Mechanism of Shell Structure Formation by HRE Grain Boundary Diffusion Process of Sintered Nd-Fe-B Magnets

摘要

In recent years, the grain boundary diffusion processing (GBDP) using heavy rare earth elements (HRE) such as Dy and Tb has evolved as an efficient method to enhance coercivity of Nd-Fe-B magnets without significant loss in remanence. It is usually carried out at a temperature of 800 to 1000℃. It is observed that heavy rare-earth elements like Dy or Tb diffuse through grain boundaries (GBs) and form shells along GBs surrounding Nd_2Fe_(14)B grains. In the present work, Dy-enriched shell structure formed by Dy GBDP of sintered Nd-Fe-B magnet is studied in detail. The shell structure surrounding the Nd_2Fe_(14)B grains is characterized by using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the Dy enriched shells exhibit clear facetted microstructure.