FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
RARE EARTH MAGNET ALLOY, METHOD OF MANUFACTURING SAME, RARE EARTH
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 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION
AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Technical Field
[0001] The present invention relates to a rare earth magnet
alloy, a method of manufacturing the same, a rare earth magnet,
a rotor, and a rotating machine.
Background Art
[0002] An R-T-B-based permanent magnet including a tetragonal
R2T14B intermetallic compound as a main phase, where R represents
a rare earth element, T represents a transition element, such as
Fe or Fe partially substituted with Co, and B represents boron,
has excellent magnetic characteristics. Accordingly, the
R-T-B-based permanent magnet is used for various high-value added
components including an industrial motor. When the R-T-B-based
permanent magnet is used for the industrial motor, its operating
temperature environment often becomes a high-temperature
environment of above 100°C, and hence there is a strong desire for
the R-T-B-based permanent magnet to achieve high heat resistance.
In order for the R-T-B-based permanent magnet to achieve high heat
resistance, the characteristics of an R-T-B-based magnet alloy
serving as a raw material therefor need to be improved. As a
technology for improving the magnetic characteristics of the
R-T-B-based magnet alloy, there is known a technology involving
replacing Nd with a heavy rare earth element, such as Dy, as R in
3
the R-T-B-based magnet alloy. However, the resource of the heavy
rare earth element is distributed unevenly, and besides, its output
is also limited, which results in concern about its supply. In view
of the foregoing, a technology for improving the magnetic
characteristics of the R-T-B-based magnet alloy without increasing
the content of the heavy rare earth element in the R-T-B-based magnet
alloy has been investigated.
[0003] For example, in Patent Literature 1, there is proposed
a rare earth sintered magnet which has a composition formula
expressed by (R1x+R2y)T100-x-y-zQz, where R1 represents at least one
kind of element selected from the group consisting of all the rare
earth elements excluding La, Y, and Sc, R2 represents at least one
kind of element selected from the group consisting of: La; Y; and
Sc, T represents at least one kind of element selected from the
group consisting of all the transition elements, and Q represents
at least one kind of element selected from the group consisting
of: B; and C, and which includes, as a main phase, crystal grains
each having a Nd2Fe14B-type crystal structure, in which the
composition ratios x, y, and z satisfy 8 at%≤x≤18 at%, 0.1 at%≤y≤3.5
at%, and 3 at%≤z≤20 at%, respectively, and the concentration of
R2 is higher in at least part of a grain boundary phase than in
the crystal grains of the main phase.
Citation List
Patent Document
4
[0004] Patent Document 1: JP 2002-190404 A
Summary of Invention
Technical Problem
[0005] However, the rare earth sintered magnet disclosed in
Patent Document 1 has a risk of being significantly reduced in
magnetic characteristics along with an increase in temperature.
[0006] An object of the present invention is to provide a rare
earth magnet alloy, in which a reduction in magnetic characteristics
along with an increase in temperature can be suppressed while a
heavy rare earth element is replaced with an inexpensive rare earth
element.
Solution to Problem
[0007] According to one embodiment of the present invention,
there is provided a rare earth magnet alloy having a tetragonal
R2Fe14B crystal structure, including: a main phase containing, as
main constituent elements, at least one kind selected from the group
consisting of: Nd; La; and Sm, Fe, and B; and a sub-phase containing,
as main constituent elements, at least one kind selected from the
group consisting of: Nd; La; and Sm, and O, wherein La substitutes
for at least one of a Nd(f) site or a Nd(g) site, wherein Sm
substitutes for at least one of a Nd(f) site or a Nd(g) site, wherein
La segregates in the sub-phase, and wherein Sm is dispersed in the
main phase and the sub-phase without segregation.
5
Advantageous Effects of Invention
[0008] According to the present invention, the rare earth
magnet alloy, in which a reduction in magnetic characteristics along
with an increase in temperature can be suppressed while a heavy
rare earth element is replaced with an inexpensive rare earth
element, can be provided.
Brief Description of Drawings
[0009] FIG. 1 is a view for illustrating atom sites in a
tetragonal Nd2Fe14B crystal structure.
FIG. 2 is a flowchart of a method of manufacturing a rare earth
magnet alloy according to one embodiment of the present invention.
FIG. 3 is a view for schematically illustrating the method
of manufacturing the rare earth magnet alloy according to the one
embodiment of the present invention.
FIG. 4 is a flowchart of a method of manufacturing a rare earth
magnet including the rare earth magnet alloy according to the one
embodiment of the present invention.
FIG. 5 is a schematic sectional view of a rotor having mounted
thereto the rare earth magnet according to the one embodiment of
the present invention in a direction perpendicular to an axial
direction of the rotor.
FIG. 6 is a schematic sectional view of a rotating machine
having mounted thereto the rare earth magnet according to the one
6
embodiment of the present invention in a direction perpendicular
to an axial direction of the rotating machine.
FIG. 7 includes a compositional image (COMPO image) and
elemental mapping of a surface of a bonded magnet including the
rare earth magnet alloy according to the one embodiment of the
present invention.
