Laser Powder Bed Fusion of metals (PBF-LB/M) is a promising Additive Manufacturing (AM) technique that enables the creation of complex, fully dense, and functionally graded magnetic geometries with minimal material loss [1, 2]. In this context, Nd-Fe-B based powder (MQP-S) has gained significant attention for fabricating bulk magnets using the Laser Powder Bed Fusion method due to its excellent flowability, making it easier to print [3]. Moreover, MQP-S powder demonstrates an isotropic remanence enhancement, meaning that its remanence Mr is higher than the theoretical 50% of its saturation magnetization Ms. This effect is based on a nanocrystalline microstructure consisting of a hard magnetic (Nd2Fe14B) and a soft magnetic (α-Fe) phase with magnetic exchange interaction between them. However, during the printing process, MQP-S powders melt completely and re-solidify with high cooling rates, resulting in the loss of their original homogeneous microstructure [4]. To date, there has been no comprehensive study examining the magnetic interactions in printed bulk MQP-S magnets. In this work, we conducted a parameter study to identify the optimal printing conditions that yield bulk magnets with favourable mechanical and magnetic properties. Subsequently, we compared the magnetic interactions using the Henkel-Plot, Thamm-Hesse-Plot, First Order Reversal Curves (FORC), and magnetic domain imaging among the initial MQP-S powders and the printed magnets that exhibited both the best and worst magnetic properties. Our studies reveal that the intergranular exchange coupling is reduced in printed MQP-S magnets, primarily due to an inhomogeneous grain size distribution and a significant decrease in soft magnetic α-Fe phase fraction.

References: [1] V. Nallathambi et al., Acta Mater., 2025, 297, 12135. [2] L. Schäfer et al., Adv. Funct. Mater., 2021, 31. [3] P. Gabriel et al., Adv. Sci., 2024, 11, 2407972. [4] J. Jaćimović et al., Adv. Eng. Mater., 2017, 19.