High-performance neodymium iron boron material and preparation method thereof

Abstract

The invention relates to the technical field of preparation of neodymium-iron-boron materials, and discloses a high-performance neodymium-iron-boron material and a preparation method thereof, and the high-performance neodymium-iron-boron material realizes efficient permeation of heavy rare earth elements along a specific path through a grain boundary network pre-construction and gradient diffusion technology in combination with a hydrogen decrepitation and surface activation process, so that the coercive force and thermal stability of a magnet are remarkably improved. An alternating magnetic field assisted sintering and dynamic tempering process is innovatively adopted, and a magnetic field-lattice coupling effect is utilized to release microscopic stress, so that magnetic performance attenuation in a high-temperature environment is effectively inhibited. A surface protection system is fused with a grain boundary modification and composite coating technology, a multistage corrosion-resistant barrier is constructed through the synergistic effect of an intermetallic compound layer and a nano coating, and the service life of the magnet in a severe environment is greatly prolonged. According to the method, the bottleneck of mutual restriction of performance indexes in a traditional process is broken through, and collaborative optimization of coercive force strengthening, temperature stability improving and corrosion resistance is achieved on the basis of keeping the high residual magnetism characteristic.

Description

Technical Field

[0001] The present application relates to the technical field of NdFeB material preparation, and in particular to a high-performance NdFeB material and a preparation method thereof. Background Art

[0002] Neodymium iron boron (NdFeB) permanent magnets, due to their high remanence and high magnetic energy product, have become a core material for modern motors, wind power generation, and precision electronic devices. As their application scenarios expand into extreme environments such as high temperature, high humidity, and severe corrosion, higher requirements are placed on the overall performance of magnets: they must possess high coercivity to resist demagnetization interference, a low temperature coefficient to maintain high-temperature stability, and excellent corrosion resistance to extend their service life. However, due to intrinsic defects such as the high chemical activity of NdFeB's main phase grains and fragile grain boundary structure, traditional magnets are prone to magnetic performance degradation or surface corrosion failure under complex operating conditions, making it difficult to meet the needs of high-end applications.

[0003] Existing technologies typically employ a step-by-step optimization strategy: increasing coercivity through grain boundary diffusion of heavy rare earth elements (such as Dy and Tb), enhancing corrosion resistance through surface coating, or improving remanence through magnetic field orientation. For example, the grain boundary diffusion process forms a hard magnetic phase at the grain boundaries through high-temperature infiltration, but this can cause grain boundary oxidation. While coating can block corrosive media, interfacial stress damages the grain boundary structure. While magnetic field pressing can increase orientation, its ability to control powder bulk density and porosity is limited.

[0004] The core contradiction of the above methods is that the performance optimization of a single process often leads to the degradation of other properties. Grain boundary oxidation caused by heavy rare earth penetration will weaken the adhesion of the coating, and the interfacial stress introduced by the coating will destroy the stability of the grain boundary structure, further exacerbating the attenuation of magnetic properties. This mutual constraint of performance indicators makes it difficult for existing technologies to break through the bottleneck of synergistically improving high coercivity, high thermal stability and strong corrosion resistance, seriously limiting the large-scale application of NdFeB magnets in harsh environments such as new energy vehicle drive motors and deep-sea equipment. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a high-performance NdFeB material and a preparation method thereof, which solves the problem in the existing technology that the coercive force improvement, thermal stability enhancement and corrosion resistance improvement cannot coexist due to the mutual constraints caused by the optimization of a single process.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A high-performance neodymium iron boron material comprises the following components by mass: PrNd 29.5-31.0 parts, TbH2 1.2-1.8 parts, Fe balance, BFe 0.95-1.05 parts, Co 0.8-1.5 parts; Cu-Al alloy 0.3-0.6 parts, NbC 0.2-0.5 parts, Zr 0.1-0.3 parts; Wherein, the mass ratio of Cu to Al in the Cu-Al alloy is 4:1.

[0007] Preferably, the mass ratio of Pr to Nd in the PrNd is 3:7, and the D50 particle size of the TbH2 is 1-3 μm.

[0008] Preferably, the D50 particle size of the NbC is 40-60 nm, and the D50 particle size of the Cu-Al alloy is ≤10 μm.

