High-temperature additive manufacturing of Nd-Fe-B by powder bed fusion

Powder bed fusion (PBF) is a promising but challenging method for the additive manufacturing (AM) of magnetic Nd-Fe-B alloys due to the material’s inherent brittleness, oxidation sensitivity, and complex phase evolution. In this study, crack-free and dense near-net-shape parts were successfully produced via electron beam powder bed fusion (PBF-EB) using a stress-reducing spot melting strategy. Identical gas-atomized powder (68.7Fe-19.2Nd-1.7B-1.9Ti-2.5Co-4.3Zr-1.4Pr) was also processed by laser powder bed fusion (PBF-LB). While PBF-EB samples showed high density and mechanical integrity, the PBF-LB parts suffered from significant porosity and cracking despite preheating, indicating insufficient thermal stress management. Magnetic characterization revealed coercivities up to 9.3 kA/m (11.7 mT) and specific saturation magnetization values of 136 Am2/kg at 310 K for PBF-EB samples. In contrast, PBF-LB samples exhibited considerably higher but still low coercivity (127 kA/m; 0.16 T) compared to the powder state, attributed to oxidation, phase inhomogeneity, and structural discontinuities. PBF-EB samples remained largely unaffected by post-processing heat treatment up to 1050 °C, suggesting a stable near-equilibrium microstructure already formed during PBF processing. PBF-LB samples underwent a breakdown of the initial finely structured matrix, the emergence of soft magnetic α-Fe phases and consequently magnetic deterioration, highlighting the metastable nature of their as-built state. These findings emphasize that magnetic performance in AM of rare-earth (RE) lean Nd-Fe-B alloys is governed not only by thermal exposure but also by process-inherent solidification kinetics and oxidation sensitivity. By highlighting the critical importance of decoupling thermal effects and solidification dynamics in AM, a framework for future alloy and process design strategies aimed at achieving high-performance, binder-free permanent magnets is provided.