High-strength r-t-b rare earth permanent magnet having amorphous grain boundary phase and method for producing the same

Abstract

The present invention discloses a high-strength R-T-B rare earth permanent magnet with an amorphous grain boundary phase. The composition of the magnet includes: large atomic radius-like elements with an atomic radius r satisfying r≥0.16 nm: 29.0 wt.% to 34.0 wt.%, and the large atomic radius-like elements contain 0.1 wt.% to 0.8 wt.% of Mf, where Mf is any one or both of Zr and Mg; small atomic radius-like elements with r≤0.12 nm: 1.05 wt.% to 1.65 wt.%, and contain 0.8 wt.% to 1.1 wt.% of boron element; and the total content C1 of the small atomic radius-like elements satisfies 0.25 wt.% ≤ [C1] - [B] ≤ 0.55 wt.%; the balance is medium atomic radius-like elements with 0.12 nm < r < 0.16 nm and impurities, and at least 60.0 wt.% of TM, where TM is at least one of Fe and Co; the content of other medium atomic radius-like elements other than TM is ≥0.2 wt.%. In the magnet of the present invention, the proportion of the amorphous grain boundary phase in the grain boundary phase is increased to more than 20 vol.%, improving the ability of the grain boundary phase of the magnet to resist crack propagation, and a high-strength R-T-B rare earth permanent magnet is prepared.

Description

Technical Field

[0001] This invention relates to a high-strength RTB rare-earth permanent magnet with an amorphous grain boundary phase and its preparation method, belonging to the field of rare-earth magnets. Background Technology

[0002] RTB-based rare-earth permanent magnets are permanent magnet materials with superior magnetic properties. Compared with other permanent magnet materials, they have the highest maximum energy product and are widely used in modern industry. In recent years, with the expansion of the application range of RTB rare-earth permanent magnets, especially in high-speed and high-torque motors, the requirements for the mechanical properties of the magnets have become increasingly stringent.

[0003] The microstructure of RTB rare earth permanent magnets contains the main phase R2T. 14 B and grain boundary phases, where the main phase is a complex intermetallic compound with high strength. Grain boundary phases mainly include two types: one is the triangular grain boundary phase distributed between the three main phase grains, and the other is the thin-layer grain boundary phase distributed between the two main phase grains. Currently, in the fabrication of RTB magnets, to achieve high coercivity, a high content of low-melting-point elements is usually added to the magnet, and tempering is used to transform the grain boundary phase of the magnet into an FCC structure with high wettability with the main phase. However, this type of grain boundary phase has low strength and poor resistance to crack propagation. When the magnet is under stress, cracks easily propagate along the grain boundary phase, leading to intergranular fracture. Therefore, improving the strength of the grain boundary phase of the magnet and enhancing its resistance to crack propagation is an effective method to improve the mechanical properties of the magnet.

[0004] Amorphous materials are a state of matter that forms when atoms in an alloy do not have enough time to crystallize in an ordered manner during solidification. The formation of amorphous materials requires suppressing atomic ordering, thus necessitating a certain degree of supercooling during solidification. Furthermore, enhancing the amorphous formation capability of the liquid grain boundary phase through rational composition design is crucial for the formation of amorphous substances. Generally, the more constituent elements there are, the stronger the amorphous formation capability of the alloy, because an increased number of components inhibits the formation of a fully crystalline phase during cooling. Three empirical guidelines are typically followed when designing amorphous compositions: more than three components; significant differences in atomic size among the three main elements; and a negative enthalpy of mixing among the three main elements. Enhancing the amorphous formation capability of an alloy through rational composition design, combined with a greater degree of supercooling during solidification, can effectively transform the alloy into an amorphous state.

[0005] Compared with traditional crystalline materials, amorphous materials have many special properties. For example, when a certain substance is in the amorphous state, its strength is significantly higher than its crystalline state, and its anti-corrosion and oxidation resistance is also higher than that of crystalline substances. Therefore, by certain process methods, transforming the grain boundary phase of the magnet into an amorphous state, enhancing the strength of the grain boundary phase, and improving its ability to resist crack propagation, it is expected to prepare high-strength R-T-B rare earth permanent magnets. Summary of the Invention

[0006] Aiming at the phenomenon that the strength of the grain boundary phase of R-T-B rare earth permanent magnets is low, and cracks are prone to expand along the grain boundary phase when stressed, resulting in poor mechanical properties of the magnets, the present invention provides a method for preparing high-strength R-T-B rare earth permanent magnets. According to the design principle of amorphous alloys, three types of elements with different atomic radii are simultaneously included in the elements prone to segregation at the grain boundary phase of R-T-B magnets, namely: large atomic radius elements with atomic radius r≥0.16nm, medium atomic radius elements with atomic radius 0.12nm < r < 0.16nm, and small atomic radius elements with atomic radius r≤0.12nm. When the grain boundary phase simultaneously contains three elements with different atomic radii and the concentration ratio is within a certain range, its ability to form amorphous will be significantly improved. Therefore, it can also be transformed into an amorphous state at a slower cooling rate after secondary aging. By virtue of the high-strength characteristics of the amorphous grain boundary phase, the mechanical properties of R-T-B magnets can be enhanced.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A high-strength R-T-B rare earth permanent magnet with an amorphous grain boundary phase, the composition of the magnet includes:

[0009] Large atomic radius elements with atomic radius r satisfying r≥0.16nm: 29.0wt.% - 34.0wt.%, the large atomic radius elements include more than three of Nd, Pr, Dy, Tb, Ho, La, Ce, Gd, Er, Mg, Zr, and the large atomic radius elements contain 0.1wt.% - 0.8wt.% of Mf, and Mf is any one or two of Zr and Mg;

[0010] Small atomic radius elements with atomic radius r satisfying r≤0.12nm: 1.05wt.% - 1.65wt.%, the small atomic radius elements include more than three of S, C, H, N, O, F, B, and contain 0.8wt.% - 1.​​That is, the total content of small atomic radius elements other than boron element is 0.25 wt.% to 0.55 wt.%, preferably 0.3 wt.% to 0.5 wt.%.

[0012] The balance is medium atomic radius elements with atomic radius r satisfying 0.12 nm < r < 0.16 nm and other inevitable impurities: The medium atomic radius elements include more than three of Fe, Co, Ti, Al, Nb, Zn, Ga, W, Mn, Mo, V, Si, P, Cu; at least 60.0 wt.% of TM is included in the medium atomic radius elements, and TM is at least one of Fe and Co; the content of other medium atomic radius elements except TM ≥ 0.2 wt.%; preferably, the content of other medium atomic radius elements except TM is 0.2 - 1.5 wt.%.

[0013] Each of the mass percentages is based on the mass of the magnet.

[0014] The magnet includes a main phase R2T 14 B and a grain boundary phase, and the grain boundary phase is composed of a crystalline grain boundary phase and an amorphous grain boundary phase;

[0015] The amorphous grain boundary phase simultaneously includes three types of elements with large, medium, and small atomic radii, and the number of small atomic radius elements included ≥ 3, the number of medium atomic radius elements ≥ 3, and the number of large atomic radius elements ≥ 3.

[0016] Furthermore, the proportion of the amorphous grain boundary phase in the grain boundary phase of the magnet is above 20 vol.% (volume ratio).

[0017] Even further, the content of large atomic radius elements in the amorphous grain boundary phase of the magnet is 30 wt.% to 70.0 wt.%, and 0.2 wt.% to 10.0 wt.% of Mf is included in the large atomic radius elements; the content of medium atomic radius elements is 20.0 wt.% to 65.0 wt.%, and the content of small atomic radius elements is 1.0 wt.% to 15.0 wt.%. Here, the mass percentages are all based on the mass of the amorphous grain boundary phase of the magnet.

