組織制御に向けた高性能Nd-Fe-B系磁石材料のナノ構造解析

Changes in microstructure of Nd-Fe-B based magnetic materials were investigated with advanced electron microscopes to study the Tb diffusion treatment for high coercivity for sintered magnets and the hydrogenation-decomposition-desorption-recombination (HDDR) process for high anistropic magnet powders. In sintered magnets, it was found that morphology of a Nd-rich wetting-layer phase changes to be continuous in shape and uniform in thickness in association with diffusion of Tb. The formation of the continuous Nd-rich wetting-layer phase containing a small amount of Tb leads to an effective increase in coercivity. In the HDDR magnet powder, a recombined Nd2Fe14B phase is formed first as a rim phase on spherical NdH2 grains during the DR-process. Small grain size of NdH2 phase and large grain size of α-Fe matrix after the HD-process can produce small grains of highly aligned Nd2Fe14B that lead to high remanence and high coercivity. These results indicate that a nano-dimensional analysis is essentially important to develop the high-performance of magnetic materials.