FIG. 8 includes a compositional image (COMPO image) and
elemental mapping of a cross section of the bonded magnet including
the rare earth magnet alloy according to the one embodiment of the
present invention.
Description of Embodiments
[0010] Embodiments of the present invention are described
below with reference to the drawings.
[0011] First Embodiment.
A rare earth magnet alloy according to a first embodiment of
the present invention has a tetragonal R2Fe14B crystal structure.
Herein, R represents a rare earth element selected from the group
consisting of: neodymium (Nd); lanthanum (La); and samarium (Sm).
Fe represents iron. B represents boron. The reason why R in the
rare earth magnet alloy according to the first embodiment having
the tetragonal R2Fe14B crystal structure represents the rare earth
element selected from the group consisting of: Nd; La; and Sm is
as follows: calculation results of magnetic interaction energy
using a molecular orbital method have revealed that a composition
7
in which La and Sm are added to Nd provides a practical rare earth
magnet alloy. When the addition amounts of La and Sm are too large,
the amount of Nd, which is an element having a high magnetic
anisotropy constant and a high saturation magnetic polarization,
is reduced, which results in a reduction in magnetic characteristics.
Accordingly, it is preferred that composition ratios of Nd, La,
and Sm satisfy Nd>(La+Sm). In addition, the rare earth magnet alloy
according to the first embodiment includes: a main phase containing,
as main constituent elements, at least one kind selected from the
group consisting of: Nd; La; and Sm, Fe, and B; and a sub-phase
containing, as main constituent elements, at least one kind selected
from the group consisting of: Nd; La; and Sm, and O. In the rare
earth magnet alloy according to the first embodiment, the sub-phase
is present while being dispersed in a grain boundary of the main
phase. La segregates in the sub-phase, and Sm is dispersed in the
main phase and the sub-phase without segregation. From the
viewpoint of further suppressing a reduction in magnetic
characteristics along with an increase in temperature, it is
preferred that the main phase and the sub-phase each contain the
three elements, Nd, La, and Sm. The main phase is hereinafter
sometimes referred to as (Nd, La, Sm)FeB crystal phase. In addition,
the sub-phase is sometimes referred to as (Nd, La, Sm)O phase. The
(Nd, La, Sm) described herein means that Nd is partially substituted
with La and Sm. Herein, in the rare earth magnet alloy according
to the first embodiment, when the concentration of La in the main
8
phase is represented by X1 and the concentration of La in the
sub-phase is represented by X2, X2/X1>1 is established.
[0012] Next, it is described with reference to FIG. 1 as to
which atom sites in the tetragonal R2Fe14B crystal structure are
substituted with La and Sm. FIG. 1 is a view for illustrating atom
sites in a tetragonal Nd2Fe14B crystal structure (reference: J. F.
Herbst et al.: PHYSICAL REVIEW B, Vol. 29, No. 7, pp. 4176-4178,
1984). The site to be substituted is judged based on the value for
stabilization energy for the substitution, which is determined by
band calculation and molecular field approximation of a Heisenberg
model.
[0013] First, a method of calculating stabilization energy for
La is described. The stabilization energy for La may be determined
by using a Nd8Fe56B4 crystal cell based on a difference in energy
between (Nd7La11)Fe56B4+Nd and Nd8(Fe55La1)B4+Fe. When the value for
the energy is smaller, the site substituted with the atom becomes
more stable. That is, La easily substitutes for the atom site having
the smallest energy among the atom sites. The calculation is
performed on the assumption that, when La substitutes for the
original atom, the lattice constant of the tetragonal R2Fe14B crystal
structure does not change due to a difference in atomic radius.
The stabilization energy for La at each substitution site with
varying environmental temperatures is shown in Table 1.
[0014]
Table 1
9
Substitution
site for La
Temperature
293 K 500 K 1,000 K 1,300 K 1,400 K 1,500 K
Nd(f) -136.372 -84.943 -48.524 -40.132 -38.132 -35.451
Nd(g) -132.613 -82.740 -47.442 -38.211 -36.358 -34.753
Fe(k1) -135.939 -80.596 -41.428 -32.390 -30.237 -17.095
Fe(k2) -127.480 -75.638 -38.948 -30.482 -28.466 -26.719
Fe(j1) -124.248 -73.076 -38.003 -29.754 -27.791 -26.089
Fe(j2) -117.148 -71.400 -35.923 -28.816 -26.917 -25.271
Fe(e) -130.814 -77.593 -39.926 -31.235 -29.164 -27.371
Fe(c) -148.317 -87.850 -45.055 -35.179 -32.828 -30.789
Unit: eV
[0015] According to Table 1, a stable substitution site for
La is a Nd(f) site at a temperature of 1,000 K or more, and is an
Fe(c) site at temperatures of 293 K and 500 K. As described below,
in the case of the rare earth magnet alloy according to the first
embodiment, a raw material for the rare earth magnet alloy is heated
at a temperature of 1,000 K or more to be melted, followed by being
rapidly cooled. It is thus conceived that the raw material for the
rare earth magnet alloy is maintained in the state of 1,000 K or
more, that is, 727°C or more. Accordingly, when the rare earth
magnet alloy is manufactured by a manufacturing method described
below, La is conceived to substitute for the Nd(f) site or a Nd(g)
site even at room temperature. Although La is conceived to
preferentially substitute for the energetically stable Nd(f) site,
La may substitute for the Nd(g) site, which has a smaller difference
in energy among the substitution sites for La. This is also
supported by the following study report: when a La-Fe-B alloy is
melted at 1,073 K (800°C), followed by being cooled with ice water,
10
a tetragonal La2Fe14B is formed, that is, La enters a site
corresponding to the Nd(f) site or the Nd(g) site of FIG. 1 without
entering the Fe(c) site (reference: YAO Qing rong et al.: JOURNAL
OF RARE EARTHS, Vol. 34, No. 11, pp. 1121-1125, 2016).
