Effect of Grain Boundary Diffusion Pr and Cu on Properties of Sintered Nd-Fe-B Permanent Magnet

The Pr, Cu, and Pr75Cu25 were deposited on the sintered NdFeB by magnetron sputtering technology, and the samples were subjected to grain boundary diffusion heat treatment. The magnetic properties, microstructure, temperature stability and bending strength of the magnet were analyzed. Compared with the blank magnet, the grain boundaries of the diffusion magnet increase and enhance the Nd phase and its continuum, thereby isolating the main phase grains and resulting in a stronger magnetic decoupling effect. The coercivity of Pr and Pr75Cu25 diffusion magnets increased from 12.86 kOe to 14.69 kOe and 15.78 kOe, respectively, while the coercivity of diffusion Cu magnets increased from 13.38 kOe to 14.83 kOe. In the temperature range of 20 ~ 120 °C, the reversible temperature coefficients of coercivity (|β|) of diffusion Pr, Cu, and Pr75Cu25 magnets decrease by 0.034%/°C, 0.021%/°C and 0.089%/°C, respectively. Meanwhile, the irreversible flux magnetic loss (Hirr) decreased by 20.96%, 0.94%, and 27.71% respectively. The average bending strength increased by 55.89 MPa, 155.65 MPa, and 130.21 MPa, respectively.