High-strength and high-toughness R-T-B rare earth permanent magnet and preparation method thereof

Abstract

The invention discloses a high-strength and high-toughness R-T-B rare earth permanent magnet and a preparation method thereof. Two high-melting-point elements of Ti and Nb are synergistically added, the ratio of the two elements is adjusted, SC sheet high-temperature heat treatment, unsaturated hydrogen absorption and segmented vacuum sintering are combined, generation of a fine-size Ti3Nb phase is promoted, precipitation of a large-size high-melting-point element boride is inhibited, fine-size Ti3Nb precipitate particles have better dispersivity, and the high-melting-point Ti3Nb-based composite material is prepared. When the R-rich phase is uniformly distributed on the grain boundary of the magnet, the grain boundary phase of the magnet can be effectively enhanced, meanwhile, main phase distortion is not caused, the hardness of the magnet is reduced, the strength and toughness of the magnet are improved, and therefore the magnet with high strength and high toughness is prepared, and the magnetic performance of the magnet is improved.

Description

Technical Field

[0001] The present invention relates to an R-T-B rare earth permanent magnet with high strength and high toughness and a preparation method thereof, belonging to the field of rare earth magnets. Background Art

[0002] As a functional material, the research on R-T-B rare earth permanent magnets has mainly focused on how to further improve their magnetic properties. In recent years, with the gradual expansion of the application fields of R-T-B magnets, especially with the development of high-speed motors and their application in the field of electric vehicles, the requirements for their mechanical properties are getting higher and higher.

[0003] The R-T-B rare earth permanent magnet is a brittle material and is prone to brittle fracture when stressed, which severely restricts the use environment of the material. The main reasons for the poor mechanical properties of the R-T-B rare earth permanent magnet are as follows: Firstly, the main phase of the magnet is an intermetallic compound with a complex structure and cannot undergo slip or twinning deformation, so it is prone to brittle fracture when stressed; Secondly, the R-rich phase at the grain boundary has low strength and poor ability to resist crack propagation, so cracks are easily propagated along the R-rich phase at the grain boundary; Finally, the R-T-B magnet has the characteristic of non-uniform microstructure, and the non-uniformity of the main phase grain size and the distribution of the R-rich phase at the grain boundary are likely to cause stress concentration.

[0004] Second-phase strengthening is a common method to enhance the mechanical properties of R-T-B magnets. Currently, in engineering practice, high melting point elements such as Zr, Ti, and Nb are usually added to the magnet and react with B to form borides. However, most of the borides of high melting point elements are strip / rod-shaped precipitates with relatively large sizes and poor dispersion in the magnet. Although they can improve the strength of the magnet, the improvement of the toughness of the magnet is limited. It is necessary to develop an R-T-B rare earth permanent magnet with both high strength and high toughness to broaden the application fields of R-T-B magnets, which is suitable for both high-load scenarios and high-impact or occasions that need to withstand repeated loads. Summary of the Invention

[0005] Aiming at the deficiencies in improving the mechanical properties of traditional R-T-B magnets, the present invention provides an R-T-B rare earth permanent magnet with high strength and high toughness and a preparation method thereof. By refining the size of the precipitates and improving the dispersion of the precipitates, the present invention is beneficial to simultaneously improving the strength and toughness of the magnet. At the same time, finer and more dispersed precipitates can more effectively inhibit the growth of the main phase grains and improve the magnetic properties of the magnet by refining the main phase grains.

[0006] The technical solution adopted by the present invention is as follows: An R-T-B rare earth permanent magnet with high strength and high toughness, the magnet composition comprising the following components: R: 28.5 wt.% to 34.0 wt.%, R contains one or more elements selected from Nd, Pr, Dy, Tb, Ho, Gd, La, Ce, Lu, Y; and R contains at least R1 element, and the R1 element is one or more of Nd, Pr, Ce; B: 0.85 to 1.1 wt.%, Ti: 0.1 to 0.4 wt.%, Nb: 0.05 to 0.5 wt.%, M: 0.01 to 8.0 wt.%, M is at least one of Al, Cu, Ga, Ni, Zn, Sn, Mn, Zr, The balance is T and other inevitable impurities, where T is Fe or Fe and Co, and more than 85.0% of the mass fraction of T is Fe, And it satisfies: [Ti] / 47.87 ≤ 4 × [Nb] / 92.91, where [Ti] is the content of Ti expressed as a mass fraction, and [Nb] is the content of Nb expressed as a mass fraction; And the magnet contains Ti3Nb precipitates, and more than 99% of the proportion of the number of Ti3Nb precipitates is distributed in the R-rich phase at the grain boundaries of the magnet.

[0007] Furthermore, the size of the Ti3Nb precipitates is 2 to 800 nm, preferably 10 to 100 nm.

[0008] The Ti3Nb precipitates are distributed at the grain boundaries between two main phases and the grain boundaries of multiple main phases. The grain boundary between two main phases is the grain boundary phase between two main phase particles, and the grain boundary of multiple main phases is the grain boundary phase formed by being surrounded by three or more main phase grains.

[0009] The magnet includes high melting point element precipitates, and the high melting point element precipitates include Ti3Nb precipitates and borides of Ti and Nb. In the magnet of the present invention, the number of borides of Ti and Nb in any cross-section of the magnet is 5% or less of the number of high melting point element precipitates.

[0010] Furthermore, the high-strength and high-toughness R-T-B rare earth permanent magnet is prepared by the following method: raw materials are taken according to the ratio, and an SC sheet is prepared by vacuum induction melting and strip casting. The SC sheet is subjected to high-temperature heat treatment. After the high-temperature heat treatment, the SC sheet is subjected to hydrogen breaking treatment with unsaturated hydrogen absorption and airflow grinding to obtain alloy powder. The alloy powder is molded by pressing in an orientation magnetic field and subjected to cold isostatic pressing. The obtained molded magnet is subjected to segmented vacuum sintering and aging treatment to obtain the high-strength and high-toughness R-T-B rare earth permanent magnet.

[0011] The present invention also provides a method for preparing an R-T-B rare earth permanent magnet with high strength and high toughness. The method is as follows: raw materials are taken according to the ratio, and an SC sheet is prepared by vacuum induction melting and melt spinning. The SC sheet is subjected to high-temperature heat treatment. After the high-temperature heat treatment, the SC sheet is subjected to hydrogen breaking treatment with unsaturated hydrogen absorption and then ground by a jet mill to obtain alloy powder. The alloy powder is molded by pressing in an orientation magnetic field and then cold isostatically pressed. The obtained molded magnet is subjected to segmented vacuum sintering and aging treatment to obtain the R-T-B rare earth permanent magnet with high strength and high toughness.

[0012] Further, the high-temperature heat treatment of the SC sheet means that the SC sheet is kept at 800 - 900 °C in an argon environment for 20 - 50 min, and the argon pressure is 30 - 50 kPa.

[0013] Further, the unsaturated hydrogen absorption means that the number of hydrogen absorption times is 0.2 - 0.8 times (preferably 0.3 - 0.5 times) of the saturated hydrogen absorption times. The saturated hydrogen absorption times are obtained by the following method: SC sheets of the same specification and weight are put into a reaction kettle, evacuated and then filled with hydrogen with a positive pressure of 0.1 Mpa. The positive pressure refers to the difference between the absolute pressure and the standard atmospheric pressure. The hydrogen absorption of the SC sheet causes the hydrogen pressure in the reaction kettle to decrease. When the positive pressure in the reaction kettle decreases to 0.05 - 0.06 MPa, hydrogen is filled into the reaction kettle again until the positive pressure is 0.1 MPa. Each hydrogen filling operation is counted as one hydrogen absorption time. After multiple hydrogen absorptions, after a certain hydrogen filling, if the pressure change within 10 minutes is less than 0.5%, it means that the SC sheet is saturated with hydrogen absorption, and the total number of hydrogen filling times at this time is the saturated hydrogen absorption times.

