CN105321645B - High-coercivity nanocrystalline thermal deformation rare earth permanent magnet material and preparation method thereof - Google Patents
High-coercivity nanocrystalline thermal deformation rare earth permanent magnet material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a preparation method of a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material, which comprises the following steps: the method comprises the steps of respectively providing alloy powder and high-melting-point additives, wherein the high-melting-point additives are at least one of refractory carbide, refractory nitride and refractory oxide; uniformly mixing the alloy powder and the high-melting-point additive to obtain mixed magnetic powder, wherein the mass ratio of the high-melting-point additive in the mixed magnetic powder is more than or equal to 0.01% and less than or equal to 10%; and thirdly, carrying out hot press forming and thermal deformation forming on the mixed magnetic powder in sequence to obtain the high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material. The invention also provides a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material.
Description
Technical Field
The invention relates to the technical field of rare earth permanent magnets, in particular to a rare earth permanent magnet material with excellent magnetic property and a preparation method thereof.
Background
The rare earth permanent magnetic material is a permanent magnetic material taking an intermetallic compound formed by rare earth metal elements and transition metals as a matrix. The neodymium iron boron permanent magnet (also called NdFeB permanent magnet) is the permanent magnet material with the highest magnetic performance at present. The neodymium iron boron permanent magnet is widely used in the fields of social production, life, national defense, aerospace and the like, and becomes an important functional material for supporting social progress.
Preparation method of NdFeB permanent magnetic materialThere are mainly a hot deformation method and a sintering method. Compared with sintering method, the thermal deformation method has the advantages of low rare earth consumption, good corrosion resistance, easy realization of near-net shaping, etc. Permanent magnetic material obtained by thermal deformation mainly consists of Nd2Fe14B main phase and Nd-rich phase. The magnetic properties of a thermally deformed magnet, particularly the product of remanence and magnetic energy, depend on the degree to which the primary phase grains are oriented along the c-axis. Besides the effects of wetting crystal grains and modifying crystal grain boundaries in the deformation process, the Nd-rich phase can also reduce the exchange coupling effect between hard magnetic phases by utilizing the obvious non-ferromagnetic characteristic of the Nd-rich phase, so that the coercivity is improved.
Fuerst and Brewer studies found that the segregation of non-magnetic Zn and Cu elements at grain boundaries can partially increase the coercivity of the magnet (see Fuerst C D, Brewer E G. enhanced coercivities in two-up Nd-Fe-B magnets with dispersion-alloyed additives (Zn, Cu, and Ni). Applied Physics letters.1990,56: 2252-. Hono et al studied the grain boundary fine structure Of the thermal deformation magnet by using the advantages Of three-dimensional atom probe in the micro-region element characterization, considering that the grain boundary Of the thermal deformation magnet contains high content Of Fe and has strong ferromagnetism, and introducing non-magnetic elements by using grain boundary diffusion technology to reduce the ferromagnetism Of the grain boundary phase and form strong domain wall pinning effect, so as to significantly improve the coercive force (please refer to Liu J, Sepeh-Amin H, Ohkubo T, Hioki K, Hattori A, Schrefl T, and Hono K.Effect Of Nd content on the microstructure and coercivity Of hot-formed Nd-Fe-B permanent. acta materials, 2013,61: 5387. Sep 5399; ehi-Amin H, Ohk Schubo T, Nagashi, Yam no, Shooji A, Kareo K, Horeft and K-gradient Nd-D Nd gradient Nd-D, K-D ]. Acta Materialia,2013,61: 6622-.
However, the Nd of the magnet is increased due to the increase of Nd-rich phase added by grain boundary diffusion2Fe14The main phase B is reduced, and although the magnet obtained by the thermal deformation process has high coercive force, the remanence is obviously reduced, so that the comprehensive magnetic performance of the magnet is poor.
