A grain boundary diffusion method to improve the diffusion performance of RTB magnets

Abstract

The invention discloses a grain boundary diffusion method for improving the diffusion performance of an R-T-B magnet. The method comprises the following steps: covering a diffusion source on the surface of an R-T-B magnet substrate, wherein the diffusion source is a heavy rare earth, and the mass of the diffusion source is 0.2% to 4% of the mass of the magnet substrate; subjecting the magnet covered with the diffusion source to a grain boundary diffusion treatment, wherein the diffusion temperature is 800° C. to 1000° C., the diffusion time is 1 h to 48 h, and within the first 1 to 3 h of the diffusion, the absolute vacuum is adjusted to 1.0*10 ‑3 ~4.6*10 ‑3 The absolute vacuum is then adjusted to a low vacuum between 3.6 kPa and 7.6 kPa, and after grain boundary diffusion, the mixture is cooled to room temperature and then heated up for tempering to obtain an R-T-B magnet after grain boundary diffusion. The present invention can increase the Hcj of the magnet and reduce the amount of residual magnetism reduction.

Description

Technical Field

[0001] The present invention provides a grain boundary diffusion method for improving the performance of RTB magnets by adjusting the vacuum degree and diffusion temperature of diffusion treatment. Background Art

[0002] Sintered NdFeB magnet material has high magnetic properties, does not contain the scarce metal Co, has a relatively low price, and has a wide range of applications and a long service life, so it has broad development prospects.

[0003] However, sintered NdFeB magnets are still in the development stage. First, after nearly 40 years of development, the magnetic energy product of sintered NdFeB magnets has not reached the theoretical limit. The current magnetic energy product of sintered NdFeB magnets can reach 93% of the theoretical value, and the magnetic energy product obtained by industrial small-scale production and large-scale production is even lower. Secondly, Br is close to the theoretical value, but Hcj is far from the theoretical value, and there is still a lot of room for improvement.

[0004] Since the coercive force and remanence temperature coefficient of sintered NdFeB are negative, the Br and Hcj of the product will decrease when working in a high-temperature environment. Therefore, higher Br and Hcj are needed at room temperature to solve this problem. Improving the Br and Hcj of the magnet is a major challenge.

[0005] Diffusion technology is a technology that can quickly improve Hcj in recent years. It has the advantages of low cost, easy operation, and high cost performance. However, the principle of diffusion technology is that the Nd-rich phase melts and volatilizes at high temperature to form a diffusion channel, and the diffusion source diffuses inward through the diffusion channel. However, there is a large amount of volatilization of the Nd-rich phase during the diffusion process, resulting in a significant increase in Hcj and a significant decrease in Br. Therefore, it is very critical to reduce the reduction in Br while increasing Hcj. Summary of the invention

[0006] The present invention provides a grain boundary diffusion method for improving the performance of RTB magnets by adjusting the vacuum degree of diffusion treatment and the diffusion temperature. The method can improve the Hcj of the magnet and reduce the amount of residual magnetism reduction.

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

[0008] A grain boundary diffusion method for improving the diffusion performance of RTB magnets, the method comprising the following steps:

[0009] (1) Covering the surface of the RTB magnet matrix with a diffusion source, wherein the diffusion source is a heavy rare earth, and the mass of the diffusion source is 0.2% to 4% of the mass of the magnet matrix, preferably 0.5% to 3.0%;

[0010] (2) The magnet covered with diffusion sources is subjected to grain boundary diffusion treatment, the diffusion temperature is 800°C to 1000°C (preferably 890°C to 920°C), the diffusion time is 1h to 48h (preferably 6h to 12h), and within the first 1 to 3h of the diffusion, the absolute vacuum is adjusted to 1.0*10 -3 ~4.6*10 -3 The absolute vacuum is then adjusted to a low vacuum between 3.6 kPa and 7.6 kPa. After grain boundary diffusion, the mixture is cooled to room temperature and then heated up for tempering to obtain the RTB magnet after grain boundary diffusion.

[0011] In the step (1), the heavy rare earth is Tb or Dy.