[0014] The segmented vacuum sintering includes low-temperature sintering and high-temperature sintering. The low-temperature sintering is that the magnet is kept at 900 - 1020 °C for 3 - 6 h, and the high-temperature sintering is that the magnet is kept at 1040 - 1080 °C for 3 - 6 h. The vacuum degree of the segmented vacuum sintering is below 10 -4 Pa.

[0015] Further, for the vacuum induction melting and melt spinning to prepare the SC sheet, generally, the raw materials are melted into an alloy liquid at 1480 - 1510 °C, and the molten alloy liquid is poured onto a rotating copper roller through a tundish to solidify at 1440 - 1460 °C to obtain the SC sheet.

[0016] Further, the vacuum induction melting and melt spinning are preferably carried out according to the following steps: raw materials with a purity of more than 99.9% are taken according to the composition ratio, and are sequentially put into the crucible in the order of decreasing melting point. The vacuum in the furnace is pumped until the vacuum degree reaches 10 -3 ~10 -4Pa, with the dew point below -50°C; then argon is filled into the furnace to make the pressure reach 30 kPa to 50 kPa, and it is heated to 1480 to 1510°C. After the raw materials are completely melted, it is held for 3 to 5 minutes; then the temperature of the alloy liquid is lowered to 1440 to 1460°C, and the molten alloy liquid is poured onto a rotating copper roller through a tundish to solidify, obtaining SC flakes. The process of strip casting is generally as follows: adjust the rotational speed of the copper roller to 70 to 75 revolutions per minute, and then rotate the crucible at a certain speed to make the molten alloy liquid pass through the tundish and be transported to the cooling roller for solidification, and then it falls onto the water-cooled plate to cool down, obtaining SC flakes.

[0017] The process of high-temperature heat treatment of the SC flakes is generally carried out according to the following steps: place the SC flakes obtained by melting in a molybdenum boat, and then place it in a heating furnace; evacuate the vacuum in the furnace to 10 -3 ~10 -4 Pa and heat to 800 to 900°C. When the temperature reaches the target temperature, argon with a pressure of 30 to 50 kPa is filled into the furnace, and it is held for 20 minutes to 50 minutes; after the heat treatment is completed, it is cooled to room temperature. There is no requirement for the cooling rate in this process, and it can be cooled with the furnace or by air cooling.

[0018] The hydrogen desorption treatment of unsaturated hydrogen absorption is carried out according to the following steps: put the SC flakes after high-temperature heat treatment into a reaction kettle, evacuate the vacuum and then fill it with hydrogen with a positive pressure of 0.1 Mpa. The positive pressure refers to the difference between the absolute pressure and the standard atmospheric pressure. The hydrogen absorption of the SC flakes causes the hydrogen pressure in the reaction kettle to decrease. When the positive pressure in the reaction kettle decreases to 0.05 to 0.06 MPa, hydrogen is filled into the reaction kettle again until the positive pressure is 0.1 MPa. Each hydrogen filling action is counted as one hydrogen absorption time; the hydrogen absorption times of unsaturated hydrogen absorption are 0.2 to 0.8 times that of saturated hydrogen absorption; the saturated hydrogen absorption times are obtained through pre-testing, which means that after the SC flakes of the same weight specification are hydrogen-absorbed multiple times, after a certain hydrogen filling, the pressure change within 10 minutes is less than 0.5%, indicating that the SC flakes are saturated with hydrogen absorption. At this time, the total hydrogen filling times are the saturated hydrogen absorption times. After the hydrogen absorption reaction is over, while evacuating the vacuum, heat up to between 400 and 600°C, hold for 2 to 6 hours to remove the hydrogen in the alloy flakes, and then cool to obtain the hydrogenated coarse powder.

[0019] The airflow milling process is carried out according to the following steps: place the hydrogenated coarse powder in an airflow milling device, in an inert gas atmosphere, adjust the nozzle pressure to be between 0.6 MPa and 0.8 MPa, and drive the coarse powder to collide with each other for crushing through high-speed gas. The inert gas is generally an inert gas such as helium or nitrogen.

[0020] Lubricants and / or antioxidants can be added to the alloy powder before die pressing. Conventional commercially available magnetic powder protection lubricants or antioxidants can be used. The addition amount of the lubricant can be 0.01-0.1% of the mass of the alloy powder, and the antioxidant can be 0.01-0.14% of the mass of the alloy powder.

[0021] The die pressing of the alloy powder in an orientation magnetic field is preferably carried out according to the following steps: the orientation magnetic field is preferably 3-6T, and the forming pressure is 5-7MPa. The green compact after orientation forming is then cold isostatically pressed, and the pressure is 150-180MPa. After orientation forming, the density of the green compact is 3.6-4.0g / cm 3 , and the density of the green compact after cold isostatic pressing is about 4.5-4.6g / cm 3 . Whether to perform cold isostatic pressing after die pressing can be selected according to the process. In the present invention, cold isostatic pressing is selected for the green compact after orientation forming to further eliminate internal cracks in the green compact.

[0022] The segmented vacuum sintering includes two-stage sintering of low temperature and high temperature. The low-temperature stage sintering is that the magnet is kept at 900-1020°C for 3-6h, and the high-temperature stage sintering is that the magnet is kept at 1040-1080°C for 3-6h.

[0023] The aging treatment refers to a primary aging treatment process in which the sintered magnet is carried out at 700-900°C for 2-8h, then cooled at a rate of not less than 20°C / min to below 100°C, and then heated to 400-600°C for 2-8h for a secondary aging treatment, and after completion, cooled at a rate of not less than 30°C / min to below 80°C.

[0024] Second-phase strengthening is a common method to enhance the mechanical properties of R-T-B magnets. Currently, in engineering practice, high melting point elements such as Zr, Ti, and Nb are usually added to the magnet and react with B to form borides. However, most of the high melting point element borides are strip / rod-shaped precipitates with relatively large sizes and poor dispersion in the magnet. Although they can improve the strength of the magnet, the improvement of the toughness of the magnet is limited. The present invention reasonably regulates the composition of the magnet so that the magnet contains 0.1-0.4wt.% of Ti and 0.05-0.5wt.% of Nb, and at the same time, the contents of Ti and Nb satisfy [Ti] / 47.87 ≤ 4×[Nb] / 92.91, where [Ti] is the content of Ti expressed as a mass fraction, and [Nb] is the content of Nb expressed as a mass fraction. Combining the SC sheet heat treatment promotes the formation of the Ti3Nb phase in the magnet and inhibits the precipitation of Ti and Nb borides. Since the size of the Ti3Nb precipitates is fine and the dispersion is better when distributed in the magnet, it can more effectively improve the strength of the magnet and increase the toughness of the magnet.

[0025] In the present invention, the melt-spun SC flakes are subjected to high-temperature short-time heat treatment to promote the nucleation and initial growth of Ti3Nb in the SC flakes. Experiments show that the starting formation temperature of Ti3Nb is about above 800 °C. To ensure that the Ti3Nb phase precipitates do not grow excessively in the spun flakes, the high-temperature heat treatment temperature adopted in the present invention is 800 - 900 °C, and the holding time is 20 - 50 min. At the same time, to prevent the SC flakes from oxidation and the volatilization of rare earths at high temperatures, the SC flakes are heat-treated under argon protection, and the pressure of argon is 30 - 50 kPa.

