AU2021100764A4 - Method for Improving Coercivity and Thermal Stability of Sintered Nd-Fe-B Magnet - Google Patents

Method for Improving Coercivity and Thermal Stability of Sintered Nd-Fe-B Magnet Download PDF

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AU2021100764A4
AU2021100764A4 AU2021100764A AU2021100764A AU2021100764A4 AU 2021100764 A4 AU2021100764 A4 AU 2021100764A4 AU 2021100764 A AU2021100764 A AU 2021100764A AU 2021100764 A AU2021100764 A AU 2021100764A AU 2021100764 A4 AU2021100764 A4 AU 2021100764A4
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sintered
magnet
rare earth
film layer
thermal stability
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Junming LUO
Yu Xie
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Nanchang Hangkong University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt

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  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

The present invention provides a method for improving coercivity and thermal stability of a sintered Nd-Fe-B magnet. The method comprises the following steps: S1. derusting and degreasing the sintered Nd-Fe-B magnet; S2. pickling the sintered Nd Fe-B magnet treated in the step S1, and then removing acid stains; S3. performing first magnetron sputtering on the sintered Nd-Fe-B magnet treated in the step S2, and depositing a first non-rare earth metal film layer on the surface of the sintered Nd-Fe B magnet; S4. performing grain boundary diffusion by microwave heating and tempering on the sintered Nd-Fe-B magnet deposited with the single non-rare earth film layer in the step S3; S5. performing second magnetron sputtering on the sintered Nd-Fe-B magnet treated in the step S4, and depositing a second non-rare earth metal film layer on the surface of the sintered Nd-Fe-B magnet deposited with the non-rare earth film layer; and S6. performing grain boundary diffusion by microwave heating treatment on the sintered Nd-Fe-B magnet deposited with the double non-rare earth film layers in the step S5.

Description

Method for Improving Coercivity and Thermal Stability of Sintered
Nd-Fe-B Magnet
TECHNICAL FIELD
The present invention relates to the technical field of surface treatment of
rare earth permanent magnet materials, in particular to a method for improving
coercivity and thermal stability of a sintered Nd-Fe-B magnet.
BACKGROUND
As one of the third generation rare earth permanent magnet materials,
sintered Nd-Fe-B has the advantages of high coercivity, high remanence and
high magnetic energy product, and has higher cost performance than other
magnets. However, due to low Curie temperature and poor temperature
stability of sintered permanent magnet materials, the magnetic loss is high and
the coercivity deteriorates rapidly in high temperature working environment,
which affects the normal use.
There is a certain correlation between coercivity and Curie temperature,
and the Curie temperature and temperature stability of sintered Nd-Fe-B can
be improved by improving intrinsic coercivity. One of the effective ways to
improve a magnetocrystalline anisotropy field is to add heavy rare earth
elements such as Dy or Tb before grain boundary diffusion to diffuse the heavy
rare earth elements into the magnet grain boundary and marginal areas of
main phase grains, which can improve the anisotropy field, and does not
significantly reduce the remanence and magnetic energy product since the
main phase grains do not contain any heavy rare earth element.
Although China is rich in rare earth resources, the proportion of heavy rare
earth resources is relatively low, and the environmental cost is high during the
mining process, so that addition of too many heavy rare earth elements in
production will significantly increase the cost. Therefore, it is of great
significance to reduce the amount of heavy rare earth elements used in
Nd-Fe-B magnets or to replace heavy rare earth elements by non-rare earth
elements. Non-rare earth elements (e.g., Al, Cu, Ga, Zn and Mg) are widely
used as additive elements because they can lower the melting points of
intercrystalline rare earth-rich phases, improve interfacial wettability, optimize
structures of the rare earth-rich phases and improve the magnetic properties of
magnets. Among the known elements, the Curie temperature of alloys can be
increased and the temperature coefficient can be decreased by adding Co and
other trace elements. When the Co content is low, Co preferentially occupies
Fe 6 (16k 2) crystal sites, which reduces negative interatomic exchange, thus
increasing the Tc of magnets. When Co exceeds a certain range, the uniaxial
anisotropy constant becomes smaller after Co substitutes Fe in the base
phase, and the new Nd(FeCo)2 phase becomes a critical nucleation point
during demagnetization. These two factors lead to a decrease of intrinsic
coercivity in the magnets, decrease of alloy remanence and decrease of
magnetic energy product. The negative effect of Co on coercivity can be offset
or suppressed by adding Dy, Ga, Al, Nb, Mo, V, W and other elements. Among
them, Al can refine 0 phase grains, and refine B-rich and granular Nd-rich
phases with a more diffuse distribution, thus increasing the coercivity (H cj). Al
also forms precipitated phases at grain boundaries or grain intersections,
improving wettability and reducing magnetic coupling.