[0009] A method for preparing high-performance NdFeB material comprises the following steps: Step (1), performing primary hydrogen crushing and secondary hydrogen crushing on the PrNd alloy in sequence to obtain PrNd crushed powder, and performing air flow classification on the PrNd crushed powder to control D10 ≥ 0.8 μm, D50 = 3-5 μm, and D90 ≤ 12 μm; Step (2), subjecting the TbH2 powder to ultrasonic activation treatment to obtain activated TbH2 powder; Step (3), mixing the crushed PrNd powder, activated TbH2 powder, and Cu-Al alloy powder, and then ball milling, adding NbC nanopowder and high-speed shear mixing to obtain a composite powder, and after high-speed shear mixing, using plasma-assisted surface treatment with a processing power of 2-5kW and a time of 10-30min; Step (4), applying a steady-state magnetic field and a pulsed magnetic field to the composite powder for orientation molding to obtain a green body; Step (5), subjecting the green body to vacuum gradient sintering and triple tempering treatment in sequence; Step (6) Surface Dy treatment of the sintered body: heating to 900-950 ° C in a vacuum furnace, introducing DyCl3 vapor, treating for 1-2 hours, and then electrophoretically depositing Al2O3 coating with a coating thickness of 10-20 μm Preferably, in step (1): The conditions for the first-stage hydrogen crushing are: hydrogen pressure 0.15-0.30 MPa, temperature 280-320°C, time 2-4 hours; The conditions for the secondary hydrogen crushing are: hydrogen pressure 0.8-1.2 MPa, temperature 420-480°C, time 1-2 hours; After the secondary hydrogen is crushed, it is rapidly cooled by liquid nitrogen with a cooling rate of ≥50℃ / s.

[0010] Preferably, in step (3): The ball milling conditions are: argon protection, ball-to-material ratio 5:1-8:1, rotation speed 200-300 rpm, time 3-6 h; The high-speed shear mixing conditions are: rotation speed 2000-3000 rpm, time 0.5-1h, During the shear mixing process, a 0.5-1.2T pulsed magnetic field with a frequency of 10-15 Hz is applied synchronously.

[0011] Preferably, in step (4): The steady-state magnetic field strength is 4.0-5.0T, the pulsed magnetic field strength is 1.0-1.5T, the frequency is 5-20Hz, and the duty cycle is 20-40%; Orientation molding pressure is 180-220MPa, holding time is 4-6min, Bidirectional pressing is adopted during the forming process, and the pressure difference between the upper and lower punches is controlled at 5-8%.

[0012] Preferably, in step (5): The vacuum gradient sintering comprises: Degassing stage: 550-650℃, vacuum degree 1×10-2-5×10-3Pa, heat preservation 0.5-1h; Main sintering stage: 1250-1280℃, vacuum degree ≤1×10-3Pa, heat preservation for 2-3h; Grain boundary liquid phase treatment stage: 1330-1380℃, vacuum degree 1×10-2-5×10-2Pa, heat preservation 0.5-1h, During the grain boundary liquid phase treatment stage, a helium-hydrogen mixed gas is introduced, wherein the volume fraction of hydrogen is 3-5%.

[0013] Preferably, in step (5): The triple tempering treatment includes: Primary tempering: 880-920℃ for 1-2h, cooling to 500-550℃ with argon injection; Secondary tempering: 730-770℃ for 2-4h, then furnace cooling to 300-350℃; Three tempering: 630-670℃ for 1.5-2.5h, applying 0.3-0.8T alternating magnetic field and then quenching in liquid nitrogen. During liquid nitrogen quenching, step cooling is used: first cool to -80°C at 20-30°C / s, hold for 3-5 minutes, and then cool to -196°C at ≥50°C / s.

[0014] In summary, this application includes at least one of the following beneficial technical effects: 1. This invention achieves a breakthrough in optimizing grain boundary diffusion efficiency through a synergistic process of graded hydrogen crushing and rare earth activation. Compared to traditional single-stage crushing processes, this solves the problem of uneven rare earth element distribution, allowing for more complete formation of grain boundary channels and significantly improving the uniformity of the material's magnetic properties. 2. This invention utilizes plasma surface modification technology to precisely repair internal defects in the material. Compared with conventional ball milling processes, surface oxidation issues are significantly reduced, and powder activity is enhanced, laying a better foundation for subsequent densification sintering. 3. This invention combines bidirectional magnetic field pressing with dynamic pressure regulation to achieve more precise control of magnetic domain orientation. This overcomes the limitations of traditional uniaxial pressing, achieving industry-leading material orientation and significantly enhancing magnetic energy product stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0016] The following is combined with Figure 1 , further describing the present application in detail, a high-performance NdFeB material and a preparation method thereof, comprising: Calculated by mass percentage, it contains PrNd 29.5-31.0%, TbH 2 1.2-1.8%, Cu-Al alloy 0.3-0.6% (Cu:Al=4:1), NbC 0.2-0.5%, Zr 0.1-0.3%, and the balance is Fe and other necessary components.

[0017] PrNd (Pr:Nd=3:7): The balance between the main phase magnetocrystalline anisotropy and magnetization is optimized by synergizing the high anisotropy field of Pr (HA=7T) with the high saturation magnetization of Nd (Js=1.6T).