[0026] The hydrogen cracking process of the SC flakes is a hydrogen absorption and expansion process of the grain boundary phase and the main phase. To prevent excessive fragmentation of the grain boundary phase during the hydrogen cracking process, resulting in a large loss of the Ti3Nb compound distributed in the grain boundary phase with the separation of the ultrafine powder during the jet milling stage, an incomplete hydrogen absorption process is adopted for hydrogen cracking in the present invention. During conventional saturated hydrogen cracking, the hydrogen pressure in the reaction kettle is generally 0.01 - 0.09 MPa. During the hydrogen absorption reaction, a change in the internal pressure of the reaction kettle not exceeding 0.5% within 10 minutes represents saturated hydrogen absorption. In the present invention, an unsaturated hydrogen absorption process is adopted, and the number of hydrogen absorption times is 0.2 - 0.8 times that of normal saturated hydrogen absorption times. After subsequent jet milling, the fine Ti3Nb precipitate particles are uniformly mixed with the magnetic powder.

[0027] In the present invention, the magnet sintering process includes two-stage sintering of low temperature and high temperature. To enhance the effect of grain refinement by Ti3Nb precipitates, the green body of the magnet is first held at 900 - 1020 °C in the low-temperature stage for 3 - 6 h. At this time, the Ti3Nb precipitates in the magnet grow sufficiently and are distributed in the grain boundary phase of the magnet, and can effectively inhibit the growth of the main phase grains during the holding at 1040 - 1080 °C in the subsequent high-temperature stage, thereby improving the grain refinement effect of the magnet and the magnetic properties of the magnet.

[0028] In the present invention, a certain content of Ti and Nb is added to the raw materials, and the ratio of Ti and Nb is regulated. The alloy powder is prepared by melt-spinning SC flakes, subjecting the SC flakes to high-temperature heat treatment, incomplete hydrogen absorption hydrogen cracking treatment and jet milling. The alloy powder is molded by pressing in an oriented magnetic field and then cold isostatically pressed. The formed magnet is prepared by the processes of segmented vacuum sintering and aging treatment.

[0029] During the high-temperature heat treatment of SC wafers, Ti and Nb in the spin-coated films react to form fine Ti3Nb precipitates. By controlling the ratio of Ti and Nb and the heat treatment temperature, the precipitation of Ti, Nb, and B elements can be suppressed. During subsequent hydrogen decrepitation and jet milling processes, the fine Ti3Nb precipitates are uniformly mixed in the magnetic powder, thus preventing the precipitation of the Ti3Nb phase inside the main-phase grains during sintering. The magnet adopts a segmented sintering process. During low-temperature sintering, the Ti3Nb precipitates further grow to 2 - 800 nm. The Ti3Nb precipitates are small in size, have good dispersion, and when evenly distributed in the R-rich grain boundaries of the magnet, they can effectively strengthen the grain boundary phase of the magnet, improve the strength and toughness of the magnet, and thus prepare a magnet with both high strength and high toughness. The growth of the main-phase grains mainly occurs during high-temperature sintering. Since the Ti3Nb precipitates grow prior to the main-phase grains, the excessive growth of the main-phase grains can be effectively suppressed, with excellent grain refinement effects, which can further improve the magnetic properties of the magnet. The beneficial effects of the present invention are as follows: By synergistically adding two high-melting-point elements, Ti and Nb, and adjusting the ratio of the two elements, combined with the high-temperature heat treatment of SC wafers, unsaturated hydrogen absorption, and segmented vacuum sintering processes, the formation of fine Ti3Nb phases is promoted while the precipitation of large-size high-melting-point element borides is suppressed. The fine Ti3Nb precipitate particles have better dispersion. When evenly distributed in the R-rich grain boundaries of the magnet, they can effectively strengthen the grain boundary phase of the magnet, and at the same time, they will not cause main-phase distortion, reduce the magnet hardness, improve the strength and toughness of the magnet. The excellent grain refinement effect of Ti3Nb can also improve the magnetic properties of the magnet, thus preparing a magnet with both high strength and high toughness and excellent magnetic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Microstructure diagrams of high-temperature heat-treated SC wafers for Experiment No. 1 to Experiment No. 3.

[0031] Figure 2 TEM microstructure and selected-area electron diffraction diagrams of the precipitates in the sintered magnet for Experiment No. 1.

[0032] Figure 3 TEM microstructure and selected-area electron diffraction diagrams of the precipitates in the sintered magnet for Experiment No. 2.

[0033] Figure 4 TEM microstructure and selected-area electron diffraction diagrams of the precipitates in the sintered magnet for Experiment No. 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] The technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0035] The present invention adopts vacuum induction melting and strip casting. Raw materials with a purity of over 99.9% are taken according to the component ratio and are sequentially placed into the crucible in the order of decreasing melting point. The furnace is evacuated until the vacuum degree reaches 10 -3 ~10 -4 Pa, and the dew point is lower than -50°C. Then, argon gas is filled into the furnace to make the air pressure reach 30~50 kPa, and it is heated to 1480~1510°C. After the raw materials are completely melted, it is kept warm for 3~5 min. Then, the temperature of the alloy liquid is reduced to 1440~1460°C, and it is kept warm and cast. The rotation speed of the copper roller is adjusted to 70~75 revolutions per minute, and then the crucible is rotated at a certain speed to make the molten alloy liquid be transported to the cooling roller through the tundish for solidification and then fall onto the water-cooled disk to cool down.

[0036] The SC sheets prepared by melting are subjected to high-temperature heat treatment. The alloy sheets obtained by melting are placed in a molybdenum boat and placed in a heating furnace. The vacuum degree in the furnace is pumped to 10 -3 ~10 -4 Pa and heated to 800~900°C. When the temperature reaches the target temperature, argon gas with a pressure of 30~50 kPa is filled into the furnace, and it is kept warm for 20 min~50 min. After the heat treatment is completed, it is cooled to room temperature. There is no requirement for the cooling speed in this process, and it can be cooled with the furnace or by air cooling.

[0037] The alloy sheets are prepared into alloy powders through hydrogen disproportionation and jet milling. During the hydrogen disproportionation treatment, the hydrogen pressure in the reaction kettle is generally 0.01~0.09 MPa. During the hydrogen absorption reaction, the internal pressure change in the reaction kettle within 110 minutes does not exceed 0.5%, indicating saturated hydrogen absorption. In the present invention, the number of hydrogen absorption times is 0.2~0.8 times the normal saturated hydrogen absorption times. After the hydrogen absorption reaction is completed, it is heated to 400~600°C while evacuating to make the hydrogen in the alloy sheets escape, and then it is cooled to obtain the disproportionated coarse powder. The obtained coarse powder is placed in a jet milling device, and in an inert gas atmosphere, the nozzle pressure is adjusted to be between 0.6 MPa and 0.8 MPa, and the coarse powder is broken by the high-speed gas driving the coarse powder to collide with each other. The inert gas is generally an inert gas such as helium or nitrogen.

[0038] After adding a lubricant and / or antioxidant to the alloy powder, it is molded by pressing in an orientation magnetic field, and a conventional commercially available magnetic powder protective lubricant or antioxidant can be used. The addition amount of the lubricant can be 0.01~0.1% of the mass of the alloy powder, and the antioxidant can be 0.01~0.14% of the mass of the alloy powder.

