Work

Surface modification of Nd-Fe-B feedstocks by Cu nanoparticles to refine the microstructure after melting and rapid solidification

Year: 2025

Type: article

Abstract: Nanoparticle (NP) surface modification of powder feedstocks has been demonstrated to achieve finer, more equiaxed grains, unlocking potential for the application field of functional materials. However, for high-performance Nd-Fe-B hard magnets, where microstructure, composition, and grain boundary control are crucial, this nano-modification strategy is underexplored. Accordingly, our study investigates the influence of surface loadings (0.1–2.5 wt%) of monomodal 8 nm Cu NPs on the microstructure and hard magnetic properties of the commercially available Nd-Fe-B-based powder feedstock MQP-S processed via the melting and rapid solidification process of suction casting (SC). To circumvent undesirable reactions with the highly reactive rare-earth elements during sample processing, Cu NPs were produced surfactant-free via laser ablation in acetone. Our findings reveal that the microstructure of unmodified samples is composed of dendritic Nd-Fe-B-rich grains and intergranular Zr-Ti-rich grains caused by the melting and rapid solidification process. Notably, the addition of Cu NPs results in a finer and more equiaxed grain microstructure. But we also found the formation of a surface loading-dependent amount of α-Fe and Zr-Ti-rich phases, gradually diminishing the overall magnetic properties, in particular at NP loadings ≥ 1.0 wt%. However, low surface modification of 0.1 and 0.5 wt% yielded 15 % and 13 % higher coercivity than the unmodified feedstock processed via SC. Overall, our study underscores the potential of minute amounts (≤ 0.5 wt%) of Cu NP additions in improving the microstructure and magnetic properties, warranting further research on their transferability to other thermal powder processing techniques like laser powder bed fusion.

Source: Journal of Alloys and Compounds

DOI: 10.1016/j.jallcom.2025.179308