Laser Powder Bed Fusion of Sm-Fe-N Bonded Magnets Employing Flake Powders

In this work, the role of the binder volumetric fraction used on the consolidation process of Sm-Fe-N-based bonded magnets obtained via the laser powder bed fusion technique has been investigated and explained. The magnetic samples have been obtained via the Selective Laser Sintering (SLS) process, using a mixture of polyamide-12 powder (PA12, DuraForm PA2200) and isotropic Sm-Fe-N melt-spun ribbons (Daido Electronics, Inc.) as feedstocks. The binder content has been varied between 34% and 65% vol. Geometrical density values increased systematically as the PA12 content was increased, reaching a maximum value of ρ = 3.35 g/cm³ (60% vol.), which represents 89% of a fully dense composite. In this composition, the maximum magnetic properties values have been achieved, J_r = 369 mT and (BH)_max = 24 kJ/m³. A further increase on the PA12 fraction up to 65% vol. resulted on magnetic samples with 97% relative density, but at the expense of magnetic performance. The formation of a continuous polymeric matrix has been observed via Scanning Electron Microscopy (SEM) analysis when PA12 fraction was on the interval between 60% and 65% vol., not observable for the other explored conditions. Volumetric binder fractions comparable with other published works, which used spherical particles as raw materials for feedstock production, showed inadequate consolidation and required adjustments for proper densification.