Cerium Added RE-TBM Sintered NdFeB Magnets

Abstract

The invention discloses a cerium-added RE-T-B-M series sintered NdFeB magnet, which relates to the technical field of NdFeB permanent magnets. 2 Fe 14 B main phase, RE-rich phase, REFe 2 phase and interlayer grain boundary phase; the interlayer grain boundary phase includes RE-rich phase, Fe-rich phase and REFe 2 phase, in the interlayer grain boundary phase, from near RE 2 Fe 14 Starting from the B main phase particle side, the first layer is RE-rich phase, the second layer is Fe-rich phase, and the third layer is REFe 2 phase; wherein RE includes cerium and at least one other rare earth element, and the mass ratio of cerium to the total elements is 3.0-15.0%, T is iron and cobalt, B is boron, and M is Al, Cu, Ga, and Ti. The cerium-added RE-T-B-M sintered NdFeB magnet of the present invention can reduce the negative impact of adding cerium on the magnet.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB permanent magnets, and in particular to a cerium-added RE-TBM system sintered NdFeB magnet. Background Art

[0002] High-abundance light rare earth elements, such as lanthanum and cerium, have very low prices and are being added to NdFeB magnets more and more widely. However, rare earth elements such as lanthanum and cerium have lower magnetic performance parameters, and their addition will cause the magnetic properties of rare earth magnetic materials to decrease significantly. In order to reduce the impact of the addition of elements such as lanthanum and cerium on the magnetic properties of rare earth magnetic materials, multi-main phase processes and surface grain boundary diffusion processes are widely used. The Chinese patent with authorization announcement number CN102800454B discloses a low-cost dual-main phase Ce permanent magnet alloy and a preparation method thereof, which obtains higher magnetic properties by forming two main phases with different HAs, Nd-Fe-B and (Ce, RE)-Fe-B. However, the HA of the (Ce, RE)-Fe-B main phase in this method is reduced too much, which limits the improvement of magnetic properties. The invention patent with publication number WO2020233316A1 discloses a REFe-containing 2 Phase grain boundary diffusion cerium magnet and its preparation method, the patent uses rare earth elements to contain CeFe 2 phase matrix, so that CeFe 2 The phase is strengthened and the strengthened phase changes to REFe 2 phase, thus increasing the coercivity. However, no matter which method is used, when the cerium addition amount is high, REFe is easily generated in the grain boundary phase. 2 Phase, pure REFe 2 The magnetic isolation effect of the phase is weak, the ability to suppress the movement of reverse magnetic domains in the demagnetization field is poor, and the coercive force of the magnet is low.

[0003] Cerium is a low-cost rare earth raw material, which can significantly reduce the cost after adding. 2 Fe 14 The magnetic parameters of B are low. When the amount of cerium added is high, the low magnetic parameters of Ce 2 Fe 14 B occupies a large proportion of the main phase, and the comprehensive magnetic properties are reduced. At the same time, the addition of cerium will also form REFe with weak magnetic isolation in the grain boundary phase. 2 Phase, which is distributed between the main phase particles. Under the demagnetization field, the reverse magnetic domain is relatively easy to transfer between the main phase grains, which is manifested macroscopically as a decrease in coercive force. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art and reduce the negative impact of adding cerium on the magnetic properties of rare earth magnetic materials, the present invention provides a cerium-added RE-TBM series sintered NdFeB magnet.

[0005] Technical solution: To achieve the above purpose, the present invention provides a cerium-added RE-TBM system sintered NdFeB magnet, the magnet structure contains an interlayer grain boundary phase; the interlayer grain boundary phase includes a RE-rich phase, an Fe-rich phase and a REFe 2 phase, in the interlayer grain boundary phase, from near RE 2 Fe 14 Starting from the B main phase particle side, the first layer is RE-rich phase, the second layer is Fe-rich phase, and the third layer is REFe 2 phase; wherein RE includes cerium and at least one other rare earth element, and the mass ratio of cerium to the total elements of the magnet is 3.0-15.0%, T is iron and cobalt, B is boron, and M is Al, Cu, Ga, and Ti.

