Grain boundary diffusion anti-adhesion method for sintered neodymium-iron-boron magnet

Abstract

The invention relates to a sintered neodymium-iron-boron magnet grain boundary diffusion anti-adhesion method which comprises the following steps: step 1, attaching a layer of diffusion source alloy on the surface of a magnet for later use; 2, the high-temperature-resistant powder is placed in a muffle furnace, water vapor and other oxidizing gas adsorbed on the surface are removed through high temperature, and the high-temperature-resistant powder is cooled to the normal temperature along with the furnace for use; thirdly, the magnets in the first step are placed in a graphite material box, the magnets are covered with the high-temperature-resistant powder in the second step layer by layer, and every two adjacent magnets do not make contact with each other and are completely isolated; 4, the magnet is subjected to diffusion treatment in a vacuum sintering furnace along with the graphite material box under the protection of vacuum or inert gas, and the magnet is cooled to the room temperature after diffusion is completed; and 5, separating by using a screen, and recovering the high-temperature-resistant powder for continuous recycling. The method has the beneficial effect that the problem of high-temperature adhesion of the magnet can be well solved under the condition that the performance of the magnet is not influenced.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a sintered NdFeB grain boundary diffusion anti-adhesion method. Background Art

[0002] Grain boundary diffusion technology has been widely used in the manufacturing process of sintered NdFeB. By attaching a layer of heavy rare earth element compounds such as corresponding hydrides, fluorides, oxides, etc., or their metals or alloys, on the surface of the magnet, the heavy rare earth elements penetrate into the interior of the magnet along the grain boundaries of the sintered NdFeB at high temperatures, and form a heavy rare earth-rich shell layer on the outer edge of the main phase grains, thereby playing a role in magnetic hardening and significantly improving the performance of the magnet. Compared with conventional technologies, since heavy rare earth elements are only distributed in the grain boundaries and the epitaxial layers of the main phase grains, their use can be greatly reduced, meeting the dual requirements of downstream applications for high comprehensive performance magnets and cost-effective products.

[0003] In order to improve the efficiency of diffusion treatment, the grain boundary diffusion of sintered NdFeB is usually placed in a graphite box for high-temperature diffusion treatment in a stacked manner to reduce space waste. However, since the grain boundary diffusion of sintered NdFeB usually undergoes long-term high-temperature diffusion above 900°C, it is easy for the magnets to diffuse each other or even stick together. In particular, in order to solve the problems of low diffusion coefficient, shallow diffusion depth, and poor diffusion uniformity of single alloys, the industry has developed composite diffusants. The diffusants usually contain low-melting-point alloys such as aluminum, copper, and zinc, and low-melting-point rare earth elements such as lanthanum, cerium, and praseodymium. During the alloy diffusion process, a liquid phase will be formed on the surface of the magnet, and the adhesion between the magnets is extremely high. In addition, sintered NdFeB itself is a brittle material. Once adhesion occurs, it is easy to knock the edges and corners when using external force to separate them, and they cannot be used anymore. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a sintered NdFeB grain boundary diffusion anti-adhesion method.

[0005] The technical solution of the present invention to solve the above technical problem is as follows: a sintered NdFeB magnet grain boundary diffusion anti-adhesion method, comprising the following steps:

[0006] Step 1, attaching a layer of diffusion source alloy on the surface of the magnet for standby use;

[0007] Step 2: placing the high temperature resistant powder in a muffle furnace to remove surface adsorbed water vapor and other oxidizing gases at high temperature, cooling the powder to room temperature with the furnace, and setting it aside;

[0008] Step 3, placing the magnets in step 1 into a graphite material box, and covering the high temperature resistant powder in step 2 layer by layer on the magnets, so that adjacent magnets are completely isolated from each other without contact;

[0009] Step 4: The magnet is diffused with the graphite box in a vacuum sintering furnace under vacuum or inert gas protection, and cooled to room temperature after the diffusion is completed;

[0010] Step 5: Use a sieve to separate and recover the high temperature resistant powder for further recycling.

[0011] The beneficial effect of the present invention is that the problem of high-temperature adhesion of magnets can be well solved without affecting the performance of the magnets.

[0012] Based on the above technical solution, the present invention can also be improved as follows.

[0013] Furthermore, in step 1, a layer of diffusion source alloy is attached to the surface of the magnet by spraying, screen printing or magnetron sputtering.

[0014] The beneficial effect of adopting the above further scheme is to prepare for subsequent diffusion.

[0015] Furthermore, the high temperature resistant powder in step 2 is a mixture of one or more of aluminum oxide, vanadium oxide, zirconium oxide, molybdenum oxide, tungsten oxide, etc., and the melting point of the high temperature resistant powder is above 1200°C.

[0016] The beneficial effect of adopting the above further solution is: cheap and easy to obtain.

[0017] Furthermore, the high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is higher than the diffusion treatment temperature.

[0018] Furthermore, the high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is 900-1000°C.

[0019] Furthermore, the high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is 950°C.

[0020] Furthermore, the high temperature resistant powder in step 2 and step 4 is cooled to room temperature and then stored in a drying oven.

[0021] The beneficial effect of adopting the above further solution is to prevent the high temperature resistant powder from absorbing water vapor.

[0022] Furthermore, in step three, the method of gradually covering the high temperature resistant powder of step two onto the magnet is as follows: the high temperature resistant powder is buried or sprinkled on the surface of the magnet through a porous nozzle so that adjacent magnets are completely isolated.