[0018] Furthermore, the medium atomic radius elements are preferably more than three of Fe, Co, Al, Nb, Ga, Cu; at least 60.0 wt.% of TM is included in the medium atomic radius elements, and TM is at least one of Fe and Co; preferably, more than 85 wt.% of TM is Fe;

[0019] Furthermore, the high-strength R-T-B rare earth permanent magnet with an amorphous grain boundary phase is prepared by one of the following methods:

[0020] (i) Magnets do not contain Mg: SC sheets are melted and spun according to the composition ratio, alloy powder is prepared by hydrogen crushing and air jet milling, the alloy powder is mixed with powder containing elements with small atomic radii, the mixed powder is molded in an orientation magnetic field, isostatically pressed to prepare a compact, vacuum sintering, first-stage aging and second-stage aging to obtain the RTB rare earth permanent magnet with amorphous grain boundary phase.

[0021] (II): Magnet containing Mg element: SC sheet is melted and spun according to the composition ratio of elements other than Mg, and alloy powder is prepared by hydrogen crushing and air jet milling. The alloy powder is mixed with Mg particles and powder containing elements with small atomic radii. The mixed powder is molded in an orientation magnetic field, isostatically pressed to prepare a compact, and vacuum sintered, first-stage aged and second-stage aged to obtain the RTB rare earth permanent magnet with amorphous grain boundary phase.

[0022] The powder containing small atomic radius elements is one or more of the powders containing S, C, O or F elements. The powders containing S, C, O or F elements are generally intermediate alloy powders and / or compound powders containing S, C, O or F elements. The intermediate alloy powders and / or compound powders containing S, C, O or F elements are generally intermediate alloy powders and / or compound powders containing S, C, O or F elements and Fe or rare earth elements.

[0023] The particle size of the powder containing small atomic radius elements is within 500 nm, preferably within 100 nm;

[0024] Preferably, the powder containing small atomic radius elements is one or more of FeS, Nd2O3, Fe3C, terbium fluoride, and dysprosium fluoride.

[0025] More preferably, the amount of FeS is 0.2 to 0.5% of the mass of the alloy powder, preferably 0.2 to 0.3 wt.%, the amount of Nd2O3 is 0.2 to 0.6% of the mass of the alloy powder, preferably 0.3 to 0.5 wt.%, and the amount of Fe3C is 0.1 to 0.3% of the mass of the alloy powder, preferably 0.1 to 0.2 wt.%.

[0026] In method (ii), the Mg particles are pure metal particles or magnesium oxide particles;

[0027] The particle size of Mg is within 500 nm, preferably within 100 nm.

[0028] In method (i) or method (ii), preferably, the mixed powder is molded under an orientation magnetic field after the addition of organic additives. The organic additives are one or more of lubricants and antioxidants, and the lubricants and antioxidants can be commercially available magnetic powder protective lubricants or antioxidants. The amount of lubricant added can be 0.05-0.1% of the alloy powder mass, and the amount of antioxidant can be 0.05-0.15% of the alloy powder mass.

[0029] After sintering, organic additives leave residual carbon in the magnet, typically ranging from 400 to 1000 ppm. Even with excessive amounts of organic additives, the carbon content of the magnet will not increase significantly, as most of the organic additives volatilize during sintering. Additionally, the magnet will also retain residual H, N, and O elements. H originates from the hydrogen decomposition step, and N from the nitrogen carrier gas in the air jet mill. However, the residual H content is generally very low, typically between 2 and 10 ppm, and is generally negligible. The residual N content in the magnet is also relatively constant, generally between 200 and 400 ppm. Furthermore, oxidation is unavoidable during magnet manufacturing, resulting in a certain degree of residual oxygen, typically between 500 and 1300 ppm.

[0030] Therefore, in method (I) or method (II), if no small atomic radius element powder is added, and the magnet is prepared according to the conventional process, the magnet will always contain residual O, N, and C (the residual amount of H atoms is negligible), which meets the requirement that the magnet contains more than three types of small atomic radius elements. The residual content of O, N, and C is approximately 0.11–0.27 wt%, but the residual amount is subject to fluctuations due to process conditions. Usually, the residual amount is mostly distributed around 0.2 wt%, which is difficult to control and difficult to guarantee that the residual amount will always reach more than 0.25 wt%. Without the addition of small atomic radius element powder, it is very likely that the requirement that the total content of small atomic radius elements other than boron be 0.25 wt.%–0.55 wt.% cannot be met. Therefore, the preparation method of the present invention preferably adds small atomic radius element powder to the alloy powder to ensure that the content of small atomic radius elements other than boron reaches more than 0.25 wt.%.

[0031] However, increasing the content of H and N elements will lead to a decrease in the magnetic properties of the magnet, so alloy or compound powders containing H and N elements are generally not added. Powders containing S, C, O, or F elements are usually added instead.

[0032] In the method described, cooling after the second-stage aging is preferably performed at a cooling rate of ≥60℃ / min. Low-temperature air cooling is generally achieved using a fan. The preferred cooling rate after the second-stage aging is 60–100℃ / min.

[0033] The amorphous forming ability of an alloy increases with the number of constituent elements because this increase inhibits the formation of a fully crystalline phase during cooling. Typically, to enhance the amorphous forming ability of the liquid phase, the alloy requires more than three constituent elements with significant differences in atomic size among the three main elements. This invention designs the alloy composition based on the principles of amorphous alloy design, ensuring that elements prone to segregation in the grain boundary phase of RTB magnets simultaneously include elements with large, medium, and small atomic radii. When the grain boundary phase simultaneously contains three elements with different atomic radii within a certain concentration range, its amorphous forming ability is significantly enhanced, thus enabling it to transform into an amorphous state even at slower cooling rates after secondary aging. The high strength of the amorphous grain boundary phase can significantly improve the mechanical properties of the RTB magnet.

[0034] Rare earth elements have large atomic radii. This invention adds rare earth elements at a stoichiometric ratio exceeding that of the main phase, thus some rare earth elements will exist in the grain boundary phase. Increasing the variety of rare earth elements ensures the simultaneous presence of several different large atomic radius elements in the grain boundary phase. This invention also discovered that the segregation of Zr and Mg, large atomic radius elements, in the grain boundary phase can significantly enhance the amorphous formation ability of the liquid grain boundary phase. After adding a certain amount of Zr and Mg to the alloy, the proportion of the amorphous grain boundary phase significantly increases after secondary aging. Therefore, in this invention, the large atomic radius elements include 0.1 wt.% to 0.8 wt.% Zr and Mg. Since Mg has a low boiling point, adding Mg during the smelting process will lead to excessive volatilization. Therefore, when the alloy contains Mg, it is added by mixing pure metal or oxide particles with magnetic powder.

[0035] Small atomic radius elements can significantly increase the viscosity of liquid alloys. Therefore, the presence of a certain concentration of small atomic radius elements in the alloy can greatly enhance the amorphous formation ability of the liquid grain boundary phase, thereby hindering the formation of the crystalline phase during cooling. Boron, one of the small atomic radius elements, needs to participate in the formation of the main phase; therefore, the content of small atomic radius elements in this invention is 1.05 wt.% to 1.65 wt.%, including 0.8 wt.% to 1.1 wt.% boron. Furthermore, due to their small atomic size, small atomic radius elements are easily dissolved into the main phase grains of the magnet. The segregation concentration of small atomic radius elements added during the melting stage in the grain boundary phase is low. Therefore, this invention employs a method of mixing nanoscale powder particles containing small atomic radius elements with magnetic powder obtained from air jet milling to ensure that most of the small atomic radius elements are enriched in the grain boundary phase of the magnet. Increasing the viscosity of the liquid grain boundary phase enhances its amorphous formation ability, promoting the transformation of the liquid grain boundary phase into an amorphous state after secondary aging. The high strength of the amorphous grain boundary phase improves the mechanical properties of the magnet. In this invention, boron is added during the smelting stage in the form of ferroboron, with the portion of boron exceeding the stoichiometric ratio of the main phase being enriched in the grain boundary phase of the magnet. Other small atomic radius elements are mixed with the magnetic powder after air jet milling in the form of intermediate alloy powder, compound powder, or a mixture of both with Fe or rare earth elements. To ensure that the small atomic radius elements are sufficiently enriched in the grain boundary phase, the particle size of the small atomic radius elements is within 500 nm, preferably within 100 nm.