Disclosure of Invention
In view of the above, it is necessary to provide a rare earth permanent magnetic material with excellent magnetic properties and a preparation method thereof.
The invention provides a preparation method of a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material, which comprises the following steps:
the method comprises the steps of respectively providing alloy powder and high-melting-point additives, wherein the high-melting-point additives are at least one of refractory carbide, refractory nitride and refractory oxide;
uniformly mixing the alloy powder and the high-melting-point additive to obtain mixed magnetic powder, wherein the mass ratio of the high-melting-point additive in the mixed magnetic powder is more than or equal to 0.01% and less than or equal to 10%;
and thirdly, carrying out hot press forming and thermal deformation forming on the mixed magnetic powder in sequence to obtain the high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material.
Wherein the high-melting point additive is WC, SiC, BN, ZrO2、Al2O3、SiO2At least one of (1).
Wherein the mass ratio of the high-melting-point additive in the mixed magnetic powder is 0.1-5%.
Wherein the chemical formula of the alloy powder is Re by mass percentxFe100-x-y-zMyBzWherein Re is one or more of Nd, Pr, Dy, Tb, La and Ce, M is one or more of Al, Co, Cu and Ga, x is more than or equal to 20 and less than or equal to 40, y is more than or equal to 0 and less than or equal to 10, and z is more than or equal to 0.7 and less than or equal to 1.5.
Wherein the grain diameter of the high-melting-point additive is 10 nanometers to 1 micron.
The step three of hot press forming the mixed magnetic powder specifically comprises the following steps: the mixed magnetic powder is placed in a first mold, the mixed magnetic powder is heated to a first temperature in a vacuum environment or a protective atmosphere, and a first pressure is applied to the first mold to obtain a hot-pressed magnet, wherein the first temperature is 600-750 ℃, and the first pressure is 100-250 MPa.
Wherein the vacuum degree of the vacuum environment is not less than 1 × 10-2Pa。
In the step three, the hot-deformation molding is to place the hot-pressed magnet into a second mold, heat the hot-pressed magnet to a second temperature in a vacuum environment or a protective atmosphere, and apply a second pressure to the hot-pressed magnet to deform the hot-pressed magnet by a deformation degree of 30% -95%, so as to obtain the hot-deformed magnet, wherein the second temperature is 750-900 ℃, and the second pressure is 30-100 MPa.
The step three is further followed by a tempering treatment step, wherein the tempering treatment process specifically comprises the following steps: and heating the thermal deformation magnet to a third temperature in a vacuum environment or a protective atmosphere, preserving heat, quenching and quenching after the heat preservation is finished, wherein the third temperature is 500-800 ℃, the heat preservation time is 1-10 hours, and the heating rate is 5-20 ℃/min during heating.
The invention also provides a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material prepared by the preparation method, which is prepared from a matrix phase Re2Fe14B. Grain boundary phase and refractory additive with high melting point, wherein Re is one or more of Nd, Pr, Dy, Tb, La and Ce, and matrix phase Re2Fe14And B is a flaky nanocrystalline, the length of the flaky nanocrystalline is 200-500 nanometers, the thickness of the flaky nanocrystalline is 50-100 nanometers, and the high-melting-point refractory additives are periodically distributed in a strip shape.
Compared with the prior art, the high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material and the preparation method thereof provided by the invention have the following advantages: first, since refractory high melting point additives, which are not easily melted during hot pressing and hot deformation, are added, the high melting point additives are uniformly distributed, thereby suppressing a coarse crystal region and Re2Fe14Growth of B grains to form Re2Fe14The size of the B grains is relatively small (less than 1 micron), i.e., Re2Fe14The size of the B crystal grain is close to the single domain critical size, and thus the magnetic domain is more easily stabilized, and generation or expansion of a reverse magnetic domain hardly occurs, which is advantageous for improvement of coercivity; second, the substances occupied by the high melting point additivesThe quantity ratio is more than or equal to 0.01 and less than or equal to 10 percent, so that the remanence of the obtained magnet is not seriously damaged, and the coercive force of the magnet is greatly improved. The preparation method is easy to operate and industrialize. The obtained high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material has excellent comprehensive magnetic performance.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) photograph of the high coercivity nanocrystalline thermally deformable rare earth permanent magnetic material obtained in example 2.
