Performance Regulation And Magnetization Behavior Of (Nd,Ce)₂Fe₁₄B Permanent Magnetic Materials

In recent years,with the rapid development of the Nd-Fe-B industry,the over-consumption of rare earth resources,especially the use of rare-earth elements such as Pr and Nd,has occurred.However,the high abundance rare earth elements(La,Ce,etc.)have appeared accumulated phenomenon.In order to promote the balanced use of rare earth resources and reduce the production cost of Nd-Fe-B permanent magnetic materials,researchers have conducted research on(Ce,Re)-Fe-B permanent magnetic materials,achieving the preperation of the low-cost,high performance permanent magnetic materials.In this paper,the performance regulation and magnetization behavior of(Nd,Ce)2Fe14B permanent magnetic materials were studied.The main research contents are as follows:The high-performance as-sintered dual-main-phase(Nd,Ce)2Fe14B magnets were prepared through process optimization.At room temperature,the magnetic properties of magnets reached:Br-13.27 kG,Hcj=12.72 kOe,(BH)max=41.16 MGOe,Hk/Hcj=0.94.Realized high-efficiency,low-energy mature technology and initially formed industrialized production.The higher coercivity of the as-sintered magnets is benefits from the tune of the main phase grains distribution and the optimization of the grain boundary phase.In addition,the thermal stability of the dual-main-phase as-sintered magnet was improved,and the coercivity temperature coefficient ?=-0.652%/K.The Kronmuller-plot curves fitting results showed that the microstructural parameter a plays a leading role in the influence of the microstructure on the coercivity for the magnets.The diffusion via coating method for Ce magnets was studied.The coercivity of magnets after diffusion of Tb for 10 hours incresed to 20.08 kOe by 61%.For Ce magnets,the effect of diffusion Tb on Hcj is significant.Microstructural analysis showed that after the diffusion of heavy rare earth,the main phase grains formed a core-shell structure,and the heavy rare earth elements were distributed in the epitaxial layers of the grains.Based on the Fick's second law,the diffusion coefficients of different diffusion types were calculated.The surface main phase grains diffusion coefficient for the Tb source in the magnet is D1=5.878×10-6 ?m/s,the grain boundary diffusion coefficient for the Tb source is D2=0.312 ?m2/s,and the main phase grains diffusion coefficient for Tb of the grain boundary is D3=3.361×10-6 ?m2/s.By calculating the diffusion coefficients of different diffusion types,it is proved that the Tb of the main phase in the magnet is derived from the grain boundary phase for the Tb diffusion process of the(Nd,Ce)-Fe-B magnets.Nanocrystalline melt-spun ribbons with Ce content(Ce/TRE,TRE is total rare earth)of 0%,10%,20%,30%,40%,and 50%were prepared by rapid quenching process.When the Ce substituted content is 20 wt.%,both the coercivity Hc and the remanence ratio Mr/Ms appeared enhancement phenomenon.Microstructural analysis showed that the optimized microstructure played an important role in promoting the coercivity.When the Ce content is 50 wt.%,the Hc of the melt-spun ribbons can still reach 14.2 kOe.The research results provide a positive guidance for the preparation of high Ce content permanent magnetic materials.According to the analysis of Henkel curve,the exchange coupling effect between hard magnetic phases in the Ce20 melt-spun ribbons is strong,which is the main reason for the enhance of Mr/Ms.