Method for integrating hydrogen decrepitation of rare earth permanent magnet alloy and atomic layer deposition of copper coating

Abstract

The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a method for integrating hydrogen decrepitation of a rare earth permanent magnet alloy and atomic layer deposition of a copper coating layer. The method is characterized in that the hydrogen decrepitation process of a rare earth permanent magnet alloy ingot or cast piece and the atomic layer deposition process of a coating layer are integrated in the same reaction cavity; first, the rare earth permanent magnet alloy ingot or cast piece is placed in a vacuum reaction cavity, high-purity argon gas is washed multiple times, and then sufficient hydrogen gas is introduced to make the rare earth permanent magnet alloy ingot or cast piece absorb hydrogen and decrepitate into powder and sufficiently dehydrogenate; the hydrogen decrepitated powder is heated to 80-250 DEG C under vacuum for 1.5-4 hours, and a copper coating layer with a total thickness of 10-50 nm is deposited by using the atomic layer deposition method. The application can simplify process steps, improve the coating coverage rate of the coating layer on the surface of the rare earth permanent magnet powder, modify the surface of the magnetic powder, optimize the microstructure of the magnet during the sintering and heat treatment of the coated copper coating layer on the rare earth permanent magnet, and improve the magnetic performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a method for integrating hydrogen decrepitation of a rare earth permanent magnet alloy and atomic layer deposition of a copper plating layer. BACKGROUND

[0002] Rare earth permanent magnets Re-Fe-B and Sm-Co are widely used in the fields of computers, transportation, medical health and aerospace technology due to their excellent magnetic properties. To improve the coercivity and temperature stability of RE-Fe-B magnets, one approach is to enhance the demagnetization coupling effect between Re2Fe 14 B main phases by optimizing the grain boundary structure, thereby improving the coercivity and temperature stability of rare earth iron-boron magnets. At present, the hydrogen decrepitation method of rare earth permanent magnet alloy ingots or cast pieces is the main method for preparing rare earth permanent magnet alloy coarse powder, because the hydrogen decrepitation coarse powder prepared based on the hydrogen decrepitation method can be used to mass-produce rare earth permanent magnet alloy fine powder through an air flow grinding process. Therefore, in the grain boundary structure optimization process, the hydrogen decrepitation fine powder based on the hydrogen decrepitation process is often used for multiphase powder mixing. The grain boundary diffusion method includes mechanically mixing low-melting auxiliary phase alloy powder with main phase rare earth permanent magnet alloy air flow grinding powder in a certain proportion, and then sintering and heat treating to achieve the purpose of grain boundary structure optimization. For example, Chinese patents CN103219117A, CN103667919A, CN104051101A and CN106653271A all disclose methods for adding auxiliary phase alloy powder by mechanical mixing. However, the mechanical mixing process of multiphase powder is complex, time-consuming and inefficient. In addition, Chinese patent CN115862986A discloses a method for coating nanometer Cu powder on the surface of rare earth iron-boron based on an organic solvent carrier. This method is not only complex, time-consuming and inefficient, but also increases the complexity of the heat treatment of rare earth iron-boron magnets.

[0003] Similarly, to improve the magnetic properties of Sm-Co magnets by improving the grain boundary structure of the magnets, Chinese patents CN102568807B and CN111145973B both disclose a method for mixing nanometer copper powder or micron copper compound powder with samarium-cobalt precursor magnetic powder by mechanical mixing to achieve the purpose of optimizing the grain boundary structure of the magnets. The two patents disclose that the copper powder is added by mechanical mixing of two powders with a large difference in particle size range, which is time-consuming and inefficient. SUMMARY

[0004] The present application aims to provide a method for integrating hydrogen breaking of rare earth permanent magnet alloy and atomic layer deposition of copper coating layer, which has a short process flow and high powder production efficiency, so as to effectively improve the coating rate and uniformity of the coating layer on the surface of the rare earth permanent magnet powder, and make the coated layer of the rare earth permanent magnet powder provide a possibility for optimizing the grain boundary structure of the rare earth permanent magnet during subsequent sintering and heat treatment.

