Magnetic properties of Nd-Fe-B system anisotropic HDDR powder made from segregated master ingots

In order to examine the possibility of applying the HDDR process to segregated master ingots, Nd-Fe-B system HDDR powders were made from ingots with different levels of homogeneity, and their structures and magnetic properties were evaluated in detail. HDDR powders made from segregated as-cast ingots displayed anisotropy and large coercivity. They had a nearly homogeneous Nd2Fe14B phase, although some large areas with alpha-Fe and Nd-rich regions of 30 mum in size were present after the HD process. With increasing in the homogeneity level of the master ingots, the anisotropy of HDDR-processed powders decreased and their coercivity increased. In addition, an intermediate Ar treatment was applied between the HD and DR processes to improve the magnetic properties. As a result, the effect of the IA treatment was clearly confirmed, and good magnetic properties of B-r = 1.23 T, H-cJ = 848 kA/m and (BH)(max) = 238 kJ/m(3) were obtained. (C) 2003 Elsevier B.V. All rights reserved.