[0018] TbH2 grain boundary diffusion: TbH2 decomposes into Tb atoms during the sintering process and diffuses along the grain boundaries to form a (Tb,Nd)2Fe14B shell structure, which enhances the grain boundary pinning effect. The coercivity enhancement follows the nucleation mechanism ΔHc∝K1 / (Js·D) (K1 is the anisotropy constant and D is the grain size).

[0019] Cu-Al alloy (4:1): The low melting point of Cu (1083°C) and the oxidation tendency of Al cooperate to form an amorphous (Cu,Al)O phase at the grain boundaries, reducing the activation energy of grain boundary diffusion (from 218 kJ / mol to 185 kJ / mol).

[0020] Preparation process: Step (1): Two-stage hydrogen crushing and liquid nitrogen quenching Primary hydrogen crushing (0.15-0.30MPa, 280-320℃), secondary hydrogen crushing (0.8-1.2MPa, 420-480℃), liquid nitrogen quenching (≥50℃ / s).

[0021] Airflow classification control: D10 ≥ 0.8 μm, D50 = 3-5 μm, D90 ≤ 12 μm.

[0022] Pressure gradient induces grain boundary pre-cracking: the first stage of low-pressure hydrogen crushing (0.15-0.30MPa) allows H2 to penetrate into the PrNd grain boundary, forming microcracks (width 50-100nm); the second stage of high pressure (0.8-1.2MPa) further expands the cracks, and the pre-cracking rate reaches more than 85%, providing a channel for subsequent Tb diffusion.

[0023] Liquid nitrogen quenching inhibits grain growth: rapid cooling (≥50℃ / s) prevents the α-Fe phase from precipitating in time, and a nano-scale rare earth-rich phase (size ≤50nm) is formed at the grain boundary.

[0024] Step (3): Plasma-assisted surface treatment After ball milling, the composite powder is treated with plasma (power 2-5kW, time 10-30min). Mechanism description: Surface activation and defect repair: Plasma high-energy electrons (5-10eV) bombard the powder surface to achieve the following effects: Remove surface oxides (such as Nd2O3), and reduce oxygen content by 200-300ppm; A TiC transition layer is formed on the surface of the NbC particles (Ti-C bonds are detected by XPS), which enhances the interfacial bonding strength with the matrix (interface energy is increased by 30%).

[0025] Step (4): Bidirectional magnetic field-pressure coupling orientation Steady-state magnetic field (4.0-5.0T) + pulsed magnetic field (1.0-1.5T, 5-20Hz), bidirectional compression (pressure difference 5-8%).

[0026] Multi-field coupling texture control: Steady-state magnetic field induced Nd2Fe 14 B grain <001> axis-parallel orientation; A pulsed magnetic field (frequency matching the lattice vibration frequency of 1012 Hz) breaks the magnetic domain energy barrier and increases the degree of orientation to 97%; The bidirectional pressure difference (5-8%) compensates for the difference in powder fluidity, and the green density deviation is ≤0.05g / cm3.

[0027] Step (5): Grain boundary liquid phase sintering and triple tempering Grain boundary liquid phase treatment (1330-1380℃) with He-H2 (H23-5vol%); Triple tempering: primary tempering (880-920℃ rapid cooling), secondary tempering (730-770℃ slow cooling), tertiary tempering (630-670℃ alternating magnetic field + liquid nitrogen quenching).

[0028] H2 induces grain boundary reconstruction: H2 reduces grain boundary oxides at high temperature (such as Nd2O3→Nd+H2O↑), forming a continuous intermetallic compound (Tb, Nd)Fe2 phase with a thickness of 2-5nm.

[0029] Alternating magnetic field assisted tempering: The alternating magnetic field (0.3-0.8T, 5-10Hz) induces magnetostrictive effect, releasing lattice distortion energy (lattice constant change Δa / a decreases from 0.15% to 0.05%).

[0030] Step (6): Surface Dy and Al2O3 coating Dy infiltration treatment (900-950℃, DyCl3 vapor 1-2h) → electrophoretic deposition of Al2O3 (10-20μm).

[0031] Dy gradient diffusion mechanism: Dy3+ replaces Nd2+ at high temperature to form a (Nd,Dy)2Fe14B surface layer (the Dy concentration decays exponentially from the surface to the inside, with an attenuation length of δ = 50 μm), thereby increasing the surface coercivity (ΔHc = +300 kA / m).

[0032] Insulation effect of Al2O3 coating: Electrophoretic deposition forms a dense α-Al2O3 layer (resistivity ≥1014Ω·cm), blocking the eddy current path and reducing high-frequency losses by 40% (test frequency 1kHz).

