Abstract
Nanocomposite Pr 2Fe 14B/α-Fe magnets have been synthesized by melt-spinning a Pr 8Fe 86B 6 alloy at low wheel speed in the range from 10 to 21.7 m/s. Microstructural and magnetic studies showed that there is an optimum wheel speed (about 16.7 m/s) at which a uniform Pr 2Fe 14B/α-Fe microstructure with fine α-Fe grains is developed directly from the melt. Lower speed gives larger grains for both the 2 : 14 : 1 and α-Fe, while higher speed leads to the appearance of an amorphous phase which will result in a Pr 2Fe 14B/α-Fe structure with larger α-Fe grains after a subsequent crystallization annealing. Magnetic properties obtained under the optimum-quenching followed by a subsequent annealing are M s=176.6 emu/g, M r=118.2 emu/g, M r /M s =0.67, H c =5.4 kOe and ( BH) m=12.6 MGOe. The coercivity and energy product are about 20% higher than those obtained by over-quenching and then annealing due to the refinement of α-Fe size which leads to an enhanced exchange coupling between Pr 2Fe 14B and α-Fe. The fine α-Fe development is associated with its solidification behavior characterized by higher nucleation rate and lower growth rate during the rapid solidification.
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