Equiaxed Nd-Fe-B fine powder with high performance prepared by mechanical alloying

Equiaxed Nd(11.9)Fe(76.9)Co(4.8)B(5.9)Zr(0.5) fine powders with high performance are fabricated by mechanical alloying method in this work. The mechanically alloyed Nd-Fe-B powders have a B(r) of 8.7 kG s, an (i)H(c) of 10 283 Oe, and a (BH)(max) of 15.03 MG Oe. Moreover, it is notable that the M(r)/M(s) ratio of these powders reaches 0.73. According to x-ray diffraction and high-resolution transmission electron microscopy studies, the powders consist of two phases, the Nd(2)Fe(14)B and alpha-Fe phase, and an average grain size of both phases is about 30 nm. These results show that the remanence enhancement of the powders may be from the exchange coupling among Nd(2)Fe(14)B grains as well as between Nd(2)Fe(14)B and Fe grains. Scanning electron microscopy studies show that the mechanically alloyed powders are equiaxed, and the powders' size distribution is very broad. Further investigation using a laser scattering particle size distribution analyzer shows that the size distribution of the powders is bimodal, and the mean size is merely about 16 mu m. Finally, thermal stability of the above powders is measured, and the initial irreversible flux loss of the above powders is about 5% at 120 degrees C at a permeance of 2. Based on the above results, it is inferred that the equiaxed Nd-Fe-B fine powders made by the mechanical alloying process are suitable for preparing injection-molded magnets. (c) 2007 American Institute of Physics.