A grain boundary diffusion method for high performance sintered neodymium-iron-boron magnets

Abstract

The application discloses a grain boundary diffusion method of high-performance sintered neodymium-iron-boron magnets. The preparation method comprises the following steps: sequentially performing hydrogen crushing, airflow milling, magnetic field forming, cold isostatic pressing and low-temperature pre-sintering treatment on a neodymium-iron-boron alloy rapid solidification piece to obtain a pre-sintered neodymium-iron-boron magnet; using a pulse laser deposition process to deposit a non-rare earth metal or metal oxide film layer on the surface of the pre-sintered magnet; performing diffusion heat treatment on the neodymium-iron-boron magnet with the deposited non-rare earth metal or metal oxide film layer; using the pulse laser deposition process again to deposit a heavy rare earth element film layer on the surface of the treated neodymium-iron-boron magnet; and performing diffusion heat treatment and tempering treatment on the treated neodymium-iron-boron magnet. The method reduces the diffusion cost, improves the diffusion depth of the heavy rare earth element in the magnet, and prepares the neodymium-iron-boron magnet with high coercivity and high magnetic energy product, thereby meeting the urgent application requirements of emerging industries such as rare earth permanent magnet motors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic materials, in particular to a grain boundary diffusion method of high-performance sintered neodymium-iron-boron magnets. BACKGROUND

[0002] The third-generation permanent magnet material sintered neodymium-iron-boron magnet is a high-performance permanent magnet material, which is widely used in many fields such as electronics, motors, medical devices, automobiles, etc. With the expansion of application fields, the performance requirements of sintered neodymium-iron-boron magnets in various aspects are becoming higher and higher. Due to the relatively low Curie temperature of sintered neodymium-iron-boron magnets, the magnetic properties decrease sharply in high-temperature working environment, which seriously affects normal use.

[0003] At present, one of the most common ways to improve the magnetic properties of sintered neodymium-iron-boron magnets at high temperatures is to diffuse heavy rare earth elements into the sintered neodymium-iron-boron magnets through grain boundary diffusion technology. The grain boundary diffusion technology can greatly improve the coercivity of the magnet, and the amount of heavy rare earth used is very low, which reduces the cost of heavy rare earth raw materials. However, there are problems such as accumulation of heavy rare earth on the surface of the magnet, insufficient diffusion depth, and possible diffusion of heavy rare earth into the main phase during the diffusion process, resulting in reduced remanence and insufficient coercivity increase of the magnet after diffusion. Therefore, how to better improve the diffusion effect of sintered neodymium-iron-boron magnets is particularly critical. SUMMARY

[0004] The purpose of the present application is to provide a grain boundary diffusion method of high-performance sintered neodymium-iron-boron magnets, which aims to solve the problem of heavy rare earth element accumulation on the surface of the magnet, improve the diffusion depth of heavy rare earth elements in the magnet, and prepare high-performance sintered neodymium-iron-boron grain boundary diffusion magnets.

[0005] In order to solve the above technical problems, the technical scheme of the present application is as follows: a grain boundary diffusion method of high-performance sintered neodymium-iron-boron magnets, which specifically comprises the following steps:

[0006] S1) The neodymium-iron-boron alloy rapid solidification piece is subjected to hydrogen crushing, air flow milling, magnetic field forming, cold isostatic pressing and low-temperature pre-sintering treatment in sequence to obtain a pre-sintered neodymium-iron-boron magnet;

[0007] S2) The neodymium-iron-boron magnet obtained by S1) is placed in a vacuum chamber and heated, and a non-rare earth metal or metal oxide is uniformly sputtered onto the surface of the neodymium-iron-boron magnet by laser pulse deposition technology;

[0008] S3) The pre-sintered neodymium-iron-boron magnet obtained by S2) is subjected to sintering and tempering process treatment;

[0009] S4) The neodymium-iron-boron magnet obtained by S3) is placed in a vacuum chamber and heated, and a heavy rare earth alloy target material is uniformly sputtered onto the surface of the neodymium-iron-boron magnet by laser pulse deposition technology;

[0010] S5) The Nd-Fe-B magnet obtained after S4) is subjected to sintering and tempering process, i.e. the grain boundary diffusion of high-performance sintered Nd-Fe-B magnet is completed.