[0039] The orientation magnetic field is preferably 3-6 T, and the molding pressure is 5-7 MPa. The green compact after orientation molding is then cold isostatically pressed, and the pressure is 150~180 MPa. After orientation molding, the density of the green compact is 3.6~4.0 g / cm 3, the green compact density after cold isostatic pressing is about 4.6 g / cm 3 .

[0040] The magnet is sintered densely by a segmented vacuum sintering process. The segmented vacuum sintering includes two stages of low-temperature and high-temperature sintering. The low-temperature sintering stage is for the magnet to be kept at 900 - 1020 °C for 3 - 6 h, and the high-temperature sintering stage is for the magnet to be kept at 1040 - 1080 °C for 3 - 6 h.

[0041] The sintered magnet needs to go through a two-stage aging process. First, a primary aging treatment process is carried out at 700 - 900 °C for 2 - 8 h, then it is cooled to below 100 °C at a rate of not less than 20 °C / min, and then heated to 400 - 600 °C for a secondary aging treatment of 2 - 8 h. After that, it is cooled to below 80 °C at a rate of not less than 30 °C / min.

[0042] After the magnet is broken, samples are taken at the center, and the magnet composition is detected by ICP. The microstructure of the magnet is observed by SEM, and the micro-area composition of the magnet is analyzed by EPMA. Three-point bending samples are prepared by using an internal circular slicing machine and double-sided grinding. The sample size is length × width × height of 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01 mm), and the sample height direction is parallel to the magnet orientation direction. According to the provisions of GB / T31967.2 - 2015, the three-point bending method is used to measure the flexural strength of the magnet. 10 samples are measured in each group of experiments and the average value is calculated. The three-point bending indenter is a cylinder with a diameter of 5 mm, the diameter of the two support columns is 5 mm, the span between the fulcrums is 14.5 mm, and the downward pressing speed of the indenter is 0.1 mm / min. Samples for magnetic property measurement are prepared by wire cutting, double-sided grinding and end face grinding. The sample is a cylinder of ϕ10 mm × 10 mm, and the magnetic properties of the magnet are measured by NIM equipment. The toughness of the magnet is characterized by the vibration weight loss method provided in the patent document CN116223262A. The sample size is length × width × height of 15 (±0.01) mm × 15 (±0.01) mm × 5 (±0.01 mm), and the sample height direction is parallel to the magnet orientation direction. After the magnet is polished, the hardness of the magnet is tested by a Vickers hardness tester. The test surface is perpendicular to the magnet orientation direction, and 10 values are tested for each sample and the average value is used as its hardness value.

[0043] Example 1: For low-melting metals, pure metals with a purity of more than 99.9 wt.% are used as raw materials. For elements with a melting point higher than that of pure iron, alloys of these elements and iron are used as raw materials. They are put into the crucible in order from the highest melting point to the lowest, and the furnace is evacuated until the vacuum degree reaches 10 -4Pa, with the dew point below -50°C. Then, argon gas is filled into the furnace to make the air pressure reach 30 kPa, and it is heated to 1490°C. After the raw materials are completely melted, it is kept warm for 3 minutes. Then, the temperature of the alloy liquid is reduced to 1450°C and casting is carried out. The rotation speed of the copper roller is adjusted to 70 revolutions per minute, and then the crucible is rotated at a certain speed so that the molten alloy liquid is transported to the cooling roller through the tundish for solidification and then drops onto the water-cooled plate to cool down, obtaining an alloy sheet with a thickness of 0.28 ± 0.05 mm.

[0044] High-temperature heat treatment is carried out on the SC sheet prepared by smelting. The alloy sheet obtained by melting is placed in a molybdenum boat and placed in a heating furnace. The vacuum degree in the furnace is pumped to 10 -3 Pa and heated to 900°C. When the temperature reaches the target temperature, argon gas with a pressure of 30 kPa is filled into the furnace, and it is kept warm for 30 minutes. After the heat treatment is completed, it is cooled to room temperature with the furnace.

[0045] The alloy sheet undergoes a hydrogen absorption reaction under a hydrogen pressure of 0.09 MPa. The number of saturated hydrogen absorption times for 20 kg of flake is 18 times. In this embodiment, unsaturated hydrogen absorption is adopted, and the number of hydrogen absorption times is 9 times. After the hydrogen absorption reaction ends, it is heated to 550°C while pumping vacuum, and kept warm for 4 hours to remove the hydrogen in the alloy sheet. Subsequently, it is cooled to obtain hydrogenated and crushed coarse powder. After cooling, 0.05 wt.% zinc stearate is added to the coarse powder and mixed for 3 hours. The coarse powder is further crushed by a nitrogen gas jet mill to obtain fine powder, and the gas pressure is 0.6 MPa.

[0046] 0.03 wt.% of an organic lubricant (Magnetic powder protection lubricant No. 3 produced by Tianjin Yuesheng New Materials Research Institute) is added to the fine powder and mixed for 3 hours. The uniformly mixed fine powder is oriented and formed under a magnetic field. The orientation magnetic field is a static magnetic field of 3.5 T, and the pressing pressure is 5 MPa. The density of the magnet after pressing is 3.9 - 4.0 g / cm 3 . Then, cold isostatic pressing is carried out, and the pressing pressure is 160 MPa. The density of the magnet after pressing is greater than 4.6 g / cm 3 .

[0047] The magnet is sintered densely by a segmented vacuum sintering process. The vacuum degree of the vacuum sintering is below 10 -4 Pa. The sintering temperature in the low-temperature section is 1000°C, and the holding time is 3 hours. After the holding in the low-temperature section ends, it is heated to 1060°C for high-temperature section sintering, and the holding time is 3 hours.

[0048] The sintered magnet needs to undergo a two-stage aging process. First, a primary aging treatment process is carried out at 880°C for 3 hours, then it is cooled to below 100°C at a speed of not less than 20°C / min, and then heated to 500°C for a secondary aging treatment for 3 hours. After the end, it is cooled to below 80°C at a speed of not less than 30°C / min.

[0049] After the magnet is broken, samples are taken at the center, and the composition of the magnet is detected by ICP. The microstructure of the magnet is observed by SEM, and the composition and structure of the magnet micro-region are analyzed by TEM. According to the provisions of GB / T31967.2-2015, the three-point bending method is used to measure the flexural strength of the magnet. 10 samples are measured in each group of experiments and the average value is calculated. The magnetic properties of the magnet are measured by NIM equipment, and the toughness of the magnet is characterized by the vibration weight loss method provided in the patent document CN116223262A. The hardness of the magnet is tested by a Vickers hardness tester.

[0050] The composition of the magnet in each experimental group is expressed in mass fraction, as shown in Table 1 specifically: Table 1 No. Nd Pr Dy B Co Cu Ga Al Ti Nb Fe 1 23.3 7.7 0.4 0.95 1.0 0.14 0.2 0.4 0.25 / Bal 2 23.3 7.7 0.4 0.95 1.0 0.14 0.2 0.4 / 0.25 Bal 3 23.3 7.7 0.4 0.95 1.0 0.14 0.2 0.4 0.15 0.1 Bal The properties of the magnet in each experimental group are shown in Table 2: Table 2 No. Br Hcj Hk / Hcj 1 13.40 20.3 97.5% 2 13.41 20.4 97.3% 3 13.45 21.1 98.0% In Experiment No. 1 and Experiment No. 2, two elements, Ti and Nb, are added to the magnet respectively. In Experiment No. 3, Ti and Nb elements are added synergistically. From the data in Table 1 and Table 2, it can be seen that the remanence of the magnet in Experiment No. 3 is slightly higher than that in Experiment No. 1 and Experiment No. 2, while the coercivity of the magnet in Experiment No. 3 is significantly higher than that in Experiment No. 1 and Experiment No. 2, indicating that the synergistic addition of Ti and Nb elements can effectively improve the coercivity of the magnet.

