High-performance r-t-b rare earth permanent magnet based on vapor deposition diffusion of composite diffusion source and preparation method therefor

Abstract

Disclosed in the present invention are a high-performance R-T-B rare earth permanent magnet based on vapor deposition diffusion of a composite diffusion source and a preparation method therefor. The preparation method comprises: using Dy and Ga elements having similar saturated vapor pressures as main components of a diffusion source to prepare a composite diffusion source; subjecting same to vapor deposition diffusion, so that the Ga element and the rare earth element R form an R-Ga phase to isolate the main phase grains, optimize the diffusion channels, and improve the grain boundary diffusion effect; adjusting the alloy composition by adding a certain amount of a high-melting-point metal element M2 to the magnet, so that the main phase grains on the surface of the magnet are pinned by virtue of the characteristics that M2 has high wettability with R-Ga phases and is easily distributed in the R-Ga phase, the rotation of the main phase grains on the surface of the magnet in the process of grain boundary diffusion is inhibited, and the remanence of the magnet after diffusion is improved, so as to prepare the high-performance R-T-B rare earth permanent magnet. Moreover, the volatilization rates of the two elements of the composite diffusion source in the present invention are substantially consistent, which can ensure the stability of the diffusion source during long-term use, thereby improving the consistency of the performance of a diffusion product.

Description

A high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion and its preparation method Technical Field

[0001] This invention relates to a high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion and its preparation method. Background Technology

[0002] Rare-earth permanent magnets (RTBs) are permanent magnet materials with excellent magnetic properties, possessing the highest energy product compared to other permanent magnet materials, and are widely used in modern industry. The high energy product of RTBs effectively enables the miniaturization of equipment, thus gradually replacing other permanent magnet materials in the field of electric motors. Grain boundary diffusion, a new technology developed in recent years, can significantly improve the coercivity of magnets while maintaining high remanence, and is a common method for preparing high-performance RTBs.

[0003] Traditional grain boundary diffusion treatment first coats the magnet surface with a diffusion source layer containing heavy rare earth elements, then heats it to a specified temperature and holds it for a period of time. During the high-temperature stage, the heavy rare earth elements in the diffusion source on the magnet surface diffuse along the R-rich phase at the grain boundaries into the magnet's interior, forming a shell with a highly anisotropic field on the surface of the main phase grains, thereby improving the magnet's coercivity. However, because the diffusion source is directly coated on the magnet surface, the heavy rare earth element content on the surface is relatively high. Simultaneously with the diffusion at the grain boundaries, bulk diffusion of these heavy rare earth elements also occurs, leading to a decrease in the magnet's remanence. Furthermore, since bulk diffusion on the magnet surface consumes a significant amount of heavy rare earth elements, the final increase in the magnet's coercivity will also be reduced.

[0004] Vapor deposition diffusion is an improved method based on traditional grain boundary diffusion. It can significantly suppress bulk diffusion, thereby reducing the decrease in Br content of the magnet after diffusion. Unlike traditional diffusion sources that are directly coated onto the magnet surface, vapor deposition diffusion does not involve direct contact between the diffusion source and the magnet; instead, a certain gap is maintained. When heated to a high temperature, heavy rare earth atoms in the diffusion source volatilize to the magnet surface and then diffuse into the magnet interior via grain boundary diffusion. By controlling the volatilization rate of heavy rare earth atoms to the magnet surface, a large accumulation of diffusion source on the magnet surface can be avoided, thus suppressing bulk diffusion. Therefore, with the same coercivity increment, vapor deposition diffusion results in a smaller decrease in Br content and a higher utilization rate of heavy rare earth elements.

[0005] Recent studies have shown that adding low-melting-point metal elements to the diffusion source to prepare a composite diffusion source can further improve grain boundary diffusion and reduce material costs. During the vapor deposition diffusion process, low-melting-point metal elements volatilize to the magnet surface along with heavy rare earth elements and diffuse into the magnet interior through grain boundaries. Low-melting-point metal elements can lower the melting point of the grain boundary phase, optimize diffusion channels, promote the diffusion rate of heavy rare earth elements into the magnet interior, and improve the diffusion effect. Compared to directly adding low-melting-point metal elements to the magnet matrix, adding low-melting-point metal elements to the diffusion source has a smaller impact on the remanence of the magnet. Therefore, using a composite diffusion source with low-melting-point metal elements for vapor deposition diffusion can prepare higher-performance RTB rare earth permanent magnets.

[0006] Engineering practice has shown that the vapor deposition diffusion process using low-melting-point metal element composite diffusion sources still faces several challenges. Firstly, the number of times a low-melting-point metal element composite diffusion source can be reused is limited, and the performance stability of the diffused product is poor. The main principle of vapor deposition diffusion is that, under certain temperature and vacuum conditions, atoms from the diffusion source evaporate to the surface of a magnet and then diffuse into the magnet's interior via grain boundary diffusion. This process requires a certain saturated vapor pressure from the magnet. For composite diffusion sources, the saturated vapor pressures of heavy rare earth elements and low-melting-point metal elements differ, and the differences in saturated vapor pressure between most elements are very large. This leads to different volatilization rates for different elements during vapor deposition diffusion. After multiple uses, the composition of the diffusion source deviates significantly from the initial composition. Elements with high saturated vapor pressure volatilize faster, and their proportion in the diffusion source gradually decreases with increasing usage, while the opposite is true for elements with lower saturated vapor pressure. Changes in the diffusion source composition lead to poor performance consistency across different batches of products, making the diffusion process difficult to control. Furthermore, the diffusion source needs to be scrapped after only a few uses, increasing material costs. Secondly, when the content of low-melting-point metal elements in the diffusion source is high, these metal elements and rare earth elements will form a series of compounds. Under strong chemical bonding, the elements in these compounds are difficult to volatilize, leading to a waste of some of the diffusion source. Finally, to improve the grain boundary diffusion effect of the composite diffusion source, the proportion of low-melting-point metal elements in the diffusion source is usually increased. During vapor deposition diffusion, the concentration of low-melting-point metal elements on the magnet surface increases significantly, and the melting point of the grain boundary phase on the magnet surface layer decreases considerably. During diffusion, the rotation of the main phase grains reduces the presence of Br to some extent.

[0007] It is necessary to further develop the vapor deposition diffusion process of low-melting-point metal composite diffusion sources, and to develop composite diffusion sources with the same or similar saturated vapor pressure to improve the consistency between different batches. Technical issues

[0008] To address the shortcomings of low-melting-point metal element composite diffusion sources, such as significant shifts in the composition of the diffusion source over time due to differences in saturated vapor between rare earth elements and low-melting-point metal elements, leading to decreased product performance consistency; the formation of compounds between low-melting-point metal elements and rare earth elements when the content of low-melting-point metal elements in the diffusion source is high, resulting in waste of the diffusion source; and the increase in the proportion of low-melting-point elements in the diffusion source leading to an increase in the concentration of low-melting-point metal elements in the grain boundary phase of the magnet surface during diffusion, resulting in a decrease in the remanence of the magnet due to the rotation of the main phase grains on the magnet surface, this invention provides a high-performance RTB rare earth permanent magnet based on composite diffusion source vapor deposition diffusion and its preparation method. Technical solutions

[0009] The technical solution adopted in this invention is as follows:

[0010] A high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion, wherein the magnet composition comprises the following components by mass fraction:

[0011] R: 28.5~34.0 wt.%, R includes Dy and R1, Dy content is 0.05~10.0 wt.% of magnet mass fraction, and the balance of R is R1, R1 is at least one of Nd, Pr, Ho, Gd, La, Ce, Er.