[0036] Among medium atomic radius elements, Fe and Co need to participate in the formation of the main phase. Therefore, this invention contains at least 60.0 wt.% Fe and Co. Fe and Co exceeding the stoichiometry of the main phase will be enriched in the magnet grain boundary phase. Furthermore, to further improve the amorphous formation capability of the liquid grain boundary phase, other medium atomic radius elements need to be added to ensure that the grain boundary phase contains ≥3 medium atomic radius elements. The content of medium atomic radius elements other than TM in the magnet needs to be ≥0.3 wt.%.

[0037] Theoretically, all materials can form amorphous states when the cooling rate is high. However, in actual production processes, it is difficult to achieve high cooling rates for large materials. Therefore, it is necessary to reduce the cooling rate requirements during amorphization by increasing the amorphous forming ability of the alloy. When the amorphous forming ability of the liquid alloy is high, amorphous states can be formed even at lower cooling rates. In this invention, by controlling the composition of the grain boundary phase alloy, the amorphous forming ability of the liquid grain boundary phase can be significantly enhanced. Therefore, after secondary aging, the grain boundary phase with the required composition can be transformed into an amorphous state even at a lower cooling rate. However, appropriately increasing the cooling rate can increase the proportion of the amorphous grain boundary phase. Therefore, in this invention, a cooling rate of ≥60℃ / min is preferred after secondary aging.

[0038] The beneficial effects of this invention are as follows: Following the design principles of amorphous alloys, the elements that readily segregate in the grain boundary phase of RTB magnets simultaneously include elements with large, medium, and small atomic radii. When the grain boundary phase simultaneously contains three elements with different atomic radii and their concentration ratio is within a certain range, its amorphous formation ability is significantly enhanced. Therefore, even at a relatively slow cooling rate after secondary aging, it can transform into an amorphous state. In this invention, the proportion of amorphous grain boundary phase in the magnet grain boundary phase is increased to over 20 vol.% (volume percentage). Utilizing the significantly higher strength of amorphous materials compared to crystalline materials of the same composition, the ability of the magnet grain boundary phase to resist crack propagation is improved, thus preparing high-strength RTB rare-earth permanent magnets. The bending strength of the magnet of this invention can reach over 560 MPa, which is more than 20% higher than that of existing technologies. Attached Figure Description

[0039] Figure 1 (a) is the bright-field image of the grain boundary phase of the magnet in Experiment No.2. (b) and (c) are the diffraction patterns of the triangular grain boundary phase between the three principal phase grains (region ① in Figure a) and the thin-layer grain boundary phase between the two principal phase grains (region ② in Figure a), respectively.

[0040] Figure 2 (a) is the bright-field image of the grain boundary phase of the magnet in Experiment No. 6. (b) and (c) are the diffraction patterns of the triangular grain boundary phase between the three principal phase grains (region ① in Figure a) and the thin-layer grain boundary phase between the two principal phase grains (region ② in Figure a), respectively.

[0041] Figure 3 (a) is the bright-field image of the grain boundary phase of the magnet in Experiment No. 10. (b) and (c) are the diffraction patterns of the triangular grain boundary phase between the three principal phase grains (region ① in Figure a) and the thin-layer grain boundary phase between the two principal phase grains (region ② in Figure a), respectively.

[0042] Figure 4 Figure (a) shows the fracture morphology of magnet No. 6 in Experiment No. 6, and Figure (b) shows a magnified view of a part of it.

[0043] Figure 5 (a) shows the fracture morphology of magnet No.10 in Experiment No.10, and (b) is a magnified view of a part of it.

[0044] Figure 6 (a) is the bright-field image of the grain boundary phase of the magnet in Experiment No. 20, and (b) is the diffraction pattern of the triangular grain boundary phase between the three principal phase grains (region ① in Figure a). Detailed Implementation

[0045] This invention employs vacuum induction melting and strip spinning to prepare alloy SC sheets. Raw materials with a purity of 99.9% or higher are selected according to the component ratio and placed into a crucible in descending order of melting point. The furnace is then evacuated until a vacuum level of 10 is reached. -3~10 - 4 The dew point is below -50℃. Argon gas is then introduced into the furnace to achieve a pressure of 30–50 kPa, and the furnace is heated to 1480–1510℃. After the raw materials are completely melted, the temperature is held for 3–5 minutes. The alloy liquid temperature is then lowered to 1440–1460℃ and held for casting. The copper roller speed is adjusted to 70–75 rpm, and the crucible is rotated at a certain speed to transport the molten alloy liquid through the tundish to the cooling roller for solidification, after which it falls onto the water-cooling plate for cooling.

[0046] SC alloy sheets are processed into alloy powder through hydrogen crushing and air jet milling. During hydrogen crushing, the hydrogen pressure inside the reactor is generally 0.01–0.09 MPa. During the hydrogen absorption reaction, the pressure change inside the reactor should not exceed 0.5% within 10 minutes, indicating the end of hydrogen absorption. After the hydrogen absorption reaction, the temperature is raised to 400–600℃ while simultaneously evacuating the reactor and held for 2–6 hours to remove hydrogen from the alloy sheets. The powder is then cooled to obtain coarse hydrogen-crushed powder. The obtained coarse powder is placed in an air jet mill, and the nozzle pressure is adjusted to 0.6–0.8 MPa. High-speed gas drives the coarse powder to collide with each other, causing it to be crushed. The gas used in the air jet mill is an inert gas such as nitrogen, helium, or argon. The powder particle size is controlled by adjusting the sorting wheel and cyclone separator of the air jet mill.

[0047] After the magnetic powder from the air jet mill is uniformly mixed with powders containing small atomic radii and powders containing Mg (when the magnet contains Mg), a lubricant and an antioxidant are added to the alloy powder. The mixture is then molded under an orientation magnetic field. Commercially available magnetic powder lubricant or antioxidant can be used. The amount of lubricant added can be 0.05–0.1% of the alloy powder mass, and the amount of antioxidant can be 0.05–0.15% of the alloy powder mass.

[0048] The preferred orientation magnetic field is 3–6 T, and the forming pressure is 5–7 MPa. The oriented compact is then subjected to cold isostatic pressing at a pressure of 150–180 MPa. The density of the oriented compact is 3.6–4.0 g / cm³. 3 The density of the compact after cold isostatic pressing is approximately 4.6 g / cm³. 3 .

[0049] The magnet is sintered to achieve a dense structure using a vacuum sintering process. The vacuum sintering process is as follows: 10... -3 ~10 -4 Under a vacuum of Pa, the sintering temperature is 1060–1120℃, and the holding time is 4–20 h. After the holding time is completed, air cooling is used for cooling.

[0050] The sintered magnets are subjected to first-stage aging at 700–900℃ for 2–8 hours, and then cooled by air cooling.

[0051] After the first stage of aging, the magnet undergoes a second stage of aging at 400–650℃ for 2–8 hours. After the aging is completed, it is cooled by air cooling, preferably at a cooling rate of ≥60℃ / min.

[0052] After the magnet was broken, samples were taken from the core, and the magnet composition was analyzed using ICP. The grain boundary phase structure of the magnet was analyzed using TEM. TEM samples were prepared using the following methods: the samples were sanded to a thickness of 30–40 μm and then ion-thinned for less than 2 hours; or the samples were polished and then prepared using FIB. The compositional distribution of the magnet was analyzed using EPMA, and the microstructure of the magnet was observed using SEM. The bending strength of the magnet was measured using a three-point bending method. The three-point bending samples were prepared by inner circular slicing and double-sided grinding. The sample dimensions were 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01) mm (length × width × height), with the sample height parallel to the magnet orientation direction. The bending strength of 10 samples in each group was measured, and the average value was calculated. The three-point bending indenter was a 5 mm diameter cylinder with two 5 mm diameter support pillars, a span between the support points of 14.5 mm, and an indenter pressing speed of 0.1 mm / min. The magnet was then processed into… A cylinder, with its height direction aligned with the magnet's orientation, is used to test the magnet's magnetic properties using a NIM magnetic performance tester.

