WO2024077966A1 - 一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法 - Google Patents

一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法 Download PDF

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WO2024077966A1
WO2024077966A1 PCT/CN2023/096203 CN2023096203W WO2024077966A1 WO 2024077966 A1 WO2024077966 A1 WO 2024077966A1 CN 2023096203 W CN2023096203 W CN 2023096203W WO 2024077966 A1 WO2024077966 A1 WO 2024077966A1
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content
magnet
core
rare earth
main phase
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PCT/CN2023/096203
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English (en)
French (fr)
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付松
陈彪
王荣杰
朱啸航
章兆能
杨晓露
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浙江英洛华磁业有限公司
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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
    • 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

Definitions

  • the invention relates to a core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment and a preparation method thereof, belonging to the field of rare earth magnets.
  • R-T-B rare earth permanent magnets can effectively realize the miniaturization of equipment due to their ultra-high magnetic energy product and are widely used in modern industry.
  • the market share of R-T-B magnets in wind power generation and electric vehicles has increased year by year.
  • the temperature coefficient of the magnetic properties of R-T-B magnets is negative, the magnetic properties of the magnets deteriorate as the temperature rises.
  • the operating temperature of the automobile engine is around 200°C. In order to ensure the normal operation of the motor, it is necessary to improve the high-temperature magnetic properties of the magnets.
  • the high-temperature magnetic properties of RTB magnets are mainly improved by increasing the coercive force and reducing the temperature coefficient of magnetic properties (the temperature coefficient itself is a negative value, and the comparison of the temperature coefficient in this article uses its absolute value, the same below).
  • the heavy rare earth element Gd can significantly reduce the temperature coefficient of the magnet, thereby improving the high-temperature magnetic properties of the magnet.
  • the Gd element will have an adverse effect on the performance of the magnet.
  • Gd is a heavy rare earth element.
  • Gd and Fe are antiferromagnetically coupled. Adding too much Gd element during the smelting stage will reduce the remanence of the magnet.
  • the anisotropy field of the Gd element corresponding to the main phase is low, and when it exists in large quantities in the magnet, it will reduce the coercive force of the magnet. Therefore, the current method of reducing the temperature coefficient of the magnet by adding Gd elements to the magnet is at the expense of reducing the remanence and coercive force of the magnet.
  • Grain boundary diffusion is an effective method to improve the coercive force of magnets.
  • the heavy rare earth element reverse shell distribution phenomenon will occur. That is, after the heavy rare earth element grain boundary diffusion forms a core-shell structure, the heavy rare earth element content in the core of the main phase of the magnet grain is high, while the heavy rare earth element content in the shell is low.
  • the diffusion source with a higher concentration on the magnet surface will diffuse into the magnet along the grain boundary R-rich phase of the magnet in the early stage of diffusion.
  • the concentration of heavy rare earth elements in the grain boundary R-rich phase is higher than that of the main phase grains of the magnet, the heavy rare earth elements will diffuse into the main phase grains of the magnet, forming a shell layer rich in heavy rare earth elements on the surface of the main phase grains.
  • the grain boundary diffusion sources on the magnet surface are consumed.
  • the concentration of heavy rare earth elements in the grain boundary R-rich phase will gradually decrease as the diffusion proceeds, and eventually the heavy rare earth element content in the main phase grains of the magnet will be higher than that in the grain boundary R-rich phase of the magnet.
  • the diffusion direction of the heavy rare earth elements changes from the main phase grains of the magnet to the grain boundary R-rich phase, and finally a main phase with a heavy rare earth element anti-shell structure is formed in the magnet. That is, the surface layer of the main phase grains of the magnet is a shell layer with a low heavy rare earth content, while the core of the main phase grains is a core with a high heavy rare earth content.
  • elements with high anisotropy fields such as Dy or Tb are generally used as grain boundary diffusion sources to increase the coercivity of the magnet by enhancing the anisotropy field of the surface layer of the main phase grains of the magnet.
  • the reverse shell structure of Dy or Tb elements appears, the coercivity of the magnet will be significantly reduced.
  • the anisotropy field of the main phase corresponding to Gd is lower than the anisotropy field of the main phase corresponding to Pr or Nd. Therefore, in order to avoid the reduction of the coercive force of the magnet, Gd is generally not used as a grain boundary diffusion source during grain boundary diffusion. However, if the process control is used to promote the formation of a special structure in which the center of the main phase grain is a Gd-rich core, and the edge of the main phase grain is a Gd-poor shell, that is, a Gd anti-shell structure is formed.
  • the low temperature coefficient of the Gd main phase can be used to improve the high-temperature magnetic properties of the magnet.
  • the coercive force mechanism of the NdFeB magnet is of the nucleation type, if the coercive force at the edge of the main phase of the magnet is low, the coercive force of the entire main phase grain will be reduced.
  • the Gd-poor shell at the edge of the main phase grains of the magnet can significantly reduce the deterioration effect of the Gd element on the coercive force of the magnet, thereby making full use of the characteristics of Gd to prepare a magnet with a low temperature coefficient and high coercive force.
  • the present invention provides a core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment and a preparation method thereof.
  • the magnet components of the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment include:
  • T is Fe or Fe and Co.
  • T contains Co, more than 75.0wt.% of T is Fe;
  • the R is composed of Gd and R1, the Gd element content is 1.0wt.% ⁇ 20.0wt.% of the mass of the magnet, and the remainder of R is R1;
  • R1 is composed of R3 or R2 and R3;
  • R2 is at least one of the rare earth elements Dy and Tb,
  • R3 is at least one of Nd, Pr, Ho, La, Ce, preferably R3 is one or two of Nd and Pr; more preferably, more than 75wt.% of R3 is Nd;
  • the content of R2 is 0.1wt.% to 2.0wt.% of the mass of the magnet, and the Gd-poor shell layer of the Gd-rich core main phase grains of the magnet contains 0.05wt.% to 0.5wt.% of the R2 element;
  • the M is at least one of Al, Cu, Ga, Zr, Ti, Nb, Zn, Sn, W, Mo, Hf, Au and Ag, preferably one or more of Cu, Ga and Zr;
  • the high temperature environment core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core is prepared according to one of the following methods:
  • High-Gd content alloy raw materials and low-Gd content alloy raw materials according to the composition ratio are respectively prepared into high-Gd content SC sheets and low-Gd content SC sheets by vacuum induction melting and belt spinning, and the high-Gd content SC sheets and the low-Gd content SC sheets are prepared into alloy powders, and the alloy powders are molded and isostatically pressed in an oriented magnetic field to prepare magnet compacts, and high-temperature diffusion treatment is performed after vacuum sintering to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment;
  • the diffusion temperature of the high-temperature diffusion treatment is 800-1000°C, the holding time is 5-25h, after the holding is completed, the temperature is cooled to below 200°C and then raised to 400-650°C, and the temperature is held for 2-10h to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment;
  • a high-Gd content alloy raw material and a low-Gd content alloy raw material according to a composition ratio, neither of which contains the R2 element, are respectively prepared through vacuum induction melting and belt spinning to obtain a high-Gd content SC sheet and a low-Gd content SC sheet.
  • the high-Gd content SC sheet and the low-Gd content SC sheet are prepared to obtain alloy powder.
  • the alloy powder is molded and isostatically pressed in an oriented magnetic field to prepare a magnet compact. After vacuum sintering, a high-temperature diffusion treatment is performed.
  • the obtained matrix magnet is processed into a magnet sheet with a thickness of 0.5-10.0 mm.
  • a heavy rare earth element diffusion layer with a thickness of 3-100 ⁇ m is deposited on the surface of the magnet sheet, and then a grain boundary diffusion treatment is performed to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high-temperature environment.
  • the heavy rare earth element diffusion layer is any one or two of Dy and Tb.
  • the heavy rare earth element diffusion layer is generally deposited by evaporation, magnetron sputtering or multi-arc ion plating.
  • the diffusion temperature of the high temperature diffusion treatment is 800-1000°C
  • the holding time is 5-25h
  • the temperature is cooled to below 200°C and then raised to 400-650°C and held for 2-10h to obtain a magnet matrix
  • the diffusion temperature of the grain boundary diffusion treatment is 800-1000°C, and the holding time is 5-25 hours. After the holding is completed, the temperature is cooled to below 200°C and then raised to 400-650°C and held for 2-10 hours to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for use in a high temperature environment.
  • the difference in Gd content between the high Gd content SC sheet and the low Gd content SC sheet is ⁇ 5.0wt.%, the Gd content in the high Gd content SC sheet is 5.0-34.0wt.%, and the Gd content in the low Gd content SC sheet is preferably 0;
  • composition of each component in the high Gd content alloy raw material is:
  • R3 0 ⁇ 29wt.%, R3 is one or more of Nd, Pr, Ho, La, Ce, preferably more than 75wt.% of R3 is Nd; Gd: 5.0 ⁇ 34.0wt.%; B: 0.9wt.% ⁇ 1.1wt.%; M: 0.1wt.% ⁇ 10.0wt.%; the remainder is T and other inevitable impurities, wherein T is Fe or Fe and Co, and when T contains Co, more than 75.0wt.% of T is Fe;
  • composition of each component in the low Gd content alloy raw material is:
  • R3 5 ⁇ 34wt.%, R3 is one or more of Nd, Pr, Ho, La, Ce, preferably more than 75wt.% of R3 is Nd;
  • Gd 0 ⁇ X wt.%, and the Gd content of the high Gd content alloy raw material -X ⁇ 5.0wt.%; preferably the Gd content is 0; B: 0.9wt.% ⁇ 1.1wt.%; M: 0.1wt.% ⁇ 10.0wt.%; the balance is T and other inevitable impurities, wherein T is Fe or Fe and Co, and when T contains Co, more than 75.0wt.% of T is Fe;
  • the mass ratio of the high Gd content alloy raw material to the low Gd content alloy raw material is to ensure that the Gd element content in the final magnet after mixing is 1.0wt.% ⁇ 20.0wt.%, and is generally 1:0.25 ⁇ 4 in actual production;
  • the alloy powder is prepared from the high Gd content SC sheets and the low Gd content SC sheets by mixing the high Gd content SC sheets and the low Gd content SC sheets, and then preparing the alloy powder by hydrogen crushing and air flow milling, or by mixing the high Gd content SC sheets and the low Gd content SC sheets after hydrogen crushing, and then preparing the alloy powder by air flow milling, or by mixing the high Gd content SC sheets and the low Gd content SC sheets after hydrogen crushing and air flow milling, respectively.
  • the vacuum sintering process is: heating to 1020-1110° C. and keeping the temperature for 3-10 hours.
  • the surface treatment process of the magnetic sheet is to remove rust and oil stains on the surface of the magnet by sandblasting, pickling or other methods.
  • the heavy rare earth element diffusion layer is pure heavy rare earth element metal, heavy rare earth element hydride or an alloy of heavy rare earth element and other metal elements, and the heavy rare earth element is at least one of Dy and Tb.
  • a heavy rare earth element diffusion layer with a thickness of 3 to 100 ⁇ m is deposited on the surface of the magnetic sheet, and the heavy rare earth element diffusion layer is preferably deposited to cover the surface of the magnet perpendicular to the orientation direction, and the surface of the magnet not perpendicular to the orientation direction is preferably not covered with the heavy rare earth element diffusion layer.
