WO2020143126A1 - 一种多层结构稀土永磁体及其制备方法 - Google Patents

一种多层结构稀土永磁体及其制备方法 Download PDF

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WO2020143126A1
WO2020143126A1 PCT/CN2019/082241 CN2019082241W WO2020143126A1 WO 2020143126 A1 WO2020143126 A1 WO 2020143126A1 CN 2019082241 W CN2019082241 W CN 2019082241W WO 2020143126 A1 WO2020143126 A1 WO 2020143126A1
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rare earth
permanent magnet
earth permanent
layer
layer structure
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PCT/CN2019/082241
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French (fr)
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靳朝相
吕忠山
邹永博
邹宇钦
李安华
冯海波
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宁波复能新材料股份有限公司
宁波铄腾新材料有限公司
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Priority to DE112019000128.0T priority Critical patent/DE112019000128T5/de
Publication of WO2020143126A1 publication Critical patent/WO2020143126A1/zh

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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
    • H01F1/0577—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

Definitions

  • the invention belongs to the technical field of rare earth permanent magnet material preparation, in particular to a multilayer structure rare earth permanent magnet and a preparation method thereof.
  • NdFeB magnets have excellent magnetic properties and are widely used in automotive motors, electric bicycles, computer hard drives, power tools and other products, as well as audio equipment, communication products, medical equipment, home appliances, magnetic separation equipment and other fields, becoming irreplaceable material. It also enables the application of some highly integrated high-tech products, such as hybrid vehicles, electric vehicles, and wind turbines. With the development of industry and the advancement of science and technology, the development of magnetic devices toward miniaturization, thinness, and intelligence has put forward higher requirements for the magnetic properties of NdFeB materials.
  • Dy 2 Fe 14 B and Tb 2 Fe 14 B have a higher magnetocrystalline anisotropy field. Therefore, the addition of heavy rare earth elements such as Dy and Tb can make NdFeB magnets more High coercivity. However, the addition of heavy rare earth elements directly through alloying will result in a decrease in remanence.
  • the introduction of heavy rare earth elements by the method of double alloy and grain boundary diffusion can optimize the distribution of rare earth elements and promote the formation of grains with a core-shell structure.
  • the shell structure enriched in heavy rare earth is conducive to significantly improve the coercive force of the magnet without significantly reducing the remanence.
  • the present invention provides a multilayer structure rare earth permanent magnet and a preparation method thereof to solve the above technical problems.
  • a multi-layer structure rare earth permanent magnet is characterized in that the rare earth permanent magnet is composed of a three-layer structure main phase grain and a rare earth-rich phase.
  • the main phase grains are divided into a three-layer structure of a core layer, an intermediate layer, and a shell layer according to different chemical compositions, and the composition components correspond to R 1 -TB, R 2 -TB, and R 3 -TB, respectively, where, R 1 It contains at least one of Ce and La, R 2 contains at least one of Pr and Nd, R 3 contains at least one of Dy, Tb and Ho, T is at least one of Fe and Co, and B is a boron element.
  • R 2 is the Pr and / or Nd content of greater than R 50% 2 a
  • R 3 of Dy and / or Tb The sum of the Ho content is greater than 50% of R 3 .
  • the rare earth-rich phase contains one or more rare earth elements among Ce, La, Pr, Nd, Dy, Tb, Ho, and Gd.
  • the invention also provides a method for preparing a multilayer structure rare earth permanent magnet, which is characterized by comprising the following steps:
  • R 1 -M 1 -B, R 2 -M 2 and R 3 -M 3 are provided, wherein R 1 contains at least one of Ce and La, and R 2 contains Pr and Nd At least one of R, R 3 contains at least one of Dy, Tb, Ho, M 1 is at least one of Fe, Co, Al, Cu, Ga, Zr, Nb, Gd, M 2 and M 3 are Fe , Co, Al, Cu, Ga, Gd, B at least one, B is a boron element.
  • the green body is made into a blank by vacuum sintering
  • the surface of the blank is coated with R 3 -M 3 fine powder, and subjected to two-stage tempering heat treatment to make the rare earth permanent magnet.
  • the mixed powder of R 1- M 1- B and R 2- M 2 is vacuum sintered to obtain a sintered blank.
