Progress of Heavy Rare Earths Reduction in High Coercivity Sintered NdFeB Magnets
Sintered NdFeB permanent magnets have high remanence and magnetic energy product,but their low intrinsic coercivity limits their application in high temperature environment.The coercivity of NdFeB magnets can be improved by grain refinement,grain boundary doping and grain boundary diffusion process(GBDP)to ensure the stability of magnetic properties in high temperature environment.In order to reduce the manufacturing cost,reducing the amount of heavy rare earths(HRE)in the manufacturing process of high coercivity sintered NdFeB magnets has become a hot research topic.In this paper,the intrinsic coercivity mechanism and the ad-vantages and disadvantages of coercivity techniques are summarized.GBDP form a HRE shell with stronger anisotropic field on the surface of the main grain through the selective diffusion of HRE,and the continuous grain boundary phase distribution can enhance the demagnetizing coupling effect,which can achieve the reduc-tion of HRE while greatly increasing the coercivity of magnets.And we further summarize and discuss the prepa-ration method of diffusion source,composition and substrate material on the coercivity improvement effect and HRE reduction.At the same time,the development trend HRE reduction in high coercivity sintered NdFeB mag-nets is prospected.
rare earthsNd-Fe-Bpermanent magnetic materialcoercivityheavy rare earthsreduction
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