There are many common methods of adding rare earth (non-rare earth)
elements by grain boundary diffusion, such as magnetron sputtering, physical
vapor deposition, thermal spraying, double alloy powder method, immersion
coating and electrodeposition. Compared with other preparation methods,
films prepared by magnetron sputtering have good binding force and dense
film layers. The kinetic energy of magnetron sputtered atoms is twice as high
as that of thermally evaporated atoms, so that diffusion layers with better
binding force and denser film layers can be produced, which is more beneficial
to the diffusion of sputtered elements. Compared with thermal vapor
deposition and immersion method, magnetron sputtering deposition has a
constant rate and precisely controllable film thickness, which can achieve
quantitative addition of elements and improve the effective utilization rate of
rare earth (non-rare earth) elements.
Microwave heating has the advantages of integral heating, low sintering
temperature, short holding time, selective heating, environmental protection
and energy saving. Compared with conventional sintering processes,
microwave sintering has thermal effects, and non-thermal effects such as
inhibited grain growth and improved material properties, which is known as "a
revolution in sintering technology". Grain boundary diffusion by microwave
heating can not only significantly shorten the time and improve production
efficiency, but also achieve more uniform diffusion and better magnetic
properties.
SUMMARY
To solve the above technical problems, the present invention provides a method for improving coercivity and thermal stability of a sintered Nd-Fe-B magnet, comprising the following steps:
S1. derusting and degreasing the sintered Nd-Fe-B magnet;
S2. pickling the sintered Nd-Fe-B magnet treated in the step S1, and then
removing acid stains;
S3. performing first magnetron sputtering on the sintered Nd-Fe-B magnet
treated in the step S2, and depositing a first non-rare earth metal film layer on
the surface of the sintered Nd-Fe-B magnet;
S4. performing grain boundary diffusion by microwave heating and
tempering on the sintered Nd-Fe-B magnet deposited with the single non-rare
earth film layer in the step S3;
S5. performing second magnetron sputtering on the sintered Nd-Fe-B
magnet treated in the step S4, and depositing a second non-rare earth metal
film layer on the surface of the sintered Nd-Fe-B magnet deposited with the
non-rare earth film layer; and
S6. performing grain boundary diffusion by microwave heating treatment
on the sintered Nd-Fe-B magnet deposited with the double non-rare earth film
layers in the step S5.
Before magnetron sputtering of the sintered Nd-Fe-B magnet, a
mechanical pump and a molecular pump are started sequentially to enable the
background vacuum degree in a chamber to reach 5-8x10-4 Pa, and then
high-purity argon with a concentration of 99.99% is charged to enable the
working vacuum degree in the chamber to reach 0.3-0.8 Pa, the negative bias voltage is set at -150V to -200V for pre-sputtering for 10-20min to clean the surface of a target, and the set power is kept stable.
In the step S1, the sintered Nd-Fe-B magnet is derusted, and then the
sintered Nd-Fe-B magnet is ultrasonically cleaned with acetone for 1-3min
after derusting to remove residual grease on the surface of the sintered
Nd-Fe-B magnet during wire cutting.
In the step S2, the sintered Nd-Fe-B magnet is ultrasonically pickled for
-40s with a nitric acid alcohol solution to remove scale on the surface of the
sintered Nd-Fe-B magnet and increase activation energy on the surface of the
sintered Nd-Fe-B magnet, wherein the concentration of nitric acid in the nitric
acid alcohol solution is 3-10wt.%; after pickling, the sintered Nd-Fe-B magnet
is ultrasonically cleaned with distilled water and absolute ethanol successively
to remove residual acid stains on the surface of the sintered Nd-Fe-B magnet.
In the step S3, the first magnetron sputtering is performed on the surface
of the sintered Nd-Fe-B magnet by DC magnetron sputtering, and the first
non-rare earth film layer is deposited on the surface of the sintered Nd-Fe-B
magnet at a deposition power of 75-150W for 1-4h.
