CN114420436A - Diffusion method for improving magnetic property of sintered magnet and high-performance sintered NdFeB magnet prepared by same - Google Patents

Diffusion method for improving magnetic property of sintered magnet and high-performance sintered NdFeB magnet prepared by same Download PDF

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CN114420436A
CN114420436A CN202210105602.8A CN202210105602A CN114420436A CN 114420436 A CN114420436 A CN 114420436A CN 202210105602 A CN202210105602 A CN 202210105602A CN 114420436 A CN114420436 A CN 114420436A
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magnet
diffusion
rare earth
heavy rare
grain boundary
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朱啸航
达明花
许丁丁
胡校铭
王黎旭
付松
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Zhejiang Innuovo Magnetics Industry Co Ltd
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Zhejiang Innuovo Magnetics Industry Co Ltd
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    • 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
    • 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
    • H01F41/0266—Moulding; Pressing

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  • Power Engineering (AREA)
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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

The invention discloses a diffusion method for improving the magnetic property of a sintered magnet, which comprises the following steps: covering a layer of carbon film on the surface of the sintered NdFeB magnet substrate, wherein the mass ratio of the carbon film is 0.2-2.0% of that of the magnet substrate, carrying out magnetron sputtering coating on the magnet substrate coated with the carbon film, and coating a heavy rare earth film, wherein the mass ratio of the heavy rare earth is 0.2-4% of that of the magnet substrate, so as to obtain a coated magnet; and performing grain boundary diffusion treatment on the coated magnet to obtain the high-performance sintered NdFeB magnet after grain boundary diffusion. The invention also discloses a high-performance sintered NdFeB magnet prepared by the method. According to the invention, the surface of the magnet is covered with the carbon film, the weight of the carbon is controlled, and then the heavy rare earth grain boundary diffusion is carried out, so that the heavy rare earth diffusion effect is improved while the reduction of Br is reduced, and finally the rare earth NdFeB magnet with high Br and high Hcj magnetic properties can be obtained.

Description

Diffusion method for improving magnetic property of sintered magnet and high-performance sintered NdFeB magnet prepared by same
Technical Field
The invention relates to a diffusion method for improving the magnetic property of a sintered magnet and a high-performance sintered NdFeB magnet prepared by the same.
Background
The sintered NdFeB magnet material has high magnetic performance, does not contain strategic metallic nickel, has relatively low price, wide application range and long service life, thereby having wide development prospect.
However, the sintered NdFeB system magnet is still in the development stage, the magnetic performance of the sintered NdFeB magnet has a great progress space, the magnetic energy product of the current sintered NdFeB magnet can only reach 83% of the theoretical value, and the magnetic energy product obtained by industrial small-batch production and large-batch production is lower. Secondly, the actually sintered Hcj is only 20-30% of theory, and still has great progress space. It is therefore particularly important to improve the magnetic properties of the sintered NdFeB magnet.
The diffusion technology is a technology capable of rapidly improving Hcj in recent years, and has the advantages of low cost, convenience in operation, high cost performance and the like, but the diffusion depth of heavy rare earth is insufficient in the diffusion technology process; the problem of heavy rare earth diffusion to the main phase results in large reduction of Br of the magnet after diffusion and insufficient increment of Hcj, so that how to better improve the diffusion effect of the sintered NdFeB is particularly critical.
Disclosure of Invention
The invention provides a diffusion method for improving the magnetic performance of a sintered magnet by pre-diffusing a layer of carbon to better improve the diffusion effect, and the method can effectively solve the problems.
Compared with the conventional diffusion process, the method can obtain the NdFeB magnet with higher magnetic performance.
The technical scheme adopted by the invention is as follows:
a diffusion method for improving the magnetic properties of a sintered magnet, said method comprising the steps of:
(1) covering a layer of carbon film on the surface of a sintered NdFeB magnet substrate by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 um (preferably 5-12 um), the mass ratio of the carbon film to the magnet substrate is 0.2-2.0% (preferably 0.89-1.15%), performing magnetron sputtering coating on the magnet substrate coated with the carbon film, coating a heavy rare earth film, the thickness of the heavy rare earth film is 1-30 um (preferably 5-25 um), the mass ratio of the heavy rare earth to the magnet substrate is 0.2-4% (preferably 0.5-3.0%), and obtaining a coated magnet;
(2) and performing grain boundary diffusion treatment on the coated magnet, wherein the diffusion temperature is 800-1000 ℃ (preferably 850-920 ℃), the diffusion time is 1-48 h (preferably 6-12 h), the vacuum degree is more than 1.0 x 10-3Pa, after the grain boundary diffusion, cooling to room temperature, heating again and tempering, thus obtaining the high-performance sintered NdFeB magnet after the grain boundary diffusion.
In the step (1), the heavy rare earth is Tb or Dy.
