Preparation method of Pr-Fe-B permanent magnet material with exchange bias phenomenon

Abstract

The invention provides a preparation method of a Pr-Fe-B permanent magnet material with an exchange bias phenomenon, which comprises the following steps: weighing Pr, Fe, Cu and B according to the stoichiometric ratio of 70at% of Pr2Fe14B and 30at% of Pr6Fe13Cu, additionally adding 1wt% of Pr, carrying out electric arc melting, carrying out induction heating, spraying on a copper roller, crushing an obtained Pr2Fe14B-Pr6Fe13Cu alloy thin strip, and carrying out SPS sintering to obtain the Pr-Fe-B permanent magnet material. By adjusting the proportion of the alloy Pr2Fe14B to the alloy Pr6Fe13Cu, a continuous and thick non-magnetic grain boundary phase is formed in the grain boundary of the magnet, and the coercive force is greatly increased through decoupling intergranular exchange. And meanwhile, under the action of an external magnetic field, the antiferromagnetic phase Pr6Fe13Cu in the grain boundary generates a pinning effect on the main phase Pr2Fe14B, so that a larger reverse external magnetic field must be applied to realize complete overturning of the magnetic moment of the ferromagnetic phase, the exchange bias phenomenon is caused, and the coercive force of the magnet is improved. In addition, based on the advantages of low sintering temperature, short sintering time and the like of a discharge plasma rapid sintering technology, rapid growth of grains can be inhibited in the sintering process, so that grain refinement is realized.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet alloy material technology, specifically relating to a method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon. Background Technology

[0002] Due to their excellent magnetic properties, Pr-Fe-B magnets are widely used in wind power generation, communication equipment, and new energy vehicles. With continuous technological advancements, the demand for high-performance Pr-Fe-B magnets is increasingly urgent. However, Pr-Fe-B magnets have a low Curie temperature and a large coercivity temperature coefficient, resulting in a significant decrease in coercivity at operating temperatures, which severely limits their application at high temperatures. To enhance the coercivity of magnets, the most common method is to replace Pr with heavy rare earth elements (Dy / Tb) to strengthen the magnetocrystalline anisotropy field. However, heavy rare earth elements (Dy / Tb) are scarce in the Earth's crust and expensive; excessive consumption is detrimental to the balanced development of rare earth resources. Therefore, improving the coercivity of magnets while reducing or eliminating the addition of heavy rare earth elements during the preparation of sintered magnets has become a pressing problem for researchers and industrialists.

[0003] Coercivity is a physical quantity that is highly sensitive to structure. The microstructure, impurities, and defects within permanent magnet materials significantly affect coercivity. Related research indicates that antiferromagnetic RE6Fe... 13 M (M = Cu, Ga, Sn, etc.) has a significant impact on the magnetic properties and microstructure of Nd-Fe-B magnets. For example, existing literature 1 (Zhu J H. Effects of Nd-Ga intergranular addition on microstructure and magnetic properties of heavy-rare-earth-free Nd-Fe-B sintered magnets, 2022) describes a method that mixes Nd-Fe-B and Nd-Ga strips in a specific ratio, then pulverizes the thin strip blanks into powder using hydrogen explosion and airflow pulverization processes. The dual-alloy powder is pressed under a magnetic field of 1800 kA / m, then isostatically pressed at 150 MPa, and finally sintered in a vacuum atmosphere at 1030 °C for 2 h. The sintered sample is then heat-treated in a vacuum for 2 h to obtain a Ga-containing sintered NdFeB magnet. The main phase grains of the magnet obtained by this technique are influenced by the antiferromagnetic Nd6Fe 13 Surrounded by a Ga phase, this structure effectively suppresses the expansion of the antimagnetic core, thus achieving a significant improvement in coercivity. However, this process has a long sample preparation cycle and high energy consumption, resulting in high production costs.

