The present application claims foreign priority of Chinese Patent Applications No. 202311508273.2, filed on Nov. 14, 2023, the entire contents of which are hereby incorporated by reference.
The present disclosure relates to the field of magnetic material technologies, and specifically to a method for preparing a high coercivity grain boundary diffusion neodymium iron boron magnet by high-pressure torsion.
In recent years, with the improvement of the magnetic properties of neodymium iron boron (NdFeB) magnets and the reduction of production costs thereof, high-power density permanent magnet motors with the NdFeB magnets as a main material have shown rapid development momentum. They have been widely applied in wind power generation, rail transit, new energy vehicles, etc. As these applications become more in-depth, higher requirements are placed on the comprehensive magnetic properties of the NdFeB magnets. High-performance NdFEB materials have always been the goal of the global magnetic materials industry.
Severe plastic deformation (SPD) is an important method for densification and nanocrystallization of materials. Applying the SPD to Nd—Fe—B alloys can further refine the grain size. Studies have shown that high-pressure torsion (HPT) SPD can induce the formation of α-Fe and Nd2Fe14B nanocrystals in an amorphous matrix. As the strain increases, the volume fraction of the α-Fe phase in the magnet increases, and the grain size of the α-Fe and Nd2Fe14B phases decreases to 10-20 nm, thereby achieving higher magnetic properties. This severe plastic thermal deformation technology, which is based on the regulation of stress, strain, and temperature fields, can achieve densification, nanocrystallization, and texturing of amorphous alloy materials.
Grain boundary diffusion technology is a new technology developed in recent years to improve the magnetic properties and reduce the weight of rare earth materials in NdFEB materials. At the same coercivity, the content of heavy rare earth is only 20-30% of that of traditional high coercivity sintered NdFeB permanent magnets, and the remanence is basically unchanged. However, there are limitations on the diffusion efficiency and depth. Regarding this problem, in order to increase the diffusion efficiency and depth of the NdFEB magnets, an in-situ grain boundary diffusion method is applied, which can essentially change the limitations of the depth of diffusion magnets. At present, there are at least two methods for in-situ grain boundary diffusion: one is to introduce heavy rare earth vapor during the air-flow milling of NdFeB powder, such that the surface of the NdFEB particles is coated with a heavy rare earth metal film of a certain thickness, where this layer of heavy rare earth film will diffuse into the 2:14:1 grain during the high-temperature sintering of the magnet, increasing the coercivity of the magnet after forming; the other is to add low melting point alloy powders such as Dy88Mn12, Dy71.5Fe28.5, and Dy32.5Fe62Cu5.5 to the NdFeB powder, which is then subjected to subsequent sintering and heat treatment during the pressing and forming process, where the coercivity can be increased by more than 30%.
The technical problem to be solved by the present disclosure is to provide a method for preparing a high coercivity grain boundary diffusion neodymium iron boron magnet by high-pressure torsion, which nucleates, elongates and refines the NdFEB magnet through high-pressure torsion, and obtains high coercivity NdFEB magnets by changing the depth of diffusion magnetization and effectively controlling the grain boundary through in-situ grain boundary diffusion.
To achieve the above-mentioned purpose and other related purposes, the technical solution provided by the present disclosure is: a method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
In some embodiments, in step 1, the NdFEB powder is a nano-biphasic NdFeB powder, which is composed of an α-Fe phase and an NdFeB phase; an average particle size of the NdFEB powder is 3-5 μm.
In some embodiments, the heavy rare earth powder is at least one of Dy, Tb, Gd, Pr, Nd, Ce, and La; an average particle size of the heavy rare earth powder is 3-5 μm.
In some embodiments, in step 2, the pre-pressing is carried out with a tablet press and comprises: pressing under a pressure of 15-30 MPa for 1-3 min.
In some embodiments, in step 3, a working condition for a high-pressure torsion treatment is: a pressure is 500-1000 MPa, a number of torsion turns is 10, and a torsion speed is 60°/min.
In some embodiments, the diffusion heat treatment is carried out at a temperature of 600-900° C. for 10-60 minutes.
By virtue of the above technical solutions, the present disclosure has the following advantages over the related art:
The following specific embodiments illustrate the implementation of the present disclosure. Those skilled in the art can easily understand other advantages and functions of the present disclosure from the content disclosed in the embodiments.
