Anisotropic nanocrystalline Nd-Fe-B based magnets producedby spark plasma sintered technique

Abstract

The anisotropic hot-deformed (HDed) Nd-Fe-B magnets have attracted much attention for their remarkable magnetic properties and various applications due to the ultrafine grained microstructure. Hot deformation process usually consists of two subprocesses, hot pressing and die-upsetting. During this process, the initially isotropic nanocrystals in melt spun flakes transform to laterally elongated platelet-shaped grains with a crystallographic c-axis texture parallel to the pressing direction, which results in a high remanence and energy product, together with exceptional corrosion resistance, thermal stability, and fracture toughness ^[1] . On the other hand, the grain growth is reported to take place close to the flake boundaries during conventional hot-pressing process, which is unfavorable for getting high coercivity and the maximum energy product of HDed Nd-Fe-B magnets. This is because the coarse grains are difficult to align and remain equiaxed after the subsequent die-upsetting process ^[2] .