[0016] Next, a method of calculating stabilization energy for
Sm is described. As for Sm, a difference in energy between
(Nd7Sm1)Fe56B4+Nd and Nd8(Fe55Sm1)B4+Fe is determined. The
calculation is performed in the same manner as in the case of La
on the assumption that, when Sm substitutes for the atom, the lattice
constant of the tetragonal R2Fe14B crystal structure does not change.
The stabilization energy for Sm in each substitution site with
varying environmental temperatures is shown in Table 2.
[0017]
Table 2
Substitution
site for Sm
Temperature
293 K 500 K 1,000 K 1,300 K 1,400 K 1,500 K
Nd(f) -164.960 -101.695 -56.921 -46.589 -44.128 -41.976
Nd(g) -168.180 -103.583 -57.865 -47.315 -44.803 -42.626
Fe(k1) -136.797 -81.098 -41.679 -32.583 -17.350 -16.343
Fe(k2) -127.769 -75.808 -38.482 -29.603 -28.528 -25.696
Fe(j1) -122.726 -73.304 -37.783 -28.392 -26.525 -24.681
Fe(j2) -124.483 -73.883 -38.072 -28.483 -26.610 -24.985
Fe(e) 125.937 72.525 35.301 26.633 24.450 22.782
Fe(c) -155.804 -94.457 -48.359 -37.720 -35.187 -32.992
Unit: eV
[0018] According to Table 2, it is revealed that a stable
substitution site for Sm is the Nd(g) site at each temperature.
Although Sm is conceived to preferentially substitute for the
11
energetically stable Nd(g) site, Sm may substitute for the Nd(f)
site, which has a smaller difference in energy among the
substitution sites for Sm.
[0019] As described above, in the rare earth magnet alloy
according to the first embodiment, La substitutes for at least one
of the Nd(f) site or the Nd(g) site, and Sm substitutes for at least
one of the Nd(f) site or the Nd(g) site. When the rare earth magnet
alloy has such feature, a reduction in magnetic characteristics
along with an increase in temperature is suppressed while a heavy
rare earth element, such as Dy, is replaced with an inexpensive
rare earth element, and excellent magnetic characteristics can be
exhibited even under a high-temperature environment of above 100°C.
[0020] Next, a method of manufacturing the rare earth magnet
alloy according to the first embodiment is described. FIG. 2 is
a flowchart of the procedure for manufacturing the rare earth magnet
alloy according to the first embodiment. FIG. 3 is a view for
schematically illustrating the operation of manufacturing the rare
earth magnet alloy according to the first embodiment. As
illustrated in FIG. 2, the method of manufacturing the rare earth
magnet alloy according to the first embodiment includes: a melting
step (S1) of heating a raw material for the rare earth magnet alloy
at a temperature of 1,000 K or more to melt the raw material; a
primary cooling step (S2) of cooling the raw material in a molten
state on a rotating rotary body to obtain a solidified alloy; and
a secondary cooling step (S3) of further cooling the solidified
12
alloy in a container. By the manufacturing method including such
steps, the rare earth magnet alloy, in which a reduction in magnetic
characteristics along with an increase in temperature can be
suppressed, can be easily obtained.
[0021] In the melting step (S1), as illustrated in FIG. 3, the
raw material for the rare earth magnet alloy is heated at a
temperature of 1,000 K or more to be melted in a crucible 1 in an
atmosphere containing an inert gas, such as argon (Ar), or in vacuum,
to thereby provide an alloy melt 2. A combination of materials such
as Nd, La, Sm, Fe, and B may be used as the raw material.
[0022] In the primary cooling step (S2), as illustrated in FIG.
3, the alloy melt 2 prepared in the melting step (S1) is caused
to flow into a tundish 3, and is then rapidly cooled on a single
roll 4 while the roll 4 is rotating in a direction of the arrow,
to thereby prepare, from the alloy melt 2, a solidified alloy 5
having a smaller thickness than an ingot alloy. The single roll
is used as the rotating rotary body in this case, but is not limited
thereto. The alloy melt 2 may be rapidly cooled by being brought
into contact with a twin roll, a rotating disc, a rotating
cylindrical mold, or the like. From the viewpoint of efficiently
obtaining the solidified alloy 5 having a small thickness, a cooling
rate in the primary cooling step (S2) is set to preferably from
10°C/sec to 107°C/sec, more preferably from 103°C/sec to 104°C/sec.
