Enhanced magnetic properties in Nd-Fe-B magnets prepared by spark plasma sintering via die-upsetting process

The magnetic properties and microstructure of Nd-Fe-B magnets prepared by spark plasma sintering with different die-upsetting processes were investigated. The results showed that the optimum magnetic properties of die-upset Nd-Fe-B magnets were obtained at 680 °C when the die-upset level was 60%, and the degree of magnetic alignment was 0.84. The microstructures showed that the coarse grains occurred predominantly within certain areas, and abnormal grain growth was not observed within the major areas of well-aligned grains. There existed many small spherical grains, which stacked together and were not aligned during die upsetting when the deformation temperature was 650 °C. These small spherical grains grew up, and were aligned when the deformation temperature increased from 650 to 680 °C, which could improve the crystallographic alignment of die-upset Nd-Fe-B magnets.