Study On The Preparation And Magnetic Properties Of （Sm,Ce）₂Fe₁₇N₃ Anisotropic Magnetic Powders

With the development of rare earth permanent magnet industry,the unbalanced utilization of rare earth resources is becoming more and more serious.So,it is of great significance to develop（Sm,Ce）₂Fe₁₇N₃ materials without Nd and Pr elements.By adjusting the ratio of Sm and Ce elements,this material shows advantages of high intrinsic magnetic properties and high Ce content.However,（Sm,Ce）₂Fe₁₇N₃ materials have the problems of poor technical magnetic properties.This disadvantage limits its application in the field of rare earth permanent magnets.Based on it,this work prepares（Sm,Ce）₂Fe₁₇N₃ materials by powder metallurgy.And then,this work improves the technical magnetic properties of(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4,0.6）anisotropic magnetic powders by adjusting microstructure and optimizating composition.Firstly,the intrinsic magnetic properties of（Sm,Ce）₂Fe₁₇N₃ with different Ce content are obtained by point-of-intersection method.Increasing Ce content from 0 to 80%,the anisotropy field H_A of（Sm,Ce）₂Fe₁₇N₃compounds decreases from 190 k Oe to 49 k Oe,and the saturation magnetization M_S increases from 140 emu/g to 151 emu/g.When Ce content is40 and 60 at.%respectively,(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4,0.6）materials show great intrinsic magnetic properties,their saturation magnetization M_Sof 135 emu/g and 138emu/g,and their anisotropy field H_Aof 109 k Oe and 67 k Oe.Then,the technical magnetic properties of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powders can be increased by adjusting their microstructure.The ways of adjusting the microstructure include reducing particle size,coating powders with Zn,shaping surface of powders with annealing process and changing composition of particle surface with diffusion process.The ball milling can reduce their particle size to increase the magnetic properties of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powders.When(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4,0.6）anisotropic magnetic powders are respectively milled to 0.79μm and 0.90μm,their coercivity H_cj separately raise to 502.28 k A/m and 197.52 k A/m and their remanence Jr are 1.15 T.Base on these powders,using the Zn plating process can futher increase their coercivity by make a Zn₇Fe₃ non-magnetic layer on their surface.The coercivity H_cj of(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4,0.6）anisotropic magnetic powders respectively increases to 936.35 k A/m and 472.07 k A/m,but their remanence J_r is significantly reduced to 0.72 T and 0.74 T.The annealing process is able to improve the magnetic properties of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powders by passivating their sharp edges and corners.After annealed at 900℃for 30 min,(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4）anisotropic magnetic powder can get higher coercivity with lager size.When its average grain size is 1.61μm,its coercivity H_cj is rised to 446.35 k A/m and its remanence J_r is 0.95 T.According segregation of Ce element,this work explores the effect of diffusion process on the technical magnetic properties of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powders.By diffusion process,the coercivity of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powders can be increased by changing composition of particle surface.After diffusing with Sm₃₅Fe₆₀Cu₅ powder at 700℃for 60 min,(Sm_1-yCe_y)₂Fe₁₇N₃（y=0.4）anisotropic magnetic powder shows higher coercivity with lager size by forming a magnetic hardening layer with high Sm content on its surface.When its average grain size is 1.11μm,its coercivity H_cj increases to 540.88 k A/m.But its remanence M_r decreases to 0.79 T due to phenomenon of magnetic powder bonding.In conclusion,in this work,the technical magnetic properties of（Sm,Ce）₂Fe₁₇N₃anisotropic magnetic powder with high Ce content and high internal magnetic properties are improved by adjusting the microstructure.These methods lay a foundation for the development of（Sm,Ce）₂Fe₁₇N₃ anisotropic magnetic powder.