Effect Of Surface Diffusion On Magnetic Properties And Microstructures Of Die-upset Nd₁₄Fe₈₀B₆

In order to improve the coercivity of Nd-Fe-B die-upset magnets without heavy rare earths,the relationship between the microstructure and coercivity of Rich-RE Nd₁₄Fe₈₀B₆ die-upset magnets with rich rare earth elements was studied,and the microstructure of the magnets surface diffusion by Nd₆₇Cu₃₃ flake of Rich-RE Nd₁₄Fe₈₀B₆ die-upset magnets was studied.The influence of the coercivity on the surface diffusion of die-upset 6wt.%Nd₆₇Cu₃₃/94wt.%Nd₁₄Fe₈₀B₆ magnets with Nd₆₇Cu₃₃ flake was studied in order to explore the ways to improve the coercivity of the Nd₆₇Cu₃₃ magnets without heavy rare earths.Under the condition of vacuum 1103K¹123K and 70%deformation,the anisotropic die-upset Nd₁₄Fe₈₀B₆ magnets were prepared,and the factors affecting the coercivity of the magnets were studied.The experimental results show that the fine Nd2Fe14B grains are arranged along the c-axis orientation and with the increase of the hot deformation temperature.The coercivity of the magnet decreases.The coercivity of the magnets decreases from 737 kA/m to 355kA/m when the deformation temperature of Nd₁₄Fe₈₀B₆ exceeds the melting point of its rare-earth-rich grain boundary phase at 150K¹70K,so it is expected to increase the coercivity of the magnets by lowering the deformation temperature near the melting point of the Rich-RE grain boundary phase.The grain size in XRD diffraction pattern was calculated by Xie Lecong formula,and a large number of images of SEM fracture microstructure were observed.The results showed that the grain size increased with the increase of thermal deformation temperature.The average sheet length of hot deformed Nd₁₄Fe₈₀B₆ magnets increases from 320nm to 500nm,and the single domain grain ratio decreases from 0.52 to 0.26.The increase of multi-domain grains is the reason for the decrease of coercivity of hot deformed magnets.Followed by the study of the effect of microstructure and magnetic properties of the magnet Nd₆₇Cu₃₃ flake surface diffusion on thermal deformation of Rich-RE Nd₁₄Fe₈₀B₆,after high temperature at 1073K diffusion for 2 hours,the coercivity increased from 394kA/m to pre diffusion diffusion after 1420kA/m,Scanning composition on the microstructure of die-upset magnet of surface diffusion it is found that Cu content in the magnet is increased from 0.13at%to7.62at%,Rich-RE content increased greatly by 14.31at.%surface diffusion prior to 24.35at.%,thereby forming a non ferromagnetic phase NdCu₂,isolated from the main phase of Nd₂Fe₁₄B grains,leading to die-upset magnet increase the coercivity after surface diffusion.The microstructure and properties of die-upset magnets mixed with Nd₁₄Fe₈₀B₆ and6wt.%Nd₆₇Cu₃₃ powder were studied.Compared with the pure Rich-RE Nd₁₄Fe₈₀B₆ die-upset magnets,the voids were obviously reduced,the densification increased,and the density reached7.52 g/cm³.The（00l）peak of die-upset magnets was enhanced.The coercivity of the magnets increased from 394kA/m to 1295 kA/m.The composition surface scanning of the fracture surface of the hot deformed magnets with mixed powder shows that the magnets contain 0.37at.%Cu,forming a certain Rich-RE grain boundary phase.At the same time,it is found that the thickness and length of flake structure of hot-deformed magnets added with 6wt.%Nd₆₇Cu₃₃3 are about 120nm and 400 nm respectively,which is obviously smaller than that of hot-deformed magnets without Nd67Cu33 powder,the thickness of which is about 160nm and the length is 600nm.Finally,Rich-RE 6wt.%Nd₆₇Cu₃₃/94wt.%Nd₁₄Fe₈₀B₆ die-upset magnets mixing powder were diffused on the surface of Nd₆₇Cu₃₃3 flake.The coercivity of magnets increased from 1295kA/m before diffusion to 1562kA/m after diffusion.The results of surface scanning showed that the Cu content of magnets increased from 0.37at.%before diffusion to 1.90at.%after diffusion,the RE content increased from 14.00at.%to 22.11at.%and the non-ferromagnetic NdCu₂ phase increased significantly.The thickness of platelet-grain size decreased from 120nm before diffusion to 100nm after diffusion,and the length decreased from 400nm before diffusion to 380 nm after diffusion.The decrease of grain size was the main reason for the increase of coercivity after diffusion.