[0005] The method for integrating hydrogen breaking of rare earth permanent magnet alloy and atomic layer deposition of copper coating layer provided by the present application is that the hydrogen breaking process of the rare earth permanent magnet alloy ingot or cast sheet and the process of atomic layer deposition of copper coating layer on the surface of the powder after hydrogen breaking are integrated in the same reaction cavity, and the specific steps are as follows:

[0006] (1) The rare earth permanent magnet alloy ingot or cast sheet in the reaction cavity is cleaned more than 3 times by using argon, hydrogen is introduced into the reaction cavity, and the rare earth permanent magnet alloy ingot or cast sheet is fully hydrogenated and broken into coarse powder;

[0007] (2) The powder in step (1) is fully dehydrogenated, and the gas by-product of the dehydrogenation reaction is extracted;

[0008] (3) The powder obtained in step (2) is heated to 80-250℃ under vacuum for 1.5-4 hours;

[0009] (4) The reaction cavity is effectively isolated from the outside air, argon is used as the carrier gas, the first precursor gas, i.e. the copper precursor, is introduced into the reaction cavity in a gas pulse mode, and the surface of the rare earth permanent magnet alloy hydrogen broken powder in the reaction cavity is fully adsorbed with the first precursor;

[0010] (5) Argon is introduced in a pulse mode as a purge gas to extract the unabsorbed first precursor;

[0011] (6) The reaction cavity is effectively isolated from the outside air, the second precursor gas is introduced into the reaction cavity in a pulse mode, so that the first precursor adsorbed on the surface of the rare earth permanent magnet alloy hydrogen broken powder fully reacts with the second precursor; the second precursor gas is hydrogen gas or hydrogen plasma mixed gas;

[0012] (7) Argon is introduced in a pulse mode as a purge gas to extract the reaction by-products of the first precursor and the second precursor and the unreacted second precursor gas;

[0013] (8) Steps (4)-(7) are repeated to deposit a copper coating layer with a desired thickness on the surface of the rare earth permanent magnet alloy hydrogen broken powder.

[0014] Preferably, the dehydrogenation time in step (2) is 4-6 hours.

[0015] Preferably, the first precursor in step (4) is a copper amidine structure, the first precursor gas flow is 10-100sccm, the precursor gas pulse width is 0.03-10s, and the argon carrier gas flow is 10-100sccm.

[0016] Preferably, the argon purge gas flow in step (5) is 10-1000sccm, and the gas pulse width is 1-120s.

[0017] Preferably, in step (6), the second precursor gas flow is 10-100sccm, and the gas pulse width is 0.03-10s.

[0018] Preferably, in step (7), the argon purge gas flow is 10-1000sccm, and the gas pulse width is 1-120s.

[0019] Preferably, after steps (5) and (7) are completed, the vacuum degree in the reaction chamber is 0.1-5Pa.

[0020] Preferably, in step (6), if the second precursor gas is a hydrogen plasma mixed gas pulse, after the pulse is over, wait for 1-60s.

[0021] In the present application, steps (4)-(7) are one cycle of atomic layer deposition, and after the cycle is completed, the thickness of the plated layer on the surface of the rare earth permanent magnet powder is 0.03-0.1nm, and the total thickness of the copper plated layer coated on the surface of the rare earth permanent magnet hydrogen broken powder is 10-50nm.

[0022] In the present application, the rare earth permanent magnet alloy comprises: a rare earth samarium cobalt (Sm(Co, Fe)7) alloy ingot, a rare earth iron boron (Re2Fe 14 B) alloy, etc.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The hydrogen breaking process of the rare earth permanent magnet alloy and the atomic layer deposition of the copper plated layer are integrated in the same reaction chamber, which can save equipment space, shorten the process flow, and simplify the subsequent processing steps;

[0025] (2) The atomic layer deposition method is introduced to the surface coating of the rare earth permanent magnet powder, which is beneficial to improve the surface coating rate of the rare earth permanent magnet powder and provides the possibility of coating a large amount of rare earth permanent magnet powder at one time;

[0026] (3) The coated copper plated layer is a low-melting-point substance, which provides the possibility of optimizing the grain boundary microstructure of the rare earth permanent magnet and further improving the magnetic properties (especially the coercive force) of the magnet. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The schematic diagram of the principle of hydrogen absorption crushing and atomic layer deposition coating of rare earth neodymium iron boron alloy cast sheet.

[0028] Figure 2 The schematic diagram of the conventional process of rare earth permanent magnet alloy ingot or cast sheet and the integrated hydrogen crushing and atomic layer deposition process.

[0029] Figure 3 The flow chart of hydrogen absorption crushing and hydrogen plasma assisted atomic layer deposition coating of copper plating layer of rare earth samarium cobalt alloy ingot.

