Understanding the role of Cu element in nanocrystalline hot deformed Nd-Fe-B magnets

Abstract

Alloying with Cu element has long been established as a means of improving the performance of sintered NdFeB magnets, but its effect on nanocrystalline hot-deformed magnets has not been thoroughly discussed yet. In this study, we conducted a systematic comparison of the microstructure and magnetic properties of nanocrystalline Nd14Fe80B6 and Nd14Fe79B6Cu magnets. The results showed that the introduction of Cu significantly enhances the coercivity of both melt-spun and hot-deformed Nd-Fe-B magnets, owing to the improved magnetically decoupling between neighboring Nd2Fe14B matrix grains by the enrichment of Cu at Nd-rich grain boundary (GB) layer. Despite the magnetic dilution resulting from the introduction of non-magnetic Cu, a significant improvement of remanence from 11.0 kGs to 12.2 kGs is observed in the hot-deformed Nd-Fe-B magnet with 1 at.% Cu addition. The enhancement is attributed to the improved orientation of the Cu-added magnet, as evidenced by the preferential grain alignment from microstructural characterization. The addition of trace Cu changes the properties of the Nd-rich GB phase, lowering its melting point and improving the hot-workability of the Nd-Fe-B magnet during the hot-deformation process. Overall, this study clarifies the positive role of Cu in nanocrystalline Nd-Fe-B magnets and highlights its importance for grain alignment during hot-deformation processing.