Study On Performance Control And Diffusion Mechanism Of Grain Boundary Diffusion Nd-Fe-B Magnet

As an important basic material for modern industry,rare earth permanent magnet materials play an irreplaceable role in related fields.Its excellent magnetic properties have also received extensive attention and in-depth research,which indirectly or directly promotes the vigorous development of related industries.Rare earth permanent magnet materials have a wide range of application scenarios,including wind power generation,electronic components,aerospace,new energy vehicles,and 5G communications.But at present,due to the low working temperature and poor adaptability of Nd-Fe-B magnets,its application range is limited.In order to obtain Nd-Fe-B magnets with high remanence and high coercivity and meet the requirements of practical applications,it is worthy of further research and exploration by related personnel.The traditional sintering method is used to prepare magnets with higher remanence by adjusting the sintering process,which provides a guarantee for the later preparation of dual-high magnets with high remanence and high coercivity.Using magnetron sputtering technology,through the grain boundary diffusion process,the diffusion of Tb metal was realized,and the influence of the grain boundary diffusion process on the sintered Nd-Fe-B magnet was studied.It is observed that the grain boundary diffusion（GBD）of the heavy rare earth（HREE）Tb is heat-treated into the inside of the magnet,and the microstructure and magnetic properties of the magnet have been studied accordingly.In order to clarify the influence of temperature on the diffusion magnet,the magnet samples were subjected to diffusion heat treatment at 850℃-1000℃for 8 h,and then annealed at 490℃-550℃for 3 h.After experimental comparison,find the best grain boundary diffusion temperature.The coercivity of the two different rare-earth-rich phase magnets increased from 11.96 k Oe and13.37 k Oe to 18.97 k Oe and 22.85 k Oe,respectively,and the remanence hardly decreased.By observing the magnet after grain boundary diffusion,it is found that a unique core-shell structure is formed inside the magnet.The coercive force of the magnet with（Nd,Tb）₂Fe₁₄B core-shell structure has been greatly improved.After the Tb element enters the magnet through the grain boundary diffusion process,a（Nd,Tb）₂Fe₁₄B phase structure is formed,which has a high magnetocrystalline anisotropy field（H_A）.Through the replacement of heavy rare earth（HREE）elements,a permanent magnet with higher coercivity can be obtained.In the experimental design,two different rare-earth-rich magnets A（N52）and B（N50）（the same below）were used to discuss the diffusion behavior of different rare-earth-rich magnets,and the microstructure and performance changes of different rare-earth-rich magnets were studied.Experiments show that under the optimal temperature condition（950℃）,this core-shell structure improves the coercivity of the magnet more significantly.The state of the rare-earth-rich phase plays an important role in the formation of the core-shell structure.The uniformly distributed grain boundary phase can smoothly diffuse the heavy rare-earth element Tb into the magnet to form more core-shell structures and effectively isolate the crystal grains.In order to achieve a good exchange decoupling effect,it promotes the increase of the coercivity of the magnet.The magnet samples before and after the diffusion heat treatment were observed with a magneto-optical Kerr（Nano MOKE）microscope,and it was found that the outer part of the grain boundary diffusion（GBD）magnet was formed due to the formation of（Nd,Tb）₂Fe₁₄B phase,Effectively isolate the expansion of magnetic domains between adjacent crystal grains.Due to the（Nd,Tb）₂Fe₁₄B core-shell structure,the decoupling between the crystal grains is enhanced and the number of trans-crystal domains is reduced.In the process of grain boundary diffusion,magnets with more rare earth-rich phases have stronger Tb element permeability,more core-shell structure inside the magnet,more effective isolation between grains,and less internal strip domain distribution.This also reflects that the magnets with more rich phases and uniform distribution have a greater increase in the coercivity of the magnets after grain boundary diffusion（GBD）.