[0030] Figure 4 The flow chart of hydrogen absorption crushing and atomic layer deposition coating of copper plating layer of rare earth neodymium iron boron alloy cast sheet.

[0031] The figure label: 1 - Re2Fe 14 B main phase grain; 2 - rare earth rich phase grain boundary; 3 - coated plating layer; 4 - rare earth permanent magnet alloy hydrogen crushed powder particles. DETAILED DESCRIPTION

[0032] In order to make the principles, objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples.

[0033] Example 1, the schematic diagram of the principle of one embodiment of the present application, see Figure 1 as shown.

[0034] S11: The microstructure of rare earth neodymium iron boron alloy cast sheet is mainly composed of grain main phase 1 (Re2Fe 14 B) and grain boundary rare earth rich phase 2, and the main phases are separated by the grain boundary phase.

[0035] S12: The grain boundary phase rich in rare earth in S11 above is more prone to adsorb hydrogen than the main phase, and the mechanical properties of the grain boundary phase 2 after absorbing hydrogen are greatly different from those of the main phase 1 after absorbing hydrogen, so that the cast sheet is fractured along the grain and transgranularly, and the cast sheet is crushed into hydrogen broken powder with a particle size range of 0.01-1 mm and strong brittleness, and the above hydrogen broken powder is subjected to sufficient dehydrogenation treatment.

[0036] S13: Copper plating layer coating is carried out on the hydrogen broken powder after dehydrogenation in S12 by using atomic layer deposition method. In this process, hydrogen gas or hydrogen plasma mixed gas is used as a reducing agent to reduce copper in the copper precursor to form elemental copper plating layer on the surface of the magnetic powder.

[0037] The above rare earth permanent magnet alloy powder coated with copper plating layer can be used in the heat treatment process or in the airflow grinding process to further refine into fine powder with an average particle size of 1-10 microns.

[0038] Embodiment 2, the schematic diagram of the conventional process of the rare earth permanent magnet alloy ingot or slab and the process integrating hydrogen decrepitation and atomic layer deposition is shown in Figure 2 The specific steps are as follows:

[0039] In the preparation process of the rare earth permanent magnet, the conventional process of adding copper powder is S2→S21→S22→S23→S24→S25, i.e. hydrogen decrepitation of the ingot or slab, jet milling, mechanical mixing of the copper powder and the jet milled powder, magnetic field orientation and cold isostatic pressing, sintering and heat treatment.

[0040] According to the method of the present application, the preparation process of the rare earth permanent magnet integrating hydrogen decrepitation and atomic layer deposition is as follows:

[0041] S2→S26→S27→S28→S29, i.e. hydrogen decrepitation of the ingot or slab and atomic layer deposition of the copper plating layer, jet milling, magnetic field orientation and cold isostatic pressing, sintering and heat treatment.

[0042] Compared with the conventional process, the process of the present application omits the mechanical mixing step of the multi-phase powder, and integrates the addition of copper elements in the hydrogen decrepitation process of the rare earth permanent magnet alloy ingot or slab.

[0043] Embodiment 3, hydrogen decrepitation of the rare earth samarium-cobalt alloy ingot and hydrogen plasma assisted atomic layer deposition of the copper plating layer, the flow chart is shown in Figure 3 The specific steps are as follows:

[0044] S31: Put the uniformly melted rare earth samarium-cobalt alloy ingot coarse broken powder into the vacuum reaction chamber, the composition of the samarium-cobalt alloy (in mass percent) is: Sm: 23-28%, Fe: 10-25%, Cu: 1-6%, Zr: 1-4%, and the balance is Co, introduce high-purity argon, wash the reaction chamber for more than 3 times, and then extract the reaction chamber to 0.1-5 Pa after washing, and close the vacuum pump;

[0045] S32: Introduce sufficient high-purity hydrogen into the reaction chamber, for safety, multiple batches of high-purity hydrogen can be introduced, the pressure in the reaction chamber after each hydrogen introduction is 100-200 kPa, and the rare earth samarium-cobalt alloy ingot is fully hydrogen decrepitated;

[0046] S33: Start the vacuum pump to extract the gas, and fully dehydrogenate the hydrogen decrepitated powder for more than 5 hours, and then close the vacuum pump after the pressure in the reaction chamber is stabilized at 0.5-5 Pa;

[0047] S34: Heat the reaction chamber to 80℃ and keep for more than 1.5 hours;

