U.S. patent application number 16/801625 was filed with the patent office on 2020-06-25 for rare earth permanent magnets and their preparation.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. The applicant listed for this patent is SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Takehisa Minowa, Hiroaki Nagata, Tadao Nomura.
Application Number | 20200203069 16/801625 |
Document ID | / |
Family ID | 46044516 |
Filed Date | 2020-06-25 |
United States Patent
Application |
20200203069 |
Kind Code |
A1 |
Nagata; Hiroaki ; et
al. |
June 25, 2020 |
RARE EARTH PERMANENT MAGNETS AND THEIR PREPARATION
Abstract
A sintered magnet body (R.sub.aT.sup.1.sub.bM.sub.cB.sub.d)
coated with a powder mixture of an intermetallic compound
(R.sup.1.sub.iM.sup.1.sub.j,
R.sup.1.sub.xT.sup.2.sub.yM.sup.1.sub.z,
R.sup.1.sub.iM.sup.1.sub.jH.sub.k), alloy
(M.sup.1.sub.dM.sup.2.sub.e) or metal (M.sup.1) powder and a rare
earth (R.sup.2) oxide is diffusion treated. The R.sup.2 oxide is
partially reduced during the diffusion treatment, so a significant
amount of R.sup.2 can be introduced near interfaces of primary
phase grains within the magnet through the passages in the form of
grain boundaries. The coercive force is increased while minimizing
a decline of remanence.
Inventors: |
Nagata; Hiroaki;
(Echizen-shi, JP) ; Nomura; Tadao; (Echizen-shi,
JP) ; Minowa; Takehisa; (Echizen-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIN-ETSU CHEMICAL CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
46044516 |
Appl. No.: |
16/801625 |
Filed: |
February 26, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15454433 |
Mar 9, 2017 |
10614952 |
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16801625 |
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13461043 |
May 1, 2012 |
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15454433 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/16 20130101;
B22F 2301/155 20130101; H01F 1/0557 20130101; B22F 2003/248
20130101; H01F 1/0577 20130101; C22C 38/002 20130101; C22C 38/06
20130101; C22C 38/10 20130101; B22F 2009/041 20130101; B32B 15/01
20130101; B22F 3/24 20130101; B22F 2009/042 20130101; H01F 41/0293
20130101; B22F 2998/10 20130101; B22F 2301/355 20130101; C22C
38/005 20130101; B22F 1/025 20130101; B22F 3/12 20130101; B22F
2009/044 20130101; C22C 19/07 20130101; C22C 33/0278 20130101; B22F
9/04 20130101 |
International
Class: |
H01F 41/02 20060101
H01F041/02; B22F 1/02 20060101 B22F001/02; C22C 33/02 20060101
C22C033/02; C22C 38/16 20060101 C22C038/16; H01F 1/055 20060101
H01F001/055; C22C 19/07 20060101 C22C019/07; B32B 15/01 20060101
B32B015/01; B22F 9/04 20060101 B22F009/04; B22F 3/24 20060101
B22F003/24; B22F 3/12 20060101 B22F003/12; C22C 38/10 20060101
C22C038/10; C22C 38/06 20060101 C22C038/06; C22C 38/00 20060101
C22C038/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2011 |
JP |
2011-102787 |
May 2, 2011 |
JP |
2011-102789 |
Claims
1. A method for preparing a rare earth permanent magnet, comprising
the steps of: disposing a powder mixture on a surface of a sintered
magnet body having the composition
R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at least one
element selected from rare earth elements inclusive of Y and Sc,
T.sup.1 is one or both of Fe and Co, M is at least one element
selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn,
Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi, B is boron, "a," "b," "2c" and "d" indicative of atomic percent
are in the range: 12.ltoreq.a.ltoreq.20, 0.ltoreq.c.ltoreq.10,
4.0.ltoreq.d.ltoreq.7.0, the balance of b, and a+b+c+d=100, the
powder mixture comprising an alloy powder having the composition
R.sup.1.sub.iM.sup.1.sub.jH.sub.k wherein R.sup.1 is at least one
element selected from rare earth elements inclusive of Y and Sc,
M.sup.1 is at least one element selected from the group consisting
of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu, Zn, Ga, Ge, Zr, Nb,
Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, H is hydrogen, "i," "j"
and "k" indicative of atomic percent are in the range:
15<j.ltoreq.99, 0<k.ltoreq.(i.times.2.5), the balance of i,
and i+j+k=100, containing at least 70% by volume of an
intermetallic compound phase, and having an average particle size
of up to 500 .mu.m, and at least 10% by weight of an R.sup.2 oxide
wherein R.sup.2 is at least one element selected from rare earth
elements inclusive of Y and Sc, having an average particle size of
up to 100 .mu.m, and heat treating the sintered magnet body having
the powder mixture disposed on its surface at a temperature lower
than or equal to the sintering temperature of the sintered magnet
body in vacuum or in an inert gas, for causing the elements
R.sup.1, R.sup.2, and M.sup.1 in the powder mixture to diffuse to
grain boundaries in the interior of the sintered magnet body and/or
near grain boundaries within the sintered magnet body primary phase
grains.
2. The method of claim 1 wherein the heat treating step includes
heat treatment at a temperature from 200.degree. C. to
(Ts-10).degree. C. for 1 minute to 30 hours wherein Ts represents
the sintering temperature of the sintered magnet body.
3. The method of claim 1 wherein the disposing step includes
dispersing the powder mixture in an organic solvent or water,
immersing the sintered magnet body in the resulting slurry, taking
up the sintered magnet body, and drying for thereby covering the
surface of the sintered magnet body with the powder mixture.
4. The method of claim 1 wherein the sintered magnet body has a
shape including a minimum portion with a dimension equal to or less
than 20 mm.
5. A rare earth permanent magnet, which is prepared by disposing a
powder mixture on a surface of a sintered magnet body having the
composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at
least one element selected from rare earth elements inclusive of Y
and Sc, T.sup.1 is one or both of Fe and Co, M is at least one
element selected from the group consisting of Al, Si, C, P, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative of atomic
percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.iM.sup.1.sub.jH.sub.k wherein
R.sup.1 is at least one element selected from rare earth elements
inclusive of Y and Sc, M.sup.1 is at least one element selected
from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe,
Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi, H is hydrogen, "i," "j" and "k" indicative of atomic percent
are in the range: 15<j.ltoreq.99, 0<k.ltoreq.(i.times.2.5),
the balance of i, and i+j+k=100, containing at least 70% by volume
of an intermetallic compound phase, and having an average particle
size of up to 500 .mu.m, and at least 10% by weight of an R.sup.2
oxide wherein R.sup.2 is at least one element selected from rare
earth elements inclusive of Y and Sc, having an average particle
size of up to 100 .mu.m, and heat treating the sintered magnet body
having the powder mixture disposed on its surface at a temperature
lower than or equal to the sintering temperature of the sintered
magnet body in vacuum or in an inert gas, wherein the elements
R.sup.1, R.sup.2 and M.sup.1 in the powder mixture are diffused to
grain boundaries in the interior of the sintered magnet body and/or
near grain boundaries within the sintered magnet body primary phase
grains so that the coercive force of the rare earth permanent
magnet is increased over the original sintered magnet body.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Divisional of U.S. application Ser.
No. 15/454,433, filed on Mar. 9, 2017, and wherein U.S. application
Ser. No. 15/454,433 is a Divisional of U.S. patent application Ser.
No. 13/461,043 filed on May 1, 2012, which is a non-provisional
application which claims priority under 35 U.S.C. .sctn. 119(a) on
Japanese Patent Application Nos. 2011-102787 and 2011-102789 filed
in Japan on May 2, 2011 and May 2, 2011, respectively, the entire
contents of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to an R--Fe--B permanent magnet
having an enhanced coercive force with a minimal decline of
remanence, and a method for preparing the same by coating a
sintered magnet body with a mixture of an intermetallic compound,
alloy or metal powder and a rare earth oxide and heat treating the
coated body for diffusion.
BACKGROUND ART
[0003] By virtue of excellent magnetic properties, Nd--Fe--B
permanent magnets find an ever increasing range of application. The
recent challenge to the environmental problem has expanded the
application range of these magnets from household electric
appliances to industrial equipment, electric automobiles and wind
power generators. It is required to further improve the performance
of Nd--Fe--B magnets.
[0004] Indexes for the performance of magnets include remanence (or
residual magnetic flux density) and coercive force. An increase in
the remanence of Nd--Fe--B sintered magnets can be achieved by
increasing the volume factor of Nd.sub.2Fe.sub.14B compound and
improving the crystal orientation. To this end, a number of
modifications have been made. For increasing coercive force, there
are known different approaches including grain refinement, the use
of alloy compositions with greater Nd contents, and the addition of
coercivity enhancing elements such as Al and Ga. The currently most
common approach is to use alloy compositions having Dy or Tb
substituted for part of Nd.
[0005] It is believed that the coercivity creating mechanism of
Nd--Fe--B magnets is the nucleation type wherein nucleation of
reverse magnetic domains at grain boundaries governs a coercive
force. In general, a disorder of crystalline structure occurs at
the grain boundary or interface. If a disorder of crystalline
structure extends several nanometers in a depth direction near the
interface of grains of Nd.sub.2Fe.sub.14B compound which is the
primary phase of the magnet, then it incurs a lowering of
magnetocrystalline anisotropy and facilitates formation of reverse
magnetic domains, reducing a coercive force (see Non-Patent
Document 1). Substituting Dy or Tb for some Nd in the
Nd.sub.2Fe.sub.14B compound increases the anisotropic magnetic
field of the compound phase so that the coercive force is
increased. When Dy or Tb is added in an ordinary way, however, a
loss of remanence is unavoidable because Dy or Tb substitution
occurs not only near the interface of the primary phase, but even
in the interior of the primary phase. Another problem arises in
that amounts of expensive Tb and Dy must be used.
[0006] Besides, a number of attempts have been made for increasing
the coercive force of Nd--Fe--B magnets. One exemplary attempt is a
two-alloy method of preparing an Nd--Fe--B magnet by mixing two
powdered alloys of different composition and sintering the mixture.
Specifically, a powder of alloy A consisting of R.sub.2Fe.sub.14B
primary phase wherein R is mainly Nd and Pr, and a powder of alloy
B containing various additive elements including Dy, Tb, Ho, Er,
Al, Ti, V, and Mo, typically Dy and Tb are mixed together. This is
followed by fine pulverization, molding in a magnetic field,
sintering, and aging treatment whereby the Nd--Fe--B magnet is
prepared. The sintered magnet thus obtained produces a high
coercive force while minimizing a decline of remanence because Dy
and Tb are absent at the center of R.sub.2Fe.sub.14B compound
primary phase grains and instead, the additive elements like Dy and
Tb are localized near grain boundaries (see Patent Documents 1 and
2). In this method, however, Dy and Tb diffuse into the interior of
primary phase grains during the sintering so that the layer where
Dy and Tb are localized near grain boundaries has a thickness equal
to or more than about 1 micrometer, which is substantially greater
than the depth where nucleation of reverse magnetic domains occurs.
The results are still not fully satisfactory.
[0007] Recently, there have been developed several processes of
diffusing certain elements from the surface to the interior of a
R--Fe--B sintered body for improving magnet properties. In one
exemplary process, a rare earth metal such as Yb, Dy, Pr or Tb, or
Al or Ta is deposited on the surface of Nd--Fe--B magnet using an
evaporation or sputtering technique, followed by heat treatment, as
described in Patent Documents 3 to 5 and Non-Patent Documents 2 and
3. Another exemplary process involves applying a powder of rare
earth inorganic compound such as fluoride or oxide onto the surface
of a sintered body and heat treatment as described in Patent
Document 6. With these processes, the elements (e.g., Dy and Tb)
disposed on the sintered body surface pass through grain boundaries
in the sintered body structure and diffuse into the interior of the
sintered body during the heat treatment. As a consequence, Dy and
Tb can be enriched in a very high concentration at grain boundaries
or near grain boundaries within sintered body primary phase grains.
