5D is a mapping
diagram of Tb, and Fig. 5E is a mapping diagram of La.
[0057]
It is confirmed from Fig. 4 and Fig. 5 that the rare earth sintered magnets 1
10 produced by the manufacturing method according to the present embodiment have the
following magnet internal structures. Fig. 4A and Fig. 5A show that there are a
plurality of regions of the main phase 2, and the grain boundary phase 3 formed among
the plurality of regions of the main phase 2. Fig. 4B and Fig. 5B show that Nd is
present throughout the grain boundary phase 3. Fig. 4C and Fig. 5C show that a part
15 of the grain boundary phase 3 has Sm enriched portions 4, and the content of Sm is
higher in the grain boundary phase 3 than in the main phase 2. Fig. 4D and Fig. 5D
show that there are heavy rare earth element RH enriched portions 5 in at least a part
of the grain boundary phase 3 on the peripheries of the Sm enriched portions 4, and the
content of the heavy rare earth element RH is higher in the grain boundary phase 3
20 than in the main phase 2. Fig. 4E and Fig. 5E show that La, like Nd, is present
throughout the grain boundary phase 3.
[0058]
Embodiment 3
The present embodiment relates to a rotor 51 that includes the rare earth sintered
25 magnet 1 according to Embodiment 1. The rotor 51 according to the present
embodiment is described with reference to Fig. 6. Fig. 6 is a schematic cross-sectional
view perpendicular to an axial direction of the rotor 51.
[0059]
The rotor 51 is rotatable about an axis of rotation 54. The rotor 51 includes a rotor
30 core 52 and a plurality of rare earth sintered magnets 1 inserted into magnet insertion
holes 53 provided in the rotor core 52 along a circumferential direction of the rotor 51.
Fig. 6 shows an example including four magnet insertion holes 53 and four rare earth
sintered magnets 1; however, the number of magnet insertion holes 53 and the number
of rare earth sintered magnets 1 may be changed according to the design of the rotor 51.
35 The rotor core 52 is formed of a plurality of disk-shaped electromagnetic steel plates
stacked in the axial direction of the axis of rotation 54.
[0060]
The rare earth sintered magnets 1 are manufactured according to the
manufacturing method of Embodiment 2. The four rare earth sintered magnets 1 are
40 inserted into their respective magnet insertion holes 53. The four rare earth sintered
magnets 1 are magnetized in such a way that, on the radially outer side of the rotor 51,
17
each of the rare earth sintered magnets 1 has a polarity different from that of the
adjacent rare earth sintered magnets 1.
[0061]
As described above, the rotor 51 according to the present embodiment includes the
5 rare earth sintered magnets 1 according to Embodiment 1, which allows the heavy rare
earth element RH to diffuse deeper into the rare earth sintered magnet 1 while
suppressing the deterioration of the magnetic properties, and enables small coercive
force difference in the rare earth sintered magnet 1 while maintaining a high residual
magnetic flux density; therefore, the deterioration of the magnetic properties is
10 suppressed even in high-temperature environments where the temperature exceeds 100
deg C. This stabilizes the operation of the rotor 51 even in high-temperature
environments where the temperature exceeds 100 deg C.
[0062]
Embodiment 4
15 The present embodiment relates to a rotating machine 61 provided with the rotor
51 according to Embodiment 3. The rotating machine 61 according to the present
embodiment is described with reference to Fig. 7. Fig. 7 is a schematic cross-sectional
view perpendicular to an axial direction of the rotating machine 61.
[0063]
20 The rotating machine 61 includes the rotor 51 according to Embodiment 3 and an
annular stator 62 provided coaxially with the rotor 51 and disposed facing the rotor 51.