Referring to
The reagents or materials described in the following examples are all commercially available, unless otherwise specified.
Embodiment 1: A method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
Embodiment 2: A method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
Embodiment 3: A method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
The Comparative Example is obtained by replacing the powder weighed in step (1) of Embodiment (1) with the pure nano-biphasic NdFeB powder without the heavy rare earth powder.
The middle part of each of the sheet magnets obtained after high-pressure torsion is taken from the samples prepared by the above-mentioned embodiments and the Comparative Example, thereby obtaining other samples. The coercivity of the samples before and after the diffusion heat treatment is tested by a vibrating sample magnetometer VSM, respectively, and an equipment model of VSM is LakeShore7407 from the United States. The results are shown in Table 1.
As can be seen from Table 1, by comparing Embodiment 1 and Embodiment 2, the coercivity can be further increased by changing the pressure of the high-pressure torsion; by comparing Embodiment 1 and Embodiment 3, the coercivity can be further increased by changing the temperature conditions of the diffusion heat treatment; by comparing Embodiments 1, 2 and 3 with the Comparative Example, and in combination with
Taking Embodiment 1 as an example,
In summary, the present disclosure relates to a method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion. The grain size is further refined by high-pressure torsion to achieve densification, nanocrystallization, and texturing of the magnet. The depth limitation of the diffusion magnet is then essentially changed by in-situ grain boundary diffusion, and a high coercivity grain boundary diffusion NdFEB magnet is finally obtained, increasing the coercivity of the diffusion magnet by about 2-3 times.
Embodiment 4: A method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
The NdFEB powder is a nano-biphasic NdFeB powder, which is composed of an α-Fe phase and a NdFeB phase; the average particle size of the composite powder is about 3-5 μm.
In nanocomposite permanent magnets, the effective range of exchange coupling between the soft and hard magnetic phases in α-Fe is about twice the thickness of the Nd2Fe14B magnetic domain wall. Exchange coupling can only work when the dimensions of both the soft and hard magnetic phases are below the critical size (about 10 nm). The smaller the grain size, the greater the volume content of the exchange coupling region in the overall material, the more obvious the exchange coupling effect, and the more prominent the remanence enhancement effect. For this reason, the present disclosure adopts nano-biphasic NdFEB powder, which not only reduces costs, but also, due to the complexity of the composition and microstructure, compared to traditional permanent magnet materials, the nano-composite permanent magnet material has the characteristics of a single ferromagnetic phase through the two-phase exchange coupling between the nanocrystals, and at the same time has the high saturation magnetization of the soft magnetic phase and the high coercivity of the hard magnetic phase.
The rare earth powder is at least one of Dy, Tb, Gd, Pr, Nd, Ce, and La. In the present embodiments, Nd powder is specifically selected.
The average particle size of the rare earth powder is about 3-5 μm.
The high-pressure torsion of the magnet is carried out at a high pressure as high as 500 MPa, the number of torsion turns is 10 turns, and the torsion speed is 60°/min.
The temperature of the diffusion heat treatment is 600° C. and the time is 10 min.
Embodiment 5: A method for preparing a high coercivity grain boundary diffusion neodymium iron boron (NdFeB) magnet by high-pressure torsion, including:
A preferred technical solution is: in step 1, the NdFEB powder is a nano-biphasic NdFeB powder, which is composed of an α-Fe phase and an NdFEB phase; the average particle size of the composite powder is 3-5 μm.
A preferred technical solution is: the heavy rare earth powder is Ce powder; the average particle size of the heavy rare earth powder is 3-5 μm.
A preferred technical solution is: in step 2, the pressing is carried out with a tablet press, and the specific steps include: pressing under a pressure of 15 MPa for 3 min.
A preferred technical solution is: in step 3, a working condition for the high-pressure torsion of the magnet is: the pressure is 1000 MPa, the number of torsion turns is 10, and the torsion speed is 60°/min.
A preferred technical solution is that the diffusion heat treatment is carried out at a temperature of 900° C. for 10 minutes.
The above is only intended to explain some embodiments of the present disclosure, and not to limit the present disclosure in any way. Therefore, any modification or change to the present disclosure that is made in the same spirit of the present disclosure should still be included in the scope of the present disclosure.
Number | Date | Country | Kind |
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202311508273.2 | Nov 2023 | CN | national |