[0033] Example 1: A high-performance NdFeB material and a preparation method thereof, comprising: Components and proportions: PrNd 29.5%, TbH 2 1.2%, Fe balance (66.95%), BFe 0.95%, Co 0.8%, Cu-Al alloy 0.3%, NbC 0.2%, Zr 0.1%.

[0034] Steps and parameters: Hydrogen crushing: PrNd alloy was first treated at 0.18 MPa hydrogen pressure and 290 ° C for 3 hours, then changed to 0.9 MPa and 450 ° C for 1.5 hours. The crushed powder was quenched with liquid nitrogen (60 ° C / s) and air flow classification was performed to obtain D50 = 4 μm powder.

[0035] Tb activation: TbH2 powder and anhydrous ethanol were mixed in a ratio of 1:5, ultrasonically treated at 400W for 30 minutes, and the water content was 0.08% after vacuum drying.

[0036] Preparation of composite powder: ball milling under argon protection, ball-to-material ratio 6:1, 250 rpm for 5 hours, adding NbC nanopowder for shear mixing (2500 rpm×40 minutes), synchronous pulse magnetic field 1.0 T / 12 Hz.

[0037] Magnetic field suppression: 4.5 T steady-state field superimposed on 1.2 T pulse field (15 Hz), bidirectional suppression pressure difference of 6%, maintaining pressure for 5 minutes.

[0038] Sintering and tempering: main sintering at 1260℃×2.5h, grain boundary liquid phase treatment at 1350℃ with 4% hydrogen; three temperings: rapid cooling at 900℃, slow cooling at 750℃, and step quenching in liquid nitrogen at 650℃ with an alternating magnetic field of 0.6T.

[0039] Surface treatment: DyCl3 vapor infiltration at 950℃ for 1.5 hours, electrophoretic deposition of Al2O3 coating 15μm thick.

[0040] The Tb diffusion depth at the grain boundary exceeds 50μm, the coating adhesion reaches ASTM4B level, and there is no corrosion point after 2000 hours of salt spray test.

[0041] Example 2: A high-performance NdFeB material and a preparation method thereof, comprising: Components and ratios: PrNd 31.0%, TbH 2 1.8%, Fe balance (63.2%), BFe 1.05%, Co 1.5%, Cu-Al alloy 0.6%, NbC 0.5%, Zr 0.3%; Steps and parameters: Hydrogen crushing: first stage 0.22MPa hydrogen pressure, 305℃×2.5h, second stage 1.1MPa, 470℃×1.2h, powder D50=3.2μm after rapid cooling.

[0042] Tb activation: Ultrasonic wave bombardment at 500W for 20 minutes, after drying, the oxygen content on the surface of TbH2 decreased by 18%.

[0043] Composite powder treatment: ball milling speed 280 rpm × 4 hours, plasma radio frequency treatment 3.5 kW × 20 minutes, argon flow rate 80 sccm.

[0044] Pressing process: steady-state magnetic field 5.0T, pulse field 1.5T / 20Hz, upper and lower punch pressure difference 7.5%, green density 7.45g / cm3.

[0045] Sintering and tempering: 3% hydrogen is passed during the grain boundary treatment stage. During the three tempering stages, the liquid nitrogen quenching stage is first stabilized at -80℃ for 5 minutes and then rapidly cooled to -196℃.

[0046] Surface modification: Dy vapor at 920℃×2h, electrophoresis voltage 70V to obtain an Al2O3 layer of 18μm.

[0047] The magnet orientation degree is 97.3%, the coercive force is only attenuated by 3.2% after thermal aging at 180°C, and the high-frequency eddy current loss is reduced by 37%.

[0048] Example 3: A high-performance NdFeB material and a preparation method thereof, comprising: Components and ratios: PrNd 30.0%, TbH2 1.5%, Fe balance (64.7%), BFe 1.0%, Co 1.0%, Cu-Al alloy 0.5%, NbC 0.4%, Zr 0.2%; Steps and parameters: Hydrogen crushing: first stage 0.25MPa, 300℃×3 hours, second stage 1.0MPa, 460℃×1.8 hours, liquid nitrogen quenching rate 55℃ / s.

[0049] Tb activation: ultrasonic treatment at 350W for 25 minutes, and the powder D50 after drying was 2.8 μm.

[0050] Composite powder processing: Synchronous 0.8T pulse field during shear mixing, plasma power 4.0kW×15 minutes.

[0051] Magnetic field forming: steady-state field 4.8T, pulse field 1.3T / 10Hz, pressure difference 5%, holding time 4 minutes and 30 seconds.

[0052] Sintering and quenching: grain boundary treatment at 1370℃×0.8h, triple tempering with alternating magnetic field 0.7T / 9Hz, liquid nitrogen quenching with two-stage temperature control.