[0048] S35: pulse the amidine copper precursor gas into the reaction cavity with argon as the carrier gas, the carrier gas flow rate being 10 sccm; the precursor gas pulse width being 10 s, and the precursor flow rate being 10 sccm;

[0049] S36: remove the copper precursor not adsorbed on the surface of the rare earth samarium-cobalt alloy powder by pulse-sweeping argon as the sweep gas, the gas flow rate being 10 sccm, and the pulse width being 120 s, and stop pumping the reaction cavity;

[0050] S37: pulse the second precursor gas, i.e., hydrogen plasma mixed gas, into the reaction cavity, the pulse width being 10 s, and the gas flow rate being 30 sccm, and wait for 45 s after the end of the precursor pulse time;

[0051] S38: remove the reaction byproducts and hydrogen not involved in the reaction by pulse-sweeping argon as the sweep gas, the gas flow rate being 10 sccm, and the pulse width being 120 s, and stop pumping the reaction cavity by closing the vacuum pump;

[0052] S39: the above steps S35-S38 form one cycle, and the thickness of the copper coating layer deposited in each cycle is 0.03-0.06 nm; and the steps S35-S38 are repeated according to the thickness of the copper coating layer required.

[0053] Example 4, hydrogen absorption and breaking of rare earth neodymium-iron-boron alloy cast sheet and atomic layer deposition of copper coating layer, the flow chart is shown in Figure 4 The specific steps are as follows:

[0054] S41: place the rare earth iron-boron alloy cast sheet melted uniformly and formed by rapid quenching and ribbon drawing in the vacuum reaction cavity, the alloy composition (in mass percentage) being: Re (Pr, Nd, Ce, La, Dy): 28.3-31.5%, TM (Co, Al, Cu, Zr, Ga): 0.8-8%, B: 0.9-1.1%, and the balance being Fe, pulse in high-purity argon, wash the reaction cavity with argon for more than 3 times, and pump the reaction cavity to 0.1-5 Pa after washing, and close the vacuum pump;

[0055] S42: pulse in sufficient high-purity hydrogen into the reaction cavity, and for safety, the high-purity hydrogen can be pulsed in multiple batches, the reaction cavity pressure being 100 kPa-200 kPa after each hydrogen pulse, and make the rare earth iron-boron alloy cast sheet fully absorb hydrogen and break;

[0056] S43: open the vacuum pump to pump, and fully dehydrogenate the hydrogen broken powder for more than 4 hours, and close the vacuum pump after the reaction cavity pressure is stabilized at 0.1-2 Pa;

[0057] S44: heat the reaction cavity to 200℃, and keep the temperature for more than 3 hours;

[0058] S45: pulse the amidine copper precursor gas into the reaction cavity with argon as the carrier gas, the carrier gas flow rate being 50 sccm; the precursor gas pulse width being 0.05 s, and the precursor flow rate being 50 sccm;

[0059] S46: remove the copper precursor not adsorbed on the surface of the rare earth iron boron alloy powder by using argon as the purge gas, the gas flow rate being 100 sccm, and the pulse width being 30 s, and stop pumping the reaction cavity;

[0060] S47: pulse the second precursor gas, i.e. hydrogen, into the reaction cavity, the pulse width being 0.05 s, and the gas flow rate being 50 sccm;

[0061] S48: remove the reaction byproducts and hydrogen not involved in the reaction by using argon as the purge gas, the gas flow rate being 100 sccm, and the pulse width being 30 s, and stop pumping the reaction cavity by closing the vacuum pump;

[0062] S49: the steps S45-S48 form a cycle, and the thickness of the copper coating layer deposited in each cycle is 0.07-0.1 nm; the steps S45-S48 are repeated according to the thickness of the copper coating layer required.

[0063] Example 5

[0064] A rare earth SmCo alloy ingot (Sm: 25%, Co: 50.5%, Fe: 20%, Cu: 2.5%, and Zr: 2% by mass) is subjected to hydrogen crushing, airflow milling, magnetic field orientation molding, cold isostatic pressing, sintering, and heat treatment process steps to obtain a raw magnet.

[0065] The rare earth SmCo alloy ingot with the above components is subjected to hydrogen crushing and surface atomic layer deposition coating of a 30 nm thick copper coating layer according to the method of the present application, airflow milling (the average powder particle size range is 3-5 microns), orientation molding in a 2T magnetic field, cold isostatic pressing at a pressure of 150 MPa, thereby obtaining a SmCo alloy compact. The compact is subjected to sintering and heat treatment processes to obtain a sintered SmCo magnet, and the sintering and heat treatment processes are as follows.

