A method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets

Abstract

An embodiment of the present invention discloses a method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets, including: pretreatment of the magnets; plasma cleaning; injection of heavy rare earth ions: on the premise of applying a negative bias voltage to the sintered Nd-Fe-B magnets, simultaneously using high-power pulsed magnetron sputtering and an ion source to sputter a heavy rare earth target to complete the injection of heavy rare earth ions; deposition of a heavy rare earth coating: introducing an inert gas to adjust the vacuum degree to 0.4 - 1 Pa, and then on the premise of applying a negative bias voltage to the sintered Nd-Fe-B magnets, using high-power pulsed magnetron sputtering to sputter a heavy rare earth target to complete the deposition of the heavy rare earth coating on the surface of the sintered Nd-Fe-B magnets; vacuum heat treatment: heat-treating the sintered Nd-Fe-B magnets deposited with the heavy rare earth coating. The effects of improving the density of structural defects in the shallow surface layer of the magnets, increasing the heavy rare earth diffusion channels, and ultimately improving the heavy rare earth diffusion efficiency are achieved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of sintered NdFeB surface engineering, and specifically relate to a method for improving the heavy rare earth grain boundary diffusion efficiency of sintered NdFeB magnets. Background Art

[0002] Sintered NdFeB magnets are key materials for new energy vehicle drive motors. However, harsh working conditions such as high speed and heavy load can easily cause the motor to heat up and result in irreversible demagnetization of the magnets, thus deteriorating the motor performance. Adding a high content of heavy rare earths Dy / Tb can effectively improve the coercivity of the magnets and enhance their thermal stability. However, due to the antiferromagnetic coupling effect between heavy rare earths and Fe, part of the remanence will be lost. In addition, heavy rare earths are expensive and are national strategic resources. There is an urgent need to reduce the usage of heavy rare earths and maximize their role. In 2000, Park et al. in Japan first proposed the heavy rare earth grain boundary diffusion technology. Through heat treatment, Dy / Tb diffuses along the grain boundaries and forms a high magnetic anisotropy field (Nd, Dy / Tb)2Fe 14 B-rich heavy rare earth layer on the surface of the main phase, which can improve the coercivity while reducing the decrease of remanence and the usage amount of heavy rare earths.

[0003] However, due to the high diffusion activation energy and low diffusion coefficient of heavy rare earths, the grain boundary diffusion process requires high temperature and long time (the temperature needs to be maintained > 920 °C and the time > 10 hours during the diffusion process) to meet the diffusion depth of heavy rare earths, thereby ensuring the improvement amplitude of the coercivity of the magnets. Obviously, the current production efficiency of heavy rare earth grain boundary diffusion is low, and the energy consumption is large, which does not meet the requirements of China's "dual carbon" strategy and the concept of green development, and is also not conducive to reducing the production cost of enterprises. The applicant adopted the existing technology and tried to carry out heavy rare earth grain boundary diffusion at a lower diffusion temperature (the temperature is 910 °C and the time is 9 h). The heavy rare earth diffusion efficiency is low, the grain boundary diffusion effect is poor, a large amount of heavy rare earths accumulate on the surface of the magnets, and the amount of heavy rare earths entering the interior of the magnets is small. Therefore, a high magnetic anisotropy field (Nd, Dy / Tb)2Fe 14 B-rich heavy rare earth layer cannot be formed on the surface of the main phase, and not only the improvement amplitude of the coercivity is limited, but also the utilization rate of heavy rare earths is low.

[0004] Therefore, there is an urgent need for a high-efficiency heavy rare earth grain boundary diffusion technology at present. Summary of the Invention

[0005] For this reason, the embodiments of the present invention provide a method for improving the heavy rare earth grain boundary diffusion efficiency of sintered NdFeB magnets. By using high-power pulsed magnetron sputtering technology before depositing the heavy rare earth coating and assisted by an anode layer ion source for ion implantation pretreatment of the sintered NdFeB magnets, and then utilizing the high-energy heavy rare earth ion bombardment effect, the density of structural defects in the shallow surface layer of the magnets is increased, the heavy rare earth diffusion channels are increased, and finally the heavy rare earth diffusion efficiency is improved.