[0004] Grain refinement is also an effective method to improve the coercivity of magnets. For example, Chinese patent CN118888308A uses a process of melting and forming sheets, hydrogen breaking and dehydrogenation, and air jet milling to prepare a particle size... The alloy powders are mechanically and uniformly mixed in a certain proportion, then pressed, sintered, and subjected to three tempering heat treatments to finally obtain sintered NdFeB magnets. Although this technical solution can refine the magnetic powder grains, the process parameters of the air jet mill need to be precisely controlled, the equipment cost is high, and the output is much lower than that of a ball mill. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing Pr-Fe-B permanent magnet materials with exchange bias phenomenon. This method obtains the main phase as Pr2Fe through spark plasma rapid sintering technology. 14 B, the intercrystalline phase is Pr6Fe 13 Cu permanent magnets. Under the action of an external magnetic field, the antiferromagnetic phase Pr6Fe in the grain boundaries... 13 Cu for the main phase Pr2Fe 14 B produces a pinning effect, therefore a larger reverse external magnetic field must be applied to achieve a complete reversal of the magnetic moment of the ferromagnetic phase, resulting in an exchange bias phenomenon, thereby enhancing the coercivity of the magnet. Meanwhile, based on the advantages of rapid sintering technology such as low sintering temperature and short sintering time, rapid grain growth can be suppressed during the sintering process, thus achieving grain refinement.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing Pr-Fe-B permanent magnet material with exchange bias phenomenon, the method being as follows: S1, based on a stoichiometric ratio of 70 at% Pr2Fe 14 B+30at%Pr6Fe 13 Cu, Pr, Fe, Cu, and B are weighed to obtain mixture a. Then, Pr is added to mixture a to obtain mixture b. The mass fraction of Pr added to mixture b is 1%. S2. The mixture b obtained in S1 is subjected to electric arc melting in a high-purity argon atmosphere to obtain an alloy ingot. S3. After cooling the alloy ingot obtained in S2, polish the surface oxide film. Then, induction heating at 1700℃ under a high-purity argon atmosphere until the alloy ingot melts, spray the molten alloy ingot onto a copper roller rotating at 25 m / s to obtain Pr2Fe. 14 B-Pr6Fe 13 Cu alloy thin strip; S4, Pr2Fe obtained in S3 14 B-Pr6Fe 13After the Cu alloy strip was broken, Pr2Fe was obtained. 14 B-Pr6Fe 13 Cu alloy powder; S5, Pr2Fe obtained in S4 14 B-Pr6Fe 13 Cu alloy powder is placed into a graphite mold and subjected to SPS sintering to obtain Pr-Fe-B permanent magnet material with exchange bias phenomenon. The conditions for SPS sintering are as follows: under a pressure of 50 MPa, the temperature is increased to 600°C at a heating rate of 70°C / min, then decreased to 500°C at a cooling rate of 50°C / min, held for 30 min, and then depressurized and allowed to cool naturally to room temperature.

[0007] Preferably, the purity of Pr, Fe, Cu and B in S1 is 99.99%.

[0008] Preferably, the arc melting method described in S2 is as follows: the gas pressure inside the furnace is drawn to 10 using a mechanical pump and a diffusion pump. - 5 Pa, then 0.5 Pa of high-purity argon gas is introduced as a protective gas, and the mixture b is melted under the current of 80 A. After the alloy cools and solidifies, the melting is repeated 4 to 5 times.

[0009] Preferably, the purity of the high-purity argon gas in S2 and S3 is 99.99%.

[0010] Preferably, the Pr2Fe in S3 14 B-Pr6Fe 13 The thickness of the Cu alloy strip is 0.3 mm.

[0011] Preferably, the Pr2Fe in S4 14 B-Pr6Fe 13 The average particle size of Cu alloy powder is .

[0012] Preferably, the main phase of the Pr-Fe-B permanent magnet material exhibiting exchange bias in S5 is Pr2Fe. 14 Phase B, intergranular phase is Pr6Fe 13 Cu phase.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention adjusts the alloy Pr2Fe 14 B and Pr6Fe 13 The proportion of Cu was used to directly obtain Pr₂Fe using melt quenching technology. 14 B, Pr6Fe 13This alloy exhibits a coexistence of Cu two phases, and the process boasts a short sample preparation cycle, low energy consumption, and low production cost. The antiferromagnetic Pr6Fe phase exists at the grain boundaries. 13 Cu for the main phase Pr2Fe 14 B produces a pinning effect, and the hysteresis loop deviates along the negative magnetic field axis, thereby increasing the coercivity of the magnet.

[0014] 2. This invention uses the SPS rapid sintering process to prepare Pr-Fe-B permanent magnet materials, which reduces the sintering temperature and shortens the sintering time, effectively avoiding grain coarsening during the sintering process.