  • the sintered blank has a certain two-layer structure, that is, a common core-shell structure, but at this stage two layers The structure may not be too conspicuous.
  • the flow of the liquid phase and the further diffusion of atoms promote the two-layer structure.
  • the surface of the sintered blank is coated with R 3 -M 3 low-melting rare earth-rich compound.
  • R 3 -M 3 dissolves during the heat treatment and diffuses into the magnet through the grain boundaries (grain boundaries are the boundaries of the crystal grains).
  • R 3- M 3 surrounds and distributes around the crystal grains and inter-diffuses with the inner layer atoms to promote the formation of the shell (third layer) structure.
  • the average particle size of the R 1 -M 1 -B fine powder is 1 to 5 microns
  • the average particle size of the R 2 -M 2 and R 3 -M 3 fine powders is 1 to 4 microns.
  • the vacuum sintering temperature is 950 to 1100°C
  • the vacuum degree is not less than 1 ⁇ 10 -1 Pa
  • the time is 2 to 6 hours.
  • the method for coating the fine powder on the surface of the blank is to mix R 3 -M 3 fine powder with alcohol uniformly, and then uniformly coat the surface of the blank magnet, wait for the surface to be fully dried, and perform two-stage tempering heat treatment .
  • the alcohols are C1-C8 linear or branched alkyl alcohols, preferably one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol.
  • the first-stage tempering temperature is 800-1000°C and the time is 2-9 hours
  • the second-stage tempering temperature is 450-600°C and the time is 2-6 hours.
  • the present invention optimizes the distribution of rare earth elements through process improvement and obtains the main phase grains with a three-layer layered structure.
  • the R 1 2 T 14 B phase with a low magnetocrystalline anisotropy field is concentrated in the core region of the grain, and the R 2 2 T 14 B with a high magnetocrystalline anisotropy field is concentrated in the intermediate layer region ,
  • the R 3 2 T 14 B phase with the highest magnetocrystalline anisotropy field is enriched in the shell region.
  • the formation of the demagnetized nuclei of the grain generally starts from the surface layer of the grain.
  • the heavy rare-earth 2:14:1 compound with strong outer magnetic rigidity can effectively resist the formation of demagnetized nuclei, thereby enhancing the coercivity of the magnet. It should be noted that during high-temperature sintering and tempering, atoms diffuse through the grain boundaries to promote the formation of layered structure grains; at the same time, some rare earth atoms will also diffuse into other layer regions and grain boundaries. Results
  • the core region, intermediate layer and shell layer mainly composed of R 1 2 T 14 B, R 2 2 T 14 B and R 3 2 T 14 B may also contain rare earth elements in other layers, while the grain boundary phase It will contain rare earth elements in various layers.
  • the three-layer grain structure of the invention has a more reasonable distribution of light and heavy rare earth elements, and contributes more to the overall performance of the magnet, especially the coercive force Big.
  • the invention improves the coercive force of the cerium-rich rare earth permanent magnet, improves the utilization value of the light rare earth element in the permanent magnet material, and is beneficial to promoting the balanced utilization of the rare earth element.
  • FIG. 1 is a schematic structural view of a multi-layer structure rare earth permanent magnet of the present invention.
  • a method for preparing a multilayer structure rare earth permanent magnet includes the following steps:
  • R 1 -M 1 -B, R 2 -M 2 and R 3 -M 3 are provided, wherein R 1 contains at least one of Ce and La, and R 2 contains Pr and Nd At least one of R 3 , R 3 contains at least one of Dy, Tb, Ho, M 1 is at least one of Fe, Co, Al, Cu, Ga, Zr, Nb, M 2 and M 3 are Fe, Co , Al, Cu, Ga, Gd, and B, and B is a boron element.
  • the average particle size of the R 1 -Fe-B fine powder is 1 to 5 microns
  • the average particle size of the R 2 -M 2 and R 3 -M 3 fine powders is 1 to 4 microns.
  • the green body is vacuum sintered, the sintering temperature is 950 to 1100°C, the vacuum degree is not less than 1 ⁇ 10 -1 Pa, and the time is 2 to 6 hours to prepare a blank.
  • the present invention also provides a multi-layer structure rare earth permanent magnet obtained by the above preparation method, as shown in FIG. 1.