[0006] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0007] In one aspect of the embodiments of the present invention, a method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets is provided, including:

[0008] S100, Pretreatment of the magnet: After the sintered Nd-Fe-B magnet is successively subjected to grinding, polishing and ultrasonic cleaning, it is dried;

[0009] S200, Plasma cleaning: Under the condition of an inert gas environment with a vacuum degree of 1-3 Pa and a temperature of 100-400 °C, a bias voltage with a preset voltage value is applied to the workpiece holder on which the pretreated sintered Nd-Fe-B magnet is placed to complete the plasma cleaning of the sintered Nd-Fe-B magnet;

[0010] S300, Injection of heavy rare earth ions: Adjust the vacuum degree to 0.1-0.4 Pa. On the premise of applying a negative bias voltage to the sintered Nd-Fe-B magnet, a high-power pulsed magnetron sputtering and an ion source are simultaneously used to sputter a heavy rare earth target to complete the injection of heavy rare earth ions on the surface of the sintered Nd-Fe-B magnet;

[0011] S400, Deposition of heavy rare earth coating: Stop applying a negative bias voltage to the sintered Nd-Fe-B magnet, turn off the high-power pulsed magnetron sputtering and the anode layer ion source, introduce an inert gas to adjust the vacuum degree to 0.4-1 Pa, and then, on the premise of applying a negative bias voltage to the sintered Nd-Fe-B magnet, use high-power pulsed magnetron sputtering to sputter a heavy rare earth target to complete the deposition of the heavy rare earth coating on the surface of the sintered Nd-Fe-B magnet;

[0012] S500, Vacuum heat treatment: The sintered Nd-Fe-B magnet deposited with a heavy rare earth coating is heat-treated.

[0013] As a preferred solution of the present invention, step S200 specifically includes:

[0014] S201, Place the pretreated sintered Nd-Fe-B magnet on the workpiece holder and face it to the heavy rare earth target as the magnetron sputtering source;

[0015] S202, After pumping to a vacuum degree not higher than 9×10-2 Pa, turn on the heating tube to heat to a temperature of 100-350 °C and keep it;

[0016] S203, Continue to pump to a vacuum degree not higher than 5×10-3 Pa, and then introduce an inert gas at a rate of 200-300 sccm until the vacuum degree rises to 1.5-3 Pa;

[0017] S204, Apply a DC bias voltage with a preset voltage value to the workpiece holder to complete the plasma cleaning of the sintered Nd-Fe-B magnet.

[0018] As a preferred embodiment of the present invention, the operating parameters of the plasma cleaning process are as follows: the voltage value of the applied DC bias voltage is 800 - 1500 V, and the cleaning time is 10 - 30 min;

[0019] The distance between the sintered neodymium iron boron magnet and the heavy rare earth target is 70 - 120 mm.

[0020] As a preferred embodiment of the present invention, after the plasma cleaning is completed, the application of the DC bias voltage is stopped, and the adjustment of the vacuum degree in step S300 is adjusted by introducing an inert gas.

[0021] As a preferred embodiment of the present invention, in step S300, the operating parameters of the high - power pulsed magnetron sputtering process are as follows: the output voltage is 750 - 1000 V, the operating frequency is 30 - 80 Hz, and the pulse width adjustment range is 60 - 100 μs;

[0022] In step S300, the operating parameters of the anode layer ion source are as follows: the power is 0.2 - 1 kW, the frequency is 40 - 150 kHz, and the duty cycle is 20% - 90%;

[0023] In step S300, the operating parameters of the DC bias voltage power supply for applying the negative bias voltage are as follows: the operating voltage is 700 - 10000 V, and the application time is 5 - 15 min.

[0024] As a preferred embodiment of the present invention, in step S400, the operating parameters of the high - power pulsed magnetron sputtering process are as follows: the output voltage is 450 - 600 V, the operating frequency is 200 - 400 Hz, and the pulse width adjustment range is 100 - 500 μs;

[0025] In step S400, the operating parameters of the DC bias voltage power supply for applying the negative bias voltage are as follows: the operating voltage is 50 - 150 V, and the application time is 20 - 40 min.

[0026] As a preferred embodiment of the present invention, in step S500, the heat treatment is carried out in an environment where the vacuum degree is not higher than 10 - 2 Pa;

[0027] The heat treatment process includes a thermal diffusion process and an annealing process.

[0028] As a preferred embodiment of the present invention, the diffusion temperature of the thermal diffusion process is 750 - 900 °C, and the thermal diffusion time is 3 - 8 h;

[0029] The annealing temperature of the annealing process is 450 - 900 °C, and the annealing time is 4 - 6 h.

[0030] As a preferred embodiment of the present invention, the inert gas is argon;

[0031] The ion source is an anode layer ion source.

[0032] As a preferred embodiment of the present invention, the heavy rare earth target is at least one of Dy and / or Tb, and heavy rare earth targets of their alloy types.