The rare earth element in the first non-rare earth film layer is Co.
In the step S5, the second magnetron sputtering is performed on the
surface of the sintered Nd-Fe-B magnet by DC magnetron sputtering, and the
second non-rare earth film is deposited on the surface of the sintered Nd-Fe-B
magnet at a deposition power of 50-125W for 1-3h.
The rare earth element in the second non-rare earth film layer is Al.
In the step S4, the grain boundary diffusion by microwave heating is
performed at 800-1100°C for 1-3h, and the tempering is performed at
450-550°C for 0.5-2h; and
in the step S6, the grain boundary diffusion by microwave heating is
performed at 500-650°C for 1-3h.
The thickness of the sintered Nd-Fe-B magnet is not more than 25mm,
and the diffusion depth of the non-rare earth metal is more than 3um.
The present invention has the following advantageous effects:
1. The non-rare earth layer deposited by the method has good binding
force with the magnet substrate, and denser film layer; meanwhile, an
additional barrier layer is formed outside the non-rare earth layer, which is
beneficial to the diffusion of non-rare earth elements into the sintered Nd-Fe-B
magnet;
2. The method can achieve completely uniform coating and continuous
coating of blocks, and can be applied to thick or irregular blocks;
3. Non-rare earth elements are deposited in the method, so that efficient
utilization of the non-rare earth elements is realized, the consumption of heavy
rare earth is reduced, and the production cost is significantly reduced;
4. The high temperature grain boundary diffusion by microwave heating
and low temperature tempering adopted in the method not only enable the
diffusion to be more sufficient and uniform, but also greatly shorten the time,
save the cost and significantly improve the production efficiency.
DESCRIPTION OF THE INVENTION
The following embodiments are only preferred embodiments of the
present invention. It should be noted that those of ordinary skill in the art can
make a plurality of improvements and modifications to the present invention
without departing from the principle of the present invention, and these
improvements and modifications should fall within the protection scope of the
present invention.
Comparative Example 1
The present invention provides a method for improving coercivity and
thermal stability of a sintered Nd-Fe-B magnet, with an unmagnetized 42EH
commercial sintered Nd-Fe-B magnet as a prepared magnet that is cut into
x3x2mm slices by wire cutting. The method specifically comprises the
following steps:
S1. derusting the sintered Nd-Fe-B magnet, and then ultrasonically
cleaning the sintered Nd-Fe-B magnet with acetone for 2min after derusting,
and rinsing with distilled water to remove residual grease on the surface of the
sintered Nd-Fe-B magnet during wire cutting;
S2. ultrasonically pickling the sintered Nd-Fe-B magnet treated in the step
S1 for 30s with a nitric acid alcohol solution to remove scale on the surface of
the sintered Nd-Fe-B magnet and increase activation energy on the surface of
the sintered Nd-Fe-B magnet, wherein the concentration of nitric acid in the
nitric acid alcohol solution was 5wt.%; after pickling, ultrasonically cleaning the
sintered Nd-Fe-B magnet with distilled water and absolute ethanol
successively to remove residual acid stains on the surface of the sintered
Nd-Fe-B magnet;
S3. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 6x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.5 Pa, setting the negative
bias voltage at -200V for pre-sputtering for 15min to clean the surface of a
target, and keeping the set power stable; performing first magnetron sputtering
on the surface of the sintered Nd-Fe-B magnet treated in the step S2 by DC
magnetron sputtering, wherein the purity of a cylindrical Co target used for
sputtering was 99.95%, and depositing a first non-rare earth Co film layer with
a thickness of 3um on the surface of the sintered Nd-Fe-B magnet at a
deposition power of 100W for 2h;
S4. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co film layer immediately after the deposition for vacuum tube
sealing, and putting a quartz tube filled with the sample and pumped to a
vacuum environment into a microwave oven for grain boundary diffusion at
950°C for 1.5h and tempering at 480°C for 1h; setting the grain boundary
diffusion heating rate at 50°C/min, setting the tempering heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Example 1
The sintered Nd-Fe-B magnet sample with the non-rare earth Co film layer
deposited on the surface treated in the step 4 of Comparative Example 1 was
put into distilled water and absolute ethanol sequentially for ultrasonic cleaning,
and then a second non-rare earth metal Al film layer was deposited on the