As compared with the two-alloy method described previously, these
processes produce an ideal morphology. Since the magnet properties
reflect the morphology, a minimized decline of remanence and an
increase of coercive force are accomplished. However, the processes
utilizing evaporation or sputtering have many problems associated
with units and steps when practiced on a mass scale and suffer from
poor productivity.
[0008] Besides the foregoing methods, Patent Document 6 discloses a
method comprising coating a surface of a sintered body with a
powdered rare earth inorganic compound such as fluoride or oxide
and heat treatment, and Patent Document 8 discloses a method
comprising mixing an Al, Cu or Zn powder with a fluoride, coating a
magnet with the mixture, and heat treatment. These methods are
characterized by a very simple coating step and a high
productivity. Specifically, since the coating step is carried out
by dispersing a non-metallic inorganic compound powder in water,
immersing a magnet in the dispersion and drying, the step is simple
as compared with sputtering and evaporation. Even when a heat
treatment furnace is packed with a large number of magnet pieces,
the magnet pieces are not fused together during heat treatment.
This leads to a high productivity. However, since Dy or Tb diffuses
through substitution reaction between the powder and the magnet
component, it is difficult to introduce a substantial amount of Dy
or Tb into the magnet.
[0009] Further Patent Document 7 discloses coating of a magnet body
with a mixture of an oxide or fluoride of Dy or Tb and calcium or
calcium hydride powder, followed by heat treatment. During the heat
treatment, once Dy or Tb is reduced utilizing calcium reducing
reaction, Dy or Tb is diffused. The method is advantageous for
introducing a substantial amount of Dy or Tb into the magnet, but
less productive because the calcium or calcium hydride powder needs
careful handling.
[0010] Patent Documents 9 to 13 disclose coating of the sintered
body surface with a metal alloy instead of a rare earth inorganic
compound powder such as fluoride or oxide, followed by heat
treatment. The method of coating with only metal alloy has the
drawback that it is difficult to coat the metal alloy onto the
magnet surface in a large and uniform coating weight. In Patent
Documents 14 and 15, a metal powder containing Dy and/or Tb is
diffused into the mother alloy. The oxygen concentration of the
mother alloy is restricted below 0.5% by weight, and the rare
earth-containing metal powder is closely contacted with the mother
alloy by a barrel painting technique of oscillating impact media
within a barrel for agitation. Diffusion takes place under these
conditions. However, this method requires many steps as compared
with the method of coating a mother alloy magnet with a dispersion
of a powder mixture of an intermetallic compound and a rare earth
oxide in a solvent. The method is time consuming and is not
industrially useful.
CITATION LIST
[0011] Patent Document 1: JP 1820677 [0012] Patent Document 2: JP
3143156 [0013] Patent Document 3: JP-A 2004-296973 [0014] Patent
Document 4: JP 3897724 [0015] Patent Document 5: JP-A 2005-11973
[0016] Patent Document 6: JP 4450239 [0017] Patent Document 7: JP
4548673 [0018] Patent Document 8: JP-A 2007-287874 [0019] Patent
Document 9: JP 4656323 [0020] Patent Document 10: JP 4482769 [0021]
Patent Document 11: JP-A 2008-263179 [0022] Patent Document 12:
JP-A 2009-289994 [0023] Patent Document 13: JP-A 2010-238712 [0024]
Patent Document 14: WO 2008/032426 [0025] Patent Document 15: WO
2008/139690 [0026] Non-Patent Document 1: K. D. Durst and H.
Kronmuller, "THE COERCIVE FIELD OF SINTERED AND MELT-SPUN NdFeB
MAGNETS," Journal of Magnetism and Magnetic Materials, 68 (1987),
63-75 [0027] Non-Patent Document 2: K. T. Park, K. Hiraga and M.
Sagawa, "Effect of Metal-Coating and Consecutive Heat Treatment on
Coercivity of Thin Nd--Fe--B Sintered Magnets," Proceedings of the
Sixteen International Workshop on Rare-Earth Magnets and Their
Applications, Sendai, p. 257 (2000) [0028] Non-Patent Document 3:
K. Machida, et al., "Grain Boundary Modification of Nd--Fe--B
Sintered Magnet and Magnetic Properties," Proceedings of 2004
Spring Meeting of the Powder & Powder Metallurgy Society, p.
202
SUMMARY OF INVENTION
[0029] An object of the invention is to provide an R--Fe--B
sintered magnet which is prepared by coating a sintered magnet body
with a powder mixture of an intermetallic compound, alloy or metal
powder and a rare earth oxide and effecting diffusion treatment and
which magnet features efficient productivity, excellent magnetic
performance, a minimal amount of Tb or Dy used, an increased
coercive force, and a minimized decline of remanence. Another
object is to provide a method for preparing the same.
[0030] Regarding the surface coating of an R--Fe--B sintered body
with a rare earth oxide which is the best from the aspect of
productivity, the inventors attempted to increase the diffusion
amount. The inventors have discovered that when a mixture of an
oxide containing a rare earth element such as Dy or Tb and an
intermetallic compound or metal powder is used for coating, a
significant amount of Dy or Tb can be introduced near interfaces of
primary phase grains within the magnet through the passages in the
form of grain boundaries, as compared with the method of effecting
heat treatment after coating with a rare earth inorganic compound
powder such as fluoride or oxide, because the oxide is partially
reduced during heat treatment. As a consequence, the coercive force
of the magnet is increased while minimizing a decline of remanence.
Additionally, the process is improved in productivity over the
prior art processes. The invention is predicated on this
discovery.
[0031] The invention provides rare earth permanent magnets and
methods for preparing the same, as defined below.
[1] A method for preparing a rare earth permanent magnet,
comprising the steps of:
[0032] disposing a powder mixture on a surface of a sintered magnet
body having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d
wherein R is at least one element selected from rare earth elements
inclusive of Y and Sc, T.sup.1 is one or both of Fe and Co, M is at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb,
Hf, Ta, W, Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative
of atomic percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.iM.sup.1.sub.j wherein R.sup.1
is at least one element selected from rare earth elements inclusive
of Y and Sc, M.sup.1 is at least one element selected from the
group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu,
Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, "i"
and "j" indicative of atomic percent are in the range:
15<j.ltoreq.99, the balance of i, and i+j=100, containing at
least 70% by volume of an intermetallic compound phase, and having
an average particle size of up to 500 .mu.m, and at least 10% by
weight of an R.sup.2 oxide wherein R.sup.2 is at least one element
selected from rare earth elements inclusive of Y and Sc, having an
average particle size of up to 100 .mu.m, and
[0033] heat treating the sintered magnet body having the powder
mixture disposed on its surface at a temperature lower than or
equal to the sintering temperature of the sintered magnet body in
vacuum or in an inert gas, for causing the elements R.sup.1,
R.sup.2 and M.sup.1 in the powder mixture to diffuse to grain
boundaries in the interior of the sintered magnet body and/or near
grain boundaries within the sintered magnet body primary phase
grains.
[2] A method for preparing a rare earth permanent magnet,
comprising the steps of:
[0034] disposing a powder mixture on a surface of a sintered magnet
body having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d
wherein R is at least one element selected from rare earth elements
inclusive of Y and Sc, T.sup.1 is one or both of Fe and Co, M is at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb,
Hf, Ta, W, Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative
of atomic percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.iM.sup.1.sub.jH.sub.k wherein
R.sup.1 is at least one element selected from rare earth elements
inclusive of Y and Sc, M.sup.1 is at least one element selected
from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe,
Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi, H is hydrogen, "i," "j" and "k" indicative of atomic percent
are in the range: 15<j.ltoreq.99, 0<k.ltoreq.(i.times.2.5),
the balance of i, and i+j+k=100, containing at least 70% by volume
of an intermetallic compound phase, and having an average particle
size of up to 500 .mu.m, and at least 10% by weight of an R.sup.2
oxide wherein R.sup.2 is at least one element selected from rare
earth elements inclusive of Y and Sc, having an average particle
size of up to 100 .mu.m, and
[0035] heat treating the sintered magnet body having the powder
mixture disposed on its surface at a temperature lower than or
equal to the sintering temperature of the sintered magnet body in
vacuum or in an inert gas, for causing the elements R.sup.1,
R.sup.2, and M.sup.1 in the powder mixture to diffuse to grain
boundaries in the interior of the sintered magnet body and/or near
grain boundaries within the sintered magnet body primary phase
grains.
[3] The method of [1] or [2] wherein the heat treating step
includes heat treatment at a temperature from 200.degree. C. to
(Ts-10).degree. C. for 1 minute to 30 hours wherein Ts represents
the sintering temperature of the sintered magnet body. [4] The
method of any one of [1] to [3] wherein the disposing step includes
dispersing the powder mixture in an organic solvent or water,
immersing the sintered magnet body in the resulting slurry, taking
up the sintered magnet body, and drying for thereby covering the
surface of the sintered magnet body with the powder mixture. [5] A
method for preparing a rare earth permanent magnet, comprising the
steps of:
[0036] disposing a powder mixture on a surface of a sintered magnet
body having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d
wherein R is at least one element selected from rare earth elements
inclusive of Y and Sc, T.sup.1 is one or both of Fe and Co, M is at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb,
Hf, Ta, W, Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative
of atomic percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.xT.sup.2.sub.yM.sup.1.sub.z
wherein R.sup.1 is at least one element selected from rare earth
elements inclusive of Y and Sc, T.sup.2 is one or both of Fe and
Co, M.sup.1 is at least one element selected from the group
consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr,
Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, x, y and z
indicative of atomic percent are in the range:
5.ltoreq.x.ltoreq.85, 15<z.ltoreq.95, x+z<100, the balance of
y, y>0, and x+y+z=100, containing at least 70% by volume of an
intermetallic compound phase, and having an average particle size
of up to 500 .mu.m, and at least 10% by weight of an R.sup.2 oxide
wherein R.sup.2 is at least one element selected from rare earth
elements inclusive of Y and Sc, having an average particle size of
up to 100 .mu.m, and
[0037] heat treating the sintered magnet body having the powder
mixture disposed on its surface at a temperature lower than or
equal to the sintering temperature of the sintered magnet body in
vacuum or in an inert gas, for causing the elements R.sup.1,
R.sup.2, M and T.sup.2 in the powder mixture to diffuse to grain
boundaries in the interior of the sintered magnet body and/or near
grain boundaries within the sintered magnet body primary phase
grains.
[6] The method of [5] wherein the heat treating step includes heat
treatment at a temperature from 200.degree. C. to (Ts-10).degree.
C. for 1 minute to 30 hours wherein Ts represents the sintering
temperature of the sintered magnet body. [7] The method of [5] or
[6] wherein the disposing step includes dispersing the powder
mixture in an organic solvent or water, immersing the sintered
magnet body in the resulting slurry, taking up the sintered magnet
body, and drying for thereby covering the surface of the sintered
magnet body with the powder mixture. [8] The method of any one of
[1] to [7] wherein the sintered magnet body has a shape including a
minimum portion with a dimension equal to or less than 20 mm. [9] A
rare earth permanent magnet, which is prepared by disposing a
powder mixture on a surface of a sintered magnet body having the
composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at
least one element selected from rare earth elements inclusive of Y
and Sc, T.sup.1 is one or both of Fe and Co, M is at least one
element selected from the group consisting of Al, Si, C, P, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative of atomic
percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.iM.sup.1.sub.j wherein R.sup.1
is at least one element selected from rare earth elements inclusive
of Y and Sc, M.sup.1 is at least one element selected from the
group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu,
Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, "i"
and "j" indicative of atomic percent are in the range:
15<j.ltoreq.99, the balance of i, and i+j=100, containing at
least 70% by volume of an intermetallic compound phase, and having
an average particle size of up to 500 .mu.m, and at least 10% by
weight of an R.sup.2 oxide wherein R.sup.2 is at least one element
selected from rare earth elements inclusive of Y and Sc, having an
average particle size of up to 100 .mu.m, and heat treating the
sintered magnet body having the powder mixture disposed on its
surface at a temperature lower than or equal to the sintering
temperature of the sintered magnet body in vacuum or in an inert
gas, wherein
[0038] the elements R.sup.1, R.sup.2 and M.sup.1 in the powder
mixture are diffused to grain boundaries in the interior of the
sintered magnet body and/or near grain boundaries within the
sintered magnet body primary phase grains so that the coercive
force of the rare earth permanent magnet is increased over the
original sintered magnet body.