In the step (1), the mass ratio of the carbon film is preferably 0.89 to 1.15% of the magnet base.
In the step (1), the mass ratio of the heavy rare earth is preferably 0.5 to 3.0%, more preferably 1.7 to 2.4% of the magnet matrix.
In the step (1), the PVD target material of the multi-arc sputtering method is a graphite target material, and the atmosphere is high-purity Ar.
In the step (1), the magnetron sputtering coating is carried out by physical vapor deposition by adopting a plasma vacuum coating machine, the atmosphere source is high-purity Ar, the vacuum degree of a cavity is between 0.3 and 0.5pa, the internal working temperature is between 100 and 150 ℃, the thickness of the obtained film layer is between 1 and 30um, and the mass ratio of the heavy rare earth is 0.2 to 4 percent of the mass of the magnet matrix.
In the step (1), the sintered NdFeB magnet matrix can be selected from various types or brands of sintered NdFeB magnets, the main components are Nd, Fe, Pr and B, and other various elements such as rare earth elements Ho, Gd, Dy and Tb, or other metal or nonmetal elements such as Al, Cu, Zn, Sn, In, Ti, V, Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo and Si, and the element composition and component ratio of the magnet matrix have no influence on the diffusion process of the present application.
In the step (2), the high-performance sintered NdFeB magnet after grain boundary diffusion has the carbon content of 0.05-0.30 wt% and the heavy rare earth content of 0.11-4%.
Generally, when the sintered NdFeB magnet matrix does not contain carbon, the carbon film covered in step (1) is the source of carbon in the finally diffused magnet, the mass ratio of the carbon film is 0.2-2.0% of the magnet matrix, and the carbon content in the diffused magnet is 0.05-0.3 wt%.
When the sintered NdFeB magnet matrix does not contain heavy rare earth elements, the heavy rare earth plated in the step (1) is the source of the heavy rare earth elements in the finally diffused magnet, the mass ratio of the plated heavy rare earth is 0.2-4% of that of the magnet matrix, and the content of the heavy rare earth obtained after grain boundary diffusion is 0.11-4%.
However, when the sintered NdFeB magnet matrix itself contains carbon, the mass ratio of the carbon film coated in step (1) is required to satisfy the requirement of the magnet after grain boundary diffusion, and the carbon content is 0.05 to 0.30 wt%.
When the sintered NdFeB magnet matrix contains heavy rare earth elements, the mass ratio of the heavy rare earth plated in the step (1) needs to meet the requirement that the content of the heavy rare earth element Dy or Tb in the magnet after grain boundary diffusion is 0.11-4%.
The mass fraction of the carbon film or the heavy rare earth coated in step (1) can be generally obtained by subtracting the carbon or heavy rare earth content in the matrix from the carbon or heavy rare earth content in the designed diffused magnet, and then adding the carbon or heavy rare earth content lost in the diffusion. This is a calculation method well known to those skilled in the art.
In the step (2), the diffusion temperature is preferably 850-920 ℃, and the diffusion time is preferably 6-12 h, and more preferably 9-12 h.
In the step (2), the temperature rise rate of the grain boundary diffusion is preferably 1-10 ℃/min, and more preferably 5-8 ℃/min.
In the step (2), the tempering temperature is 400-800 ℃, preferably 400-500 ℃, and the tempering time is 0.2-24 hours, preferably 3-6 hours.
The invention also provides the high-performance sintered NdFeB magnet prepared by the method, wherein the carbon content of the magnet is 0.05-0.3 wt%, the carbon content is gradually reduced from the outer layer to the inner layer of the magnet, and the mass content of the heavy rare earth after grain boundary diffusion is 0.11-4%.
Further, in the high-performance sintered NdFeB magnet, the carbon content gradually decreases from the outer layer toward the inner layer within 5mm from the outer surface toward the inner layer, and the average carbon content in the grain boundary is much higher than the average carbon content in the grain, which is observed for at least 5mm from the surface to the inner portion of the magnet, i.e., 10mm from the upper portion to the lower portion.
In the case where the average carbon content in the grain boundary is much higher than the average carbon content in the grain, the average carbon content in the grain boundary is higher than the average carbon content in the grain by 50% or more, preferably 70% or more.
The carbon content gradually decreases from the outer layer to the inner layer of the magnet, and the decreasing range is 40-100 ppm/5 mm.