surface of the sample in the following steps:
S1. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 6x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.5 Pa, setting the negative
bias voltage at -200V for pre-sputtering for 15min to clean the surface of a
target, and keeping the set power stable; performing second magnetron
sputtering on the surface of the sample treated in the step S4 by DC
magnetron sputtering, wherein the purity of a cylindrical Al target used for
sputtering was 99.999%, and depositing a second non-rare earth Al film layer
with a thickness of 3um on the surface of the sintered Nd-Fe-B magnet sample
deposited with the non-rare earth Co film layer at a deposition power of 75W
for 1h;
S2. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co and Al film layers immediately after the deposition for
vacuum tube sealing, and putting a quartz tube filled with the sample and
pumped to a vacuum environment into a microwave oven for grain boundary
diffusion at 550°C for 1.5h; setting the grain boundary diffusion heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Comparative Example 2
The present invention provides a method for improving coercivity and
thermal stability of a sintered Nd-Fe-B magnet, with an unmagnetized 42EH
commercial sintered Nd-Fe-B magnet as a prepared magnet that is cut into
x3x6mm slices by wire cutting. The method specifically comprises the
following steps:
S1. derusting the sintered Nd-Fe-B magnet, and then ultrasonically
cleaning the sintered Nd-Fe-B magnet with acetone for 3min after derusting,
and rinsing with distilled water to remove residual grease on the surface of the
sintered Nd-Fe-B magnet during wire cutting;
S2. ultrasonically pickling the sintered Nd-Fe-B magnet treated in the step
S1 for 25s with a nitric acid alcohol solution to remove scale on the surface of
the sintered Nd-Fe-B magnet and increase activation energy on the surface of
the sintered Nd-Fe-B magnet, wherein the concentration of nitric acid in the
nitric acid alcohol solution was 3wt.%; after pickling, ultrasonically cleaning the
sintered Nd-Fe-B magnet with distilled water and absolute ethanol
successively to remove residual acid stains on the surface of the sintered
Nd-Fe-B magnet;
S3. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 5x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.3 Pa, setting the negative
bias voltage at -180V for pre-sputtering for 10min to clean the surface of a
target, and keeping the set power stable; performing first magnetron sputtering
on the surface of the sintered Nd-Fe-B magnet treated in the step S2 by DC
magnetron sputtering, wherein the purity of a cylindrical Co target used for
sputtering was 99.95%, and depositing a first non-rare earth Co film layer with
a thickness of 2um on the surface of the sintered Nd-Fe-B magnet at a
deposition power of 125W for 1.5h;
S4. taking out the sintered Nd-Fe-B magnet sample deposited with the non-rare earth Co film layer immediately after the deposition for vacuum tube sealing, and putting a quartz tube filled with the sample and pumped to a vacuum environment into a microwave oven for grain boundary diffusion at
1000°C for 2h and tempering at 500°C for 0.5h; setting the grain boundary
diffusion heating rate at 50°C/min, setting the tempering heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Example 2
The sintered Nd-Fe-B magnet sample with the non-rare earth Co film layer
deposited on the surface treated in the step 4 of Comparative Example 2 was
put into distilled water and absolute ethanol sequentially for ultrasonic cleaning,
and then a second non-rare earth metal Al film layer was deposited on the
surface of the sample in the following steps:
S1. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 5x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.3 Pa, setting the negative
bias voltage at -180V for pre-sputtering for 10min to clean the surface of a
target, and keeping the set power stable; performing second magnetron
sputtering on the surface of the sample treated in the step S4 by DC
magnetron sputtering, wherein the purity of a cylindrical Al target used for
sputtering was 99.999%, and depositing a second non-rare earth Al film layer
with a thickness of 4um on the surface of the sintered Nd-Fe-B magnet sample
deposited with the non-rare earth Co film layer at a deposition power of 100W
for 1.5h;
S2. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co and Al film layers immediately after the deposition for
vacuum tube sealing, and putting a quartz tube filled with the sample and
pumped to a vacuum environment into a microwave oven for grain boundary
diffusion at 500°C for 2h; setting the grain boundary diffusion heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Comparative Example 3