[0033] The embodiments of the present invention have the following advantages:

[0034] The present invention mainly realizes the improvement of the heavy rare earth grain boundary diffusion efficiency from the perspective of magnet surface modification. Specifically, aiming at the problems that the heavy rare earth grain boundary diffusion process requires high temperature and long time (temperature > 920 °C, time > 10 hours), before preparing the heavy rare earth coating, high power pulsed magnetron sputtering technology (HiPIMS) is used and assisted by an anode layer ion source to perform ion implantation pretreatment on the sintered neodymium iron boron magnet. HiPIMS can excite high-density heavy rare earth plasmas, and the anode layer ion source can further improve the plasma ionization rate. At the same time, with the regulation of the substrate bias voltage, the process of heavy rare earth ion implantation on the magnet surface layer can be realized. Thus, by utilizing the bombardment effect of high-energy heavy rare earth ions, the density of structural defects in the shallow surface layer of the magnet can be increased, the heavy rare earth diffusion channels can be increased, and the heavy rare earth diffusion efficiency can be improved. Description of the Drawings

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0036] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0037] Figure 1 It is a partial structural schematic diagram of the magnetron sputtering equipment provided by the embodiment of the present invention;

[0038] Figure 2 It is a flowchart of the method provided by the embodiment of the present invention;

[0039] Figure 3 It is a demagnetization curve and magnetic property test result diagram of Example 1 and Comparative Example 1 in the present invention;

[0040] Figure 4This is the demagnetization curve and magnetic property test result diagram of Example 2 and Comparative Example 2 in the present invention;

[0041] Figure 5 This is the demagnetization curve and magnetic property test result diagram of Example 3 and Comparative Example 3 in the present invention.

[0042] In the figure:

[0043] 1 - Heavy rare earth target magnetron sputtering source; 2 - First standby magnetron sputtering source; 3 - Second standby magnetron sputtering source; 4 - Third standby magnetron sputtering source; 5 - Anode layer ion source; 6 - Fourth standby magnetron sputtering source; 7 - Workpiece holder; 8 - Sintered NdFeB magnet; 9 - Vacuum chamber; 10 - Heating tube; 11 - HiPIMS power supply; 12 - Anode layer ion source power supply; 13 - DC bias power supply. Specific Embodiments

[0044] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] The present invention provides a method for improving the boundary diffusion efficiency of heavy rare earths in sintered NdFeB magnets. Specifically, it includes the following steps:

[0046] First step: Pretreatment. The sintered NdFeB magnet is successively subjected to grinding, polishing, ultrasonic cleaning and drying treatments.

[0047] Second step: Plasma cleaning. Place the sintered NdFeB magnet 8 on the workpiece holder 7 of the magnetron sputtering equipment as shown in Figure 1 and face the heavy rare earth target magnetron sputtering source 1. Then evacuate the vacuum chamber 9; when the vacuum degree drops below the order of magnitude of 10 -2 Pa, turn on the heating tube 10 and heat to 100°C - 350°C and keep this temperature throughout the subsequent process; when the vacuum degree drops below 5×10 -3 Pa, introduce argon gas Ar so that the vacuum degree of the vacuum chamber 9 is 1.5 Pa - 3 Pa; turn on the DC bias power supply 13 connected to the workpiece holder 7 to complete the plasma cleaning of the surface of the sintered NdFeB magnet. The specific parameters of the DC bias power supply 13 in the working state are: voltage 800V - 1500V, cleaning time 10 min - 30 min; the distance range between the sintered NdFeB magnet 8 and the heavy rare earth target magnetron sputtering source 1 is: 70 mm - 120 mm.

[0048] Step 3: Heavy rare earth ion implantation. After the plasma cleaning is completed, stop the gas supply, turn off the DC bias power supply 13, and keep the others unchanged. Introduce argon gas Ar to make the pressure in the vacuum chamber 9 be 0.1 Pa - 0.4 Pa. Turn on the HiPIMS power supply 11 to sputter a heavy rare earth target (Dy and / or Tb heavy rare earth or its alloy, that is, here it can be a Dy target and / or a Tb target, or an alloy material containing Dy and / or Tb elements, for example, AlDy alloy, etc. Of course, the present invention is not limited thereto, etc.), to generate a high-density heavy rare earth plasma. At the same time, turn on the anode layer ion source 5 to further improve the ionization rate of the heavy rare earth. In addition, apply a negative bias to the sintered neodymium iron boron magnet 8 to complete the heavy rare earth ion implantation process. The parameter range of the HiPIMS power supply 11 is: pulse power 750 V - 1000 V, frequency 30 Hz - 80 Hz, pulse width 60 μs - 100 μs; the specific parameter range of the anode layer ion source power supply 12 is: power 0.2 kW - 1 kW, frequency 40 kHz - 150 kHz, duty cycle 20% - 90%; the parameter range of the DC bias power supply 13 is: voltage 700 V - 10000 V; the implantation time is 5 min - 15 min.

