Microstructure and magnetic properties of anisotropic Nd–Fe–B magnets produced by spark plasma sintering technique

Bulk anisotropic Nd–Fe–B magnets were synthesized by hot pressing and subsequent hot deforming melt-spun ribbons using spark plasma sintering (SPS) technique. Influences of grains morphology and Nd-rich intergranular phase distribution on magnetic properties of both hot pressing and hot deforming magnets were investigated. Compared with starting ribbons, randomly oriented Nd2Fe14B grains in hot pressing magnets increased their average size from 40 to 100 nm, which led to a slightly reduction of coercive force of the magnets. After hot deformation, the interior of the magnets consisted of well-aligned platelet shaped Nd2Fe14B grains with 80 nm in thickness and 200–500 nm in length. On the other hand, most Nd-rich phase in the magnets redistributed from grain boundaries to triple junctions of the Nd2Fe14B grains. The resultant magnets exhibited a remanence (Br) of 1.34 T, coercive force (Hci) of 512 kA/m, and maximum energy product ((BH)max) of 280 kJ/m3.