  • the present invention also provides a method for preparing a core-shell structure R-T-B rare earth permanent magnet having a Gd-rich core for use in a high temperature environment, the method being one of the following:
  • High-Gd content alloy raw materials and low-Gd content alloy raw materials according to the composition ratio are respectively prepared into high-Gd content SC sheets and low-Gd content SC sheets by vacuum induction melting and belt spinning, and the high-Gd content SC sheets and the low-Gd content SC sheets are prepared into alloy powders, and the alloy powders are molded and isostatically pressed in an oriented magnetic field to prepare magnet compacts, and high-temperature diffusion treatment is performed after vacuum sintering to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment;
  • the diffusion temperature of the high-temperature diffusion treatment is 800-1000°C, the holding time is 5-25h, after the holding is completed, the temperature is cooled to below 200°C and then raised to 400-650°C, and the temperature is held for 2-10h to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment;
  • a high-Gd content alloy raw material and a low-Gd content alloy raw material according to a composition ratio, neither of which contains the R2 element, are respectively prepared by vacuum induction melting and belt spinning, and the high-Gd content SC sheet and the low-Gd content SC sheet are prepared to obtain alloy powder, the alloy powder is molded and isostatically pressed in an oriented magnetic field to prepare a magnet compact, and a high-temperature diffusion treatment is performed after vacuum sintering, and the obtained matrix magnet is processed into a magnetic sheet with a thickness of 0.5-10.0 mm, and a heavy rare earth element diffusion layer with a thickness of 3-100 ⁇ m is deposited on the surface of the magnetic sheet after surface treatment, and then a grain boundary diffusion treatment is performed to obtain the core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment;
  • the heavy rare earth element diffusion layer is any one or two of Dy and Tb;
  • composition of each component in the high Gd content alloy raw material is:
  • R3 0 ⁇ 29wt.%, R3 is one or more of Nd, Pr, Ho, La, Ce; Gd: 5.0 ⁇ 34.0wt.%; B: 0.9wt.% ⁇ 1.1wt.%; M: 0.1wt.% ⁇ 10.0wt.%; the remainder is T and other unavoidable impurities, wherein T is Fe or Fe and Co, and when T contains Co, more than 75.0wt.% of T is Fe;
  • composition of each component in the low Gd content alloy raw material is:
  • R3 5 ⁇ 34wt.%, R3 is one or more of Nd, Pr, Ho, La, Ce, preferably more than 75wt.% of R3 is Nd; Gd: 0 ⁇ Xwt.%, and the Gd content of the high Gd content alloy raw material -X ⁇ 5.0wt.%; B: 0.9wt.% ⁇ 1.1wt.%; M: 0.1wt.% ⁇ 10.0wt.%; the balance is T and other inevitable impurities, wherein T is Fe or Fe and Co, and when T contains Co, more than 75.0wt.% of T is Fe;
  • composition of the obtained core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment is:
  • T is Fe or Fe and Co.
  • T contains Co, more than 75.0wt.% of T is Fe;
  • the R is composed of Gd and R1, the Gd element content is 1.0wt.% ⁇ 20.0wt.% of the magnet mass, and the remainder of R is R1; R1 is R3 or is composed of R2 and R3; R3 is at least one of Nd, Pr, Ho, La, and Ce;
  • R2 is at least one of the rare earth elements Dy and Tb.
  • the content of R2 is 0.1wt.% to 2.0wt.% of the mass of the magnet, and the Gd-poor shell layer of the Gd-rich core main phase grains of the magnet contains 0.05wt.% to 0.5wt.% of the R2 element;
  • the M is at least one of Al, Cu, Ga, Zr, Ti, Nb, Zn, Sn, W, Mo, Hf, Au and Ag;
  • the present invention adopts a double alloy method to prepare a core-shell structure R-T-B rare earth permanent magnet with a Gd-rich core for high temperature environment, that is, two alloy sheets with high Gd content and low Gd content are smelted separately, and then two SC sheets are mixed and hydrogen crushed and air flow milled to prepare alloy powder, or two SC sheets are hydrogen crushed and mixed and air flow milled to prepare alloy powder, or two SC sheets are hydrogen crushed and air flow milled to prepare alloy powder, and then oriented molding, isostatic pressing and sintering are performed to obtain a sintered magnet.
  • the sintered magnet is subjected to a high temperature diffusion treatment at 800-1000°C for 5-25h, cooled to below 200°C after the high temperature diffusion treatment, and then heated to 400-650°C and kept warm for 2-10h.
  • the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature.
  • the Gd element diffused into the R-rich phase at the grain boundary will continue to diffuse along the molten grain boundary phase to the low Gd concentration, thereby diluting the Gd in the R-rich phase at the grain boundary near the main phase grains with high Gd content, further promoting the outward diffusion of the Gd element in the main phase.
  • the diffusion rate of the Gd element inside the main phase grains of the magnet is much lower than the diffusion rate of Gd from the main phase grains to the R-rich phase at the grain boundary, that is, the diffusion rate of the Gd element from the core of the main phase grains to the edge of the main phase grains is much lower than the diffusion rate of the Gd element from the edge of the main phase grains to the R-rich phase at the grain boundary. Therefore, the main phase grains with high Gd content will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • the presence of the heavy rare earth element Gd in the main phase grains of the magnet can significantly reduce the temperature coefficient of the magnet, thereby improving the high-temperature magnetic properties of the magnet.
  • Gd and Fe are antiferromagnetically coupled, and adding too much Gd element during the smelting stage will reduce the remanence of the magnet.
  • the anisotropy field of the Gd element corresponding to the main phase is relatively low, and when it exists in large quantities in the magnet, it will reduce the coercive force of the magnet.
  • the method of the present invention when the main phase grains with high Gd content are controlled to form an anti-shell structure with a Gd-poor shell and a Gd-rich core, on the one hand, the low temperature coefficient of the Gd main phase can be utilized to improve the high-temperature magnetic properties of the magnet.
  • the deterioration effect of the Gd element on the coercive force of the magnet can be significantly reduced, thereby making full use of the characteristics of Gd to prepare a magnet with a low temperature coefficient and a high coercive force.
  • a dual alloy process is used to melt two alloy sheets with high Gd content and low Gd content respectively and prepare a mixed powder, in order to ensure that the Gd element in the main phase grains with high Gd content has a large concentration difference with the surrounding grain boundary R-rich phase, so that the Gd element in the main phase grains with high Gd content can smoothly diffuse outward during high temperature diffusion, it is necessary to ensure that the Gd content difference between the high Gd content SC alloy sheet and the low Gd content SC alloy sheet is ⁇ 5.0wt.%.
  • the Gd content of the high Gd content SC sheet is 5.0 ⁇ 34.0wt.%
  • the low Gd content SC sheet is preferably free of Gd.
  • the rare earth content of the magnet will also affect the diffusion of the Gd element in the main phase grains with high Gd content.
  • the content of the R-rich phase at the grain boundary of the magnet is also higher, and the Gd element diffused from the main phase grains with high Gd content is also easily diluted by the grain boundary phase, so it can promote the further outward diffusion of the Gd element in the main phase grains with high Gd content.
  • the present invention can further improve the coercive force of the magnet and reduce the temperature coefficient of the magnet through Dy/Tb grain boundary diffusion, so as to prepare R-T-B rare earth permanent magnet suitable for use at higher working temperatures.
  • the present invention prepares the main phase grains with the Gd element reverse shell structure first, and then performs grain boundary diffusion of elements such as Dy/Tb, so that the Gd-rich core main phase grains in the magnet are enriched with a higher concentration of Dy/Tb elements in the Gd-poor shell, so that the Gd-rich core main phase grains form a Dy/Tb-rich shell with a higher anisotropy field, thereby further improving the coercive force of the magnet. Since the generation energy of heavy rare earth elements when generating the main phase is more negative, it is easier for heavy rare earth elements to replace light rare earth elements (Pr, Nd, La, Ce, etc.) to generate the main phase.
  • light rare earth elements Pr, Nd, La, Ce, etc.
  • the present invention first prepares a magnet with Gd-rich core main phase grains, because the magnet has a core-shell structure, and the heavy rare earth element Gd content at the shell layer is low and the light rare earth element content is high. Therefore, during the grain boundary diffusion of heavy rare earth elements, Dy/Tb is more likely to form a Dy/Tb-rich shell in the Gd-rich core main phase grains. If the Gd element is evenly distributed in the main phase grains of the magnet, the Gd element will hinder the formation of the Dy/Tb-rich shell in the main phase grains of the magnet during the grain boundary diffusion of the heavy rare earth elements, thereby reducing the grain boundary diffusion effect.
  • the beneficial effects of the present invention are embodied in that two alloy sheets with high Gd content and low Gd content are melted separately by a dual alloy method, and then a mixed powder is prepared.
  • a sintered magnet is obtained through orientation molding, isostatic pressing and sintering.
  • the Gd element will diffuse from the main phase grains with high Gd content to the R-rich phase at the magnet grain boundary at high temperature.
  • the main phase grains with high Gd content of the magnet will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • the low temperature coefficient of the Gd main phase can improve the high-temperature magnetic properties of the magnet.
  • the deterioration effect of the Gd element on the coercive force of the magnet can be significantly reduced, thereby making full use of the characteristics of Gd to prepare a magnet with a low temperature coefficient and a high coercive force.
  • the Gd-poor shell of the Gd-rich core main phase grains of the magnet is enriched with a higher concentration of Dy/Tb elements; and the main phase grains without Gd-rich core will also form a shell with a higher concentration of Dy/Tb during the grain boundary diffusion process, further improving the coercive force of the magnet, thereby preparing R-T-B rare earth permanent magnets suitable for use at higher temperatures.
  • Figure 1 (a), (b) and (c) are the SEM microstructure photographs of the final magnets of Experiment No. 2, Experiment No. 5 and Experiment No. 6, respectively.
  • FIG. 2 is a schematic diagram of the energy spectrum point scanning of the microstructure of the Gd-rich core main phase grains and the Gd-poor shell and Gd-rich core of the Gd-rich core main phase grains of the Experiment No. 5 magnet.
  • FIG. 3 is an EPMA surface scanning Tb spectrum of the magnet of Experiment No. 9 after Tb diffusion.
  • the magnet is prepared according to the following method:
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare two types of SC alloy sheets with high Gd content and low Gd content respectively.
  • the two SC sheets are mixed and then hydrogen crushed and jet milled to prepare alloy powder, or the two SC sheets are hydrogen crushed and then mixed and jet milled to prepare alloy powder, or the two SC sheets are hydrogen crushed and jet milled to prepare alloy powder.
  • the alloy powder is oriented and molded and isostatically pressed to prepare magnet green body, and then the magnet is heated to 1020 ⁇ 1110°C in a vacuum environment and kept warm for 3 ⁇ 10h to prepare sintered magnet.
  • the sintered magnet is heated to 800-1000°C and kept at this temperature for 5-25 hours to perform high temperature diffusion treatment. After the heat preservation is completed, it is cooled to below 200°C and then heated to 400-650°C and kept at this temperature for 2-10 hours to obtain the magnet.