[0049] It should be further noted that the magnetron sputtering source 1 of the heavy rare earth target and the anode layer ion source 5 can be arranged in the circumferential direction, and the workpiece holder 7 can be arranged in a ring shape so that the distances between the magnetron sputtering source 1 of the heavy rare earth target and the anode layer ion source 5 and the outer circumference of the workpiece holder 7 are basically the same. At the same time, multiple spare magnetron sputtering sources can also be set here. The magnetron sputtering source 1 of the heavy rare earth target, the anode layer ion source 5 and the multiple spare magnetron sputtering sources are arranged in the circumferential direction. By setting the multiple spare magnetron sputtering sources, it is possible to select the spare magnetron sputtering source facing it specifically according to the placement direction of the sintered neodymium iron boron magnet 8. Specifically, for example, according to actual needs, the total number of the magnetron sputtering source 1 of the heavy rare earth target, the anode layer ion source 5 and the multiple spare magnetron sputtering sources can be set to six. In this case, the spare magnetron sputtering sources at least include the first spare magnetron sputtering source 2, the second spare magnetron sputtering source 3, the third spare magnetron sputtering source 4, and the fourth spare magnetron sputtering source 6. Preferably, a spare magnetron sputtering source is spaced between the magnetron sputtering source 1 of the heavy rare earth target and the anode layer ion source 5.

[0050] Step 4: Deposition of heavy rare earth coating. After the heavy rare earth ion implantation is completed, stop the gas supply, and turn off the HiPIMS power supply 11, the anode layer ion source power supply 12, and the DC bias power supply 13, while keeping the others unchanged. Introduce argon gas Ar to make the pressure in the vacuum chamber 9 be 0.4 Pa - 1 Pa. Turn on the HiPIMS power supply 11 to sputter the heavy rare earth target (Dy or Tb heavy rare earth or their alloy). At the same time, apply a negative bias voltage to the sintered NdFeB magnet 8 to complete the deposition of the heavy rare earth coating. The parameter range of the HiPIMS power supply 11 is: pulse power supply 450 V - 600 V, frequency 200 Hz - 400 Hz, pulse width 100 μs - 500 μs; the parameter range of the DC bias power supply 13 is: 50 V - 150 V; the deposition time is 20 min - 40 min.

[0051] Step 5: Vacuum heat treatment. After the deposition of the heavy rare earth coating is completed, put the sintered NdFeB magnet 8 into a vacuum heat treatment furnace for heat treatment. The heat treatment parameter range is: diffusion temperature 750 °C - 950 °C, time 3 - 8 hours; annealing temperature 450 °C - 490 °C, time 4 - 6 hours; vacuum degree less than 10 -2 Pa. Wait for the magnet to cool to room temperature, take out the sample and conduct magnetic property detection.

[0052] It should be noted that the voltage value when applying a negative bias voltage by the DC bias power supply 13 during the third step of heavy rare earth ion implantation is greater than the voltage value when applying a negative bias voltage during the fourth step of heavy rare earth coating deposition.

[0053] In the above setting method, an ion source is further adopted in the third step (for example, it can be an anode layer ion source, or a thermal filament ion source or an arc discharge ion source, etc. Preferably, an anode layer ion source is selected here). In this way, by using HiPIMS to sputter the heavy rare earth target to generate heavy rare earth particles, while high-density heavy rare earth plasma has been generated itself, an ion source is further used to make high-energy and high-density inert gas ions (for example, when the gas filled in the vacuum chamber 9 is argon, it is Ar ions) be generated in the entire vacuum chamber 9. Through the ionization collision with respect to the heavy rare earth particles, the ionization rate of the heavy rare earth particles can be further increased. Based on the synergy of the two, by increasing the ionization rate, the energy and density of the heavy rare earth plasma are further increased. Thus, on the premise of applying the same negative bias voltage to the sintered NdFeB magnet 8, the implantation energy of the heavy rare earth ions is higher and the implantation effect is better, that is, more heavy rare earth particles enter the shallow surface layer of the sintered NdFeB magnet 8, and the bombardment of the sintered NdFeB magnet 8 is stronger. Therefore, the density of structural defects in the shallow surface layer of the sintered NdFeB magnet 8 is further increased in advance, the diffusion channels of the heavy rare earth on the sintered NdFeB 8 are increased, and the subsequent deposition efficiency is effectively improved.