[0012] Ga: 0.1~3.0 wt.%;

[0013] M1: 0.0~5.0 wt.%, M1 is one or more of Al, Cu, Zn, W, Mo, V, and Mn, where 0 means that M1 may not be present;

[0014] M2: 0.1~2.0 wt.%, M2 is a high melting point element, and M2 is at least one of Zr, Ti and Nb.

[0015] B: 0.85~1.1 wt.%

[0016] The balance is T and other unavoidable impurities, where T contains Fe or Fe and Co.

[0017] The magnet comprises 2:14:1 main phase particles, R-rich grain boundary phase, and M2-containing grain boundary R-Ga phase. Among the M2-containing grain boundary R-Ga phase, more than 60.0 vol.% of the grain boundary R-Ga phase is distributed in the grain boundary phase of the three main phase particles of the magnet.

[0018] In the magnet, 2% to 60 vol.% of the grain boundary phase is an M2-containing R-Ga phase.

[0019] Three principal phase grain boundary phase refers to a grain boundary phase in a magnet that is surrounded by three or more principal phase particles.

[0020] The magnet has at least one surface A, the average Ga content of surface A is higher than the average Ga content of the magnet, and the Ga concentration in the grain boundary R-Ga phase containing M2 gradually decreases with increasing depth from surface A to a depth of 100 μm inside the magnet.

[0021] Surface A is the diffusion surface of the magnet, which is a magnet surface with a heavy rare earth thin film prepared by vapor deposition.

[0022] The diffusion surface can be perpendicular to the magnet orientation direction, parallel to the magnet orientation direction, or at any angle to the magnet orientation direction, preferably perpendicular to the magnet orientation direction.

[0023] The 2:14:1 main phase is a phase in which the atomic ratio of rare earth elements R, T, and B is close to 2:14:1; the grain boundary R-rich phase is a grain boundary phase in which the proportion of rare earth element R is higher than that in the 2:14:1 main phase, and the grain boundary R-rich phase does not belong to the M2-containing grain boundary R-Ga phase; the Ga content in the M2-containing grain boundary R-Ga phase is 2.0~25.0 wt.%, the M2 content is 0.2~15.0 wt.%, and the balance is the grain boundary phase of R and other elements, and the M2 element exists in the grain boundary R-Ga phase in the form of solid solution or precipitate.

[0024] Due to the influence of the M2 content in the magnet, some grain boundary R-Ga phases may not contain M2 elements. R-Ga phases without M2 elements are considered as the aforementioned grain boundary R-rich phases.

[0025] Furthermore, Ga in the magnet can be added to the magnet matrix as a raw material during the smelting stage, with another portion added via grain boundary diffusion. Alternatively, it can be added entirely via grain boundary diffusion without being added to the matrix.

[0026] Preferably, Ga, accounting for more than 0.05 wt% of the magnet mass, is added to the magnet via grain boundary diffusion.

[0027] Engineering practice shows that adding Ga can improve the coercivity of the magnet matrix, but the improvement in coercivity tends to stabilize when the Ga addition exceeds 0.2 wt.%, and further addition has limited effect on improving coercivity. Furthermore, when a large amount of Ga is added to the magnet matrix, oxidation easily occurs during magnet fabrication, resulting in poor squareness of the magnet. This invention introduces Ga through grain boundary diffusion, avoiding the squareness problem caused by the melting point of the grain boundary phase and the growth of some main phase grains during the sintering stage. Therefore, in this invention, Ga, preferably less than 0.2 wt% of the magnet mass, is added to the magnet matrix as a raw material during the smelting stage.

[0028] The high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion can be prepared by the following method:

[0029] (1) Preparation of diffusion source: The raw materials of diffusion source are smelted according to the ratio to prepare alloy sheets or alloy powder as diffusion source; the diffusion source includes Dy and Ga;

[0030] The preferred composition of the diffusion source is as follows:

[0031] Dy: 20.0wt.%~90.0wt.%

[0032] Ga: 2.0 wt.%~30.0 wt.%

[0033] The margin is R1.

[0034] The preferred composition of the diffusion source is:

[0035] Dy: 50.0wt.%~90.0wt.%

[0036] Ga: 5.0 wt.%~30.0 wt.%

[0037] The margin is R1.

[0038] The preferred composition of the diffusion source is:

[0039] Dy: 60.0wt.%~90.0wt.%

[0040] Ga: 5.0 wt.%~20.0 wt.%

[0041] The margin is R1.

[0042] Adding a small amount of R1 to the diffusion source can stabilize the diffusion source and reduce oxidation problems during the preparation process. However, increasing the proportion of R1 will reduce the content of effective elements Dy and Ga. Therefore, it is preferred that the content of R1 in the diffusion source is 0~10%, where 0 means that R1 can be omitted.

[0043] The preferred composition of the diffusion source is:

[0044] Dy: 60.0wt.%~90.0wt.%

[0045] Ga: 5.0 wt.%~20.0 wt.%

[0046] R1: 0~10%.

[0047] The preferred composition of the diffusion source is:

[0048] Dy: 80.0wt.%~90.0wt.%

[0049] Ga: 10.0 wt.%~20.0 wt.%;

[0050] Alternatively, the preferred composition of the diffusion source is:

[0051] Dy: 80.0wt.%~89.5wt.%

[0052] Ga: 10.0 wt.%~19.5 wt.%;

[0053] R1: 0.1~1%.

[0054] Generally, alloy sheets or alloy powders are prepared by rapid solidification after smelting. Specifically, alloy sheets can be prepared by the spinning method or alloy powders can be prepared by the atomization method.

[0055] During the preparation of the diffusion source, rapid solidification is employed to suppress precipitate formation, ensuring the diffusion source is amorphous. Generally, the cooling rate of the alloy melt, v ≥ 10°C, is required. 3 K / s.

[0056] The thickness of the diffusion source can be 0.5-5mm.

[0057] (2) The RTB magnet substrate is processed into a diffuser sheet of the required shape and size. The diffuser sheets and the diffuser source are arranged alternately to form a diffuser body, and a diffuser source is provided on both sides of each diffuser sheet.

[0058] In the diffuser, the diffuser sheet and the diffuser source are arranged alternately and at intervals, which are face-to-face alternating arrangements. That is, the diffuser surface of the diffuser sheet and the surface of the diffuser source are face-to-face and arranged alternately.

[0059] In the diffuser, the diffuser sheet and the diffusion source do not contact each other and are kept at a distance.

[0060] Furthermore, the spacing between the diffuser sheet and the diffuser source is preferably 0.1 mm to 5 mm.

[0061] Furthermore, a mesh partition is used to isolate the diffusion source from the diffusion sheet. The mesh partition is a high-temperature resistant mesh partition, such as a molybdenum mesh, molybdenum wire, iron wire mesh with alumina or zirconium oxide coating, or tungsten mesh, preferably a molybdenum mesh.

[0062] The function of the mesh spacer is to prevent the diffusion source frame from coming into contact with and bonding to the pre-diffusion magnet substrate.

[0063] The pore size of the mesh spacer is generally above 0.02 mm. The mesh pores of the mesh spacer are larger than the atomic size of the diffusion source, allowing atoms to diffuse through the mesh.