[0053] Example 1:

[0054] Raw materials with a purity of 99.9% or higher were selected according to the component ratio and placed into the crucible in descending order of melting point. The furnace was then evacuated until a vacuum of 10⁻⁶ was achieved. -3 ~10 -4 Pa, dew point below -50℃. Then, argon gas is introduced into the furnace to reach a pressure of 30 kPa, and the temperature is raised to 1490℃. After the raw materials are completely melted, the temperature is held for 3 minutes. The alloy liquid temperature is then lowered to 1450℃ and held for casting. The copper roller speed is adjusted to 70 rpm, and the crucible is rotated at a certain speed, allowing the molten alloy liquid to be transported through the tundish to the cooling roller for solidification, and then falling onto the water-cooled plate for cooling, thus preparing SC sheets of different compositions.

[0055] SC wafers were processed into alloy powder through hydrogen crushing and air jet milling. During hydrogen crushing, the hydrogen pressure inside the reactor was adjusted to 0.05 MPa. The hydrogen absorption reaction was considered complete when the internal pressure change within the reactor did not exceed 0.5% within 10 minutes. After the hydrogen absorption reaction, the temperature was raised to 550℃ while simultaneously evacuating the reactor and held for 3 hours to remove hydrogen from the alloy wafers. The resulting coarse powder was then cooled. This coarse powder was placed in an air jet mill, with the nozzle pressure adjusted to 0.6 MPa. High-speed gas was used to drive the coarse powder to collide with each other, causing it to be crushed. Nitrogen was used as the carrier gas in the air jet mill. The powder particle size (SMD) was adjusted to 3.0 μm by controlling the sorting wheel and cyclone separator of the air jet mill.

[0056] A mixed powder was obtained by mixing FeS, Nd2O3, and Fe3C powder particles with a particle size of 100 nm into the air-jet mill powder. The relative mass percentages of the three powder particles to the air-jet mill powder were 0.3 wt.%, 0.5 wt.%, and 0.2 wt.%, respectively. In Experiments No. 7 and No. 11, an additional 0.4 wt.% of MgO powder particles with a particle size of 100 nm were mixed into the magnetic powder.

[0057] After adding lubricant and antioxidant to the alloy powder, it is molded under an orientation magnetic field. Commercially available magnetic powder protective lubricant or antioxidant can be used. In this example, the lubricant used is "Magnetic Powder Protective Lubricant #3" produced by Tianjin Yuesheng New Materials Research Institute, and the antioxidant is "NdFeB Special Antioxidant #1" produced by Tianjin Yuesheng New Materials Research Institute. The amount of lubricant added is 0.08% of the alloy powder mass, and the amount of antioxidant is 0.1% of the alloy powder mass.

[0058] The magnets are oriented and formed under a magnetic field of 5T and a forming pressure of 5MPa. The oriented compact is then subjected to cold isostatic pressing at a pressure of 150MPa. The density of the compact after orientation forming is 3.6–4.0 g / cm³. 3 The density of the compact after cold isostatic pressing is approximately 4.6 g / cm³. 3 .

[0059] The magnet is sintered to achieve a dense structure using a vacuum sintering process. The vacuum sintering process is as follows: 10... -3 ~10 -4 Under a vacuum of Pa, the sintering temperature was 1090℃, the holding time was 6h, and the temperature was cooled by air after the holding time was completed.

[0060] The sintered magnets undergo first-stage aging at a temperature of 880℃ for 3 hours, followed by air cooling.

[0061] After the first stage of aging, the magnet undergoes a second stage of aging at a temperature of 520℃ for 3 hours. After the holding period, -20℃ cryogenic argon gas is introduced into the furnace, and a cold air blower is started for rapid cooling, with a magnet cooling rate of 60-70℃ / min.

[0062] After the magnet was broken up, samples were taken from the core, and the magnet composition was analyzed using ICP. TEM was used to analyze the grain boundary phase structure of the magnet. TEM samples were prepared using ion thinning and FIB, with the ion thinning time being less than 2 hours. EPMA was used to analyze the compositional distribution of the magnet, and SEM was used to observe the magnet microstructure. The bending strength of the magnet was measured using a three-point bending method. The three-point bending samples were prepared by inner circular slicing and double-sided grinding. The sample dimensions were 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01) mm (length × width × height), with the sample height direction parallel to the magnet orientation direction. The bending strength of 10 samples in each group was measured, and the average value was calculated. The three-point bending indenter was a 5 mm diameter cylinder, with two 5 mm diameter support columns and a span of 14.5 mm between the support points. The indenter's downward pressing speed was 0.1 mm / min.

[0063] The magnet compositions of Experiments No.1 to No.11 are shown in Table 1. The magnet compositions of each experimental group are expressed as mass percentages, where A1 represents the total content of small atomic radius elements (O, S, H, N, C) in the magnet, excluding element B.

[0064] Table 1. Magnet composition, in wt%.

[0065] No. Nd Pr Dy Mg Zr Fe Co Al Nb Ga Cu B <![CDATA[A1]]> Ingredient requirements 1 31.8 / / / / <![CDATA[B a l]]> / / / / / 0.96 0.39 Not satisfied 2 31.8 / / / 0.2 <![CDATA[B a l]]> 0.3 0.2 / / / 0.96 0.39 Not satisfied 3 28.6 3.2 / / 0.2 <![CDATA[B a l]]> / / 0.1 / / 0.96 0.39 Not satisfied 4 28.6 3.2 / / 0.2 <![CDATA[B a l]]> / / / / 0.1 0.96 0.39 Not satisfied 5 28.6 3.2 0.15 / / <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 Not satisfied 6 28.6 3.2 / / 0.05 <![CDATA[B a l]]> 0.3 0.2 / / / 0.96 0.39 Not satisfied 7 28.6 3.2 / 0.2 / <![CDATA[B a l]]> 0.3 0.2 / / / 0.96 0.39 satisfy 8 28.6 3.2 / / 0.2 <![CDATA[B a l]]> 0.3 0.2 / / / 0.96 0.39 satisfy 9 28.6 3.2 / / 0.2 <![CDATA[B a l]]> 0.3 / / 0.2 / 0.96 0.39 satisfy 10 28.6 3.2 0.15 / 0.2 <![CDATA[B a l]]> 0.3 0.2 / 0.2 / 0.96 0.39 satisfy 11 28.6 3.2 0.15 0.2 0.2 <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 satisfy

[0066] In this embodiment, the content of S, O, and C elements in the grain boundary phase of the magnet is adjusted by adding FeS, Nd2O3, and Fe3C particles. However, due to the high chemical reactivity of the RTB powder, slight oxidation is unavoidable during magnet preparation. Furthermore, the use of organic additives also results in some carbon residue. However, these small atomic radius elements are mainly enriched in the grain boundary phase of the magnet during preparation, so as long as the concentration is within the recommended range of this invention, they will have a beneficial effect. The powder preparation process involves a hydrogen dehydrogenation process, and a certain amount of hydrogen will remain in the powder after dehydrogenation. However, after measurement, the hydrogen content was found to be less than 3 ppm, so the H content can be ignored.

[0067] The bending strength of the magnet was tested using the three-point bending method. Ten data points were collected for each test group, and the average value was calculated. The results are shown in Table 2.

[0068] Table 2

[0069] No. 1 2 3 4 5 6 7 8 9 10 11 Bending strength (MPa) 465 470 462 468 472 471 568 574 575 592 617

[0070] The bending strength data of the magnets show that when the magnet composition does not meet the requirements of this invention, i.e., when the quantity and content of elements with different atomic radii are not satisfied, the bending strength of the magnets is low. However, when the magnet composition meets the requirements, the bending strength is significantly improved. Comparative experiments No. 5 to No. 7 show that when the magnet does not contain Zr or Mg, or when the content of Zr or Mg is less than 0.1 wt.%, even if other components meet the requirements of this invention, the final bending strength of the magnet is still low. It is evident that Zr or Mg is very important for the mechanical properties of the magnets in this invention; therefore, the alloy must contain 0.1 wt.% Mf element.