[0054] It should be noted that in the present invention, the bias voltage mentioned in terms such as negative bias voltage, bias voltage, or applying bias voltage all refers to the negative bias voltage.

[0055] The following is a detailed description through specific embodiments.

[0056] Example 1

[0057] A sintered neodymium iron boron magnet with a grade of N52 and dimensions of 25 mm × 25 mm × 3 mm (denoted as Sample 1#) is used. A Dy target is selected as the heavy rare earth element target material. Plasma cleaning, Dy ion implantation, and Dy coating deposition are sequentially performed on the magnet surface, followed by vacuum heat treatment. The specific process is as follows:

[0058] 1. Pretreatment: The sintered neodymium iron boron magnet is sequentially ground, polished, ultrasonically cleaned, and dried.

[0059] 2. Plasma cleaning: The sintered neodymium iron boron magnet is placed on the workpiece holder and facing the Dy target, and then the vacuum chamber is evacuated; when the vacuum degree drops to 9×10 -2 Pa, the heating tube is turned on and heated to 300 °C and maintained at this temperature throughout the subsequent process; when the vacuum degree drops to 4×10 -3 Pa, 250 sccm of argon gas Ar is introduced to make the vacuum degree of the vacuum chamber 1.5 Pa; the DC bias voltage power supply connected to the workpiece holder is turned on to complete the plasma cleaning of the sintered neodymium iron boron magnet surface. The specific parameters of the DC bias voltage power supply are: voltage 900 V, cleaning time 15 min; the distance between the sintered neodymium iron boron magnet and the magnetron sputtering source of the heavy rare earth target is 90 mm.

[0060] 3. Dy ion implantation: After the plasma cleaning is completed, the gas supply is stopped, the DC bias voltage power supply is turned off, and the rest remains unchanged. Argon gas Ar is introduced to make the air pressure in the vacuum chamber 0.2 Pa. The HiPIMS power supply and the anode layer ion source power supply are turned on to generate high-density Dy plasma. In addition, a negative bias voltage is applied to the sintered neodymium iron boron magnet to complete the heavy rare earth ion implantation process. The parameters of the HiPIMS power supply are: pulse voltage 800 V, frequency 40 Hz, pulse width 70 μs; the specific parameters of the anode layer ion source power supply are: power 1 kW, frequency 100 kHz, duty cycle 60%; the parameters of the DC bias voltage power supply are: voltage 1300 V; the implantation time is 10 min.

[0061] 4. Dy coating deposition: After the Dy ion implantation is completed, stop the gas supply, turn off the HiPIMS power supply, the anode layer ion source power supply, and the DC bias power supply, and keep the rest unchanged. Introduce argon gas Ar to make the pressure in the vacuum chamber 0.8 Pa. Turn on the HiPIMS power supply and sputter the Dy target. At the same time, apply a negative bias voltage to the sintered NdFeB magnet to complete the Dy coating deposition. The parameters of the HiPIMS power supply are: pulsed power supply 500 V, frequency 200 Hz, pulse width 200 μs; the parameters of the DC bias power supply are: 75 V; the deposition time is 25 min, and the thickness of the finally deposited coating is about 5 μm.

[0062] 5. Vacuum heat treatment: After the Dy coating deposition is completed, put the sintered NdFeB magnet with the Dy coating into a vacuum heat treatment furnace for heat treatment. The heat treatment parameters are: diffusion temperature 850 °C, time 5 h; annealing temperature 450 °C, time 5 h; vacuum degree 8×10 -3 Pa. Wait for the magnet to cool to room temperature, take out the sample and perform magnetic property testing.

[0063] Example 2

[0064] Use a sintered NdFeB magnet (denoted as sample 3#) with a grade of N52 and dimensions of 25 mm × 25 mm × 3 mm. Select a Tb target as the heavy rare earth element target. Perform plasma cleaning, Tb ion implantation, and Tb coating deposition on the magnet surface in sequence, and then perform vacuum heat treatment.

[0065] 1. Pretreatment: Grind, polish, ultrasonically clean, and dry the sintered NdFeB magnet in sequence.

[0066] 2. Plasma cleaning: Place the sintered NdFeB magnet on the workpiece holder and face the Tb target, and then evacuate the vacuum chamber; when the vacuum degree drops to 9×10 -2 Pa, turn on the heating tube, heat to 350 °C and keep this temperature throughout the subsequent process; when the vacuum degree drops to 5×10 -3 Pa, introduce 300 sccm of argon gas Ar to make the vacuum degree of the vacuum chamber 2 Pa; turn on the DC bias power supply connected to the workpiece holder to complete the plasma cleaning on the surface of the sintered NdFeB magnet. The specific parameters of the DC bias power supply are: voltage 1200 V, cleaning time 10 min; the distance between the sintered NdFeB magnet and the magnetron sputtering source of the heavy rare earth target is 70 mm.