[0064] In a preferred embodiment, a plurality of diffuser sheets are arranged in a row with their front faces facing each other at equal intervals, and each diffuser sheet has a diffusion source on both sides, and each diffusion source covers an adjacent diffuser sheet, with a mesh partition separating each diffusion source from the diffuser sheet.

[0065] In a preferred embodiment, the thickness of the mesh spacer is 0.1 mm to 5 mm, and they are arranged and stacked in a cyclical manner in the order of diffusion source, mesh spacer, diffusion sheet, mesh spacer, with a diffusion source provided on both sides of any diffusion sheet.

[0066] The diffuser sheet and the diffuser source can be stacked alternately horizontally or vertically.

[0067] Furthermore, the diffusion source can be an alloy sheet or alloy powder.

[0068] In a preferred embodiment, when the diffusion source is an alloy sheet, the alloy sheet is trimmed neatly and then placed on a mesh partition. The diffusion sheet is placed on another mesh partition, so that the interval between the diffusion source and the diffusion sheet is 0.1mm to 5mm. The diffusion sheet and the diffusion source are stacked alternately.

[0069] In a preferred embodiment, when the diffusion source is alloy powder, the alloy powder is evenly spread onto a mesh spacer, or the alloy powder is evenly spread onto a mesh spacer and compacted, and the diffusion sheet is placed on another mesh spacer, so that the interval between the diffusion source and the diffusion powder is 0.1 mm to 5 mm, and they are arranged alternately. When the diffusion source is alloy powder, the diffusion sheets and the diffusion source are generally arranged and stacked horizontally alternately.

[0070] There is no limit to the number of layers of diffuser sheets that are stacked alternately in a diffuser body. Generally, at least four layers of diffuser sheets are stacked to improve production efficiency.

[0071] The shape and size of the diffusion source should be compatible with the shape and size of the diffusion surface of the diffusion sheet. To account for tolerances, the size of the diffusion source may be slightly larger than the size of the diffusion surface, and may completely cover the diffusion surface of the diffusion sheet, but it must not be smaller than the size of the diffusion surface.

[0072] In a preferred embodiment, the diffusion source may also correspond to multiple diffusion plates, that is, multiple diffusion plates are arranged horizontally with their sides facing each other and placed on the same layer of mesh spacers. A diffusion source that can cover the diffusion surface of all diffusion plates is provided on the adjacent mesh spacers, and they are arranged alternately in this manner to form a diffuser.

[0073] (3) The diffuser is placed in a vacuum sintering furnace for grain boundary diffusion treatment and aging treatment to obtain the high-performance RTB rare earth permanent magnet; the vacuum degree of grain boundary diffusion is 9.0 × 10⁻⁶. -4 Pa ~ 100 Pa.

[0074] The optimal vacuum level for grain boundary diffusion is 5.0 × 10⁻⁶. -3 Pa ~ 5.0 × 10 -2 Pa.

[0075] Furthermore, it is preferred that the temperature of the grain boundary diffusion treatment is 850~1000℃ and the time is 6~30h.

[0076] In this invention, vacuum degree is absolute gas pressure, representing the pressure inside the furnace.

[0077] When the pressure inside the furnace is low, the diffusion source evaporates quickly, so the grain boundary diffusion time can be shortened appropriately; conversely, when the pressure is high, the grain boundary diffusion treatment time can be extended appropriately.

[0078] The aging treatment temperature is 400-600℃, the holding time is 1-10h, and after the holding time is completed, it is cooled to below 80℃ to obtain the high-performance RTB rare earth permanent magnet.

[0079] The RTB magnet substrate is typically prepared using the following method:

[0080] According to the magnet matrix formula, the raw materials are mixed in proportion and then prepared by vacuum induction melting and spun SC sheet, hydrogen breaking, air jet milling, orientation molding, isostatic pressing, vacuum sintering and heat treatment to obtain the RTB magnet matrix.

[0081] In step (2), the RTB magnet substrate is processed into a diffuser sheet of the required shape and size. Generally, the RTB magnet substrate is processed and cut to the required shape and size by machining. After surface treatment, the magnet is cleaned and dried to obtain the diffuser sheet.

[0082] Cleaning methods can include acid washing followed by water washing and drying, or sandblasting.

[0083] This invention uses Dy and Ga as the main components of the diffusion source, and a portion of R1 element can be added as needed. Dy and Tb are two heavy rare earth elements commonly used in grain boundary diffusion processes, but near the grain boundary diffusion temperature (900℃), the saturated vapor pressure of Tb element is relatively low (10). -6 Therefore, Tb has a slow volatilization rate and poor compatibility with the saturated vapor pressures of other low-melting-point metals. In contrast, Dy has a saturated vapor pressure of around 10 Pa in this temperature range. -2 With a Pa level, a high and more controllable evaporation rate, and high efficiency when used for vapor deposition diffusion, this invention selects Dy as the main component of the diffusion source.

[0084] Commonly used low-melting-point metallic elements include Al, Ga, and Cu. A comparison of the saturated vapor pressures of these elements shows that Ga has a good compatibility with the saturated vapor pressure of Dy at grain boundary diffusion temperature, both being within 10°C. -2The concentration is on the order of Pa. Using an alloy of Ga and Dy as the main component of the diffusion source ensures that the volatilization rates of both are essentially the same, and the composition of the diffusion source will not change significantly after long-term use, thus improving the consistency of the diffusion product performance. Simultaneously, to prevent Ga from forming compounds with other rare earth elements that affect the utilization rate of the diffusion source, this invention employs rapid solidification during the preparation of the diffusion source to suppress the formation of precipitates, requiring a cooling rate v ≥ 10 for the alloy liquid. 3 K / s. The rapid solidification method results in less segregation of the diffusion source components, more uniform volatilization of different elements during diffusion, and no large regional differences. By rapidly solidifying, the diffusion source is partially or completely transformed into an amorphous state, further improving the uniformity of the diffusion source.

[0085] Furthermore, vapor deposition diffusion requires maintaining a certain gap between the diffusion source and the magnet substrate. Due to the influence of atomic free path, when the gap between the diffusion source and the magnet is small, Dy and Ga elements volatilize to the magnet surface too quickly, easily causing heavy rare earth elements to accumulate on the magnet surface and inducing bulk diffusion. Conversely, when the gap between the diffusion source and the magnet is large, the diffusion source atoms have difficulty reaching the magnet surface, resulting in a small increase in the coercivity of the magnet after diffusion. Therefore, in this invention, when assembling the diffuser, the gap between the diffusion source and the diffusion magnet is between 0.1 mm and 5 mm.

[0086] This invention employs a rapid solidification method to prepare the composite diffusion source, thus allowing for the preparation of alloy sheets using a spinning method or alloy powder using an atomization method. Therefore, when assembling the diffuser, the diffusion source layer can be prepared in the following ways, depending on the different states of the diffusion source:

[0087] The diffusion source is an alloy sheet: the alloy sheet is trimmed neatly and then placed on a support. The diffusion source is alloy powder: the alloy powder is evenly spread on the support, or evenly spread on the support and compacted. The support can be a molybdenum mesh, a wire mesh / tungsten mesh with an alumina / zirconia coating, etc., with a molybdenum mesh being preferred.

