| Effects of mean powder size and size distribution on the microstructure and magnetic properties of anisotropic NdFeB sintered magnets were investigated. The hydrogen-decrepitated NdFeB alloy was jet milled and the jet-milled powder was subsequently divided by a classifier in order to eliminate coarse and fine particles. The classified powder was then compacted, sintered, and annealed at certain conditions to make anisotropic sintered magnets. The maximum energy product of the sintered magnet improved with the removal of fine particles while the coercivity of the magnet increased effectively by eliminating coarse particles. However, when the magnet was made with the powder mostly consisting of fine particles (mean particle size = 3.35 µm), the coercivity dropped significantly due to extreme abnormal grain growth caused by too high sintering temperature and too much oxygen content in the powder |
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