Abstract
Anisotropic magnet powders are generally prepared via the usual hydrogenation decomposition desorption recombination.(HDDR) process after heat-treating raw material master alloys for a long time to homogenize them. In this study, the possibility of omitting the homogenization heat treatment, i.e., the applicability of the HDDR process to as-cast Nd-Fe-B system master alloys with segregation, was examined with the aim of reducing the process cost. The HDDR powders made from the as-cast alloy with segregation showed anisotropy, large coercive force, and good magnet characteristics. At the conclusion of the hydrogen decomposition (HD) process, areas having a fine structure composed of NdH2+α-Fe+Fe2B and large-scale areas with α-Fe and Nd-rich parts measuring 30μm in size were observed. However, after the desorption recombination (DR) process was completed, the Nd2Fe14B phase was formed over the whole alloy. The Nd2Fe14B phase after the HDDR process had an almost homogeneous structure, which was composed of recombined crystals with a fine grain size of 300-400nm.