[0071] The proportion (volume ratio) of amorphous grain boundary phase in the grain boundary phase within a 300μm×300μm range of the sample was statistically analyzed using TEM bright-field imaging and selected area electron diffraction results. The results are shown in Table 3.

[0072] Table 3

[0073] No. 1 2 3 4 5 6 7 8 9 10 11 Percentage (vol.%) 0.9 0.8 1.1 0.9 1.3 1.5 23.5 23.8 24.0 25.6 27.3

[0074] Experiment No. 2 Bright-field image of magnet grain boundary phase as shown Figure 1 As shown in (a), the diffraction patterns of the triangular grain boundary phase between the three principal phases and the thin-layer grain boundary phase between the two principal phases are as follows: Figure 1 As shown in (b) and (c).

[0075] Experiment No. 6 Bright-field image of magnet grain boundary phase Figure 2 As shown in (a), the diffraction patterns of the triangular grain boundary phase between the three principal phases and the thin-layer grain boundary phase between the two principal phases are as follows: Figure 2 As shown in (b) and (c).

[0076] Experiment No. 10 Bright-field image of magnet grain boundary phase as follows Figure 3 As shown in (a), the diffraction patterns of the triangular grain boundary phase between the three principal phases and the thin-layer grain boundary phase between the two principal phases are as follows: Figure 3 As shown in (b) and (c).

[0077] From the TEM bright-field images and diffraction patterns of the triangular grain boundary phase and thin-layer grain boundary phase of magnets in Experiments No.2, No.6 and No.10, and the data in Table 3, it can be seen that when the alloy composition (Experiment No.2) deviates from the composition of the present invention, the grain boundary phase of the magnet is mostly crystalline, and the proportion of amorphous grain boundary phase is very small.

[0078] In Experiment No. 6, although the other components of the magnet met the requirements of this invention, the content of Zr or Mg elements was low, the concentration of Zr and Mg atoms in the grain boundary phase was insufficient, and the amorphous formation ability of the liquid grain boundary phase was weak. Combining the diffraction pattern of Experiment No. 6 and the data in Table 3, it can be seen that the grain boundary phase of the magnet in Experiment No. 6 is polycrystalline, the proportion of amorphous grain boundary phase is still small, and the bending strength of the magnet is low.

[0079] When the alloy composition meets the requirements of this invention (Experiments No. 7 to No. 11), the proportion of amorphous grain boundary phase in the magnet increases significantly. Since the strength of the amorphous grain boundary phase is significantly higher than that of the crystalline grain boundary phase, it can effectively hinder crack propagation under stress, thus significantly improving the bending strength of the magnet. Comparing the fracture surfaces of magnets from Experiments No. 6 and No. 10, it was found that the fracture surface of magnet No. 6 was relatively smooth, and its magnified partial image showed that the fracture type was primarily intergranular fracture. In contrast, the fracture surface of magnet No. 10 clearly showed traces of crack propagation in different directions, and its magnified partial image also showed a significant increase in the proportion of transgranular fracture. This is because the proportion of amorphous grain boundary phase increased in magnet No. 10; the high-strength amorphous grain boundary phase hindered crack propagation along the grain boundary phase, thus increasing the proportion of transgranular fracture.

[0080] The composition of the grain boundary phase of the No. 10 magnet was analyzed by EPMA, and then TEM samples were prepared by FIB. The structure of the grain boundary phase was analyzed by selected electron diffraction. The experimental results are shown in Table 4.

[0081] Table 4. Elemental composition (wt%) in grain boundary phases

[0082] Grain boundary phase state Nd Pr Dy Zr Fe Co Al Ga B O S N C 1 Crystalline 42.46 12.8 1.08 0.05 35.62 0.13 0.32 0.71 1.07 1.57 3.01 0 1.18 2 Crystalline 43.86 5.28 1.71 0 34.21 0.21 0.93 1.87 0.26 1.56 4.35 0.04 2.21 3 amorphous state 44.10 10.60 0.05 2.58 31.94 2.11 0.82 1.67 0.42 3.01 1.52 0.03 1.15 4 amorphous state 39.00 13.20 2.24 1.35 31.85 2.85 0.92 1.61 0.32 2.25 3.43 0.00 0.98 5 amorphous state 43.93 13.24 4.28 0.35 27.17 2.23 0.68 1.12 0.72 1.74 2.96 0.10 1.48

[0083] Analysis of the composition of amorphous and crystalline grain boundary phases revealed that the amorphous grain boundary phases simultaneously contain elements of large, medium, and small atomic radii, with at least 3 elements of small atomic radii, at least 3 elements of medium atomic radii, and at least 3 elements of large atomic radii. Further analysis of multiple amorphous grain boundary phases showed that the content of large atomic radii ranged from 30 wt.% to 70.0 wt.%, medium atomic radii from 20.0 wt.% to 65.0 wt.%, and small atomic radii from 1.0 wt.% to 15.0 wt.%, with 0.2 wt.% to 10.0 wt.% of Mf among the atomic radii. Statistical analysis of the composition of multiple grain boundary phases revealed that when the composition of the grain boundary phase of the magnet does not meet the requirements of this invention, it cannot be transformed into an amorphous state.

[0084] This invention, based on the design principles of amorphous alloys, incorporates elements with large, medium, and small atomic radii among those that readily segregate in the grain boundary phase of RTB magnets. When the grain boundary phase simultaneously contains elements with large, medium, and small atomic radii, and satisfies the following conditions: the number of each of the three atomic radii in the grain boundary phase is ≥3; the content of large atomic radius elements is 30 wt.%–70.0 wt.%, and these large atomic radius elements contain 0.2 wt.%–10.0 wt.% Mf; the content of medium atomic radius elements is 20.0 wt.%–65.0 wt.%; and the content of small atomic radius elements is 1.0 wt.%–15.0 wt.%, its amorphous formation capability is significantly enhanced. Therefore, even at a relatively slow cooling rate after secondary aging, it can transform into an amorphous state. By leveraging the fact that amorphous materials have significantly higher strength than crystalline materials of the same composition, the ability of the grain boundary phase of the magnet to resist crack propagation is improved, thereby obtaining a high-strength RTB rare-earth permanent magnet.

[0085] Example 2:

[0086] Raw materials with a purity of 99.9% or higher were selected according to the component ratio and placed into the crucible in descending order of melting point. The furnace was then evacuated until a vacuum of 10⁻⁶ was achieved. -3 ~10 -4 Pa, dew point below -50℃. Then, argon gas is introduced into the furnace to reach a pressure of 30 kPa, and the temperature is raised to 1490℃. After the raw materials are completely melted, the temperature is held for 3 minutes. The alloy liquid temperature is then lowered to 1450℃ and held for casting. The copper roller speed is adjusted to 70 rpm, and the crucible is rotated at a certain speed, allowing the molten alloy liquid to be transported through the tundish to the cooling roller for solidification, and then falling onto the water-cooled plate for cooling, thus preparing SC sheets of different compositions.

[0087] SC wafers were processed into alloy powder through hydrogen crushing and air jet milling. During hydrogen crushing, the hydrogen pressure inside the reactor was adjusted to 0.05 MPa. The hydrogen absorption reaction was considered complete when the internal pressure change within the reactor did not exceed 0.5% within 10 minutes. After the hydrogen absorption reaction, the temperature was raised to 550℃ while simultaneously evacuating the reactor and held for 3 hours to remove hydrogen from the alloy wafers. The resulting coarse powder was then cooled. This coarse powder was placed in an air jet mill, with the nozzle pressure adjusted to 0.6 MPa. High-speed gas was used to drive the coarse powder to collide with each other, causing it to be crushed. Nitrogen was used as the carrier gas in the air jet mill. The powder particle size (SMD) was adjusted to 3.0 μm by controlling the sorting wheel and cyclone separator of the air jet mill.

[0088] A mixed powder was obtained by mixing FeS, Nd2O3 and Fe3C powder particles with a particle size of 100 nm into the air jet mill powder. The relative mass of the three powder particles to the air jet mill powder were 0.3 wt.%, 0.5 wt.% and 0.2 wt.%, respectively.

