Magnetic and structural properties of spark plasma sintered nanocrystalline NdFeB-powders

Near-stoichiometric NdFeB melt-spun ribbons have been subjected to spark plasma sintering varying the process temperature TSPS and pressure pSPS between 600 and 800 °C and 50-300 MPa, respectively. Produced bulk magnets were analyzed regarding microstructure and magnetic properties. For all samples the intrinsic coercivity Hc,J gradually decreases with increasing sintering temperature and pressure, while residual induction Br increases simultaneously with sample density. Densities close to the theoretical limit were achieved for pSPS>90 MPa and TSPS>650 °C. With increasing TSPS precipitations of Nd-rich and Fe-rich phases have been observed as a result of a decomposition of the hard magnetic Nd2Fe14B phase. Under optimum sintering conditions of pSPS=300 MPa and TSPS=650 °C high-density bulk magnets with Hc,J=652 kA/m, Br=0.86 T and (BH)max=106 kJ/m3 have been produced.