Fig. 2 is a photograph of back-scattered electron imaging (BSE) of the high coercivity nanocrystalline thermally deformable rare earth permanent magnet material obtained in example 2.
The following specific embodiments will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
The high coercivity nanocrystalline thermally deformable rare earth permanent magnet material and the preparation method thereof provided by the invention are further explained below.
The invention provides a preparation method of a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material, which comprises the following steps:
s1, respectively providing alloy powder and refractory additives, wherein the refractory additives are at least one of refractory carbide, refractory nitride and refractory oxide;
s2, uniformly mixing the alloy powder and the high-melting-point additive to obtain mixed magnetic powder, wherein the mass ratio of the high-melting-point additive in the mixed magnetic powder is more than or equal to 0.01 and less than or equal to 10%; and
and S3, sequentially carrying out hot press molding and thermal deformation molding on the mixed magnetic powder to obtain the nanocrystalline thermal deformation rare earth permanent magnet material with high coercivity.
In step S1, the chemical formula of the alloy powder is Re by mass percentagexFe100-x-y-zMyBzWherein Re is one or more of Nd, Pr, Dy, Tb, La and Ce, M is one or more of Al, Co, Cu and Ga, x is more than or equal to 20 and less than or equal to 40, y is more than or equal to 0 and less than or equal to 10, and z is more than or equal to 0.7 and less than or equal to 1.5. The alloy powder may be a commercially available product or may beAnd (4) self-made. The alloy powder can be prepared by the following method:
(a) preparing materials according to the proportion of each element in the alloy powder;
(b) mixing the prepared raw materials and smelting in an inert atmosphere to obtain a master alloy;
(c) spraying the master alloy to a water-cooling roller for quick quenching to prepare a quick quenching belt; and
(d) and mechanically crushing the rapid quenching belt to obtain alloy powder.
The high-melting-point additive is at least one of refractory carbide, nitride and oxide. Specifically, the high-melting point additive is WC, SiC, BN, ZrO2、Al2O3、SiO2At least one of (1). The grain size of the high-melting point additive is 10 nanometers to 1 micron. The particle size of the high melting point additive is preferably 10 nm to 100nm, considering that the smaller the particle size of the additive, the easier the diffusion, the less the inhibition of the rheology, and the less the formation of texture. By adding high melting point additive, the coarse crystal region and Re can be inhibited in the subsequent thermal deformation forming process2Fe14Growth of B grains to obtain Re2Fe14The size of the B crystal grain is small, so that the obtained high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material is excellent in coercivity.
In step S2, the refractory additions are uniformly distributed in the alloy powder by mixing the alloy powder with the refractory additions. The mixing may be performed in a three-dimensional blender. The mass proportion of the high-melting-point additive in the mixed magnetic powder is preferably 0.1% -5%, so that the phenomenon that when the mass proportion of the high-melting-point additive is too high, the rheology of a magnet is hindered, and further the formation of texture is influenced is avoided, and the high-melting-point additive is a non-magnetic substance, and the residual magnetism is reduced due to the fact that the mass proportion of the high-melting-point additive is too high; and when the mass proportion of the high-melting-point additive is too low, the additive is not uniformly distributed and cannot play a role in inhibition.
In step S3, the loose mixed magnetic powder may be formed to have a certain density and a certain degree of hardness by a hot press molding processA strong hot-pressed magnet. In the thermal deformation forming process, the hot-pressed magnet Re is under the action of high temperature and pressure2T14The B-phase crystal grains form flaky nanocrystals which are consistently oriented along the c-axis of the easy magnetization axis through the processes of dissolution, mass transfer and recrystallization, so that the obtained high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material has excellent magnetic performance.
