Process-structure-property relationships in laser powder bed fusion of permanent magnetic Nd-Fe-B

Laser powder-bed fusion (L-PBF), as an additive manufacturing (AM) technique, has demonstrated excellent capabilities in achieving degrees of freedom in manufacturing that are otherwise unattainable. The potential of combining Nd-Fe-B as a permanent magnet and the manufacturing capabilities of L-PBF promises new prospects for functional AM in applications such as electric machines. In this study, high density L-PBF Nd-Fe-B samples (91%) with remanence of 0.65 T and maximum energy product of 62 kJ/m3 were successfully produced, comparable to the state-of-the-art in this field. A parametric study correlating the integrity of the parts to the process parameters, such as, the scan speed and hatch distance is presented. From a metallurgy perspective, the microstructure of the additively manufactured samples was different from the conventionally-sintered material. Interestingly, similarities to the microstructures of laser spot welded material were observed. The fabricated magnets mainly consisted of Nd2Fe14B with small fractions of precipitated phases and suffered from the presence of cracks at input energies sufficient for powder fusion. The relative density and integrity was constrained by the intrinsic brittle nature of the intermetallic Nd2Fe14B phase, the high energy input required to melt some phases, as well as the rapid heating and cooling rates experienced during processing