[0011] Further, the specific steps of S2) are:

[0012] S2.1) First, fill the vacuum chamber with pure argon gas, the gas pressure is 1-5 Pa, and the pre-sintered Nd-Fe-B magnet obtained in S1) is heated to a temperature of 900-1000℃;

[0013] S2.2) The target material is uniformly sputtered on the surface of the rotating pre-sintered Nd-Fe-B magnet at a rotating speed of 1-100 rpm by using laser pulse deposition technology.

[0014] Further, the specific process of laser pulse deposition technology in S2.2) is: the laser energy density is 1-10 J / cm 2 , the laser frequency is 1-10 Hz, and the laser pulse deposition time is 1-100 mins.

[0015] Further, the target material in S2.2) is a non-rare earth metal or a metal oxide; the non-rare earth metal is one or a combination of Cu, Al, Mg, Ni, and Zn; and the metal oxide is one or a combination of MgO and ZnO.

[0016] Further, the sintering temperature in S3) is 1000-1200℃, and the time is 4-48h; the tempering temperature is 400-600℃, and the time is 1-8h.

[0017] Further, in S4), the vacuum chamber is filled with pure argon gas, the gas pressure is 1-5 Pa, and the heating temperature is 900-1000℃.

[0018] Further, the process parameters of laser pulse deposition technology in S4) are: the laser energy density is 1-10 J / cm 2 , the laser frequency is 1-10 Hz, and the laser pulse deposition time is 1-100 mins.

[0019] Further, in S4), the heavy rare earth alloy target material has a composition of RE x (Ho a Tm 1-a ) y M 1-x-y , wherein RE is one or a combination of Dy, Tb, and Gd, M is one or a combination of Fe, Al, Ga, and Cu, 0≤a≤0.1at.%, 0.5≤x≤0.9at.%, and 0≤y≤0.1at.%.

[0020] Further, the high-performance sintered neodymium-iron-boron magnet processed by the grain boundary diffusion method has a coercivity increase of not less than 12 kOe and a squareness of not less than 0.95.

[0021] A high-performance sintered neodymium-iron-boron magnet prepared by the preparation method.

[0022] The grain boundary diffusion method has the advantages that the raw material cost and the production cost are reduced, the accumulation of heavy rare earth elements on the surface of the magnet is effectively avoided, the diffusion depth of the heavy rare earth elements in the magnet is improved, the sintered neodymium-iron-boron magnet with high coercivity and high squareness is prepared, and the operation is simple and easy to implement and is convenient for batch production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The grain boundary diffusion method of the high-performance sintered neodymium-iron-boron magnet is shown in the flowchart. DETAILED DESCRIPTION

[0024] The application will be further illustrated below by combining examples and comparative examples, and it should be understood that the following detailed description is only used to illustrate the features and advantages of the application and is not used to limit the scope of the application.

[0025] As shown in the formula (I), the grain boundary diffusion method of the high-performance sintered neodymium-iron-boron magnet has the following specific preparation process. Figure 1

[0026] Step 1: smelting neodymium-iron-boron alloy raw materials and performing flake casting to obtain a rapid solidification flake.

[0027] Specifically, the chemical formula of the neodymium-iron-boron raw material is RE x M y B z Fe bal. ; wherein RE is one or a combination of multiple of Pr, Nd, La and Ce elements, M is one or a combination of multiple of Al, Cu, Ga, Zr, Ni, Zn and Sn elements, x is 28-33 wt.%, y is 0.5-5.5 wt.% and z is 0.85-1.2 wt.%.

[0028] The neodymium-iron-boron rapid solidification flake alloy is prepared by a rapid solidification furnace, and the thickness of the rapid solidification flake is 200-350 μm.

[0029] Step 2: sequentially performing hydrogen crushing, airflow milling, magnetic field forming and cold isostatic pressing on the neodymium-iron-boron alloy rapid solidification flake to obtain a green compact of the neodymium-iron-boron magnet.