Specifically, the hot press forming specifically comprises: putting the mixed magnetic powder into a first mold, and keeping the temperature of the mixed magnetic powder in a protective atmosphere or vacuum degree not lower than 1 × 10-2Heating the mixed magnetic powder to a first temperature in a Pa vacuum environment, and applying a first pressure to a first mold to obtain a hot-pressed magnet, wherein the first temperature is 600-750 ℃, and the first pressure is 100-250 MPa. Preferably, the first temperature is 650-680 ℃, and the first pressure is 170-220 MPa.
And the thermal deformation molding is to place the hot-pressed magnet into a second mold, heat the hot-pressed magnet to a second temperature in a vacuum environment or a protective atmosphere, and apply a second pressure on the hot-pressed magnet to deform the hot-pressed magnet by a deformation degree of 30% -95% to obtain the thermal deformation magnet, wherein the second temperature is 750-900 ℃, and the second pressure is 30-100 MPa. Preferably, the second temperature is 800-850 ℃, and the second pressure is 30-70 MPa.
A tempering step is also included after the hot deformation step. The tempering treatment process specifically comprises the following steps: and heating the thermal deformation magnet to a third temperature in a vacuum environment or a protective atmosphere, preserving heat, quenching and quenching after the heat preservation is finished, wherein the third temperature is 500-800 ℃, the heat preservation time is 1-10 hours, and the heating rate is 5-20 ℃/min during heating. It should be noted that, during the tempering treatment, atoms in the hot deformed magnet gradually diffuse, and the composition phase and the grain composition change to some extent, but the grain morphology and size do not change substantially.
The invention also provides a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material prepared by the preparation method, which is prepared from a matrix phase Re2Fe14B. The grain boundary phase and refractory additives with high melting point, wherein Re is one or more of Nd, Pr, Dy, Tb, La and Ce. Matrix phase Re2Fe14B is a flaky nanocrystal. The refractory additives with high melting points are periodically distributed in a strip shape. The length of the flaky nanocrystalline is 200-500 nanometers, and the thickness of the flaky nanocrystalline is 50-100 nanometers.
The high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material and the preparation method thereof provided by the invention have the following advantages: first, since refractory high melting point additives, which are not easily melted during hot pressing and hot deformation, are added, the high melting point additives are uniformly distributed, thereby suppressing a coarse crystal region and Re2Fe14Growth of B grains to form Re2Fe14The size of the B grains is relatively small (less than 1 micron), i.e., Re2Fe14The size of the B crystal grain is close to the single domain critical size, and thus the magnetic domain is more easily stabilized, and generation or expansion of a reverse magnetic domain hardly occurs, which is advantageous for improvement of coercivity; secondly, the mass ratio of the high-melting-point additive is more than or equal to 0.01 and less than or equal to 10 percent, so that the residual magnetism of the obtained magnet is not seriously damaged, and the coercive force of the magnet is greatly improved. The preparation method is easy to operate and industrialize. The obtained high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material has excellent comprehensive magnetic performance.
Hereinafter, the present invention will be described in more detail with reference to specific examples.
Examples 1 to 9
In the composition of Nd30Ga0.5Febal.Co4B1The alloy powder is respectively added with high-melting point additives with the granularity of 10-50 nanometers and uniformly mixed. The amounts and types of the refractory additives are shown in Table 1.
Induction heating the mixed powder in a vacuum environment, when the temperature is raised to 200 ℃, starting to apply a first pressure to a first mould, and controlling the highest temperature to 670 ℃, so as to obtain a hot-pressed magnet, wherein the time for raising the temperature from room temperature to the highest temperature is 5-6 minutes, the first pressure is 150MPa, and the vacuum degree is not low in the hot-pressing processAt 5X 10-2Pa。
And putting the hot-pressed blank into a second die with a larger diameter, and carrying out induction heating on the hot-pressed magnet in an argon atmosphere to deform the hot-pressed magnet by 70%. When the temperature reached the maximum temperature of 830 ℃ and then held for 1 minute, a second pressure was applied to obtain a thermally deformed magnet. Wherein the time from room temperature to the maximum temperature is 6 minutes to 7 minutes, and the second pressure is 50 MPa.
