Grain boundary structure and chemistry of Dy-diffusion processed Nd–Fe–B sintered magnets

We have investigated the microstructure of grain boundary diffusion processed Nd–Fe–B sintered magnets by high resolution scanning electron microscopy, high resolution transmission electron microscopy, and laser assisted atom probe to understand the mechanism of coercivity enhancement. After the vapor coating of Dy to the sintered magnets, the sample were annealed to let it diffuse in the sample through the grain boundary diffusion. The composition of the outer region of the Nd2Fe14B grains changed to (Nd,Dy)2Fe14B due to the substitution of Dy for Nd. Excess Nd ejected from the Nd2Fe14B grains led to the formation of continuous Nd-rich grain boundaries.