[0015] 3. This invention does not contain heavy rare earth elements, thus saving rare earth resources and reducing production costs.

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 It is the hysteresis loop of 70%PrFeB-30%PrFeCu prepared in Example 1 of this invention.

[0018] Figure 2 This is the SEM image of 70%PrFeB-30%PrFeCu prepared in Example 1 of this invention.

[0019] Figure 3 This is the XRD pattern of 70%PrFeB-30%PrFeCu prepared in Example 1 of this invention.

[0020] Figure 4 This is the EDS diagram of 70%PrFeB-30%PrFeCu prepared in Example 1 of this invention.

[0021] Figure 5 This is the hysteresis loop of Pr-Fe-B prepared in Comparative Example 1 of this invention.

[0022] Figure 6 This is the hysteresis loop of 70%PrFeB-30%PrFeTi prepared in Comparative Example 2 of this invention.

[0023] Figure 7 This is the hysteresis loop of 90%PrFeB-10%PrFeCu prepared in Comparative Example 3 of this invention.

[0024] Figure 8 This is the hysteresis loop of 70%PrFeB-30%PrFeCu-500℃ prepared in Comparative Example 4 of this invention. Detailed Implementation

[0025] Example 1 The method for preparing Pr-Fe-B permanent magnet material with exchange bias phenomenon in this embodiment is as follows: S1, based on a stoichiometric ratio of 70 at% Pr2Fe 14 B+30at%Pr6Fe 13 Cu, Pr, Fe, Cu, and B are weighed to obtain mixture a. Then, Pr is added to mixture a to obtain mixture b. The mass fraction of Pr added to mixture b is 1%. The purity of Pr, Fe, Cu and B is 99.99%; S2. Place the mixture b obtained in S1 into an electric arc melting furnace and perform electric arc melting in a high-purity argon atmosphere to obtain an alloy ingot. The gas pressure inside the furnace is pumped to 10 using mechanical pumps and diffusion pumps. -5 Pa, then 0.5 Pa of high-purity argon gas is introduced as a protective gas, and the mixture b is melted under the current of 80 A. After the alloy cools and solidifies, the melting is repeated 4 to 5 times. In this embodiment, it is 5 times. S3, the Pr2Fe obtained in S2 14 B-Pr6Fe 13 After cooling, the Cu alloy ingot is polished to remove the oxide film on its surface. It is then placed in a quartz tube and induction heated to 1700℃ in a high-purity argon atmosphere until it melts. The molten alloy ingot is then sprayed onto a copper roller rotating at 25 m / s, resulting in a Pr2Fe alloy with a thickness of 0.3 mm. 14 B-Pr6Fe 13 Cu alloy thin strip; The purity of the high-purity argon gas mentioned in S2 and S3 is 99.99%; S4, Pr2Fe obtained in S3 14 B-Pr6Fe 13 After the Cu alloy ribbon was crushed in an agate mortar, an average particle size of [missing value] was obtained. Pr2Fe 14 B-Pr6Fe 13 Cu alloy powder; S5, Pr2Fe obtained in S4 14 B-Pr6Fe 13 Cu alloy powder is placed into a graphite mold and sintered by SPS to obtain a Pr-Fe-B permanent magnet material with exchange bias phenomenon, abbreviated as 70%PrFeB-30%PrFeCu. The main phase of the Pr-Fe-B permanent magnet material exhibiting exchange bias is Pr2Fe. 14 Phase B, intergranular phase is Pr6Fe 13 Cu phase; The magnet prepared by the graphite mold has the following dimensions: length 40mm, width 20mm, and height 4mm. The conditions for SPS sintering are as follows: under a pressure of 50 MPa, the temperature is increased to 600°C (sintering temperature) at a heating rate of 70°C / min, then decreased to 500°C at a cooling rate of 50°C / min, held for 30 min, and then depressurized and allowed to cool naturally to room temperature.

[0026] The magnetic properties of 70%PrFeB-30%PrFeCu were measured using a vibrating sample magnetometer (VSM), and the test results are as follows: Figure 1 As shown, the coercivity is 9.177 kOe and the remanence is 48.99 emu / g.

[0027] The microstructure of 70%PrFeB-30%PrFeCu was observed using scanning electron microscopy (SEM). Figure 2 As shown, it mainly consists of a black-contrast main phase and a gray-contrast intergranular phase.