[0051] The flexural strength, Vickers hardness and vibration weight loss of the magnet in each experimental group are shown in Table 3: Table 3 No. Flexural strength (MPa) Vibration weight loss (%) Hardness (Hv) 1 480.3 0.16 590.1 2 462.5 0.14 582.7 3 512.9 0.08 560.3 It can be seen that the flexural strength of the magnet in Experiment No. 3 is significantly higher than that in Experiment No. 2 and Experiment No. 1, indicating that the method of synergistically adding Ti and Nb elements can effectively improve the strength of the magnet. From the data of the magnet hardness and vibration weight loss, it can be known that the hardness and vibration weight loss of the magnet in Experiment No. 3 are both lower than those in Experiment No. 1 and Experiment No. 2. The smaller the vibration weight loss of the magnet, the stronger the ability of the magnet to absorb impact energy during the collision process, that is, the higher the toughness of the magnet. The synergistic addition of Ti and Nb elements in the present invention can improve the strength and toughness of the magnet simultaneously.

[0052] Figure 1 is the microstructure of the SC sheet after high-temperature heat treatment of Experiment No. 1 to Experiment No. 3. In Experiment No. 1, only Ti element is added. After high-temperature heat treatment, long fibrous precipitates are precipitated in the grain boundary phase of the SC sheet. The precipitate morphology of the SC sheet in Experiment No. 2 is blocky, while the precipitate of the SC sheet in Experiment No. 3 is fine flocculent. These precipitates are fully mixed with the magnetic powder during the subsequent hydrogen embrittlement and jet milling processes, and are distributed in the grain boundary phase of the magnet, which can improve the mechanical properties of the magnet and refine the main phase grains.

[0053] Figures 2 - 4 They are respectively the TEM microstructures and selected area electron diffraction patterns of the precipitates in the sintered magnets of Experiment No.1 to Experiment No.3. Only Ti element was added to the magnet of Experiment No.1, and the morphology of the precipitates in the sintered magnet was rod-shaped. The results of selected area electron diffraction showed that the precipitates were TiB2. Only Nb element was added to the magnet of Experiment No.2, and the precipitates mainly presented a massive shape. The results of selected area electron diffraction showed that the precipitates were NbFeB. While for the magnet of Experiment No.3, Ti and Nb elements were added synergistically. From the TEM microstructure, it can be seen that the precipitates in the sintered magnet were in the form of fine particles, distributed in the grain boundaries of the two main phases and the multi-main phase grain boundaries of the magnet. The size of the particles was all below 100 nm, much smaller than the particle sizes in Experiment No.1 and Experiment No.2. Through the results of selected area electron diffraction, it was known that the precipitate was Ti3Nb. The fine Ti3Nb precipitates had better dispersion. Distributed in the grain boundaries of the two main phases and the multi-main phase grain boundaries of the magnet, they could significantly strengthen the grain boundaries of the magnet without causing distortion of the main phase and reducing the hardness of the magnet. Thus, the enhancement and toughening of the magnet were achieved simultaneously, and an R-T-B rare earth permanent magnet with both high strength and high toughness was prepared.

[0054] Example 2: For low-melting metals, pure metals with a purity of more than 99.9 wt.% were used as raw materials. For elements with a melting point higher than that of pure iron, alloys of these elements and iron were used as raw materials. They were placed in the crucible in order of decreasing melting point. The vacuum in the furnace was pumped until the vacuum degree reached 10 -4 Pa, and the dew point was lower than -50 °C. Then argon gas was filled into the furnace to make the air pressure reach 30 kPa, and it was heated to 1490 °C. After the raw materials were completely melted, it was kept warm for 3 min. Then the temperature of the alloy liquid was lowered to 1450 °C, and casting was carried out. The rotation speed of the copper roller was adjusted to 70 revolutions per minute, and then the crucible was rotated at a certain speed so that the molten alloy liquid was transported to the cooling roller through the tundish for solidification and then dropped onto the water-cooled plate to cool down, obtaining an alloy sheet with a thickness of 0.28 ± 0.05 mm.

[0055] The SC sheets prepared by melting were subjected to high-temperature heat treatment. The alloy sheets obtained by melting were placed in a molybdenum boat and placed in a heating furnace. The vacuum in the furnace was pumped to 10 -3 Pa and heated to 900 °C. When the temperature reached the target temperature, argon gas with a pressure of 30 kPa was filled into the furnace, and it was kept warm for 30 min. After the heat treatment was completed, it was cooled to room temperature with the furnace.

[0056] The alloy sheet undergoes a hydrogen absorption reaction under a hydrogen pressure of 0.09 MPa. The saturation hydrogen absorption times for 20 kg of the spun flakes is 18 times. In this example, unsaturated hydrogen absorption is adopted, and the hydrogen absorption times is 9 times. After the hydrogen absorption reaction ends, the temperature is raised to 550 °C while evacuating the vacuum, and it is held for 4 h to remove the hydrogen in the alloy sheet. Subsequently, it is cooled to obtain the hydrogenated and crushed coarse powder. After cooling, 0.05 wt.% zinc stearate is added to the coarse powder and mixed for 3 h. The coarse powder is further crushed using a nitrogen gas jet mill to obtain fine powder, and the gas pressure is 0.6 MPa.

[0057] 0.03 wt.% of an organic lubricant (Magnetic powder protection lubricant No. 3 produced by Tianjin Yuesheng New Materials Research Institute) is added to the fine powder and mixed for 3 h. The uniformly mixed fine powder is oriented and formed under a magnetic field. The orientation magnetic field is a static magnetic field of 3.5 T, and the pressing pressure is 5 MPa. The density of the magnet after pressing is 3.9 - 4.0 g / cm 3 . Then cold isostatic pressing is carried out, and the pressing pressure is 160 MPa. The density of the magnet after pressing is greater than 4.6 g / cm 3 .

[0058] The magnet is sintered densely using a segmented vacuum sintering process. The vacuum degree of the vacuum sintering is below 10 -4 Pa. The sintering temperature in the low-temperature section is 1000 °C, and the holding time is 3 h. After the holding in the low-temperature section ends, the temperature is raised to 1060 °C for high-temperature section sintering, and the holding time is 3 h.

[0059] The sintered magnet needs to undergo a two-stage aging process. First, a primary aging treatment process is carried out at 880 °C for 3 h, then it is cooled to below 100 °C at a rate of not less than 20 °C / min, and then heated to 500 °C for a secondary aging treatment for 3 h. After the end, it is cooled to below 80 °C at a rate of not less than 30 °C / min.

[0060] After the magnet is broken, samples are taken at the center, and the composition of the magnet is detected using ICP. The microstructure of the magnet is analyzed using SEM, and the proportion of high-melting-point element borides in the high-melting-point element precipitates within a range of 1 mm 2 is statistically analyzed. According to the provisions of GB / T31967.2 - 2015, the three-point bending method is used to measure the flexural strength of the magnet. 10 samples are measured in each group of experiments and the average value is calculated. The magnetic properties of the magnet are measured using NIM equipment, and the toughness of the magnet is characterized according to the vibration weight loss method provided in the patent document CN116223262A. The hardness of the magnet is tested using a Vickers hardness tester.

