Preparation method of a neodymium iron boron material with large gradient and high coercivity

Abstract

The present invention discloses a preparation method of a large-gradient and high-coercivity neodymium iron boron material. In the present invention, for the blank neodymium iron boron magnetic powder material, the heavy rare earth elements (heavy rare earths Dy, Tb, Er, Lu and Gd) and low-melting-point metals (Al, Cu, Ga and In) to be diffused are coated on the surface of the neodymium iron boron block. By using femtosecond laser to focus on the coated layer of the neodymium iron boron, the heavy rare earth ions and low-melting-point metals diffuse into the interior of the neodymium iron boron block under the action of a thermal field and an electric field, and a large-gradient and high-coercivity diffusion neodymium iron boron magnet is obtained. The preparation method has a simple preparation process, high femtosecond laser energy, short time required for ion diffusion and sintering and phase formation of the neodymium iron boron. Under the dual action of the electric field and the thermal gradient, the diffusion depth of the ions is deeper, and the coercivity and magnetic properties of the magnet are effectively improved.

Description

Technical Field

[0001] The present invention relates to a preparation method of a neodymium iron boron material with a large gradient and high coercivity, belonging to the field of high-performance magnetic materials. Background Art

[0002] Sintered neodymium iron boron is one of the permanent magnetic materials with the strongest magnetism discovered in the world at present. Its magnetic properties are ten times higher than those of ferrite permanent magnets and nearly twice as high as those of the first and second generation rare earth permanent magnets SmCo. Moreover, the abundant and inexpensive iron replaces the scarce and expensive cobalt, greatly reducing the dependence on strategic resources and lowering the cost. Therefore, it is widely used in high-tech fields such as computer hard disk drive motors (VCM), aerospace aircraft instruments, and medical nuclear magnetic resonance imagers (MRI), becoming an indispensable magnetic material in people's daily lives.

[0003] The demagnetization phenomenon of neodymium iron boron caused by the reverse magnetic field in practical applications is the main problem to be overcome in its practical applications, and the most direct method is to increase the coercivity of the magnet itself.

[0004] The present invention uses laser ablation under voltage application, which can achieve rapid reactions between high-temperature plasmas. The preparation process is not only simple but also effectively reduces the high time consumption in previous processes such as annealing and strip casting. It makes the depth of coating ion diffusion deeper, and the obtained magnetic material shows a large gradient, and has a higher saturation magnetization intensity and coercivity compared with single-phase magnetic materials. Compared with the laser perforation three-dimensional diffusion technology, since there is no need to perforate the magnet, the required laser energy is lower (due to the presence of low melting points in the diffusion source). At the same time, under the action of the electric field, rare earth ions in the diffusion source can diffuse into the magnet interior, solving the problem of shallow diffusion depth of rare earth ions and greatly improving the coercivity and magnetic energy product of the magnet. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a preparation method of laser ablation under voltage application, which is a preparation method of a magnet material with a large gradient, high coercivity, simple process, low energy consumption, low temperature coefficient, and low time consumption.

[0006] The specific preparation includes the following steps:

[0007] (1) Pretreatment: Use a polishing machine to polish the surface of the neodymium iron boron magnet.

[0008] (2) Coating stage: Coat the heavy rare earth element and low melting point metal on the upper surface of the neodymium iron boron block.

[0009] (3) Electrode preparation: Add electrodes to the upper and lower surfaces of the coated neodymium iron boron block.

[0010] (4) Diffusion stage: While applying a voltage to the electrodes, a femtosecond laser is focused on the NdFeB coating layer. Heavy rare earth ions and low melting point metals diffuse into the interior of the NdFeB bulk under the thermal and electric fields to form a large-gradient high coercivity diffusion magnet;

[0011] Specifically, the coating metal described in step (2) is one or more of heavy rare earths Dy, Tb, Er, Lu, and Gd, and low melting point metals Al, Cu, Ga, and In. The heavy rare earth accounts for 10-50% of the total mass of the coating metal, and the coating method is magnetron sputtering, evaporation coating, or spin coating.

[0012] Specifically, for the addition of electrodes in step (3), the method is to bond graphite electrodes to the upper and lower surfaces of the NdFeB after coating through conductive adhesives.

[0013] Specifically, for the applied electrode voltage in step (4), the magnitude is 10-100 V, the laser frequency of the femtosecond laser is 10 Hz, the wavelength is 1064 nm, the pulse width is 1-7 ns, the laser pulse intensity is 100-350 mJ / pulse, and the spot diameter is 1-3 mm.

[0014] Compared with traditional grain boundary diffusion, the present invention has the following advantages:

[0015] (1) High laser energy, short time required for diffusion and finally forming the target NdFeB;

[0016] (2) Under the dual action of the electric field and thermal gradient, the diffusion depth is deeper and the coercivity of the formed magnet is greater;

[0017] (3) For the present invention, the process is environmentally friendly, simple, easy to operate, time-saving and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the dual-field diffusion coating of NdFeB thermal field and electric field. SPECIFIC EMBODIMENTS

[0019] The present invention will be further described below in conjunction with specific embodiments and comparative examples.