  • the magnet contains R2 element
  • the magnet is prepared according to the following method:
  • the two SC sheets are mixed and then hydrogen crushed and jet milled to prepare alloy powder, or the two SC sheets are hydrogen crushed and then mixed and jet milled to prepare alloy powder, or the two SC sheets are hydrogen crushed and jet milled to prepare alloy powder.
  • the alloy powder is oriented and molded and isostatically pressed to prepare magnet green body, and then the magnet is heated to 1020 ⁇ 1110°C in a vacuum environment and kept warm for 3 ⁇ 10h to prepare sintered magnet.
  • the sintered magnet is heated to 800 ⁇ 1000°C and kept at this temperature for 5 ⁇ 25h for high temperature pre-diffusion treatment. After the heat preservation, it is cooled to below 200°C and then heated to 400 ⁇ 650°C and kept at this temperature for 2 ⁇ 10h to obtain the matrix magnet.
  • the base magnet is machined into a magnetic sheet with a thickness of 0.5-10.0 mm, and the surface is treated by sandblasting, pickling and other methods to remove rust and oil stains on the surface of the magnet.
  • a heavy rare earth element diffusion layer with a thickness of 3 to 100 ⁇ m is deposited on the surface of the magnetic sheet by evaporation, magnetron sputtering or multi-arc ion plating, and a heavy rare earth diffusion source is covered on the surface of the magnet perpendicular to the orientation direction, and preferably no heavy rare earth diffusion source is covered on the surface of the magnet not perpendicular to the orientation direction.
  • the heavy rare earth diffusion source is a pure heavy rare earth element metal, a heavy rare earth element hydride or an alloy of a heavy rare earth element and other metal elements, and the heavy rare earth element is at least one of Dy and Tb.
  • the magnetic sheet with diffusion source deposited on the surface is subjected to grain boundary diffusion treatment, the diffusion temperature is 800-1000°C, the insulation time is 5-25h, after the insulation is completed, it is cooled to below 200°C and then heated to 400-650°C and maintained for 2-10h to obtain the magnet.
  • the final magnet was treated with sandblasting to expose the fresh surface.
  • the room temperature and high temperature magnetic properties of the magnet were tested with NIM magnetic property testing equipment, and the temperature coefficient of the magnet was calculated.
  • the magnet microstructure was observed with SEM, and the volume ratio of the Gd-rich core main phase grains to the magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed with ICP, and the magnet micro-region composition was analyzed with EPMA.
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare high Gd content SC sheets with compositions of Nd 12 Pr 3.0 B 0.95 Co 0.95 Cu 0.1 Ga 0.15 Gd 17 Zr 0.15 Fe bal and Gd-free SC sheets with compositions of Nd 24.75 Pr 7.25 B 0.95 Co 0.95 Cu 0.1 Ga 0.15 Zr 0.15 Fe bal respectively.
  • the two SC sheets were mixed in different weight ratios and pulverized by hydrogen crushing and air flow grinding.
  • the alloy powder was oriented and molded and isostatically pressed to prepare magnet green body. Then, the magnet was heated to 1090°C in a vacuum environment and kept warm for 6 hours to prepare a sintered magnet.
  • the sintered magnet is heated to 880°C and kept at this temperature for 15 hours to perform a high temperature diffusion treatment. After the heat preservation is completed, the magnet is cooled to below 200°C and then heated to 520°C and kept at this temperature for 5 hours to obtain the magnet.
  • the final magnet was treated with sandblasting to expose the fresh surface.
  • the NIM magnetic property test equipment was used to test the magnetic properties of the magnet at room temperature of 20°C and high temperature of 150°C, and the temperature coefficient of the magnet was calculated.
  • the magnet microstructure was observed by SEM, and the volume ratio of the Gd-rich core main phase grains to the magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed by ICP, and the magnet micro-region composition was analyzed by EPMA.
  • the volume ratio of the Gd-containing main phase grains in the magnet is regulated by mixing high Gd content and Gd-free SC sheets in different weight ratios (in this embodiment, the densities of high Gd content and Gd-free magnets are close, and the volume ratio of high Gd content and Gd-free main phase grains can be approximately regulated by controlling the weight ratio of different SC sheets), and the proportion of Gd-rich core main phase grains in the main phase grains is analyzed by SEM and image J software.
  • the proportion of high Gd content SC sheets, the final Gd content of the magnet, the proportion of Gd-containing main phase grains and the proportion of Gd-rich core main phase when the SC sheets are mixed in Experiment No. 1 to Experiment No. 7 are shown in Table 1.
  • Experiment No. 1 and Experiment No. 7 are magnets prepared from single alloys containing no Gd and high Gd content, respectively.
  • the Gd content of the magnet is zero, and at this time, there are no main phase grains rich in Gd core in the main phase of the magnet.
  • the magnet is completely made of high Gd content flakes (Experiment No.
  • the temperature coefficient of the magnet is also low at this time, due to the lack of sufficient Gd-rich core main phase grains to optimize the distribution of Gd elements, the room temperature magnetic properties of the magnet deteriorate.
  • the compensation effect of the temperature coefficient cannot make up for the influence of the lower room temperature magnetic properties, so the high temperature magnetic properties of the magnet will also deteriorate.
  • the microstructure of the magnet of Experiment No. 5 was observed by SEM (Fig. 1(b)), and the magnet composition was analyzed by EPMA point scanning.
  • the schematic diagram of the point scanning of the core-shell composition is shown in Fig. 2.
  • the results show that the Gd contents in the shell and core of the Gd-rich core main phase grains of the magnet of Experiment No. 5 are 8.8wt.% and 15.3wt.%, respectively. It can be seen that after the grain boundary diffusion, the Gd element outside the high Gd content main phase grains diffuses outward in a large amount, and the high Gd content main phase grains are fully transformed into a structure with a poor Gd shell and a Gd-rich core.
  • This embodiment adopts a dual alloy method to melt two alloy sheets with high Gd content and without Gd respectively, and then prepare a mixed powder. After orientation molding, isostatic pressing and sintering, a sintered magnet is obtained.
  • the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature. Due to the influence of the rare earth element content and diffusion rate of the magnet, the main phase grains with high Gd content of the magnet will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • the low temperature coefficient of the Gd main phase can improve the high-temperature magnetic properties of the magnet.
  • the deterioration effect of the Gd element on the coercive force of the magnet can be significantly reduced, thereby making full use of the characteristics of Gd to prepare a magnet with a low temperature coefficient and a high coercive force.
  • the temperature coefficient of the magnet can be significantly improved, and the high temperature magnetic properties of the magnet can be improved.
  • the improvement of the temperature coefficient of the magnet is not obvious.
  • Embodiment 2 is a diagrammatic representation of Embodiment 1:
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare high Gd content SC sheets with compositions of Nd 12 Pr 3.0 B 0.95 Co 0.95 Cu 0.1 Ga 0.15 Gd 17 Zr 0.15 Fe bal and Gd-free SC sheets with compositions of Nd 24.75 Pr 7.25 B 0.95 Co 0.95 Cu 0.1 Ga 0.15 Zr 0.15 Fe bal respectively.
  • the two SC sheets were mixed in different weight ratios and pulverized by hydrogen crushing and air flow grinding.
  • the alloy powder was oriented and molded and isostatically pressed to prepare magnet green body. Then, the magnet was heated to 1090°C in a vacuum environment and kept warm for 6 hours to prepare a sintered magnet.
  • the sintered magnet is heated to 880°C and kept at this temperature for 15 hours for high temperature diffusion treatment. After the heat preservation is completed, it is cooled to below 200°C and then heated to 520°C and kept at this temperature for 5 hours to obtain the base magnet.
  • the base magnet is machined into a magnetic sheet with a thickness of 2.0 mm, with the thickness direction of the magnet being the magnet orientation direction, and the surface is treated by sandblasting and pickling to remove rust and oil stains on the surface of the magnet.
  • a pure Tb layer with a thickness of 15 ⁇ m was deposited on the surface of the magnet perpendicular to the orientation direction by multi-arc ion plating, and no Tb layer was deposited on other surfaces.
  • the magnetic sheet with diffusion source deposited on the surface is subjected to grain boundary diffusion treatment, the diffusion temperature is 900° C., the insulation time is 15 hours, after the insulation is completed, it is cooled to below 200° C. and then heated to 520° C. and maintained for 3 hours to obtain the magnet.
  • the final magnet was treated with sandblasting to expose the fresh surface.
  • the NIM magnetic property test equipment was used to test the room temperature and high temperature magnetic properties of the magnet, and the temperature coefficient of the magnet was calculated.
  • the magnet microstructure was observed by SEM, and the volume ratio of the Gd-rich core main phase grains to the magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed by ICP, and the magnet micro-region composition was analyzed by EPMA.
  • the base magnet compositions of Experiment No. 8 to Experiment No. 10 are the same as those of Experiment No. 2, Experiment No. 5, and Experiment No. 6, respectively.
  • the main phase grains with high Gd content in the magnet are all transformed into Gd-rich core main phase grains after the first high-temperature diffusion. Since the Gd content in the shell of the Gd-rich core main phase grains is relatively low, Tb atoms replace more Pr and Nd atoms in the shell of the Gd-rich core main phase grains during the grain boundary diffusion of the Tb element, so a certain concentration of Tb atoms will be enriched in the Gd-poor shell of the Gd-rich core main phase grains. From the EPMA surface scanning Tb distribution spectrum of the magnet after Tb diffusion in experiment No.
  • Tb can easily replace Pr and Nd elements in the Gd-poor shell, thereby forming a relatively uniform Gd-poor Tb-rich shell.
  • the Tb content of the Gd-poor shell of the Gd-rich core main phase grains was between 0.05wt.% and 0.5wt.%.
  • the non-Gd-rich core main phase grains will also form a Tb-rich shell outside the main phase grains after Tb diffusion.
  • the Tb element improves the room temperature coercivity of the magnet by increasing the anisotropy field of the Gd-rich core main phase grains and the Gd-poor shell.
  • R-T-B rare earth permanent magnets suitable for higher working temperatures can be prepared.
  • This embodiment adopts a dual alloy method to melt two alloy sheets with high Gd content and without Gd respectively, and then prepare a mixed powder. After orientation molding, isostatic pressing and sintering, a sintered magnet is obtained.
  • the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature. Due to the influence of the rare earth element content and diffusion rate of the magnet, the main phase grains with high Gd content of the magnet will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • Dy/Tb In the grain boundary diffusion process of the Dy/Tb heavy rare earth element, since the Gd content at the shell of the Gd-rich core main phase grains is relatively low, Dy/Tb can replace the Pr and Nd elements at the Gd-poor shell to enter the main phase grains.
  • the coercive force of the magnet is increased by increasing the anisotropy field of the Gd-poor shell, and combined with the effect of the Gd element on improving the temperature coefficient of the magnet, the high-temperature magnetic properties of the magnet can be significantly improved, and R-T-B rare earth permanent magnets suitable for higher operating temperatures can be prepared.
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare high Gd content SC sheets with a composition of Nd 12 B 0.95 Cu 0.1 Ga 0.15 Gd 20 Zr 0.15 Fe bal and Gd-free SC sheets with a composition of Nd 32+x B 0.95 Cu 0.1 Ga 0.15 Zr 0.15 Fe bal.