[0089] After adding lubricant and antioxidant to the alloy powder, it is molded under an orientation magnetic field. Commercially available magnetic powder protective lubricant or antioxidant can be used. In this example, the lubricant used is "Magnetic Powder Protective Lubricant #3" produced by Tianjin Yuesheng New Materials Research Institute, and the antioxidant is "NdFeB Special Antioxidant #1" produced by Tianjin Yuesheng New Materials Research Institute. The amount of lubricant added is 0.08% of the alloy powder mass, and the amount of antioxidant is 0.1% of the alloy powder mass.

[0090] The magnets are oriented and formed under a magnetic field of 5T and a forming pressure of 5MPa. The oriented compact is then subjected to cold isostatic pressing at a pressure of 150MPa. The density of the compact after orientation forming is 3.6–4.0 g / cm³. 3 The density of the compact after cold isostatic pressing is approximately 4.6 g / cm³. 3 .

[0091] The magnet is sintered to achieve a dense structure using a vacuum sintering process. The vacuum sintering process is as follows: 10... -3 ~10 -4 Under a vacuum of Pa, the sintering temperature was 1090℃, the holding time was 6h, and the temperature was cooled by air after the holding time was completed.

[0092] The sintered magnets undergo first-stage aging at a temperature of 880℃ for 3 hours, followed by air cooling.

[0093] After the first stage of aging, the magnet undergoes a second stage of aging at a temperature of 520℃ for 3 hours. After the holding period, -20℃ cryogenic argon gas is introduced into the furnace, and a cold air blower is started for rapid cooling, with a magnet cooling rate of 60-70℃ / min.

[0094] After the magnet was broken, samples were taken from the core, and the magnet composition was analyzed using ICP. TEM was used to analyze the grain boundary phase structure of the magnet. TEM samples were prepared using ion thinning and FIB, with the ion thinning time being less than 2 hours. EPMA was used to analyze the compositional distribution of the magnet, and SEM was used to observe the magnet microstructure. The bending strength of the magnet was measured using a three-point bending method. The three-point bending samples were prepared by inner circular slicing and double-sided grinding. The sample dimensions were 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01) mm (length × width × height), with the sample height direction parallel to the magnet orientation direction. The bending strength of 10 samples in each group was measured, and the average value was calculated. The three-point bending indenter was a 5 mm diameter cylinder with two 5 mm diameter support pillars. The span between the support points was 14.5 mm, and the indenter's downward speed was 0.1 mm / min. The magnet was then processed into… A cylinder, with its height direction aligned with the magnet's orientation, is used to test the magnet's magnetic properties using a NIM magnetic performance tester.

[0095] The magnet compositions of Experiments No.12 to No.15 are shown in Table 5. The magnet compositions of each experimental group are expressed as mass percentages, where A1 represents the total content of small atomic radius elements (O, S, H, N, C) in the magnet, excluding element B.

[0096] Table 5. Magnet composition, in wt%.

[0097] <![CDATA[N o .]]> Nd <![CDATA[P r ]]> <![CDATA[Z r ]]> <![CDATA[F e ]]> <![CDATA[C o ]]> Al Nb <![CDATA[G a ]]> <![CDATA[C u ]]> B <![CDATA[A1]]> Ingredient requirements 12 28.6 3.2 / <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 Not satisfied 13 28.6 3.2 0.05 <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 Not satisfied 14 28.6 3.2 0.5 <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 satisfy 15 28.6 3.2 0.9 <![CDATA[B a l]]> 0.3 0.2 0.1 0.2 0.1 0.96 0.39 Not satisfied

[0098] The bending strength of the magnet was tested using the three-point bending method. Ten data points were collected for each test and the average value was calculated. The magnetic properties were tested using NIM. The results are shown in Table 6.

[0099] Table 6

[0100] No. 12 13 14 15 Bending strength (MPa) 468 475 605 596 Remanence Br (kGs) 13.7 13.7 13.65 13.58 Coercivity Hcj(kOe) 16.0 15.8 15.3 13.8

[0101] The proportion (volume ratio) of amorphous grain boundary phase in the grain boundary phase within a 300μm×300μm range of the sample was statistically analyzed using TEM bright-field images and selected area electron diffraction results. The results are shown in Table 7.

[0102] Table 7

[0103] No. 12 13 14 15 Percentage (vol.%) 1.1 1.3 24.1 23.9

[0104] When Mf element in the alloy is enriched in the grain boundary phase, it can significantly enhance the amorphous formation ability of the liquid grain boundary phase, thereby promoting the transformation of the liquid grain boundary phase into an amorphous state during the cooling process of secondary aging. In Experiments No. 12 and No. 13, the Mf element content was low (<0.1 wt.%), and its concentration in the grain boundary phase was low. As shown in Table 7, the proportion of amorphous grain boundary phase after secondary aging was low, and the bending strength of the magnet was poor. When the Mf element content is within the recommended range of this invention, the proportion of amorphous grain boundary phase in the magnet increases significantly after secondary aging. The high strength of the amorphous grain boundary phase can improve the mechanical properties of the magnet, thus increasing the bending strength of the magnet. However, it is worth noting that since the wettability of the amorphous grain boundary phase with the main phase of the magnet is lower than that of the grain boundary phase with the main phase in the FCC structure, the formation of the amorphous grain boundary phase will lead to a certain degree of reduction in the coercivity of the magnet. When the Mf element content of the magnet is too high (>0.8 wt.%), the amorphous grain boundary phase and bending strength of the magnet are not significantly improved, but the remanence and coercivity of the magnet decrease, resulting in a significant reduction in magnetic properties. Therefore, in this invention, to ensure the mechanical and magnetic properties of the magnet, the Mf element content is 0.1 wt.% to 0.8 wt.%.

[0105] Example 3:

[0106] Raw materials with a purity of 99.9% or higher were selected according to the component ratio and placed into the crucible in descending order of melting point. The furnace was then evacuated until a vacuum of 10⁻⁶ was achieved. -3 ~10 -4 Pa, dew point below -50℃. Then, argon gas is introduced into the furnace to reach a pressure of 30 kPa, and the temperature is raised to 1490℃. After the raw materials are completely melted, the temperature is held for 3 minutes. The alloy liquid temperature is then lowered to 1450℃ and held for casting. The copper roller speed is adjusted to 70 rpm, and the crucible is rotated at a certain speed, allowing the molten alloy liquid to be transported through the tundish to the cooling roller for solidification, and then falling onto the water-cooling plate for cooling, thus preparing SC alloy sheets.

[0107] SC wafers were processed into alloy powder through hydrogen crushing and air jet milling. During hydrogen crushing, the hydrogen pressure inside the reactor was adjusted to 0.05 MPa. The hydrogen absorption reaction was considered complete when the internal pressure change within the reactor did not exceed 0.5% within 10 minutes. After the hydrogen absorption reaction, the temperature was raised to 550℃ while simultaneously evacuating the reactor and held for 3 hours to remove hydrogen from the alloy wafers. The resulting coarse powder was then cooled. This coarse powder was placed in an air jet mill, with the nozzle pressure adjusted to 0.6 MPa. High-speed gas was used to drive the coarse powder to collide with each other, causing it to be crushed. Nitrogen was used as the carrier gas in the air jet mill. The powder particle size (SMD) was adjusted to 3.0 μm by controlling the sorting wheel and cyclone separator of the air jet mill.

[0108] The air jet mill powder is mixed with powder containing elements with small atomic radii, the particle size of which is 100 nm.

[0109] After adding lubricant and antioxidant to the alloy powder, it is molded under an orientation magnetic field. Commercially available magnetic powder protective lubricant or antioxidant can be used. In this example, the lubricant used is "Magnetic Powder Protective Lubricant #3" produced by Tianjin Yuesheng New Materials Research Institute, and the antioxidant is "NdFeB Special Antioxidant #1" produced by Tianjin Yuesheng New Materials Research Institute. The amount of lubricant added is 0.08% of the alloy powder mass, and the amount of antioxidant is 0.1% of the alloy powder mass.