[0088] Engineering practice shows that increasing the proportion of low-melting-point metal elements in the diffusion source can improve the diffusion effect of composite diffusion source evaporation. However, this leads to an increase in the concentration of low-melting-point metal elements on the magnet surface layer during diffusion, a significant decrease in the melting point of the grain boundary phase on the magnet surface layer, and a weakening of the pinning effect of the grain boundaries on the main phase grains. During diffusion, the main phase grains will rotate, resulting in a decrease in the Br content of the magnet. In this invention, when Ga elements in the diffusion source volatilize to the magnet surface and diffuse into the magnet interior through grain boundaries, they will form an R-Ga phase with rare earth elements. 60.0 vol.% of the R-Ga phase will exist at the three main phase grain boundaries of the magnet. The R-Ga phase can effectively isolate the main phase grains of the magnet, playing a role in decoupling the main phase and improving the coercivity of the magnet. However, due to the low melting point of the R-Ga phase, at high temperatures, the main phase grains will rotate in the grain boundary R-Ga phase, resulting in a decrease in the remanence of the magnet after diffusion. When a certain concentration of the high-melting-point element M2 is added to a magnet, M2 tends to distribute within the R-Ga phase due to its good affinity with the R-Ga phase, forming the M2-containing R-Ga phase. When the M2 content is low, M2 exists in the R-Ga phase in a solid solution manner, forming the M2-containing R-Ga phase. When the M2 content is high, it exists in the R-Ga phase as a precipitate. Due to the effect of M2, the main phase grains on the magnet surface can be pinned to a certain extent, thereby improving the remanence of the magnet after diffusion. Beneficial effects

[0089] The beneficial effects of this invention are as follows:

[0090] (1) By using a composite diffusion source vapor deposition diffusion method, the Ga element in the diffusion source is deposited onto the diffusion surface, and forms an R-Ga phase with the rare earth element R in the magnet to isolate the main phase grains, optimize the diffusion channel, improve the grain boundary diffusion effect, and improve the coercivity of the magnet after diffusion. (2) Adjust the composition of the magnet matrix, add a certain amount of high melting point metal element M2 to the magnet matrix, and take advantage of the high wettability between M2 and the R-Ga phase and its easy distribution in the R-Ga phase to generate a pinning phase in the magnet grain boundary phase. By pinning the main phase grains on the magnet surface, the rotation of the main phase grains on the magnet surface is suppressed during the grain boundary diffusion process, and the remanence of the magnet after diffusion is improved. (3) Adjust the composition of the diffusion source, use Dy and Ga elements with similar saturated vapor pressure as the main components of the composite diffusion source, ensure that the volatilization rates of the two are basically the same, improve the stability of the diffusion source during long-term use, and thus improve the consistency of the performance of different batches of diffusion products. (4) Adjust the diffusion source preparation process and use a rapid solidification process to prepare the diffusion source, suppress the formation of high-melting-point compounds between low-melting-point metal elements and rare earth elements, improve the uniformity of the diffusion source composition, and reduce the material cost of the diffusion source. Attached Figure Description

[0091] Figure 1 is a schematic diagram of the magnet's microstructure.

[0092] Figure 2 shows two schematic diagrams of the placement of the magnet diffuser and the diffusion source.

[0093] Figure 3 shows the SEM microstructure of magnet No.1 at a certain depth from surface A and magnet No.2 at a certain depth from the diffusion source coating surface.

[0094] Figure 4 shows SEM micrographs of the magnets from Experiments No. 3 and No. 4.

[0095] Figure 5 shows the Ga content in the R-Ga phase containing M2 in the magnets of Experiments No.3 and No.4, from the surface parallel to the diffusion source to a depth of 100 μm inside the magnet.

[0096] Figure 6 shows the microstructure of magnets from Experiments No. 5 and No. 6. The best embodiment of the present invention

[0097] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0098] The raw materials are mixed in a certain proportion and then processed using vacuum induction melting and spun SC sheets, hydrogen melting, air jet milling, orientation molding, isostatic pressing, vacuum sintering, and heat treatment to prepare the magnet matrix. The matrix magnet is then machined into diffuser sheets of the required size and cleaned.

[0099] The raw materials Dy, R1, and Ga are smelted in a certain proportion, and alloy sheets or powders are prepared by rapid solidification. The cooling rate of the alloy liquid is v≥10. 3 K / s. The cleaned diffuser sheets and diffusion sources are arranged alternately to form a diffuser body. The diffuser sheets and diffusion sources do not contact each other, maintaining a certain distance between them, and it is required that diffusion sources exist on both sides of each diffuser sheet.

[0100] The diffuser sheet and the diffuser source can be arranged alternately horizontally or vertically, as shown in Figure 2. In the left image of Figure 2, arrangement 1 is an alternating horizontal stacking, while in the right image, arrangement 2 is an alternating vertical stacking.

[0101] In a preferred embodiment, when the diffusion source is an alloy sheet, the alloy sheet is trimmed neatly and then placed on a mesh partition. The diffusion sheet is placed on another mesh partition, so that the interval between the diffusion source and the diffusion sheet is 0.1mm to 5mm. The diffusion sheet and the diffusion source are stacked alternately.

[0102] In another preferred embodiment, when the diffusion source is alloy powder, the alloy powder is evenly spread onto a mesh partition, or the alloy powder is evenly spread onto a mesh partition and compacted, and the diffusion sheet is placed on another mesh partition, so that the interval between the diffusion source and the diffusion powder is 0.1mm~5mm, and they are arranged and stacked alternately. When the diffusion source is alloy powder, the diffusion sheets and the diffusion source are generally arranged and stacked horizontally alternately.

[0103] There is no limit to the number of layers of diffuser sheets that are stacked alternately in a diffuser body. Generally, at least four layers of diffuser sheets are stacked to improve production efficiency.

[0104] The shape and size of the diffusion source should be compatible with the shape and size of the diffusion surface of the diffusion sheet. To account for tolerances, the size of the diffusion source may be slightly larger than the size of the diffusion surface, and may completely cover the diffusion surface of the diffusion sheet, but it must not be smaller than the size of the diffusion surface.

[0105] In a preferred embodiment, the diffusion source may also correspond to multiple diffusion plates, that is, multiple diffusion plates are arranged horizontally with their sides facing each other and placed on the same layer of mesh spacers. A diffusion source that can cover the diffusion surface of all diffusion plates is provided on the adjacent mesh spacers, and they are arranged alternately in this manner to form a diffuser.

[0106] The diffuser was placed in a vacuum sintering furnace for grain boundary diffusion treatment. The grain boundary diffusion temperature was 850~1000℃, the holding time was 6~30h, and the vacuum degree was 9.0×10⁻⁶. -4 Pa~100Pa, after which it is cooled to below 80℃. Then the magnet is heated to 400~600℃ for heat treatment, and held for 1~10h. After the holding time is completed, it is cooled to below 80℃ to obtain the high-performance RTB rare earth permanent magnet.

[0107] The magnetic properties of the magnet were tested using NIM testing equipment, the microstructure of the magnet was observed using SEM, and the phase volume percentage was calculated using image analysis software. The overall composition of the magnet was tested using ICP, and the microstructure of the magnet was analyzed using EPMA.

[0108] The magnet comprises 2:14:1 main phase particles, R-rich grain boundary phase, and M2-containing R-Ga grain boundary phase.