The present invention provides a method for improving coercivity and
thermal stability of a sintered Nd-Fe-B magnet, with an unmagnetized 42EH
commercial sintered Nd-Fe-B magnet as a prepared magnet that is cut into
x3x4mm slices by wire cutting. The method specifically comprises the
following steps:
S1. derusting the sintered Nd-Fe-B magnet, and then ultrasonically
cleaning the sintered Nd-Fe-B magnet with acetone for 2min after derusting,
and rinsing with distilled water to remove residual grease on the surface of the
sintered Nd-Fe-B magnet during wire cutting;
S2. ultrasonically pickling the sintered Nd-Fe-B magnet treated in the step
S1 for 30s with a nitric acid alcohol solution to remove scale on the surface of
the sintered Nd-Fe-B magnet and increase activation energy on the surface of
the sintered Nd-Fe-B magnet, wherein the concentration of nitric acid in the
nitric acid alcohol solution was 5wt.%; after pickling, ultrasonically cleaning the
sintered Nd-Fe-B magnet with distilled water and absolute ethanol
successively to remove residual acid stains on the surface of the sintered
Nd-Fe-B magnet;
S3. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 6x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.5 Pa, setting the negative
bias voltage at -200V for pre-sputtering for 15min to clean the surface of a
target, and keeping the set power stable; performing first magnetron sputtering
on the surface of the sintered Nd-Fe-B magnet treated in the step S2 by DC
magnetron sputtering, wherein the purity of a cylindrical Co target used for
sputtering was 99.95%, and depositing a first non-rare earth Co film layer with
a thickness of 2um on the surface of the sintered Nd-Fe-B magnet at a
deposition power of 100W for 3h;
S4. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co film layer immediately after the deposition for vacuum tube
sealing, and putting a quartz tube filled with the sample and pumped to a
vacuum environment into a microwave oven for grain boundary diffusion at
950°C for 2h and tempering at 480°C for 1.5h; setting the grain boundary
diffusion heating rate at 50°C/min, setting the tempering heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Example 3
The sintered Nd-Fe-B magnet sample with the non-rare earth Co film layer
deposited on the surface treated in the step 4 of Comparative Example 3 was
put into distilled water and absolute ethanol sequentially for ultrasonic cleaning,
and then a second non-rare earth metal Al film layer was deposited on the
surface of the sample in the following steps:
S1. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 6x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.5 Pa, setting the negative
bias voltage at -200V for pre-sputtering for 15min to clean the surface of a
target, and keeping the set power stable; performing second magnetron
sputtering on the surface of the sample treated in the step S4 by DC
magnetron sputtering, wherein the purity of a cylindrical Al target used for
sputtering was 99.999%, and depositing a second non-rare earth Al film layer
with a thickness of 3um on the surface of the sintered Nd-Fe-B magnet sample
deposited with the non-rare earth Co film layer at a deposition power of 100W
for 1.2h;
S2. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co and Al film layers immediately after the deposition for
vacuum tube sealing, and putting a quartz tube filled with the sample and
pumped to a vacuum environment into a microwave oven for grain boundary
diffusion at 550°C for 2h; setting the grain boundary diffusion heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Comparative Example 4
The present invention provides a method for improving coercivity and
thermal stability of a sintered Nd-Fe-B magnet, with an unmagnetized 42EH
commercial sintered Nd-Fe-B magnet as a prepared magnet that is cut into
x30x10mm slices by wire cutting. The method specifically comprises the
following steps:
S1. derusting the sintered Nd-Fe-B magnet, and then ultrasonically
cleaning the sintered Nd-Fe-B magnet with acetone for 3min after derusting,
and rinsing with distilled water to remove residual grease on the surface of the
sintered Nd-Fe-B magnet during wire cutting;
S2. ultrasonically pickling the sintered Nd-Fe-B magnet treated in the step
S1 for 30s with a nitric acid alcohol solution to remove scale on the surface of
the sintered Nd-Fe-B magnet and increase activation energy on the surface of
the sintered Nd-Fe-B magnet, wherein the concentration of nitric acid in the
nitric acid alcohol solution was lOwt.%; after pickling, ultrasonically cleaning
the sintered Nd-Fe-B magnet with distilled water and absolute ethanol
successively to remove residual acid stains on the surface of the sintered
Nd-Fe-B magnet;