Further, the invention provides a high-performance sintered NdFeB magnet, which comprises the components of R1RhM1M2C1A1T1, wherein R1 is one or more of Nd, Pr, Ho and Gd, the content of the R1 is 27-33 wt% (preferably 28.5-32 wt%), Rh is a heavy rare earth element, Dy or Tb, and the content of the Rh is 0.11-4%; m1 is selected from one or more of Al, Cu, Zn, Sn, In, Ti and V, the content of the M1 is 0.1-1.5 wt% (preferably 0.2-0.5 wt%), M2 is selected from one or more of Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo and Si, the content of the M2 is 0.5-1.5 wt% (preferably 0.70-1.20 wt%), A1 is boron, the content of the M1 is carbon, the content of the C1 is 0.05-0.3 wt%, the balance is T1, and T1 is Fe;
in the magnet, the carbon content gradually decreases from outside to inside within 5mm from the outer surface to inside, the average carbon content in a grain boundary is far higher than the average carbon content in the grain boundary, and the magnet has the phenomenon from the surface to the inside by at least 5mm, namely 10mm from the upper part to the lower part.
The carbon content gradually decreases from outside to inside, and the decreasing range is 40-100 ppm/5 mm.
In the case where the average carbon content in the grain boundary is much higher than the average carbon content in the grain, the average carbon content in the grain boundary is higher than the average carbon content in the grain by 50% or more, preferably 70% or more.
Further, the high-performance sintered NdFeB magnet is prepared by the following method:
A. preparing a magnet matrix:
taking raw materials of elements of a magnet matrix according to the component ratio, and obtaining a throwing sheet after smelting and casting; hydrogen breaking and airflow milling the throwing sheet to obtain powder, pressing and molding the powder, and vacuum sintering to obtain magnet blank as matrix for later use
B. Performing diffusion source film coating:
covering a layer of carbon film on the surface of the magnet matrix by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 um (preferably 5-12 um), the mass ratio of the carbon film is 0.2-2.0% (preferably 0.89-1.15%) of the magnet matrix, magnetic steel coated with the carbon film is subjected to magnetron sputtering coating by using a plasma vacuum coating machine, a heavy rare earth film is coated, the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film layer is 1-30 um (preferably 5-25 um), the mass ratio of the heavy rare earth is 0.2-4% (preferably 0.5-3.0%) of the magnet matrix, and a coated magnet is obtained;
the PVD target material of the multi-arc sputtering method is a graphite target material, and the atmosphere is high-purity Ar.
The magnetron sputtering coating is carried out physical vapor deposition, the atmosphere source is high-purity Ar, the vacuum degree of a cavity is 0.3-0.5pa, the internal working temperature is 100-150 ℃, the thickness of the obtained film layer is 1-30 um, the mass ratio of the heavy rare earth is 0.2-4%, preferably 0.5-3.0% of the magnet matrix, and more preferably 1.7-2.4%.
C. And (3) diffusion treatment:
and carrying out grain boundary diffusion treatment on the obtained magnetic steel B, wherein the diffusion temperature is 800-1000 ℃ (preferably 850-920 ℃), the diffusion time is 1-48 h (preferably 6-12 h), the vacuum degree is more than 1.0 x 10-3Pa, the heating rate is 1-10 ℃/min (preferably 5-8 ℃/min), after the grain boundary diffusion, cooling to room temperature, then heating for tempering treatment, the tempering temperature is 400-800 ℃ (preferably 400-500 ℃), and the tempering time is 0.2-24 h (preferably 3-6 h), thus obtaining the high-performance sintered NdFeB magnet.
In the magnet component, the total amount of Nd and Pr in R1 is preferably 50% or more, more preferably 80% or more of R1.
The total content of Al and Cu in M1 is preferably more than 55%, more preferably more than 85% of M1; wherein the Cu accounts for more than 15 percent of M1, and more preferably more than 30 percent.
The total amount of the components of Co, Ga and Zr in M2 is preferably 55% or more, more preferably 85% or more, based on the total amount of M2; wherein the content of Ga is 5% or more, more preferably 10% or more of M2.
In the step B, when the magnet matrix contains carbon element, the mass of the covered carbon film accounts for 0.05-0.30 wt% of the magnet after the crystal boundary diffusion.
In the step B, when the magnet matrix contains heavy rare earth elements, the mass ratio of the heavy rare earth plated in the step (1) needs to meet the requirement that the content of the heavy rare earth element Dy or Tb in the magnet after grain boundary diffusion is 0.11-4%.
The invention also provides a preparation method of the high-performance sintered NdFeB magnet, which comprises the following steps:
A. preparing a magnet matrix:
taking raw materials of elements of a magnet matrix according to the component ratio, and obtaining a throwing sheet after smelting and casting; hydrogen breaking and airflow milling the throwing sheet to obtain powder, pressing and molding the powder, and vacuum sintering to obtain magnet blank as matrix for later use
B. Performing diffusion source film coating:
covering a layer of carbon film on the surface of the magnet matrix by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 um (preferably 5-12 um), the mass ratio of the carbon film is 0.2-2.0% (preferably 0.89-1.15%) of the magnet matrix, magnetic steel coated with the carbon film is subjected to magnetron sputtering coating by using a plasma vacuum coating machine, a heavy rare earth film is coated, the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film layer is 1-30 um (preferably 5-25 um), the mass ratio of the heavy rare earth is 0.2-4% (preferably 0.5-3.0%) of the magnet matrix, and a coated magnet is obtained;
the PVD target material of the multi-arc sputtering method is a graphite target material, and the atmosphere is high-purity Ar.