  • the rare earth permanent magnet is composed of multiple layers (R 1 , R 2 , R 3 )-TB main phase grains and a rare earth-rich phase. According to the composition, the grains are divided into three layers: the core layer, the middle layer, and the outer layer.
  • the chemical compositions correspond to R 1 -T--B, R 2 -T--B, and R 3 -TB; where R 1 contains Ce At least one of La, R 2 contains at least one of Pr and Nd, R 3 contains at least one of Dy, Tb, and Ho, T is at least one of Fe and Co, and B is a boron element.
  • R 2 is the Pr and Nd content of greater than R 50% 2 a
  • R 3 of Dy, Tb Ho sum of the contents is greater than R 50% of 3
  • the rare earth-rich phase contains one or more rare earth elements among Ce, La, Pr, Nd, Dy, Tb, Ho, and Gd.
  • the preparation process of the multi-layer structure rare earth permanent magnet is as follows:
  • the green body is vacuum sintered, the sintering temperature is 960°C, the vacuum degree is not less than 5 ⁇ 10 -2 Pa, and the time is 5 hours, to prepare a blank.
  • the preparation process of the multi-layer structure rare earth permanent magnet is as follows:
  • the preparation process of the multi-layer structure rare earth permanent magnet is as follows:
  • (1) percentage by mass of each of the constituent elements are provided as components Ce 17.5 Nd 10.5 Gd 1 Fe 68.88 Co 0.6 Al 0. 2 Cu 0.1 Ga 0.15 Nb 0.15 B 0.92, P 14.5 Nd 58.2 Ho 8 Fe 7.2 Cu 7.5 Ga 4.6 , Tb 20.1 Dy 65.5 Al 5.6 Ga 8.8 three fine powders, the average particle size corresponding to 2.8 microns, 2.7 microns, and 2.3 microns.
  • the magnet composition of the comparative example in Examples 1 to 3 is equivalent to that of the corresponding example.
  • the preparation process is a traditional sintering process, and the magnet grains do not have a layered structure. From the comparison of the magnetic properties in Tables 1 to 3, it can be seen that the coercive force of the multilayer structure magnet of the present invention is significantly higher than that of the magnet prepared by the conventional technology, and the residual magnetism and magnetic energy product are comparable to the conventional magnet.