[0110] The magnets are oriented and formed under a magnetic field of 5T and a forming pressure of 5MPa. The oriented compact is then subjected to cold isostatic pressing at a pressure of 150MPa. The density of the compact after orientation forming is 3.6–4.0 g / cm³. 3 The density of the compact after cold isostatic pressing is approximately 4.6 g / cm³. 3 .

[0111] The magnet is sintered to achieve a dense structure using a vacuum sintering process. The vacuum sintering process is as follows: 10... -3 ~10 -4Under a vacuum of Pa, the sintering temperature was 1090℃, the holding time was 6h, and the temperature was cooled by air after the holding time was completed.

[0112] The sintered magnets undergo first-stage aging at a temperature of 880℃ for 3 hours, followed by air cooling.

[0113] After the first stage of aging, the magnet undergoes a second stage of aging at a temperature of 520℃ for 3 hours. After the holding period, -20℃ cryogenic argon gas is introduced into the furnace, and a cold air blower is started for rapid cooling, with a magnet cooling rate of 60-70℃ / min.

[0114] After the magnet was broken up, samples were taken from the core, and the magnet composition was analyzed using ICP. TEM was used to analyze the grain boundary phase structure of the magnet. TEM samples were prepared using ion thinning and FIB, with the ion thinning time being less than 2 hours. EPMA was used to analyze the compositional distribution of the magnet, and SEM was used to observe the magnet microstructure. The bending strength of the magnet was measured using a three-point bending method. The three-point bending samples were prepared by inner circular slicing and double-sided grinding. The sample dimensions were 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01) mm (length × width × height), with the sample height direction parallel to the magnet orientation direction. The bending strength of 10 samples in each group was measured, and the average value was calculated. The three-point bending indenter was a 5 mm diameter cylinder, with two 5 mm diameter support columns and a span of 14.5 mm between the support points. The indenter's downward pressing speed was 0.1 mm / min.

[0115] In this embodiment, the composition of the alloy SC sheet is the same as that in Experiment No. 10. The types and contents of small atomic radius element powders mixed in the air jet mill powder in Experiments No. 16 to No. 18 are shown in Table 8.

[0116] Table 8

[0117] Experiment No. FeS <![CDATA[Nd2O3]]> <![CDATA[Fe3C]]> 16 0.3 wt.% 0.5 wt.% 0.2 wt.% 17 0.3 wt.% / 0.2 wt.% 18 / / /

[0118] The magnet compositions of Experiments No. 16 to No. 18 are shown in Table 9. The magnet compositions of each experimental group are expressed as mass ratios, where A1 represents the total content of small atomic radius elements (O, S, H, N, C) in the magnet, excluding element B.

[0119] Table 9

[0120] No. Nd Pr Dy Zr Fe Co Al Ga B <![CDATA[A1]]> Ingredient requirements 16 28.6 3.2 0.15 0.2 <![CDATA[B a l]]> 0.3 0.2 0.2 0.96 0.39 satisfy 17 28.6 3.2 0.15 0.2 <![CDATA[B a l]]> 0.3 0.2 0.2 0.96 0.33 satisfy 18 28.6 3.2 0.15 0.2 <![CDATA[B a l]]> 0.3 0.2 0.2 0.96 0.20 Not satisfied

[0121] The bending strength of the magnets was tested using a three-point bending method, with 10 data points collected for each test group and the average value calculated. The proportion (volume ratio) of amorphous grain boundary phase in the grain boundary phase within a 300μm×300μm range of the sample was statistically analyzed using TEM bright-field imaging and selected area electron diffraction results. The results are shown in Table 10.

[0122] Table 10

[0123] No. 16 17 18 Bending strength (MPa) 596 582 465 Volume ratio (vol.%) 26.1 25.2 0.9

[0124] Small atomic radius elements can improve the amorphous formation ability of the grain boundary phase in magnets. Elements with different atomic radii can enhance the viscosity of the liquid grain boundary phase and increase the crystallization resistance during cooling, thereby promoting the formation of the amorphous grain boundary phase. In Experiments No. 16 and No. 17, the total content of small atomic radius elements in the magnets met the requirements. However, with the increase in the types and content of small atomic radius elements, the liquid grain boundary phase is more likely to form an amorphous phase during cooling, enhancing the mechanical properties of the magnet. Data from Table 10 shows that the magnet in Experiment No. 16 has better bending strength. In Experiment No. 18, no small atomic radius element powder was added. During magnet preparation, the residual amount of small atomic radius elements was 0.20 wt.%, which does not meet the requirements of this invention. Therefore, the amorphous formation ability of the grain boundary phase is weak, and a crystalline grain boundary phase is more likely to form during cooling after secondary aging. The low proportion of amorphous phase results in poor mechanical properties of the magnet.

[0125] Example 4:

[0126] Raw materials with a purity of 99.9% or higher were selected according to the component ratio and placed into the crucible in descending order of melting point. The furnace was then evacuated until a vacuum of 10⁻⁶ was achieved. -3 ~10 -4 Pa, dew point below -50℃. Then, argon gas is introduced into the furnace to reach a pressure of 30 kPa, and the temperature is raised to 1490℃. After the raw materials are completely melted, the temperature is held for 3 minutes. The alloy liquid temperature is then lowered to 1450℃ and held for casting. The copper roller speed is adjusted to 70 rpm, and the crucible is rotated at a certain speed, allowing the molten alloy liquid to be transported through the tundish to the cooling roller for solidification, and then falling onto the water-cooling plate for cooling, thus preparing SC alloy sheets.

[0127] SC wafers were processed into alloy powder through hydrogen crushing and air jet milling. During hydrogen crushing, the hydrogen pressure inside the reactor was adjusted to 0.05 MPa. The hydrogen absorption reaction was considered complete when the internal pressure change within the reactor did not exceed 0.5% within 10 minutes. After the hydrogen absorption reaction, the temperature was raised to 550℃ while simultaneously evacuating the reactor and held for 3 hours to remove hydrogen from the alloy wafers. The resulting coarse powder was then cooled. This coarse powder was placed in an air jet mill, with the nozzle pressure adjusted to 0.6 MPa. High-speed gas was used to drive the coarse powder to collide with each other, causing it to be crushed. Nitrogen was used as the carrier gas in the air jet mill. The powder particle size (SMD) was adjusted to 3.0 μm by controlling the sorting wheel and cyclone separator of the air jet mill.

[0128] In this embodiment, Experiment No. 19 used FeS, Nd2O3, and Fe3C powder particles with a particle size of 100 nm mixed into the air-jet mill powder to obtain a mixed powder. The mass percentages of the three powder particles relative to the air-jet mill powder were 0.3 wt.%, 0.5 wt.%, and 0.2 wt.%, respectively. Experiment No. 20 used FeS, Nd2O3, and Fe3C powder particles with a particle size of 100 nm added to the smelting raw materials. The mass percentages of the three powder particles were 0.3 wt.%, 0.5 wt.%, and 0.2 wt.%, respectively.

[0129] After adding lubricant and antioxidant to the alloy powder, it is molded under an orientation magnetic field. Commercially available magnetic powder protective lubricant or antioxidant can be used. In this example, the lubricant used is "Magnetic Powder Protective Lubricant #3" produced by Tianjin Yuesheng New Materials Research Institute, and the antioxidant is "NdFeB Special Antioxidant #1" produced by Tianjin Yuesheng New Materials Research Institute. The amount of lubricant added is 0.08% of the alloy powder mass, and the amount of antioxidant is 0.1% of the alloy powder mass.

[0130] The magnets are oriented and formed under a magnetic field of 5T and a forming pressure of 5MPa. The oriented compact is then subjected to cold isostatic pressing at a pressure of 150MPa. The density of the compact after orientation forming is 3.6–4.0 g / cm³. 3 The density of the compact after cold isostatic pressing is approximately 4.6 g / cm³. 3 .

[0131] The magnet is sintered to achieve a dense structure using a vacuum sintering process. The vacuum sintering process is as follows: 10... -3 ~10 -4 Under a vacuum of Pa, the sintering temperature was 1090℃, the holding time was 6h, and the temperature was cooled by air after the holding time was completed.