  • the values of x in Experiment No. 11 to Experiment No. 14 were -2, 0, 2 and 4, respectively.
  • the two SC sheets with high Gd content and without Gd were mixed in a weight ratio of 1:1 and pulverized by hydrogen crushing and air flow grinding.
  • the alloy powder was prepared into a magnet green body by orientation molding and isostatic pressing. Then, the magnet was heated to 1080°C in a vacuum environment and kept warm for 6 hours to prepare a sintered magnet.
  • the sintered magnet was heated to 880°C and kept at this temperature for 15 hours to perform a high temperature diffusion treatment. After the heat preservation was completed, the magnet was cooled to below 200°C and then heated to 505°C and kept at this temperature for 5 hours to obtain the magnet.
  • the final magnet was treated with sandblasting to expose the fresh surface.
  • the magnet microstructure was observed by SEM, and the volume ratio of Gd-rich core main phase grains to magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed by ICP, and the magnet micro-region composition was analyzed by EPMA.
  • the total rare earth content, the proportion of high Gd content main phase grains and the proportion of Gd-rich core main phase grains of the magnets of Experiment No. 11 to Experiment No. 14 are shown in Table 5.
  • EPMA point scanning was used to analyze the difference ⁇ H between the Gd element content H1 (wt.%) of the Gd-rich core of the Gd-rich core main phase grains of magnets with different total rare earth contents and the Gd element content H2 (wt.%) of the Gd-poor shell. The results are shown in Table 6.
  • the present embodiment adopts the method of double alloy to melt two kinds of alloy sheets with high Gd content and without Gd respectively, and then prepares mixed powder. After orientation molding, isostatic pressing and sintering, a sintered magnet is obtained.
  • the Gd element due to the large Gd element concentration difference between the main phase grains with high Gd content and the R-rich phase at the magnet grain boundary, the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature. Due to the influence of the rare earth element content and diffusion rate of the magnet, the main phase grains with high Gd content of the magnet will eventually form an anti-shell structure with a poor Gd shell and a Gd-rich core.
  • the Gd concentration in the grain boundary R-rich phase around the main phase grains with high Gd content will decrease, so the Gd element in the main phase grains with high Gd content is easier to diffuse outward.
  • the volume ratio of the R-rich phase at the grain boundary of the magnet increases, which will further dilute the Gd element diffused from the high Gd content main phase grains, and finally the Gd content difference between the Gd-rich core and the Gd-poor shell of the Gd-rich core main phase grains in the magnet will increase with the increase of the total rare earth content of the magnet.
  • Embodiment 4 is a diagrammatic representation of Embodiment 4:
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare high Gd content SC sheets with a composition of Nd 32-x B 0.95 Cu 0.1 Ga 0.15 Gd x Zr 0.15 Fe bal and Gd-free SC sheets with a composition of Nd 32 B 0.95 Cu 0.1 Ga 0.15 Zr 0.15 Fe bal.
  • the values of x in experiments No. 15 to No. 17 were 1, 3 and 5, respectively.
  • the high Gd and Gd-free SC sheets were mixed in a weight ratio of 1:1 and pulverized by hydrogen crushing and air flow grinding.
  • the alloy powder was oriented and molded and isostatically pressed to prepare a magnet green body.
  • the magnet was then heated to 1080°C in a vacuum environment and kept warm for 6 hours to prepare a sintered magnet.
  • the sintered magnet was heated to 880°C and kept at this temperature for 15 hours to perform a high temperature diffusion treatment. After the heat preservation was completed, the magnet was cooled to below 200°C and then heated to 505°C and kept at this temperature for 5 hours to obtain the magnet.
  • the final magnet was surface treated by sandblasting to expose the fresh surface of the magnet.
  • the NIM magnetic property test equipment was used to test the magnetic properties of the magnet at room temperature of 20°C and high temperature of 150°C, and the temperature coefficient of the magnet was calculated.
  • the magnet microstructure was observed by SEM, and the volume ratio of the Gd-rich core main phase grains to the magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed by ICP, and the magnet micro-region composition was analyzed by EPMA.
  • the present invention adopts a dual alloy method to melt two alloy sheets with high Gd content and without Gd respectively, and then prepare a mixed powder. After orientation molding, isostatic pressing and sintering, a sintered magnet is obtained.
  • the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature. Due to the influence of the rare earth element content and diffusion rate of the magnet, the main phase grains containing Gd in the magnet will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • the formation of the Gd-rich core main phase grains mainly relies on the large Gd concentration gradient between the main phase grains with high Gd content and the surrounding grain boundary R-rich phase to promote the outward diffusion of the Gd element in the Gd-containing main phase grains.
  • the Gd content in the high Gd content main phase grains of the magnet is too low, the driving force for the outward diffusion of the Gd element is small, because the difference in the concentration of the high Gd content main phase grains and the grain boundary R-rich phase is small, so the formation process of the Gd-rich core main phase grains is hindered, and finally the proportion of the Gd-rich core main phase grains in the high temperature diffusion magnet is reduced. Therefore, in the present invention, the Gd element content in the high Gd content alloy sheet is 5.0 ⁇ 34.0wt.%.
  • the raw materials were mixed in a certain proportion and vacuum induction melting and strip spinning were used to prepare high Gd content SC sheets with a composition of Nd 12 B 0.95 Cu 0.1 Ga 0.15 Gd 20 Zr 0.15 Fe bal and low Gd content SC sheets with a composition of Nd 12+x B 0.95 Cu 0.1 Ga 0.15 Gd 20-x Zr 0.15 Fe bal .
  • the values of x in Experiment No. 18 to Experiment No. 21 were 2, 5, 7 and 20, respectively.
  • the two SC sheets with high Gd content and low Gd content were mixed in a weight ratio of 1:1 and pulverized by hydrogen crushing and air flow grinding.
  • the alloy powder was prepared into a magnet green body by orientation molding and isostatic pressing. Then, the magnet was heated to 1080°C in a vacuum environment and kept warm for 6 hours to prepare a sintered magnet.
  • the sintered magnet was heated to 880°C and kept at this temperature for 15 hours to perform a high temperature diffusion treatment. After the heat preservation was completed, the magnet was cooled to below 200°C and then heated to 505°C and kept at this temperature for 5 hours to obtain the magnet.
  • the final magnet was treated with sandblasting to expose the fresh surface.
  • the magnet microstructure was observed by SEM, and the volume ratio of Gd-rich core main phase grains to magnet main phase grains was calculated using image J software.
  • the magnet composition was analyzed by ICP, and the magnet micro-region composition was analyzed by EPMA.
  • the present invention adopts a dual alloy method to melt two alloy sheets with high Gd content and low Gd content respectively, and then prepare a mixed powder. After orientation molding, isostatic pressing and sintering, a sintered magnet is obtained.
  • the Gd element will diffuse from the main phase grains of the magnet to the R-rich phase at the magnet grain boundary at high temperature. Due to the influence of the rare earth element content and diffusion rate of the magnet, the main phase grains containing Gd in the magnet will eventually form an anti-shell structure with a Gd-poor shell and a Gd-rich core.
  • the formation of the Gd-rich core main phase grains mainly relies on the large Gd concentration gradient between the main phase grains with high Gd content and the surrounding grain boundary R-rich phase to promote the outward diffusion of the Gd element in the main phase grains with high Gd content.
  • the Gd concentration difference between the main phase grains with high Gd content and the main phase grains with low Gd content in the magnet is less than 5.0wt.%, the outward diffusion process of the Gd element in the main phase grains with high Gd content is suppressed, the amount of Gd-rich core main phase grains generated is small, and the magnetic properties of the magnet are poor.
  • the Gd concentration difference between the main phase grains with high Gd content and the main phase grains with low Gd content needs to be ⁇ 5.0wt.%.
  • the greater the difference in Gd concentration between the main phase grains with high Gd content and the main phase grains with low Gd content the higher the magnetic properties of the magnet. Therefore, in the present invention, the main phase grains with low Gd content are preferably free of Gd.

