Preparation and process research of anisotropic Nd-Fe-B spherical magnetic powder

The study innovatively synthesized spherical single-crystal Nd 2 Fe 14 B precursor powder by combining solid/liquid interface non-wetting effects with abnormal grain growth (AGG) mechanisms, and successfully produced anisotropic spherical permanent magnet powder through hydrogenation-disproportionation-desorption-recombination (HDDR) processing. Based on the Cassie–Baxter model and AGG mechanism, the preparation parameters for spherical single-crystal powder were elucidated: 1310 °C - 12 min, 870 °C - 12 h and 1140 °C - 3 h. Using this spherical single-crystal powder as the raw material, an in-depth optimization study of the HDDR process was conducted, focusing on how regulation by hydrogen disproportionation pressure (P HD ) regulates phase composition, microstructure, magnetic anisotropy, and magnetic properties. The results showed that a P HD of ≥30 kPa was required to trigger a complete HD reaction and disproportionation phases (NdH 2+x , α-Fe and Fe 2 B) exhibited a dispersed rod-like structure. At P HD = 50 kPa, the recombined Nd 2 Fe 14 B nanocrystals demonstrated strong preferential orientation, distinct c-axis texture, and high pole density, with an texture strength ( I 006 / I 105 ) of 1.08—a result of efficient crystallographic inheritance from the parent alloy. The grain size was refined from an initial 100 - 150 μm to 200 - 300 nm, accompanied by relatively continuous rare-earth-rich phases at grain boundaries, significantly enhancing the permanent magnetic properties of the powder (B r = 12.5 kGs, H c j = 14.12 kOe and (BH) max = 32.2 MGOe). This study marks the successful implementation of magnetic hardening in the powder using spherical single-crystal precursor powder via the HDDR process, providing an innovative solution for developing high-energy-product anisotropic bonded magnets.