The obtained thermally deformed magnet was subjected to a test of magnetic properties at room temperature, and the test results are shown in Table 1. Wherein, BrRepresents the remanence, in units of kGs; hcjRepresents the coercivity, in kOe; (BH)mRepresents the magnetic energy product in MGOe.
Examples 10 to 14
The hot deformed magnets of example 1, example 2, example 3, example 5 and example 6 were placed in a vacuum atmosphere and tempered at 700 c for 2 hours, respectively. After cooling, the magnetic properties of the magnet were measured in the manner of example 1, and the results are shown in Table 2.
Comparative example
The preparation process was substantially the same as in example 1, except that no high melting point additive was added.
The obtained thermally deformed magnet was subjected to a test of magnetic properties at room temperature, and the test results are shown in Table 1.
TABLE 1 magnetic Properties of high coercivity nanocrystalline thermally deformable rare earth permanent magnet materials of examples 1-9, comparative examples
As can be seen from table 1, the addition of a certain amount of high melting point carbide powder is helpful for improving the coercive force of the rare earth permanent magnet, and the effect is most obvious in example 2. To better analyze the microscopic morphology of the rare earth permanent magnet of example 2,SEM (see fig. 1) and BSE (see fig. 2) analyses were also performed on the rare earth permanent magnet of example 2. As shown in FIG. 1, the rare earth permanent magnet is made of Nd2Fe14B matrix phase composition, Nd2Fe14The B-phase crystal grains are mostly plate-like nanocrystals, and there are also equiaxed crystals with no deformation in part. The size of the flaky nanocrystalline is nano-scale, the length of the flaky nanocrystalline is about 250-400 nm, and the thickness of the flaky nanocrystalline is about 50-100 nm. As can be seen from FIG. 2, WC is distributed periodically in the form of stripes, and WC is mainly distributed in the gaps between the stripes, thereby suppressing the coarse crystal region and Nd2Fe14And the growth of B-phase crystal grains further improves the coercive force of the rare earth permanent magnet.
TABLE 2 magnetic Properties of the high coercivity nanocrystalline thermally deformable rare earth permanent magnet materials of examples 10-14
As is clear from tables 1 and 2, the magnetic properties of the magnets of examples 10 to 14 were all improved to some extent after the tempering treatment, and particularly, the remanence Br and the coercive force were increased to some extent as is most evident in examples 10 and 11. This is because the tempering treatment accelerates the diffusion of the high melting point additives and makes them more uniformly distributed, thereby better suppressing the coarse crystal region and Re2Fe14And (4) growth of B crystal grains.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (3)
1. A preparation method of a high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material comprises the following steps:
the method comprises the steps of providing alloy powder and high-melting-point additives respectively, wherein the high-melting-point additives are WC, the grain diameter of the high-melting-point additives is 10-50 nanometers, and the chemical formula of the alloy powder is Nd30Ga0.5Febal.Co4B1；
Uniformly mixing the alloy powder and the high-melting-point additive to obtain mixed magnetic powder, wherein the mass ratio of the high-melting-point additive in the mixed magnetic powder is more than or equal to 0.5% and less than or equal to 2.5%;
thirdly, carrying out hot press molding and thermal deformation molding on the mixed magnetic powder in sequence to obtain the nanocrystalline thermal deformation rare earth permanent magnet material with high coercive force,