The magnetron sputtering coating is carried out physical vapor deposition, the atmosphere source is high-purity Ar, the vacuum degree of a cavity is 0.3-0.5pa, the internal working temperature is 100-150 ℃, the thickness of the obtained film layer is 1-30 um, the mass ratio of the heavy rare earth is 0.2-4%, preferably 0.5-3.0%, more preferably 1.7-2.4% of the magnet matrix.
C. And (3) diffusion treatment:
and carrying out grain boundary diffusion treatment on the obtained magnetic steel B, wherein the diffusion temperature is 800-1000 ℃ (preferably 850-920 ℃), the diffusion time is 1-48 h (preferably 6-12 h), the vacuum degree is more than 1.0 x 10-3Pa, the heating rate is 1-10 ℃/min (preferably 5-8 ℃/min), after the grain boundary diffusion, cooling to room temperature, then heating for tempering treatment, the tempering temperature is 400-800 ℃ (preferably 400-500 ℃), and the tempering time is 0.2-24 h (preferably 3-6 h), thus obtaining the high-performance sintered NdFeB magnet.
In the step B, when the magnet matrix contains carbon element, the mass of the covered carbon film accounts for 0.05-0.30 wt% of the magnet after the crystal boundary diffusion.
In the step B, when the magnet matrix contains heavy rare earth elements, the mass ratio of the heavy rare earth plated in the step (1) needs to meet the requirement that the content of the heavy rare earth element Dy or Tb in the magnet after grain boundary diffusion is 0.11-4%.
In the invention, the grain boundary diffusion is carried out in a vacuum tube furnace, the temperature rise adopts a sectional temperature rise mode, and the cooling mode adopts a vacuum air cooling mode.
The applicant finds that a carbon film is added in the diffusion process through a large number of research and combination property tests, the performance of the diffused magnet is influenced to a certain extent, and the Nd-C phase diagram shows that the melting point of Nd is reduced along with the increase of the carbon content, so that the addition of the carbon is beneficial to reducing the melting point of the Nd-rich phase, and the diffusion mechanism is that heavy rare earth enters the interior of the magnet through a diffusion channel to be diffused, and the diffusion channel is formed by melting of the Nd-rich phase, so that the low-melting-point Nd-rich phase can form the diffusion channel earlier, and the diffusion effect is better.
Therefore, the addition of carbon is beneficial to the earlier formation of a diffusion channel and the diffusion, and the magnetic property is improved. Meanwhile, the low diffusion temperature is favorable for reducing the diffusion of the heavy rare earth into the main phase, thereby reducing the reduction amount of the residual magnetism after diffusion and realizing the magnet with double high residual magnetism and coercive force. However, in the conventional sintering process, if the amount of carbon added is not manually controlled, an excessively high sintering temperature introduces excessive impurity carbon, which may cause deterioration in performance. Meanwhile, excessive carbon also enters the gap of the main phase to react with the main phase, so that Br is greatly reduced, and therefore, the addition amount of the diffusion carbon needs to be proper to achieve the optimal diffusion effect. If the magnet matrix contains carbon element, when the carbon content is increased, the carbide in the grain boundary is greatly increased, the Nd-rich phase is greatly destroyed, the grain boundary phase is difficult to flow, particularly after 0.30 wt%, the Hcj increase is not high, and the Br decrease is larger, so that the C content in the prepared magnet is controlled within 0.30%.
The invention has the beneficial effects that: by covering a carbon film on the surface of the magnet, controlling the weight of the carbon and then performing heavy rare earth grain boundary diffusion, the heavy rare earth diffusion effect is improved while the reduction of Br is reduced, and finally the rare earth NdFeB magnet with high Br and high Hcj magnetic performance can be obtained.
Drawings
FIG. 1 is a graph of the carbon content measured every 1mm depth from the outside inwards for magnets of various embodiments.
FIG. 2 SEM image of the grain boundary and the C content difference inside the grain of the magnet prepared in example 3, wherein the depth of the grain boundary is 5mm from the outer surface.
FIG. 3 SEM image of the grain boundary and the C content difference inside the grain of the magnet prepared in example 3, wherein the depth of the grain boundary is 1mm from the outer surface.
Detailed Description
The technical solution of the present invention is further described with specific examples, but the scope of the present invention is not limited thereto.