[0006] The cerium content must be within the above-specified range, which is crucial to its beneficial effects: in the process of preparing the sample alloy according to the above-specified cerium addition amount, cerium is easily precipitated from the main phase to form REFe 2 Phase. There is RE in the magnet 2 Fe 14 B main phase, REFe 2 The RE-rich phase has good wettability to the main phase grains. When heat treatment is performed near the eutectic point of the RE-rich phase, the RE-rich phase in the grain boundary is enriched around the main phase grains to form the first grain boundary layer. 2 The rare earth elements in the REFe phase can be precipitated and diffused into the RE-rich phase by heat treatment near its eutectic point. The rare earth content in the original RE-rich phase becomes higher. At the same time, the REFe 2 The phase changes to Fe-rich phase (Fe-rich phase), forming the second grain boundary layer. REFe is far away from the main phase grains. 2 The original state is maintained and the third grain boundary layer is formed. The three phases form a sandwich structure similar to a sandwich. For samples with lower cerium content, the concentration of cerium in the main phase is lower, and it is not easy to precipitate and form REFe during heat treatment. 2 Phase; samples with too high cerium content have a relatively high cerium content in the grain boundary phase, and a large amount of REFe is formed in the grain boundary phase 2 phase, which is widely distributed, leaving no space for the formation of a RE-rich phase with high rare earth content, and thus unable to form a sandwich grain boundary structure.

[0007] Furthermore, in the RE-rich phase of the interlayer grain boundary phase, the element RE atoms account for 50.2-62.3%, the element T atoms account for 32.2-39.7%, and the element M atoms account for 2.2-10.1%.

[0008] Furthermore, in the Fe-rich phase of the interlayer grain boundary phase, the element RE atoms account for 12.4-26.0%, the element T atoms account for 68.1-81.4%, and the element M atoms account for 1.3-6.2%.

[0009] Furthermore, the REFe of the interlayer grain boundary phase 2 In the phase, element RE atoms account for 28.1-33.8%, element T atoms account for 61.4-69.8%, and element M atoms account for 0.6-4.8%.

[0010] Furthermore, in the interlayer grain boundary phase, the thickness of the RE-rich phase is 1-21 nm, the thickness of the Fe-rich phase is 1-15 nm, and the thickness of the REFe2 phase is 8-550 nm.

[0011] Furthermore, the magnet structure also includes RE 2 Fe 14 B main phase, RE-rich phase, REFe 2 Phase, the magnet structure includes elements RE, boron, aluminum, cobalt, copper, gallium, titanium, iron and impurities, and the content of each element relative to the total mass is as follows: element RE 30.10-33.50wt.%, boron 0.85-1.05wt.%, aluminum 0.05-0.60wt.%, cobalt 0.50-2.00wt.%, copper 0.10-0.50wt.%, gallium 0.10-0.50wt.%, titanium 0.10-0.40wt.%, and the rest are iron and impurities.

[0012] A cerium-added RE-TBM-based sintered NdFeB magnet of the present invention has at least the following technical effects: in the sandwich grain boundary structure, in the RE-rich phase in the first grain boundary layer that contacts the outer side of the main phase grain, the rare earth content exceeds 50 at.%, and the Fe content is less than 50 at.%. Such high rare earth content grain boundary phases have poor magnetic permeability and better magnetic isolation, and can effectively inhibit the movement of magnetic domains during the demagnetization process. In addition, the periphery of the main phase particles has a grain boundary phase with a high rare earth content, which reduces the defects of the periphery of the main phase particles, and the reverse domain is not easy to nucleate. The Fe-rich phase of the second grain boundary layer outside the RE-rich phase has a high iron content and has a certain magnetic permeability, but when the reverse magnetic domain is transmitted through the sandwich structure, it is isolated by the RE-rich phase of the first layer, and the transmission ability becomes weak. The third layer REFe 2 Although the magnetic isolation effect of the RE phase is not as strong as that of the first layer, it can also prevent the transfer of reverse magnetic domains to adjacent main phase particles due to its thick thickness. Through the effective magnetic isolation of the sandwich structure, the main phase grains are magnetically isolated, which improves the coercivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1It is a schematic diagram of the microstructure of a magnet with an interlayer grain boundary phase and a schematic diagram of a test method for each grain boundary layer according to the present invention;

[0014] Figure 2 These are HAADF-STEM and EDS images of the grain boundary positions of the magnet in Example 1.

[0015] exist Figure 1 1. Main phase; 2. RE-rich grain boundary phase; 2a. Center of RE-rich grain boundary phase; 3. Fe-rich grain boundary phase; 3a. Center of Fe-rich grain boundary phase; 4. REFe 2 Grain boundary phase; 5. Interlayer grain boundary phase thickness test position. DETAILED DESCRIPTION

[0016] The following combination Figure 1 to Figure 2 The principles and features of the present invention are described, and the examples given are only used to explain the present invention, rather than to limit the scope of the present invention.

[0017] A method for preparing a cerium-added RE-TBM system sintered NdFeB magnet comprises the following steps:

[0018] (S1) Preparation of alloy sheets: The ingredients are prepared according to the addition amount of each element in Table 1, and then the raw materials are made into alloy strip sheets using a rapid solidification thin strip process so that the alloy has a uniform composition distribution; a total of four embodiments and two comparative examples are included in this process.