[0030] Specifically, the airflow milling grinding pressure is set to 520-620 kPa, and the sorting wheel rotating speed is 4000-5600 rpm. The magnetic field forming size is 30x16x13 mm​3 , density 3.8-4.1 g / cm 3 . The maximum pressure of cold isostatic pressing is 200 MPa, the holding time is 1-5 mins, and the density of the blank after isostatic pressing is 4.4-4.6 g / cm 3 .

[0031] Step 3: the green body obtained in step 2 is subjected to low-temperature pre-sintering to obtain a semi-dense pre-sintered magnet containing a rich-rare earth grain boundary phase with wide spacing and uniform distribution.

[0032] Specifically, the low-temperature pre-sintering temperature is 700-900℃, the holding time is 1-3h, the pre-sintering gas pressure is <5×10 -3 Pa, and the generated rich-rare earth grain boundary phase is distributed in a network in the semi-dense magnet, and the phase composition is (Pr a Nd 1-a ) x (La b Ce 1-b ) y M 1-x-y , x is 55-80 at.%, y is 0-35 at.%, and M is one or a combination of Al, Cu, and Ga.

[0033] Step 4: using the pre-sintered magnet obtained in step 4 as a diffusion substrate, heating it, and using a pulsed laser deposition process to deposit a non-rare earth metal or metal oxide film layer on the surface of the pre-sintered magnet.

[0034] Specifically, the size of the pre-sintered magnet as the diffusion substrate is φ10×10mm 3 ; the diffusion source is a non-rare earth metal or metal oxide, and the composition is one or a combination of Cu, Al, Mg, Ni, Zn, MgO, and ZnO.

[0035] Step 5: the coated blank obtained in step 4 is subjected to diffusion heat treatment, followed by sintering and tempering processes to obtain a grain boundary diffusion sintered neodymium-iron-boron magnet.

[0036] Specifically, the temperature for grain boundary diffusion of the pre-sintered magnet is 800-1000℃, and the time is 4-24h; the sintering temperature is 1050-1200℃, and the time is 1-12h; the first tempering temperature is 750-980℃, and the time is 1-6h; the second tempering temperature is 450-650℃, and the time is 1-6h.

[0037] Step 6: using the magnet obtained in step 5 as a diffusion substrate, heating it, and using a pulsed laser deposition process to deposit a heavy rare earth element film layer on the surface of the pre-sintered magnet.

[0038] Specifically, the diffusion source is a heavy rare earth alloy with the composition RE x (Ho a Tm 1-a ) y M 1-x-y (at.%), wherein RE is one or more combinations of Dy, Tb, and Gd, M is one or more combinations of Fe, Al, Ga, and Cu, 0≤a≤10, and 50≤x≤90, which is 0≤y≤10.

[0039] Step 7: The coated blank obtained in step 6 is subjected to diffusion heat treatment, followed by a tempering process to obtain a grain boundary diffusion high coercivity sintered NdFeB magnet.

[0040] Specifically, the magnet is subjected to a first-stage tempering temperature of 750-980° C. for 1-6 hours; and a second-stage tempering temperature of 450-650° C. for 1-6 hours.

[0041] The present invention is described in detail below with reference to several specific embodiments.

