Processing of high-performance anisotropic permanent magnets by die-upset forging

Nd–Fe–B high-performance permanent magnets were prepared by die-upset forging. The studies proved that the structural anisotropy can only be produced by deformation of two-phase alloys, which contain hard magnetic Nd2Fe14B crystallites and Nd-rich boundary phase. This phase, which is liquid in the course of deformation, is supposed to play the role of a fast diffusion path. Diffusion creep mechanism, which is considered to be decisive in the texture formation, is supposed to be followed by mechanical rotation of grains under one-directional stress. TEM observations revealed existence of equiaxed and platelet crystallites in the starting material and hot-pressed, and die-upset forged magnets, respectively. At least 50% deformation ratio is required for the formation of useful anisotropy. No significant effect of deformation rate on the magnetic properties was found.