A spark-plasma-sintering approach to the manufacture of anisotropic Nd-Fe-B permanent magnets

Abstract Sintered Nd-Fe-B permanent magnets are the first choice for electro-mechanical devices that rely on hard-magnetic materials to provide strong magnetic fields in a variety of operating conditions. However, the limitations of conventional powder-metallurgy methods regarding the complexity of the magnet’s geometry restrict the design freedom for electrical motors. Here, we propose a spark-plasma-sintering (SPS) approach to the waste-free net-shape manufacture of anisotropic Nd-Fe-B magnets. We investigated the effect of the SPS parameters on the density, magnetic properties and microstructure of disc-shaped samples prepared from a rare-earth-lean jet-milled powder. The absence of a grain-boundary phase and the presence of α-Fe in the as-sintered samples were identified as the main factors hindering the development of the intrinsic coercivity. The observed microstructural features were correlated with electrical effects specific to the rapid, non-equilibrium SPS. A post-SPS thermal treatment was found to be necessary for achieving the hard-magnetic properties. Our findings pave the way towards developing an SPS-based sintering procedure with great potential for the manufacture of complex- and net-shape permanent magnets for high-performance electrical devices.