The orientation dependence of grain boundary diffusion process of a sintered Nd-Fe-B magnet under pressure

Abstract The dependence of the grain boundary diffusion process (GBDP) on the orientation and pressure of a sintered Nd-Fe-B magnet was studied. At 750 °C the GBDP under an uniaxial pressure of 40 MPa parallel to the alignment direction (c-axis) is much more effective to enhance the coercivity than that performed perpendicular to the c-axis. Obvious macroscopic cracks appeared on the surface of the magnet after GBDP under an uniaxial pressure of 50 MPa along the c-axis at 750 °C, and the corresponding coercivity and the squareness factor of demagnetization curve decreased greatly. The Nd-Fe-B magnet was crushed totally when loaded under an uniaxial pressure of 50 MPa perpendicular to the c-axis at 750 °C. The mechanism was discussed based on the anisotropy of the elastic strain energy of the Nd2Fe14B main phase and the anisotropy distribution of the grain boundary Nd-rich phases.