[0053] Coating process: electrophoretic deposition parameters 60V × 3 minutes, Al2O3 layer thickness 12μm, surface roughness Ra ≤ 0.5μm.

[0054] The magnetic energy product (BH) max reaches 52MGOe, and the loss under 10kHz conditions is only 58% of that of conventional products, with comprehensive performance leading the industry.

[0055] Comparative Example 1: The two-stage hydrogen crushing gradient design is cancelled and the traditional single-stage hydrogen crushing process is adopted.

[0056] Preparation process: Hydrogen crushing: PrNd alloy was crushed at 0.8 MPa hydrogen pressure and 400°C for 4 hours without liquid nitrogen quenching. The powder D50 was 6 μm after air flow classification.

[0057] Other steps are exactly the same as those in Example 1 (including Tb activation, composite powder treatment, pressing, sintering and tempering, and surface treatment).

[0058] Comparative Example 2: The plasma-assisted surface treatment was eliminated and conventional ball milling mixing was adopted.

[0059] Preparation process: Composite powder preparation: direct shear mixing after ball milling, no pulsed magnetic field application, and no plasma treatment.

[0060] Suppression parameters: Only a steady-state magnetic field of 4.0 T was used, without pulsed magnetic field superposition.

[0061] Other steps: the sintering, tempering and surface treatment processes are the same as those in Example 2.

[0062] Comparative Example 3: The triple alternating magnetic field tempering is cancelled and the traditional two-stage tempering is adopted.

[0063] Preparation process: Tempering process: Only 880℃ rapid cooling tempering and 730℃ slow cooling tempering were performed, and the third alternating magnetic field tempering was not implemented.

[0064] Sintering stage: No He-H2 mixed gas was introduced into the grain boundary liquid phase treatment, and conventional vacuum sintering was maintained.

[0065] Other steps: the hydrogen crushing, composite powder preparation and pressing process are the same as those in Example 3.

[0066] Verify the effect of alternating magnetic field tempering and grain boundary atmosphere control on improving thermal stability.

[0067] Comparative Example 4: The surface treatment only retains the electrophoretic deposition of Al2O3 coating, and cancels the gradient Dy infiltration process.

[0068] Preparation process: Surface treatment: 15μm Al2O3 coating was directly electrophoretically deposited on the sintered body without DyCl3 vapor deposition.

[0069] Other steps: the hydrogen crushing, composite powder preparation, pressing and sintering and tempering process are completely consistent with Example 1.

[0070] Comparative Example 5: The surface treatment only retains the electrophoretic deposition of Al2O3 coating, and the gradient Dy infiltration process is eliminated. Preparation process: Surface treatment: 15μm Al2O3 coating was directly electrophoretically deposited on the sintered body without DyCl3 vapor deposition.

[0071] Other steps: the hydrogen crushing, composite powder preparation, pressing and sintering and tempering process are completely consistent with Example 1.

[0072] Verify the synergistic enhancement effect of gradient Dy infiltration and coating composite technology on corrosion resistance.

[0073] Comparative Example 6: The hydrogen injection during the grain boundary liquid phase treatment stage is cancelled and pure argon protection is adopted.

[0074] Preparation process: Sintering process: Pure argon is introduced during the grain boundary liquid phase treatment stage without adding 3-5% hydrogen.

[0075] Other steps: the hydrogen crushing, composite powder preparation, pressing and tempering process are completely consistent with Example 3.

[0076] Experimental Example 1: Sample preparation: Example 1: Two-stage hydrogen crushing (0.18 MPa / 290°C → 0.9 MPa / 450°C) and liquid nitrogen quenching (60°C / s) were used, and D50 = 4 μm after airflow classification.

[0077] Comparative Example 1: Single-stage hydrogen crushing (0.8 MPa / 400°C×4h), no quenching treatment, D50=6 μm.

[0078] Experimental steps: Determination of grain boundary pre-cracking rate: SEM observation: The powder was crushed by hydrogen and treated with gold spraying. The powder was observed using a field emission scanning electron microscope (FE-SEM, accelerating voltage 5 kV, working distance 8 mm).

[0079] Statistical method: 100 grains were randomly selected and the proportion of grain boundaries with grain boundary crack length ≥ 1 μm was measured (crack length / total grain boundary length × 100%).

[0080] Repeat the experiment: each group of samples was tested 3 times and the average value was taken.

[0081] Tb element utilization detection: Slice preparation: After sintering, the magnet is sliced along the vertical orientation axis and polished to a mirror surface.

[0082] ICP-OES detection: points were taken every 50 μm from the surface to the inside (depth 0-200 μm) to detect the Tb content.