[0132] The sintered magnets undergo first-stage aging at a temperature of 880℃ for 3 hours, followed by air cooling.

[0133] After the first stage of aging, the magnet undergoes a second stage of aging at a temperature of 520℃ for 3 hours. After the holding period, -20℃ cryogenic argon gas is introduced into the furnace, and a cold air blower is started for rapid cooling, with a magnet cooling rate of 60-70℃ / min.

[0134] After the magnet was broken up, samples were taken from the core, and the magnet composition was analyzed using ICP. TEM was used to analyze the grain boundary phase structure of the magnet. TEM samples were prepared using ion thinning and FIB, with the ion thinning time being less than 2 hours. EPMA was used to analyze the compositional distribution of the magnet, and SEM was used to observe the magnet microstructure. The bending strength of the magnet was measured using a three-point bending method. The three-point bending samples were prepared by inner circular slicing and double-sided grinding. The sample dimensions were 25 (±0.01) mm × 6 (±0.01) mm × 5 (±0.01) mm (length × width × height), with the sample height direction parallel to the magnet orientation direction. The bending strength of 10 samples in each group was measured, and the average value was calculated. The three-point bending indenter was a 5 mm diameter cylinder, with two 5 mm diameter support columns and a span of 14.5 mm between the support points. The indenter's downward pressing speed was 0.1 mm / min.

[0135] In this embodiment, the composition of other alloying elements is the same as that in Experiment No. 10. The magnet compositions of Experiment No. 19 and Experiment No. 20 are shown in Table 11.

[0136] Table 11

[0137] No. Nd Pr Dy Zr Fe Co Al Ga B <![CDATA[A1]]> Ingredient requirements 19 28.6 3.2 0.15 0.2 <![CDATA[B a l]]> 0.3 0.2 0.2 0.96 0.39 satisfy 20 28.6 3.2 0.15 0.2 <![CDATA[B a l]]> 0.3 0.2 0.2 0.96 0.38 satisfy

[0138] The bending strength of the magnets was tested using a three-point bending method, with 10 data points collected for each test group and the average value calculated. The proportion (volume ratio) of amorphous grain boundary phase in the grain boundary phase within a 300μm×300μm range of the sample was statistically analyzed using TEM bright-field imaging and selected area electron diffraction results. The results are shown in Table 12.

[0139] Table 12

[0140] No. 19 20 Bending strength (MPa) 598 456 Volume ratio (vol.%) 26.3 0.82

[0141] Small atomic radius elements, due to their extremely small atomic size, easily dissolve into the main phase grains of the magnet. The segregation concentration of small atomic radius elements added during the melting stage in the grain boundary phase is relatively low. Experiment No. 20 used a method of adding small atomic radius elements during the melting stage. Although the content of small atomic radius elements in the final alloy still met the concentration requirements of this invention, most of them dissolved into the main phase. Therefore, the concentration of small atomic radius elements in the grain boundary phase decreased, and the amorphous forming ability of the liquid grain boundary phase weakened. As shown in Table 12 and the TEM bright-field image and selected area electron diffraction results of the magnet in Experiment No. 20, the proportion of the amorphous phase in the final grain boundary phase decreased, and the mechanical properties of the magnet also decreased accordingly. Therefore, in this invention, nanoscale powder particles containing small atomic radius elements are mixed with magnetic powder obtained from air jet milling to ensure that most of the small atomic radius elements are enriched in the grain boundary phase of the magnet. By increasing the viscosity of the liquid grain boundary phase, its amorphous forming ability is improved, promoting the transformation of the liquid grain boundary phase into an amorphous state after secondary aging. The mechanical properties of magnets can be improved by taking advantage of the high strength of amorphous grain boundary phases.

Claims

1. A high-strength RTB rare-earth permanent magnet with an amorphous grain boundary phase, characterized in that the atomic radius r is ≥ 0.16 nm and consists of 29.0 wt.% to 34.0 wt.% of large atomic radius elements, wherein the large atomic radius elements include three or more of Nd, Pr, Dy, Tb, Ho, La, Ce, Gd, Er, Mg, and Zr, and the large atomic radius elements contain 0.1 wt.% to 0.8 wt.% Mf, wherein Mf is any one or two of Zr and Mg; Elements with atomic radii r ≤ 0.12 nm: 1.05 wt.% to 1.65 wt.%, where the elements with small atomic radii include more than three of S, C, H, N, O, F, and B, and include 0.8 wt.% to 1.1 wt.% of boron element; and the total content C1 of the elements with small atomic radii satisfies 0.25 wt.% ≤ [C1] - [B] ≤ 0.55 wt.%, where [C1] and [B] are the contents of C1 and B expressed in weight percentages; The balance is medium-atomic-radius elements with atomic radius r satisfying 0.12 nm < r < 0.16 nm and other inevitable impurities: The medium-atomic-radius elements include more than three of Fe, Co, Ti, Al, Nb, Zn, Ga, W, Mn, Mo, V, Si, P, and Cu, and at least 60.0 wt.% of TM is included in the medium-atomic-radius elements, and TM is at least one of Fe and Co; the content of other medium-atomic-radius elements other than TM ≥ 0.2 wt.%; The magnet comprises a main phase R2T 14 B and a grain boundary phase, the grain boundary phase is composed of a crystalline grain boundary phase and an amorphous grain boundary phase; the amorphous grain boundary phase simultaneously comprises three types of elements with large, medium and small atomic radii, and the number of small-atomic-radius type elements is ≥3, the number of medium-atomic-radius type elements is ≥3, and the number of large-atomic-radius type elements is ≥3.

2. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 1, characterized in that... The total content of elements with small atomic radii other than boron element is 0.3 wt.% to 0.5 wt.%.

3. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 1, characterized in that... The content of other medium-atomic-radius elements other than TM is 0.2 to 1.5 wt.%.

4. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 1, characterized in that... The proportion of the amorphous grain boundary phase in the grain boundary phase of the magnet is more than 20 vol.%.

5. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 1, characterized in that... In the amorphous grain boundary phase of the magnet, the content of elements with large atomic radii is 30 wt.% to 70.0 wt.%, and 0.2 wt.% to 10.0 wt.% of Mf is included in the elements with large atomic radii; the content of medium-atomic-radius elements is 20.0 wt.% to 65.0 wt.%, and the content of elements with small atomic radii is 1.0 wt.% to 15.0 wt.%.

6. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in any one of claims 1 to 5, characterized in that... The high-strength R-T-B rare earth permanent magnet with an amorphous grain boundary phase is prepared by one of the following methods: (1) The magnet does not contain Mg element: Melt and spin SC flakes according to the composition ratio, prepare alloy powder by hydrogenation disproportionation and jet milling, mix the alloy powder with powder containing elements with small atomic radii, perform die pressing and isostatic pressing on the mixed powder in an orientation magnetic field to prepare a green compact, and obtain the R-T-B rare earth permanent magnet with an amorphous grain boundary phase by vacuum sintering, primary aging, and secondary aging; (2) The magnet contains Mg element: Melt and spin SC flakes according to the composition ratio of elements other than Mg, prepare alloy powder by hydrogenation disproportionation and jet milling, mix the alloy powder with Mg particles and powder containing elements with small atomic radii, perform die pressing and isostatic pressing on the mixed powder in an orientation magnetic field to prepare a green compact, and obtain the R-T-B rare earth permanent magnet with an amorphous grain boundary phase by vacuum sintering, primary aging, and secondary aging.

7. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 6, characterized in that... The powder containing elements with small atomic radii is one or more of powders containing S, C, O, or F elements, and the particle size of the powder containing elements with small atomic radii is within 500 nm.

8. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 6, characterized in that... In the method (2), the Mg particles are pure metal particles or magnesium oxide particles; the particle size of the Mg particles is within 500 nm.

9. The high-strength RTB rare-earth permanent magnet with amorphous grain boundary phase as described in claim 6, characterized in that... In the method (1) or method (2), after secondary aging, it is cooled at a cooling rate of ≥ 60 °C / min.

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