  • the high cerium magnet prepared by the present invention can still obtain excellent coercive force when the cerium content is greater than 50% of the total rare earth content.
  • the increase in coercivity is mainly due to the layered structure of the magnet grains.
  • the technical improvement in the invention effectively regulates the distribution of rare earth elements, promotes the light rare earth elements to be concentratedly distributed inside the crystal grains, the middle and heavy rare earth elements are distributed in the middle layer, and the heavy rare earth elements are concentrated in the grain shell layer.
  • This layered structure in which the magnetocrystalline anisotropic field increases layer by layer from inside to outside effectively weakens the weakening effect of the light rare earth element on the coercive force, and enhances the effect of the heavy rare earth element to enhance the coercive force.

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Abstract

一种多层结构稀土永磁体及其制备方法，稀土永磁体由三层结构的主相晶粒和富稀土相组成，主相晶粒根据化学成分不同分成核层、中间层、壳层三层结构，成分组成分别对应为R1-T-B、R2-T-B和R3-T-B，其中，R1包含Ce、La的至少一种，R2包含Pr、Nd中的至少一种，R3包含Dy、Tb、Ho中的至少一种，T为Fe、Co的至少一种，B为硼元素。富稀土相包含Ce、La、Pr、Nd、Dy、Tb、Ho、Gd中的一种或多种稀土元素。稀土永磁体的制备方法为利用双合金工艺制备磁体毛坯，然后通过晶界扩散工艺制得多层结构稀土永磁体。

Description

一种多层结构稀土永磁体及其制备方法 技术领域
本发明属于稀土永磁材料制备技术领域，具体为一种多层结构稀土永磁体及其制备方法。
背景技术
钕铁硼磁体具有优异的磁性能，广泛用于汽车电机、电动自行车、电脑硬盘、电动工具等产品，以及音响设备、通讯产品、医疗设备、家电产品、磁选设备等领域，成为不可替代的材料。并使一些高度集成的高新技术产品的应用成为可能，如混合动力汽车、电动汽车、发电风车等。随着工业的发展和科技的进步，磁性器件向小型化、薄型化、智能化方向发展，对钕铁硼材料磁性能提出了更高要求。
比较于Nd 2Fe 14B化合物，Dy 2Fe 14B与Tb 2Fe 14B具有更高的磁晶各向异性场，因此，添加Dy、Tb等重稀土元素，可以使钕铁硼磁体获得更高的矫顽力。但是，直接通过合金化的方式加入重稀土元素会导致剩磁降低。采用双合金与晶界扩散的方法引入重稀土元素，能够优化稀土元素分布，促进具有核壳结构的晶粒形成。富集重稀土的壳层结构有利于显著提高磁体的矫顽力，同时不会明显剩磁降低。
为了节约紧缺型稀土的使用，平衡稀土利用，同时降低生产成本，近年来，研究者对Ce产生了持久的兴趣，新型铈磁体[见专利CN102969111A]得到了快速发展。由于Ce 2Fe 14B相的磁晶各向异性场较低，Ce 2Fe 14B单主相化合物也难以获得较高的矫顽力。利用Ce部分地取代Nd以形成(Ce,Nd) 2Fe 14B相为主相的化合物，是制备具有实际应用价值永磁材料的有效方式，例如[CN102800454A]专利公开了(Ce,Nd)-Fe-B富烧结永磁材料。
然而，目前利用传统烧结工艺制备的富铈磁体，矫顽力较低，性能仅达到中低档钕铁硼磁体的水平，无法满足等高端市场的需求。