[0061] The composition of the magnet in each experimental group is expressed in mass fraction, as shown in Table 4 specifically: Table 4 No. Nd Tb B Co Cu Ga Ti Nb Fe 4 30.25 0.3 0.95 0.5 0.2 0.3 0.35 0.20 Bal 5 30.25 0.3 0.95 0.5 0.2 0.3 0.35 0.05 Bal 6 30.25 0.3 0.95 0.5 0.2 0.3 0.50 0.25 Bal The properties of the magnet in each experimental group are shown in Table 5: Table 5 No. Br Hcj Hk / Hcj 4 14.40 13.5 98.1% 5 14.35 12.6 97.6% 6 14.20 11.5 89.7% The bending strength, Vickers hardness, and vibration weight loss of the magnets in each experimental group are shown in Table 6 as follows: Table 6 No. Flexural strength (MPa) Vibration weight loss (%) Hardness (Hv) 4 462.3 0.12 540.6 5 425.6 0.20 590.6 6 380.6 0.35 634.3 The quantity ratios of borides of high melting point elements in the magnets of each experimental group to the precipitates are shown in Table 7 as follows: Table 7 No. Proportion of boride (%) 4 2.1% 5 20.6% 6 3.8% In this embodiment, the contents and ratios of Ti and Nb elements in the magnet of Experiment No. 4 meet the requirements of the present invention. Therefore, the magnet has high strength and toughness. The contents of Ti and Nb elements in the magnet of Experiment No. 5 are within the range required by the present invention, but the ratio of [Ti] / 47.87 ≤ 4×[Nb] / 92.91 is not satisfied. From the data in Table 7, it can be seen that among the precipitates of the magnet of Experiment No. 5, the proportion of borides of high melting point elements (TiB2) is relatively large. In the present invention, a certain amount of Nb element needs to be added to promote the formation of Ti3Nb phase and inhibit the precipitation of TiB2. However, in Experiment No. 5, the addition of Nb element is less, and Ti element cannot fully form Ti3Nb phase. Therefore, the remaining Ti will react with the B element in the magnet to form TiB2. The size of the TiB2 precipitates is relatively large. The distribution of precipitates with larger size near the main phase grains will cause stress concentration near the main phase grains, and the main phase grains will be distorted. Therefore, the hardness of the magnet is relatively large. In addition, the coarse precipitates have poor dispersion distribution and poor strengthening effect on the magnet. Therefore, the strength and toughness of the magnet are lower than those of the magnet of Experiment No. 4. In addition, due to the precipitation of more TiB2, more B element is consumed, resulting in a decrease in the formation ratio of the main phase of the magnet. Therefore, the remanence of the final magnet decreases.

[0062] The content ratio of Ti and Nb elements in the magnet of Experiment No. 6 satisfies the ratio requirement of [Ti] / 47.87 ≤ 4×[Nb] / 92.91. However, the magnet contains too much high melting point element Ti, exceeding the range of 0.1 - 0.4 wt.%, resulting in difficulty in sintering the magnet densely and reducing the mechanical properties of the material. At the same time, the presence of too many non-magnetic phases will cause a decrease in the remanence of the magnet. Therefore, both the magnetic properties and mechanical properties of the magnet of Experiment No. 6 are at a relatively low level.

[0063] Example 3: For low melting point metals, pure metals with a purity of more than 99.9 wt.% are used as raw materials. For elements with a melting point higher than that of pure iron, alloys of these elements and iron are used as raw materials. They are placed in the crucible in order from high to low melting point, and the furnace is evacuated until the vacuum degree reaches 10 -4Pa, the dew point is lower than -50 °C. Then, argon gas is filled into the furnace to make the air pressure reach 30 kPa, and it is heated to 1490 °C. After the raw materials are completely melted, it is kept warm for 3 minutes. Then, the temperature of the alloy liquid is lowered to 1450 °C, and casting is carried out. The rotation speed of the copper roller is adjusted to 70 revolutions per minute, and then the crucible is rotated at a certain speed to make the molten alloy liquid pass through the tundish and be transported to the cooling roller for solidification, and then it falls onto the water-cooled plate to cool down, obtaining an alloy sheet with a thickness of 0.30 ± 0.05 mm.

[0064] The SC sheets prepared by melting are subjected to high-temperature heat treatment. The alloy sheets obtained by melting are placed in a molybdenum boat and placed in a heating furnace. The vacuum degree in the furnace is pumped to 10 -3 Pa and heated to 900 °C. When the temperature reaches the target temperature, argon gas with a pressure of 30 kPa is filled into the furnace, and it is kept warm for 30 minutes. After the heat treatment is completed, it is cooled to room temperature with the furnace. In this embodiment, Experiment No. 7 and Example 9 adopt the SC sheet heat treatment process, while Experiment No. 8 does not adopt the SC sheet heat treatment process.

[0065] The alloy sheet undergoes a hydrogen absorption reaction under a hydrogen pressure of 0.09 MPa. The saturated hydrogen absorption times for 20 kg of flaked samples is 18 times. In this embodiment, unsaturated hydrogen absorption is adopted, and the hydrogen absorption times is 9 times. After the hydrogen absorption reaction ends, it is heated to 550 °C while evacuating the vacuum to remove the hydrogen in the alloy sheet during the 4-hour holding period, and then it is cooled to obtain hydrogenated and crushed coarse powder. After cooling, 0.05 wt.% zinc stearate is added to the coarse powder and mixed for 3 hours, and the coarse powder is further crushed by a nitrogen gas jet mill to obtain fine powder, with the gas pressure being 0.6 MPa.

[0066] 0.03 wt.% of an organic lubricant (Magnetic Powder Protection Lubricant No. 3 produced by Tianjin Yuesheng New Materials Research Institute) is added to the fine powder and mixed for 3 hours. The uniformly mixed fine powder is oriented and formed under a magnetic field. The orientation magnetic field is a static magnetic field of 3.5 T, and the pressing pressure is 5 MPa. The density of the magnet after pressing is 3.9 - 4.0 g / cm 3 . Then, cold isostatic pressing is carried out, and the pressing pressure is 160 MPa. The density of the magnet after pressing is greater than 4.6 g / cm 3 .

[0067] The magnet is sintered densely by a segmented vacuum sintering process. The vacuum degree of the vacuum sintering is below 10 -4 Pa. The sintering temperature in the low-temperature section is 1000 °C, and the holding time is 3 hours. After the holding in the low-temperature section ends, it is heated to 1060 °C for high-temperature section sintering, and the holding time is 3 hours. In this embodiment, Experiment No. 7 and Experiment No. 8 magnets adopt a two-stage sintering process. Experiment No. 9 does not adopt a two-stage sintering process and is directly heated to 1060 °C and held for 6 hours.

[0068] The sintered magnet needs to undergo a two-stage aging process. First, a primary aging treatment process is carried out at 880 °C for 3 h, then it is cooled to below 100 °C at a rate of not less than 20 °C / min, and then heated to 500 °C for a secondary aging treatment for 3 h. After that, it is cooled to below 80 °C at a rate of not less than 30 °C / min.

[0069] After the magnet is broken, samples are taken at the center, and the composition of the magnet is detected by ICP. The microstructure of the magnet is observed by SEM. According to the provisions of GB / T31967.2-2015, the three-point bending method is used to measure the flexural strength of the magnet. 10 samples are measured in each group of experiments and the average value is calculated. The magnetic properties of the magnet are measured by NIM equipment, and the toughness of the magnet is characterized by the vibration weight loss method provided by the patent document CN116223262A. The hardness of the magnet is tested by a Vickers hardness tester.

