Study On Grain Boundary Diffusion And Element Doping Enhancement Of Coercivity Of （Nd,Ce）₂Fe₁₄B Magnet And Its Optimization Mechanism

Since Nd-based permanent magnets was first invented in the 1980s,it has been widely used in the fields of network information,aerospace,electrical appliances,communication equipment,and optical components.In recent years,due to the mass production of permanent magnets,rare earth elements such as Pr,Nd,Dy or Tb are overused,but the high abundance elements Ce and other mined with it are not effectively used,resulting in waste of rare earth resources and uneven utilization.The intrinsic magnetic properties of Ce₂Fe₁₄B are low,resulting in low coercivity of the magnet.This is the main problem of the development of Ce-containing magnets.There are two main types of（Nd,Ce）₂Fe₁₄B magnets:sintered Ce-containing Nd-Fe-B magnets andα-Fe/（Nd,Ce）₂Fe₁₄B nanocrystalline composite magnets,which are coercive due to the low intrinsic properties of Ce₂Fe₁₄B.The coercive force is low.This article studies the grain boundary diffusion and element doping to enhance the coercivity of the（Nd,Ce）₂Fe₁₄B magnet and its optimization mechanism.The main research contents are as follows:1.Grain boundary diffusion experiments of surface-coated TbF₃ powder on Ce sintered Nd-Fe-B magnets with magnetic properties of H_cj=14.9 kOe,B_r=13.66 k G,and（BH）_max=44.6 MGOe.Optimizing the diffusion process based on the coercive force increase:the optimal diffusion temperature is 900°C;the optimal heat treatment time is 6 h;the optimal powder particle size is 4.1μm;the coercivity of the magnet is increased by 44.3%after diffusion.2.The effect of surface roughness on diffusion was studied,and it was found that the magnet with a surface roughness of 1998（?）treated with 600 Cw sandpaper has better comprehensive magnetic properties after diffusion:H_cj=22.5 kOe,B_r=13.37k G,（BH）_max=43.7 MGOe,which is 51%higher than the original magnet H_cj,and12.8%higher than the coercivity of the diffused magnet after polishing.The microstructure analysis shows that the bare grain boundary phase content on the surface of the magnet treated with 600 Cw sandpaper（R_a=1998（?））is the most,and the Tb element can diffuse into the magnet through the grain boundary phase during the diffusion process,making it have more and the uniformly distributed core-shell structure is the main reason for the better coercive force improvement effect of the magnet.3.(Nd_0.8Ce_0.2)₂Fe₁₂Co_2-xBZr_x（x=0,0.5）nanocrystalline fast quenching bands were prepared by melt-spun method.Zr element doping can effectively improve the magnetic properties of nanocomposite magnets to achieve:H_cj=8.18 k Oe,B_r=9.31k G,（BH）_max=16.45 MGOe.Zr element doping can increase the content of 2:14:1type hard magnetic phase in the alloy,and refine the grain size of the alloy,and also promote the more uniform distribution of soft and hard magnetic phases.The analysis of Henkel curve andδM curve shows that Zr element doping is beneficial to enhance the exchange coupling effect in the magnet.The angle-dependent model analysis based on Stoner-Wohlfarth model shows that the coercive force mechanism after Zr doping is the pinning mechanism.