Study on Microstructure and Coercivity of Thermally Processed Nd-Fe-B–type HDDR Material

Variation of intrinsic coercivity of the HDDR-treated NdSUB12.5/SUBFeSUB80.8/SUBBSUB6.4/SUBGaSUB0.3/SUB alloy after heating in various modes was investigated. Influence of vacuum degree and cooling after heating on the coercivity of the HDDR material was examined. The heat-treated HDDR material had consistently higher coercivity when it was quenched after heating compared to when slow-cooled. Higher coercivity in the quenched material was attributable to the grain boundary with lower Fe content. HDDR-treated material heated in high vacuum showed consistently higher coercivity than the material heated in lower vacuum, and this was attributed to less heavily oxidized surface. Reduced coercivity of the HDDR-treated material heated at moderate temperature was noticeably recovered at higher temperature, and this was attributed to lower Fe content in the grain boundary.