[0070] The processes adopted by the magnets in different experimental groups are shown in Table 8: Table 8 No. Heat treatment of SC flakes Two - stage sintering process 7 √ √ 8 × √ 9 √ × The composition of the magnets in each experimental group is expressed in mass fraction, as shown in Table 9 specifically: Table 9 No. Nd Tb B Co Cu Ga Ti Nb Fe 7 30.25 0.3 0.95 0.5 0.2 0.3 0.35 0.20 Bal 8 30.25 0.3 0.95 0.5 0.2 0.3 0.35 0.20 Bal 9 30.25 0.3 0.95 0.5 0.2 0.3 0.35 0.20 Bal The properties of the magnets in each experimental group are shown in Table 10: Table 10 No. Br Hcj Hk / Hcj 7 14.40 13.5 98.1% 8 14.40 12.6 97.6% 9 14.40 12.3 97.6% The flexural strength, Vickers hardness and vibration weight loss of the magnets in each experimental group are shown in Table 11: Table 11 No. Flexural strength (MPa) Vibration weight loss (%) Hardness (Hv) 7 462.3 0.12 540.6 8 440.3 0.16 568.5 9 451.8 0.14 552.3 From the data in Table 9, it can be seen that the SC sheet heat treatment and the two-stage sintering process will not affect the composition of the magnet. However, the results in Table 10 show that there are obvious differences in the magnetic properties of the final magnets. The coercivities of the magnets in Experiment No. 8 and No. 9 are both lower than that in Experiment No. 7. By statistically analyzing the grain sizes of the magnets in Experiment No. 7 to Experiment No. 9, it is found that the average grain size of the magnet in Experiment No. 7 is 4.6 μm, while the average grain sizes of the magnets in Experiment No. 8 and Experiment No. 9 are 5.1 μm and 5.3 μm respectively. It shows that the SC sheet heat treatment and the two-stage sintering process can significantly refine the grains, thereby improving the coercivity of the magnet.

[0071] From the data in Table 11, it can be seen that the flexural strengths of the magnets in Experiment No. 8 and Experiment No. 9 are significantly lower than that in Experiment No. 7, and at the same time the vibration weight loss is higher than that in Experiment No. 7, indicating that the strength and toughness of the magnets in Experiment No. 8 and Experiment No. 9 are at a lower level compared with Experiment No. 7. By statistically analyzing the distribution of precipitates of high-melting-point elements in the magnet, the results are shown in Table 12: Table 12 No. Proportion of R - rich phase Ti3Nb distributed at grain boundaries 7 99.8% 8 90.2% 9 93.1% As can be seen from Table 12, most of the Ti3Nb precipitates in the magnet of Experiment No. 7 are distributed in the R-rich phase at the grain boundaries of the magnet. However, a relatively large number of Ti3Nb precipitates in the magnets of Experiment No. 8 and Experiment No. 9 are distributed inside the grains of the main phase of the magnet. Since Ti3Nb belongs to the precipitates of high melting point elements and has poor wettability with the main phase of the magnet, the interface between the two phases is a natural crack source, which results in poor mechanical properties of the magnets of Experiment No. 8 and Experiment No. 9. In the present invention, the SC sheet heat treatment process can make the Ti3Nb precipitates precipitate in the SC sheet stage. After hydrogen decrepitation and jet milling, the Ti3Nb precipitates are uniformly mixed with the magnetic powder. In the subsequent sintering process, a two-stage sintering process is adopted to make the Ti3Nb precipitates distributed in the grain boundary phase of the magnet grow preferentially. The precipitation of the precipitates prior to the growth of the main phase grains can effectively refine the grains, avoid the merger and growth of the main phase and the precipitation of Ti3Nb inside the main phase grains. Therefore, in the present invention, the SC sheet heat treatment process and the two-stage sintering process are preferably adopted.

[0072] Example 4: For low melting point metals, pure metals with a purity of more than 99.9 wt.% are used as raw materials. For elements with a melting point higher than that of pure iron, alloys of these elements and iron are used as raw materials. They are placed in the crucible in the order of decreasing melting point. The furnace is evacuated until the vacuum degree reaches 10 -4 Pa, and the dew point is lower than -50 °C. Then argon is filled into the furnace to make the air pressure reach 30 kPa, and it is heated to 1490 °C. After the raw materials are completely melted, it is kept warm for 3 min. Then the temperature of the alloy liquid is lowered to 1450 °C and casting is carried out. The rotation speed of the copper roller is adjusted to 70 revolutions per minute, and then the crucible is rotated at a certain speed to make the molten alloy liquid pass through the tundish and be transported to the cooling roller for solidification and then fall onto the water-cooled plate to cool down, obtaining alloy sheets with a thickness of 0.28 ± 0.05 mm.

[0073] The SC sheets prepared by melting are subjected to high-temperature heat treatment. The alloy sheets obtained by melting are placed in a molybdenum boat and placed in a heating furnace. The vacuum degree in the furnace is pumped to 10 -3 Pa and heated to 900 °C. When the temperature reaches the target temperature, argon with a pressure of 30 kPa is filled into the furnace, and it is kept warm for 30 min. After the heat treatment is completed, it is cooled to room temperature with the furnace.

[0074] The alloy sheet undergoes a hydrogen absorption reaction under a hydrogen pressure of 0.09 MPa. The saturation hydrogen absorption times for 20 kg of flaked samples is 24 times. In Experiment No. 11, unsaturated hydrogen absorption is adopted, with the hydrogen absorption times being 10 times; in Experiment No. 12, saturated hydrogen absorption is adopted, with the hydrogen absorption times being 24 times. After the hydrogen absorption reaction ends, the temperature is raised to 550 °C while evacuating the vacuum, and held for 4 h to remove the hydrogen in the alloy sheet. Subsequently, it is cooled to obtain hydrogenated and crushed coarse powder. After cooling, 0.05 wt.% zinc stearate is added to the coarse powder and mixed for 3 h. The coarse powder is further crushed using a nitrogen gas jet mill to obtain fine powder, and the gas pressure is 0.6 MPa.

[0075] 0.03 wt.% of an organic lubricant (Magnetic Powder Protection Lubricant 3# produced by Tianjin Yuesheng New Material Research Institute) is added to the fine powder and mixed for 3 h. The uniformly mixed fine powder is oriented and formed under a magnetic field. The orientation magnetic field is a static magnetic field of 3.5 T, and the pressing pressure is 5 MPa. The density of the magnet after pressing is 3.9 - 4.0 g / cm 3 . Then cold isostatic pressing is carried out, with the pressing pressure being 160 MPa. The density of the magnet after pressing is greater than 4.6 g / cm 3 .

[0076] The magnet is sintered densely using a segmented vacuum sintering process. The vacuum degree of the vacuum sintering is below 10 -4 Pa. The sintering temperature in the low-temperature section is 950 °C, and the holding time is 4.5 h. After the holding in the low-temperature section ends, the temperature is raised to 1050 °C for high-temperature section sintering, and the holding time is 4.5 h.

[0077] The sintered magnet needs to undergo a two-stage aging process. First, a primary aging treatment process is carried out at 880 °C for 3 h, then cooled at a rate of not less than 20 °C / min to below 100 °C, and then heated to 500 °C for a secondary aging treatment for 3 h. After the end, it is cooled at a rate of not less than 30 °C / min to below 80 °C.

