Toward Low-Energy Spark-Plasma Sintering of Hot-Deformed Nd-Fe-B Magnets

Abstract

High-coercivity Nd-Fe-B permanent magnets are key materials for producing electrical components on the macro- and nanoscale. We present a newly developed, economically efficient method for processing Nd-Fe-B magnets based on spark-plasma sintering (SPS) that makes it possible to retain the technologically essential properties of the magnet, but by consuming about 30% less energy compared to the conventional SPS process. A magnet with an anisotropic microstructure was fabricated from MQU-F commercial ribbons with a low energy consumption (0.37 MJ) during the deformation process and compared to a conventionally prepared hot-deformed magnet that consumed three-times more energy (1.2 MJ). Both magnets were post-annealed at 650°C for 120 min in a vacuum. After the post-annealing process, the low-energy processing (LEP) hot-deformed magnet exhibited a coercivity of 1327 kAm-1, and a remanent magnetization of 1.27 T. In comparison, the high-energy processing (HEP) hot-deformed magnet had a coercivity of 1337 kAm-1 and a remanent magnetization of 1.31 T. A complete microstructural characterization and detailed statistical analyses revealed a better texture orientation for the HEP hot-deformed magnet processed with the larger energy consumption. This texture is the main reason for the difference in the remanent magnetization between the two hot-deformed magnets. The results show that although the LEP hot-deformed magnet was processed with three-times less energy than in a typical hot-deformation process, the maximum energy product is only 8% lower than that of a HEP hot-deformed magnet.