The Magnetic Properties And Texture Of Anisotropic Nanocrystalline Rare-earth Permanent Magnets

Since its inception,rare earth permanent magnets have received extensive attention and research due to their excellent magnetic properties.It has promoted the rapid development of aerospace,wind power,electronic components,new energy vehicles and communications industries.In recent years,nanocrystalline rare earth permanent magnets have been extensively studied due to their high coercivity(H_cj).Obtaining strong c-axis texture is an important factor to improve the remanence?M_r?of nanocrystalline magnets.Researchers have studied the macroscopic texture of nanocrystalline magnets by means of X-ray diffraction?XRD?pole figure,magneto-optical Kerr microscopes and magnetic microscopes?MFM?.However,the study of micro-textures between grains needs to be supplemented.In this thesis,Sm₂Co₇ bulk anisotropic magnets were prepared by spark plasma sintering?SPS?and hot deformation process.The relationship between the texture strength and deformation amount of the hot deformed magnets was obtained and the formation mechanism of the texture was analyzed.The H_cjj of the hot-pressed Sm₂Co₇ magnet is34.76 kOe,and the phase composition is?-Sm₂Co₇.Hot-deformed magnets with different deformation amounts were prepared by using hot-pressed magnets as precursors.When the deformation amount is 70%,the H_cjj of the magnet is 33.48 kOe,and the M_r is 4.24 kGs.As the amount of deformation increases,the H_cjj decreases,and the M_r increases.When the deformation amount is 90%,the H_cjj of the magnet is 4.60 kOe,the M_r is 6.71 kGs,the maximum magnetic energy product(?BH?_max)is 8.25 MGOe.The texture of the magnet gradually increases with the increase of the deformation amount.The formation mechanism of the strong texture of the Sm₂Co₇ hot deformed magnet is based on recrystallization mechanism.In order to improve the M_r and?BH?_maxax of Sm₂Co₇ magnets,Sm₂Co₇/?-Fe composite anisotropic nanocrystalline bulk permanent magnets were prepared by SPS hot pressing and hot deformation process,and the relationship between the texture strength and Fe content of composite magnets was studied.When the Fe content is 5 wt%,the H_cjj of the composite magnet is 11.68 kOe,the M_r is 6.74 kGs,and the?BH?_maxax is 11.28 MGOe,which is 69.62%higher than that of the deformed Sm₂Co₇ magnet.The phase composition analysis of the hot deformed composite magnet shows that when the Fe content is 5 wt%,the magnet contains the phases of Sm₂Co₇ and?-Fe.As the Fe content further increases,element diffusion occurs in the magnet,forming a Sm₂?CoFe?₁₇7 phase with the structure of rhombohedral.The texture analysis shows that the hard magnetic phase Sm₂Co₇ forms a strong c-axis texture in the hot deformed composite magnet,however,the Sm₂?CoFe?₁₇with the rhombohedral structure displays no c-axis texture formation.Anisotropic hot-pressed nanocrystalline Nd₂Fe₁₄B magnets were prepared by one-step hot pressing method using anisotropic HDDR magnetic powder as raw material,fusion magnetic field orientation molding and hot pressing process.The magnet exihibits H_cjj of7.50 kOe and?BH?_maxax of 20.17 MGOe.The calculated results of the grain orientation angle indicate that grains with an angle of more than 35°with respect to the c-axis exist in the magnet.The results of micro-texture analysis in different regions indicate that the grain orientation in each regional concentrates but collectively deviates from the c-axis of the magnet.This may be related to the size and shape of HDDR magnetic particles.Large particle size and sheet-like shape hinder the magnetic powder from rotating toward to the c-axis during the magnetic field orientation process.It is inferred that reducing the particle size of the HDDR magnetic powder and controlling the shape of the particles to be spherical or ellipsoidal improve the texture strength of the HDDR oriented hot-pressed magnet,thereby enhance the?BH?_maxax of the magnet.