Optimization of core–shell structure distribution in sintered Nd-Fe-B magnets by titanium addition

In view of the uneven distribution of the core–shell structure of sintered Nd-Fe-B magnets after grain boundary diffusion, this study proposes to use high-melting-point and reactive element titanium (Ti) as an additive to increase the diffusion channels and to enhance the diffusion of heavy rare earth elements along the grain boundary phase. By adding Ti element, the diffusion depth and hence the intrinsic coercivity of magnets are increased significantly. The addition of Ti increases the coercivity at two stages: initially from 16.07 to 16.29 kOe by addition effect, and then from 16.29 to 25.16 kOe by facilitating the diffusion of Tb element. The formation of TiB2 phase improves the periodic arrangement of the crystal structure in the surroundings of the grain boundary phase and enhances its activity. The improved grain boundary diffusion and better core-shell structure distribution provide a theoretical guidance for solving the problem of diffusion depth in bulk magnets.