[0067] 3. Tb Ion Implantation: After the plasma cleaning is completed, stop the gas supply, turn off the DC bias power supply, and keep the rest unchanged. Introduce argon gas Ar to make the pressure in the vacuum chamber 0.15 Pa. Turn on the HiPIMS power supply and the anode layer ion source to generate high-density Tb plasma. In addition, apply a negative bias voltage to the sintered NdFeB magnet to complete the heavy rare earth ion implantation process. The parameters of the HiPIMS power supply are as follows: pulse voltage 950 V, frequency 30 Hz, pulse width 80 μs; the specific parameters of the anode layer ion source power supply are: power 0.5 kW, frequency 40 kHz, duty cycle 50%; the parameters of the DC bias power supply are: 3000 V; the implantation time is 6 min.

[0068] 4. Tb Coating Deposition: After the Tb ion implantation is completed, stop the gas supply, turn off the HiPIMS power supply, the anode layer ion source power supply, and the DC bias power supply, and keep the rest unchanged. Introduce argon gas Ar to make the pressure in the vacuum chamber 0.7 Pa. Turn on the HiPIMS power supply and sputter the Tb target. At the same time, apply a negative bias voltage to the sintered NdFeB magnet to complete the Tb coating deposition. The parameters of the HiPIMS power supply are as follows: pulse power 550 V, frequency 300 Hz, pulse width 150 μs; the parameters of the DC bias power supply are: 100 V; the deposition time is 20 min, and the final thickness of the deposited coating is about 5 μm.

[0069] 5. Vacuum Heat Treatment: After the Tb coating deposition is completed, put the sintered NdFeB magnet with the deposited Tb coating into a vacuum heat treatment furnace for heat treatment. The heat treatment parameters are as follows: diffusion temperature 900 °C, time 8 h; annealing temperature 470 °C, time 6 h; vacuum degree 5×10 -3 Pa. Wait for the magnet to cool to room temperature, take out the sample and conduct magnetic property testing.

[0070] Example 3

[0071] Use a sintered NdFeB magnet with the grade N52 and dimensions of 25 mm × 25 mm × 3 mm (denoted as sample 5#). Select an AlDy alloy target as the heavy rare earth element target, and the atomic ratio of Al to Dy is 1:9. Perform plasma cleaning, AlDy ion implantation, and AlDy alloy coating deposition on the magnet surface in sequence, and then conduct vacuum heat treatment.

[0072] 1. Pretreatment: Grind, polish, ultrasonically clean, and dry the sintered NdFeB magnet in sequence.

[0073] 2. Plasma Cleaning: Place the sintered NdFeB magnet on the workpiece holder and face the AlDy alloy target, and then evacuate the vacuum chamber; when the vacuum degree drops to 6×10 -2 Pa, turn on the heating tube, heat it to 250 °C and keep this temperature throughout the subsequent process; when the vacuum degree drops to 2×10-3 Pa, introduce 300 sccm of argon gas Ar to make the vacuum degree of the vacuum chamber 2 Pa; turn on the DC bias power supply connected to the workpiece holder to complete the surface plasma cleaning of the sintered NdFeB magnet. The specific parameters of the DC bias power supply are: voltage 800 V, cleaning time 20 min; the distance between the sintered NdFeB magnet and the magnetron sputtering source of the heavy rare earth target is 110 mm.

[0074] 3. AlDy ion implantation: After the plasma cleaning is completed, stop the gas introduction, turn off the DC bias power supply, and keep the rest unchanged. Introduce argon gas Ar to make the air pressure in the vacuum chamber 0.3 Pa. Turn on the HiPIMS power supply and the anode layer ion source to generate high-density AlDy plasma. In addition, apply a negative bias to the sintered NdFeB magnet to complete the heavy rare earth ion implantation process. The parameters of the HiPIMS power supply are: pulsed power supply 750 V, frequency 35 Hz, pulse width 65 μs; the specific parameters of the DC pulsed power supply are: power 0.7 kW, frequency 120 kHz, duty cycle 80%; the parameters of the DC bias power supply are: 5000 V; the implantation time is 5 min.