[0066] Sintering and heat treatment process: the SmCo alloy compact is sintered at 1210°C for 0.6 hours in an argon environment, then solution treated at 1175°C for 3.5 hours, and air cooled to room temperature to obtain a SmCo precursor magnet. The aforementioned SmCo precursor magnet is heat treated at 820°C for 15 hours, cooled to 410°C at a cooling rate of 0.8°C / min, then heat treated at 410°C for 2 hours to obtain a sintered SmCo permanent magnet.

[0067] The SmCo permanent magnets obtained by the two methods have the following room temperature magnetic properties.

[0068]

Claims

1. A method for integrating rare earth permanent magnet alloy hydrogen fragmentation and atomic layer deposition to coat a copper layer, characterized in that, The hydrogen decomposition process of rare earth permanent magnet alloy ingots or sheets, and the subsequent atomic layer deposition and copper plating process on the powder surface, are integrated into the same reaction chamber. The specific steps are as follows: (1) Use argon gas to clean the rare earth permanent magnet alloy ingot or casting sheet in the reaction chamber more than 3 times, and introduce sufficient hydrogen gas into the reaction chamber so that the rare earth permanent magnet alloy ingot or casting sheet can fully absorb hydrogen and break into coarse powder. (2) The powder in step (1) is fully dehydrogenated, and the gaseous byproducts of the dehydrogenation reaction are extracted; (3) Under vacuum, heat the powder obtained in step (2) to 80~250℃ and keep it at that temperature for 1.5~4 hours; (4) Keep the reaction chamber effectively isolated from the outside air. Use argon as the carrier gas to introduce the first precursor gas, namely the amidine-based copper precursor, into the reaction chamber in a gas pulse manner, so that the surface of the rare earth permanent magnet alloy hydrogen crushing powder in the reaction chamber can fully adsorb the first precursor gas. (5) Argon gas is pulsed in and used as a purge gas to remove the first precursor gas that has not been adsorbed; (6) Keep the reaction chamber effectively isolated from the outside air, and introduce the second precursor gas into the reaction chamber in a gas pulse manner so that the first precursor gas adsorbed on the surface of rare earth permanent magnet alloy hydrogen crushing powder and the second precursor gas can fully react; the second precursor gas is hydrogen or hydrogen plasma mixture. (7) Argon gas is pulsed in as a purge gas to remove the reaction byproducts of the first precursor gas and the second precursor gas, as well as the unreacted second precursor gas. (8) Repeat steps (4)-(7) to deposit a copper plating layer of the required thickness on the surface of rare earth permanent magnet alloy hydrogen-broken magnetic powder.

2. The method according to claim 1, characterized in that, The dehydrogenation time in step (2) is 4 to 6 hours.

3. The method according to claim 1, characterized in that, In step (4), the flow rate of the first precursor gas is 10~100 sccm, the pulse width of the first precursor gas is 0.03~10s, and the flow rate of the argon carrier gas is 10~100 sccm.

4. The method according to claim 1, characterized in that, In step (5), the flow rate of the argon purge gas is 10~1000 sccm, and the pulse width of the purge gas is 1~120s.

5. The method according to claim 1, characterized in that, In step (6), the flow rate of the second precursor gas is 10~100 sccm and the gas pulse width is 0.03~10s.

6. The method according to claim 1, characterized in that, In step (7), the flow rate of the argon purge gas is 10~1000 sccm, and the gas pulse width is 1~120s.

7. The method according to claim 1, characterized in that, After steps (5) and (7) are completed, the vacuum level in the reaction chamber is 0.1~5 Pa.

8. The method according to claim 1, characterized in that, In step (6), if the second precursor gas introduced is a hydrogen plasma mixed gas pulse, then wait 1~60s after the pulse ends.

9. The method according to claim 1, characterized in that, Steps (4)-(7) are one cycle of atomic layer deposition. After one cycle, the coating thickness on the surface of rare earth permanent magnet powder is 0.03~0.1nm, and the total thickness of the copper coating on the surface of rare earth permanent magnet alloy hydrogen crushing powder is 10~50nm.

10. The method according to any one of claims 1-9, characterized in that, The rare earth permanent magnet alloy is a rare earth samarium-cobalt alloy or a rare earth iron-boron alloy.

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