Example 1:
firstly, preparing a substrate, and plating a carbon film and then plating a pure Tb layer by a magnetron sputtering method. After film coating, the film is placed in a vacuum tube furnace for diffusion, and the method comprises the following specific steps:
the magnet composition of R1RhM1M2C1A1T1, wherein R1 is Nd and Pr, Rh is Tb and accounts for 22.33%, 7.12% and 0.11% respectively, M1 is selected from Al and Cu and accounts for 0.17% and 0.101% respectively, M2 is selected from Co, Zr and Ga and accounts for 0.49%, 0.096% and 0.139% respectively, A1 is boron and accounts for 0.96%, C1 is carbon and accounts for 0.05% and the balance is T1 is Fe.
The preparation method comprises the following steps:
s1, preparing an R1M1M2BFe matrix, wherein the matrix comprises the following selected components: r1 is Nd + Pr with the mass ratio of 22.33 percent and 7.12 percent respectively, M1 is Al and Cu with the mass ratio of 0.17 percent and 0.101 percent respectively, M2 is Co, Ca and Zr with the mass ratio of 0.49 percent, 0.096 percent and 0.139 percent, B content is 0.96 percent, and the rest is Fe. Taking raw materials of R1, M1, M2 and B, T1 according to the component ratio, and obtaining the flail after smelting and casting. And sintering the throwing sheet into a blank by conventional processes such as hydrogen breaking, jet milling, press forming, vacuum sintering and the like. And cleaning the blank, then performing wire cutting, and cutting the magnet into a plurality of magnetic steels A with phi 10 x 10mm for the convenience of magnetic property and component detection. Magnetic steel A was crushed and sampled at the center, and the magnet components were detected by ICP-MSOES, and the results are shown in Table 1.
S2: performing magnetron sputtering coating of a diffusion source, coating a carbon film on magnetic steel A with phi 10mm x 10mm by using a multi-arc sputtering method, wherein the thickness of the carbon film is 1.7um, the mass ratio of the carbon film is 0.20%, then performing magnetron sputtering physical vapor deposition in a plasma vacuum coating machine, and coating a Tb film to obtain magnetic steel B, wherein the atmosphere source of the magnetic steel B is high-purity Ar, the vacuum degree of a cavity is 0.3-0.5pa, the internal working temperature is 120 ℃, the thickness of the Tb film is 15um, and the mass ratio of the Tb is about 1.7%.
S3: and (3) diffusion treatment: and putting the obtained magnetic steel B into a material boat, and introducing the magnetic steel B into a vacuum tube furnace for diffusion treatment, wherein the diffusion treatment is divided into two groups, one group is at 905 ℃ and the diffusion time is 9h, the other group is at 905 diffusion temperature and the diffusion time is 6h, the vacuum degree is more than 1.0 x 10-3Pa, the heating rate of the vacuum tube furnace is 6.5 ℃/min, the tempering temperature is 445 ℃ and the tempering time is 4.5 h.
And S4, testing the magnetic performance of the obtained magnet, then carrying out sand blasting and demagnetization treatment, carrying out component testing from outside to inside, and testing the content of C in the magnet by using a high-frequency infrared carbon-sulfur analyzer. The test method comprises the steps of carrying out sand blasting treatment after wire cutting every 1mm thickness from outside to inside, carrying out component test, and measuring the magnet component by adopting ICP-OES, wherein the obtained result is shown in figure 1.
The magnetic performance of the magnet at 20 +/-3 ℃ is measured by adopting NIM15000, and the microscopic structure analysis and the micro-area component analysis are carried out on the magnet by utilizing SEM and EPMA.
Example 2:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 0.55 percent.
Example 3:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 0.89 percent.
Example 4:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 1.05 percent.
Example 5:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 1.15 percent.
Example 6:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 1.53 percent.
Example 7:
the preparation method is the same as that of the example 1, except that the weight ratio of the diffusion source graphite is as follows: 2.0 percent.
Example 8:
the preparation method is the same as that of the embodiment 4, except that the weight ratio of the diffusion source terbium is as follows: 2.03 percent.
Example 9:
the preparation method is the same as that of the embodiment 4, except that the weight ratio of the diffusion source terbium is as follows: 2.40 percent. The control group was subjected to the steps of S1, S3, S4, and not to the step of S2 diffusion.
The composition of magnetic steel a is shown in the following table 1:
TABLE 1
Figure BDA0003493402270000071
Figure BDA0003493402270000081
The properties after diffusion treatment are shown in Table 2 below.
TABLE 2
Figure BDA0003493402270000082
Figure BDA0003493402270000091
The control properties are given in Table 3 below
TABLE 3
Figure BDA0003493402270000092
The SEM image of the content difference of C in the grain boundary and the grain inside of the magnet prepared in example 3 at a depth of 5mm from the surface is shown in FIG. 2, and the content data of C and other elements corresponding to different positions in the SEM image are shown in Table 4.