[10] A rare earth permanent magnet, which is prepared by disposing
a powder mixture on a surface of a sintered magnet body having the
composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at
least one element selected from rare earth elements inclusive of Y
and Sc, T.sup.1 is one or both of Fe and Co, M is at least one
element selected from the group consisting of Al, Si, C, P, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative of atomic
percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.iM.sup.1.sub.jH.sub.k wherein
R.sup.1 is at least one element selected from rare earth elements
inclusive of Y and Sc, M.sup.1 is at least one element selected
from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe,
Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi, H is hydrogen, "i," "j" and "k" indicative of atomic percent
are in the range: 15<j.ltoreq.99, 0<k.ltoreq.(i.times.2.5),
the balance of i, and i+j+k=100, containing at least 70% by volume
of an intermetallic compound phase, and having an average particle
size of up to 500 .mu.m, and at least 10% by weight of an R.sup.2
oxide wherein R.sup.2 is at least one element selected from rare
earth elements inclusive of Y and Sc, having an average particle
size of up to 100 .mu.m, and heat treating the sintered magnet body
having the powder mixture disposed on its surface at a temperature
lower than or equal to the sintering temperature of the sintered
magnet body in vacuum or in an inert gas, wherein
[0039] the elements R.sup.1, R.sup.2 and M.sup.1 in the powder
mixture are diffused to grain boundaries in the interior of the
sintered magnet body and/or near grain boundaries within the
sintered magnet body primary phase grains so that the coercive
force of the rare earth permanent magnet is increased over the
original sintered magnet body.
[11] A rare earth permanent magnet, which is prepared by disposing
a powder mixture on a surface of a sintered magnet body having the
composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at
least one element selected from rare earth elements inclusive of Y
and Sc, T.sup.1 is one or both of Fe and Co, M is at least one
element selected from the group consisting of Al, Si, C, P, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative of atomic
percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition R.sup.1.sub.xT.sup.2.sub.yM.sup.1.sub.z
wherein R.sup.1 is at least one element selected from rare earth
elements inclusive of Y and Sc, T.sup.2 is one or both of Fe and
Co, M.sup.1 is at least one element selected from the group
consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr,
Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, x, y and z
indicative of atomic percent are in the range:
5.ltoreq.x.ltoreq.85, 15<z.ltoreq.95, x+z<100, the balance of
y, y>0, and x+y+z=100, containing at least 70% by volume of an
intermetallic compound phase, and having an average particle size
of up to 500 .mu.m, and at least 10% by weight of an R.sup.2 oxide
wherein R.sup.2 is at least one element selected from rare earth
elements inclusive of Y and Sc, having an average particle size of
up to 100 .mu.m, and heat treating the sintered magnet body having
the powder mixture disposed on its surface at a temperature lower
than or equal to the sintering temperature of the sintered magnet
body in vacuum or in an inert gas, wherein
[0040] the elements R.sup.1, R.sup.2, M.sup.1 and T.sup.2 in the
powder mixture are diffused to grain boundaries in the interior of
the sintered magnet body and/or near grain boundaries within the
sintered magnet body primary phase grains so that the coercive
force of the rare earth permanent magnet is increased over the
original sintered magnet body.
[12] A method for preparing a rare earth permanent magnet,
comprising the steps of:
[0041] disposing a powder mixture on a surface of a sintered magnet
body having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d
wherein R is at least one element selected from rare earth elements
inclusive of Y and Sc, T.sup.1 is one or both of Fe and Co, M is at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb,
Hf, Ta, W, Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative
of atomic percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an alloy powder
having the composition M.sup.1.sub.dM.sup.2.sub.e wherein M.sup.1
and M.sup.2 each are at least one element selected from the group
consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu, Zn, Ga,
Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, M.sup.1 and
M.sup.2 are different, "d" and "e" indicative of atomic percent are
in the range: 0.1.ltoreq.e.ltoreq.99.9, the balance of d, and
d+e=100, containing at least 70% by volume of an intermetallic
compound phase, and having an average particle size of up to 500
.mu.m, and at least 10% by weight of an R.sup.2 oxide wherein
R.sup.2 is at least one element selected from rare earth elements
inclusive of Y and Sc, having an average particle size of up to 100
.mu.m, and
[0042] heat treating the sintered magnet body having the powder
mixture disposed on its surface at a temperature lower than or
equal to the sintering temperature of the sintered magnet body in
vacuum or in an inert gas, for causing the elements R.sup.2,
M.sup.1 and M.sup.2 in the powder mixture to diffuse to grain
boundaries in the interior of the sintered magnet body and/or near
grain boundaries within the sintered magnet body primary phase
grains.
[13] A method for preparing a rare earth permanent magnet,
comprising the steps of:
[0043] disposing a powder mixture on a surface of a sintered magnet
body having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d
wherein R is at least one element selected from rare earth elements
inclusive of Y and Sc, T.sup.1 is one or both of Fe and Co, M is at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb,
Hf, Ta, W, Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative
of atomic percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an M.sup.1 powder
wherein M.sup.1 is at least one element selected from the group
consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu, Zn, Ga,
Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, having an
average particle size of up to 500 .mu.m, and at least 10% by
weight of an R.sup.2 oxide wherein R.sup.2 is at least one element
selected from rare earth elements inclusive of Y and Sc, having an
average particle size of up to 100 .mu.m, and
[0044] heat treating the sintered magnet body having the powder
mixture disposed on its surface at a temperature lower than or
equal to the sintering temperature of the sintered magnet body in
vacuum or in an inert gas, for causing the elements R.sup.2 and
M.sup.1 in the powder mixture to diffuse to grain boundaries in the
interior of the sintered magnet body and/or near grain boundaries
within the sintered magnet body primary phase grains.
[14] The method of [12] or [13] wherein the heat treating step
includes heat treatment at a temperature from 200.degree. C. to
(Ts-10).degree. C. for 1 minute to 30 hours wherein Ts represents
the sintering temperature of the sintered magnet body. [15] The
method of any one of [12] to [14] wherein the disposing step
includes dispersing the powder mixture in an organic solvent or
water, immersing the sintered magnet body in the resulting slurry,
taking up the sintered magnet body, and drying for thereby covering
the surface of the sintered magnet body with the powder mixture.
[16] The method of any one of [12] to [15] wherein the sintered
magnet body has a shape including a minimum portion with a
dimension equal to or less than 20 mm. [17] A rare earth permanent
magnet, which is prepared by disposing a powder mixture on a
surface of a sintered magnet body having the composition
R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at least one
element selected from rare earth elements inclusive of Y and Sc,
T.sup.1 is one or both of Fe and Co, M is at least one element
selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn,
Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi, B is boron, "a," "b," "c" and "d" indicative of atomic percent
are in the range: 12.ltoreq.a.ltoreq.20, 0.ltoreq.c.ltoreq.10,
4.0.ltoreq.d.ltoreq.7.0, the balance of b, and a+b+c+d=100, the
powder mixture comprising an alloy powder having the composition
M.sup.1.sub.dM.sup.2.sub.e wherein M.sup.1 and M.sup.2 each are at
least one element selected from the group consisting of Al, Si, C,
P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In,
Sn, Sb, Hf, Ta, W, Pb, and Bi, M.sup.1 and M.sup.2 are different,
"d" and "e" indicative of atomic percent are in the range:
0.1.ltoreq.e.ltoreq.99.9, the balance of d, and d+e=100, containing
at least 70% by volume of an intermetallic compound phase, and
having an average particle size of up to 500 .mu.m, and at least
10% by weight of an R.sup.2 oxide wherein R.sup.2 is at least one
element selected from rare earth elements inclusive of Y and Sc,
having an average particle size of up to 100 .mu.m, and heat
treating the sintered magnet body having the powder mixture
disposed on its surface at a temperature lower than or equal to the
sintering temperature of the sintered magnet body in vacuum or in
an inert gas, wherein
[0045] the elements R.sup.2, M.sup.1 and M.sup.2 in the powder
mixture are diffused to grain boundaries in the interior of the
sintered magnet body and/or near grain boundaries within the
sintered magnet body primary phase grains so that the coercive
force of the rare earth permanent magnet is increased over the
original sintered magnet body.
[18] A rare earth permanent magnet, which is prepared by disposing
a powder mixture on a surface of a sintered magnet body having the
composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d wherein R is at
least one element selected from rare earth elements inclusive of Y
and Sc, T.sup.1 is one or both of Fe and Co, M is at least one
element selected from the group consisting of Al, Si, C, P, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi, B is boron, "a," "b," "c" and "d" indicative of atomic
percent are in the range: 12.ltoreq.a.ltoreq.20,
0.ltoreq.c.ltoreq.10, 4.0.ltoreq.d.ltoreq.7.0, the balance of b,
and a+b+c+d=100, the powder mixture comprising an M.sup.1 powder
wherein M.sup.1 is at least one element selected from the group
consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Fe, Co, Cu, Zn, Ga,
Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, having an
average particle size of up to 500 .mu.m, and at least 10% by
weight of an R.sup.2 oxide wherein R.sup.2 is at least one element
selected from rare earth elements inclusive of Y and Sc, having an
average particle size of up to 100 .mu.m, and heat treating the
sintered magnet body having the powder mixture disposed on its
surface at a temperature lower than or equal to the sintering
temperature of the sintered magnet body in vacuum or in an inert
gas, wherein
[0046] the elements R.sup.2 and M.sup.1 in the powder mixture are
diffused to grain boundaries in the interior of the sintered magnet
body and/or near grain boundaries within the sintered magnet body
primary phase grains so that the coercive force of the rare earth
permanent magnet is increased over the original sintered magnet
body.
Advantageous Effects of Invention
[0047] When a mixture of an oxide containing a rare earth element
such as Dy or Tb and an intermetallic compound or metal powder is
used for coating, the oxide is partially reduced during subsequent
heat treatment. Thus a significant amount of the rare earth element
such as Dy or Tb can be introduced near interfaces of primary phase
grains within the magnet through the passages in the form of grain
boundaries, as compared with the method of effecting heat treatment
after coating with a rare earth inorganic compound powder such as
fluoride or oxide. As a consequence, the coercive force of the
magnet is increased while minimizing a decline of remanence.
Additionally, the process is improved in productivity over the
prior art processes. The R--Fe--B sintered magnet exhibits
excellent magnetic performance, an increased coercive force, and a
minimal decline of remanence, despite a minimal amount of Tb or Dy
used.
DESCRIPTION OF EMBODIMENTS
[0048] Briefly stated, an R--Fe--B sintered magnet is prepared
according to the invention by applying a powder mixture of an
intermetallic compound-based alloy powder and a rare earth oxide or
metal powder onto a sintered magnet body and effecting diffusion
treatment. The resultant magnet has advantages including excellent
magnetic performance and a minimal amount of Tb or Dy used.