The thickness of the solidified alloy 5 falls within the range of
0.03 mm or more and 10 mm or less. The alloy melt 2 starts to be
13
solidified from a portion brought into contact with the rotary body,
and a crystal is grown in a columnar shape (needle shape) in a
thickness direction from a contact surface with the rotary body.
[0023] In the secondary cooling step (S3), as illustrated in
FIG. 3, the solidified alloy 5 having a small thickness prepared
in the primary cooling step (S2) is put in a tray container 6 and
cooled. The solidified alloy 5 having a small thickness is broken
at the time of entering the tray container 6 to become a flake rare
earth magnet alloy 7, and is cooled in that state. A ribbon-shaped
rare earth magnet alloy 7 may be obtained depending on a cooling
rate, and the shape of the rare earth magnet alloy 7 is not limited
to a flake shape. From the viewpoint of obtaining the rare earth
magnet alloy 7 having a structure having satisfactory temperature
characteristics of the magnetic characteristics, the cooling rate
in the secondary cooling step (S3) is set to preferably from
10-2°C/sec to 105°C/sec, more preferably from 10-1°C/sec to 102°C/sec.
The rare earth magnet alloy 7 obtained through those steps has a
fine crystal structure including: a (Nd, La, Sm)FeB crystal phase
having a size in a short-axis direction of 3 μm or more and 10 μm
or less and a size in a long-axis direction of 10 μm or more and
300 μm or less; and a (Nd, La, Sm)O phase present while being
dispersed in a grain boundary of the (Nd, La, Sm)FeB crystal phase.
The (Nd, La, Sm)O phase is a non-magnetic phase formed of an oxide
having a relatively high concentration of a rare earth element.
The thickness of the (Nd, La, Sm)O phase (corresponding to the width
14
of the grain boundary) is 10 μm or less. The rare earth magnet alloy
7 according to the first embodiment undergoes the rapid cooling
step, and hence its structure is finer and its crystal grain diameter
is smaller than those of a rare earth magnet alloy obtained by a
mold casting method. In addition, the (Nd, La, Sm)O phase spreads
thinly in the grain boundary, and hence the sintering property of
the rare earth sintered magnet alloy 7 is improved.
[0024] Second Embodiment.
Next, in a second embodiment of the present invention, a
method of manufacturing a rare earth magnet using the rare earth
magnet alloy according to the first embodiment is described. FIG.
4 is a flowchart of the procedure for manufacturing the rare earth
magnet according to the second embodiment.
[0025] As illustrated in FIG. 4, a method of manufacturing the
magnet according to the second embodiment includes: a pulverization
step (S4) of pulverizing the rare earth magnet alloy according to
the first embodiment; a molding step (S5) of molding the pulverized
rare earth magnet alloy; and a sintering step (S6) of sintering
the molded rare earth magnet alloy.
[0026] In the pulverization step (S4), the rare earth magnet
alloy manufactured in accordance with the method of manufacturing
the rare earth magnet alloy according to the first embodiment is
pulverized, to thereby obtain rare earth magnet alloy powder having
a particle diameter of 200 μm or less, preferably 0.5 μm or more
and 100 μm or less. The pulverization of the rare earth magnet alloy
15
may be performed, for example, with an agate mortar, a stamp mill,
a jaw crusher, or a jet mill. Particularly when the particle
diameter of the powder is to be reduced, it is preferred that the
pulverization of the rare earth magnet alloy be performed in an
atmosphere containing an inert gas. When the pulverization of the
rare earth magnet alloy is performed in the atmosphere containing
an inert gas, the mixing of oxygen in the powder can be suppressed.
When the atmosphere in which the pulverization is performed does
not affect the magnetic characteristics of the magnet, the
pulverization of the rare earth magnet alloy may be performed in
the atmospheric atmosphere.
[0027] In the molding step (S5), the pulverized rare earth
magnet alloy is compression-molded, or a mixture of the pulverized
rare earth magnet alloy and a resin is heat-molded. The molding
of each mode may be performed while a magnetic field is applied.
Herein, a magnetic field of, for example, 2 T may be applied. The
compression molding may be performed by directly
compression-molding the pulverized rare earth magnet alloy, or by
compression-molding a mixture of the pulverized rare earth magnet
alloy and an organic binder. The resin to be mixed with the rare
earth magnet alloy may be a thermosetting resin, such as an epoxy
resin, or may be a thermoplastic resin, such as a polyphenylene
sulfide resin. When the mixture of the rare earth magnet alloy and
the resin is heat-molded, a bonded magnet in the shape of a product
can be obtained.