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Abstract

本发明提供了一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，所述磁体中，稀土元素R含量为29.0wt.%~34.0wt.%，R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%；主相晶粒中包含体积比20vol.%~80vol.%的富Gd核、贫Gd壳层的主相晶粒。本发明采用双合金的方法分别熔炼高Gd含量和低Gd含量的合金片，然后制得烧结磁体，其中在高温扩散处理时高Gd含量主相中的Gd元素会向晶界富R相中扩散，最终高Gd含量主相晶粒会形成具有贫Gd壳层和富Gd核心的反壳层结构，贫Gd的壳层，可以显著降低Gd元素对磁体矫顽力的劣化作用，从而充分利用Gd的特点，制备得到具有低温度系数，同时具有较高矫顽力的磁体。Dy/Tb元素的晶界扩散处理，可以进一步提高磁体的矫顽力，制备适合更高工作温度使用的R-T-B稀土永磁体。

Description

一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法 技术领域
本发明涉及一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法，属于稀土磁体领域。
 背景技术
R-T-B稀土永磁体由于其超高的磁能积，可以有效地实现设备的小型化，广泛应用在现代工业。近些年来，随着新能源产业的发展，R-T-B磁体在风力发电和电动汽车中的市场份额逐年增加。但由于R-T-B磁体磁性能温度系数为负，随着温度的升高磁体的磁性能变差。而汽车发动机的工作温度在200℃左右，为保证电机正常工作，需要提高磁体的高温磁性能。
目前主要通过提高矫顽力和降低磁性能温度系数（温度系数本身为负值，文中对于温度系数大小的比较均采用其绝对值，下同）的方法提高R-T-B磁体的高温磁性能。重稀土元素Gd能够显著地降低磁体的温度系数，从而提高磁体的高温磁性能。但是Gd元素会对磁体性能造成不利的影响，一方面Gd属于重稀土元素，在R 2T 14B相中Gd与Fe呈反铁磁性耦合，在熔炼阶段添加过多的Gd元素会降低磁体的剩磁。另一方面，Gd元素对应主相的各向异性场较低，在磁体中大量存在时会降低磁体的矫顽力。因此目前通过在磁体中添加Gd元素来降低磁体的温度系数是以降低磁体的剩磁和矫顽力为代价的。
晶界扩散是提高磁体矫顽力的有效方法，但在晶界扩散中，如果扩散工艺不合理、扩散时间太长会出现重稀土元素反壳层分布现象。即经过重稀土元素晶界扩散磁体主相晶粒形成核壳结构后，出现磁体主相晶粒核心处的重稀土元素含量高，而壳层处的重稀土元素含量低的现象。
晶界扩散过程中，在扩散初期磁体表面较高浓度的扩散源会沿磁体的晶界富R相向磁体内部扩散。此时，由于晶界富R相中的重稀土元素浓度高于磁体主相晶粒，因此重稀土元素会向磁体主相晶粒内部扩散，在主相晶粒表面形成一层富重稀土元素的壳层。但随着扩散时间的延长，磁体表面的晶界扩散源被消耗完。处于晶界富R相中的重稀土元素随着扩散的进行其浓度会逐渐降低，最终会出现磁体主相晶粒中的重稀土元素含量高于磁体晶界富R相的情况。此时的重稀土元素扩散方向转变为由磁体主相晶粒向晶界富R相中扩散，最终在磁体中形成了具有重稀土元素反壳层结构的主相。即磁体主相晶粒表层为重稀土含量较少的壳层，而主相晶粒心部为重稀土元素含量较多的核心。传统的晶界扩散中，一般采用Dy或Tb等具有较高各向异性场的元素作为晶界扩散源，通过增强磁体主相晶粒表层各向异性场的方式提高磁体的矫顽力。而当出现Dy或Tb元素的反壳层结构时，磁体的矫顽力会显著降低。
R-T-B系稀土永磁体中，Gd对应主相的各向异性场要低于Pr或Nd所对应主相的各向异性场。因此为了避免磁体矫顽力降低，在晶界扩散时一般不采用Gd作为晶界扩散源。但如果通过工艺控制，促进磁体形成主相晶粒心部为富Gd的核心，而主相晶粒边部为贫Gd壳层的特殊结构，即形成Gd的反壳层结构。磁体具备这种结构时，一方面可以利用Gd主相低温度系数的特点提高磁体的高温磁性能。另一方面，由于在磁体主相晶粒边缘形成了贫Gd的壳层，而钕铁硼磁体的矫顽力机制属于形核型，如果磁体主相边缘部的矫顽力较低时会导致整个主相晶粒的矫顽力降低，因此磁体主相晶粒边缘的贫Gd的壳层可以显著降低Gd元素对磁体矫顽力的劣化作用，从而充分利用Gd的特点，制备具有低温度系数，同时具有高矫顽力的磁体。
 技术问题
针对R-T-B稀土永磁体制备过程中，添加Gd元素降低磁体温度系数时会显著降低磁体剩磁和矫顽力的技术问题，本发明提供了一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法。
 解决方案
本发明采用的技术方案如下：
一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，所述磁体中，稀土元素R含量为29.0wt.%~34.0wt.%，R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；
所述磁体包含主相R 2T 14B和晶界富R相，主相晶粒中包含20vol.%~80vol.%（体积比）的富Gd核主相晶粒，所述富Gd核主相晶粒是由富Gd的核心和贫Gd的壳层组成，核心Gd含量H1(wt.%)和壳层Gd含量H2(wt.%)的差值δH=H1-H2，δH与磁体中稀土元素总含量R满足δH=(0.05~0.40)R。
 进一步，所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体的磁体成分包含：
R：29.0wt.%~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所述R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；R1由R3或者R2与R3组成；R2为稀土元素Dy和Tb中的至少一种，R3为Nd、Pr、Ho、La、Ce中的至少一种，优选R3为Nd和Pr中一种或两种；更优选R3的75wt.%以上为Nd;
所述磁体包含R2时，R2含量为磁体质量的0.1wt.%~2.0wt.%，磁体的富Gd核主相晶粒的贫Gd壳层中包含0.05wt.%~0.5wt.%的R2元素；
所述M为Al、Cu、Ga、Zr、Ti、Nb、Zn、Sn、W、Mo、Hf、Au和Ag中的至少一种，优选为Cu、Ga、Zr中的一种或多种；
所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体按照以下方法之一制备：
方法（一）：磁体中不含R2元素时
将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
所述高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
方法（二）：磁体中含有R2元素时：
将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，所述原料中均不含R2元素，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，所得基体磁体加工成厚度为0.5~10.0mm的磁片，表面处理后在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，然后进行晶界扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体。
所述重稀土元素扩散层为Dy、Tb中的任意一种或两种。
所述重稀土元素扩散层一般采用蒸镀、磁控溅射或多弧离子镀膜的方式沉积得到。
所述方法（一）或方法（二）中，所述高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得磁体基体；
所述方法（二）中，所述晶界扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束后，冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体。
所述高Gd含量SC片与低Gd含量SC片的Gd含量差别≥5.0wt.%，高Gd含量SC片中的Gd含量为5.0~34.0wt.%，低Gd含量SC片中的Gd含量优选为0；
进一步，所述高Gd含量合金原料中各组分的成分为：
R3：0~29wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种，优选R3的75wt.%以上为Nd;Gd：5.0~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所述低Gd含量合金原料中各组分的成分为：
R3：5~34wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种，优选R3的75wt.%以上为Nd;
Gd：0~X wt.%，且高Gd含量合金原料的Gd含量-X≥5.0wt.%；优选Gd含量为0；B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所述高Gd含量合金原料和低Gd含量合金原料的质量比要保证混合后最终磁体中的Gd元素含量为1.0wt.%~20.0wt.%，实际生产中一般为1：0.25~4；
进一步，所述高Gd含量SC片和低Gd含量SC片制备得到合金粉末，是将高Gd含量SC片和低Gd含量SC片混合后，通过氢破碎和气流磨制备合金粉末，或者将高Gd含量SC片和低Gd含量SC片分别经过氢破碎后混合、再通过气流磨制备合金粉末，或者将高Gd含量SC片和低Gd含量SC片分别经过氢破碎、气流磨后，再将所得粉末混合制备合金粉末。
所述真空烧结的工艺为：加热至1020~1110℃，保温3~10h。
所述方法（二）中，磁片的表面处理工艺为采用喷砂、酸洗等方法去除磁体表面锈斑和油污。
所述方法（二）中，所述重稀土元素扩散层为纯重稀土元素金属、重稀土元素氢化物或重稀土元素与其他金属元素的合金，所述重稀土元素为Dy和Tb中的至少一种。
所述方法（二）中，在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，优选在磁体垂直于取向方向的表面沉积覆盖重稀土元素扩散层，在磁体不垂直于取向方向的表面优选不覆盖重稀土元素扩散层。
本发明还提供一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体的制备方法，所述方法为以下之一：
方法（一）：磁体中不含R2元素时：
将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
所述高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
方法（二）：磁体中含有R2元素时：
将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，所述原料中均不含R2元素，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，所得基体磁体加工成厚度为0.5~10.0mm的磁片，表面处理后在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，然后进行晶界扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
所述重稀土元素扩散层为Dy、Tb中的任意一种或两种；
所述高Gd含量合金原料中各组分的成分为：
R3：0~29wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种；Gd：5.0~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所述低Gd含量合金原料中各组分的成分为：
R3：5~34wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种，优选R3的75wt.%以上为Nd;Gd：0~Xwt.%，且高Gd含量合金原料的Gd含量-X≥5.0wt.%；B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所得到的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体的成分为：
R：29.0wt.%~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
所述R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；R1为R3或者由R2与R3组成；R3为Nd、Pr、Ho、La、Ce中的至少一种；
R2为稀土元素Dy和Tb中的至少一种，所述磁体包含R2时，R2含量为磁体质量的0.1wt.%~2.0wt.%，磁体的富Gd核主相晶粒的贫Gd壳层中包含0.05wt.%~0.5wt.%的R2元素；
所述M为Al、Cu、Ga、Zr、Ti、Nb、Zn、Sn、W、Mo、Hf、Au和Ag中的至少一种；
所述磁体包含主相R 2T 14B和晶界富R相，并且主相晶粒中包含体积比20vol.%~80vol.%的富Gd核主相晶粒，所述富Gd核主相晶粒由富Gd的核心和贫Gd的壳层组成，核心Gd含量H1(wt.%)和壳层Gd含量H2(wt.%)的差值δH=H1-H2，δH与磁体中稀土元素总含量R满足δH=(0.05~0.40)R。