[0049] The mother material used herein is a sintered magnet body
having the composition R.sub.aT.sup.1.sub.bM.sub.cB.sub.d, which is
sometimes referred to as "mother sintered body." Herein R is one or
more elements selected from rare earth elements inclusive of
yttrium (Y) and scandium (Sc), specifically from among Sc, Y, La,
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. The rare earth
elements inclusive of Sc and Y account for 12 to 20 atomic percent
(at %), and preferably 13 to 18 at % of the sintered magnet body,
differently stated, 12.ltoreq.a.ltoreq.20, preferably
13.ltoreq.a.ltoreq.18. Preferably the majority of R is Nd and/or
Pr. Specifically Nd and/or Pr accounts for 50 to 100 at %, more
preferably 70 to 100 at % of the rare earth elements. T.sup.1 is
one or both of iron (Fe) and cobalt (Co). M is one or more elements
selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn,
Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and
Bi and accounts for 0 to 10 at %, and preferably 0 to 5 at % of the
sintered magnet body, differently stated, 0.ltoreq.c.ltoreq.10,
preferably 0.ltoreq.c5. B is boron and accounts for 4 to 7 at % of
the sintered magnet body (4.ltoreq.d.ltoreq.7). Particularly when B
is 5 to 6 at % (5.ltoreq.d.ltoreq.6), a significant improvement in
coercive force is achieved by diffusion treatment. The balance
consists of T.sup.1. Preferably T.sup.1 accounts for 60 to 84 at %,
more preferably 70 to 82 at % of the sintered magnet body,
differently stated, 60.ltoreq.b.ltoreq.84, preferably
70.ltoreq.b.ltoreq.82. The subscripts "a," "b," "c" and "d"
indicative of atomic percent meet a+b+c+d=100.
[0050] The alloy for the mother sintered magnet body is prepared by
melting metal or alloy feeds in vacuum or an inert gas atmosphere,
preferably argon atmosphere, and casting the melt into a flat mold
or book mold or strip casting. A possible alternative is a
so-called two-alloy process involving separately preparing an alloy
approximate to the R.sub.2Fe.sub.14B compound composition
constituting the primary phase of the relevant alloy and a rare
earth-rich alloy serving as a liquid phase aid at the sintering
temperature, crushing, then weighing and mixing them. Notably, the
alloy approximate to the primary phase composition is subjected to
homogenizing treatment, if necessary, for the purpose of increasing
the amount of the R.sub.2Fe.sub.14B compound phase, since primary
crystal .alpha.-Fe is likely to be left depending on the cooling
rate during casting and the alloy composition. The homogenizing
treatment is a heat treatment at 700 to 1,200.degree. C. for at
least one hour in vacuum or in an Ar atmosphere. Alternatively, the
alloy approximate to the primary phase composition may be prepared
by the strip casting technique. To the rare earth-rich alloy
serving as a liquid phase aid, the melt quenching and strip casting
techniques are applicable as well as the above-described casting
technique.
[0051] The alloy is generally crushed or coarsely ground to a size
of 0.05 to 3 mm, especially 0.05 to 1.5 mm. The crushing step uses
a Brown mill or hydrogen decrepitation, with the hydrogen
decrepitation being preferred for those alloys as strip cast. The
coarse powder is then finely divided to an average particle size of
0.2 to 30 .mu.m, especially 0.5 to 20 .mu.m, for example, on a jet
mill using high-pressure nitrogen.
[0052] The fine powder is compacted on a compression molding
machine under a magnetic field. The green compact is then placed in
a sintering furnace where it is sintered in vacuum or in an inert
gas atmosphere usually at a temperature of 900 to 1,250.degree. C.,
preferably 1,000 to 1,100.degree. C. The sintered block thus
obtained contains 60 to 99% by volume, preferably 80 to 98% by
volume of the tetragonal R.sub.2Fe.sub.14B compound as the primary
phase, with the balance being 0.5 to 20% by volume of a rare
earth-rich phase and 0.1 to 10% by volume of at least one compound
selected from among rare earth oxides, and carbides, nitrides and
hydroxides of incidental impurities, and mixtures or composites
thereof.
[0053] The resulting sintered magnet block may be machined or
worked into a predetermined shape. In the invention, the elements
(including R.sup.1, R.sup.2, M.sup.1, M.sup.2 and T.sup.2) which
are to be diffused into the sintered magnet body interior are
supplied from the sintered magnet body surface. Thus, if a minimum
portion of the sintered magnet body has too large a dimension, the
objects of the invention are not achievable. For this reason, the
shape includes a minimum portion having a dimension equal to or
less than 20 mm, and preferably equal to or less than 10 mm, with
the lower limit being equal to or more than 0.1 mm. The sintered
body includes a maximum portion whose dimension is not particularly
limited, with the maximum portion dimension being desirably equal
to or less than 200 mm.
[0054] According to the invention, a diffusion powder selected from
the following powder mixtures (i) to (iv) is disposed on the
sintered magnet body before diffusion treatment is carried out.
[0055] (i) a powder mixture of an alloy of the composition
R.sup.1.sub.iM.sup.1.sub.j containing at least 70% by volume of a
rare earth intermetallic compound phase and an R.sup.2 oxide [0056]
(ii) a powder mixture of an alloy of the composition
R.sup.1.sub.iM.sup.1.sub.jH.sub.k containing at least 70% by volume
of a rare earth intermetallic compound phase and an R.sup.2 oxide
[0057] (iii) a powder mixture of an alloy of the composition
R.sup.1.sub.xT.sup.2.sub.yM.sup.1.sub.z containing at least 70% by
volume of a rare earth intermetallic compound phase and an R.sup.2
oxide [0058] (iv) a powder mixture of an alloy of the composition
M.sup.1.sub.dM.sup.2.sub.e containing at least 70% by volume of an
intermetallic compound phase and an R.sup.2 oxide [0059] (v) a
powder mixture of a metal M.sup.1 and an R.sup.2 oxide
[0060] The alloy which is often referred to as "diffusion alloy" is
in powder form having an average particle size of less than or
equal to 500 m. The R.sup.2 oxide wherein R.sup.2 is one or more
elements selected from rare earth elements inclusive of Y and Sc is
in powder form having an average particle size of less than or
equal to 100 .mu.m. The powder mixture consists of the diffusion
alloy and at least 10% by weight of the R.sup.2 oxide. The powder
mixture is disposed on the surface of the sintered magnet body. The
sintered magnet body having the powder mixture disposed on its
surface is heat treated at a temperature lower than or equal to the
sintering temperature of the sintered magnet body in vacuum or in
an inert gas, whereby the oxide in admixture with the (rare earth)
intermetallic compound is partially reduced. During the heat
treatment, the elements R.sup.1, R.sup.2, M.sup.1, M.sup.2 and
T.sup.2 in the powder mixture (selected depending on a particular
diffusion powder used) can be diffused to grain boundaries in the
interior of the sintered magnet body and/or near grain boundaries
within the sintered magnet body primary phase grains, in a more
amount than achievable by the prior art methods.
[0061] Herein R.sup.1 is one or more elements selected from rare
earth elements inclusive of Y and Sc. Preferably the majority of
R.sup.1 is Nd and/or Pr. Specifically Nd and/or Pr accounts for 1
to 100 at %, more preferably 20 to 100 at % of R.sup.1. M.sup.1 is
one or more elements selected from the group consisting of Al, Si,
C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn,
Sb, Hf, Ta, W, Pb, and Bi. T.sup.2 is Fe and/or Co.
[0062] In the alloy R.sup.1.sub.iM.sup.1.sub.j, M.sup.1 accounts
for 15 to 99 at %, preferably 20 to 90 at %, differently stated,
j=15 to 99, preferably j=20 to 90, with the balance of R.sup.1
(meaning i+j=100).
[0063] In the alloy R.sup.1.sub.iM.sup.1.sub.jH.sub.k, M.sup.1
accounts for 15 to 99 at %, preferably 20 to 90 at %, differently
stated, j=15 to 99, preferably j=20 to 90. Hydrogen (H) is present
in an amount of 0<k.ltoreq.(i.times.2.5) at %, preferably at
least 0.1 at % (k.ltoreq.0.1). The balance consists of R.sup.1
(meaning i+j+k=100), and R.sup.1 is preferably present in an amount
of 20 to 90 at %, namely i=20 to 90.
[0064] In the alloy R.sup.1.sub.xT.sup.2.sub.yM.sup.1.sub.z,
M.sup.1 accounts for 15 to 95 at %, preferably 20 to 90 at %,
differently stated, z=15 to 90, preferably z=20 to 90. R.sup.1
accounts for 5 to 85 at %, preferably 10 to 80 at %, differently
stated, x=5 to 85, preferably x=10 to 80. The sum of M.sup.1 and
R.sup.2 is less than 100 at % (x+z<100), preferably 25 to 99.5
at % (x+y=25 to 99.5). The balance consists of T.sup.2 which is Fe
and/or Co (meaning x+y+z=100), and y>0. Typically T.sup.2
accounts for 0.5 to 75 at %, preferably 1 to 60 at %, differently
stated, y=0.5 to 75, preferably y=1 to 60.
[0065] In the alloy M.sup.1.sub.dM.sup.2.sub.e, M.sup.1 and M.sup.2
are different from each other and each is one or more elements
selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn,
Ni, Fe, Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi. The subscripts d and e indicative of atomic percent are
in the range: 0.1.ltoreq.e.ltoreq.99.9, preferably
10.ltoreq.e.ltoreq.90, and more preferably 20.ltoreq.e.ltoreq.80,
with the balance of d.
[0066] In the M.sup.1 metal powder, M.sup.1 is one or more elements
selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn,
Ni, Fe, Co, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
Pb, and Bi.
[0067] The diffusion alloy may contain incidental impurities such
as nitrogen (N) and oxygen (O), with an acceptable total amount of
such impurities being equal to or less than 4 at %, preferably
equal to or less than 2 at %, and more preferably equal to or less
than 1 at %.
[0068] The diffusion alloy containing at least 70% by volume of the
intermetallic compound phase may be prepared, like the alloy for
the mother sintered magnet body, by melting metal or alloy feeds in
vacuum or an inert gas atmosphere, preferably argon atmosphere, and
casting the melt into a flat mold or book mold. A high-frequency
melting method and a strip casting method may also be employed. The
alloy is then crushed or coarsely ground to a size of about 0.05 to
3 mm, especially about 0.05 to 1.5 mm by means of a Brown mill or
hydrogen decrepitation. The coarse powder is then finely divided,
for example, by a ball mill, vibration mill or jet mill using
high-pressure nitrogen. The smaller the powder particle size, the
higher becomes the diffusion efficiency. The diffusion alloy
containing the intermetallic compound phase, when powdered,
preferably has an average particle size equal to or less than 500
.mu.m, more preferably equal to or less than 300 .mu.m, and even
more preferably equal to or less than 100 .mu.m. However, if the
particle size is too small, then the influence of surface oxidation
becomes noticeable, and handling is dangerous. Thus the lower limit
of average particle size is preferably equal to or more than 1
.mu.m. As used herein, the "average particle size" may be
determined as a weight average diameter D.sub.50 (particle diameter
at 50% by weight cumulative, or median diameter) using, for
example, a particle size distribution measuring instrument relying
on laser diffractometry or the like.
[0069] The M.sup.1 metal powder may be prepared by crushing or
coarsely grinding a metal mass to a size of 0.05 to 3 mm,
especially 0.05 to 1.5 mm on a suitable grinding machine such as a
jaw crusher or Brown mill. The coarse powder is then finely
divided, for example, by a ball mill, vibration mill or jet mill
using high-pressure nitrogen. Alternatively, fine division may be
achieved by an atomizing method of ejecting a metal melt through
small nozzles under high-pressure gas as mist. The M.sup.1 metal
powder has an average particle size equal to or less than 500
.mu.m, more preferably equal to or less than 300 .mu.m, and even
more preferably equal to or less than 100 .mu.m. However, if the
particle size is too small, then the influence of surface oxidation
becomes noticeable, and handling is dangerous. Thus the lower limit
of average particle size is preferably equal to or more than 1
.mu.m.
[0070] The other component of the powder mixture is an R.sup.2
oxide which may be any of oxides of rare earth elements inclusive
of Y and Sc, preferably oxides containing Dy or Tb. The R.sup.2
oxide powder has an average particle size equal to or less than 100
.mu.m, more preferably equal to or less than 50 .mu.m, and even
more preferably equal to or less than 20 .mu.m. The R.sup.2 oxide
is present in an amount of at least 10% by weight, preferably at
least 20% by weight, and more preferably at least 30% by weight of
the powder mixture. Less than 10% by weight of the R.sup.2 oxide is
too small for the rare earth oxide to exert its mixing effect. The
upper limit of the amount of the R.sup.2 oxide is up to 99% by
weight, especially up to 90% by weight.