[0083] Utilization rate calculation: effective Tb concentration (gradient average from surface to 100 μm) / theoretical addition amount × 100%.

[0084] Table 1. Comparison of grain boundary pre-cracking rate and Tb element utilization rate Fluctuation of pre-cracking rate: Example 1 has a ±1% deviation due to the uniformity of liquid nitrogen quenching; Comparative Example 1 has a statistical error of ±2% due to the coarse grains of single-stage crushing.

[0085] Tb gradient difference: In Example 1, the surface Tb utilization rate reaches 90.5%, and the internal Tb utilization rate remains at 88% due to sufficient diffusion; in Comparative Example 1, the internal utilization rate drops sharply to 62%.

[0086] The two-stage hydrogen crushing gradient pressure and liquid nitrogen quenching significantly improved the grain boundary pre-cracking rate (average 87% vs. 43%), and the effective diffusion depth of the Tb element increased by more than 2 times, verifying the decisive role of grain boundary channel optimization on rare earth utilization.

[0087] Experimental Example 2: Sample preparation: Example 2: Plasma-assisted treatment (3.5 kW / 20 min) combined with multi-field coupling suppression (5.0 T steady-state field + 1.5 T pulsed field).

[0088] Comparative Example 2: No plasma treatment, only conventional ball milling and mixing, and single field pressing (4.0 T steady-state field) was used.

[0089] Experimental steps: Surface oxygen content detection: XPS analysis: The composite powder sample was taken and monochromatic AlKα radiation (1486.6 eV) was used in the scanning range of 0-1200 eV. The binding energy correction was based on C1s (284.8 eV).

[0090] Data collection: The surface oxygen atomic concentration was calculated as the arithmetic mean of the measured values at three random areas (accuracy ±0.3 at%).

[0091] Depth profiling: Sputtering depth down to 50nm, recording oxygen content changes every 10nm.

[0092] Orientation determination: EBSD scanning: The green body was cut along the pressing direction and polished using a 20 kV electron beam, a step size of 0.2 μm, and a collection area of 200 × 200 μm. 2 .

[0093] Data processing: statistics <001> The proportion of grains with a crystal orientation deviation of ≤5° from the pressing axis (excluding 5% outliers at the edge).

[0094] Table 2. Test data on the correlation between surface oxygen content and orientation Surface oxygen fluctuation: In Example 2, due to differences in plasma uniformity, the oxygen content fluctuated by ±0.4% between regions; in Comparative Example 2, due to aggravated ball milling oxidation, the regional difference reached ±0.6%.

[0095] Orientation deviation: In Example 2, due to multi-field coupling pressing, the orientation difference in region A / B is ≤0.3%; in Comparative Example 2, due to uneven stress in single-field pressing, the regional difference reaches 0.8%.

[0096] Plasma treatment reduced surface oxygen adsorption by 65%, and multi-field coupling pressing increased the orientation degree to more than 97%, verifying the core role of surface activity optimization and magnetic field synergy in magnetic domain arrangement.

[0097] Experimental Example 3: Sample preparation: Example 3: Triple alternating magnetic field tempering (900°C rapid cooling → 750°C slow cooling → 650°C alternating field) combined with hydrogen grain boundary treatment (1370°C×0.8h, 4% H2).

[0098] Comparative Example 3: Two-stage tempering (880°C rapid cooling → 730°C slow cooling), grain boundary treatment without hydrogen (pure Ar protection).

[0099] Experimental steps: Thermal aging test: Condition setting: The magnet sample was placed in a constant temperature oven at 180°C for 500 hours, and the temperature fluctuation (±1.5°C) was recorded every hour.

[0100] Coercive force attenuation detection: The Hcj values before and after aging were measured using a BH analyzer (NIM-3000C), and the attenuation rate was calculated (ΔHcj / Hcj initial × 100%).

[0101] Repeatability control: Each group of samples was tested 3 times, and the median was taken after eliminating extreme values.

[0102] Grain boundary phase observation: TEM sample preparation: Focused ion beam (FIB) cutting of the grain boundary area with a thickness of ≤80 nm, avoiding obvious defects in the observation area.

[0103] Thickness measurement: 10 points were randomly selected along the grain boundary, and the average thickness and continuity (proportion of continuous phase) of the (Tb,Nd)Fe2 phase were calculated.

[0104] Composition analysis: EDS line scanning verifies the Nd / Tb atomic ratio of the grain boundary phase.

[0105] Table 3. Thermal aging properties and grain boundary phase parameters Attenuation rate fluctuation: Due to the stability of the triple tempering process, the deviation of sample 1 / sample 2 in Example 3 is ≤0.4%; due to the discontinuity of the grain boundary phase in Comparative Example 3, the deviation of sample 1 / sample 2 reaches 0.7%.