[0109] The 2:14:1 main phase is a phase with a rare earth element R, T, and B atomic ratio close to 2:14:1. The R-rich grain boundary phase is a grain boundary phase with a higher proportion of rare earth element R than that in the 2:14:1 main phase, but it does not belong to the M2-containing grain boundary R-Ga phase. The M2-containing grain boundary R-Ga phase has a Ga content of 2.0~25.0 wt.%, an M2 content of 0.2~15.0 wt.%, and the balance being R and other elements in the grain boundary phase. The M2 element exists in the grain boundary R-Ga phase in the form of solid solution or precipitates. A schematic diagram of the magnet microstructure is shown in Figure 1. Figure 1 shows the 2:14:1 main phase particles, the R-rich grain boundary phase, and the M2-containing grain boundary R-Ga phase. Due to the influence of the M2 content in the magnet, some grain boundary R-Ga phases may not contain the M2 element. The R-Ga phase without the M2 element is considered as the aforementioned R-rich grain boundary phase.

[0110] In Figure 1, the grain boundary phase formed by three or more principal phase particles is a three-principal-phase grain boundary phase. Example

[0111] The component is Nd 23 Pr 7.0 B 0.96 Ga 0.2 Co 1.0 Cu 0.1 Ti 0.2 Fe bal (By mass ratio) After batching, the matrix magnet is prepared by vacuum induction melting, hydrogen crushing, air jet milling, orientation molding, isostatic pressing, vacuum sintering, and heat treatment. The diffuser sheet is machined and cut into 25mm x 10mm x 5mm length x width x height, with the height direction of the diffuser sheet parallel to the orientation direction of the magnet.

[0112] The component is Dy 80.0 Ga 20.0The diffusion source (by mass ratio) was prepared using vacuum induction melting and casting. The cooling rate of the alloy liquid was 1000 K / s. The dimensions of the diffusion source sheet were (25 + 0.2~0.4) × (10 + 0.2~0.4) mm × 2 mm (length × width × height). The diffusion source sheet was placed on a molybdenum mesh. The cleaned diffusion sheets and diffusion sources were aligned face-to-face and stacked alternately to form a diffuser. Diffusion sources were placed on both sides of any diffusion sheet. The distance between the diffusion sheet and the diffusion source was 1.0 mm ± 0.2 mm. Experiment No. 1 used the placement method 1 in the left figure of Figure 2 to arrange the diffusion sheets and diffusion sources. As shown in placement method 1 in the left figure of Figure 2, 5 diffusion source sheets and 4 diffusion sheets were aligned face-to-face and stacked alternately to form a diffuser. A molybdenum mesh was used to isolate the diffusion source and diffusion sheet, which is not shown in Figure 2. Both the diffusion sheet and the diffusion source were placed on the molybdenum mesh. The molybdenum mesh can be erected on a support with vertical ends. The molybdenum mesh can be fixed to the support or detachably mounted on the support. Experiment No. 2 is a comparative example, prepared using the traditional grain boundary diffusion method, that is, the diffusion source sheet is used as the target material and deposited on two surfaces of the magnet perpendicular to the orientation direction by PVD. The total weight of the diffusion source is 0.5 wt.% of the magnet weight.

[0113] The diffuser from Experiment No. 1 and the magnet coated with the diffusion source from Experiment No. 2 were placed in a vacuum sintering furnace for grain boundary diffusion treatment. The grain boundary diffusion temperature was 890℃, the holding time was 20h, and the vacuum degree was 3.0×10⁻⁶. -2 The temperature was approximately 80°C after the process was completed. Then, the magnet was heated to 500°C for heat treatment and held at that temperature for 2.5 hours. After the heat treatment was completed, the temperature was cooled to below 80°C to obtain the high-performance RTB rare-earth permanent magnet.

[0114] The magnetic properties of the magnet were tested using NIM testing equipment, the microstructure of the magnet was observed using SEM, the phase volume percentage was calculated using image analysis software, and the overall composition of the magnet was tested using ICP.

[0115] The magnetic properties of magnets in Experiments No.1 and No.2 and the Dy content of magnets after diffusion are shown in Table 1. The matrix magnetic properties are the magnetic properties of magnets in Experiments No.1 and No.2 before diffusion.

[0116] Table 1

[0117] Experiment No. Dy (wt.%) Br (kGs) Hcj (kOe) Matrix 0.01 4.52 13.81 0.42 14.41 22.72 0.42 14.12 20.6

[0118] Experiments No. 1 and No. 2 used the same substrate, and the Dy content in the magnets after diffusion was also the same. Table 1 shows that the remanence and coercivity of the magnets prepared using the vapor deposition diffusion method provided by this invention are higher than those prepared using the traditional grain boundary diffusion method, indicating that the vapor deposition diffusion method using a low-melting-point element composite diffusion source can significantly improve the grain boundary diffusion effect.

[0119] Figure 3 shows the SEM microstructure of the magnet at a certain depth from surface A in Experiment No. 1 and the magnet at a certain depth from the diffusion source coating surface in Experiment No. 2. Experiment No. 2 used a diffusion source coating method for grain boundary diffusion treatment. It can be seen that bulk diffusion occurred in the main phase grains within a 50 μm depth of the magnet from the diffusion source coating surface, and an anti-shell structure appeared (the heavy rare earth element content in the core of the main phase grains was higher than that on the surface of the main phase grains). Traditionally, coating the magnet surface with a diffusion source causes heavy rare earth elements to accumulate on the magnet surface. Because grain boundary diffusion requires a long time, the heavy rare earth elements accumulated on the magnet surface during heat preservation can induce bulk diffusion, causing heavy rare earth elements to diffuse into the interior of the main phase grains of the magnet within a certain depth range near the diffusion source coating surface. As the heavy rare earth diffusion source on the surface of the magnet is exhausted, the concentration of heavy rare earth elements on the surface of the main phase grains that have undergone bulk diffusion is higher than the concentration of heavy rare earth elements in the surrounding grain boundary phase. Therefore, the diffusion direction of heavy rare earth elements changes from the main phase grains that have undergone bulk diffusion to the grain boundary phase, resulting in the formation of an anti-shell structure in the main phase grains.

[0120] The heavy rare earth element Dy exhibits antiferromagnetic coupling with Fe atoms, leading to a decrease in remanence after bulk diffusion in the magnet. Furthermore, the coercivity mechanism of RTB magnets is nucleation-type, with the overall coercivity primarily determined by the coercivity of the main phase grain surface. When anti-shell main phase grains form within the magnet, the low coercivity of the anti-shell main phase grain surface results in a decrease in the overall coercivity of the magnet. Simultaneously, the bulk diffusion at the magnet surface consumes a significant amount of heavy rare earth element diffusion sources, resulting in insufficient coercivity increment after grain boundary diffusion.

[0121] This invention employs a composite diffusion source vapor deposition diffusion method for grain boundary diffusion treatment. The diffusion source does not contact the magnet; at high temperatures, the diffusion source atoms volatilize to the magnet surface via metal vapor, thus preventing the diffusion source from accumulating excessively on the magnet surface. As can be seen from the microstructure of the magnet in Experiment No. 1 in Figure 3, the magnet prepared using the vapor deposition diffusion method of this invention does not exhibit bulk diffusion, and the main phase grains of the magnet form a clear heavy rare earth element shell. Because no bulk diffusion occurs, the magnet maintains a high remanence, and more heavy rare earth elements can form a shell on the surface of the main phase particles. Therefore, after grain boundary diffusion, with the same Dy element content, the magnet of this invention exhibits a higher increase in coercivity.

