Consolidation Behavior and Magnetic Properties of Nanocrystalline Nd-Fe-B Magnets Prepared by Spark Plasma Sintering

Spark Plasma Sintering (SPS) was studied as a means to consolidate Nd-Fe-B powders, previously subjected to grain refinement by HDDR (Hidrogenation–Disproportionation–Dessorption–Recombination). The sintering process was carried out under 60 MPa constant pressure, varying the maximum processing temperature from 500 °C to 900 °C with a holding time of 5 min. Densification was observed above 600 °C related to the melting of Nd-rich phase. The magnetic properties are clearly related to microstructure coarsening associated with the SPS temperature regime. A monotonic decrease for coercivity (Hcj) was observed as a function of maximum SPS operating temperature with values varying from maximum of 750 kA/m at 500 °C to less than 200 kA/m for SPS at 900 °C. Remanence (Br) and maximum energy product (BH)max showed optimum values for intermediate temperatures, since these properties benefit from the densification developed by SPS.