发明内容
有鉴于此，本发明提供了一种多层结构稀土永磁体及其制备方法，以解决上述技术问题。
一种多层结构稀土永磁体，其特征在于，所述稀土永磁体由三层结构的主相晶粒和富稀土相组成。所述主相晶粒，根据化学成分不同，分成核层、中间层、壳层三层结构，成分组成分别对应R 1-T-B、R 2-T-B和R 3-T-B，其中，其中，R 1包含Ce、La的至少一种，R 2包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，T为Fe、Co的至少一种，B为硼元素。按质量百分比计，R 1中Ce和/或La含量之和大于R 1的50％，R 2中Pr和/或Nd含量之和大于R 2的50％，R 3中Dy和/或Tb和/或Ho含量之和大于R 3的50％。所述富稀土相包含Ce、La、Pr、Nd、Dy、Tb、Ho、Gd中的一种或多种稀土元素。
本发明还提供了一种多层结构稀土永磁体的制备方法，其特征在于，包含如下步骤：
(1)分别提供R 1-M 1-B、R 2-M 2和R 3-M 3三种细粉，其中，R 1包含Ce、La中的至少一种，R 2 包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，M 1为Fe、Co、Al、Cu、Ga、Zr、Nb、Gd中的至少一种，M 2与M 3为Fe、Co、Al、Cu、Ga、、Gd、B中的至少一种，B为硼元素。
(2)将R 1-M 1-B与R 2-M 2细粉混合均匀，并进行磁体取向成型和等静压，制成生坯；
(3)生坯经过真空烧结制成毛坯；
(4)毛坯表面涂覆R 3-M 3细粉，并进行两级回火热处理，制成所述稀土永磁体。
在真空高温烧结和热处理的过程，各原子发生互扩散现象。R 1-M 1-B与R 2-M 2混合粉体经真空烧结得到烧结态毛坯，烧结态毛坯已经具有一定程度的两层结构，也就是常见的核-壳结构，但这个阶段两层结构可能不是太显著，随后的热处理过程中液相的流动和原子的进一步扩散，促进两层结构现象更明显。另外，在烧结态毛坯表面涂覆R 3-M 3低熔点富稀土化合物，R 3-M 3在热处理过程溶解，通过晶界(晶界就是晶粒的边界)扩散进入磁体。R 3-M 3包围分布在晶粒周围，并与内层原子相互扩散，促进壳层(第三层)结构的形成。
进一步地，所述的R 1-M 1-B细粉的平均粒度为1～5微米，所述的R 2-M 2和R 3-M 3细粉的平均粒度为1～4微米。
进一步地，所述的真空烧结温度为950～1100℃，真空度不低于1×10 -1Pa，时间为2～6小时。
进一步地，所述的毛坯表面涂覆细粉的方法为，将R 3-M 3细粉与醇类混合均匀，然后均匀涂覆在毛坯磁体表面，待表面充分干燥，进行两级回火热处理。所述醇类为C1-C8直链或支链烷基醇,优选为甲醇、乙醇、正丙醇、异丙醇、正丁醇、异丁醇或叔丁醇中的一种或多种。
进一步地，所述的两级回火热处理，第一级回火温度为800～1000℃，时间为2～9小时，第二级回火温度为450～600℃，时间为2～6小时。
与现有技术比较，本发明通过工艺改进，优化了稀土元素分布，获得了具有三层层状结构的主相晶粒。在本发明中，磁晶各向异性场较低的R 1 2T 14B相集中分布在晶粒心部区域，磁晶各向异性场较高的R 2 2T 14B集中在中间层区域，磁晶各向异性场最高的R 3 2T 14B相富集在壳层区域。在外磁场作用下，晶粒的反磁化核的形成一般始于晶粒表层。外层磁硬性较强的重稀土2:14:1化合物，可以有效抵制反磁化核的形成，进而提升磁体的矫顽力。需要说明的是，在高温烧结和回火过程中，原子通过晶界扩散，促进层状结构晶粒的形成；同时部分稀土原子也会通过扩散进入到其他层区和晶界。结果分别以R 1 2T 14B、R 2 2T 14B与R 3 2T 14B为主要组成的心部区域、中间层和壳层也可能含有其他层区的稀土元素，而晶界相中会含有各层区的稀土元素。
与现有的两次层晶粒结构比较，在磁体成分相当的情况下，本发明的三层晶粒结构，轻、重稀土元素分布更合理，对磁体综合性能，特别是矫顽力贡献更大。此外，本发明提升了富铈稀土永磁体的矫顽力，提高了轻稀土元素在永磁材料中的利用价值，有利于促进稀土元素的平衡利用。
附图说明
图1为本发明多层结构稀土永磁体结构示意图。
具体实施方式
以下将结合附图和实施例对本发明的实施方式做作进一步阐述。
一种多层结构稀土永磁体的制备方法包含如下步骤：
(1)分别提供R 1-M 1-B、R 2-M 2和R 3-M 3三种细粉，其中，R 1包含Ce、La中的至少一种，R 2包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，M 1为Fe、Co、Al、Cu、Ga、Zr、Nb中的至少一种，M 2与M 3为Fe、Co、Al、Cu、Ga、Gd、B中的至少一种，B为硼元素。R 1-Fe-B细粉的平均粒度为1～5微米，所述的R 2-M 2和R 3-M 3细粉的平均粒度为1～4微米。