16
[0028] In the sintering step (S6), the compression-molded rare
earth magnet alloy is sintered, and thus a permanent magnet can
be obtained. In order to suppress oxidation, it is preferred that
the sintering be performed in an atmosphere containing an inert
gas or in vacuum. The sintering may be performed while a magnetic
field is applied. In addition, in order to improve the magnetic
characteristics, that is, to increase the anisotropy of the magnetic
field or improve a coercive force, a hot processing step or an aging
treatment step may be added to the sintering step. Further, a step
of causing a compound containing copper, aluminum, a heavy rare
earth element, or the like to permeate the crystal grain boundary,
which is a boundary between the main phases, may be added.
[0029] The permanent magnet and the bonded magnet manufactured
through such steps each have a tetragonal R2Fe14B crystal structure,
and include: a main phase containing, as main constituent elements,
at least one kind selected from the group consisting of: Nd; La;
and Sm, Fe, and B; and a sub-phase containing, as main constituent
elements, at least one kind selected from the group consisting of:
Nd; La; and Sm, and O. Further, in the permanent magnet and the
bonded magnet, La substitutes for at least one of a Nd(f) site or
a Nd(g) site, Sm substitutes for at least one of the Nd(f) site
or the Nd(g) site, La segregates in the sub-phase, and Sm is
dispersed in the main phase and the sub-phase without segregation.
Accordingly, in the permanent magnet and the bonded magnet, a
reduction in magnetic characteristics along with an increase in
17
temperature can be suppressed.
[0030] Third Embodiment.
Next, a rotor having mounted thereto the rare earth magnet
according to the second embodiment is described with reference to
FIG. 5. FIG. 5 is a schematic sectional view of the rotor having
mounted thereto the rare earth magnet according to the second
embodiment in a direction perpendicular to an axial direction of
the rotor.
[0031] The rotor is rotatable about a rotation axis. The rotor
includes: a rotor core 10; and rare earth magnets 11 inserted into
magnet insertion holes 12 formed in the rotor core 10 along a
circumferential direction of the rotor. While four rare earth
magnets 11 are used in FIG. 5, the number of the rare earth magnets
11 is not limited thereto, and may be changed depending on the design
of the rotor. In addition, while four magnet insertion holes 12
are formed in FIG. 5, the number of the magnet insertion holes 12
is not limited thereto, and may be changed depending on the number
of the rare earth magnets 11. The rotor core 10 is formed by
laminating a plurality of disc-shaped electromagnetic steel sheets
in an axial direction of the rotation axis.
[0032] The rare earth magnet 11 has been manufactured in
accordance with the manufacturing method according to the second
embodiment. The four rare earth magnets 11 are inserted into the
corresponding magnet insertion holes 12. The four rare earth
magnets 11 are magnetized so that magnetic poles of the adjacent
18
rare earth magnets 11 on a radially outer side of the rotor differ
from each other.
[0033] When the coercive force of the permanent magnet is
reduced under a high-temperature environment, the operation of the
rotor is destabilized. When the rare earth magnet 11 manufactured
in accordance with the manufacturing method according to the second
embodiment is used as the permanent magnet, the absolute value for
a temperature coefficient of the magnetic characteristics is small,
and hence a reduction in magnetic characteristics is suppressed
even under a high-temperature environment of above 100°C.
Consequently, according to the third embodiment, the operation of
the rotor can be stabilized even under a high-temperature
environment of above 100°C.
[0034] Fourth Embodiment.
Next, a rotating machine having mounted thereto the rotor
according to the third embodiment is described with reference to
FIG. 6. FIG. 6 is a schematic sectional view of the rotating machine
having mounted thereto the rotor according to the third embodiment
in a direction perpendicular to an axial direction of the rotor.
[0035] The rotating machine includes: the rotor according to
the third embodiment rotatable about a rotation axis; and an annular
stator 13 arranged coaxially with the rotor and opposite to the
rotor. The stator 13 is formed by laminating a plurality of
electromagnetic steel sheets in an axial direction of the rotation
axis. The configuration of the stator 13 is not limited thereto,
19
and an existing configuration may be adopted. The stator 13 is
provided with a winding 14. The winding manner of the winding 14
is not limited to concentrated winding, and distributed winding
may be adopted. The number of magnetic poles of the rotor in the
rotating machine only needs to be 2 or more, that is, the number
of the rare earth magnets 11 only needs to be 2 or more. In addition,
while an interior magnet rotor is adopted in FIG. 6, a surface magnet
rotor in which the rare earth magnet 11 is fixed to an outer periphery
thereof with an adhesive may be adopted.
[0036] When the coercive force of the permanent magnet is
reduced under a high-temperature environment, the operation of the
rotor is destabilized. When the rare earth magnet 11 manufactured
in accordance with the manufacturing method according to the second
embodiment is used as the permanent magnet, the absolute value for
a temperature coefficient of the magnetic characteristics is small,
and hence a reduction in magnetic characteristics is suppressed
even under a high-temperature environment of above 100°C.
Consequently, according to the fourth embodiment, the rotor can
be stably driven and the operation of the rotating machine can be
stabilized even under a high-temperature environment of above
100°C.