[0042] Example 1

[0043] Prepared by rapid solidification furnace with nominal composition (PrNd) 29 Al 0.1 Cu 0.2 Co 0.2 Zr 0.2 B 0.9 Fe bal. (wt.%) of quick-setting sheets. The thickness of the quick-setting sheets is controlled at 200-350μm. The quick-setting sheets are placed in a rotary heat treatment furnace for heat treatment, and then hydrogen crushing treatment is carried out in the rotary heat treatment furnace. The pre-diffusion temperature is 600℃, the pre-diffusion time is 6h, the hydrogen absorption pressure is 0.1MPa, the hydrogen absorption time is 0.5h, the dehydrogenation temperature is 540℃, and the dehydrogenation time is 3h. Subsequently, 0.08wt.% of antioxidant is added to the hydrogen crushing powder, and the powder is mixed under nitrogen protection for 3h; the mixed hydrogen crushing powder is further refined to 2.5-3.5μm in a jet mill; wherein the grinding pressure of the jet mill is set to 580kPa, and the speed of the sorting wheel is set to 5500rpm. 0.05wt.% of lubricant is added to the fine powder prepared by the jet mill, and the powder is mixed under nitrogen protection for 3h; the fine powder is oriented and formed in a magnetic field forming press to prepare a blank with a size of 30×16×13mm 3 , density is 3.8~4.1g / cm 3 Subsequently, the green compact was further compacted in a cold isostatic pressing device with a maximum pressure of 200 MPa and a holding time of 5 min. The density of the green compact after isostatic pressing was 4.4-4.6 g / cm 3The green body obtained is pre-sintered at a temperature of 800°C for 1 h, and the pre-sintering gas pressure is <5x10 -3 Pa. The pre-sintered magnet obtained is used as a base material, and a non-rare earth metal or metal oxide is selected as a diffusion source for laser pulse deposition; specifically, the size of the pre-sintered magnet used as a diffusion base material is φ10x10 mm 3 , and the pre-sintered magnet is rotated at a speed of 10 rpm, and MgO is selected as the diffusion source, and the laser pulse deposition is performed in an argon atmosphere, and the laser pulse deposition uses a laser energy density of 2 J / cm 2 , a laser frequency of 5 Hz, and a laser pulse deposition time of 10 mins. Subsequently, the pre-sintered magnet obtained after deposition is directly subjected to grain boundary diffusion, and then subjected to sintering and tempering processes; specifically, the pre-sintered magnet is subjected to grain boundary diffusion at a temperature of 900°C for 10 h, and sintering at a temperature of 1080°C for 4 h. The magnet obtained is used as a base material, and a heavy rare earth alloy is selected as a diffusion source for laser pulse deposition; specifically, the size of the pre-sintered magnet used as a diffusion base material is φ10x10 mm 3 , and the pre-sintered magnet is rotated at a speed of 10 rpm, and Dy 78 Al 22 is selected as the diffusion source, and the laser pulse deposition is performed in an argon atmosphere, and the laser pulse deposition uses a laser energy density of 5 J / cm 2 , a laser frequency of 10 Hz, and a laser pulse deposition time of 10 mins. Subsequently, the pre-sintered magnet obtained after deposition is directly subjected to grain boundary diffusion, and then subjected to sintering and tempering processes; specifically, the magnet is subjected to grain boundary diffusion at a temperature of 900°C for 10 h, and sintering at a temperature of 1080°C for 4 h, and primary tempering at a temperature of 900°C for 2 h, and secondary tempering at a temperature of 500°C for 2 h.

[0044] Comparative Example 1

[0045] A nominal composition of (PrNd) 29 Al 0.1 Cu 0.2 Co 0.2 Zr 0.2 B 0.9 Fe bal.(wt.%) of the rapidly solidified flakes. The thickness of the rapidly solidified flakes is controlled in the range of 200-350 μm. The rapidly solidified flakes are placed in a rotary heat treatment furnace for heat treatment, and then subjected to hydrogen decrepitation treatment in the rotary heat treatment furnace. The pre-diffusion temperature is 600 °C, the pre-diffusion time is 6 h, the hydrogen absorption pressure is 0.1 MPa, the hydrogen absorption time is 0.5 h, the dehydrogenation temperature is 540 °C, and the dehydrogenation time is 3 h. Then, 0.08 wt.% of antioxidant is added to the hydrogen decrepitated powder, and the powder is mixed for 3 h under nitrogen protection. The mixed hydrogen decrepitated powder is further refined in an air jet mill to a size of 2.5-3.5 μm. The refining pressure of the air jet mill is set to 580 kPa, and the rotating speed of the sorting wheel is set to 5500 rpm. 0.05 wt.% of lubricant is added to the refined powder, and the powder is mixed for 3 h under nitrogen protection. The powder is oriented and formed in a magnetic field forming press to obtain a green compact with a size of 30 x 16 x 13 mm 3 , and a density of 3.8-4.1 g / cm 3 . Then, the compact is further compacted in a cold isostatic press with a maximum pressure of 200 MPa and a holding time of 5 min. The density of the compact after isostatic pressing is 4.4-4.6 g / cm 3 . The obtained green compact is pre-sintered at a temperature of 800 °C for 1 h under a pressure of < 5 x 10 -3 Pa. The pre-sintered magnet is used as a base material for sintering and tempering. The sintering temperature is 1080 °C, and the time is 8 h. The first tempering temperature is 900 °C, and the time is 2 h. The second tempering temperature is 500 °C, and the time is 2 h.