[0012] In the step (2), the diffusion temperature is preferably 890° C. to 920° C., and the diffusion time is preferably 6 h to 12 h.

[0013] In the step (2), the heating rate of the grain boundary diffusion is preferably 1-10°C / min, more preferably 5-8°C / min.

[0014] In the step (2), the tempering temperature is 400° C. to 800° C., preferably 400° C. to 500° C., and the tempering time is 0.2 h to 24 h, preferably 3 h to 6 h.

[0015] Furthermore, in step (1), the method of covering the diffusion source on the surface of the RTB magnet substrate can be a magnetron sputtering physical vapor deposition method or a coating method; or other methods of covering the diffusion source commonly used by those skilled in the art can be used in the present invention.

[0016] Furthermore, the magnetron sputtering physical vapor deposition method utilizes a plasma vacuum coating machine to coat a layer of high-purity heavy rare earth film on the surface of the RTB magnet substrate. Specifically, the atmosphere source of the magnetron sputtering coating is high-purity Ar, the vacuum degree of the cavity is between 0.3-0.5 Pa, the internal operating temperature is between 100°C and 150°C, and the thickness of the obtained heavy rare earth film layer is between 1um and 30um. The mass of the heavy rare earth is 0.2% to 4% of the mass of the magnet substrate.

[0017] Furthermore, the coating method is to use a wet film machine to evenly coat the mixture of heavy rare earth and ethanol on the surface of the RTB magnet substrate. The specific operation method is: in an argon environment, with an oxygen content below 40ppm, ethanol with a mass concentration of more than 99% and heavy rare earth are mixed at a mass ratio of 0.5 to 1.2:1, where the mass of the heavy rare earth is 0.2% to 4.0% of the mass of the magnet substrate, and the mixture of heavy rare earth and ethanol is evenly coated on the magnet surface using a wet film machine.

[0018] In the step (1), the RTB magnet matrix can be selected from various types or brands of RTB magnets, that is, NdFeB magnets, the main components of which are Nd, Fe, and B. It can also contain various other elements such as rare earth elements Ho, Gd, Dy, Tb, or other metal or non-metal elements such as Al, Cu, Zn, Sn, In, Ti, V, Co, Mn, Ni, Ca, Zr, Ga, Nb, Mo, Si, etc. The element composition and component ratio of the magnet matrix have no effect on the diffusion process of the present application.

[0019] The grades of the magnet substrates used in the embodiments of the present application are N46M to N50M.

[0020] Furthermore, the thickness of the heavy rare earth film layer obtained by the magnetron sputtering physical vapor deposition method is preferably 5 to 25 um, and the mass of the heavy rare earth is 0.5% to 3.0% of the mass of the magnet matrix.

[0021] Furthermore, in the coating method, the mass ratio of ethanol to heavy rare earth is preferably 0.8:1 to 1:1, wherein the mass of the heavy rare earth is 0.5% to 3.0% of the mass of the magnet matrix.

[0022] In the present invention, absolute vacuum refers to absolute pressure, which refers to the actual air pressure value rather than the difference from atmospheric pressure.

[0023] The principle of the present invention is that the mechanism of grain boundary diffusion is mainly that the Nd-rich phase melts to form a diffusion channel, and the heavy rare earth of the diffusion source diffuses inward along the diffusion channel. However, there is inevitably a certain gap between the diffusion source and the matrix, especially between the covered heavy rare earths. Under high vacuum and high temperature, the grain boundary rare earth-rich phase in the matrix melts and volatilizes, combines with the diffusion source, and establishes a diffusion channel. Therefore, the more the Nd-rich phase volatilizes, the more diffusion channels there are, and the easier it is for the heavy rare earth source to diffuse into the matrix. However, two problems need to be considered at the same time. First, the large amount of volatilization of the Nd-rich phase will also lead to a double reduction in Br and Hcj; secondly, the large amount of volatilization of the Nd-rich phase will cause the destruction of the grain boundary phase structure. Even if the crystal is diffused to form a shell structure later, the Hcj of the magnet cannot be improved. At the same time, the sintered body cannot be dense, and the internal voids of the magnet become more, which greatly reduces the function of the magnet. Therefore, the appropriate amount of volatilization of the Nd-rich phase can solve the problem of the reduction of Br in the diffusion process and the greater increase of Hcj.