Examples
[0037] A plurality of samples of rare earth magnet alloys
having different compositions of main phases were produced as
20
samples according to Examples 1 to 6 and Comparative Examples 1
to 7. The samples according to Examples 1 to 6 and Comparative
Examples 2 to 7 were produced by changing "x" and "y" in a composition
formula of (Nd1-x-yLaxSmy)2Fe14B. Accordingly, the combinations of
"x" and "y" in (Nd1-x-yLaxSmy) in the samples according to Examples
1 to 6 and Comparative Examples 2 to 7 differ from one another.
The sample according to Comparative Example 1 was a Nd2Fe14B magnet
alloy including Dy, which was a heavy rare earth element. The
composition formulae of the main phases of the samples are shown
in Table 3.
[0038]
Table 3
Composition of main phase
Temperature
coefficient
|α| [%/°C] of
residual
magnetic
flux density
Temperature
coefficient
|β| [%/°C] of
coercive
force
Judgment
Residual
magnetic
flux
density
Coercive
force
Comparative
Example 1 (Nd0.850Dy0.150)2Fe14B 0.191 0.404 - -
Comparative
Example 2 (Nd0.980La0.020)2Fe14B 0.190 0.409 Good Poor
Comparative
Example 3 (Nd0.950La0.050)2Fe14B 0.185 0.415 Good Poor
Comparative
Example 4 (Nd0.850La0.150)2Fe14B 0.180 0.486 Good Poor
Comparative
Example 5 (Nd0.980Sm0.020)2Fe14B 0.201 0.405 Poor Poor
Comparative
Example 6 (Nd0.950Sm0.050)2Fe14B 0.256 0.412 Poor Poor
Comparative
Example 7 (Nd0.850Sm0.150)2Fe14B 0.282 0.456 Poor Poor
Example 1 (Nd0.980La0.010Sm0.010)2Fe14B 0.189 0.400 Good Good
Example 2 (Nd0.960La0.020Sm0.020)2Fe14B 0.186 0.390 Good Good
Example 3 (Nd0.906La0.047Sm0.047)2Fe14B 0.181 0.327 Good Good
Example 4 (Nd0.828La0.086Sm0.086)2Fe14B 0.171 0.272 Good Good
Example 5 (Nd0.734La0.133Sm0.133)2Fe14B 0.186 0.339 Good Good
Example 6 (Nd0.600La0.200Sm0.200)2Fe14B 0.189 0.401 Good Good
21
[0039] Next, a method of analyzing an alloy structure of the
rare earth magnet alloy is described. The alloy structure of the
rare earth magnet alloy may be determined by elemental analysis
with a scanning electron microscope (SEM) and an electron probe
micro analyzer (EPMA). Herein, the elemental analysis was
performed with a field emission-electron probe micro analyzer
(JXA-8530F manufactured by JEOL Ltd.) as a SEM and an EPMA under
the conditions of an acceleration voltage of 15.0 kV, an irradiation
current of 2.000e-008 A, an irradiation time of 10 ms, a number of
pixels of 256 pixels×192 pixels, a magnification of 2,000 times,
and a number of scans of 1.
[0040] Next, a method of evaluating the magnetic
characteristics of the rare earth magnet alloy is described. The
evaluation of the magnetic characteristics may be performed by
measuring the coercive forces of a plurality of samples with a pulse
excitation-type BH tracer. The maximum application magnetic field
of the BH tracer is 6 T or more, which brings the rare earth magnet
alloy into a completely magnetized state. Other than the pulse
excitation-type BH tracer, a direct current recording fluxmeter,
which is also called a direct current-type BH tracer, a vibrating
sample magnetometer (VSM), a magnetic property measurement system
(MPMS), a physical property measurement system (PPMS), or the like
may be used as long as the maximum application magnetic field of
6 T or more can be generated. The measurement is performed in an
atmosphere containing an inert gas, such as nitrogen. The magnetic
22
characteristics of each sample are measured at each of a first
measurement temperature T1 and a second measurement temperature
T2 that differ from each other. A temperature coefficient α [%/°C]
of the residual magnetic flux density is a value obtained by dividing
a ratio of a difference between a residual magnetic flux density
at the first measurement temperature T1 and a residual magnetic
flux density at the second measurement temperature T2 to the
residual magnetic flux density at the first measurement temperature
T1 by a difference in temperature (T2-T1). In addition, a
temperature coefficient β [%/°C] of the coercive force is a value
obtained by dividing a ratio of a difference between a coercive
force at the first measurement temperature T1 and a coercive force
at the second measurement temperature T2 to the coercive force at
the first measurement temperature T1 by a difference in temperature
(T2-T1). Accordingly, when the absolute values |α| and |β| for the
temperature coefficients of the magnetic characteristics become
smaller, a reduction in magnetic characteristics of the magnet along
with an increase in temperature is suppressed more.
[0041] First, the analysis results of the samples according
to Examples 1 to 6 and Comparative Examples 1 to 7 are described.