[0071] After the powder mixture of the diffusion alloy powder or
M.sup.1 metal powder and the R.sup.2 oxide powder is disposed on
the surface of the mother sintered magnet body, the mother sintered
magnet body coated with the powder mixture is heat treated in
vacuum or in an atmosphere of an inert gas such as argon (Ar) or
helium (He) at a temperature equal to or below the sintering
temperature (designated Ts in .degree. C.) of the sintered magnet
body. This heat treatment is referred to as "diffusion treatment."
The diffusion treatment causes the rare earth oxide in admixture
with the intermetallic compound to be partially reduced, whereby
elements R.sup.1, R.sup.2, M.sup.1, M.sup.2 and T.sup.2 in the
powder mixture are diffused to grain boundaries in the interior of
the sintered magnet body and/or near grain boundaries within
sintered magnet body primary phase grains in more amounts than
achievable in the prior art.
[0072] The powder mixture of the diffusion alloy powder or M.sup.1
metal powder and the R.sup.2 oxide powder is disposed on the
surface of the mother sintered magnet body, for example, by
dispersing the powder mixture in water or an organic solvent to
form a slurry, immersing the magnet body in the slurry, taking up
the magnet body, and drying the magnet body by hot air drying or in
vacuum or in air. Spray coating is also possible. The slurry may
contain 1 to 90% by weight, and preferably 5 to 70% by weight of
the powder mixture.
[0073] The conditions of diffusion treatment vary with the type and
composition of the powder mixture (including the type and
composition of two components) and are preferably selected such
that elements R.sup.1, R.sup.2, M.sup.1, M.sup.2 and T.sup.2 in the
diffusion powder are enriched at grain boundaries in the interior
of the sintered magnet body and/or near grain boundaries within
sintered magnet body primary phase grains. The temperature of
diffusion treatment is equal to or below the sintering temperature
(designated Ts in .degree. C.) of the sintered magnet body. If
diffusion treatment is effected above Ts, there arise problems that
(1) the structure of the sintered magnet body can be altered to
degrade magnetic properties, and (2) the machined dimensions cannot
be maintained due to thermal deformation. For this reason, the
temperature of diffusion treatment is equal to or below Ts.degree.
C. of the sintered magnet body, and preferably equal to or below
(Ts-10).degree. C. The lower limit of temperature may be selected
as appropriate though the temperature is typically at least
200.degree. C., preferably at least 350.degree. C., and more
preferably at least 600.degree. C. The time of diffusion treatment
is typically from 1 minute to 30 hours. Within less than 1 minute,
the diffusion treatment is not complete. If the treatment time
exceeds 30 hours, the structure of the sintered magnet body can be
altered, oxidation or evaporation of components inevitably occurs
to degrade magnetic properties, or R.sup.1, R.sup.2, M.sup.1,
M.sup.2 and T.sup.2 are not only enriched near grain boundaries in
the interior of the sintered body and/or grain boundaries within
sintered body primary phase grains, but also diffused into the
interior of primary phase grains. The preferred time of diffusion
treatment is from 1 minute to 10 hours, and more preferably from 10
minutes to 6 hours.
[0074] Through appropriate diffusion treatment, the constituent
elements R.sup.1, R.sup.2, M.sup.1, M.sup.2 and T.sup.2 in the
powder mixture disposed on the surface of the sintered magnet body
are diffused into the sintered magnet body while traveling mainly
along grain boundaries in the sintered magnet body structure. This
results in the structure in which R.sup.1, R.sup.2, M.sup.1,
M.sup.2 and T.sup.2 are enriched near grain boundaries in the
interior of the sintered magnet body and/or grain boundaries within
sintered magnet body primary phase grains.
[0075] The permanent magnet thus obtained is improved in coercivity
because the diffusion of R.sup.1, R.sup.2, M.sup.1, M.sup.2 and
T.sup.2 modifies the morphology near the primary phase grain
boundaries within the structure so as to suppress a decline of
magnetocrystalline anisotropy at primary phase grain boundaries or
to create a new phase at grain boundaries. Since the elements in
the powder mixture have not diffused into the interior of primary
phase grains, a decline of remanence is restrained. The magnet is a
high performance permanent magnet.
[0076] After the diffusion treatment, the magnet may be further
subjected to aging treatment at a temperature of 200 to 900.degree.
C. for augmenting the coercivity enhancement.
EXAMPLE
[0077] Examples are given below for further illustrating the
invention although the invention is not limited thereto.
Example 1 and Comparative Examples 1 and 2
[0078] An alloy was prepared by weighing amounts of Nd, Co, Al and
Fe metals having a purity of at least 99% by weight and ferroboron,
high-frequency heating in an argon atmosphere for melting, and
casting the alloy melt on a single roll of copper in an argon
atmosphere, that is, strip casting into a strip of alloy. The alloy
consisted of 12.8 at % of Nd, 1.0 at % of Co, 0.5 at % of Al, 6.0
at % of B, and the balance of Fe. This is designated alloy A. Alloy
A was then subjected to hydrogen decrepitation by causing the alloy
to absorb hydrogen, vacuum evacuating and heating up to 500.degree.
C. for desorbing part of hydrogen. In this way, alloy A was
pulverized into a coarse powder under 30 mesh.
[0079] Another alloy was prepared by weighing amounts of Nd, Dy,
Fe, Co, Al and Cu metals having a purity of at least 99% by weight
and ferroboron, high-frequency heating in an argon atmosphere for
melting, and casting the alloy melt. The alloy consisted of 23 at %
of Nd, 12 at % of Dy, 25 at % of Fe, 6 at % of B, 0.5 at % of Al, 2
at % of Cu, and the balance of Co. This is designated alloy B.
Alloy B was ground on a Brown mill in a nitrogen atmosphere into a
coarse powder under 30 mesh.
[0080] Next, 94 wt % of alloy A powder and 6 wt % of alloy B powder
were mixed in a nitrogen-purged V-blender for 30 minutes. The
powder mixture was finely pulverized on a jet mill using
high-pressure nitrogen gas into a fine powder having a mass median
particle diameter of 4.1 .mu.m. The fine powder was compacted in a
nitrogen atmosphere under a pressure of about 1 ton/cm.sup.2 while
being oriented in a magnetic field of 15 kOe. The green compact was
then placed in a sintering furnace where it was sintered in an
argon atmosphere at 1,060.degree. C. for 2 hours, obtaining a
magnet block of 10 mm.times.20 mm.times.15 mm (thick). Using a
diamond grinding tool, the magnet block was machined on all the
surfaces into a shape having dimensions of 4 mm.times.4 mm.times.2
mm (magnetic anisotropy direction). The machined magnet body was
washed in sequence with alkaline solution, deionized water, acid
solution, and deionized water, and dried, obtaining a mother
sintered magnet body which had the composition:
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0.
[0081] Tb and Al metals having a purity of at least 99% by weight
were used and high-frequency melted in an argon atmosphere to form
a diffusion alloy having the composition Tb.sub.33Al.sub.67 and
composed mainly of an intermetallic compound phase TbAl.sub.2. The
alloy was finely pulverized on a ball mill using an organic solvent
into a fine powder having a mass median particle diameter of 8.6
.mu.m. On electron probe microanalysis (EPMA), the alloy contained
94% by volume of the intermetallic compound phase TbAl.sub.2.
[0082] The diffusion alloy Tb.sub.33Al.sub.67 powder was mixed with
terbium oxide (Tb.sub.4O.sub.7) having an average particle size of
1 .mu.m in a weight ratio of 1:1. The powder mixture was combined
with deionized water in a weight fraction of 50% to form a slurry,
in which the mother sintered magnet body was immersed for 30
seconds under ultrasonic agitation. The magnet body was pulled up
and immediately dried with hot air. The magnet body covered with
the powder mixture was diffusion treated in an argon atmosphere at
900.degree. C. for 8 hours, aged at 500.degree. C. for 1 hour, and
quenched, yielding a magnet of Example 1.
[0083] Separately, the diffusion alloy Tb.sub.33Al.sub.67 powder
having a mass median particle diameter of 8.6 .mu.m alone was
combined with deionized water in a weight fraction of 50% to form a
slurry, in which the magnet body was immersed for 30 seconds under
ultrasonic agitation. The magnet body was pulled up and immediately
dried with hot air. The magnet body covered with the diffusion
alloy powder was diffusion treated in an argon atmosphere at
900.degree. C. for 8 hours, aged at 500.degree. C. for 1 hour, and
quenched, yielding a magnet of Comparative Example 1. In the
absence of the diffusion powder, only the mother sintered magnet
body was similarly heated treated in vacuum at 900.degree. C. for 8
hours, yielding a magnet of Comparative Example 2.
[0084] Table 1 summarizes the composition of the mother sintered
magnet body, diffusion rare earth alloy and diffusion rare earth
oxide, and a mixing ratio (by weight) of the diffusion powder in
Example 1 and Comparative Examples 1 and 2. Table 2 shows the
temperature (.degree. C.) and time (hr) of diffusion treatment and
the magnetic properties of the magnets. It is seen that the magnet
of Example 1 has a coercive force (Hcj) which is greater by 90
kAm.sup.-1 than that of Comparative Example 1 and a remanence (Br)
which is higher by 8 mT than that of Comparative Example 1. The
coercive force (Hcj) of the magnet of Example 1 is greater by 1,090
kAm.sup.-1 than that of Comparative Example 2 while a decline of
remanence (Br) is only 5 mT.
TABLE-US-00001 TABLE 1 Diffusion powder mixture Mother sintered
Rare earth Rare earth Mixing ratio magnet body alloy oxide (by
weight) Example 1
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.s-
ub.6.0 Tb.sub.33Al.sub.67 Tb.sub.4O.sub.7 50:50 Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
Tb.sub.33Al.sub.67 -- Tb.sub.33Al.sub.67 alone Example 1
Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
-- -- -- Example 2
TABLE-US-00002 TABLE 2 Diffusion treatment Temperature Time Br Hcj
(BH).sub.max (.degree. C.) (hr) (T) (kAm.sup.-1) (kJ/m.sup.3)
Example 1 900 8 1.415 2,130 390 Comparative 900 8 1.407 2,040 386
Example 1 Comparative 900 8 1.420 1,040 380 Example 2
Example 2 and Comparative Example 3
[0085] As in Example 1, a mother sintered magnet body having the
composition:
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
was prepared.
[0086] Tb, Co, Fe and Al metals having a purity of at least 99% by
weight were used and high-frequency melted in an argon atmosphere
to form a diffusion alloy having the composition
Tb.sub.35Fe.sub.21Co.sub.24Al.sub.20. The alloy was finely
pulverized on a ball mill using an organic solvent into a fine
powder having a mass median particle diameter of 8.9 .mu.m. On EPMA
analysis, the alloy contained intermetallic compound phases
Tb(FeCoAl).sub.2, Tb.sub.2(FeCoAl) and Tb.sub.2(FeCoAl).sub.17,
which summed to 87% by volume.
[0087] The diffusion alloy Tb.sub.35Fe.sub.21Co.sub.24Al.sub.20
powder was mixed with Tb.sub.4O.sub.7 having an average particle
size of 1 .mu.m in a weight ratio of 1:1. The powder mixture was
combined with deionized water in a weight fraction of 50% to form a
slurry, in which the mother sintered magnet body was immersed for
30 seconds under ultrasonic agitation. The magnet body was pulled
up and immediately dried with hot air. The magnet body covered with
the powder mixture was diffusion treated in an argon atmosphere at
900.degree. C. for 8 hours, aged at 500.degree. C. for 1 hour, and
quenched, yielding a magnet of Example 2.
[0088] In the absence of the diffusion powder, only the mother
sintered magnet body was similarly heat treated in vacuum at
900.degree. C. for 8 hours, yielding a magnet of Comparative
Example 3.