[0046] Example 2

[0047] The rapidly solidified flakes with the same composition as in Example 1 are used, and the same preparation process is adopted, except that the step of selecting a heavy rare earth alloy as a diffusion source for laser pulse deposition is omitted.

[0048] Example 3

[0049] The rapidly solidified flakes with the same composition as in Example 1 are used, and the same preparation process is adopted, except that the step of selecting a heavy rare earth alloy as a diffusion source for laser pulse deposition is omitted.

[0050] The magnets prepared in the above examples and comparative examples are subjected to magnetic property testing at room temperature (20 °C) using a permanent magnet material measuring system. The performance results are shown in Table 1.

[0051] Table 1 Comparison of performance parameters of magnets in examples and comparative examples

[0052]

[0053] Comparing the magnetic property data of Example 1 and Comparative Example 1, it is found that the coercivity (H cj ), squareness (H k / H cj ) and maximum magnetic energy product ((BH)max) of the Example magnets are significantly higher than those of the Comparative Example. Further, by comparing the magnetic property data of Examples 2-3, it is found that the magnetic properties of Example 1 are superior to those of Examples 2 and 3. Thus, by using the laser pulse deposition technique to diffuse non-rare earth metals or metal oxides in the pre-sintered magnets to form diffusion channels at the grain boundaries and then directly performing grain boundary diffusion treatment, the accumulation of heavy rare earth elements on the surface of the magnets can be effectively avoided, the diffusion depth of the heavy rare earth elements in the magnets is improved, and sintered Nd-Fe-B grain boundary diffusion magnets with high coercivity and high squareness are obtained.

[0054] The grain boundary diffusion method of the high-performance sintered Nd-Fe-B magnet of the application constructs diffusion channels at the grain boundaries in the pre-sintered magnet, then directly performs grain boundary diffusion treatment on the pre-sintered magnet, and then performs sintering and tempering processes, effectively avoiding the accumulation of heavy rare earth elements on the surface of the magnet, improving the diffusion depth of the heavy rare earth elements in the magnet, and obtaining sintered Nd-Fe-B grain boundary diffusion magnets with high coercivity and high squareness, which has important guiding significance.

[0055] The above provides a detailed description of the grain boundary diffusion method of the high-performance sintered Nd-Fe-B magnet of the application. The above description of the examples is only used to help understand the method of the application and its core idea; at the same time, for those skilled in the art, according to the idea of the application, the specific implementation and application range will be changed, and the above description should not be understood as limiting the application.

[0056] As some terms are used in the description and claims to refer to certain components. Those skilled in the art should understand that hardware manufacturers may use different names to refer to the same component. The description and claims of this specification do not distinguish components by name, but by the functional difference of the components. As mentioned throughout the description and claims, "including" and "including" are open-ended terms, which should be interpreted as "including / including but not limited to". "Approximately" means within an acceptable error range, and those skilled in the art can solve the technical problem within a certain error range, and basically achieve the technical effect. The subsequent description in the specification is a preferred embodiment of the application, which is for the purpose of illustrating the general principles of the application, and is not intended to limit the scope of the application. The scope of protection of the application is defined by the appended claims.

[0057] It should also be noted that the terms "comprising," "including," and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0058] It should be understood that the term "and / or" as used herein merely describes associated objects, and can exist in three forms: A and / or B can mean: A alone, both A and B, and B alone. In addition, the character " / " is generally used to represent an "or" relationship between the associated objects.

[0059] The above description illustrates and describes several preferred embodiments of the present application, but as previously noted, it is not intended to limit the application to the forms disclosed, but rather to cover all modifications and alternatives that fall within the scope of the application as contemplated by the above teachings and the associated drawings and specification. Changes and modifications can be made to the application in light of the above teachings and the application should not be limited to the details shown and described.