TABLE 4
Figure BDA0003493402270000101
The SEM image of the content difference of C in the grain boundary and the grain inside of the magnet of example 3 at a depth of 1mm from the surface is shown in FIG. 3, and the content data of C and other elements corresponding to different positions in the SEM image are shown in Table 5.
TABLE 5
Figure BDA0003493402270000102
Figure BDA0003493402270000111
The conclusion is drawn from the above figures and tables:
1. as shown in figure 1, the average value of the content of C gradually decreases from the outer surface to the inner surface, and the decreasing range is 40-100 ppm/5 mm.
2. Fig. 2, 3, tables 4 and 5 show that, from the surface to the inside of the magnet, the closer to the surface, the higher the C content in the grain boundary phase, the lower the C content further from the surface, and at the same time, the C weight ratio in the grain boundary phase is much higher than the C weight ratio in the grain, and the C content in the grain boundary phase is more than 70% higher than the average C value in the grain, which is beneficial to improving the diffusion effect and increasing the magnetic performance more significantly.
The method of the invention can greatly improve the magnetic performance of the magnet by comparing the examples 1-7 in tables 2 and 3 and comparing the diffusion performance of 905 ℃ 6h and 905 h 9h, and simultaneously shows that the addition of a proper amount of graphite reduces the melting point of Nd-rich, so that a diffusion channel is formed earlier, the heavy rare earth is prevented from diffusing to the main phase, the diffusion depth of the heavy rare earth is increased, and therefore, the increase of Hcj can be improved while the reduction of Br is reduced, and the overall diffusion effect is improved.
Example 10:
the procedure is as in example 4, except that the diffusion temperature is 850 ℃ and the time is 9 hours.
The control group 10 was prepared in the same manner as in the example, except that there was no graphite layer diffusion step and there was a Tb diffusion step in S2.
Example 11 was prepared according to the same procedure as example 4 except that the diffusion temperature was 920 ℃ and the time was 9 hours.
The control group 11 was prepared in the same manner as in the example, except that there was no graphite layer diffusion step and there was a Tb diffusion step in S2.
TABLE 6 EXAMPLES 10, 11 AND COMPARATIVE GROUP PERFORMANCES
Figure BDA0003493402270000121
And (4) conclusion:
table 6 shows that, after the graphite diffusion source is added, compared with the high diffusion temperature, the low diffusion temperature is favorable for reducing the diffusion of the heavy rare earth into the main phase, so that the reduction of the remanence after diffusion is reduced, the magnet with both high remanence and coercive force is realized, and the reduction of the squareness degree is not large.
Example 12
The preparation method is the same as that of example 4 except that the composition of the matrix is different, the matrix contains Tb, the specific composition is shown in Table 7, in example 12, the film layer of the diffusion source Tb is 30nm, the mass accounts for 4.0 wt% of the magnet, the diffusion time is 36h, and the rest is the same as that of example 4.
Example 13 was prepared in the same manner as in example 12, except that the diffusion source Tb was 3.8 wt% based on the mass of the sample,
example 14 was prepared in the same manner as example 12, except that the diffusion source Tb accounted for 3.5 wt% of the magnet by mass,
example 15 was prepared according to the same procedure as example 12 except that the diffusion time was 24 hours, the rest being the same.
Example 16 was prepared according to the same procedure as example 12, except that the diffusion time was 12h, and the rest was the same.
The control was matrix performance.
TABLE 7 composition of matrix and content (wt%) of diffused component in examples 12 to 16
Group of Nd Pr B Al Co Cu Ga Tb Zr Fe
Example 12 19.00 6.10 0.95 0.15 1.17 0.10 0.18 4.30 0.10 67.65
Example 13 19.50 6.10 0.95 0.15 1.16 0.10 0.18 4.10 0.10 67.85
Example 14 19.80 6.10 0.95 0.15 1.17 0.10 0.18 4.00 0.10 67.65
Example 15 21.10 6.10 0.95 0.15 1.16 0.10 0.18 2.80 0.10 67.36
Example 16 23.00 6.10 0.95 0.15 1.16 0.10 0.18 1.30 0.10 66.96
Base body 23.80 6.20 0.10 0.16 1.18 0.10 0.18 0.90 0.10 67.28
TABLE 8 examples 12-16 and control Performance
Figure BDA0003493402270000131
And (4) conclusion:
examples 12 to 16 show
1. The expansion temperature is prolonged, so that a large amount of Nd-rich phase volatilizes, the Nd content is greatly reduced, Br is greatly reduced, Tb diffusion is greatly increased, and the increase of Hcj is obvious.
2. After Tb content after diffusion exceeds 4 wt%, Br and SQ are reduced greatly, and Br reduction is uncontrollable, so that Tb content after diffusion is controlled within 4.0 wt%, Br reduction is not controlled greatly, and Hcj increment is high.
Example 17 was prepared according to the same method as example 4, except that the base had a different composition as shown in Table 8. The diffusion time was 9 h.