[0089] Table 3 summarizes the composition of the mother sintered
magnet body, diffusion rare earth alloy and diffusion rare earth
oxide, and a mixing ratio (by weight) of the diffusion powder in
Example 2 and Comparative Example 3. Table 4 shows the temperature
(.degree. C.) and time (hr) of diffusion treatment and the magnetic
properties of the magnets. It is seen that the coercive force (Hcj)
of the magnet of Example 2 is greater by 1,020 kAm.sup.-1 than that
of Comparative Example 3 while a decline of remanence (Br) is only
4 mT.
TABLE-US-00003 TABLE 3 Diffusion powder mixture Mother sintered
Rare earth Rare earth Mixing ratio magnet body alloy oxide (by
weight) Example 2
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.s-
ub.6.0 Tb.sub.35Fe.sub.21Co.sub.24Al.sub.20 Tb.sub.4O.sub.7 50:50
Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
-- -- -- Example 3
TABLE-US-00004 TABLE 4 Diffusion treatment Temperature Time Br Hcj
(BH).sub.max (.degree. C.) (hr) (T) (kAm.sup.-1) (kJ/m.sup.3)
Example 2 900 8 1.416 2,060 390 Comparative 900 8 1.420 1,040 380
Example 3
Examples 3 to 55
[0090] As in Example 1, a series of mother sintered magnet bodies
were coated with a different powder mixture of diffusion alloy and
rare earth oxide and diffusion treated at a selected temperature
for a selected time. Table 5 summarizes the composition of the
mother sintered magnet body, diffusion rare earth alloy and rare
earth oxide, and a mixing ratio (by weight) of the diffusion
powder. Table 6 shows the temperature (.degree. C.) and time (hr)
of diffusion treatment and the magnetic properties of the resulting
magnets. All the diffusion alloys contained at least 70% by volume
of intermetallic compounds.
TABLE-US-00005 TABLE 5 Diffusion powder mixture Mother sintered
Rare earth Rare earth Mixing ratio magnet body alloy oxide (by
weight) Example 3 Nd.sub.15.0Fe.sub.balCo.sub.1.0B.sub.5.4
Nd.sub.35Fe.sub.20Co.sub.15Al.sub.30 Tb.sub.4O.sub.7 30:70 Example
4 Nd.sub.15.0Fe.sub.balCo.sub.1.0B.sub.5.4
Nd.sub.35Fe.sub.25Co.sub.20Si.sub.20 Dy.sub.2O.sub.3 60:40 Example
5 Nd.sub.15.0Fe.sub.balCo.sub.1.0B.sub.5.4
Nd.sub.33Fe.sub.20Co.sub.27Al.sub.15Si.sub.5 Nd.sub.2O.sub.3 10:90
Example 6
Nd.sub.11.0Dy.sub.2.0Tb.sub.2.0Fe.sub.balCo.sub.1.0B.sub.5.5
Nd.sub.28Pr.sub.5Al.sub.67 Pr.sub.2O.sub.3 90:10 Example 7
Nd.sub.16.5Fe.sub.balCo.sub.1.5B.sub.6.2 Y.sub.21Mn.sub.78Cr.sub.1
Dy.sub.2O.sub.3 50:50 Example 8
Nd.sub.13.0Pr.sub.2.5Fe.sub.balCo.sub.2.8B.sub.4.8
La.sub.33Cu.sub.60Co.sub.4Ni.sub.3 Tb.sub.2O.sub.3 50:50 Example 9
Nd.sub.13.0Pr.sub.2.5Fe.sub.balCo.sub.2.8B.sub.4.8
La.sub.50Ni.sub.49V.sub.1 CeO.sub.2 70:30 Example 10
Nd.sub.13.0Dy.sub.1.5Fe.sub.balCo.sub.1.0B.sub.5.9
La.sub.33Cu.sub.66.5Nb.sub.0.5 La.sub.2O.sub.3 30:70 Example 11
Nd.sub.16.5Fe.sub.balCo.sub.3.0B.sub.4.7
Ce.sub.22Ni.sub.14Co.sub.58Zn.sub.6 Tb.sub.4O.sub.7 80:20 Example
12 Nd.sub.16.5Fe.sub.balCo.sub.3.0B.sub.4.7 Ce.sub.17Ni.sub.83
CeO.sub.2 50:50 Example 13 Nd.sub.17.3Fe.sub.balCo.sub.3.5B.sub.6.3
Ce.sub.11Zn.sub.89 Gd.sub.2O.sub.3 50:50 Example 14
Nd.sub.16.0Dy.sub.1.5Fe.sub.balCo.sub.4.5B.sub.5.1
Pr.sub.33Ge.sub.67 Y.sub.2O.sub.3 50:50 Example 15
Nd.sub.12.2Pr.sub.2.5Fe.sub.balCo.sub.1.0B.sub.5.3
Tb.sub.33Al.sub.60H.sub.7 Dy.sub.2O.sub.3 50:50 Example 16
Nd.sub.14.5Pr.sub.2.5Fe.sub.balCo.sub.3.5B.sub.5.6
Pr.sub.33Al.sub.66Zr.sub.1 Tb.sub.4O.sub.7 75:25 Example 17
Nd.sub.13.0Tb.sub.1.5Fe.sub.balB.sub.5.5
Gd.sub.32Mn.sub.30Fe.sub.31Nb.sub.7 Dy.sub.2O.sub.3 50:50 Example
18 Nd.sub.12.0Fe.sub.balCo.sub.1.0B.sub.4.8
Gd.sub.37Mn.sub.40Co.sub.20Mo.sub.3 Tb.sub.4O.sub.7 25:75 Example
19 Nd.sub.13.0Tb.sub.1.5Fe.sub.balB.sub.5.5
Gd.sub.21Mn.sub.78Mo.sub.1 Dy.sub.2O.sub.3 40:60 Example 20
Nd.sub.12.0Fe.sub.balCo.sub.1.0B.sub.4.8 Gd.sub.33Mn.sub.66Ta.sub.1
Tb.sub.4O.sub.7 50:50 Example 21
Nd.sub.12.0Pr.sub.2.7Fe.sub.balCo.sub.2.5B.sub.5.2
Tb.sub.29Fe.sub.45Ni.sub.20Ag.sub.6 Yb.sub.2O.sub.3 50:50 Example
22 Nd.sub.13.0Pr.sub.2.0Fe.sub.balCo.sub.2.5B.sub.5.2
Tb.sub.50Ag.sub.50 Tb.sub.4O.sub.7 60:40 Example 23
Nd.sub.12.5Dy.sub.3.0Fe.sub.balCo.sub.0.7B.sub.5.9
Tb.sub.50In.sub.50 Dy.sub.2O.sub.3 50:50 Example 24
Nd.sub.12.5Pr.sub.2.5Tb.sub.0.5Fe.sub.balCo.sub.0.5B.sub.5.0
Dy.sub.31Ni.sub.8Cu.sub.55Sn.sub.6 Tb.sub.4O.sub.7 50:50 Example 25
Nd.sub.10.0Pr.sub.2.5Dy.sub.2.5Fe.sub.balCo.sub.0.6B.sub.5.7
Dy.sub.33Cu.sub.66.5Hf.sub.0.5 Pr.sub.2O.sub.3 50:50 Example 26
Nd.sub.13.0Pr.sub.2.2Fe.sub.balCo.sub.1.0B.sub.5.3
Dy.sub.33Fe.sub.67 Dy.sub.2O.sub.3 50:50 Example 27
Nd.sub.12.8Pr.sub.2.5Tb.sub.0.2Fe.sub.balCo.sub.1.0B.sub.4.5
Er.sub.33Mn.sub.30Co.sub.35Ta.sub.2 Tb.sub.4O.sub.7 50:50 Example
28 Nd.sub.13.2Pr.sub.2.5Dy.sub.0.5Fe.sub.balCo.sub.3.0B.sub.6.3
Er.sub.21Mn.sub.78.6W.sub.0.4 Er.sub.2O.sub.3 50:50 Example 29
Nd.sub.12.0Tb.sub.3.5Fe.sub.balCo.sub.3.5B.sub.6.2
Yb.sub.24Co.sub.5Ni.sub.69Bi.sub.2 Tb.sub.4O.sub.7 50:50 Example 30
Nd.sub.13.0Dy.sub.3.0Fe.sub.balCo.sub.2.0B.sub.4.8
Yb.sub.50Cu.sub.49Ti.sub.1 Pr.sub.2O.sub.3 50:50 Example 31
Nd.sub.11.0Tb.sub.3.5Fe.sub.balCo.sub.3.5B.sub.6.2
Yb.sub.25Ni.sub.74.5Sb.sub.0.5 Yb.sub.2O.sub.3 50:50 Example 32
Nd.sub.15.5Fe.sub.balCo.sub.1.0B.sub.5.3 Nd.sub.33Al.sub.67
Tb.sub.4O.sub.7 90:10 Example 33
Nd.sub.15.1Fe.sub.balCo.sub.1.0B.sub.5.4 Nd.sub.50Si.sub.50
Dy.sub.2O.sub.3 80:20 Example 34
Nd.sub.14.8Fe.sub.balCo.sub.1.0B.sub.5.3
Nd.sub.33Al.sub.37Si.sub.30 Dy.sub.2O.sub.3 20:80 Example 35
Nd.sub.11.8Pr.sub.3.0Fe.sub.balCo.sub.1.0B.sub.5.3
Nd.sub.34Al.sub.61H.sub.5 Tb.sub.4O.sub.7 50:50 Example 36
Nd.sub.12.3Dy.sub.2.5Fe.sub.balCo.sub.3.5B.sub.5.4
Nd.sub.27Pr.sub.6Al.sub.67 Tb.sub.4O.sub.7 50:50 Example 37
Nd.sub.15.1Fe.sub.balCo.sub.1.0B.sub.5.3 Dy.sub.33Al.sub.67
Dy.sub.2O.sub.3 75:25 Example 38
Nd.sub.13.6Tb.sub.1.5Fe.sub.balCo.sub.3.5B.sub.5.2
Dy.sub.33Ga.sub.67 Tb.sub.4O.sub.7 50:50 Example 39
Nd.sub.15.1Fe.sub.balCo.sub.1.0B.sub.5.3 Tb.sub.33Al.sub.67
Dy.sub.2O.sub.3 80:20 Example 40
Nd.sub.13.5Pr.sub.2.0Dy.sub.2.0Fe.sub.balCo.sub.2.5B.sub.5.3
Tb.sub.22Mn.sub.78 Tb.sub.4O.sub.7 50:50 Example 41
Nd.sub.12.5Pr.sub.2.5Fe.sub.balCo.sub.1.0B.sub.5.3
Tb.sub.33Co.sub.67 Dy.sub.2O.sub.3 50:50 Example 42
Nd.sub.19.0Fe.sub.balCo.sub.3.0B.sub.5.4 Y.sub.10Co.sub.15Zn.sub.75
Y.sub.2O.sub.3 70:30 Example 43
Nd.sub.18.0Fe.sub.balCo.sub.2.5B.sub.6.6 Y.sub.68Fe.sub.2In.sub.30
Tb.sub.4O.sub.7 50:50 Example 44
Nd.sub.18.0Fe.sub.balCo.sub.3.0B.sub.5.4 Y.sub.11Zn.sub.89
Dy.sub.2O.sub.3 80:20 Example 45
Nd.sub.13.5Pr.sub.1.5Dy.sub.0.8Fe.sub.balCo.sub.2.5B.sub.4.5
La.sub.32Co.sub.4Cu.sub.64 Tb.sub.4O.sub.7 50:50 Example 46
Nd.sub.13.5Pr.sub.1.5Dy.sub.0.8Fe.sub.balCo.sub.2.5B.sub.4.5
La.sub.33Cu.sub.67 Pr.sub.2O.sub.3 50:50 Example 47
Nd.sub.20.0Fe.sub.balCo.sub.5.5B.sub.4.1 Ce.sub.26Pb.sub.74
Tb.sub.4O.sub.7 40:60 Example 48
Nd.sub.15.2Fe.sub.balCo.sub.1.0B.sub.5.3 Ce.sub.56Sn.sub.44
CeO.sub.2 50:50 Example 49
Nd.sub.15.5Dy.sub.2.5Tb.sub.0.5Fe.sub.balCo.sub.2.6B.sub.4.4
Pr.sub.33Fe.sub.3C.sub.64 Dy.sub.2O.sub.3 50:50 Example 50
Nd.sub.12.5Dy.sub.2.0Tb.sub.0.5Fe.sub.balCo.sub.3.8B.sub.6.2
Pr.sub.50P.sub.50 Nd.sub.2O.sub.3 50:50 Example 51
Nd.sub.12.7Pr.sub.2.5Dy.sub.0.6Fe.sub.balCo.sub.1.4B.sub.5.6
Gd.sub.52Ni.sub.48 Tb.sub.4O.sub.7 70:30 Example 52
Nd.sub.13.1Pr.sub.1.5Tb.sub.0.5Fe.sub.balCo.sub.2.8B.sub.6.3
Gd.sub.37Ga.sub.63 Dy.sub.2O.sub.3 60:40 Example 53
Nd.sub.15.3Dy.sub.0.6Fe.sub.balCo.sub.1.0B.sub.4.9
Er.sub.32Mn.sub.67Ta.sub.1 Nd.sub.2O.sub.3 50:50 Example 54
Nd.sub.14.5Pr.sub.1.0Dy.sub.0.5Fe.sub.balCo.sub.2.8B.sub.4.6
Yb.sub.68Pb.sub.32 Tb.sub.4O.sub.7 50:50 Example 55
Nd.sub.12.0Pr.sub.1.5Dy.sub.0.5Fe.sub.balCo.sub.4.2B.sub.5.3
Yb.sub.69Sn.sub.29Bi.sub.2 Yb.sub.2O.sub.3 80:20
TABLE-US-00006 TABLE 6 Diffusion treatment Temperature Time Br Hcj
(BH)max (.degree. C.) (hr or min) (T) (kAm.sup.-1) (kJ/m.sup.3)
Example 3 780 8 h 1.404 2,032 385 Example 4 880 8 h 1.419 1,992 390
Example 5 820 6 h 1.416 2,036 389 Example 6 750 5 h 1.411 1,987 388
Example 7 930 10 h 1.343 1,008 343 Example 8 780 5 h 1.367 1,225
354 Example 9 890 7 h 1.388 1,219 363 Example 10 820 8 h 1.432
1,052 396 Example 11 450 12 h 1.348 920 349 Example 12 840 6 h
1.353 940 343 Example 13 400 5 h 1.327 1,052 340 Example 14 830 5 h
1.328 1,890 341 Example 15 820 8 h 1.412 2,130 385 Example 16 850 8
h 1.371 2,048 363 Example 17 960 10 h 1.410 1,785 376 Example 18