FIG. 7 includes a compositional image (COMPO image) and elemental
mapping obtained by analyzing a surface of a bonded magnet including
each of the samples according to Examples 1 to 6 with a field
emission-electron probe micro analyzer (FE-EPMA). In addition,
FIG. 8 includes a compositional image (COMPO image) and elemental
23
mapping obtained by analyzing a cross section of the bonded magnet
including each of the samples according to Examples 1 to 6 with
a field emission-electron probe micro analyzer. As shown in FIG.
7 and FIG. 8, in each of the samples according to Examples 1 to
6, it was able to be recognized that a sub-phase 9 serving as the
(Nd, La, Sm)O phase was present in a grain boundary of a main phase
8 serving as the (Nd, La, Sm)FeB crystal phase. Further, in each
of the samples according to Examples 1 to 6, it was able to be
recognized that La segregated in the sub-phase 9, and Sm was
dispersed in the main phase 8 and the sub-phase 9 without segregation.
Herein, when the concentration of La present in the main phase 8
was represented by X1, and the concentration of La present in the
sub-phase 9 was represented by X2, it was able to be recognized from
intensity ratios in the elemental mapping obtained through the
analysis with an EPMA that X2/X1>1 was established.
[0042] Next, the measurement results of the magnetic
characteristics of the samples according to Examples 1 to 6 and
Comparative Examples 1 to 7 are described. In order to measure the
magnetic characteristics, each of the samples was made in the form
of a bonded magnet by mixing powder of the rare earth magnet alloy
and a resin, followed by molding through curing of the resin. Each
of the samples had a block shape measuring 7 mm in length, width,
and height. The first measurement temperature T1 was set to 23°C,
and the second measurement temperature T2 was set to 200°C. 23°C
is room temperature. 200°C is a possible temperature as an
24
operation environment of an automobile motor and an industrial motor.
The temperature coefficient α of the residual magnetic flux density
was calculated by using the residual magnetic flux density at 23°C
and the residual magnetic flux density at 200°C. In addition, the
temperature coefficient β of the coercive force was calculated by
using the coercive force at 23°C and the coercive force at 200°C.
The absolute value |α| for the temperature coefficient of the
residual magnetic flux density and the absolute value |β| for the
temperature coefficient of the coercive force in each of the samples
according to Examples 1 to 6 and Comparative Examples 1 to 7 are
shown in Table 3. For each of the samples, as compared to |α| and
|β| in the sample according to Comparative Example 1, a case of
having a lower value was judged as "Good", and a case of having
a higher value was judged as "Poor".
[0043] The sample according to Comparative Example 1 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, Dy, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd0.850Dy0.150)2Fe14B. The magnetic characteristics of the sample
were evaluated in accordance with the above-mentioned method, and
as a result, |α| and |β| were found to be 0.191%/°C and 0.404%/°C,
respectively. Those values were used as references.
[0044] The sample according to Comparative Example 2 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, La, Fe, and
25
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.020, y=0). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.190%/°C
and 0.409%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
judged as "Good", and the temperature coefficient of the coercive
force was judged as "Poor". This result reflects the result that
the concentration of Nd present in the main phase is increased by
causing a La element to segregate in the grain boundary, and thus
an excellent magnetic flux density is obtained at room temperature.
[0045] The sample according to Comparative Example 3 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, La, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.050, y=0). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.185%/°C
and 0.415%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
judged as "Good", and the temperature coefficient of the coercive
force was judged as "Poor". This result is similar to that of
Comparative Example 2, and reflects the result that the
concentration of Nd present in the main phase is increased by causing
a La element to segregate in the grain boundary, and thus an
26
excellent magnetic flux density is obtained at room temperature.
[0046] The sample according to Comparative Example 4 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, La, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.150, y=0). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.180%/°C
and 0.486%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
judged as "Good", and the temperature coefficient of the coercive
force was judged as "Poor". This result is similar to that of
Comparative Example 2, and reflects the result that the
concentration of Nd present in the main phase is increased by causing
a La element to segregate in the grain boundary, and thus an
excellent magnetic flux density is obtained at room temperature.
[0047] The sample according to Comparative Example 5 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, Sm, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0, y=0.020). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.201%/°C
and 0.405%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
27
judged as "Poor", and the temperature coefficient of the coercive
force was judged as "Poor". This result reflects the result that
the addition of Sm alone does not contribute to an improvement in
characteristics.
[0048] The sample according to Comparative Example 6 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, Sm, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0, y=0.050). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.256%/°C
and 0.412%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
judged as "Poor", and the temperature coefficient of the coercive
force was judged as "Poor". This result is similar to that of
Comparative Example 5, and reflects the result that the addition
of Sm alone does not contribute to an improvement in
characteristics.
[0049] The sample according to Comparative Example 7 is a rare
earth magnet alloy produced in accordance with the manufacturing
method according to the first embodiment by using Nd, Sm, Fe, and
FeB as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0, y=0.150). The magnetic characteristics
of the sample were evaluated in accordance with the above-mentioned
method, and as a result, |α| and |β| were found to be 0.282%/°C
28
and 0.456%/°C, respectively. Accordingly, for the sample, the
temperature coefficient of the residual magnetic flux density was
judged as "Poor", and the temperature coefficient of the coercive
force was judged as "Poor". This result is similar to that of
Comparative Example 5, and reflects the result that the addition
of Sm alone does not contribute to an improvement in
characteristics.
