Effects Of Dy And Tb Diffusion On Properties And The Microstructure Of NdFeB

That NdFeB can be used in the applications of automotive production,transportation,energy and environment and other fields still depends on its high performance.However,the lack of rare earth resources and the emergence of new fields have higher requirements on the performance of permanent magnetic materials.The key point of the current research is how to use less heavy rare earth to improve the coercivity and high performance of NdFeB magnets.Now,performance of the magnets after the diffusion of Dy and Tb coatings were studied.Properties of the magnets after the diffusion of heavy rare earths were improved.Using magnetron sputtering technology to sputter Dy films with different thicknesses on the surface of NdFeB magnets.Performance enhanced with the increase of the coating thickness.Among them,the magnet with the thickness of 2.100μm,has maximum of coercivity.The best heat treatment process for the magnet is 850℃x8h+500℃x4h.Under this heat treatment condition,the coercivity of the Dy diffusion magnet is significantly improved,from 872.36 k A/m without coating to 1134.02 k A/m after coating and heat-treatment,an increase of 29.99%,and the remanence is almost unchanged.Although there is no obvious core-shell structure in the morphology observed after Dy diffusion,it can be found that the Nd-rich phase near the surface of the magnet is more homogenious,which the coercivity can be effectively increased.Dy atoms are diffused at least 150 μm deep in the magnet.The magnetic performance is enhanced with the increase of the thickness of the Tb sputtering film.The magnet with the thickness of 3.137μm has the most obvious increase in the coercivity.The optimal heat treatment process for the magnet under this film thickness is 850℃x7h+500℃x2h.The coercivity of the magnet has increased by 433.31 k A/m,an increase of 49.67%,and the remanence has been well maintained.It can be observed from the BSE that there is a more homogenious.Nd-rich phase near the surface of the magnet,and there is an obvious core-shell structure.The shell composition is(Nd,Tb)2Fe14B,which increases the NdFeB anisotropy field,thus coercivity of magnet has been significantly improved.The Tb atoms are diffused at least 200 μm in the magnet.This research work also explores the thermal stability and corrosion resistance of the magnet after the diffusion of Dy and Tb.The study found that: in the range of 20℃-160℃,αBr and βHcj of Dy diffusion magnet are-0.1217%/℃ and-0.5373%/℃,respectively,which are improved compared with the magnet without treatment.The αBr and βHcj of Tb diffused magnet are-0.1230%/℃ and-0.5297%/℃,respectively.Compared with the original magnet,although αBr is slightly lower,βHcj is obviously larger.Meanwhile,compared with the original magnet,hirr of Dy and Tb diffusion magnets at different temperatures is improved.After corrosion process in 4% Na Cl solution for 21 days,the mass loss of Dy and Tb diffused magnet decreased.The magnetic flux loss is also decreased,and the corrosion resistance is slightly improved.