[0020] Example 1: A method for preparing a large-gradient NdFeB magnet by laser ablation under voltage application. The specific steps of the present invention are as follows:

[0021] (1) Pretreatment: Polish the surface of NdFeB (Nd9Dy 0.4 Fe 80.24 InNb 0.36 Co3B) with a diameter of 10 mm and a thickness of 2 mm;

[0022] (2) Coating stage: Mix Tb and Al metal powders with acetone to form a coating solution, where Tb accounts for 20% of the total mass of Tb and Al. Coat the upper surface of the NdFeB by spin coating.

[0023] (3) Adding electrodes: Bond graphite electrodes to the surface of the coated NdFeB through a conductive adhesive respectively.

[0024] (4) Diffusion stage: At a voltage of 50 V, use the third harmonic of a Nd:YAG laser as the ablation laser source. The laser frequency is 10 Hz, the wavelength is 1064 nm, the pulse width is 1 ns, the laser pulse intensity is 160 mJ / pulse, and the spot diameter is 3 mm. Focus the laser pulse beam on the surface of the precursor for 30 s, and adjust the position of the sample until the diffusion of the entire sample surface is completed, finally obtaining a NdFeB magnet with a large gradient and high coercivity, as Figure 1 shown.

[0025] Comparative example 1: Coat the coating solution in Example 1 on the surface of a NdFeB (Nd9Dy 0.4 Fe 80.24 InNb 0.36 Co3B) magnet and perform diffusion at high temperature to obtain a NdFeB magnet.

[0026] Example 2: A method for preparing a NdFeB magnet with a large gradient by laser ablation under voltage application. The specific steps of the present invention are as follows:

[0027] (1) Pretreatment: Polish the surface of a NdFeB with a diameter of 10 mm and a thickness of 3 mm.

[0028] (2) Coating stage: Mix Dy and Cu metal powders with acetone to form a coating solution, where Dy accounts for 50% of the total mass of Dy and Cu. Coat the upper surface of the NdFeB by spin coating.

[0029] (3) Adding electrodes: Bond graphite electrodes to the surface of the coated NdFeB through a conductive adhesive respectively.

[0030] (4) Diffusion stage: At a voltage of 50 V, use the third harmonic of a Nd:YAG laser as the ablation laser source. The laser frequency is 10 Hz, the wavelength is 1064 nm, the pulse width is 1 ns, the laser pulse intensity is 200 mJ / pulse, and the spot diameter is 2 mm. Focus the laser pulse beam on the surface of the precursor for 15 s, and adjust the position of the sample until the diffusion of the entire sample surface is completed, finally obtaining a NdFeB magnet with a large gradient and high coercivity.

[0031] Comparative example 2: Coat the coating solution in Example 2 on the surface of a NdFeB magnet and perform diffusion at high temperature to obtain a NdFeB magnet.

[0032] As can be seen from Table 1, compared with the traditional grain boundary diffusion, for the magnets obtained by diffusion under thermal field and electric field, due to the dual action of electric field and thermal gradient, the diffusion depth of ions is deeper, and both the coercivity and the maximum energy product are greatly improved.

[0033]

[0034] Table 1 Magnetic properties of the magnets obtained by the coating diffusion of the present invention and the traditional coating diffusion.

Claims

1. A preparation method of a large-gradient high-coercivity neodymium iron boron material, characterized in that It includes the following steps: (1) Pretreatment: Use a polishing machine to polish the surface of the neodymium-iron-boron magnet; (2) Coating stage: Coat the upper surface of the neodymium-iron-boron block with heavy rare earth elements and low-melting-point metals; (3) Electrode preparation: Add electrodes to the upper and lower surfaces of the coated neodymium-iron-boron block; (4) Diffusion stage: While applying a voltage to the electrodes, use femtosecond laser to focus on the coated layer of neodymium-iron-boron. Heavy rare earth ions and low-melting-point metals diffuse into the interior of the neodymium-iron-boron block under the thermal field and electric field, forming a diffusion magnet with a large gradient and high coercivity; The coating metals described in step (2) are one or more of heavy rare earths Dy, Tb, Er, Lu, and Gd, and one or more of low-melting-point metals Al, Cu, Ga, and In. The heavy rare earth metal accounts for 10-50% of the total mass of the coating metals. The coating method is magnetron sputtering, evaporation coating, or spin coating; For the applied electrode voltage described in step (4), the magnitude is 10-100 V. The laser frequency of the femtosecond laser is 10 Hz, the wavelength is 1064 nm, the pulse width is 1-7 ns, the laser pulse intensity is 100-300 mJ / pulse, and the spot diameter is 1-3 mm.

2. According to the method described in claim 1, for the addition of electrodes in step (3), the method is to bond graphite electrodes to the surface of the neodymium-iron-boron after coating through a conductive adhesive.

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