[0075] 4. AlDy alloy coating deposition: After the AlDy ion implantation is completed, stop the gas introduction, turn off the HiPIMS power supply, the anode layer ion source power supply, and the DC bias power supply, and keep the rest unchanged. Introduce argon gas Ar to make the air pressure in the vacuum chamber 0.5 Pa. Turn on the HiPIMS power supply to sputter the AlDy alloy target. At the same time, apply a negative bias to the sintered NdFeB magnet to complete the AlDy alloy coating deposition. The parameters of the HiPIMS power supply are: pulsed power supply 550 V, frequency 300 Hz, pulse width 150 μs; the parameter range of the DC bias power supply is: 50 V; the deposition time is 30 min, and the thickness of the deposited coating is about 7 μm.

[0076] 5. Vacuum heat treatment: After the AlDy alloy coating deposition is completed, put the sintered NdFeB into a vacuum heat treatment furnace for heat treatment. The heat treatment parameter range is: diffusion temperature 780 °C, time 4 h; annealing temperature 460 °C, time 4.5 h; vacuum degree 5×10 -3 Pa. Wait for the magnet to cool to room temperature, take out the sample and conduct magnetic property testing.

[0077] Comparative Example 1

[0078] Use a sintered NdFeB magnet with a grade of N52 and dimensions of 25 mm × 25 mm × 3 mm (denoted as sample 2#), and the preparation process refers to the preparation of Example 1. The difference is that step 3 is not carried out, and the diffusion time in step 5 is extended to 6 h.

[0079] Comparative Example 2

[0080] A sintered neodymium iron boron magnet with grade N52 and dimensions of 25 mm × 25 mm × 3 mm (denoted as Sample 4#) was used. The preparation process referred to the preparation in Example 2. The difference was that step 3 was not carried out, and the diffusion time in step 5 was extended to 10 h.

[0081] Comparative Example 3

[0082] A sintered neodymium iron boron magnet with grade N52 and dimensions of 25 mm × 25 mm × 3 mm (denoted as Sample 6#) was used. The preparation process referred to the preparation in Example 3. The difference was that step 3 was not carried out, and the diffusion time in step 5 was extended to 5 h.

[0083] Detection Example

[0084] The magnetic properties of the samples prepared from 1# to 6# (i.e., the sintered neodymium iron boron magnets after depositing the coating) were detected using a pulsed magnetic field magnetometer. Their demagnetization curves and magnetic property detection results are respectively as Figures 3 - 5 , and shown in Table 1 - Table 3. Among them,

[0085] Figure 3 Table 1 shows the detection results of Samples 1# and 2#. It can be seen from this that for the sintered neodymium iron boron magnets treated by the technical solution of the present invention, on the premise that the thermal diffusion time is reduced by 1 h, the coercivity has instead increased by 0.59 kOe, and the remanence has no obvious change, effectively proving that it has indeed improved the efficiency of the grain boundary diffusion of Dy heavy rare earth target materials for sintered neodymium iron boron magnets. Among them, the starting point at the bottommost and on the left is 1#, and the one on the right is 2#.

[0086] Figure 4 Table 2 shows the detection results of Samples 3# and 4#. It can be seen from this that for the sintered neodymium iron boron magnets treated by the technical solution of the present invention, on the premise that the thermal diffusion time is reduced by 2 h, the coercivity has instead increased by 0.27 kOe, and the remanence has no obvious change, effectively proving that it has indeed improved the efficiency of the grain boundary diffusion of Tb for sintered neodymium iron boron magnets. Among them, the starting point at the bottommost and on the left is 3#, and the one on the right is 4#.

[0087] Figure 5 Table 3 shows the detection results of Samples 5# and 6#. It can be seen from this that for the sintered neodymium iron boron magnets treated by the technical solution of the present invention, on the premise that the thermal diffusion time is reduced by 1 h, the coercivity has instead increased by 0.2 kOe, and the remanence has no obvious change, effectively proving that it has indeed improved the efficiency of the grain boundary diffusion of AlDy for sintered neodymium iron boron magnets. Among them, the starting point at the bottommost and on the left is 5#, and the one on the right is 6#.

[0088] Table 1

[0089] Number Coercivity / kOe Remanence / kGs 1# 17.01 14.19 2# 16.42 14.10

[0090] Table 2

[0091] Number Coercivity / kOe Remanence / kGs 3# 19.81 14.00 4# 19.54 14.11

[0092] Table 3

[0093] Number Coercivity / kOe Remanence / kGs 5# 17.48 14.29 6# 17.28 14.23

[0094] In summary, it can be seen that the technical solution of the present invention can further improve the coercivity on the premise of reducing the thermal diffusion time, and is effective for both heavy rare earth targets or their alloy materials, effectively proving that the solution of the present invention can indeed improve the efficiency of heavy rare earth grain boundary diffusion of sintered NdFeB magnets.