本发明采用双合金的方法制备高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，即分别熔炼高Gd含量和低Gd含量的两种合金片，然后将两种SC片混合后通过氢破碎和气流磨制备合金粉末，或将两种SC片分别氢破后混合并通过气流磨制备合金粉末，或将两种SC片分别氢破、气流磨后混合制备合金粉末，然后经过取向成型、等静压和烧结制得烧结磁体。烧结后的磁体在800~1000℃进行5~25h的高温扩散处理，高温扩散处理结束后冷却至200℃以下后再升温至400~650℃，保温2~10h。
磁体在高温扩散过程中，由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。扩散到晶界富R相中的Gd元素则会沿着熔融的晶界相向低Gd浓度处继续扩散，从而对高Gd含量主相晶粒附近的晶界富R相的Gd进行稀释，进一步促进主相中的Gd元素向外扩散。由于Gd元素在磁体主相晶粒内部的扩散速率远低于Gd从主相晶粒向晶界富R相的扩散速率，即Gd元素从主相晶粒心部向主相晶粒边部的扩散速率远低于Gd元素从主相晶粒边部向晶界富R相中的扩散速率。因此高Gd含量的主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。
重稀土元素Gd存在于磁体主相晶粒中可以显著降低磁体的温度系数，从而提高磁体的高温磁性能。但是一方面Gd与Fe呈反铁磁性耦合，在熔炼阶段添加过多的Gd元素会降低磁体的剩磁。另一方面，Gd元素对应主相的各向异性场较低，在磁体中大量存在时会降低磁体的矫顽力。但是通过本发明的方法，控制高Gd含量主相晶粒形成具有贫Gd壳层和富Gd核心的反壳层结构时，一方面可以利用Gd主相低温度系数的特点提高磁体的高温磁性能。另一方面，由于在磁体主相晶粒边缘形成了贫Gd的壳层，可以显著降低Gd元素对磁体矫顽力的劣化作用，从而充分利用Gd的特点，制备具有低温度系数，同时具有较高矫顽力的磁体。
为了保证高Gd含量主相晶粒中的Gd元素能够向磁体晶界富R相中扩散，必须确保磁体主相晶粒和晶界富R相间具有较大的Gd元素浓度梯度。因此在本发明中采用了双合金工艺分别熔炼高Gd含量和低Gd含量两种合金片并制备混合粉末，为保证高Gd含量主相晶粒与周围晶界富R相的Gd元素具有较大的浓度差，从而使高Gd含量主相晶粒中的Gd元素在高温扩散时能够顺利向外扩散，因此必须保证高Gd含量SC合金片和低Gd含量SC合金片的Gd含量差别≥5.0wt.%。本发明中高Gd含量SC片的Gd含量为5.0~34.0wt.%，低Gd含量SC片优选为不含Gd。
此外，磁体的稀土含量也会影响高Gd含量主相晶粒中Gd元素的扩散。随着磁体稀土含量的增加，磁体的晶界富R相含量也就越高，从高Gd含量主相晶粒中扩散出的Gd元素也容易被晶界相稀释，因此可以促进高Gd含量主相晶粒中Gd元素的进一步向外扩散。本发明发现，在具有Gd元素反壳层结构的主相晶粒中，主相晶粒核心的Gd元素含量H1(wt.%)和壳层Gd元素含量H2(wt.%)之间的差值δH与磁体稀土元素含量R满足δH=(0.05~0.40)R。即随着磁体稀土含量的升高，最终具有Gd元素反壳层结构主相晶粒核壳之间的Gd元素差别越大，也说明主相晶粒壳层处Gd元素向外扩散的量越多。
同时本发明还可以通过Dy/Tb晶界扩散进一步提高磁体的矫顽力并降低磁体的温度系数，制备适合更高工作温度使用的R-T-B稀土永磁体。
本发明通过先制备具有Gd元素反壳层结构的主相晶粒，然后进行Dy/Tb等元素的晶界扩散，使磁体中的富Gd核主相晶粒的贫Gd壳层中富集较高浓度的Dy/Tb元素，使富Gd核主相晶粒形成具有更高各向异性场的富Dy/Tb壳层，从而进一步提高磁体的矫顽力。由于重稀土元素生成主相时的生成能更负，因此重稀土元素在取代轻稀土元素（Pr、Nd、La、Ce等）生成主相时更容易进行。本发明通过首先制备具有富Gd核主相晶粒的磁体，由于磁体具有核壳结构，且壳层处的重稀土元素Gd含量较低、轻稀土元素含量较高。因此磁体在重稀土元素晶界扩散过程中Dy/Tb更容易在富Gd核主相晶粒形成富Dy/Tb的壳层。如果Gd元素在磁体主相晶粒中均匀分布，那么在重稀土元素的晶界扩散过程中Gd元素会阻碍磁体主相晶粒中富Dy/Tb壳层的形成，从而降低晶界扩散效果。同时在重稀土元素的晶界扩散过程中，其他非富Gd核的主相晶粒也会形成具有富稀土元素Dy/Tb壳层结构的晶粒，从而进一步提高磁体的矫顽力，制备适合更高工作温度使用的R-T-B稀土永磁体。
 有益效果
本发明的有益效果体现在：采用双合金的方法分别熔炼高Gd含量和低Gd含量的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从高Gd含量主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体高Gd含量主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。Gd主相温度系数低的特征可以提高磁体的高温磁性能。同时由于在磁体主相晶粒边缘形成了贫Gd的壳层，可以显著降低Gd元素对磁体矫顽力的劣化作用，从而充分利用Gd的特点，制备具有低温度系数，同时具有较高矫顽力的磁体。此外，通过后续Dy/Tb元素的晶界扩散处理，使磁体富Gd核主相晶粒的贫Gd壳层中富集较高浓度的Dy/Tb元素；而非富Gd核的主相晶粒在晶界扩散过程中也会形成具有较高浓度的Dy/Tb壳层，进一步提高磁体的矫顽力，从而制备适合更高温度使用的R-T-B稀土永磁体。
 附图说明
图1（a）、（b）和（c）分别为实验No.2、实验No.5和实验No.6最终磁体SEM显微组织照片。
图2为实验No.5磁体富Gd核主相晶粒显微组织及富Gd核主相晶粒的贫Gd壳层和富Gd核心能谱点扫描示意图。
图3为实验No.9磁体经过Tb扩散的EPMA面扫描Tb图谱。
 本发明的最佳实施方式
下面结合具体实施例对本发明的技术方案进行进一步说明，但本发明的保护范围不限于此。
当磁体不含R2元素时，磁体按照以下方法制备：
将原材料按照一定比例配比后采用真空感应熔炼甩带分别制备高Gd含量和低Gd含量的两种SC合金片。
将两种SC片混合后通过氢破碎和气流磨制备合金粉末，或将两种SC片分别氢破后混合并通过气流磨制备合金粉末，或将两种SC片分别氢破、气流磨后混合制备合金粉末。合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1020~1110℃，保温3~10h，制备烧结磁体。
烧结磁体加热到800~1000℃保温5~25h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述磁体。
当磁体含有R2元素时，磁体按照以下方法制备：
原材料按照一定比例配比后采用真空感应熔炼甩带分别制备高Gd含量和低Gd含量的两种SC合金片。
将两种SC片混合后通过氢破碎和气流磨制备合金粉末，或将两种SC片分别氢破后混合并通过气流磨制备合金粉末，或将两种SC片分别氢破、气流磨后混合制备合金粉末。合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1020~1110℃，保温3~10h，制备烧结磁体。
烧结磁体加热到800~1000℃保温5~25h，进行高温预扩散处理。保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得基体磁体。
采用机加工将基体磁体加工成厚度为0.5~10.0mm的磁片，并采用喷砂、酸洗等方法进行表面处理，去除磁体表面锈斑和油污。
采用蒸镀、磁控溅射或多弧离子镀膜的方式在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，在磁体垂直于取向方向的表面覆盖重稀土扩散源，在磁体不垂直于取向方向的表面优选不覆盖重稀土扩散源。重稀土扩散源为纯重稀土元素金属、重稀土元素氢化物或重稀土元素与其他金属元素的合金，所述重稀土元素为Dy和Tb中的至少一种。
表面沉积扩散源的磁片进行晶界扩散处理，扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用NIM磁性能测试设备测试磁体的常温和高温磁性能，并计算磁体温度系数。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
实施例一：
将原材料按照一定比例配比后采用真空感应熔炼、甩带分别制备成分为Nd 12Pr 3.0B 0.95Co 0.95Cu 0.1Ga 0.15Gd 17Zr 0.15Fe bal的高Gd含量SC片和成分为Nd 24.75Pr 7.25B 0.95Co 0.95Cu 0.1Ga 0.15Zr 0.15Fe bal的不含Gd元素SC片。
将两种SC片按照不同重量比混合后通过氢破碎和气流磨制粉，合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1090℃，保温6h，制备烧结磁体。
烧结磁体加热到880℃保温15h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至520℃，保温5h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用NIM磁性能测试设备测试磁体的20℃常温磁性能和150℃的高温磁性能，并计算磁体温度系数。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
通过混合不同重量比的高Gd含量和不含Gd甩片调控磁体含Gd主相晶粒的体积比，（在本实施例中，高Gd含量和不含Gd磁体的密度接近，可以通过控制不同SC片的重量比来近似调控高Gd含量和不含Gd主相晶粒的体积比），并采用SEM和image J软件分析主相晶粒中富Gd核主相晶粒占比，实验No.1~实验No.7甩片混合时高Gd含量甩片占比、最终磁体Gd含量、含Gd主相晶粒占比及富Gd核主相占比如表1所示。
表1
实验No. 1 2 3 4 5 6 7
高Gd含量甩片占比(wt.%) 0 10.1 20.3 50.2 80.2 90.1 100.0
磁体Gd含量(wt.%) 0 1.7 3.4 8.4 13.5 15.4 17.0
高Gd含量主相晶粒占比(vol.%) 0 9.3 20.0 50.2 79.9 90.0 100.0
富Gd核主相体积比(vol.%) 0 9.3 20.0 50.2 79.9 8.1 0
实验No.1~实验No.7磁体常温和高温（150℃）磁性能、150℃剩磁温度系数α以及矫顽力温度系数β的绝对值如表2所示。
表2
实验No. Br(kGs) 20℃ Hcj(kOe) 20℃ Br(kGs) 150℃ Hcj(kOe) 150℃ ∣α∣(%/℃) ∣β∣(%/℃)
1 13.50 14.30 10.26 3.15 0.16 0.52
2 13.41 13.57 10.39 3.19 0.15 0.51
3 13.10 13.15 11.33 4.27 0.09 0.45
4 12.73 12.70 11.20 4.32 0.08 0.44
5 12.15 12.01 10.69 4.26 0.08 0.43
6 11.20 9.95 10.02 3.53 0.07 0.43
7 10.98 8.25 9.83 3.05 0.07 0.42
从表1数据可知，实验No.1和实验No.7分别为由不含Gd和高Gd含量甩片单合金制备的磁体。在实验No.1中，当磁体完全由不含Gd元素的单合金制备而成时，磁体的Gd含量为零，此时磁体主相中不存在富Gd核的主相晶粒。而当磁体完全由高Gd含量甩片制得时（实验No.7），由于磁体主相晶粒中均存在Gd元素，含Gd主相晶粒周围的Gd浓度梯度较小，含Gd主相晶粒的Gd元素难以向外扩散，此时富Gd核主相晶粒也无法形成。可见最终磁体中富Gd核主相晶粒占比并不随着含Gd主相晶粒占比的增大而线性增加。
结合实验No.2磁体SEM图（图1（a））和性能数据可知，当高Gd含量主相晶粒体积比小于20vol.%时，经过高温晶界扩散后高Gd含量主相晶粒会全部转变为富Gd核主相晶粒，此时晶界扩散前磁体中高Gd含量主相晶粒和晶界扩散以后磁体富Gd核主相晶粒占比相同。然而磁体由于富Gd核主相晶粒占比较少，对磁体温度系数的改善效果有限，磁体的高温磁性能较差。
实验No.3~实验No.5中，当磁体高Gd含量主相晶粒占比在20vol.%~80vol.%之间时，此时磁体中仍存在较大比例的不含Gd主相晶粒和晶界富R相，因此高Gd含量主相晶粒周围存在着较大的Gd元素浓度差，能够促进高Gd含量主相晶粒外侧的Gd元素向外扩散，从而形成富Gd核主相晶粒。此时高Gd含量主相晶粒经过高温晶界扩散后也会全部转变为富Gd核主相晶粒，即晶界扩散前磁体高Gd含量主相晶粒占比与晶界扩散后富Gd核主相晶粒占比相同。此时由于磁体含量较多的富Gd核主相晶粒，能够显著地改善磁体的磁性能和温度系数，因此磁体的高温磁性能要高于实验No.1和实验No.2。
实验No.6中，当磁体高Gd含量主相晶粒占比超过80vol.%时，此时由于磁体中不含Gd磁体主相晶粒占比较少，高Gd含量主相晶粒周围的Gd元素浓度梯度小，因此高Gd含量主相晶粒的Gd元素难以向外扩散，最终导致磁体的富Gd核主相晶粒占比远低于磁体中高Gd含量主相晶粒占比（图1（c））。从实验No.6可以看出，磁体中高Gd含量主相晶粒占比为90.0vol.%，而经过高温扩散后富Gd核主相晶粒占比仅为8.1vol.%。此时虽然磁体的温度系数也较低，但是由于缺乏足够的富Gd核主相晶粒优化Gd元素分布，导致磁体的常温磁性能变差，温度系数的补偿作用无法弥补较低常温磁性能的影响，因此磁体的高温磁性能也会变差。