[0019] (S2) Crushing process: The prepared alloy stripping flakes are crushed. In this embodiment, the crushing process adopts two steps of dehydrogenation process and air flow grinding. Specifically, the alloy flakes are subjected to hydrogen absorption under a hydrogen pressure of 0.2 MPa for 2 hours, and then dehydrogenated at a temperature of 550° C. for 6 hours. The alloy flakes after hydrogen treatment are ground into magnetic powder with an average particle size of 4.0 μm by air flow grinding.

[0020] (S3) Molding and orientation process: The magnetic powder is loaded into a mold, and a magnetic field with a strength of 2.0 T is applied to press the magnetic powder to make it have a suitable density and be oriented along the easy magnetization axis.

[0021] (S4) Cold isostatic pressing process: The cold isostatic pressing process is to place the green body pressed by the press into a liquid such as water or oil, and apply a pressure of 200 MPa to make the green body evenly stressed in all directions, reduce the porosity in the green body, and further densify and homogenize the green body.

[0022] (S5) Sintering process: Sintering is the densification process of the green body under vacuum or inert gas protection conditions. During the sintering process, appropriate heating rate, insulation period, etc. are set to promote the removal of gas, water vapor and organic matter adsorbed in the magnetic powder, eliminate stress, reduce porosity, and at the same time, the particles grow and the green body is dense. The suitable sintering temperature range is 1000-1050℃, and the sintering time is 4-12 hours. Too high sintering temperature will cause the main phase grains and REFe 2 The wettability of the phase is improved, which makes it difficult for the RE-rich phase to diffuse to the periphery of the main phase to form the first grain boundary layer. Based on this, the sintering temperature is set to 1010° C. and the sintering time is set to 6 hours in this embodiment.

[0023] (S5) Sequential process: The aging process is to anneal the blank after sintering to promote the formation and uniform distribution of grain boundary phase and improve the coercive force of the magnet. The aging conditions are related to the composition of the magnet. A reasonable aging process can obtain a continuous and clear effective grain boundary phase, which plays an important role in improving the coercive force of the magnet. During the primary aging treatment, the temperature is suitable to be 630-730℃, which is near the eutectic point temperature of the RE-rich phase. Heat treatment within this temperature range can make the RE-rich phase diffuse to the periphery of the main phase grains, and because the RE-rich phase has better wettability to the main phase, it is easy to coat the main phase particles to form the first layer of grain boundary phase; during the secondary aging treatment, the temperature is suitable to be 820-930℃, which is near the REFe-rich phase. 2 Near the eutectic point temperature, REFe occurs during heat treatment 2 The rare earth elements precipitate from the phase, and the precipitated rare earth elements diffuse into the RE-rich phase on the surface of the main phase grains, precipitating the REFe of the rare earth elements. 2 The REFe phase becomes a Fe-rich phase, forming a second grain boundary phase and resulting in a higher rare earth element content in the RE-rich phase. 2 The phase maintains its original form and exists as the third layer of grain boundary phase; the temperature of the three-level aging treatment is preferably carried out at 450-540°C to optimize the grain boundary distribution. In this implementation, the first-level aging temperature in the embodiment is set to 650°C, and the cooling rate is ≥10°C / min during cooling to room temperature; the second-level aging temperature in the embodiment is set to 850°C, and the cooling rate is ≥10°C / min during cooling to room temperature; the third-level aging temperature in the embodiment is set to 480°C, and the cooling rate is ≥10°C / min during cooling to room temperature. In the cooling process of each level of aging, increasing the cooling rate helps to maintain the generated grain boundary structure.

[0024] By controlling the proportion of Ce element, the primary aging temperature is set near the eutectic point of RE-rich phase to promote its diffusion to the periphery of main phase particles. 2 phase near the eutectic point, which is conducive to REFe 2The rare earth atoms in the RE phase diffuse into the RE-rich phase, forming a new RE-rich phase with high rare earth content, which has better magnetic isolation. 2 Phase transformation to Fe-rich phase. 2 The phase is distributed in the outer layer of the Fe-rich phase, in which the Fe content is higher than that of the RE-rich phase, but lower than that of the Fe-rich phase, and the thickness is thicker. It can also weaken the transmission of the reverse magnetization domain to a certain extent.

[0025] The magnet prepared by steps (S1) to (S5) was processed into a cylinder with a diameter of 10 mm and a height of 10 mm for magnetic property testing. The test results are shown in Table 1.