S3. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 8x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.8 Pa, setting the negative
bias voltage at -170V for pre-sputtering for 20min to clean the surface of a
target, and keeping the set power stable; performing first magnetron sputtering
on the surface of the sintered Nd-Fe-B magnet treated in the step S2 by DC
magnetron sputtering, wherein the purity of a cylindrical Co target used for
sputtering was 99.95%, and depositing a first non-rare earth Co film layer with
a thickness of 3um on the surface of the sintered Nd-Fe-B magnet at a
deposition power of 150W for 1h;
S4. taking out the sintered Nd-Fe-B magnet sample deposited with the non-rare earth Co film layer immediately after the deposition for vacuum tube sealing, and putting a quartz tube filled with the sample and pumped to a vacuum environment into a microwave oven for grain boundary diffusion at
1050°C for 1.5h and tempering at 520°C for 1h; setting the grain boundary
diffusion heating rate at 50°C/min, setting the tempering heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Example 4
The sintered Nd-Fe-B magnet sample with the non-rare earth Co film layer
deposited on the surface treated in the step 4 of Comparative Example 4 was
put into distilled water and absolute ethanol sequentially for ultrasonic cleaning,
and then a second non-rare earth metal Al film layer was deposited on the
surface of the sample in the following steps:
S1. starting a mechanical pump and a molecular pump sequentially to
enable the background vacuum degree in a chamber to reach 7x10-4 Pa, and
then charging high-purity argon with a concentration of 99.99% to enable the
working vacuum degree in the chamber to reach 0.6 Pa, setting the negative
bias voltage at -180V for pre-sputtering for 10min to clean the surface of a
target, and keeping the set power stable; performing second magnetron
sputtering on the surface of the sample treated in the step S4 by DC
magnetron sputtering, wherein the purity of a cylindrical Al target used for
sputtering was 99.999%, and depositing a second non-rare earth Al film layer
with a thickness of 2um on the surface of the sintered Nd-Fe-B magnet sample
deposited with the non-rare earth Co film layer at a deposition power of 125W
for 1h;
S2. taking out the sintered Nd-Fe-B magnet sample deposited with the
non-rare earth Co and Al film layers immediately after the deposition for
vacuum tube sealing, and putting a quartz tube filled with the sample and
pumped to a vacuum environment into a microwave oven for grain boundary
diffusion at 600°C for 2h; setting the grain boundary diffusion heating rate at
°C/min, and cooling the sample to room temperature in the oven.
Table 1 shows the comparison of magnetic properties of an original
sintered Nd-Fe-B magnet sample without magnetron sputtering, a sintered
Nd-Fe-B magnet deposited with a non-rare earth Co film layer by first
magnetron sputtering (referring to Comparative Examples 1, 2, 3 and 4), and a
sintered Nd-Fe-B magnet deposited with double non-rare earth Co and Al film
layers by second magnetron sputtering (referring to Examples 1, 2, 3 and 4).
Table 1 Comparison of magnetic properties of sintered Nd-Fe-B magnets
before and after the experiment
Br/KGs HCJ/kOe BH/MGOe P/%K<sup>-1</sup> a/%K<sup>-1</sup>
non-rare earth content/% original sample 12.96 28.5 42.8 -0.69 -0.16 0
Comparative Example 1 12.89 27.8 41.5 -0.65 -0.13 1.1 Example 1 12.93 30.3
42.1 -0.67 -0.14 1.9 Comparative Example 2 12.86 27.6 41.2 -0.66 -0.14 1.0
Example 2 12.92 30.5 42.3 -0.67 -0.15 2.1 Comparative Example 3 12.87 27.5
40.9 -.0.64 -0.12 1.2 Example 3 12.92 30.4 41.7 -0.65 -0.14 2.1 Comparative
Example 4 12.90 27.7 40.6 -0.65 -0.13 1.1 Example 4 12.95 30.6 41.5 -0.66
-0.151.9
As can be seen from Table 1, the coercivity of the magnet increased
significantly after grain boundary diffusion by magnetron sputtering, the remanence and magnetic energy product decreased not significantly, but the temperature coefficient decreased, indicating that the thermal stability was improved. The magnetic properties of the magnet degraded after the first magnetron sputtering of Co, but the absolute values of coercivity temperature coefficient P and remanence temperature coefficient a of the magnet decreased significantly, indicating that the thermal stability was improved. The magnetic properties of the magnet after magnetron sputtering of Co and the second magnetron sputtering of Al were improved significantly, exceeding the original magnet, but the temperature coefficient decreased slightly, indicating that the magnetic properties of the magnets were improved to some extent after magnetron sputtering of Co and Al compared with the original magnet, but the thermal properties were improved significantly compared with the original magnet.