[0024] After extensive research, the applicant found that the amount of Nd volatilization in high vacuum is higher than that of Nd-rich volatilization in low vacuum. Therefore, in the diffusion process, high vacuum is required in the early stage to volatilize the Nd-rich phase and form a diffusion channel. In the middle and late stages, the vacuum degree is adjusted to low vacuum to reduce the amount of Nd-rich phase volatilization, so as to reduce the reduction of Br and Hcj and make the diffusion enhancement effect more obvious. The change of diffusion temperature can cause the precipitation phase to change during high temperature insulation, such as precipitation (Nd 1-x Tbx ) 2 Fe 14 B phase (where the larger the X, the larger the anisotropy field of the crystal), adjusting the temperature can adjust the X value to improve the magnetic properties. In summary, the present application improves the diffusion process, adjusts the vacuum degree and the diffusion temperature during the diffusion process, greatly improves the diffusion effect, significantly reduces the Br reduction, and can be reduced to less than 0.06KGs at most. The Br value before and after diffusion is basically unchanged, and Hcj is significantly improved, which can be increased by more than 11KOe after diffusion, which improves the magnetic properties of the diffused magnet compared to the existing process. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] Embodiment 1:

[0027] (1) Select several N48M magnets from our company's product warehouse. To facilitate subsequent performance testing, the magnets are wire-cut into several small magnets of φ10*5mm as experimental substrates. In actual production, the shape of the magnet substrate is not restricted.

[0028] The diffusion source Tb is covered on the surface of the substrate by physical vapor deposition: on a φ10mm*5mm magnetic steel, magnetron sputtering physical vapor deposition is carried out inside a plasma vacuum coating machine, and the atmosphere source is high-purity Ar. The principle is to use a magnetic field to accelerate electrons to bombard Ar atoms and form plasma after high-voltage glow discharge, and then use the electric field and magnetic field to control Ar+ ions to bombard the target material, so that Tb atoms are dispersed in the cavity after sputtering; finally, the gravity field is used to evenly coat the metal Tb on the surface of the magnetic steel. The vacuum degree of the cavity is between 0.3-0.5pa, and its purpose is to control the number of Ar atoms and guide the generation of a more efficient plasma chain reaction. The internal working temperature is between 100℃ and 150℃, and the resulting film thickness is about 15um, and the mass proportion of terbium is about 1.7%.

[0029] (2) Magnet diffusion treatment:

[0030] The magnet coated with Tb film is placed in a material boat and placed in a vacuum tube furnace for diffusion treatment. The diffusion temperature is 905℃, the diffusion time is 9h, and the absolute vacuum is adjusted to 1.0*10 -3 Pa, heating rate 6℃ / min, after grain boundary diffusion, cool to room temperature and then heat up for tempering, tempering temperature within 445℃, tempering time is 4.5h. The cooling method adopts vacuum air cooling

[0031] The diffused magnets were subjected to performance tests and composition comparisons before and after.

[0032] The diffused magnets are sandblasted and tested for magnetic properties. After demagnetization and sandblasting, ICP-OES composition measurement is performed to compare the Tb diffusion amount and Nd loss amount before and after.

[0033] The magnetic properties of the magnet at 20℃±3℃ were measured by NIM15000, and the magnet composition was measured by ICP-OES.

[0034] Example 2: The preparation method is the same as that of Example 1, except that the absolute vacuum degree is adjusted to 4.0*10 -2 Pa.

[0035] Example 3: The preparation method is the same as that of Example 1, except that the absolute vacuum degree is adjusted to 3.6 kPa.

[0036] Example 4: The preparation method is the same as that of Example 1, except that the absolute vacuum degree is adjusted to 5.6 kPa.

[0037] Example 5: The preparation method is the same as that of Example 1, except that the absolute vacuum degree is adjusted to 7.6 kPa.

