Refinement of α-Fe and its improvement on magnetic properties of melt-spun nanocomposite Pr2Fe14B/α-Fe magnets by low wheel speed spinning

Nanocomposite Pr2Fe14B/alpha-Fe magnets with uniform microstructure and enhanced magnetic properties have been synthesized by melt-spinning a Pr8Fe86B6 alloy at law wheel speed range. Microstructural and magnetic studies showed that there is an optimum wheel speed (about 16.7 mis) at which a uniform Pr2Fe14B/alpha-Fe structure with fine alpha-Fe grains (about 10 nm) is developed directly from the melt. Lower speed,gives larger grains for both the 2:14:1 and alpha-Fe, while higher speed leads to the appearance of an amorphous phase which will result in a Pr2Fe14B/alpha-Fe structure with larger alpha-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 204 higher than those obtained by crystallization of over-quenched samples due to the refinement of alpha-Fe size which leads to an enhanced exchange coupling between Pr2Fe14B and alpha-Fe. (C) 2000 Acta Metallurgica Inc.