Influence of Colloidal Additivation with Surfactant-Free Laser-Generated Metal Nanoparticles on the Microstructure of Suction-Cast Nd-Fe-B Alloy

Development of new powder feedstocks using nanoparticles (NPs) has the potential to influence the microstructure of as-built parts and overcome the limitations of current powder-based additive manufacturing (AM) techniques. The focus of this study is to investigate the impact of NP-modified magnetic microparticle powder feedstock on the microstructure of suction-cast Nd-Fe-B-based alloys. This particular casting method has been recognized for its ability to replicate, to some extent, the melting and rapid solidification stages inherent to metal powder-based AM techniques such as powder bed fusion using a laser beam. Two types of NP materials, Ag and ZrB2, are used, and their effects on the grain size distribution and dendritic structures are evaluated after suction casting. Ag NPs result in smaller, more uniform grain sizes. ZrB2 NPs result in uniformly distributed grain sizes at much lower mass loadings. The results show that feedstock powder surface modification with low-melting-point metal NPs can improve permanent magnets' microstructure and magnetic properties, at below 1 vol%, equal to submonolayer surface loads. Herein, the potential of using NPs to develop new powder feedstocks for AM is highlighted, significantly improving the final part's properties. Melting and rapid resolidification of Nd-Fe-B permanent magnets leads to elongated grains with cracks and reduced magnetic performance. The surface additivation of Nd-Fe-B microparticles with different loadings of Ag and ZrB2 nanoparticles improves the processability, achieved microstructure, and magnetic properties.image & COPY; 2023 WILEY-VCH GmbH