High coercive Nd-Fe-B magnets fabricated via two-step sintering

The fabrication of Nd11Dy4Fe76.5TM2.5B6 (TM=Co, Cu, Al, and Nb: at%) sintered magnets via a two-step sintering process was demonstrated. A densification of greater than 99% was achieved using the two-step sintering of the Nd-Fe-B powder. This process produced a sample with an average grain size of 6.2 μm in the Nd2Fe14B phase, resulting in an enhancement of the coercivity compared to that of the isothermally sintered sample. The suppression of grain growth was considered to be affected by the relatively low temperature during the two-step sintering and by the presence of a B-rich phase at the triple junction. Consequently, the two-step sintering process led to suppression of grain growth and a uniform grain size distribution, which resulted in improved magnetic properties, in particular in the intrinsic coercivity. - Highlights: → Two-step sintering to achieve a higher coercivity via grain refinement. → Successfully obtained a smaller average grain size of 6.2 μm by two-step sintering process. → Two-step sintered sample had a higher coercivity of 2080 kA/m compared to the 1830 kA/m of the isothermal sintering.