[0122] Example 2:

[0123] The component is Nd 23 Pr 7.0 B 0.96 Ga 0.2 Co 1.0 Cu 0.1 Ti 0.2 Fe bal (By mass ratio) After batching, the matrix magnet is prepared by vacuum induction melting, hydrogen crushing, air jet milling, orientation molding, isostatic pressing, vacuum sintering, and heat treatment. The diffuser sheet is machined and cut into 25mm x 10mm x 5mm length x width x height, with the height direction of the diffuser sheet parallel to the orientation direction of the magnet.

[0124] The component is Dy 80.0 Ga 20.0 Diffusion source A (by mass ratio) was prepared by vacuum induction melting and casting, while diffusion source B was prepared by vacuum induction melting and casting of pure Dy. The diffusion sources were then placed on a molybdenum grid. The dimensions of the diffusion source sheet were (25 + 0.2~0.4) × (10 + 0.2~0.4) mm × 2 mm (length × width × height). The cleaned diffusion sources and diffusion sheets were aligned face-to-face and arranged alternately to form a diffuser. The distance between the diffusion sheets and diffusion sources was 1.0 mm ± 0.2 mm. Diffusion source A was used in Experiment No. 3, and diffusion source B was used in Experiment No. 4. The diffusion sources and magnets were stacked as shown in arrangement 1 on the left side of Figure 2.

[0125] The diffusers from Experiments No. 3 and No. 4 were subjected to grain boundary diffusion treatment in a vacuum sintering furnace at a temperature of 890℃ for 20 hours and a vacuum degree of 3.0 × 10⁻⁶. -2 The temperature was approximately 80°C after the process was completed. Then, the magnet was heated to 500°C for heat treatment and held at that temperature for 2.5 hours. After the heat treatment was completed, the temperature was cooled to below 80°C to obtain the high-performance RTB rare-earth permanent magnet.

[0126] The magnetic properties of the magnet were tested using NIM testing equipment, the microstructure of the magnet was observed using SEM, and the phase volume percentage was calculated using image analysis software. The overall composition of the magnet was tested using ICP, and the microstructure of the magnet was analyzed using EPMA.

[0127] The magnetic properties of Experiments No.3 and No.4 and the Dy and Ga contents of the magnets after diffusion are shown in Table 2. The matrix magnetic properties are the magnetic properties of the magnets in Experiments No.3 and No.4 before diffusion.

[0128] Table 2

[0129] Experiment No. Dy (wt.%) Ga (wt.%) Br (kGs) Hcj (kOe) Matrix 0.0 0.21 14.5 213.8 30.4 20.27 14.4 122.7 40.5 30.20 14.3 121.5

[0130] In this embodiment, both Experiment No. 3 and Experiment No. 4 magnets were prepared by vapor deposition diffusion. Experiment No. 3 used the diffusion source provided by this invention, while Experiment No. 4 used pure Dy as the diffusion source. As shown in Table 2, Experiment No. 4, using pure Dy as the diffusion source, had a higher Dy content than Experiment No. 3 magnet after diffusion. Comparing the magnetic properties of Experiment No. 3 and Experiment No. 4, the remanence and coercivity of Experiment No. 3 magnet were both higher than those of Experiment No. 4 magnet, indicating that using the diffusion source of this invention can significantly improve the grain boundary diffusion effect.

[0131] Figure 4 shows the SEM microstructure of the diffusion magnets in Experiments No. 3 and No. 4. The surface composition of the parallel plane between the magnet and the diffusion source was analyzed by EPMA surface scanning. The Dy and Ga element contents on the magnet surface are shown in Table 3.

[0132] Table 3

[0133] Experiment No.Dy(wt.%)Ga(wt.%)313.22.1418.50.02

[0134] In Experiment No. 3, a Ga-containing composite diffusion source was used for grain boundary diffusion treatment. The average Ga content on the surface parallel to the magnet and the diffusion source (surface A) was significantly higher than the average Ga content of the magnet. This indicates that during grain boundary diffusion, Ga from the diffusion source is deposited onto the magnet surface through evaporation and then diffuses into the magnet interior through the grain boundaries.

[0135] As shown in Figure 4, the grain boundary phase of magnet No. 3 contains a significant amount of M2-containing R-Ga phase. Due to the addition of Ga to the magnet matrix, some M2-containing R-Ga phase also formed in the grain boundary phase of magnet No. 4, but its area was relatively small. Image processing analysis revealed that in Experiment No. 3, over 56.3 vol.% of the grain boundary phase volume was composed of M2-containing R-Ga phase, and over 60.0 vol.% of this M2-containing R-Ga phase volume was distributed within the three main phase grain boundary phases of the magnet. EPMA point scan analysis showed that the M2 content in the M2-containing R-Ga phase ranged from 0.2 to 15.0 wt.%. In contrast, in magnet No. 4, the M2-containing R-Ga phase accounted for only 6.5 vol.% of the grain boundary phase volume, and over 90.0 vol.% of this phase volume was distributed within the three main phase grain boundary phases.

[0136] The Ga content in the M2-containing R-Ga phase was statistically analyzed from the surface of the magnet parallel to the diffusion source to a depth of 100 μm inside the magnet, and the results are shown in Figure 5. It can be seen that in Experiment No. 3, the Ga content in the M2-containing R-Ga phase remained at a high level, while the Ga content gradually decreased with increasing distance from the magnet surface A. The high Ga content in the M2-containing R-Ga phase can promote the diffusion rate of the heavy rare earth element Dy, thereby improving the grain boundary diffusion effect. In Experiment No. 4, the Ga content in the M2-containing R-Ga phase was generally low, and the Ga content in the magnet did not change significantly with increasing distance from the parallel surface of the magnet diffusion source.

[0137] This invention employs a Ga-containing composite diffusion source for grain boundary diffusion treatment via vapor deposition. Since the saturated vapor pressures of Ga and Dy are on the same order of magnitude, Ga and Dy are simultaneously deposited as metal vapors on the magnet surface during grain boundary diffusion, and then diffuse into the magnet's interior via grain boundary diffusion. Ga has a very low melting point; as Ga diffuses into the grain boundary phase of the magnet, it forms an R-Ga phase with rare earth elements, promoting the grain boundary diffusion depth of Dy and thus improving the magnet's magnetic properties. Experimental No. 4 magnet used pure Dy as the grain boundary diffusion source. After vapor deposition diffusion, the Dy content of the magnet was higher than that of Experimental No. 3 magnet. However, because the magnet contained only a small amount of M2-containing grain boundary R-Ga phase, and the Ga content in this phase was low, the promoting effect on Dy diffusion was lower than that of Experimental No. 3 magnet. Therefore, the coercivity increment of Experimental No. 4 magnet was lower after diffusion. Furthermore, due to the low grain boundary diffusion rate of magnet Dy in Experiment No. 4, although no bulk diffusion occurred, a thicker shell was formed on the main phase grains on the magnet surface, resulting in a greater decrease in the remanence of the magnet after diffusion.