(2)将R 1-M 1-B与R 2-M 2细粉混合均匀，并进行磁体取向成型和等静压，制成生坯；
(3)将生坯进行真空烧结，烧结温度为950～1100℃，真空度不低于1×10 -1Pa，时间为2～6小时，制备成毛坯。
(4)将R 3-M 3细粉与醇类混合均匀，然后均匀涂覆在毛坯磁体表面，待表面充分干燥，进行两级回火热处理，其中，第一级回火温度为800～1000℃，时间为2～9小时，第二级回火温度为450～600℃，时间为2～6小时，最终制成所述多层结构稀土永磁体。
本发明还提供一种采用上述制备方法得到的多层结构稀土永磁体，如图1所示。所述稀土永磁体由多层(R 1,R 2,R 3)-T-B主相晶粒和富稀土相组成。根据成分划分，晶粒分成核层、中间层、外层三层结构，化学组成分别对应R 1-T--B、R 2-T--B与R 3-T-B；其中，R 1包含Ce、La的至少一种，R 2包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，T为Fe、Co的至少一种，B为硼元素。按质量百分比计，R 1中Ce与La含量之和大于R 1的50％，R 2中Pr与Nd含量之和大于R 2的50％，R 3中Dy、Tb、Ho含量之和大于R 3的50％。富稀土相包含Ce、La、Pr、Nd、Dy、Tb、Ho、Gd中的一种或多种多种稀土元素。
实施例1
多层结构稀土永磁体的制备工艺如下：
(1)按各组成元素的质量百分比计，分别提供成分为Ce 21La 10Fe 68B 1、Nd 88Fe 11.8B 0.2、Dy 88Fe 8Cu 4的三种细粉，平均粒度分别对应为3.2微米、3.0微米、与2.5微米。
(2)将Ce 21La 10Fe 68B 1与Nd 88Fe 11.8B 0.2两种细粉，按质量比例98：2，混合均匀，然后进行取向成型和等静压，制成生坯；
(3)将生坯进行真空烧结，烧结温度为960℃，真空度不低于5×10 -2Pa，时间为5小时，制备成毛坯。
(4)将Dy 88Fe 8Cu 4细粉与乙醇，按质量比例2：1，混合均匀，然后均匀涂覆在直径为10毫米，高度为10毫米的毛坯磁体表面，待表面充分干燥，再进行两级回火热处理，其中，第一级回火温度为850℃，时间为8小时，第二级回火温度为500℃，时间为5小时，最终制成所述多层结构稀土永磁体。
采用永磁特性能测量仪测试磁体室温磁性能，测试结果如表1所示。
表1实施例1与对比例磁体磁性能对比
  Hcj/kOe Br/kGs (BH)max
实施例1 8.51 10.42 26.23
对比例 6.7 10.46 26.51
实施例2
多层结构稀土永磁体的制备工艺如下：
(1)按各组成元素的质量百分比计，分别提供成分为Ce 18La 5Nd 7.5Fe 66.95Co 1Al 0.3Ga 0.15Zr 0.15B 0.95、Pr 15.3Nd 64.2Fe 5.5Cu 4Al 11、Ho 12Dy 74.5Fe 7.3Co 2Cu 4.2的三种细粉，平均粒度分别对应为3.0微米、2.8微米、与2.3微米。
(2)将Ce 18La 5Nd 7.5Fe 66.95Co 1Al 0.3Ga 0.15Zr 0.15B 0.95与Pr 15.3Nd 64.2Fe 5.5Cu 4Al 1两种细粉，按质量比例97：3，混合均匀，然后进行取向成型和等静压，制成生坯；
(3)将生坯进行真空烧结，烧结温度为1000℃，真空度不低于5×10 -2Pa，时间为4小时，制备成毛坯。
(4)将Ho 12Dy 74.5Fe 7.3Co 2Cu 4.2细粉与乙醇，按质量比例2：1，混合均匀，然后均匀涂覆在直径为10毫米，高度为10毫米的毛坯磁体表面，待表面充分干燥，再进行两级回火热处理，其中，第一级回火温度为900℃，时间为6小时，第二级回火温度为500℃，时间为5小时，最终制成所述多层结构稀土永磁体。
采用永磁特性能测量仪测试磁体室温磁性能，测试结果如表2所示。
表2实施例2与对比例磁体磁性能对比
  Hcj/kOe Br/kGs (BH)max
实施例2 13.25 11.62 33.16
对比例 10.85 11.75 33.64
实施例3
多层结构稀土永磁体的制备工艺如下：
(1)按各组成元素的质量百分比计，分别提供成分为Ce 17.5Nd 10.5Gd 1Fe 68.88Co 0.6Al 0. 2Cu 0.1Ga 0.15Nb 0.15B 0.92、P 14.5Nd 58.2Ho 8Fe 7.2Cu 7.5Ga 4.6、Tb 20.1Dy 65.5Al 5.6Ga 8.8的三种细粉，平均粒度分别对应为2.8微米、2.7微米、与2.3微米。
(2)将Ce 17.5Nd 10.5Gd 1Fe 68.88Co 0.6Al 0.2Cu 0.1Ga 0.15Nb 0.15B 0.92与P 14.5Nd 58.2Ho 8Fe 7.2Cu 7.5Ga 4.6两种细粉，按质量比例97：3，混合均匀，然后进行取向成型和等静压，制成生坯；