Example 18 was prepared in the same manner as example 17, except that the content of the diffusion source Tb was 2.8 wt%.
Example 19 was prepared in the same manner as example 17, except that the content of the diffusion source Tb was 3.2% by weight.
Example 20 was prepared in the same manner as in example 17, except that the content of the diffusion source Tb was 0.2 wt%.
The control was matrix performance.
TABLE 9 base component and diffused component contents (wt%) in examples 17 to 20
Nd Pr B Co Cu Ga Tb Zr Fe
Example 17 19.30 6.10 0.90 0.79 0.13 0.24 3.99 0.085 68.465
Example 18 19.10 6.10 0.90 0.80 0.14 0.24 4.10 0.086 68.534
Example 19 19.00 6.10 0.90 0.78 0.13 0.24 4.15 0.088 68.612
Example 20 19.48 6.20 0.90 0.80 0.14 0.24 3.81 0.088 68.42
Base body 19.50 6.20 0.90 0.80 0.14 0.24 3.80 0.088 68.42
TABLE 10 Performance of examples 17-20 and control
Figure BDA0003493402270000141
And (4) conclusion:
as can be seen from table 9 and table 10, when the Tb content in the magnet matrix itself is high, the Hcj increase is not significantly increased before the Tb content after diffusion is higher than 4.0 wt%, and therefore the diffusion amount of Tb element after diffusion is preferably controlled to be within 4.0 wt%.
Example 21 was prepared in the same manner as example 7, except that 0.05% carbon was previously added to the matrix in the form of a binary alloy. The diffusion time was 9 h.
Example 22 was prepared in the same manner as example 7, except that 0.10% carbon was previously added to the matrix in the form of a binary alloy.
Example 23 was prepared in the same manner as example 7, except that 0.15% carbon was previously added to the matrix in the form of a binary alloy.
Example 24 was prepared in the same manner as example 7, except that 0.20% carbon was previously added to the matrix in the form of a binary alloy.
Example 25 was prepared in the same manner as example 7, except that 0.25% carbon was previously added to the matrix in the form of a binary alloy.
Example 26 was prepared in the same manner as example 7, except that 0.30% carbon was previously added to the matrix in the form of a binary alloy.
The control was matrix performance.
TABLE 11 carbon content after diffusion and magnetic properties after diffusion and control Performance for examples 21-26
Br/KGs Hcj/KOe HK/Hcj Carbon content/wt%
Control group 21 14.72 14.73 0.98 0.05
Control group 22 14.71 14.71 0.98 0.10
Example 21 14.28 22.51 0.97 0.18
Example 22 14.23 20.91 0.97 0.23
Example 23 14.18 20.91 0.97 0.27
Example 24 14.11 21.21 0.96 0.30
Example 25 13.95 15.92 0.94 0.34
Example 26 13.73 15.56 0.93 0.37
And (4) conclusion: after research, the carbon content is increased to cause that carbides in grain boundaries are greatly increased and Nd-rich phases are greatly damaged, the grain boundary phases are difficult to flow, and particularly after 0.30 wt%, the Hcj increase amount is not high and the Br decrease amount is larger, so that the C content in the prepared magnet is controlled within 0.30%.

Claims (10)

1. A diffusion method for improving the magnetic properties of a sintered magnet, said method comprising the steps of:
(1) covering a layer of carbon film on the surface of a sintered NdFeB magnet substrate by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 mu m, the mass ratio of the carbon film to the magnet substrate is 0.2-2.0%, carrying out magnetron sputtering coating on the magnet substrate coated with the carbon film, and coating a heavy rare earth film, wherein the thickness of the heavy rare earth film is 1-30 mu m, and the mass ratio of the heavy rare earth to the magnet substrate is 0.2-4%, so as to obtain a coated magnet;
(2) performing grain boundary diffusion treatment on the coated magnet, wherein the diffusion temperature is 800-1000 ℃, the diffusion time is 1-48 h, and the vacuum degree is 1.0 x 10-3And Pa above, after grain boundary diffusion, cooling to room temperature, heating and tempering to obtain the high-performance sintered NdFeB magnet after grain boundary diffusion.
2. The method according to claim 1, wherein in the step (1), the heavy rare earth is Tb or Dy.
3. The method according to claim 1, wherein in the step (2), the high performance sintered NdFeB magnet after grain boundary diffusion has a carbon content of 0.05 to 0.30 wt% and a heavy rare earth content of 0.11 to 4 wt%.
4. The method according to claim 1, wherein in the step (2), the diffusion temperature is 850 ℃ to 920 ℃ and the diffusion time is 6h to 12 h.
5. The method according to claim 1, wherein in the step (2), the tempering temperature is 400-800 ℃ and the tempering time is 0.2-24 h.