[0028] The phase composition of 70%PrFeB-30%PrFeCu was measured using X-ray diffraction (XRD), and the test results are as follows: Figure 3 As shown, the diffraction peaks of 70%PrFeB-30%PrFeCu are similar to those of Pr2Fe. 14 Corresponding to B, it can be known that the dominant phase of black contrast is Pr2Fe. 14 B.

[0029] The phase composition of 70%PrFeB-30%PrFeCu was measured using energy-dispersive spectroscopy (EDS), and the test results are as follows: Figure 4 As shown, the percentages (%) of intercrystalline phases Pr, Fe, and Cu atoms are 29.1, 66.0, and 4.9, respectively. Calculations indicate that the intercrystalline phase with gray contrast is Pr6Fe. 13 Cu.

[0030] To prove Pr6Fe 13 The role of Cu in the technical solution is illustrated in Comparative Examples 1, 2, and 3, and Pr6Fe 13 PrFeB-PrFeCu sintered magnets with Cu contents of 0 at% and 10 at% respectively, Pr6Fe 13 PrFeB-PrFeTi sintered magnets with a Ti content of 30 at%

[0031] Comparative Example 1 The preparation method of the Pr-Fe-B permanent magnet material in this comparative example is the same as that in Example 1, except that the stoichiometric ratio in step S1 is Pr2Fe. 14B means that no Cu is added during weighing, and the final sintered magnet is named Pr-Fe-B.

[0032] The magnetic properties of Pr-Fe-B were measured using a vibrating sample magnetometer (VSM), and the test results are as follows: Figure 5 As shown, the coercivity is 1.65 kOe, and the remanence is 29.31 emu / g. There is no exchange bias phenomenon.

[0033] Comparative Example 2 The preparation method of the Pr-Fe-B permanent magnet material in this comparative example is the same as that in Example 1, except that the stoichiometric ratio in step S1 is 70 at% Pr2Fe. 14 B+30at%Pr6Fe 13 Ti was used to replace Cu, and the final sintered magnet was named 70%PrFeB+30%PrFeTi.

[0034] 70% Pr2Fe was measured using a vibrating sample magnetometer (VSM). 14 The magnetic properties of B+30%PrFeTi are shown in the test results. Figure 6 As shown, the coercivity is 5.16 kOe, and the remanence is 61.68 emu / g. There is no exchange bias phenomenon.

[0035] Comparative Example 3 The preparation method of the Pr-Fe-B permanent magnet material in this comparative example is the same as that in Example 1, except that the stoichiometric ratio in step S1 is 90 at% Pr2Fe. 14 B-10at%Pr6Fe 13 Cu, the final sintered magnet was named 90%PrFeB-10%PrFeCu.

[0036] The magnetic properties of 90%PrFeB-10%PrFeCu were measured using a vibrating sample magnetometer (VSM), and the test results are as follows: Figure 7 As shown, the coercivity is 2.91 kOe and the remanence is 21.84 emu / g.

[0037] Comparisons of Comparative Examples 1 and 2 with Example 1 show that Pr6Fe is not added when designing the sample composition. 13 Cu or Pr6Fe added 13 In Ti, the main phase grains of the magnet are not surrounded by the non-antiferromagnetic phase, the magnet does not exhibit exchange bias, and the magnet has low coercivity.

[0038] A comparison between Comparative Example 3 and Example 1 shows that Pr6Fe was used when designing the sample composition. 13Insufficient Cu addition resulted in the absence of exchange bias in the magnet. This is because the antiferromagnetic layer has a thin grain thickness, leading to weak exchange coupling at the ferromagnetic / antiferromagnetic interface. Consequently, the pinning effect of the antiferromagnetic phase on the ferromagnetic phase is weak, thus failing to induce exchange bias.

[0039] To demonstrate the effect of sintering temperature on the technical solution, Comparative Example 4 is provided.

[0040] Comparative Example 4 The preparation method of the Pr-Fe-B permanent magnet material in this comparative example is the same as that in Example 1, except that the sintering temperature in step S5 is 500℃, and the resulting magnet is named 70%PrFeB-30%PrFeCu-500℃.