[0023] The beneficial effect of adopting the above further solution is that the magnets are prevented from contacting each other and sticking together at high temperature.

[0024] Furthermore, the particle size of the high temperature resistant powder is 3-50 microns.

[0025] Furthermore, the particle size of the high temperature resistant powder is 5-20 microns.

[0026] The beneficial effect of adopting the above further solution is that the high temperature resistant powder can be easily sprayed into the extremely small gap between the magnets. DETAILED DESCRIPTION

[0027] The principles and features of the present invention are described below in conjunction with specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] A sintered NdFeB magnet grain boundary diffusion anti-adhesion method comprises the following steps:

[0029] Step 1: A layer of diffusion source alloy is attached to the surface of the magnet by spraying, screen printing or magnetron sputtering, and the mixture is set aside.

[0030] Step two, place the high temperature resistant powder in a muffle furnace to remove surface adsorbed water vapor and other oxidizing gases at high temperature, cool to room temperature with the furnace, and set aside. The high temperature resistant powder is a mixture of one or more of aluminum oxide, vanadium oxide, zirconium oxide, molybdenum oxide, tungsten oxide, etc., and the melting point of the high temperature resistant powder is above 1200°C. The high temperature resistant powder does not react with magnets and diffusion sources. Preferably, the high temperature resistant powder is cheap and readily available aluminum oxide. The high temperature for removing surface adsorbed water vapor and other oxidizing gases is higher than the diffusion treatment temperature, the treatment temperature is 900-1000°C, and the preferred treatment temperature is 950°C. After the high temperature resistant powder is cooled to room temperature, it is placed in a drying oven for storage.

[0031] Step three, put the magnet of step one into the graphite box, and cover the high temperature resistant powder of step two on the magnet layer by layer, so that the adjacent magnets are completely isolated from each other without contact. The method of covering the high temperature resistant powder of step two on the magnet layer by layer is: the high temperature resistant powder is filled or sprinkled on the surface of the magnet through a porous nozzle to completely isolate the adjacent magnets. The filling method completely isolates the adjacent magnets between layers to avoid adhesion of the magnets during the high temperature diffusion process; the porous nozzle sprinkling method only needs to use a small amount of high temperature resistant isolation powder to form a bridge between the magnets, reduce the influence of the powder on the vacuum system, and reduce the distance between the magnet pieces. At the same time, the diffusion process forms a diffusion atmosphere between the pieces to promote the diffusion effect. Among them, the particle size of the high temperature resistant powder sprinkled by the porous nozzle is 3-50 microns, and the preferred particle size of the high temperature resistant powder is 5-20 microns.

[0032] Step 4: The magnet is diffused with the graphite box in a vacuum sintering furnace under vacuum or inert gas protection, and cooled to room temperature after diffusion. The magnet has completed the grain boundary diffusion anti-adhesion treatment. After the high temperature resistant powder is cooled to room temperature, it is placed in a drying oven for storage.

[0033] Step five, using a sieve to separate and recover the high temperature resistant powder for further recycling, that is, the recovered high temperature resistant powder is continuously used in the next magnet grain boundary diffusion anti-adhesion process.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preventing adhesion of sintered NdFeB magnets by grain boundary diffusion, characterized in that: The steps include: Step 1, attaching a layer of diffusion source alloy on the surface of the magnet for standby use; Step 2: placing the high temperature resistant powder in a muffle furnace to remove surface adsorbed water vapor and other oxidizing gases at high temperature, cooling the powder to room temperature with the furnace, and setting it aside; Step 3, placing the magnets of step 1 into a graphite material box, and covering the high temperature resistant powder of step 2 layer by layer on the magnets, so that adjacent magnets are completely isolated from each other without contact; Step 4: The magnet is diffused with the graphite box in a vacuum sintering furnace under vacuum or inert gas protection, and cooled to room temperature after the diffusion is completed; Step 5: Use a sieve to separate and recover the high temperature resistant powder for further recycling.

2. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 1, characterized in that: In step 1, a layer of diffusion source alloy is attached to the surface of the magnet by spraying, screen printing or magnetron sputtering.

3. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 1, characterized in that: The high temperature resistant powder in step 2 is a mixture of one or more of aluminum oxide, vanadium oxide, zirconium oxide, molybdenum oxide, tungsten oxide, etc., and the melting point of the high temperature resistant powder is above 1200°C.

4. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 1, characterized in that: The high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is higher than the diffusion treatment temperature.

5. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 4, characterized in that: The high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is 900-1000°C.

6. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 5, characterized in that: The high temperature for removing the surface adsorbed water vapor and other oxidizing gases in step 2 is 950°C.

7. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 1, characterized in that: The high temperature resistant powder in step 2 and step 4 is stored in a drying oven after being cooled to room temperature.

8. The sintered NdFeB grain boundary diffusion anti-adhesion method according to any one of claims 1 to 7, characterized in that: In step three, the method of gradually covering the high temperature resistant powder of step two onto the magnet is as follows: the high temperature resistant powder is buried or sprinkled on the surface of the magnet through a porous nozzle so that adjacent magnets are completely isolated.

9. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 8, characterized in that: The particle size of the high temperature resistant powder is 3-50 microns.

10. The sintered NdFeB grain boundary diffusion anti-adhesion method according to claim 8, characterized in that: The particle size of the high temperature resistant powder is 5-20 microns.