The strategy of solid-liquid phase separation diffusion with DyH3 to approach a trade-off between properties and cost for sintered Nd-Fe-B magnets

Abstract

Approach a trade-off between properties and cost for sintered Nd-Fe-B magnets in grain boundary diffusion (GBD) helps widen their application. In this study, we fabricated GBD Nd-Fe-B magnets via solid-liquid phase separation diffusion (SepD) with DyH3 nanopowder as the diffusion source. Investigations and comparisons with the traditional solid-liquid phase simultaneous diffusion (SimD) magnets were made regarding the liquid phase diffusion (LPD) temperature, magnetic characteristics, microstructures, diffusion coefficient, and domain morphology of SepD magnets. In addition, the cost was calculated and compared with TbH3 SepD magnets. It is determined that the optimal LPD temperature of DyH3 was 625 °C. Compared to the SimD magnet, Dy had a faster LPD rate in the SepD magnet, which leads to a deeper diffusion depth of 1200 µm. Consequently, the SepD magnet develops more core-shell structures. Additionally, SepD could prevent the development of anti-core-shell formations in the magnet's surface region. As a result, the SepD magnet had higher comprehensive magnetic properties and coercivity temperature stability. Impressively, compared to TbH3 SepD magnets, the cost of per kOe coercivity enhancement for per kilogram magnets of DyH3 SepD magnets can be reduced by more than 50 %.