The stator 62 is formed of a plurality of electromagnetic steel plates stacked in the axial
direction of the axis of rotation 54. The configuration of the stator 62 is not limited to
this, and existing configurations may be employed. The stator 62 is provided with
25 windings 63. The windings 63 may be wound in a concentrated manner or a
distributed manner, for example. The number of magnetic poles of the rotor 51 in the
rotating machine 61 should be two or more; in other words, the number of rare earth
sintered magnets 1 should be two or more. Fig. 7 shows an example of a magnetembedded type rotor 51; however, a surface-magnet type rotor 51 having the rare earth
30 magnets fixed to the outer periphery with adhesive may also be used.
[0064]
As described above, the rotating machine 61 according to the present embodiment
includes the rare earth sintered magnets 1 according to Embodiment 1, which allows
the heavy rare earth element RH to diffuse deeper into the rare earth sintered magnet
35 1 while suppressing the deterioration of the magnetic properties and enables small
coercive force difference in the rare earth sintered magnet 1 while maintaining a high
residual magnetic flux density; therefore, the deterioration of the magnetic properties
is suppressed even in high-temperature environments where the temperature exceeds
100 deg C. This stabilizes the drive of the rotor 51 and the operation of the rotating
40 machine 61 even in high-temperature environments where the temperature exceeds 100
deg C.
Reference Signs List
18
[0065]
1 rare earth sintered magnet
2 main phase
3 grain boundary phase
5 4 Sm enriched portion
5 heavy rare earth element RH enriched portion
11 raw alloy production process
12 melting process
13 primary cooling process
10 14 secondary cooling process
21 sintered magnet production process
22 pulverization process
23 molding process 23
24 sintering-and-aging process
15 31 grain boundary diffusion process
32 adhesion process
33 diffusion process
41 crucible
42 molten alloy
20 43 tundish
44 rotator
45 solidified alloy
46 tray
47 rare earth magnet alloy
25 51 rotor
52 rotor core
53 magnet insertion hole
54 axis of rotation
61 rotating machine
30 62 stator
63 winding
19
We Claim :
1. A rare earth sintered magnet comprising:
a plurality of regions of a main phase each having an R2Fe14B crystal structure
containing at least Nd as a rare earth element R; and
5 a grain boundary phase formed among the plurality of regions of the main phase
and having Sm enriched portions in which Sm is enriched by Sm substitution in a
crystalline NdO phase and heavy rare earth element RH enriched portions in which a
heavy rare earth element RH is enriched at least on part of peripheries of the Sm
enriched portions.
10
2. The rare earth sintered magnet according to claim 1, wherein the Sm enriched
portions are dispersed throughout the grain boundary phase from a surface layer to a
center of the rare earth sintered magnet.
15 3. The rare earth sintered magnet according to claim 1 or claim 2, wherein a content
of the Sm is higher in the grain boundary phase than in the main phase.
4. The rare earth sintered magnet according to any one of claims 1 to 3, wherein a
content of the heavy rare earth element RH is higher in the grain boundary phase than
20 in the main phase.
5. The rare earth sintered magnet according to any one of claims 1 to 4, wherein the
rare earth element R includes La.
25 6. A method of manufacturing a rare earth sintered magnet comprising:
a pulverization process of pulverizing an R-Fe-B system rare earth magnet alloy
containing Nd and Sm as rare earth elements R;
a molding process of molding a powder of the R-Fe-B system rare earth magnet alloy
to produce a compact;
30 a sintering-and-aging process of sintering the compact at a temperature between
600 deg C and 1300 deg C, inclusive, and aging the compact at a temperature lower than
a temperature of the sintering to produce a sintered compact; and
a grain boundary diffusion process of adhering a heavy rare earth element RH to
the sintered compact and performing a heat treatment to diffuse the heavy rare earth
35 element RH into a grain boundary.
7. The method of manufacturing a rare earth sintered magnet according to claim 6,
wherein the heat treatment in the grain boundary diffusion process is performed at a
temperature lower than the temperature of the sintering.
40
8. A rotor comprising:
a rotor core; and
20
the rare earth sintered magnet according to any one of claims 1 to 5 provided in the
rotor core.
9. A rotating machine comprising:
5 the rotor according to claim 8; and
a stator disposed to face the rotor.