Dy gradient and coercivity in grain boundary diffusion processed Nd-Fe-B magnet

By controlling Dy vapor deposition process, the amount of Dy that diffused into the magnet was increased gradually from 0.1 wt.% to 0.3 wt.%. Compared with the original status, the coercivity increment was not proportional to the Dy diffusion amount. Subsequent H;and Dy content gradient data showed that slope of the 0.3 wt.% sample gradient was bigger than that of 0.1 wt.% one, and the gaps between outer flakes and inner flakes enlarged with the increasement of Dy diffusion amount. Although Dy mostly enriched in triple-junction regions in electron-probe microscope analysis（EPMA） images, the following Auger depth graph showed that Dy content was as high as 3.0 at.% in 1.5 mm deep center. It proved that Dy tended to get into the main phase rather than stayed in the grain boundary during the diffusion process, and over-diffusion of Dy in the main phase was unhelpful for the coercivity enhancement.