Isotropic and anisotropic nanocrystalline NdFeB bulk magnets prepared by binder-free high-velocity compaction technique

NdFeB powders were consolidated into nanocrystalline bulk magnets by a near-net-shape process of high-velocity compaction (HVC) at room temperature with no binder employed. The nanostructure can be maintained after compaction. The compacted magnets with relatively high density can inherit the coercivity of the starting powders. The mechanical strength of the HVCed magnet after heat treatment is comparable to that of the conventional bonded NdFeB magnets. The anisotropic magnet has also been prepared by hot deformation using HVCed magnet as the precursor. The remanence value along the pressing direction increased from 0.64 to 0.95 T and maximum energy product (BH)max increased from 65 to 120 kJ/m3 after hot deformation. The processing-structure-properties relationships for both isotropic and anisotropic magnets are discussed.