[0026] Subsequently, a transmission electron microscope (TEM) and an X-ray energy spectrometer (EDS) were used to analyze the microstructure of the magnet. The specific test method is as follows: take one sample from each of Examples 1 to 4, select 5 main phase particles for each sample, and make 4 equal lines according to the length of the longest grain boundary phase with a sandwich structure outside each main phase particle, divide the longest grain boundary into 5 equal parts, make a vertical line perpendicular to the grain boundary phase, and measure the thickness of each grain boundary layer in the sandwich structure corresponding to the 4 equal lines. 20 groups of interlayer grain boundary phase thickness data are obtained for each sample. The maximum value, minimum value, and average value are statistically calculated. The test method for the composition of the grain boundary phase with a sandwich structure is as follows: select the center point of each grain boundary phase on the above-mentioned equal lines, use an X-ray energy spectrometer (EDS) to analyze the element content, and obtain 20 groups of composition data for each sample, and take the average value.

[0027] The thickness information of each grain boundary phase in the interlayer grain boundary structure is summarized in Table 2. The element contents in the RE-rich phase in the interlayer grain boundary structure are summarized in Table 3, the element contents in the Fe-rich phase in the interlayer grain boundary structure are summarized in Table 4, and the REFe 2 The element contents in the phases are summarized in Table 5.

[0028] Table 1 Composition and magnetic properties of samples of embodiments and comparative examples

[0029]

[0030] Table 2 Thickness of each grain boundary phase in the interlayer grain boundary structure

[0031]

[0032] Table 3 Element contents in RE-rich phase in interlayer grain boundary structure

[0033]

[0034] Table 4 Element contents in Fe-rich phase in interlayer grain boundary structure

[0035]

[0036] Table 5 REFe in interlayer grain boundary structure 2 Element content

[0037]

[0038] In Example 1, the Ce addition amount is 6.0% by mass, the remanence reaches 13.77kGs, and the coercivity reaches 12.51kOe. In Example 4, although the Ce addition mass ratio reaches 15.0%, its coercivity can still reach 10.4kOe. Combined with the analysis of the microstructure, it can be seen that the samples of Example 1 to Example 4 form a phase rich in RE, a phase rich in Fe and a phase rich in REFe. 2 The existence of this structure can suppress the decrease of coercivity when the Ce addition is large. In comparative example 1, in the sample with a Ce addition of 2.0% by mass, the Ce concentration is low and no REFe is detected. 2 In comparative example 2, the addition amount of Ce is 18.0% by mass, and a large amount of REFe is formed in the sample. 2 Phase, REFe 2 The phase content is high and widely distributed between the main phase particles. 2 The rare earth elements in the phase have no diffusion space and cannot diffuse into the adjacent RE-rich phase to form a RE-rich phase with a higher rare earth content. Therefore, no interlayer grain boundary structure is formed, and the coercivity is significantly reduced.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A cerium-added RE-TBM sintered NdFeB magnet, characterized in that: The magnet structure contains an interlayer grain boundary phase; the interlayer grain boundary phase includes an RE-rich phase, an Fe-rich phase and a REFe2 phase. 14 Starting from the B main phase particle side, the first layer is RE-rich phase, the second layer is Fe-rich phase, and the third layer is REFe2 phase; RE includes cerium and at least one other rare earth element, and the mass ratio of cerium to the total elements of the magnet is 3.0-15.0%, T is iron and cobalt, B is boron, and M is Al, Cu, Ga, and Ti; in the interlayer grain boundary phase, the thickness of the RE-rich phase is 1-21nm, the thickness of the Fe-rich phase is 1-15nm, and the thickness of the REFe2 phase is 8-550nm.

2. The cerium-added RE-TBM sintered NdFeB magnet according to claim 1, characterized in that: In the RE-rich phase of the interlayer grain boundary phase, the element RE atoms account for 50.2-62.3%, the element T atoms account for 32.2-39.7%, and the element M atoms account for 2.2-10.1%.

3. The cerium-added RE-TBM sintered NdFeB magnet according to claim 1, characterized in that: In the Fe-rich phase of the interlayer grain boundary phase, the element RE atoms account for 12.4-26.0%, the element T atoms account for 68.1-81.4%, and the element M atoms account for 1.3-6.2%.

4. The cerium-added RE-TBM sintered NdFeB magnet according to claim 1, characterized in that: In the REFe2 phase of the interlayer grain boundary phase, the element RE atoms account for 28.1-33.8%, the element T atoms account for 61.4-69.8%, and the element M atoms account for 0.6-4.8%.

5. The cerium-added RE-TBM sintered NdFeB magnet according to claim 1, characterized in that: The magnet structure also includes RE2Fe 14 B main phase, RE-rich phase, REFe2 phase, the magnet structure includes elements RE, boron, aluminum, cobalt, copper, gallium, titanium, iron and impurities, and the content of each element relative to the total mass is as follows: element RE 30.10-33.50wt.%, boron 0.85-1.05wt.%, aluminum 0.05-0.60wt.%, cobalt 0.50-2.00wt.%, copper 0.10-0.50wt.%, gallium 0.10-0.50wt.%, titanium 0.10-0.40wt.%, and the rest are iron and impurities.

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