Claims

1. A grain boundary diffusion method of high performance sintered neodymium-iron-boron magnets, characterized in that, The grain boundary diffusion method specifically comprises the following steps: S1) sequentially performing hydrogen crushing, air flow milling, magnetic field forming, cold isostatic pressing and low-temperature pre-sintering treatment on the neodymium-iron-boron alloy rapid solidification sheet to obtain a pre-sintered neodymium-iron-boron magnet; S2) placing the pre-sintered neodymium-iron-boron magnet obtained in S1) into a vacuum chamber and heating, and then uniformly sputtering a non-rare earth metal or metal oxide target material onto the surface of the neodymium-iron-boron magnet by using a laser pulse deposition technology, so that a non-rare earth metal or metal oxide film layer deposited on the surface of the neodymium-iron-boron magnet forms a composition for later diffusion channel construction; The specific steps are: S2.1) first filling the vacuum chamber with pure argon gas at a pressure of 1-5 Pa, and heating the pre-sintered neodymium-iron-boron magnet obtained in S1) to a temperature of 900-1000 ℃; S2.2) uniformly sputtering the target material onto the surface of the rotating pre-sintered neodymium-iron-boron magnet by using a laser pulse deposition technology at a rotating speed of 1-100 rpm; The specific process of the laser pulse deposition technology is: laser energy density is 1-10 J / cm 2 , laser frequency is 1-10 Hz, and laser pulse deposition time is 1-100 mins; The target material is a non-rare earth metal or a metal oxide; the non-rare earth metal is one or a combination of multiple of Cu, Al, Mg, Ni and Zn; and the metal oxide is one or a combination of MgO and ZnO; S3) performing sintering and tempering process treatment on the pre-sintered neodymium-iron-boron magnet obtained in S2), so that the non-rare earth metal or metal oxide film layer deposited on the surface of the neodymium-iron-boron magnet uniformly penetrates into the deep part of the neodymium-iron-boron magnet to form a pre-diffusion channel; The sintering temperature is 1000-1200 ℃, and the time is 4-48 h; and the tempering temperature is 400-600 ℃, and the time is 1-8 h; S4) placing the neodymium-iron-boron magnet obtained in S3) into a vacuum chamber and heating, and then uniformly sputtering a heavy rare earth alloy target material onto the surface of the neodymium-iron-boron magnet by using a laser pulse deposition technology, so that a heavy rare earth alloy film layer deposited on the surface of the neodymium-iron-boron magnet forms a composition for later grain boundary diffusion; The heavy rare earth alloy target material has a composition of RE x (Ho a Tm 1-a ) y M 1-x-y wherein RE is one or a combination of Dy, Tb, Gd, M is one or a combination of Fe, Al, Ga, Cu, 0 ≤ a ≤ 0.1 at.%, and 0.5 ≤ x ≤ 0.9 at.%, and 0 ≤ y ≤ 0.1 at.%. S5) performing sintering and tempering process treatment on the neodymium-iron-boron magnet obtained after S4), so that the heavy rare earth alloy deposited on the surface of the neodymium-iron-boron magnet uniformly penetrates into the deep part of the neodymium-iron-boron magnet through the pre-diffusion channel, i.e., the grain boundary diffusion of the high-performance sintered neodymium-iron-boron magnet is completed.

2. The grain boundary diffusion method according to claim 1, characterized by, In S4), the vacuum chamber is filled with pure argon gas at a pressure of 1-5 Pa, and the heating temperature is 900-1000 ℃.

3. The grain boundary diffusion method of claim 1, wherein The process parameters of the laser pulse deposition technology in S4) are: laser energy density is 1-10 J / cm 2 , laser frequency is 1-10 Hz, and laser pulse deposition time is 1-100 mins.

4. The grain boundary diffusion method of claim 1, wherein The high-performance sintered neodymium-iron-boron magnet processed by the grain boundary diffusion method has a coercive force increase of not less than 12 kOe and a squareness of not less than 0.

95.

5. A high performance sintered neodymium-iron-boron magnet, characterized in that The high-performance sintered neodymium-iron-boron magnet is prepared by using the grain boundary diffusion method according to any one of claims 1-4.

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