[0138] Example 3:

[0139] The component is Nd 22.5 Pr 7.5 Dy 0.2 B 0.96 Ga 0.1 Co 2.0 Zr 0.3 Fe bal (mass ratio, Experiment No. 5 matrix) and Nd 22.5 Pr 7.5 Dy 0.2 B 0.96 Ga 0.1 Co 2.0 Fe bal(Material ratio, Experiment No. 6) After separate batching, the matrix magnets were prepared using a process of vacuum induction melting, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and heat treatment. Diffusion sheets with dimensions of 25mm × 10mm × 5mm (length × width × height) were machined and cut, with the height direction of the diffusion sheets parallel to the orientation direction of the magnets. The composition was Dy 89.0 Ga 10.0 Nd 1.0 The diffusion source (by mass ratio) was prepared using vacuum induction melting and casting. The cooling rate of the alloy liquid was 1000 K / s, and the dimensions of the diffusion source sheet were (25 + 0.2~0.4) × (10 + 0.2~0.4) mm × 2 mm (length × width × height). The cleaned diffusion sheets and diffusion sources were alternately arranged to form a diffuser, with a distance of 1.0 mm ± 0.2 mm between them. The stacking method is shown in arrangement 2 on the right side of Figure 2.

[0140] The diffusers from Experiments No. 5 and No. 6 were subjected to grain boundary diffusion treatment in a vacuum sintering furnace at a temperature of 900℃ for 20 hours and a vacuum degree of 3.0 × 10⁻⁶. -2 The temperature was approximately 80°C after the initial heat treatment. The magnet was then heated to 520°C for 2.5 hours, and then cooled to below 80°C to obtain the high-performance RTB rare-earth permanent magnet.

[0141] The magnetic properties of the magnet were tested using NIM testing equipment, the microstructure of the magnet was observed using SEM, and the phase volume percentage was calculated using image analysis software. The overall composition of the magnet was tested using ICP, and the microstructure of the magnet was analyzed using EPMA.

[0142] The magnetic properties of magnets in Experiments No. 5 and No. 6, as well as the Dy and Ga contents of the magnets after diffusion, are shown in Table 4. The matrix magnetic properties are the magnetic properties of magnets in Experiments No. 5 and No. 6 before diffusion.

[0143] Table 4

[0144] Experiment No. Dy (wt.%) Ga (wt.%) Br (kGs) Hcj (kOe) Matrix 0.20 0.10 14.02 14.65 0.73 0.16 13.93 23.56 0.73 0.16 13.80 23.6

[0145] The results show that after diffusion, the Ga and Dy element contents of magnets No. 5 and No. 6 are the same, and the coercivity increments are also the same. However, the remanence of magnet No. 6 is lower than that of magnet No. 5. Figure 6 shows the microstructure of magnets No. 5 and No. 6. The composition of the R-Ga phase in the magnets was analyzed by EPMA spot scanning. M2 element is present in the R-Ga phase of magnet No. 5, partly in solid solution and partly in precipitates. Analysis of the M2 element composition in the R-Ga phase revealed that the M2 element content ranges from 0.2% to 15 wt.%. M2 element is absent in the R-Ga phase of magnet No. 6.

[0146] High-melting-point element M2 has a high affinity for the R-Ga phase, therefore, when added to a magnet, M2 readily distributes within the R-Ga phase. This invention employs a Ga-containing composite diffusion source for grain boundary diffusion treatment via vapor deposition. During grain boundary diffusion, Ga significantly lowers the melting point of the grain boundary phase, increasing its fluidity and eliminating its pinning effect on the main phase grains. This causes the main phase grains to rotate during grain boundary diffusion, leading to a decrease in the magnet's remanence. Therefore, a certain amount of high-melting-point metal element is needed to pin the main phase grains; this invention requires the addition of a specific amount of M2 element to the magnet.

[0147] Example 4:

[0148] The component is Nd 22.5 Pr 7.5 Dy 0.2 B 0.96 Ga 0.1 Co 2.0 Zr 0.3 Fe bal (By mass ratio) After batching, the matrix magnet is prepared through a process of vacuum induction melting, hydrogen crushing, air jet milling, orientation molding, isostatic pressing, vacuum sintering, and heat treatment. Diffusion sheets with dimensions of 25mm x 10mm x 5mm (length x width x height) are machined and cut, with the height direction of the diffusion sheets parallel to the orientation direction of the magnet. The composition is Dy 89.0 Ga 10.0 Nd 1.0The diffusion source (by mass ratio) was prepared using vacuum induction melting and casting. The cooling rate of the alloy liquid was 1000 K / s, and the dimensions of the diffusion source sheet were (25 + 0.2~0.4) × (10 + 0.2~0.4) mm × 2 mm (length × width × height). The cleaned diffusion sheets and diffusion sources were alternately arranged to form a diffuser. The distances between the diffusion sheets and diffusion sources in Experiments No. 7 to No. 9 were 0.1 mm ± 0.05 mm, 1.0 mm ± 0.05 mm, and 5.0 mm ± 0.05 mm, respectively. The stacking method is shown in arrangement 2 on the right side of Figure 2. As shown in arrangement 2 on the right side of Figure 2, 5 diffusion source sheets and 4 diffusion sheets were aligned face-to-face and vertically alternated to form a diffuser. A molybdenum mesh was used for isolation between the diffusion source and the diffusion sheets (not shown in Figure 2). The diffusion source and diffusion sheets could be vertically fixed using horizontal supports at both ends. The distance between the diffusion source and the diffusion sheet can be adjusted by changing the thickness of the molybdenum mesh or by adjusting the spacing of the molybdenum mesh.

[0149] The diffusers from Experiments No. 7 to No. 9 were subjected to grain boundary diffusion treatment in a vacuum sintering furnace at a temperature of 900℃ for 20 hours and a vacuum degree of 3.0 × 10⁻⁶. -2 The temperature was approximately 80°C after the initial heat treatment. The magnet was then heated to 520°C for 2.5 hours, followed by cooling to below 80°C to obtain the high-performance RTB rare-earth permanent magnet. The magnetic properties of the magnet were tested using NIM testing equipment, and the overall composition of the magnet was analyzed using ICP.

[0150] The Dy and Ga contents and magnetic properties of the magnets after diffusion in Experiments No.7 to No.9 are shown in Table 5, where the matrix magnetic properties are the same as those of the magnets before diffusion in Experiments No.7 to No.9.

[0151] Table 5

[0152] Experiment No. Dy (wt.%) Ga (wt.%) Br (kGs) Hcj (kOe) Matrix 0.20 0.10 14.02 14.67 0.85 0.21 13.86 23.78 0.73 0.16 13.94 23.69 0.67 0.13 13.95 23.1

[0153] Under certain temperature and vacuum conditions, the free path of atoms is within a certain range. This invention requires controlling the volatilization rate of Dy and Ga atoms from the diffusion source to the magnet surface. When the distance between the diffusion source and the diffusion sheet is small, the volatilization rate from the diffusion source to the magnet surface is fast, leading to a certain degree of reduction in the remanence of the magnet after diffusion. Conversely, when the distance between the diffusion source and the diffusion sheet is large, exceeding the range of atomic free paths, the amount of diffusion source deposited on the diffusion sheet surface decreases, affecting the increase in coercivity of the magnet. Therefore, in this invention, the distance between the diffusion source and the diffusion sheet needs to be adjusted to between 0.1 and 5.0 mm, more preferably between 0.1 and 1.0 mm.