the step three of hot press forming the mixed magnetic powder specifically comprises the following steps: putting the mixed magnetic powder into a first mould, heating the mixed magnetic powder to a first temperature in a vacuum environment or a protective atmosphere, and applying a first pressure to the first mould to obtain a hot-pressed magnet, wherein the first temperature is 670 ℃, and the first pressure is 150 MPa;
the hot deformation molding is to place the hot-pressed magnet into a second mold, heat the hot-pressed magnet to a second temperature in a vacuum environment or a protective atmosphere, and apply a second pressure to the hot-pressed magnet to deform the hot-pressed magnet by 70% of deformation degree, so as to obtain the hot-deformed magnet, wherein the second temperature is 830 ℃, and the second pressure is 50 MPa;
in the step three, a tempering treatment step is further included after the hot deformation forming step, and the tempering treatment process specifically comprises the following steps: heating the thermal deformation magnet to a third temperature in a vacuum environment or a protective atmosphere, preserving heat, quenching and quenching after the heat preservation is finished, wherein the third temperature is 500-800 ℃, the heat preservation time is 1-10 hours, and the heating rate is 5-20 ℃/min during heating;
the high-coercivity nanocrystalline thermal deformation rare earth permanent magnet material consists of a matrix phase Re2Fe14B. Grain boundary phase and WC nanometer phase, Re is Nd, matrix phase Re2Fe14B is sheet nanocrystalline, WC nanophase is distributed in the strip gap and in strip periodic distribution, and the role of the WC nanophase is to inhibit the coarse crystal region and Re2Fe14B growth of crystal grains to make the matrix phase Re2Fe14The size of B is 200-500 nm.
2. The method for producing a high coercive force nanocrystalline thermally deformable rare earth permanent magnet material as claimed in claim 1, wherein the vacuum degree of the vacuum environment is not less than 5 x 10-2Pa。
3. A high coercivity nanocrystalline heat deformable rare earth permanent magnet material prepared by the preparation method of any one of claims 1-2 and composed of a matrix phase Re2Fe14B. A grain boundary phase and a high-melting-point refractory additive WC nano-phase, wherein Re is Nd, and a matrix phase Re2Fe14B is a flaky nanocrystalline, the length of the flaky nanocrystalline is 200-500 nanometers, the thickness of the flaky nanocrystalline is 50-100 nanometers, and the WC nanophase of the high-melting-point refractory additive is periodically distributed in a strip shape.
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| CN105702405B (en) * | 2016-04-29 | 2017-08-08 | 湖北工程学院 | A kind of nano combined neodymium-iron-boron magnetic material and preparation method |
| CN106252011B (en) * | 2016-08-29 | 2019-01-29 | 浙江东阳东磁稀土有限公司 | A kind of method that the compound addition of Grain-Boundary Phase improves coercivity of sintered ndfeb |
| TWI719259B (en) * | 2016-09-23 | 2021-02-21 | 日商日東電工股份有限公司 | Sintered body for forming rare earth sintered magnet and manufacturing method thereof |
| CN107464647B (en) * | 2017-09-29 | 2019-06-11 | 中国科学院宁波材料技术与工程研究所 | High microcosmic uniformity thermal deformation nanocrystalline rare-earth permanent magnetic material and preparation method thereof |
| CN107557551B (en) * | 2017-10-27 | 2019-08-23 | 华北理工大学 | A kind of preparation method of samarium iron nitrogen series permanent magnetic material |
| CN109473248A (en) * | 2018-11-21 | 2019-03-15 | 重庆科技学院 | A kind of NdCeFeB anisotropic permanent magnet and preparation method thereof |
| CN110534280A (en) * | 2019-09-23 | 2019-12-03 | 广西科技大学 | A kind of preparation method of the performance Nd Fe B sintered magnet based on crystal boundary addition |
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| CN104036898A (en) * | 2014-06-13 | 2014-09-10 | 钢铁研究总院 | High-resistivity permanent magnet alloy prepared by chemical synthetic coating and preparation method thereof |
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