(3)将生坯进行真空烧结，烧结温度为1015℃，真空度不低于5×10 -2Pa，时间为4小时，制备成毛坯。
(4)将Tb 20.1Dy 65.5Al 5.6Ga 8.8细粉与乙醇，按质量比例2：1，混合均匀，然后均匀涂覆在直径为10毫米，高度为10毫米的毛坯磁体表面，待表面充分干燥，再进行两级回火热处理，其中，第一级回火温度为920℃，时间为6小时，第二级回火温度为500℃，时间为5小时，最终制成所述多层结构稀土永磁体。
采用永磁特性能测量仪测试磁体室温磁性能，测试结果如表3所示。
表3实施例3与对比例磁体磁性能对比
  Hcj/kOe Br/kGs (BH)max
实施例3 16.58 12.12 35.36
对比例 12.43 12.06 34.88
实施例1～3中的比较例磁体成分与对应实施例磁体相当，制备工艺为传统烧结工艺，磁体晶粒不具有层状结构。从表1～3的磁性能比较，可以看出，本发明多层结构磁体的矫顽力明显高于传统技术制备的磁体，而且，剩磁和磁能积与传统磁体相当。
与传统技术比较，本发明制备的高铈磁体，在铈含量大于总稀土含量的50％情况下，仍然能够获得优异的矫顽力。矫顽力的提高主要得益于磁体晶粒的层状结构。本发明中的技术改进，有效调控了稀土元素的分布，促进轻稀土元素集中分布在晶粒内部，中重稀土分布在中间层，重稀土元素富集在晶粒壳层。这种从里到外，磁晶各向异性场逐层增加的层状结构有效减弱了轻稀土元素对矫顽力的弱化作用，增强了重稀土元素提升矫顽力的效果。
以上，仅为本发明较佳的具体实施方式，但发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求书的保护范围为准。

Claims (10)

  1. 一种多层结构稀土永磁体，其特征在于所述稀土永磁体由三层结构的主相晶粒和富稀土相组成。
  2. 如权利要求1所述的多层结构稀土永磁体，其特征在于所述稀土永磁体主相晶粒根据化学成分不同分成核层、中间层、壳层三层结构，成分组成分别对应R 1-T-B、R 2-T-B和R 3-T-B，其中，R 1包含Ce、La的至少一种，R 2包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，T为Fe、Co的至少一种，B为硼元素。
  3. 如权利要求1或2任一项所述的多层结构稀土永磁体，其特征在于按元素质量百分比计，所述R 1中Ce和/或La含量之和大于R 1的50％，R 2中Pr和/或Nd含量之和大于R 2的50％，R 3中Dy和/或Tb和/或Ho含量之和大于R 3的50％。
  4. 如权利要求1或2任一项所述的多层结构稀土永磁体，其特征在于所述富稀土相包含Ce、La、Pr、Nd、Dy、Tb、Ho、Gd中的一种或多种稀土元素。
  5. 如权利要求1至4任一项所述的多层结构稀土永磁体的制备方法，其特征在于包含如下步骤：
    (1)分别提供R 1-M 1-B、R 2-M 2和R 3-M 3三种细粉，其中，R 1包含Ce、La中的至少一种，R 2包含Pr、Nd中的至少一种，R 3包含Dy、Tb、Ho中的至少一种，M 1为Fe、Co、Al、Cu、Ga、Zr、Nb、Gd中的至少一种，M 2与M 3为Fe、Co、Al、Cu、Ga、B、Gd中的至少一种，B为硼元素；
    (2)将R 1-M 1-B与R 2-M 2细粉混合均匀，并进行磁体取向成型和等静压，制成生坯；
    (3)生坯经过真空烧结制成毛坯；
    (4)毛坯表面涂覆R 3-M 3细粉，并进行两级回火热处理，制成所述稀土永磁体。
  6. 如权利要求5所述的多层结构稀土永磁体的制备方法，其特征在于所述的R 1-M 1-B细粉的平均粒度为1～5微米，所述的R 2-M 2和R 3-M 3细粉的平均粒度为1～4微米。
  7. 如权利要求5所述的多层结构稀土永磁体的制备方法，其特征在于所述的真空烧结温度为950～1100℃，真空度不低于1×10 -1Pa，时间为2～6小时。
  8. 如权利要求5所述的多层结构稀土永磁体的制备方法，其特征在于所述的毛坯表面涂覆细粉的方法为，将R 3-M 3细粉与醇类混合均匀，然后均匀涂覆在毛坯磁体表面。
  9. 如权利要求8所述的多层结构稀土永磁体的制备方法，其特征在于所述醇类为C1-C8直链或支链烷基醇,优选为甲醇、乙醇、正丙醇、异丙醇、正丁醇、异丁醇或叔丁醇中的一种或多种。
  10. 如权利要求5所述的多层结构稀土永磁体的制备方法，其特征在于所述的两级回火热处理，第一级回火温度为800～1000℃，时间为2～9小时，第二级回火温度为450～600℃，时间为2～6小时。
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