The above examples are presented herein solely for the purpose of
illustrating several embodiments of the present invention, and should not be
construed as a limitation to the scope of the present invention despite of
specific and detailed description. It should be noted that a person skilled in the
art can make various changes and improvements without departing from the
concept of the present invention, which should be incorporated in the
protection scope of the invention. Therefore, the protection scope of the
present invention shall be subject to appended claims.

Claims (10)

1. A method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet, characterized by comprising the following steps:
S1. derusting and degreasing the sintered Nd-Fe-B magnet;
S2. pickling the sintered Nd-Fe-B magnet treated in the step S1, and then
removing acid stains;
S3. performing first magnetron sputtering on the sintered Nd-Fe-B magnet
treated in the step S2, and depositing a first non-rare earth metal film layer on
the surface of the sintered Nd-Fe-B magnet;
S4. performing grain boundary diffusion by microwave heating and
tempering on the sintered Nd-Fe-B magnet deposited with the single non-rare
earth film layer in the step S3;
S5. performing second magnetron sputtering on the sintered Nd-Fe-B
magnet treated in the step S4, and depositing a second non-rare earth metal
film layer on the surface of the sintered Nd-Fe-B magnet deposited with the
non-rare earth film layer; and
S6. performing grain boundary diffusion by microwave heating treatment
on the sintered Nd-Fe-B magnet deposited with the double non-rare earth film
layers in the step S5.
2. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1, characterized in that before magnetron
sputtering of the sintered Nd-Fe-B magnet, a mechanical pump and a
molecular pump are started sequentially to enable the background vacuum degree in a chamber to reach 5-8x10-4 Pa, and then high-purity argon with a concentration of 99.99% is charged to enable the working vacuum degree in the chamber to reach 0.3-0.8 Pa, the negative bias voltage is set at -150V to
-200V for pre-sputtering for 10-20min to clean the surface of a target, and the
set power is kept stable.
3. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that in the step S1,
the sintered Nd-Fe-B magnet is derusted, and then the sintered Nd-Fe-B
magnet is ultrasonically cleaned with acetone for 1-3min after derusting to
remove residual grease on the surface of the sintered Nd-Fe-B magnet during
wire cutting.
4. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that in the step S2,
the sintered Nd-Fe-B magnet is ultrasonically pickled for 20-40s with a nitric
acid alcohol solution to remove scale on the surface of the sintered Nd-Fe-B
magnet and increase activation energy on the surface of the sintered Nd-Fe-B
magnet, wherein the concentration of nitric acid in the nitric acid alcohol
solution is 3-10wt.%; after pickling, the sintered Nd-Fe-B magnet is
ultrasonically cleaned with distilled water and absolute ethanol successively to
remove residual acid stains on the surface of the sintered Nd-Fe-B magnet.
5. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that in the step S3,
the first magnetron sputtering is performed on the surface of the sintered
Nd-Fe-B magnet by DC magnetron sputtering, and the first non-rare earth film layer is deposited on the surface of the sintered Nd-Fe-B magnet at a deposition power of 75-150W for 1-4h.
6. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 5, characterized in that the rare earth
element in the first non-rare earth film layer is Co.
7. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that in the step S5,
the second magnetron sputtering is performed on the surface of the sintered
Nd-Fe-B magnet by DC magnetron sputtering, and the second non-rare earth
film is deposited on the surface of the sintered Nd-Fe-B magnet at a deposition
power of 50-125W for 1-3h.
8. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 7, characterized in that the rare earth
element in the second non-rare earth film layer is Al.
9. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that:
in the step S4, the grain boundary diffusion by microwave heating is
performed at 800-1100°C for 1-3h, and the tempering is performed at
450-550°C for 0.5-2h; and
in the step S6, the grain boundary diffusion by microwave heating is
performed at 500-650°C for 1-3h.
10. The method for improving coercivity and thermal stability of a sintered
Nd-Fe-B magnet according to claim 1 or 2, characterized in that the thickness of the sintered Nd-Fe-B magnet is not more than 25mm, and the diffusion depth of the non-rare earth metal is more than 3um.
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