[0106] Thickness difference: The thickness of the grain boundary phase in Example 3 fluctuates between 3.9 and 4.3 nm (hydrogen promotes phase growth); the thickness of Comparative Example 3 is only 1.4 to 1.6 nm (no reducing atmosphere inhibits phase precipitation).

[0107] Alternating magnetic field annealing and hydrogen treatment increased the thickness of the grain boundary phase by 2.7 times, increased the proportion of the continuous phase to more than 90%, and stabilized the coercive force attenuation rate within 4% after thermal aging, breaking through the 12% bottleneck of the traditional process.

[0108] Experimental Example 4: Sample preparation: Example 1: Gradient Dy infiltration (DyCl3 vapor 950℃×1.5h) combined with electrophoretic deposition of Al2O3 coating (15μm).

[0109] Comparative Example 4: Only Al2O3 coating (15 μm) was electrophoretically deposited without Dy plating.

[0110] Experimental steps: Salt spray corrosion resistance test: Conditions: 5% NaCl solution, constant temperature at 35°C, spray rate 1.5 mL / 80 cm 2 / h, refer to ASTMB117 standard.

[0111] Observation indicators: record the time when rust spots first appear (h), and calculate the density of rust spots on the surface after 2000h (pieces / cm 2 ).

[0112] Cross-sectional analysis: Cut the sample and observe the corrosion penetration depth (μm) at the interface between the coating and the substrate.

[0113] High frequency eddy current loss detection: Test equipment: Use high-frequency hysteresis loop instrument (1kHz-100kHz), constant temperature 25℃, sample size 10×10×5mm 3 .

[0114] Parameter settings: 10kHz alternating magnetic field (peak value 0.05T), measurement of unit mass loss value (W / kg).

[0115] Repeated test: Each group of samples was tested 5 times, and the average was taken after removing the maximum and minimum values.

[0116] Table 4. Corrosion resistance and high frequency performance comparison data table Rusting time fluctuation: Example 1 has a deviation of about 7% for Sample 1 / Sample 2 due to the difference in local coating thickness (±1.2 μm); Comparative Example 4 has a fast corrosion rate and a deviation of 8% due to the lack of Dy bottom layer protection.

[0117] Difference in loss values: In Example 1, due to the gradient Dy infiltration to optimize the magnetic domain structure, the loss difference of the test 1 / 2 is ≤7%; in Comparative Example 4, due to the eddy current concentration, the loss fluctuation reaches 12%.

[0118] The gradient Dy infiltration process extends the corrosion resistance life to more than 2000h and reduces the high-frequency loss by 35%, verifying the dual benefits of the composite coating in corrosion protection and magnetic domain optimization.

[0119] Experimental Example 5: Sample preparation Example 1: Two-stage hydrogen crushing + gradient Dy infiltration (DyCl3 steam 950℃×1.5h) + Al2O3 coating is used.

[0120] Comparative Example 5: The gradient Dy infiltration process was cancelled, and only the Al2O3 coating was retained (the other steps were exactly the same as those in Example 1).

[0121] Experimental steps: Salt spray corrosion resistance test: Conditions: 5% NaCl solution, 35°C constant temperature spray, according to ISO9227 standard.

[0122] Observation indicators: record the time of first rust appearance (h), and count the density of rust spots (pieces / cm2) after 2000h. 2 ).

[0123] Repeat the test: 3 parallel samples in each group, and take the median after excluding outliers.

[0124] High frequency eddy current loss detection: Equipment: High-frequency hysteresis loop instrument (frequency 10 kHz, magnetic field strength 0.05 T).

[0125] Parameters: Measure unit mass loss (W / kg), repeat 5 times and take the average value.

[0126] Cross-sectional analysis: SEM was used to observe the interface bonding state between the coating and the substrate.

[0127] Table 5. Comparative data on the impact of gradient Dy infiltration process on performance Difference in rusting time: Example 1 forms a dense Dy-O barrier layer due to gradient Dy infiltration, and the corrosion resistance time reaches 2000h; Comparative Example 5 has no Dy infiltration layer, and rusting occurs earlier within 500h.

[0128] Loss fluctuation: In Example 1, the loss value is stabilized at 12-13 W / kg due to Dy optimization of the magnetic domain structure; in Comparative Example 5, the loss increases by 55% and fluctuates significantly due to magnetic domain distortion.

[0129] The gradient Dy infiltration process increases the corrosion resistance life by more than 4 times by forming a Dy-O transition layer, while reducing high-frequency eddy current loss by about 40%.

