Preparation Of Micro-nano Rare Earth Permanent Magnet With Flake Morphology And Their Physical Properties

Recently, it is found that when the RCo5（R=Sm、Pr、Y、Ce） materials areprocessed by the surfactant assisted high energy ball milling (SAHEBM), whatproduced are flake-liked polycrystalline particles with aspect ratio as high as103.Further more, the RCo5flakes are crystalloid graphically textured and the c-axis (alsoeasy magnetization axis) of constituent grains orients along the flake’s thicknessdirection. Such textured flakes of rare earth magnet can be used to produce anisotropicbonded permanent magnets. Nd2Fe14B material exhibits the best inherent magneticproperties and sintered magnet based on Nd2Fe14B is wildly applied and the bondedmagnet based on Nd2Fe14B is in the process of developing. If the anisotropic flake-likedparticle could achieved by SAHEBM in Nd2Fe14B material, a new approach for thepreparation of anisotropic bonded NdFeB permanent magnet will be developed. In thisthesis, SAHEBM is applied to Nd2Fe14B material and the main works are as fellow.1．Flake-liked Nd2Fe14B particles are achieved by SAHEBM technique when thearc-melted Nd2Fe14B is used as the precursor and is made into granular film at thepresence of magnetic field. It is proved by XRD and magnetic measurement that theparticles composing the granular film are single crystalline and can be aligned bymagnetic field, when the milling time is relatively short. Increasing the milling time,single crystalline particle are turned into poly crystalline ones with flake-liked aspectand the constituent grains orient randomly, making the granular film lose its anisotropy.The coercivity increases first and decrease subsequently, a maximum of5kOe isobtained when the milling time is120minutes.2. Flake-liked Nd2Fe14B particles are achieved by SAHEBM technique when themelt-spinning NdFeB powder is used as the precursor and is made into granular film atthe presence of magnetic field. The particles (or flakes) of various milling time are poly crystalline and cannot be aligned by magnetic field, for the melt-spinning powderconsists of even more fine grains of about80nm. Coercivity remains nearly unchangedas the milling time is short than120minutes, due to the maintenance of microstructure.Exceeding120minutes, deformation occurs in the particles and microstructure ischanged, resulting in the drop of coercivity.3．SAHEBM technique has been applied to arc-melted Pr2Fe14B and result beingsimilar to that of arc-melted Nd2Fe14B is achieved. The Pr2Fe14B flake is moreflexible than Nd2Fe14B flake.4．SAHEBM technique has been applied to arc-melted Pr2Co14B and result beingsimilar to that of arc-melted Nd2Fe14B is achieved. This proves that the formation offlake-liked aspect and the texture is not relative to the especial element of Co, butdetermined by the crystalline structure.5．Processed by SAHEBM for a certain time, arc-melted SmCo5-xFex（x=0.1，0.2，0.3，0.4，0.5）material exhibit flake-liked aspect. The flakes are textured polycrystal and the constituent grains align their c axis to the direction perpendicular toflake’s surface, being similar to the situation of SmCo5。Though the coercivity maydecrease due to the substitute of Fe, the magnetization and hence the maximummagnetic product will be enhanced, being very suitable for the preparation of highperformance anisotropic bonded permanent magnet.