940 6 h 1.454 1,620 398 Example 19 920 5 h 1.411 1,615 381 Example
20 860 5 h 1.452 1,748 396 Example 21 920 10 h 1.414 1,672 379
Example 22 920 6 h 1.412 1,910 384 Example 23 940 12 h 1.405 1,955
381 Example 24 870 12 h 1.404 1,930 382 Example 25 860 10 h 1.409
1,870 383 Example 26 850 8 h 1.408 2,060 382 Example 27 1,020 8 h
1.376 1,610 362 Example 28 980 12 h 1.368 1,521 363 Example 29 320
15 min 1.397 1,580 370 Example 30 380 25 min 1.351 1,430 354
Example 31 410 40 min 1.430 1,243 390 Example 32 790 8 h 1.404
2,070 382 Example 33 820 10 h 1.421 2,034 388 Example 34 910 5 h
1.416 2,095 386 Example 35 760 8 h 1.417 2,100 386 Example 36 770 8
h 1.421 2,120 387 Example 37 830 8 h 1.410 2,130 384 Example 38 760
3 h 1.414 2,140 386 Example 39 880 8 h 1.416 2,170 389 Example 40
660 20 h 1.353 1,860 354 Example 41 860 8 h 1.414 2,110 386 Example
42 450 12 h 1.317 1,290 326 Example 43 1,030 2 h 1.286 1,346 309
Example 44 450 8 h 1.332 1,211 334 Example 45 660 14 h 1.350 1,407
347 Example 46 620 12 h 1.347 1,314 344 Example 47 520 10 h 1.203
1,305 276 Example 48 460 14 h 1.361 1,120 350 Example 49 860 30 h
1.278 1,258 312 Example 50 360 40 min 1.412 1,185 368 Example 51
960 2 h 1.390 1,545 366 Example 52 850 30 min 1.415 1,410 382
Example 53 700 10 h 1.373 1,099 355 Example 54 750 12 h 1.351 1,460
346 Example 55 420 10 h 1.448 1,020 396
Example 56 and Comparative Example 4
[0091] An alloy was prepared by weighing amounts of Nd, Co, Al and
Fe metals having a purity of at least 99% by weight and ferroboron,
high-frequency heating in an argon atmosphere for melting, and
casting the alloy melt on a single roll of copper in an argon
atmosphere, that is, strip casting into a strip of alloy. The alloy
consisted of 12.8 at % of Nd, 1.0 at % of Co, 0.5 at % of Al, 6.0
at % of B, and the balance of Fe. This is designated alloy A. Alloy
A was then subjected to hydrogen decrepitation by causing the alloy
to absorb hydrogen, vacuum evacuating and heating up to 500.degree.
C. for desorbing part of hydrogen. In this way, alloy A was
pulverized into a coarse powder under 30 mesh.
[0092] Another alloy was prepared by weighing amounts of Nd, Dy,
Fe, Co, Al and Cu metals having a purity of at least 99% by weight
and ferroboron, high-frequency heating in an argon atmosphere for
melting, and casting the alloy melt. The alloy consisted of 23 at %
of Nd, 12 at % of Dy, 25 at % of Fe, 6 at % of B, 0.5 at % of Al, 2
at % of Cu, and the balance of Co. This is designated alloy B.
Alloy B was ground on a Brown mill in a nitrogen atmosphere into a
coarse powder under 30 mesh.
[0093] Next, 94 wt % of alloy A powder and 6 wt % of alloy B powder
were mixed in a nitrogen-purged V-blender for 30 minutes. The
powder mixture was finely pulverized on a jet mill using
high-pressure nitrogen gas into a fine powder having a mass median
particle diameter of 4 .mu.m. The fine powder was compacted in a
nitrogen atmosphere under a pressure of about 1 ton/cm.sup.2 while
being oriented in a magnetic field of 15 kOe. The green compact was
then placed in a sintering furnace where it was sintered in an
argon atmosphere at 1,060.degree. C. for 2 hours, obtaining a
magnet block of 10 mm.times.20 mm.times.15 mm (thick). Using a
diamond grinding tool, the magnet block was machined on all the
surfaces into a shape having dimensions of 4 mm.times.4 mm.times.2
mm (magnetic anisotropy direction). The machined magnet body was
washed in sequence with alkaline solution, deionized water, acid
solution, and deionized water, and dried, obtaining a mother
sintered magnet body which had the composition:
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0.
[0094] Al and Co metals having a purity of at least 99% by weight
were used and high-frequency melted in an argon atmosphere to form
a diffusion alloy having the composition Al.sub.50Co.sub.50 and
composed mainly of an intermetallic compound phase AlCo. The alloy
was finely pulverized on a ball mill using an organic solvent into
a fine powder having a mass median particle diameter of 8.9 .mu.m.
On EPMA analysis, the alloy contained 94% by volume of the
intermetallic compound phase AlCo.
[0095] The diffusion alloy Al.sub.50Co.sub.50 powder was mixed with
terbium oxide (Tb.sub.4O.sub.7) having an average particle size of
1 .mu.m in a weight ratio of 1:1. The powder mixture was combined
with deionized water in a weight fraction of 50% to form a slurry,
in which the mother sintered magnet body was immersed for 30
seconds under ultrasonic agitation. The magnet body was pulled up
and immediately dried with hot air. The magnet body covered with
the powder mixture was diffusion treated in an argon atmosphere at
900.degree. C. for 8 hours, aged at 500.degree. C. for 1 hour, and
quenched, yielding a magnet of Example 56.
[0096] Separately, terbium oxide having an average particle size of
1 .mu.m alone was combined with deionized water in a weight
fraction of 50% to form a slurry, in which the magnet body was
immersed for 30 seconds under ultrasonic agitation. The magnet body
was pulled up and immediately dried with hot air. The coated magnet
body was diffusion treated in an argon atmosphere at 900.degree. C.
for 8 hours, aged at 500.degree. C. for 1 hour, and quenched,
yielding a magnet of Comparative Example 4.
[0097] Table 7 summarizes the composition of the mother sintered
magnet body, diffusion alloy and diffusion rare earth oxide, and a
mixing ratio (by weight) of the diffusion powder mixture in Example
56 and Comparative Example 4. Table 8 shows the temperature
(.degree. C.) and time (hr) of diffusion treatment and the magnetic
properties of the magnets. It is seen that the coercive force (Hcj)
of the magnet of Example 56 is greater by 90 kAm.sup.-1 than that
of Comparative Example 4 while a decline of remanence (Br) is only
3 mT. The coercive force (Hcj) of the magnet of Example 56 is
greater by 1,040 kAm.sup.-1 than that of previous Comparative
Example 2 while a decline of remanence (Br) is only 4 mT.
TABLE-US-00007 TABLE 7 Diffusion powder mixture Mother sintered
Diffusion Rare earth Mixing ratio magnet body alloy oxide (by
weight) Example 56
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.-
sub.6.0 Al.sub.50Co.sub.50 Tb.sub.4O.sub.7 50:50 Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
-- Tb.sub.4O.sub.7 Tb.sub.4O.sub.7 alone Example 4 Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
-- -- -- Example 2
TABLE-US-00008 TABLE 8 Diffusion treatment Temperature Time Br Hcj
(BH).sub.max (.degree. C.) (hr) (T) (kAm.sup.-1) (kJ/m.sup.3)
Example 56 900 8 1.416 2,080 390 Comparative 900 8 1.419 1,990 393
Example 4 Comparative 900 8 1.420 1,040 380 Example 2
Example 57 and Comparative Example 5
[0098] As in Example 56, a mother sintered magnet body having the
composition: Nd.sub.13.3DY.sub.0.5Fe.sub.bal
Co.sub.2.4CU.sub.0.1Al.sub.0.5B.sub.6.0 was prepared.
[0099] Ni and Al metals having a purity of at least 99% by weight
were used and high-frequency melted in an argon atmosphere to form
a diffusion alloy having the composition Ni.sub.25Al.sub.75 and
composed mainly of an intermetallic compound phase NiAl.sub.3. The
alloy was finely pulverized on a ball mill using an organic solvent
into a fine powder having a mass median particle diameter of 9.3
.mu.m. On EPMA analysis, the alloy contained 94% by volume of the
intermetallic compound phase NiAl.sub.3.
[0100] The diffusion alloy Ni.sub.25Al.sub.75 powder was mixed with
terbium oxide (Tb.sub.4O.sub.7) having an average particle size of
1 .mu.m in a weight ratio of 1:1. The powder mixture was combined
with deionized water in a weight fraction of 50% to form a slurry,
in which the mother sintered magnet body was immersed for 30
seconds under ultrasonic agitation. The magnet body was pulled up
and immediately dried with hot air. The magnet body covered with
the powder mixture was diffusion treated in an argon atmosphere at
900.degree. C. for 8 hours, aged at 500.degree. C. for 1 hour, and
quenched, yielding a magnet of Example 57. In the absence of the
diffusion powder mixture, the sintered magnet body alone was heat
treated in vacuum at 900.degree. C. for 8 hours, yielding a magnet
of Comparative Example 5.