[0130] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high performance NdFeB material, characterized in that: Contains the following components by mass: PrNd 29.5-31.0 parts, TbH2 1.2-1.8 parts, Fe balance, BFe 0.95-1.05 parts, Co 0.8-1.5 parts; Cu-Al alloy 0.3-0.6 parts, NbC 0.2-0.5 parts, Zr 0.1-0.3 parts; Wherein, the mass ratio of Cu to Al in the Cu-Al alloy is 4:

1.

2. A high performance NdFeB material according to claim 1, characterized in that: The mass ratio of Pr to Nd in the PrNd is 3:7, and the D50 particle size of the TbH2 is 1-3 μm.

3. A high performance NdFeB material according to claim 1, characterized in that: The D50 particle size of the NbC is 40-60 nm, and the D50 particle size of the Cu-Al alloy is ≤10 μm.

4. A method for preparing a high-performance NdFeB material, according to a high-performance NdFeB material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step (1), performing primary hydrogen crushing and secondary hydrogen crushing on the PrNd alloy in sequence to obtain PrNd crushed powder, and performing air flow classification on the PrNd crushed powder to control D10 ≥ 0.8 μm, D50 = 3-5 μm, and D90 ≤ 12 μm; Step (2), subjecting the TbH2 powder to ultrasonic activation treatment to obtain activated TbH2 powder; Step (3), mixing the crushed PrNd powder, activated TbH2 powder, and Cu-Al alloy powder, and then ball milling, adding NbC nanopowder and high-speed shear mixing to obtain a composite powder, and after high-speed shear mixing, using plasma-assisted surface treatment with a processing power of 2-5kW and a time of 10-30min; Step (4), applying a steady-state magnetic field and a pulsed magnetic field to the composite powder for orientation molding to obtain a green body; Step (5), subjecting the green body to vacuum gradient sintering and triple tempering treatment in sequence; Step (6), subjecting the sintered body to surface Dy treatment: heating to 900-950°C in a vacuum furnace, introducing DyCl3 vapor, treating for 1-2 hours, and then electrophoretically depositing an Al2O3 coating with a coating thickness of 10-20 μm.

5. The method for preparing a high-performance NdFeB material according to claim 4, wherein: In step (1): The conditions for the first-stage hydrogen crushing are: hydrogen pressure 0.15-0.30 MPa, temperature 280-320°C, time 2-4 hours; The conditions for the secondary hydrogen crushing are: hydrogen pressure 0.8-1.2 MPa, temperature 420-480°C, time 1-2 hours; After the secondary hydrogen is crushed, it is rapidly cooled by liquid nitrogen with a cooling rate of ≥50℃ / s.

6. The method for preparing a high-performance NdFeB material according to claim 4, wherein: In step (3): The ball milling conditions are: argon protection, ball-to-material ratio 5:1-8:1, rotation speed 200-300 rpm, time 3-6 h; The high-speed shear mixing conditions are: rotation speed 2000-3000 rpm, time 0.5-1h, During the shear mixing process, a pulsed magnetic field of 0.5-1.2 T is applied synchronously with a frequency of 10-15 Hz.

7. The method for preparing a high-performance NdFeB material according to claim 4, wherein: In step (4): The steady-state magnetic field strength is 4.0-5.0T, the pulsed magnetic field strength is 1.0-1.5T, the frequency is 5-20Hz, and the duty cycle is 20-40%; Orientation molding pressure is 180-220MPa, holding time is 4-6min, Bidirectional pressing is used during the forming process, and the pressure difference between the upper and lower punches is controlled at 5-8%.

8. The method for preparing a high-performance NdFeB material according to claim 4, wherein: In step (5): The vacuum gradient sintering comprises: Degassing stage: 550-650℃, vacuum degree 1×10-2-5×10-3Pa, heat preservation 0.5-1h; Main sintering stage: 1250-1280℃, vacuum degree ≤1×10-3Pa, heat preservation for 2-3h; Grain boundary liquid phase treatment stage: 1330-1380℃, vacuum degree 1×10-2-5×10-2Pa, heat preservation 0.5-1h, During the grain boundary liquid phase treatment stage, a helium-hydrogen mixed gas is introduced, in which the hydrogen volume fraction is 3-5%.

9. The method for preparing a high-performance NdFeB material according to claim 4, wherein: In step (5): The triple tempering treatment includes: Primary tempering: 880-920℃ for 1-2h, cooling to 500-550℃ with argon injection; Secondary tempering: 730-770℃ for 2-4h, then furnace cooling to 300-350℃; Three tempering: 630-670℃ for 1.5-2.5h, applying 0.3-0.8T alternating magnetic field and then quenching in liquid nitrogen. During liquid nitrogen quenching, step cooling is used: first cool to -80°C at 20-30°C / s, hold for 3-5 minutes, and then cool to -196°C at ≥50°C / s.

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