通过SEM观察实验No.5磁体显微组织（图1（b）），并采用EPMA点扫描分析磁体成分，核壳成分的点扫描示意图如图2所示。结果表明，实验No.5磁体富Gd核主相晶粒壳层和核心的Gd含量分别为8.8wt.%和15.3wt.%，可见晶界扩散以后磁体，高Gd含量主相晶粒外侧的Gd元素向外的扩散量较大，高Gd含量主相晶粒充分转变成具有贫Gd壳层和富Gd核心的结构。
本实施例采用双合金的方法分别熔炼高Gd含量和不含Gd的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体高Gd含量的主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。Gd主相温度系数低的特征可以提高磁体的高温磁性能。同时由于在磁体主相晶粒边缘形成了贫Gd的壳层，可以显著降低Gd元素对磁体矫顽力的劣化作用，从而充分利用Gd的特点，制备具有低温度系数，同时具有较高矫顽力的磁体。
本发明中需要将扩散前磁体高Gd含量主相晶粒占比控制在20vol.%~80vol.%之间，在此范围的高Gd含量主相晶粒经过高温扩散后会充分转变为富Gd核主相晶粒。可以显著改善磁体的温度系数，提高磁体的高温磁性能。当磁体晶界扩散前高Gd含量主相晶粒太少时（小于20vol.%），虽然经过高温扩散后磁体高Gd含量主相晶粒也会转变为富Gd核主相晶粒，但是对磁体温度系数的改善不明显。当扩散前磁体的高Gd含量主相晶粒超过80vol.%时，由于高Gd含量主相晶粒周围的Gd元素浓度过高，会抑制主相晶粒中Gd元素向外扩散，从而导致磁体的富Gd核主相晶粒数量减少，导致磁体的常温和高温磁性能均变差。
实施例二：
将原材料按照一定比例配比后采用真空感应熔炼、甩带分别制备成分为Nd 12Pr 3.0B 0.95Co 0.95Cu 0.1Ga 0.15Gd 17Zr 0.15Fe bal的高Gd含量SC片和成分为Nd 24.75Pr 7.25B 0.95Co 0.95Cu 0.1Ga 0.15Zr 0.15Fe bal的不含Gd元素SC片。
将两种SC片按照不同重量比混合后通过氢破碎和气流磨制粉，合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1090℃，保温6h，制备烧结磁体。
烧结磁体加热到880℃保温15h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至520℃，保温5h，制得基体磁体。
采用机加工将基体磁体加工成厚度为2.0mm的磁片，磁体厚度方向为磁体取向方向，并采用喷砂、酸洗的方法进行表面处理，去除磁体表面锈斑和油污。
采用多弧离子镀膜的方式在磁体垂直于取向方向表面沉积厚度为15μm的纯Tb层，其他表面不沉积。
表面沉积扩散源的磁片进行晶界扩散处理，扩散温度为900℃，保温时间为15h，保温结束冷却至200℃以下后再升温至520℃，保温3h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用NIM磁性能测试设备测试磁体的常温和高温磁性能，并计算磁体温度系数。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
实验No.8~实验No.10基体磁体成分分别与实验No.2、实验No.5和实验No.6相同。
实验No.8~实验No.10最终磁体Gd含量、Tb含量和、高Gd含量主相晶粒和富Gd核主相晶粒占比如表3所示。
表3
实验No. 8 9 10
磁体Gd含量(wt.%) 1.7 13.5 15.3
磁体Tb含量(wt.%) 0.42 0.42 0.40
高Gd含量主相晶粒占比(vol.%) 9.3 80.1 90.0
富Gd核主相体积比(vol.%) 9.3 80.1 8.2
实验No.8~实验No.10磁体常温和高温（150℃）磁性能、150℃剩磁温度系数α以及矫顽力温度系数β的绝对值如表4所示。
表4
实验No. Br(kGs) 20℃ Hcj(kOe) 20℃ Br(kGs) 150℃ Hcj(kOe) 150℃ ∣α∣(%/℃) ∣β∣(%/℃)
8 13.15 22.69 10.38 6.35 0.14 0.48
9 11.92 21.32 10.84 8.21 0.06 0.41
10 10.95 16.85 9.96 6.23 0.06 0.42
当磁体中高Gd含量主相晶粒体积比在本发明推荐范围内（实验No.9），经过第一次高温扩散后高Gd含量主相晶粒全部转变为富Gd核主相晶粒。由于富Gd核主相晶粒的壳层处Gd含量较低，Tb元素的晶界扩散时Tb原子更多取代富Gd核主相晶粒壳层中的Pr、Nd原子，因此富Gd核主相晶粒的贫Gd壳层中会富集一定浓度Tb原子。从实验No.9经过Tb扩散后磁体的EPMA面扫描Tb分布图谱（图3）可以看出经过Tb扩散后Tb能够比较容易的取代贫Gd壳层中的Pr、Nd元素，从而形成比较均匀的贫Gd富Tb壳层。通过EPMA点扫描分析发现，经过Tb晶界扩散后，富Gd核主相晶粒贫Gd壳层的Tb含量在0.05wt.%~0.5wt.%之间。同时，非富Gd核主相晶粒在经过Tb扩散后也会在主相晶粒外侧形成富Tb的壳层。Tb元素通过提高富Gd核主相晶粒贫Gd壳层的各向异性场提高磁体的室温矫顽力，结合Gd元素改善磁体温度系数的作用，可以制备适合更高工作温度使用的R-T-B稀土永磁体。
实验No.8中，当富Gd核主相晶粒比例较少（<20vol.%）时，虽然经Tb扩散后磁体的室温剩磁和矫顽力较高，但由于温度系数较大，加热到高温后磁性能下降量较大。实验No.10中，当富Gd核主相晶粒占比太多（>80vol.%）时，在初次高温扩散时磁体无法形成足够多的富Gd核主相晶粒，Tb晶界扩散处理时Tb元素需要取代Gd元素进入主相晶粒，由于Gd和Tb对应主相的生成能接近，导致Tb进入磁体主相困难，因此Tb扩散后磁体的矫顽力提升量较小。加之磁体的常温磁性能较差，此时磁体虽然温度系数较低，但高温的磁性能仍较差。
本实施例采用双合金的方法分别熔炼高Gd含量和不含Gd的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体高Gd含量的主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。在Dy/Tb重稀土元素的晶界扩散过程中，由于富Gd核主相晶粒的壳层处Gd含量较低，因此Dy/Tb可以取代贫Gd壳层处的Pr、Nd元素进入主相晶粒。通过提高贫Gd壳层的各向异性场提高磁体的矫顽力，同时结合Gd元素改善磁体温度系数的作用，可以显著提高磁体的高温磁性，制备适合更高工作温度使用的R-T-B稀土永磁体。
实施例三：
将原材料按照一定比例配比后采用真空感应熔炼、甩带分别制备成分为Nd 12B 0.95Cu 0.1Ga 0.15Gd 20Zr 0.15Fe bal的高Gd含量SC片和成分为Nd 32+xB 0.95Cu 0.1Ga 0.15Zr 0.15Fe bal的不含Gd元素SC片，实验No.11~实验No.14中x的值分别为-2、0、2和4。
将高Gd含量和不含Gd两种SC片按照1:1的重量比混合后通过氢破碎和气流磨制粉，合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1080℃，保温6h，制备烧结磁体。
烧结磁体加热到880℃保温15h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至505℃，保温5h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
实验No.11~实验No.14磁体的总稀土含量、高Gd含量主相晶粒占比和富Gd核主相晶粒占比如表5所示。
表5
实验No. 11 12 13 14
总稀土含量R 31.0 32.0 33.0 34.0
高Gd含量主相晶粒占比(vol.%) 49.5 49.5 49.7 49.8
富Gd核主相体积比(vol.%) 49.5 49.5 49.7 49.8
由表5可知总稀土含量不同的各实验组磁体中高Gd含量主相晶粒占比均在49.0vol.%~50.0vol.%之间，且经过高温扩散后高Gd含量主相晶粒全部转变为富Gd核主相晶粒。
采用EPMA点扫描分析不同总稀土含量磁体富Gd核主相晶粒富Gd核心的Gd元素含量H1(wt.%)和贫Gd壳层Gd元素含量H2(wt.%)之间的差值δH，结果如表6所示。
表6
实验No. 11 12 13 14
δH(wt.%) 5.52~6.64 6.45~7.63 7.05~8.72 8.41~9.18
由表6数据可知，在磁体的富Gd核主相晶粒占比相同的情况下，随着磁体总稀土含量的增加，磁体富Gd核主相晶粒富Gd核心和贫Gd壳层之间的Gd元素含量差值越大，即随着磁体总稀土元素含量的增加，在高温扩散处理过程中高Gd含量主相晶粒中的Gd元素更容易向外扩散。
本实施例采用双合金的方法分别熔炼高Gd含量和不含Gd的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体高Gd含量主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。随着磁体总稀土含量的增加，高Gd含量主相晶粒周围的晶界富R相中Gd浓度会降低，因此高Gd含量主相晶粒中的Gd元素更容易向外扩散。同时随着磁体总稀土元素含量的增加，磁体的晶界富R相体积比增大，会进一步稀释高Gd含量主相晶粒扩散出的Gd元素，最终磁体中富Gd核主相晶粒富Gd核心和贫Gd壳层之间的Gd含量差值会随着磁体总稀土含量的增加而增大。在本发明中，根据磁体总稀土含量和高Gd含量主相晶粒中Gd浓度的不同，经高温扩散后富Gd核主相晶粒富Gd核心和贫Gd壳层之间的Gd元素差值δH与磁体的总稀土含量R之间满足δH=(0.05~0.40)R。
实施例四：
将原材料按照一定比例配比后采用真空感应熔炼、甩带分别制备成分为Nd 32-xB 0.95Cu 0.1Ga 0.15Gd xZr 0.15Fe bal的高Gd含量SC片和成分为Nd 32B 0.95Cu 0.1Ga 0.15Zr 0.15Fe bal的不含Gd元素SC片，实验No.15~实验No.17中x的值分别为1、3和5。
将高Gd和不含Gd两种SC片按照1:1的重量比混合后通过氢破碎和气流磨制粉，合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1080℃，保温6h，制备烧结磁体。
烧结磁体加热到880℃保温15h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至505℃，保温5h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用NIM磁性能测试设备测试磁体的20℃常温磁性能和150℃的高温磁性能，并计算磁体温度系数。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
实验No.15~实验No.17磁体高Gd主相晶粒占比和富Gd核主相晶粒占比如表7所示。
表7
实验No. 15 16 17
高Gd含量主相晶粒占比(vol.%) 49.3 49.2 49.5
富Gd核主相体积比(vol.%) 0.3 1.2 25.3
由表7数据可知，实验No.15~实验No.17磁体的高Gd含量主相晶粒占比相同，但是经过高温扩散后富Gd核主相占比不同。富Gd核主相晶粒的形成主要是依靠高Gd含量主相晶粒与周围晶界富R相间较大的Gd浓度梯度来促进含Gd主相晶粒中的Gd元素向外扩散。当磁体高Gd含量主相晶粒中的Gd含量太低时，由于高Gd含量主相晶粒与晶界富R相中的Gd元素浓度差距较小，Gd元素向外扩散的驱动力较小，因此富Gd核主相晶粒的形成过程受阻，最终导致高温扩散磁体中富Gd核主相晶粒的占比减少。
实验No.15~实验No.17磁体在150℃的温度系数如表8所示。
表8
实验No. ∣α∣ (%/℃) ∣β∣ (%/℃)
15 0.16 0.51
16 0.15 0.50
17 0.1 0.46
由表8数据可知，实验No.15和实验No.16由于磁体的Gd含量较低以及富Gd核主相晶粒的占比较少，磁体在150℃的温度系数较大，因此磁体的高温磁性较差。
本发明采用双合金的方法分别熔炼高Gd含量和不含Gd的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体含Gd的主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。富Gd核主相晶粒的形成主要是依靠高Gd含量主相晶粒与周围晶界富R相间较大的Gd浓度梯度来促进含Gd主相晶粒中的Gd元素向外扩散。当磁体高Gd含量主相晶粒中的Gd含量太低时，由于高Gd含量主相晶粒与晶界富R相中的Gd元素浓度差距较小，Gd元素向外扩散的驱动力较小，因此富Gd核主相晶粒的形成过程受阻，最终导致高温扩散磁体中富Gd核主相晶粒的占比减少。因此在本发明中，高Gd含量合金片中Gd元素含量为5.0~34.0wt.%。
实施例五：
将原材料按照一定比例配比后采用真空感应熔炼、甩带分别制备成分为Nd 12B 0.95Cu 0.1Ga 0.15Gd 20Zr 0.15Fe bal的高Gd含量SC片和成分为Nd 12+xB 0.95Cu 0.1Ga 0.15Gd 20-xZr 0.15Fe bal的低Gd含量SC片，实验No.18~实验No.21中x的值分别为2、5、7和20。
将高Gd含量和低Gd含量两种SC片按照1:1的重量比混合后通过氢破碎和气流磨制粉，合金粉末经取向成型和等静压制备磁体生坯，然后在真空环境中将磁体加热至1080℃，保温6h，制备烧结磁体。
