2004 Volume 51 Issue 3 Pages 149-156
Fine ground powders of Nd-Fe-B sintered magnets (particle size = 46-125 μm in diameter) were coated and alloyed with Zn, Mg or Yb metal by sorbing them. For the sorption of Zn or Mg metal vapor, any effective recovery of magnetic properties of the ground powders was not observed. On the contrary, a significant recovery of the decreased magnetic properties of the ground powders was observed when the Yb metal was used as a sorbing material. The sorbing temperature and time for Yb metal vapor were optimized and after heating at 800°C for 90 min and annealing subsequently at 610°C for 60 min, the remanence (Br), coercivity (HcJ) and maximum energy product ((BH)max) values were increased to be 0.98T, 712kA/m and 173kJ/m3, respectively. From the microstructural characterizations of resulting samples, it was found that the sorbed Yb metal uniformly covered the surface and diffused to the grain boundary of fine powders forming a (Nd, Yb)Fe2 Phase. The Yb metal repairs the surface defects produced by grinding and oxidation. In addition, the surface of ground powders becomes smooth through the Yb metal sorption, so that the Hk/Hc value was improved.
