Study On The Properties And Microstructure Of Sintered NdFeB Magnet Grain Boundary Diffusion Tb-M-H Alloy

Sintered NdFeB magnets are widely used because of their excellent magnetic properties,but their low coercivity and poor thermal stability limit their application in high-temperature fields.Although the addition of heavy rare earth can improve its coercive force,heavy rare earth is expensive and resources are scarce.Too much addition will cause a significant drop in residual magnetism.The grain boundary diffusion technology uses a small amount of heavy rare earth Dy/Tb,which can greatly improve the coercive force of the magnet while keeping the residual magnetism basically unchanged.Therefore,this article uses a coating process to diffuse Tb-H,Tb₇₀Cu₃₀-H,Tb₇₀Cu₂₀Ga₁₀-H?at.%?Three low melting point terbium alloy hydrides on the surface of the sintered NdFeB magnet to sdudy the effect of the coercivity and Thermal stability of the magnet,and The diffusion process and The influence of the middle element on the performance and microstructure of the magnet has been studied in depth.Firstly,the boundary diffusion Tb-H of sintered NdFeB magnets is studied.The best heat treatment process is 890?×10h+490?×3h.Under this process,the coercive force reaches the maximum value of 24.97 kOe,which is 43.8%higher than that of the original magnet.Compared with the original magnet,the absolute value of the remanence temperature coefficient|?|of the diffusion magnet is reduced from 0.124%/?to 0.113%/?at 200?,The absolute value of coercive force temperature coefficient|?|decreased from 0.454%/?to 0.422%/?.Secondly,the low melting point Tb₇₀Cu₃₀-H alloy was used as the diffusion source to optimize the heat treatment process of the magnet.The best heat treatment process was 810?×6h+490?×3h.In this heat treatment process,the coercive force of the magnet is increased from 17.37 kOe to 20.03 kOe,and the remanence and the maximum magnetic energy product are basically not decreased.Compared with the original magnet,the absolute value of the remanence temperature coefficient of the magnet after diffusion at 200?is reduced from 0.124%/?to 0.120%/?,and the absolute value of the coercive force temperature coefficient is reduced from 0.454%/?to0.442%/?;The irreversible loss of flux decreased from 37.96%to 24.69%.Finally,on the basis of boundary diffusion Tb-H and Tb₇₀Cu₃₀-H binary low melting point terbium alloy,Tb₇₀Cu₂₀Ga₁₀-H ternary alloy is selected as diffusion source,and the best heat treatment process is 930?×10h+490?×3h.On the premise of a small reduction of remanence,the coercive force of the magnet increases from17.37 kOe to 23.03 kOe;at 200?,the absolute value of remanence temperature coefficient|?|decreases from 0.124%/?to 0.097%/?,and the absolute value of coercive force temperature coefficient|?|decreases from 0.454%/?to 0.424%/?;the irreversible loss of flux at 200?decreases from 37.96%to 3.05%.The microstructure analysis shows that Tb-H,Tb₇₀Cu₃₀-H and Tb₇₀Cu₂₀Ga₁₀-H are diffused from the grain boundary,and the heavy rare earth element Tb diffuses into the edge of the main phase grain to form?Tb,Nd?₂Fe₁₄B hard shell phase,they increases the magnetocrystalline anisotropy field of the magnet,hinders the exchange coupling between grains.At the same time,Cu and Ga elements entering the grain boundary phase improve the wettability of the grain boundary phase,make the grain boundary distribution more continuous and smooth,and enhance the demagnetization coupling effect between grains.Therefore,the continuous grain boundary phase and the formation of high magnetocrystalline anisotropic field magnetically hardened layer are the main reasons for increasing the coercive force of the magnet.