[0038] Example 6: The preparation method is the same as that of Example 1, except that the absolute vacuum degree is adjusted to 1.0*10 -3 Pa, and the absolute vacuum was adjusted to 3.6 kPa in the next 8 hours.

[0039] Example 7: The preparation method is the same as that of Example 1, except that the relative vacuum degree is adjusted to 1.0*10 -3 Pa, and the relative vacuum degree was adjusted to 5.6 kPa in the next 7 hours.

[0040] Example 8: The preparation method is the same as that of Example 1, except that the diffusion source Tb is covered on the surface of the substrate by coating: in a glove box filled with argon, the oxygen content displayed by the oxygen controller is below 40ppm, 99% mass concentration of alcohol is mixed with Tb in a weight ratio of 1:1, and the weight of Tb accounts for 1.7% of the magnet. The mixture of Tb and ethanol is evenly coated on the surface of the magnet with a wet film machine.

[0041] Example 9: The preparation method is the same as that of Example 8, except that the vacuum degree is adjusted to 5.6 kPa.

[0042] Example 10: The preparation method is the same as that of Example 8, except that the vacuum degree is adjusted to 1.0*10 during the first 3 hours of the diffusion heating process. -3 kpa, and the vacuum degree was adjusted to 7.6 kpa in the next 6 hours.

[0043] The control group did not undergo the step of covering the diffusion source Tb to the substrate surface, and the remaining steps were the same as those in the embodiment.

[0044] Table 1 Comparison of Nd and Tb components before and after diffusion

[0045] Nd loss / % Tb diffusion amount / % Example 1 1.65 0.18 Example 2 1.03 0.166 Example 3 0.5 0.143 Example 4 0.42 0.15 Example 5 0.39 0.142 Example 6 0.75 0.156 Example 7 0.7 0.159 Example 8 1.73 0.19 Example 9 0.52 0.147 Example 10 0.72 0.161

[0046] The proportion is the ratio of the weight of the entire magnetic steel

[0047] Nd loss amount = Nd weight percentage in the magnet before diffusion - Nd weight percentage in the magnet after diffusion.

[0048] The Tb diffusion amount was obtained by measuring the magnet composition using ICP-OES.

[0049] Table 2 Magnetic properties of the control group

[0050]

[0051] Table 3 Magnetic properties of the examples and the difference between the control group

[0052]

[0053] Based on Tables 1 to 3 above, we can draw the following conclusions:

[0054] 1. As the vacuum degree increases and the absolute pressure decreases, the loss of Nd increases, and the diffusion of Tb also increases, indicating that the increase in vacuum degree has a positive effect on the volatilization of the Nd-rich phase. At the same time, the greater the volatilization of the Nd-rich phase, the more diffusion channels are formed, and the greater the diffusion of the heavy rare earth Tb.

[0055] 2. Combining Table 1 and Table 3, we can see that the more Nd volatilizes, the more Br decreases. At the same time, it is not the case that the more heavy rare earth diffuses, the greater the Hcj of the magnet. This is determined by the diffusion and volatilization. Although the magnetocrystalline anisotropy Tb>Nd, the diffusion of Tb is much smaller than the volatilization of Nd, which will lead to a non-prominent increase in the Hcj of the magnet and an excessive decrease in Br.

[0056] 3. The diffusion process of high vacuum in the early stage and low vacuum in the later stage is beneficial to reduce the volatilization of Nd-rich phase. At the same time, the diffusion amount of heavy rare earth will not decrease too much compared with the complete high vacuum. The final magnetic properties of the magnet will have a considerable effect whether from the increase of Hcj or the decrease of Br.

[0057] 4. Compared with the diffusion coating method, the PVD method improves Hcj more because PVD has a high vacuum to prevent Tb from being oxidized, and the diffusion source coverage is more uniform, and the overall diffusion amount is larger.

[0058] Example 11: The preparation method is the same as that of Example 7, except that the diffusion temperature is 800°C.

[0059] Example 12: The preparation method is the same as that of Example 7, except that the diffusion temperature is 860°C.

[0060] Example 13: The preparation method is the same as that of Example 7, except that the diffusion temperature is 890°C.