[0050] The sample according to Example 1 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.010, y=0.010). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
to be 0.189%/°C and 0.400%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
the coercive force was judged as "Good".
[0051] The sample according to Example 2 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.020, y=0.020). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
29
to be 0.186%/°C and 0.390%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
the coercive force was judged as "Good".
[0052] The sample according to Example 3 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.047, y=0.047). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
to be 0.181%/°C and 0.327%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
the coercive force was judged as "Good".
[0053] The sample according to Example 4 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.086, y=0.086). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
to be 0.171%/°C and 0.272%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
30
the coercive force was judged as "Good".
[0054] The sample according to Example 5 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.133, y=0.133). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
to be 0.186%/°C and 0.339%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
the coercive force was judged as "Good".
[0055] The sample according to Example 6 is a rare earth magnet
alloy produced in accordance with the manufacturing method
according to the first embodiment by using Nd, La, Sm, Fe, and FeB
as raw materials so that the composition of the main phase became
(Nd1-x-yLaxSmy)2Fe14B (x=0.200, y=0.200). The magnetic
characteristics of the sample were evaluated in accordance with
the above-mentioned method, and as a result, |α| and |β| were found
to be 0.189%/°C and 0.401%/°C, respectively. Accordingly, for the
sample, the temperature coefficient of the residual magnetic flux
density was judged as "Good", and the temperature coefficient of
the coercive force was judged as "Good".
[0056] As apparent from the results of Examples 1 to 6, each
of the rare earth magnet alloys has the tetragonal R2Fe14B crystal
31
structure, and includes: the main phase containing, as main
constituent elements, the three elements, Nd, La, and Sm, Fe, and
B; and the sub-phase containing, as main constituent elements, the
three elements, Nd, La, and Sm, and O. Further, in each of the rare
earth magnet alloys, La substitutes for at least one of the Nd(f)
site or the Nd(g) site, and Sm substitutes for at least one of the
Nd(f) site or the Nd(g) site. La segregates in the sub-phase, and
Sm is dispersed in the main phase and the sub-phase without
segregation. As a result, with the rare earth magnet alloys, a
reduction in magnetic characteristics along with an increase in
temperature is suppressed while a heavy rare earth element, such
as Dy, is replaced with an inexpensive rare earth element, and
excellent magnetic characteristics can be exhibited even under a
high-temperature environment of above 100°C.
Explanation on Numerals
[0057]
1 crucible
2 alloy melt
3 tundish
4 single roll
5 solidified alloy
6 tray container
7 rare earth magnet alloy
8 main phase
32
9 sub-phase
10 rotor core
11 rare earth magnet
12 magnet insertion hole
13 stator
14 winding
33
WE CLAIM:
1. A rare earth magnet alloy having a tetragonal R2Fe14B crystal
structure, comprising:
a main phase containing, as main constituent elements, at
least one kind selected from the group consisting of: Nd; La; and
Sm, Fe, and B; and
a sub-phase containing, as main constituent elements, at
least one kind selected from the group consisting of: Nd; La; and
Sm, and O,
wherein La substitutes for at least one of a Nd(f) site or
a Nd(g) site,
wherein Sm substitutes for at least one of a Nd(f) site or
a Nd(g) site,
wherein La segregates in the sub-phase, and
wherein Sm is dispersed in the main phase and the sub-phase
without segregation.
2. The rare earth magnet alloy according to claim 1, wherein the
main phase and the sub-phase each comprise three elements of Nd,
La, and Sm.
3. The rare earth magnet alloy according to claim 1 or 2, wherein,
when a concentration of La in the main phase is represented by X1
and a concentration of La in the sub-phase is represented by X2,
X2/X1>1 is established.
34
4. The rare earth magnet alloy according to any one of claims 1
to 3, wherein composition ratios of Nd, La, and Sm satisfies
Nd>(La+Sm).
5. A method of manufacturing the rare earth magnet alloy of any
one of claims 1 to 4, comprising:
a melting step of heating a raw material for the rare earth
magnet alloy at a temperature of 1,000 K or more to melt the raw
material;
a primary cooling step of cooling the raw material in a molten
state on a rotating rotary body to obtain a solidified alloy; and
a secondary cooling step of further cooling the solidified
alloy in a container.
6. The method of manufacturing the rare earth magnet alloy according
to claim 5, wherein the primary cooling step comprises setting a
cooling rate to from 10°C/sec to 107°C/sec.
7. A rare earth magnet, comprising the rare earth magnet alloy of
any one of claims 1 to 4.
8. A rotor, comprising:
a rotor core; and
the rare earth magnet of claim 7 mounted to the rotor core.

9. A rotating machine, comprising:
the rotor of claim 8; and
a stator arranged opposite to the rotor.