[0078] After the magnet is broken, samples are taken at the center, and the magnet composition is detected using ICP. The microstructure of the magnet is observed using SEM, and the number of high-melting-point element precipitates within the range of 1 mm 2 is counted. According to the provisions of GB / T31967.2 - 2015, the three-point bending method is used to measure the flexural strength of the magnet. 10 samples are measured in each group of experiments and the average value is calculated. The magnetic properties of the magnet are measured using NIM equipment, and the toughness of the magnet is characterized according to the vibration weight loss method provided in the patent document CN116223262A. The hardness of the magnet is tested using a Vickers hardness tester.

[0079] The magnet composition of each experimental group is expressed in mass fraction, as shown in Table 13 specifically: Table 13 No. Nd Pr B Co Al Cu Ga Dy Ti Nb Fe 11 20.6 6.5 0.92 1.0 0.2 0.2 0.3 1.9 0.18 0.1 Bal 12 20.6 6.5 0.92 1.0 0.2 0.2 0.3 1.9 0.16 0.09 Bal The flexural strength, Vickers hardness, and vibration weight loss of the magnets in each experimental group are shown in Table 14: Table 14 No. Flexural strength (MPa) Vibration weight loss (%) Hardness (Hv) 11 496.3 0.11% 580.3 12 471.0 0.12% 583.6 As can be seen from Table 13, the saturation hydrogen absorption process was used in the preparation of Experiment No. 12. The contents of Ti and Nb elements in the final sintered magnet were lower than those in Experiment No. 11, indicating that the loss amounts of Ti and Nb elements were greater during the magnet preparation process in Experiment No. 12. Comparing the mechanical properties of the magnets in Experiment No. 11 and Experiment No. 12, the hardness and vibration weight loss of the magnets in the two experimental groups were basically the same, but the flexural strength of the magnet in Experiment No. 12 was lower than that in Experiment No. 11.

[0080] In the present invention, Ti3Nb phase will precipitate in the grain boundary phase during the high-temperature heat treatment of the SC sheet. When saturated hydrogen absorption is used in the hydrogen crushing stage, the grain boundary phase will be overly crushed, resulting in a large amount of loss of the Ti3Nb compound distributed in the grain boundary phase during the jet milling stage along with the separation of the ultrafine powder. Eventually, the number of Ti3Nb precipitates in the magnet decreases, and the strengthening and toughening effects of Ti3Nb on the magnet are reduced. Therefore, an unsaturated hydrogen absorption process is adopted in the present invention.

Claims

1. A high-strength and high-toughness RTB rare earth permanent magnet, characterized in that The magnet composition comprises the following components: R: 28.5wt.%~34.0wt.%, R includes one or more elements selected from Nd, Pr, Dy, Tb, Ho, Gd, La, Ce, Lu, and Y; and R contains at least R1 element, and the R1 element is one or more of Nd, Pr, and Ce; B: 0.85~1.1wt.%, Ti: 0.1~0.4wt.%, Nb: 0.05~0.5wt.%, M: 0.01-8.0wt.%, M is at least one of Al, Cu, Ga, Ni, Zn, Sn, Mn, and Zr, The balance is T and other unavoidable impurities, where T is Fe or Fe and Co, and more than 85.0% of the mass fraction of T is Fe; And satisfy: [Ti] / 47.87≤4×[Nb] / 92.91, wherein [Ti] is the content of Ti expressed in mass fraction, and [Nb] is the content of Nb expressed in mass fraction; The magnet contains Ti3Nb precipitates, and more than 99% of the Ti3Nb precipitates are distributed in the R-rich phase at the grain boundaries of the magnet.

2. The high-strength and high-toughness RTB rare earth permanent magnet according to claim 1, characterized in that The size of the Ti3Nb precipitates is between 2 and 800 nm.

3. The high-strength and high-toughness RTB rare earth permanent magnet according to claim 1, characterized in that The Ti3Nb precipitates are distributed on the two-main-phase grain boundaries and the multi-main-phase grain boundaries of the magnet.

4. The high-strength and high-toughness RTB rare earth permanent magnet according to claim 1, characterized in that The magnet includes high melting point element precipitates, which include Ti3Nb precipitates and borides of Ti and Nb. The amount of borides of Ti and Nb in a cross section of the magnet in any direction is less than 5% of the amount of high melting point element precipitates.

5. The high-strength and high-toughness RTB rare earth permanent magnet according to any one of claims 1 to 4, characterized in that The high-strength and high-toughness RTB rare earth permanent magnet is prepared according to the following method: raw materials are taken according to a ratio and vacuum induction melting and belt spinning are used to prepare SC sheets, the SC sheets are subjected to high-temperature heat treatment, the SC sheets after high-temperature heat treatment are subjected to hydrogen cracking treatment for unsaturated hydrogen absorption and air flow grinding to obtain alloy powder, the alloy powder is molded in an oriented magnetic field and cold isostatically pressed, and the obtained molded magnet is subjected to segmented vacuum sintering and aging treatment to obtain the high-strength and high-toughness RTB rare earth permanent magnet.

6. The method for preparing the high-strength and high-toughness RTB rare earth permanent magnet according to any one of claims 1 to 4, characterized in that The method comprises the following steps: raw materials are taken according to a ratio, and SC sheets are prepared by vacuum induction melting and belt spinning; the SC sheets are subjected to high-temperature heat treatment; the SC sheets after the high-temperature heat treatment are subjected to hydrogen cracking treatment for unsaturated hydrogen absorption and air flow grinding to obtain alloy powder; the alloy powder is molded in an oriented magnetic field and cold isostatically pressed; the obtained molded magnets are subjected to segmented vacuum sintering and aging treatment to obtain the high-strength and high-toughness RTB rare earth permanent magnets.

7. The method according to claim 6, characterized in that The high temperature heat treatment of the SC sheet refers to keeping the SC sheet in an argon environment at 800-900° C. for 20-50 minutes, with the argon pressure being 30-50 kPa.

8. The method according to claim 6, characterized in that The unsaturated hydrogen absorption means that the number of hydrogen absorption is 0.2 to 0.8 times the number of saturated hydrogen absorption; the saturated hydrogen absorption number is obtained by testing according to the following method: SC sheets of the same specification and weight are placed in a reactor, and after evacuation, hydrogen is filled with a positive pressure of 0.1 MPa. The positive pressure refers to the difference between the absolute pressure and the standard atmospheric pressure. The hydrogen absorption of the SC sheet causes the hydrogen pressure in the reactor to decrease, and the positive pressure in the reactor is reduced to 0.05 to 0.06 MPa. Hydrogen is filled into the reactor again until the positive pressure is 0.1 MPa. Each hydrogen filling action is counted as one hydrogen absorption number; after multiple hydrogen absorptions, after a certain hydrogen filling, the pressure change within 10 minutes is less than 0.5%, indicating that the SC sheet is saturated with hydrogen absorption, and the total number of hydrogen fillings at this time is the saturated hydrogen absorption number.

9. The method according to claim 6, characterized in that The segmented vacuum sintering includes low-temperature segment sintering and high-temperature segment sintering. The low-temperature segment sintering is carried out at a temperature of 900-1020°C for 3-6 hours, and the high-temperature segment sintering is carried out at a temperature of 1040-1080°C for 3-6 hours. The vacuum degree of the segmented vacuum sintering is 10 -4 Below Pa.

10. The method according to claim 6, characterized in that The aging treatment refers to a primary aging treatment process in which the sintered magnet is subjected to a temperature of 700-900°C for 2-8 hours, then cooled to below 100°C at a rate of not less than 20°C / min, and then heated to 400-600°C for a secondary aging treatment of 2-8 hours, and then cooled to below 80°C at a rate of not less than 30°C / min.

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