[0061] Example 14: The preparation method is the same as that of Example 7, except that the diffusion temperature is 920°C.

[0062] Example 15: The preparation method is the same as that of Example 7, except that the diffusion temperature is 960°C.

[0063] Example 16: The preparation method is the same as that of Example 7, except that the diffusion temperature is 1000°C.

[0064] Example 17: The preparation method is the same as that of Example 13, except that the vacuum degree during diffusion is 1.0*10 -3 Pa.

[0065] The control group was prepared in the same manner as in the above embodiment, except that the step of covering the diffusion source Tb to the substrate surface was not performed.

[0066] Table 4 Magnetic properties of the control group at different diffusion temperatures

[0067]

[0068] Table 5 Magnetic properties of Examples 7, 11 to 16 and the difference with the control group

[0069]

[0070] The following conclusions can be drawn from Tables 4 and 5:

[0071] 1. Too high a diffusion temperature or too low a diffusion temperature during the diffusion process will result in a low increase in Hcj and also result in a low overall squareness. An appropriate diffusion temperature can maximize the diffusion effect.

[0072] Combining Example 13 with Example 17 once again illustrates that the diffusion vacuum degree is low in the early stage of diffusion and high in the later stage, which increases Hcj more, reduces Br less, and has a better diffusion effect.

Claims

1. A grain boundary diffusion method for improving the diffusion performance of RTB magnets, Features The method comprises the following steps: (1) Covering the surface of the RTB magnet matrix with a diffusion source, wherein the diffusion source is a heavy rare earth, and the mass of the diffusion source is 0.2% to 4% of the mass of the magnet matrix; (2) The magnet covered with diffusion source is subjected to grain boundary diffusion treatment, the diffusion temperature is 800℃~1000℃, the diffusion time is 1h~48h, and the absolute vacuum is adjusted to 1.0*10 -3 ~4.6*10 -3 The absolute vacuum is then adjusted to a low vacuum between 3.6 kPa and 7.6 kPa. After grain boundary diffusion, the magnet is cooled to room temperature and then heated up for tempering to obtain the RTB magnet after grain boundary diffusion.

2. The method according to claim 1, It is characterized in that In the step (1), the heavy rare earth is Tb or Dy.

3. The method according to claim 1, It is characterized in that In the step (2), the diffusion temperature is 890°C to 920°C.

4. The method according to claim 1, It is characterized in that In the step (2), the diffusion time is 6 h to 12 h.

5. The method according to claim 1, It is characterized in that In the step (2), the heating rate of the grain boundary diffusion is 1-10°C / min.

6. The method according to claim 1, It is characterized in that In the step (2), the tempering temperature is 400° C. to 800° C., and the tempering time is 0.2 h to 24 h.

7. The method according to claim 1, It is characterized in that In the step (1), the method for covering the diffusion source on the surface of the RTB magnet substrate is a magnetron sputtering physical vapor deposition method or a coating method.

8. The method according to claim 7, Features The magnetron sputtering physical vapor deposition method utilizes a plasma vacuum coating machine to coat a layer of high-purity heavy rare earth film on the surface of the RTB magnet substrate. The atmosphere source is high-purity Ar, the cavity vacuum degree is between 0.3-0.5 Pa, the internal operating temperature is between 100° C. and 150° C., the thickness of the obtained heavy rare earth film layer is between 1um and 30um, and the mass of the heavy rare earth is 0.2% to 4% of the mass of the magnet substrate.

9. The method according to claim 7, It is characterized in that The coating method is to use a wet film machine to evenly coat the mixture of heavy rare earth and ethanol on the surface of the RTB magnet substrate.

10. The method according to claim 9, It is characterized in that The operation method of the coating method is: in an argon environment, with an oxygen content below 40 ppm, ethanol with a mass concentration of more than 99% is mixed with heavy rare earth at a mass ratio of 0.5 to 1.2:1, wherein the mass of the heavy rare earth is 0.2% to 4.0% of the mass of the magnet matrix, and the mixture of heavy rare earth and ethanol is evenly coated on the surface of the magnet using a wet film machine.

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