[0041] The magnetic properties of 70%PrFeB-30%PrFeCu at 500℃ were measured using a vibrating sample magnetometer (VSM). The test results are as follows: Figure 8 As shown, the coercivity is 4.40 kOe, and the remanence is 39.67 emu / g. There is no exchange bias phenomenon.

[0042] Comparing Example 1 and Comparative Example 4, it can be seen that when the sintering temperature is too low, the magnet does not exhibit exchange bias, and the coercivity is significantly reduced. This is because Pr6Fe 13 Cu phase has a high melting point, and at lower sintering temperatures, Pr6Fe 13 The enrichment of the Cu phase inside the magnet weakens the exchange coupling between the antiferromagnetic phase and the ferromagnetic phase, thus preventing the induction of exchange bias.

[0043] As can be seen from Example 1 and Comparative Examples 1-4 above, the preparation method of the Pr-Fe-B permanent magnet material with exchange bias phenomenon of the present invention optimizes the sintering temperature and raw material dosage to achieve the desired antiferromagnetic phase Pr6Fe in the magnet. 13 The increased and uniform distribution of Cu content enhances its influence on the main phase Pr2Fe. 14 The pinning effect generated by boron induces exchange bias, thereby significantly improving the coercivity of Pr-Fe-B permanent magnet materials. This method does not rely on heavy rare earth elements, has a simple process, low cost, and is suitable for industrial production. It provides an effective way to solve the problem of decreased coercivity of Pr-Fe-B magnets at high temperatures. This has significant industrial value for saving rare earth resources and expanding the application scenarios of Pr-Fe-B permanent magnet materials in high-temperature conditions, communication equipment, new energy vehicles, and other fields.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a Pr-Fe-B permanent magnet material exhibiting exchange bias phenomenon, characterized in that, The method is as follows: S1, based on a stoichiometric ratio of 70 at% Pr2Fe 14 B+30at%Pr6Fe 13 Cu, Pr, Fe, Cu, and B are weighed to obtain mixture a. Then, Pr is added to mixture a to obtain mixture b. The mass fraction of Pr added to mixture b is 1%. S2. The mixture b obtained in S1 is subjected to electric arc melting in a high-purity argon atmosphere to obtain an alloy ingot. S3. After cooling the alloy ingot obtained in S2, polish the surface oxide film. Then, induction heating at 1700℃ under a high-purity argon atmosphere until the alloy ingot melts, spray the molten alloy ingot onto a copper roller rotating at 25 m / s to obtain Pr2Fe. 14 B-Pr6Fe 13 Cu alloy thin strip; S4, Pr2Fe obtained in S3 14 B-Pr6Fe 13 After the Cu alloy strip was broken, Pr2Fe was obtained. 14 B-Pr6Fe 13 Cu alloy powder; S5, Pr2Fe obtained in S4 14 B-Pr6Fe 13 Cu alloy powder is placed into a graphite mold and subjected to SPS sintering to obtain Pr-Fe-B permanent magnet material with exchange bias phenomenon. The conditions for SPS sintering are as follows: under a pressure of 50 MPa, the temperature is increased to 600°C at a heating rate of 70°C / min, then decreased to 500°C at a cooling rate of 50°C / min, held for 30 min, and then depressurized and allowed to cool naturally to room temperature.

2. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, The purity of Pr, Fe, Cu and B mentioned in S1 is 99.99%.

3. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, The electric arc melting method described in S2 is as follows: the gas pressure inside the furnace is pumped to 10 using a mechanical pump and a diffusion pump. -5 Pa, then 0.5 Pa of high-purity argon gas is introduced as a protective gas, and the mixture b is melted under the current of 80 A. After the alloy cools and solidifies, the melting is repeated 4 to 5 times.

4. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, The purity of the high-purity argon gas mentioned in S2 and S3 is 99.99%.

5. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, Pr2Fe in S3 14 B-Pr6Fe 13 The thickness of the Cu alloy strip is 0.3 mm.

6. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, Pr2Fe as described in S4 14 B-Pr6Fe 13 The average particle size of Cu alloy powder is .

7. The method for preparing a Pr-Fe-B permanent magnet material with exchange bias phenomenon according to claim 1, characterized in that, The main phase of the Pr-Fe-B permanent magnet material with exchange bias phenomenon described in S5 is Pr2Fe. 14 Phase B, intergranular phase is Pr6Fe 13 Cu phase.

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