[0095] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it on the basis of the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets, characterized in that, Including: S100, Pretreatment of the magnet: After the sintered neodymium iron boron magnet is successively ground, polished and ultrasonically cleaned, it is dried. S200, Plasma cleaning: Under the condition of an inert gas environment with a vacuum degree of 1 - 3 Pa and a temperature of 100 - 400 °C, a bias voltage with a preset voltage value is applied to the workpiece holder on which the pretreated sintered neodymium iron boron magnet is placed to complete the plasma cleaning of the sintered neodymium iron boron magnet. S300, Implantation of heavy rare earth ions: Adjust the vacuum degree to 0.1 - 0.4 Pa. On the premise of applying a negative bias voltage to the sintered neodymium iron boron magnet, a high-power pulsed magnetron sputtering and an ion source are simultaneously used to sputter the heavy rare earth target to complete the implantation of heavy rare earth ions on the surface of the sintered neodymium iron boron magnet. S400, Deposition of heavy rare earth coating: Stop applying the negative bias voltage to the sintered neodymium iron boron magnet, turn off the high-power pulsed magnetron sputtering and the anode layer ion source, introduce an inert gas to adjust the vacuum degree to 0.4 - 1 Pa, and then, on the premise of applying a negative bias voltage to the sintered neodymium iron boron magnet, use high-power pulsed magnetron sputtering to sputter the heavy rare earth target to complete the deposition of the heavy rare earth coating on the surface of the sintered neodymium iron boron magnet. S500, Vacuum heat treatment: The sintered neodymium iron boron magnet with a deposited heavy rare earth coating is heat-treated. The diffusion temperature of the thermal diffusion process is 750 - 900 °C.

2. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to claim 1, characterized in that, Step S200 specifically includes: S201, Place the pretreated sintered neodymium iron boron magnet on the workpiece holder and face the heavy rare earth target as the magnetron sputtering source. S202. After evacuating to a vacuum degree not higher than 9×10 -2 Pa, turn on the heating tube to heat to a temperature of 100 - 350 °C and then maintain it; S203. Continue to evacuate to a vacuum degree not higher than 5×10 -3 Pa, and then introduce an inert gas at a rate of 200 - 300 sccm until the vacuum degree rises to 1.5 - 3 Pa; S204, Apply a DC bias voltage with a preset voltage value to the workpiece holder to complete the plasma cleaning of the sintered neodymium iron boron magnet.

3. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to claim 2, characterized in that, The working parameters of the plasma cleaning process are: the voltage value of the applied DC bias voltage is 800 - 1500 V, and the cleaning time is 10 - 30 min. The distance between the sintered neodymium iron boron magnet and the heavy rare earth target is 70 - 120 mm.

4. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to claim 2 or 3, characterized in that, After the plasma cleaning is completed, stop applying the DC bias voltage. The adjustment of the vacuum degree in step S300 is adjusted by introducing an inert gas.

5. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to claim 4, characterized in that, In step S300, the working parameters of the high-power pulsed magnetron sputtering process are: the output voltage is 750 - 1000 V, the working frequency is 30 - 80 Hz, and the pulse width adjustment range is 60 - 100 μs. In step S300, the working parameters of the anode layer ion source are: the power is 0.2 - 1 kW, the frequency is 40 - 150 kHz, and the duty cycle is 20% - 90%. In step S300, the working parameters of the DC bias voltage power supply for applying the negative bias voltage are: the working voltage is 700 - 10000 V, and the application time is 5 - 15 min.

6. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to any one of claims 1-3, characterized in that, In step S400, the working parameters of the high-power pulsed magnetron sputtering process are: the output voltage is 450 - 600 V, the working frequency is 200 - 400 Hz, and the pulse width adjustment range is 100 - 500 μs. In step S400, the working parameters of the DC bias voltage power supply for applying the negative bias voltage are: the working voltage is 50 - 150 V, and the application time is 20 - 40 min.

7. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to any one of claims 1-3, characterized in that, In step S500, heat treatment is carried out in an environment where the vacuum degree is not higher than 10 -2 Pa. The heat treatment process includes a thermal diffusion process and an annealing process.

8. The method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to claim 7, characterized in that, The thermal diffusion time is 3 - 8 h; The annealing temperature in the annealing process is 450 - 900 °C, and the annealing time is 4 - 6 h.

9. A method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to any one of claims 1-3, characterized in that, The inert gas is argon; The ion source is an anode layer ion source.

10. A method for improving the heavy rare earth grain boundary diffusion efficiency of sintered Nd-Fe-B magnets according to any one of claims 1-3, characterized in that, The heavy rare earth target material is selected from at least one of Dy and / or Tb, and heavy rare earth target materials of their alloy types.

Images