6. The high-performance sintered NdFeB magnet prepared by the method according to any one of claims 1 to 5, wherein the carbon content in the magnet is 0.05 to 0.30 wt%, the carbon content decreases from the outer layer to the inner layer of the magnet, and the mass content of the heavy rare earth after grain boundary diffusion is 0.11 to 4%.
7. The high-performance sintered NdFeB magnet as claimed in claim 6, wherein the magnet has a carbon content gradually decreasing from the outside toward the inside within 5mm from the outside surface, and the average carbon content in the grain boundary is higher than the average carbon content in the grain by 50% or more.
8. A high-performance sintered NdFeB magnet is characterized in that the component of the magnet is R1RhM1M2C1A1T1Wherein R is1Is one or more of Nd, Pr, Ho and Gd, the content of which is 27-33 wt percent, and RhIs a heavy rare earth element, is Dy or Tb, and has the content of 0.11 to 4 percent; m1One or more selected from Al, Cu, Zn, Sn, In, Ti and V, the content of which is 0.1-1.5 wt%, M2One or more selected from Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo and Si, the content of which is 0.5-1.5 wt%, A1Boron in an amount of 0.5 to 1.5 wt%, C1Carbon in 0.05-0.30 wt%, and T for the rest1，T1Is Fe;
in the magnet, the carbon content gradually decreases from outside to inside within the range of 5mm from the outer surface to inside, and the average carbon content in a grain boundary is far higher than the average carbon content in the grain boundary;
in the phenomenon that the average carbon content in the grain boundary is far higher than the average carbon content in the grain, the average carbon content in the grain boundary is higher than the average carbon content in the grain by more than 50 percent.
9. The high-performance sintered NdFeB magnet according to claim 8, characterized in that it is produced by the following method:
A. preparing a magnet matrix:
taking raw materials of elements of a magnet matrix according to the component ratio, and obtaining a throwing sheet after smelting and casting; hydrogen breaking and airflow milling the throwing sheet to obtain powder, pressing and molding the powder, and vacuum sintering to obtain magnet blank as matrix for later use
B. Performing diffusion source film coating:
covering a layer of carbon film on the surface of the magnet substrate by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 um, the mass ratio of the carbon film is 0.2-2.0% of the magnet substrate, performing magnetron sputtering coating on the magnetic steel coated with the carbon film by using a plasma vacuum coating machine, and coating a heavy rare earth film, wherein the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film is 1-30 um, and the mass ratio of the heavy rare earth is 0.2-4% of the magnet substrate, so as to obtain a coated magnet;
C. and (3) diffusion treatment:
carrying out grain boundary diffusion treatment on the obtained magnetic steel B, wherein the diffusion temperature is 800-1000 ℃, the diffusion time is 1-48 h, and the vacuum degree is 1.0 x 10-3Pa above, the heating rate is 1-10 ℃/min, after crystal boundary diffusion, the magnet is cooled to room temperature and then is heated for tempering treatment, the tempering temperature is 400-800 ℃, and the tempering time is 0.2-24 h, thus obtaining the high-performance sintered NdFeB magnet.
10. The method for producing a high-performance sintered NdFeB magnet according to claim 8, characterized in that the method comprises:
A. preparing a magnet matrix:
taking raw materials of elements of a magnet matrix according to the component ratio, and obtaining a throwing sheet after smelting and casting; hydrogen breaking and airflow milling the throwing sheet to obtain powder, pressing and molding the powder, and vacuum sintering to obtain magnet blank as matrix for later use
B. Performing diffusion source film coating:
covering a layer of carbon film on the surface of the magnet substrate by using a multi-arc sputtering method, wherein the thickness of the carbon film is 2-20 um, the mass ratio of the carbon film is 0.2-2.0% of the magnet substrate, performing magnetron sputtering coating on the magnetic steel coated with the carbon film by using a plasma vacuum coating machine, and coating a heavy rare earth film, wherein the heavy rare earth is Dy or Tb, the thickness of the heavy rare earth film is 1-30 um, and the mass ratio of the heavy rare earth is 0.2-4% of the magnet substrate, so as to obtain a coated magnet;
C. and (3) diffusion treatment:
and carrying out grain boundary diffusion treatment on the obtained magnetic steel B, wherein the diffusion temperature is 800-1000 ℃, the diffusion time is 1-48 h, the vacuum degree is more than 1.0 x 10-3Pa, the heating rate is 1-10 ℃/min, after the grain boundary diffusion, cooling to room temperature, heating again, carrying out tempering treatment, the tempering temperature is 400-800 ℃, and the tempering time is 0.2-24 h, thus obtaining the high-performance sintered NdFeB magnet.
CN202210105602.8A 2022-01-28 2022-01-28 Diffusion method for improving magnetic property of sintered magnet and high-performance sintered NdFeB magnet prepared by same Pending CN114420436A (en)

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