[0154] Example 5:

[0155] The component is Nd 22.5 Pr 7.5 Dy 0.2 B 0.96 Ga 0.1 Co 2.0 Zr 0.3 Fe bal (By mass ratio) After batching, the matrix magnet is prepared through a process of vacuum induction melting, hydrogen crushing, air jet milling, orientation molding, isostatic pressing, vacuum sintering, and heat treatment. Diffusion sheets with dimensions of 25mm x 10mm x 5mm (length x width x height) are machined and cut, with the height direction of the diffusion sheets parallel to the orientation direction of the magnet. The composition is Dy 89.0 Ga 10.0 Nd 1.0 The diffusion source (by mass ratio) was prepared using vacuum induction melting and casting. The cooling rate of the alloy liquid was 1000 K / s, and the dimensions of the diffusion source sheet were (25 + 0.2~0.4) × (10 + 0.2~0.4) mm × 2 mm (length × width × height). The cleaned diffusion sheets and diffusion sources were alternately arranged to form a diffuser. The distance between the diffusion sheets and diffusion sources in experiments No. 10 to No. 12 was 1.0 mm ± 0.05 mm, and the stacking method is shown in arrangement 2 on the right side of Figure 2.

[0156] Experiment No. 10 was the first diffusion experiment after the diffusion source was prepared; Experiment No. 11 was the 20th diffusion experiment after the diffusion source was prepared; and Experiment No. 12 was the 50th diffusion experiment after the diffusion source was prepared. The diffuser was placed in a vacuum sintering furnace for grain boundary diffusion treatment at a temperature of 900℃, a holding time of 20 h, and a vacuum degree of 3.0 × 10⁻⁶. -2 The temperature was approximately 80°C after the initial heat treatment. The magnet was then heated to 520°C for 2.5 hours and cooled to below 80°C to obtain the high-performance RTB rare-earth permanent magnet. The magnetic properties of the magnet were tested using NIM testing equipment.

[0157] The magnetic properties of magnets No.10 to No.12 after diffusion are shown in Table 6, where the magnetic properties of the matrix are the magnetic properties of magnets No.10 to No.12 before diffusion.

[0158] Table 6

[0159] Experiment No. Br (kGs) Hcj (kOe) Matrix 14.0 214.6 10 13.94 23.7 11 13.94 23.6 12 13.94 23.6

[0160] This invention uses Dy and Ga as the main components of the diffusion source and prepares the diffusion source through rapid solidification. At the grain boundary diffusion temperature, the saturated vapor pressures of Dy and Ga are on the same order of magnitude, and their volatilization rates are comparable. Therefore, after multiple uses, the composition of the diffusion source will not deviate significantly from the original composition. In this embodiment, the diffusion source can still maintain the consistency of the diffusion magnet's performance after 50 uses.

Claims

1. A high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion, characterized in that, The magnet composition includes the following components by mass fraction: R: 28.5~34.0 wt.%, R includes Dy and R1, the Dy content is 0.05~10.0 wt.% of the magnet mass fraction, and the balance of R is R1, which is at least one of Nd, Pr, Ho, Gd, La, Ce, and Er. Ga: 0.1~3.0 wt.%; M1: 0.0~5.0 wt.%, M1 is one or more of Al, Cu, Zn, W, Mo, V, and Mn, where 0 represents the absence of M1; M2: 0.1~2.0 wt.%, M2 is a high melting point element, and M2 is at least one of Zr, Ti and Nb; B: 0.85~1.1 wt.%; The balance is T and other unavoidable impurities, where T contains Fe or Fe and Co; The magnet comprises 2:14:1 main phase particles, R-rich grain boundary phase, and M2-containing grain boundary R-Ga phase. Among the M2-containing grain boundary R-Ga phase, more than 60.0 vol.% of the grain boundary R-Ga phase is distributed in the grain boundary phase of the three main phase particles of the magnet.

2. The high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion as described in claim 1, characterized in that, The magnet has at least one surface A, the average Ga content of surface A is higher than the average Ga content of the magnet, and the Ga concentration in the grain boundary R-Ga phase containing M2 gradually decreases with increasing depth from surface A to a depth of 100 μm inside the magnet.

3. The high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion as described in claim 1, characterized in that, The 2:14:1 main phase is a phase in which the atomic ratio of rare earth elements R, T, and B is close to 2:14:1; the grain boundary R-rich phase is a grain boundary phase in which the proportion of rare earth element R is higher than that in the 2:14:1 main phase; the M2-containing grain boundary R-Ga phase contains 2.0~25.0 wt.% Ga element, 0.2~15.0 wt.% M2 element, and the balance is a grain boundary phase of R and other elements, and the M2 element exists in the grain boundary R-Ga phase in the form of solid solution or precipitate.

4. The high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion as described in claim 1, characterized in that, The high-performance RTB rare-earth permanent magnet based on composite diffusion source evaporation diffusion is prepared according to the following method: (1) Preparation of diffusion source: The raw materials of diffusion source are smelted according to the ratio to prepare alloy sheets or alloy powder as diffusion source; the diffusion source includes Dy and Ga; (2) The RTB magnet substrate is processed into a diffuser sheet of the required shape and size. The diffuser sheets and the diffuser source are arranged alternately to form a diffuser body, and a diffuser source is provided on both sides of each diffuser sheet. (3) The diffuser is placed in a vacuum sintering furnace for grain boundary diffusion treatment and aging treatment to obtain the high-performance RTB rare earth permanent magnet; the vacuum degree of grain boundary diffusion is 9.0 × 10⁻⁶. -4 Pa ~ 100 Pa.

5. The method for preparing high-performance RTB rare-earth permanent magnets based on composite diffusion source evaporation diffusion as described in any one of claims 1 to 3, characterized in that, The method includes the following steps: (1) Preparation of diffusion source: The raw materials of diffusion source are smelted according to the ratio to prepare alloy sheets or alloy powder as diffusion source; the diffusion source includes Dy and Ga; (2) The RTB magnet substrate is processed into a diffuser sheet of the required shape and size. The diffuser sheets and the diffuser source are arranged alternately to form a diffuser body, and a diffuser source is provided on both sides of each diffuser sheet. (3) The diffuser is placed in a vacuum sintering furnace for grain boundary diffusion treatment and aging treatment to obtain the high-performance RTB rare earth permanent magnet; the vacuum degree of grain boundary diffusion is 9.0 × 10⁻⁶. -4 Pa ~ 100 Pa.

6. The method as described in claim 5, characterized in that, In step (1), The composition of the diffusion source is as follows: Dy: 20.0wt.%~90.0wt.% Ga: 2.0 wt.%~30.0 wt.% The margin is R1.

7. The method as described in claim 5, characterized in that, In step (2), the spacing between the diffuser and the diffuser source is 0.1 mm to 5 mm.

8. The method as described in claim 7, characterized in that, A mesh partition is used to isolate the diffusion source from the diffusion sheet. The mesh partition is a high-temperature resistant mesh partition.

9. The method as described in claim 5, characterized in that, In step (1), alloy sheets or alloy powder are prepared by rapid solidification after melting, requiring the cooling rate v of the alloy liquid to be ≥10. 3 K / s.

10. The method as described in claim 5, characterized in that, In step (3), the temperature of the grain boundary diffusion treatment is 850~1000℃ and the time is 6~30h; the temperature of the aging treatment is 400-600℃ and the holding time is 1~10h. After the holding time is completed, the temperature is cooled to below 80℃ to obtain the high-performance RTB rare earth permanent magnet.

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