Effect of Tb diffusion anisotropy on mechanical and magnetic properties of Nd-Fe-B magnet

The surfaces parallel and perpendicular to c-axis of commercial N52 Nd-Fe-B magnet were coated with Tb by magnetron sputtering, respectively. The effect of Tb diffusion anisotropy on magnetic and mechanical properties was investigated. The coercivity increased from original 13.66 kOe to 21.90 kOe for the magnet diffusing parallel to c-axis and 19.68 kOe for the perpendicular diffusion, mainly resulting from the formation of (Nd, Tb)(2)Fe14B shells. The bending strength sigma(b) of original magnet revealed obvious anisotropy. The sigma(b) of diffused magnets for parallel to c-axis and perpendicular to c-axis showed a decrease by 1.76% and 6.14%, respectively. The deterioration in mechanical properties was related to internal stress resulting in transgranular fracture near surface of diffused magnet. The difference of magnetic and mechanical properties for the magnets with diverse diffusion direction was mainly caused by anisotropy of Tb diffusion in magnet.