Anisotropic Nanocrystalline Nd–Fe–B-Based Magnets Produced by Spark Plasma Sintering Technique

Anisotropic hot-deformed nanocyrstalline Nd-Fe-B magnets were prepared by spark plasma sintering technique using MQU-F melt-spun flakes. Magnetic properties with a coercivity of 20 kOe and (BH)max of over 17.5 MGOe were obtained for the isotropic magnet after hot pressing (HP) process, due to the formation of superfine nanocrystalline grains without grain growth and coarse grain regions. Anisotropic Nd-Fe-B magnets were obtained with 60% and 80% degrees of deformation after die upsetting (DU) process. The remanence of 13.9 kG and (BH)max of 45 MGOe were achieved for the anisotropic Nd-Fe-B magnets with 80% degree of deformation. A distinct two-region microstructure with fine plated-shaped region and coarse grain region was formed in the vicinity of the flake boundaries after hot deformation. The microstructure evolution from HP process to DU process and the effect on the magnetic properties were discussed in detail.