[0101] Table 9 summarizes the composition of the mother sintered
magnet body, diffusion alloy and diffusion rare earth oxide, and a
mixing ratio (by weight) of the diffusion powder mixture in Example
57 and Comparative Example 5. Table 10 shows the temperature
(.degree. C.) and time (hr) of diffusion treatment and the magnetic
properties of the magnets. It is seen that the coercive force (Hcj)
of the magnet of Example 57 is greater by 1,010 kAm.sup.-1 than
that of Comparative Example 5 while a decline of remanence (Br) is
only 4 mT.
TABLE-US-00009 TABLE 9 Diffusion powder mixture Mother sintered
Diffusion Rare earth Mixing ratio magnet body alloy oxide (by
weight) Example 57
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.-
sub.6.0 Ni.sub.25Al.sub.75 Tb.sub.4O.sub.7 50:50 Comparative
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.4Cu.sub.0.1Al.sub.0.5B.sub.6.0
-- -- -- Example 5
TABLE-US-00010 TABLE 10 Diffusion treatment Temperature Time Br Hcj
(BH).sub.max (.degree. C.) (hr) (T) (kAm.sup.-1) (kJ/m.sup.3)
Example 57 900 8 1.416 2,050 390 Comparative 900 8 1.420 1,040 380
Example 5
Examples 58 to 96
[0102] As in Example 56, a series of mother sintered magnet bodies
were coated with a different powder mixture of diffusion alloy (or
metal) and rare earth oxide and diffusion treated at a selected
temperature for a selected time. Table 11 summarizes the
composition of the mother sintered magnet body, diffusion alloy and
rare earth oxide, and a mixing ratio (by weight) of the diffusion
powder mixture. Table 12 shows the temperature (.degree. C.) and
time (hr) of diffusion treatment and the magnetic properties of the
resulting magnets. All the diffusion alloys contained at least 70%
by volume of intermetallic compounds.
TABLE-US-00011 TABLE 11 Diffusion powder mixture Mother sintered
Diffusion Rare earth Mixing ratio magnet body alloy or metal oxide
(by weight) Example 58 Nd.sub.15.0Fe.sub.balCo.sub.1.0B.sub.5.4
Mn.sub.27Al.sub.73 Tb.sub.4O.sub.7 30:70 Example 59
Nd.sub.12.0Pr.sub.3.0Fe.sub.balCo.sub.3.0B.sub.5.2
Ni.sub.25Al.sub.75 Dy.sub.2O.sub.3 90:10 Example 60
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.0B.sub.6.0 Al
Tb.sub.4O.sub.7 50:50 Example 61
Nd.sub.14.3Dy.sub.1.2Fe.sub.balCo.sub.2.0B.sub.5.3
Cr.sub.12.5Al.sub.87.5 Nd.sub.2O.sub.3 20:80 Example 62
Nd.sub.13.8Tb.sub.0.7Fe.sub.balCo.sub.1.0B.sub.5.5
Co.sub.33Si.sub.67 Pr.sub.2O.sub.3 70:30 Example 63
Nd.sub.15.8Fe.sub.balCo.sub.1.5B.sub.5.3
Mn.sub.25Al.sub.25Cu.sub.50 Tb.sub.4O.sub.7 50:50 Example 64
Nd.sub.14.4Dy.sub.0.8Tb.sub.0.3Fe.sub.balCo.sub.1.0B.sub.5.4
Fe.sub.50Si.sub.50 CeO.sub.2 60:40 Example 65
Nd.sub.18.2Fe.sub.balCo.sub.4.0B.sub.5.3
Fe.sub.49.9C.sub.0.1Si.sub.50 La.sub.2O.sub.3 30:70 Example 66
Nd.sub.13.3Dy.sub.0.5Fe.sub.balCo.sub.2.0B.sub.6.0 Si
Tb.sub.4O.sub.7 50:50 Example 67
Nd.sub.17.6Fe.sub.balCo.sub.3.5B.sub.4.2 Cr.sub.12.5Al.sub.87.5
Tb.sub.4O.sub.7 50:50 Example 68
Nd.sub.15.6Fe.sub.balCo.sub.1.0B.sub.6.8 Mn.sub.67P.sub.33
Dy.sub.2O.sub.3 50:50 Example 69
Nd.sub.12.0Fe.sub.balCo.sub.2.0B.sub.6.0 Ti.sub.50Cu.sub.50
Gd.sub.2O.sub.3 50:50 Example 70
Nd.sub.12.9Dy.sub.1.0Fe.sub.balCo.sub.2.0B.sub.6.0 Cu
Dy.sub.2O.sub.3 50:50 Example 71
Nd.sub.15.2Fe.sub.balCo.sub.1.0B.sub.5.5 V.sub.75Sn.sub.25
Tb.sub.4O.sub.7 75:25 Example 72 Nd.sub.14.3Fe.sub.balB.sub.6.1
Cr.sub.67Ta.sub.33 Dy.sub.2O.sub.3 50:50 Example 73
Nd.sub.14.8Fe.sub.balCo.sub.3.0B.sub.5.4 Cu.sub.75Sn.sub.25
Y.sub.2O.sub.3 50:50 Example 74
Pr.sub.15.0Fe.sub.balCo.sub.6.5B.sub.5.3 Cu.sub.70Zn.sub.5Sn.sub.25
Er.sub.2O.sub.3 60:40 Example 75
Nd.sub.13.8Dy.sub.0.8Fe.sub.balCo.sub.2.0B.sub.6.2 Zn
Dy.sub.2O.sub.3 50:50 Example 76
Nd.sub.15.8Pr.sub.1.5Fe.sub.balCo.sub.2.5B.sub.5.2
Ga.sub.40Zr.sub.60 Tb.sub.4O.sub.7 60:40 Example 77
Nd.sub.13.5Dy.sub.1.0Fe.sub.balCo.sub.2.0B.sub.6.0 Ga
Tb.sub.4O.sub.7 50:50 Example 78
Nd.sub.15.2Fe.sub.balCo.sub.3.0B.sub.5.3 Cr.sub.75Ge.sub.25
Yb.sub.2O.sub.3 50:50 Example 79
Nd.sub.14.0Dy.sub.0.8Fe.sub.balCo.sub.3.0B.sub.6.0 Ge
Dy.sub.2O.sub.3 50:50 Example 80
Nd.sub.14.6Pr.sub.2.0Dy.sub.0.8Fe.sub.balCo.sub.2.0B.sub.5.3
Nb.sub.33Si.sub.67 Dy.sub.2O.sub.3 50:50 Example 81
Pr.sub.13.7Dy.sub.1.0Fe.sub.balCo.sub.1.0B.sub.5.4
Al.sub.73Mo.sub.27 Pr.sub.2O.sub.3 40:60 Example 82
Nd.sub.15.0Fe.sub.balCo.sub.1.0B.sub.6.4 Ti.sub.50Ag.sub.50
Nd.sub.2O.sub.3 60:40 Example 83
Nd.sub.13.8Dy.sub.1.0Fe.sub.balCo.sub.1.0B.sub.5.8 Ag
Tb.sub.4O.sub.7 50:50 Example 84
Nd.sub.14.3Fe.sub.balCo.sub.1.0B.sub.5.3 In.sub.25Mn.sub.75
Tb.sub.4O.sub.7 50:50 Example 85 Nd.sub.13.9Fe.sub.balB.sub.5.6
Hf.sub.33Cr.sub.67 Dy.sub.2O.sub.3 70:30 Example 86
Nd.sub.15.2Fe.sub.balCo.sub.1.0B.sub.5.6 Cr.sub.25Fe.sub.55W.sub.20
Tb.sub.4O.sub.7 50:50 Example 87
Nd.sub.15.1Yb.sub.0.2Fe.sub.balCo.sub.1.0B.sub.4.8
Ni.sub.50Sb.sub.50 Er.sub.2O.sub.3 50:50 Example 88
Nd.sub.15.7Fe.sub.balCo.sub.5.0B.sub.6.9 Ti.sub.80Pb.sub.20
Tb.sub.4O.sub.7 60:40 Example 89
Nd.sub.14.6Fe.sub.balCo.sub.1.0B.sub.5.3
Mn.sub.25Co.sub.50Sn.sub.25 La.sub.2O.sub.3 70:30 Example 90
Nd.sub.14.9Fe.sub.balCo.sub.0.7B.sub.5.3 Co.sub.60Sn.sub.40
Tb.sub.4O.sub.7 50:50 Example 91
Nd.sub.14.6Fe.sub.balCo.sub.1.5B.sub.5.5 V.sub.75Sn.sub.25
Er.sub.2O.sub.3 30:70 Example 92
Nd.sub.12.8Pr.sub.2.0Fe.sub.balCo.sub.3.0B.sub.5.6 Sn
Tb.sub.4O.sub.7 50:50 Example 93
Nd.sub.14.2Fe.sub.balCo.sub.0.5B.sub.5.6
Cr.sub.21Fe.sub.62Mo.sub.17 Tb.sub.4O.sub.7 50:50 Example 94
Nd.sub.15.0Dy.sub.0.6Fe.sub.balCo.sub.0.1B.sub.4.1
Bi.sub.40Zr.sub.60 Dy.sub.2O.sub.3 40:60 Example 95
Nd.sub.15.2Fe.sub.balCo.sub.3.5B.sub.6.4 Ni.sub.50Bi.sub.50
Yb.sub.2O.sub.3 50:50 Example 96
Nd.sub.12.0Pr.sub.3.0Fe.sub.balCo.sub.2.0B.sub.6.1 Bi
Dy.sub.2O.sub.3 50:50
TABLE-US-00012 TABLE 12 Diffusion treatment Temperature Time Br Hcj
(BH).sub.max (.degree. C.) (hr or min) (T) (kAm.sup.-1)
(kJ/m.sup.3) Example 58 790 3 h 1.413 2,087 387 Example 59 810 3 h
30 min 1.407 2,187 384 Example 60 850 8 h 1.414 1,980 388 Example
61 760 1 h 1.380 1,928 368 Example 62 820 2 h 30 min 1.423 2,042
394 Example 63 770 5 h 1.394 2,223 373 Example 64 820 4 h 1.402
1,861 383 Example 65 940 12 h 1.298 1,904 328 Example 66 870 8 h
1.415 1,930 389 Example 67 1,060 28 h 1.284 1,713 319 Example 68
380 15 min 1.358 1,512 353 Example 69 680 8 h 1.476 1,498 409
Example 70 820 8 h 1.417 1,820 390 Example 71 940 5 h 1.414 1,816
387 Example 72 1,020 10 h 1.426 1,896 393 Example 73 650 8 h 1.420
1,641 387 Example 74 600 10 h 1.406 1,689 379 Example 75 760 8 h
1.403 1,760 379 Example 76 840 5 h 1.355 1,940 351 Example 77 870 8
h 1.415 1,950 389 Example 78 850 7 h 1.420 1,816 390 Example 79 880
8 h 1.411 1,890 387 Example 80 1,000 10 h 1.358 1,896 355 Example
81 770 1 h 1.417 2,085 386 Example 82 760 4 h 1.404 1,530 380
Example 83 920 8 h 1.413 1,910 386 Example 84 630 13 h 1.446 1,780
401 Example 85 960 7 h 1.433 1,620 394 Example 86 920 15 h 1.413
1,940 385 Example 87 750 6 h 1.381 1,537 363 Example 88 920 5 h
1.369 1,338 355 Example 89 640 6 h 1.424 1,418 391 Example 90 880
40 min 1.414 2,040 383 Example 91 1,020 10 h 1.420 1,450 387
Example 92 730 5 h 1.408 1,820 383 Example 93 880 15 h 1.454 1,800
406 Example 94 510 20 h 1.346 1,430 343 Example 95 360 5 min 1.392
1,211 362 Example 96 420 15 min 1.382 1,510 358
[0103] Japanese Patent Application Nos. 2011-102787 and 2011-102789
are incorporated herein by reference.
[0104] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *