CN113270241B - Neodymium-iron-boron magnet and preparation method thereof - Google Patents
Neodymium-iron-boron magnet and preparation method thereof Download PDFInfo
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Abstract
A neodymium-iron-boron magnet and a preparation method thereof are provided, wherein neodymium-iron-boron crystal grains on the surface layer of the neodymium-iron-boron magnet have Dy-Tb double-layer core-shell structure neodymium-iron-boron. The sintered NdFeB magnet with Dy-Tb double-layer core-shell structure of the NdFeB crystal grains on the surface layer is obtained by a method that a matrix with Dy core-shell structure is placed in a Tb-containing substance to be heated and diffused so that Tb is diffused into the surface of the magnet. The NdFeB magnet prepared by the invention has the advantages of small quantity of added medium and heavy rare earth Dy and Tb, high coercive force and maximum magnetic energy product, good thermal stability and other excellent magnetic properties.
Description
Technical Field
The invention relates to the technical field of magnet material preparation, in particular to a neodymium-iron-boron magnet and a preparation method thereof.
Background
The sintered Nd-Fe-B magnet has excellent magnetic energy density and is widely applied to the fields of wind power generation, rail transit, new energy automobiles and the like. However, the coercive force is low, the thermal stability is poor, so that the thermal demagnetization phenomenon occurs in the high-temperature working process, and the application of the high-temperature magnetic material in the high-temperature field is limited.
Chinese patent application publication No. CN109859921a, publication No. 2019.06.07 discloses a "method for preparing an R-Fe-B type magnet", in which "a) a substance a and an R1-Fe-B-M sample are mixed and then subjected to diffusion treatment; the substance A is at least one of dysprosium compound and terbium compound; b) Carrying out hydrogen crushing treatment on the crude product after diffusion treatment, and carrying out air flow grinding on the obtained crude product; c) The R-Fe-B type magnet is obtained by molding and sintering the fine powder after air flow grinding, and the technical scheme of the R-Fe-B type magnet is obtained, so that the prepared magnet has the technical effect of obviously improving the coercive force of the magnet by using a small amount of heavy rare earth Dy or Tb on the premise of basically keeping the residual magnetism and the maximum magnetic energy product of the sintered magnet.
Chinese patent application publication No. CN1 10148507a, publication No. 2019.08.20 discloses a grain boundary diffusion cerium magnet containing a REFe2 phase and a method for preparing the same, in which "RE" element in rare earth diffusion source is diffused into the original cerium magnet through grain boundary diffusion treatment, and the diffusion treatment temperature is the melting point temperature of the REFe2 phase; then directly cooling or tempering and cooling to room temperature to obtain the final cerium magnet; the final cerium magnet contains a new 2-14-1 main phase, a new reinforced REFe2 phase and a new rare earth-rich phase, the new 2-14-1 main phase is (Ce, RE ') 2Fe14B or (Ce, RE ') 2Fe14B major phase, the new enhanced REFe2 phase is the (CERE ") Fe2 phase or the (Ce, RE ', RE") Fe2 phase; RE 'is one or more of La, pr, nd, pm, eu, gd, tb, dy, ho, er, tm, yb, lu and Y, and the melting point temperature of REFe2 phase is selected as the grain boundary diffusion treatment temperature, so that the technical scheme of improving the diffusion efficiency of RE' element in a diffusion source is achieved, and the technical effect of greatly improving the coercivity of cerium magnet is achieved.
The Chinese patent application publication No. CN1109509605A, publication No. 2019, no. 03 and No. 22 discloses a multi-layer rare earth permanent magnet and a preparation method thereof, wherein the rare earth permanent magnet consists of three layers of main phase grains and rare earth-rich phases, the rare main phase grains are divided into three layers of a nucleation layer, a middle layer and a shell layer according to different chemical components, and the compositions of the components respectively correspond to R 1 -T-B、R 2 -T-B and R 3 -T-B, wherein R 1 Comprises at least one of Ce and La, R 2 Comprises at least one of Pr and Nd, R 3 Comprises at least one of Dy, tb and Ho, T is at least one of Fe and Co, and B is boron. The rare earth-rich phase comprises one or more rare earth elements of Ce, la, pr, nd, dy, tb, ho, gd. The invention utilizes a double-alloy process to prepare a magnet blank, and then prepares the technical scheme of the multi-layer structure rare earth permanent magnet through a grain boundary diffusion process, so that the rare earth permanent magnet of the invention has a three-layer layered structure, the main rare earth components of the crystal grain are light rare earth, medium heavy rare earth and heavy rare earth in sequence from inside to outside, the structure is optimized, and the technical effect of the magnet coercivity is obviously improved.
However, the method is a core-shell structure of a formed Dy/Tb single layer, the efficiency of Tb and Dy is not high, particularly, in order to reduce the cost in industrial production, high-performance magnets are obtained at the same time, dy or Tb is singly diffused, dy or Tb elements are added in the process of preparing alloys, and the coercivity and the heavy rare earth utilization rate of the magnets can not be improved to the maximum extent.
Inventive creation of the invention
In order to overcome the defects in the prior art, the invention provides a method for preparing a neodymium-iron-boron magnet, which adopts the following technical scheme:
the preparation method of the neodymium-iron-boron magnet comprises the steps that neodymium-iron-boron crystal grains on the surface layer of the neodymium-iron-boron magnet are provided with an inner core shell and an outer core shell, the outer core shell is positioned on the outermost layer and/or between the neodymium-iron-boron crystal grains, the inner core shell is positioned in the outer core shell, the inner core shell contains a first rare earth element, the outer core shell contains a second rare earth element, the first element and the second element are at least one of Dy, tb, ho, gd elements, the first rare earth element is different from the second rare earth element, and the neodymium-iron-boron crystal grains do not contain La or Ce, sm, eu, gd, er, tm, yb, lu, Y elements, and the preparation method comprises the following steps:
placing a substrate in a substance containing a second rare earth element, or attaching the substance containing the second rare earth element on the surface of the substrate to obtain an intermediate;
step two, the intermediate is placed in a sintering furnace for diffusion, and a second rare earth element enters a neodymium-iron-boron crystal grain and/or a crystal boundary between the neodymium-iron-boron crystal grains to obtain a neodymium-iron-boron magnet with a neodymium-iron-boron crystal grain surface layer having an inner core shell and an outer core shell structure;
the core-shell structure of the first rare earth element contained in the outermost layer of the neodymium-iron-boron crystal grain of the matrix becomes the inner core shell of the neodymium-iron-boron crystal grain on the surface layer of the neodymium-iron-boron magnet and becomes the basis of the outer core shell. The neodymium-iron-boron magnet with the surface layer and the neodymium-iron-boron crystal grain having the inner core shell and the outer core shell structure can be also called as a diffusion magnet.
According to one of the preferred technical schemes of the preparation method of the neodymium iron boron magnet, the preparation method further comprises the following steps of preparing a matrix:
mixing neodymium iron boron main alloy powder A which does not contain a first rare earth element with auxiliary alloy powder B which contains a first element but does not contain a second rare earth element according to a proportion, and sintering to obtain a matrix containing an inner core shell structure.
According to the preparation method of the neodymium-iron-boron magnet, according to the further preferable technical scheme, the neodymium-iron-boron main alloy powder A does not contain a second rare earth element.
According to the preparation method of the neodymium-iron-boron magnet, according to a further preferred technical scheme, the neodymium-iron-boron main alloy powder is T x Fe bal B y Co z M w (wt.%, t=at least one of Pr, nd, m= Nb, al, cu, zr, ga, supra). More preferably, the neodymium iron boron main alloy powder is (PrNd) 30.5 Fe 67.74 B 0.98 Co 0.6 Al 0.08 Cu 0.1 。
According to the preparation method of the neodymium-iron-boron magnet, according to a further preferable technical scheme, the neodymium-iron-boron auxiliary alloy powder is T n Dy b Fe bal B c Co d M e . More preferably, the neodymium-iron-boron auxiliary alloy powder is (PrNd) 25.5 Dy 6.5 Fe 65.09 B 0.96 Co 1.5 Al 0.3 Cu 0. 15 。
According to the preparation method of the neodymium-iron-boron magnet, according to the further preferred technical scheme, the sum (BH) of the magnetic energy product and the coercive force of the neodymium-iron-boron magnet max (MGOe)+H cj (kOe)≥65。
According to another preferred technical scheme of the preparation method of the neodymium-iron-boron magnet, the first step of attaching the substance containing the second rare earth element on the surface of the substrate is at least one of coating a compound and/or metal Tb powder of the second rare earth element on the surface of the substrate and sputtering the metal of the second rare earth element.
According to the preparation method of the neodymium-iron-boron magnet, in a further preferable technical scheme, the first rare earth element and the second rare earth element are Dy or Tb elements respectively.
According to the preparation method of the neodymium-iron-boron magnet, in a further preferable technical scheme, the first rare earth element is Dy, and the second rare earth element is Tb.
The invention relates to a preparation method of a neodymium-iron-boron magnet, which adopts a preferable technical scheme that the Tb compound is terbium hydride, terbium copper hydride or Tb 70 Cu 20 Ga 10 At least one of them.
According to another preferable technical scheme of the preparation method of the neodymium iron boron magnet, the diffusion temperature is 850-930 ℃, and the diffusion time is 4-16 h.
According to the preparation method of the neodymium iron boron magnet, in a further preferable technical scheme, the diffusion temperature is 890 ℃, and the diffusion time is 10 hours.
According to another preferable technical scheme of the preparation method of the neodymium iron boron magnet, a tempering step is further included after diffusion.
According to the preparation method of the neodymium iron boron magnet, a preferable technical scheme is adopted, and the tempering step is carried out at the temperature of 490 ℃ for 3 hours.
The invention also provides a neodymium-iron-boron magnet, wherein neodymium-iron-boron crystal grains on the surface layer of the neodymium-iron-boron magnet are provided with an inner core shell and an outer core shell structure, the outer core shell is positioned on the outermost layer of the neodymium-iron-boron crystal grains, the inner core shell is positioned in the outer core shell, the inner core shell contains a first rare earth element, the outer core shell contains a second rare earth element, the first element and the second element are at least one of Dy, tb, ho, gd elements, and the first rare earth element contained in the inner core shell is different from the second rare earth element contained in the outer core shell.
According to one of the preferred technical schemes of the neodymium-iron-boron magnet, the neodymium-iron-boron magnet is prepared by adopting the preparation method of the neodymium-iron-boron magnet.
According to the another preferable technical scheme of the neodymium-iron-boron magnet, the first rare earth element and the second rare earth element are Dy or Tb elements respectively.
According to the neodymium-iron-boron magnet, in a further preferable technical scheme, the second rare earth element is Tb element, and the first rare earth element is Dy element.
According to the another preferable technical scheme of the neodymium-iron-boron magnet, the neodymium-iron-boron magnet does not contain La and/or Ce, sm, eu, gd, er, tm, yb, lu, Y elements.
According to the another preferable technical scheme of the neodymium-iron-boron magnet, the thickness of the surface layer of the neodymium-iron-boron magnet with the inner core shell and the outer core shell is less than or equal to 500 mu m. Further, the thickness of the surface layer of the NdFeB magnet is less than or equal to 150 mu m. Still further, the thickness of the surface layer of the NdFeB magnet is 100-150 mu m. Further, the thickness of the surface layer of the NdFeB magnet is less than or equal to 20 mu m. Optimally, the thickness of the surface layer of the NdFeB magnet is less than or equal to 15 mu m.
According to the another preferable technical scheme of the neodymium-iron-boron magnet, the sum (BH) of the magnetic energy product and the coercive force of the neodymium-iron-boron magnet max (MGOe)+H cj (kOe)≥65。
According to the neodymium-iron-boron magnet, according to the further preferable technical scheme, the coercivity is improved by more than or equal to 10%. More preferably, the coercivity is improved by more than or equal to 15 percent. Optimally, the coercivity is improved by more than or equal to 30 percent.
According to a further preferred technical scheme of the neodymium-iron-boron magnet, the coercive force H cj The lifting rate is more than or equal to 1.7kOe. Preferably, the coercivity is increased by more than or equal to 2.6kOe. More preferably, the coercivity is improved by more than or equal to 3.5kOe. Optimally, the coercivity is improved by more than or equal to 7kOe.
According to a further preferred technical scheme of the neodymium-iron-boron magnet, the magnetic energy product (MGOe) and the coercive force H of the neodymium-iron-boron magnet cj The sum of (kOe) is not less than 65.
Compared with the prior art, the invention has the beneficial effects that:
the matrix containing the inner core-shell structure is prepared by adopting a double-alloy method, and a small amount of second rare earth element Tb is diffused in the grain boundary of the surface layer of the matrix, so that the sintered NdFeB magnet with the double-layer core-shell structure is formed, and the coercive force and the thermal stability are greatly improved. H cj Up to 24.97kOe. While the residual magnetism and magnetic energy product are little or no reduced, (BH) max Up to 47.52MGOe. And H is cj +(BH) max And the magnetic performance of the diffusion magnet is obviously improved and is more than or equal to 65 (up to more than 70).
The microstructure of the diffusion magnet is obviously better than that of a matrix, no large neodymium-rich phase agglomeration exists, the grain boundary is more continuous, and the second rare earth Tb enters the outer edge layer of the main phase to form high H A Is (NdDyTb) 2 Fe 14 B and other core-shell structures, which are wrapped by NdDy 2 Fe 14 B, etc., the content of the second rare earth element Tb, etc., gradually decreases as the diffusion depth increases.
The coercive force temperature coefficient of the diffusion magnet at 20-200 ℃ is superior to that of the matrix, and the thermal stability of the sintered Nd-Fe-B magnet is obviously improved after Tb is diffused.
The magnetocrystalline anisotropic field is further improved, the exchange coupling effect among the grains is effectively isolated, and the coercive force and the magnetic energy product are further improved.
Drawings
FIG. 1 is a graph of demagnetizing a 4h diffusion magnet and a substrate according to an embodiment.
Fig. 2 is a graph of demagnetization of a diffusion magnet over 6h for an embodiment.
Fig. 3 is a graph of the demagnetization of an 8h diffusion magnet for an embodiment.
FIG. 4 is a graph of the demagnetization of a diffusion magnet over 10h and 16h for an embodiment.
FIG. 5 is a microscopic topography and elemental distribution of a substrate according to an embodiment. Wherein a is an initial topography map, b is an Nd element distribution map, c is a Fe element distribution map, and d is a Dy element distribution map.
FIG. 6 is a microscopic topography and elemental distribution of a 10h diffusion magnet of an embodiment. Where a is the initial morphology, b is the Nd element distribution map, c is the Dy element distribution map, and d is the Tb element distribution map.
FIG. 7 is a scan of an electron probe with a diffusion depth of 0-150 μm for a substrate and a 10h diffusion magnet according to an embodiment. Wherein a is the initial appearance of the matrix, b is the Nd element scanning pattern of the diffusion magnet, c is the Dy element scanning pattern of the diffusion magnet, d is the Tb element scanning pattern of the diffusion magnet, and e is the O element scanning pattern.
FIG. 8 is a graph of thermal stability over a range of 20-200℃for a substrate and 10h diffusion magnet of example one. Wherein a is a graph of coercive force versus temperature, and b is a graph of remanence versus temperature.
FIG. 9 is a graph of demagnetizing the diffusion magnets for the second substrate and different diffusion times. Wherein the diffusion time of a is 2h, the diffusion time of b is 4h and 6h, and the diffusion time of c is 8h and 10h.
FIG. 10 is a graph of demagnetization of a diffusion magnet for a three-substrate and different diffusion times of an embodiment. Wherein the diffusion time of a is 4h, the diffusion time of b is 6h and 8h, and the diffusion time of c is 10h and 116h.
Detailed Description
Example 1
See fig. 1-8.
Selecting pure terbium (99.9%) and placing the pure terbium into a hydrogen crushing furnace, preserving the heat for 3 hours at the temperature of 300 ℃ under the pressure of 0.1MPa for hydrogenation treatment, and then obtaining terbium hydride fine powder with the particle size smaller than 5 mu m through ball milling.
The matrix is prepared by adopting a double alloy method: mixing the main alloy powder A and the auxiliary alloy powder B=3:1, smelting and quick setting to obtain an alloy cast sheet; performing hydrogen blasting crushing on the alloy cast sheet, and performing air flow grinding to obtain magnetic powder with the average granularity of about 3 mu m; the obtained magnetic powder is oriented and molded in an externally added 2T magnetic field, and is further densified by 200MPa isostatic pressing to obtain a green body, the green body is sintered for 4 hours at 1050-1070 ℃, tempered for 2 hours at about 890 ℃ and tempered for 3 hours at 490 ℃ to obtain a sintered NdFeB magnet, and then the sintered NdFeB magnet is cut into the size by a wire cutting method
A cylinder of mm; and (3) obtaining a magnet with a Dy-containing core-shell structure, and performing polishing, degreasing and pickling pretreatment to obtain a matrix (or called as the original shape, and the same applies below). The components of the main alloy powder A and the auxiliary alloy powder B are shown in the table II in detail.
The substrate was placed in terbium hydride absolute ethanol suspension for coating. Then diffusion treatment is carried out in a high vacuum sintering furnace at 890 ℃ and different diffusion times, and tempering is carried out for 3 hours at 490 ℃ to obtain the neodymium-iron-boron magnet (hereinafter referred to as diffusion magnet and the same hereinafter) with the structure that the surface layer neodymium-iron-boron crystal grain has Dy inner core shell and Tb outer core shell (Dy-Tb double-layer core shell).
The magnetic properties of the matrix and the diffusion magnet are tested by adopting a NIM-500C high-temperature permanent magnet measuring instrument; observing the microstructure of the magnet by adopting an MLA650 field emission scanning electron microscope; the distribution of the components in the micro domain of the magnet was analyzed by using an electron probe (Japanese electron JXA-8530F type). The magnetic properties of the resulting magnets at different diffusion times are detailed in table one and fig. 1-7.
The composition of the matrix and the diffusion magnet is shown in Table II. Wherein the composition of each diffusion magnet is substantially the same.
As can be seen from the first table, the coercivity Hcj of the diffusion magnet is obviously improved, and the remanence and the maximum magnetic energy product (BH) max Basically unchanged, the maximum magnetic energy product is even slightly improved. From Table 1 and FIGS. 1 to 4Compared with the matrix, the maximum coercivity of the diffusion magnet reaches 24.97kOe after 10 hours of diffusion, and the coercivity improvement rate reaches 43.75%; after diffusion for 6 hours, the maximum value of the magnetic energy product of the diffusion magnet reaches 47.07MGOe.
List one
Exterior two (Unit: wt.)
| Name of the name | PrNd | Co | Al | Cu | Fe | B | Dy | Tb |
| Main alloy powder A | 30.5 | 0.6 | 0.08 | 0.1 | 67.74 | 0.98 | ||
| Auxiliary alloy powder B | 25.5 | 1.5 | 0.3 | 0.15 | 65.09 | 0.96 | 6.5 | |
| Matrix body | 29.25 | 0.82 | 0.14 | 0.11 | 67.08 | 0.98 | 1.62 | |
| 10h diffusion magnet | 29.08 | 0.82 | 0.14 | 0.11 | 66.68 | 0.97 | 1.61 | 0.59 |
From fig. 5, it can be seen that the distribution of Nd, fe and Dy in the matrix, and after the mixed powder of the neodymium-iron-boron main alloy powder a containing no first rare earth element and no second rare earth element and the auxiliary alloy powder B containing Dy as the first element is sintered, the Dy element in the auxiliary alloy powder B diffuses into the main alloy powder a, and is distributed in the grain epitaxial layer to form a core-shell structure layer containing Dy. Namely (PrNdDy) 2 Fe 14 B core-shell coating (PrNd) 2 Fe 14 B core-shell structure.
From fig. 6, it can be seen that the distribution of Nd, dy and Tb in the matrix, and that after terbium hydride diffusion in the matrix, tb enters the sintered neodymium-iron-boron magnet along the grain boundary, and a double-layer Dy-Tb core-shell structure is formed on the basis of forming a Dy-containing core-shell by the grain epitaxial layer. The epitaxial layer of the crystal grain is in a double-layer core-shell structure, the outer layer is mainly in a Tb core-shell structure (about 11 mu m), the range of surrounding crystal grains is larger, and the inner layer is in a Dy core-shell structure (about 7.8 mu m). The reason for forming the double-layer core-shell structure is that Tb element diffused in the grain boundary is substituted for Nd element in Dy core-shell structure in the crystal grain to form new (PrNdDyTb) 2 Fe 14 B core-shell structure of the compound (PrNdDy) 2 Fe 14 And B a core-shell structure. The magnetocrystalline anisotropy field of the magnet is further improved, nucleation and growth of the reverse magnetization domain are effectively restrained, and the coercive force of the magnet is maximally improved. Wherein Tb wraps Nd and Dy. Such as (red) circle marks.
The distribution of the elements in the diffusion magnet can be seen from fig. 7. Wherein Nd element and Dy element are uniformly distributed in the display range (0-150 μm); the Tb elements are distributed at 0-150 mu m from the surface, wherein the Tb elements are densely distributed in the range of 0-15 mu m, are thinner and thinner along with the distance from the surface, and are only sporadically distributed in the range of 130-150 mu m. It can be seen that, after diffusion, the second rare earth element Tb is mainly distributed in the surface layer at the near surface of the diffusion magnet.
As is clear from fig. 8, in the temperature range of 20 to 200 ℃, both the coercive force and the remanence of the matrix and the diffusion magnet decrease with an increase in temperature, but in this temperature range, the coercive force of the diffusion magnet is always higher than that of the matrix. Indicating diffusion of TbH 2 The thermal stability of the sintered Nd-Fe-B magnet is improved.
In summary, in this embodiment, a dual-alloy method is used to prepare a core-shell structure matrix containing Dy, and then TbH is diffused in the grain boundary 2 And preparing the sintered neodymium-iron-boron magnet with the Dy-Tb double-layer core-shell structure. The coercive force is maximally improved from 17.37kOe to 24.97kOe, and the thermal stability of the magnet is improved.
In this embodiment, terbium hydride is coated on the surface of the substrate, and the terbium hydride is decomposed into terbium and hydrogen before reaching the diffusion temperature, so that the method can be changed into a method of coating terbium powder or sputtering metal Tb on the surface of the substrate, or wrapping the substrate with a metal Tb sheet, placing the substrate in the metal Tb, and the like. Wherein, the Tb metal is sputtered on the matrix to lead the terbium to tightly wrap the matrix, and the effect and the efficiency are better.
Example two
See fig. 9.
The surface of the substrate of example one was coated with terbium copper hydrogen powder (Tb 70 Cu 30 H) And (3) placing the magnet into a vacuum sintering furnace to be diffused at 810 ℃ and different diffusion times respectively, and tempering the magnet for 3 hours at 490 ℃ to obtain the diffused magnet.
The magnetic properties of the diffusion magnet after Tb-Cu-H diffusion at different diffusion times are shown in Table III.
Watch III
As can be seen from FIG. 8 and Table III, H cj Are all obviously increased, (BH) max There is an increase in both. Squareness H of 10H diffusion magnet k /H cj Slightly better than the matrix.
The components of each diffusion magnet of this example are substantially identical, as detailed in table four.
| Name of the name | PrNd | Co | Al | Cu | Fe | B | Dy | Tb |
| Matrix body | 29.25 | 0.82 | 0.14 | 0.11 | 67.08 | 0.98 | 1.62 | |
| 10h diffusion magnet | 29.04 | 0.81 | 0.14 | 0.33 | 66.60 | 0.97 | 1.61 | 0.50 |
Example III
See fig. 10.
The substrate surface of example one was coated with TbCuGaH powder (Tb 70 Cu 20 Ga 10 H) The mixture was placed in a vacuum sintering furnace to perform diffusion at a diffusion temperature of 830℃for various times, and tempered at 490℃for 3 hours.
The magnetic properties of the diffusion magnets obtained with different diffusion times are detailed in table five.
TABLE five
As can be seen from table five and fig. 8, the coercivity of the TbCuGaH diffusion magnet is obviously improved; the coercivity had a maximum of 23.03kOe when diffused at 830℃for 10h. The residual magnetism was reduced less than that of the matrix, and the maximum reduction value was 0.2kGs. The maximum magnetic energy product is improved to different degrees, and the maximum value is 47.79MGOe.
The components of each diffusion magnet of this example are substantially identical, as detailed in Table six.
TABLE six
| Name of the name | PrNd | Co | Al | Cu | Fe | B | Dy | Tb | Ga |
| Matrix body | 29.25 | 0.82 | 0.14 | 0.11 | 67.08 | 0.98 | 1.62 | ||
| 10h diffusion magnet | 29.02 | 0.81 | 0.14 | 0.27 | 66.55 | 0.97 | 1.61 | 0.55 | 0.08 |
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered by the scope of the claims of the present invention.
Claims (8)
1. The preparation method of the neodymium-iron-boron magnet is characterized by comprising the following steps of:
mixing and sintering Dy-free neodymium-iron-boron main alloy powder A and Dy-containing neodymium-iron-boron auxiliary alloy powder B in proportion to obtain a Dy-containing core-shell structure matrix;
placing a matrix in a Tb-containing substance to obtain an intermediate; the method comprises the steps of placing a substrate in a material containing Tb, coating the surface of the substrate with at least one of Tb compound or metal Tb powder, and sputtering the metal Tb, wherein the Tb compound is terbium hydride, terbium copper hydride or Tb 70 Cu 20 Ga 10 At least one of (a) and (b);
and placing the intermediate in a sintering furnace for Tb diffusion to obtain a sintered NdFeB magnet with a Dy-Tb double-layer core-shell structure, wherein the NdFeB magnet does not contain La and/or Ce, sm, eu, gd, er, tm, yb, lu, Y elements.
2. The method of claim 1, wherein neodymium-iron-boron grains on the surface layer of the neodymium-iron-boron magnet have a Dy-Tb double-layer core-shell structure, a Dy core-shell is located inside the Tb core-shell in the Dy-Tb double-layer core-shell structure, and the thickness of the surface layer of the neodymium-iron-boron magnet is less than or equal to 150 μm.
3. The method according to claim 2, wherein the thickness of the surface layer of the NdFeB magnet is less than or equal to 20 μm.
4. The method according to claim 2, wherein the thickness of the surface layer of the NdFeB magnet is less than or equal to 15 μm.
5. The method of claim 1, wherein the diffusion temperature is 850-930 ℃ and the diffusion time is 4-16 h.
6. The method of claim 1, further comprising a tempering step after the diffusing.
7. The method of claim 6, wherein the tempering step is performed at a temperature of 490 ℃ for a period of 3 hours.
8. The method of claim 1, wherein the increase in magnetic energy product of the neodymium-iron-boron magnet is greater than or equal to 0.29MGOe.
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| CN107256795A (en) * | 2017-06-27 | 2017-10-17 | 北京科技大学 | The method that performance Nd Fe B sintered magnet is prepared using two step grain boundary diffusion process |
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