烧结磁体加热到880℃保温15h，进行高温扩散处理。保温结束冷却至200℃以下后再升温至505℃，保温5h，制得所述磁体。
采用喷砂工艺对最终磁体进行表面处理，使磁体露出新鲜表面。采用SEM观察磁体显微组织，并使用image J软件统计富Gd核主相晶粒占磁体主相晶粒体积比。采用ICP分析磁体成分，采用EPMA分析磁体微区成分。
实验No.18~实验No.21磁体的高Gd含量主相晶粒占比和富Gd核主相晶粒占比如表9所示。
表9
实验No. 18 19 20 21
高Gd含量主相晶粒占比(vol.%) 50.1 50.0 49.9 49.5
富Gd核主相体积比(vol.%) 0.1 50.6 51.2 49.5
由表9数据可知，实验No.18~实验No.21磁体的高Gd含量主相晶粒占比相同，但是经过高温扩散后富Gd核主相占比不同。富Gd核主相晶粒的形成主要是依靠高Gd含量主相晶粒与周围晶界富R相间存在较大的Gd浓度梯度，并通过促进高Gd含量主相晶粒中的Gd元素向外扩散形成的。实验No.18中，当磁体高Gd主相晶粒和低Gd主相晶粒的Gd浓度差太小时，高Gd主相晶粒中Gd元素向外扩散的驱动力较小，因此富Gd核主相晶粒的形成过程受阻，最终导致高温扩散后磁体中富Gd核主相晶粒占比减少。实验No.19和实验No.20中，由于高Gd含量主相晶粒和低Gd含量主相晶粒之间的Gd浓度差≥5.0wt.%，高Gd含量主相晶粒中的Gd元素向外扩散的驱动力较大，经高温扩散后高Gd含量主相晶粒全部转变为富Gd核主相晶粒，同时在实验No.19和实验No.20中部分低Gd含量主相晶粒也转变为富Gd核主相晶粒。
实验No.18~实验No.21磁体室温磁性和150℃磁性能、150℃剩磁温度系数α以及矫顽力温度系数β的绝对值如表10所示。
表10
实验No. Br(kGs) 20℃ Hcj(kOe) 20℃ Br(kGs) 150℃ Hcj(kOe) 150℃ ∣α∣(%/℃) ∣β∣(%/℃)
18 11.20 9.98 9.86 3.39 0.08 0.44
19 12.21 11.85 10.75 4.03 0.08 0.44
20 12.35 12.03 10.87 4.09 0.08 0.44
21 12.72 12.65 11.19 4.30 0.08 0.44
实验No.18中，磁体富Gd核主相晶粒的生成量较少，导致磁体的常温磁性能较差，此时虽然磁体也具有较低的温度系数，但温度系数的补偿作用无法弥补较低常温磁性能的影响，因此磁体的高温磁性能也会变差。实验No.19~实验No.20中，由于富Gd核主相晶粒较多，磁体的常温磁性能和高温磁性均较佳。同时对比实验No.19~实验No.21可知，随着高Gd含量主相晶粒和低Gd含量主相晶粒间的Gd浓度差增大，磁体的磁性能升高。
本发明采用双合金的方法分别熔炼高Gd含量和低Gd含量的两种合金片，然后制备混合粉末。经过取向成型、等静压和烧结制得烧结磁体。烧结磁体在高温扩散处理时由于高Gd含量主相晶粒与磁体晶界富R相间存在较大的Gd元素浓度差，在高温下Gd元素会从磁体主相晶粒向磁体晶界富R相中扩散。由于磁体稀土元素含量和扩散速率的影响，磁体含Gd的主相晶粒最终会形成具有贫Gd壳层和富Gd核心的反壳层结构。富Gd核主相晶粒的形成主要是依靠高Gd含量主相晶粒与周围晶界富R相间较大的Gd浓度梯度来促进高Gd含量主相晶粒中的Gd元素向外扩散。当磁体中高Gd含量主相晶粒与低Gd含量主相晶粒之间的Gd浓度差＜5.0wt.%时，由于高Gd含量主相晶粒中的Gd元素向外扩散过程受到抑制，富Gd核主相晶粒生成量较少，磁体的磁性能较差。因此在本发明中，为了保证高Gd含量主相晶粒顺利转变为富Gd核主相晶粒，高Gd含量主相晶粒与低Gd含量主相晶粒间Gd浓度差需要≥5.0wt.%。此外高Gd含量主相晶粒与低Gd主相晶粒间Gd浓度差异越大，磁体的磁性能越高。因此在本发明中，低Gd含量主相晶粒优选为不含Gd。

Claims (10)

  1. 一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述磁体中，稀土元素R含量为29.0wt.%~34.0wt.%，R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；
    所述磁体包含主相R 2T 14B和晶界富R相，并且主相晶粒中包含体积比20vol.%~80vol.%的富Gd核主相晶粒，所述富Gd核主相晶粒由富Gd的核心和贫Gd的壳层组成，核心Gd含量H1(wt.%)和壳层Gd含量H2(wt.%)的差值δH=H1-H2，δH与磁体中稀土元素总含量R满足δH=(0.05~0.40)R。
  2. 如权利要求1所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体的磁体成分包含：
    R：29.0wt.%~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所述R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；R1为R3或者由R2与R3组成；R3为Nd、Pr、Ho、La、Ce中的至少一种；
    R2为稀土元素Dy和Tb中的至少一种，所述磁体包含R2时，R2含量为磁体质量的0.1wt.%~2.0wt.%，磁体的富Gd核主相晶粒的贫Gd壳层中包含0.05wt.%~0.5wt.%的R2元素；
    所述M为Al、Cu、Ga、Zr、Ti、Nb、Zn、Sn、W、Mo、Hf、Au和Ag中的至少一种。
  3. 如权利要求2所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体按照以下方法之一制备：
    方法（一）：磁体中不含R2元素时：
    将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
    所述高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
    方法（二）：磁体中含有R2元素时：
    将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，所述原料中均不含R2元素，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，所得基体磁体加工成厚度为0.5~10.0mm的磁片，表面处理后在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，然后进行晶界扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；所述重稀土元素扩散层为Dy、Tb中的任意一种或两种。
  4. 如权利要求3所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述高Gd含量SC片与低Gd含量SC片的Gd含量差别≥5.0wt.%，高Gd含量SC片中的Gd含量为5.0~34.0wt.%。
  5. 如权利要求3所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述高Gd含量合金原料中各组分的成分为：
    R3：0~29wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种；Gd：5.0~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所述低Gd含量合金原料中各组分的成分为：
    R3：5~34wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种，优选R3的75wt.%以上为Nd;
    Gd：0~X wt.%，且高Gd含量合金原料的Gd含量-X≥5.0wt.%；B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所述高Gd含量合金原料和低Gd含量合金原料的质量比要保证混合后最终磁体中的Gd元素含量为1.0wt.%~20.0wt.%。
  6. 如权利要求4或5所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述低Gd含量SC片中的Gd含量为0。
  7. 如权利要求3所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述高Gd含量SC片和低Gd含量SC片制备得到合金粉末，是将高Gd含量SC片和低Gd含量SC片混合后，通过氢破碎和气流磨制备合金粉末，或者将高Gd含量SC片和低Gd含量SC片分别经过氢破碎后混合、再通过气流磨制备合金粉末，或者将高Gd含量SC片和低Gd含量SC片分别经过氢破碎、气流磨后，再将所得粉末混合制备合金粉末。
  8. 如权利要求3所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述方法（一）或方法（二）中，高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h；
    所述方法（二）中，所述晶界扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束后，冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体。
  9. 如权利要求3所述的高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体，其特征在于所述方法（二）中，在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，在磁体垂直于取向方向的表面沉积覆盖重稀土元素扩散层，在磁体不垂直于取向方向的表面不覆盖重稀土元素扩散层。
  10. 一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体的制备方法，其特征在于所述方法为以下之一：
    方法（一）：磁体中不含R2元素时
    将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
    所述高温扩散处理的扩散温度为800~1000℃，保温时间为5~25h，保温结束冷却至200℃以下后再升温至400~650℃，保温2~10h，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
    方法（二）：磁体中含有R2元素时：
    将按照成分配比的高Gd含量合金原料和低Gd含量合金原料，所述原料中均不含R2元素，通过真空感应熔炼和甩带分别制备高Gd含量SC片和低Gd含量SC片，高Gd含量SC片和低Gd含量SC片制备得到合金粉末，合金粉末经取向磁场进行模压成型、等静压制备磁体压坯，真空烧结后进行高温扩散处理，所得基体磁体加工成厚度为0.5~10.0mm的磁片，表面处理后在磁片表面沉积厚度为3~100μm的重稀土元素扩散层，然后进行晶界扩散处理，制得所述高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体；
    所述重稀土元素扩散层为Dy、Tb中的任意一种或两种；
    所述高Gd含量合金原料中各组分的成分为：
    R3：0~29wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种；Gd：5.0~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所述低Gd含量合金原料中各组分的成分为：
    R3：5~34wt.%，R3为Nd、Pr、Ho、La、Ce中的一种或多种，优选R3的75wt.%以上为Nd;Gd：0~X wt.%，且高Gd含量合金原料的Gd含量-X≥5.0wt.%；B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所得到的磁体成分为：
    R：29.0wt.%~34.0wt.%;B：0.9wt.%~1.1wt.%;M：0.1wt.%~10.0wt.%;余量为T以及其他不可避免杂质，其中T为Fe或Fe和Co，T中含有Co时，T的75.0wt.%以上为Fe；
    所述R由Gd和R1组成，Gd元素含量为磁体质量的1.0wt.%~20.0wt.%，R的余量为R1；R1为R3或者由R2与R3组成；R3为Nd、Pr、Ho、La、Ce中的至少一种；
    R2为稀土元素Dy和Tb中的至少一种，所述磁体包含R2时，R2含量为磁体质量的0.1wt.%~2.0wt.%，磁体的富Gd核主相晶粒的贫Gd壳层中包含0.05wt.%~0.5wt.%的R2元素；
    所述M为Al、Cu、Ga、Zr、Ti、Nb、Zn、Sn、W、Mo、Hf、Au和Ag中的至少一种；
    所述磁体包含主相R 2T 14B和晶界富R相，并且主相晶粒中包含体积比20vol.%~80vol.%的富Gd核主相晶粒，所述富Gd核主相晶粒由富Gd的核心和贫Gd的壳层组成，核心Gd含量H1(wt.%)和壳层Gd含量H2(wt.%)的差值δH=H1-H2，δH与磁体中稀土元素总含量R满足δH=(0.05~0.40)R。
PCT/CN2023/096203 2022-10-14 2023-05-25 一种高温环境用具有富Gd核的核壳结构R-T-B稀土永磁体及其制备方法 WO2024077966A1 (zh)

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