Alloying Pr-Tb-Cu diffusion source with Ni for enhancing both coercivity and corrosion resistance of Nd-Fe-B magnets

Grain boundary diffusion of heavy rare earth-based alloys can effectively enhance the coercivity of Nd-Fe-B magnets. Although the light rare earth elements can further improve the diffusion efficiency of Dy and Tb, they generally lead to reduced anti-corrosion properties of the magnets. Here, we successfully enhanced the coercivity and corrosion resistance of Nd-Fe-B magnets by GBD of Ni alloyed Pr-Tb-Cu diffusion source. The ternary Pr35Tb35Cu30 alloy diffusion increased the coercivity of Nd-Fe-B magnet from 1330 to 1923 kA/m, but the coercivity was enhanced to 1990 kA/m by Pr35Tb35Ni15Cu15 alloy diffusion. The formation of high-anisotropy (Nd,Tb)2Fe14B phase is the main reason for the coercivity improvement. Partially substitution of Cu by Ni can reduce the melting point of Pr35Tb35Cu30 alloy, which is effective in promoting the infiltration of Tb. Cu is also a necessary element for improving the diffusion process, and the diffusion of Pr35Tb35Ni30 alloy only increased the coercivity to 1747 kA/m. More interestingly, the diffusion of Pr35Tb35Ni15Cu15 also enhanced the chemical stability of the magnet in NaCl solution. Scanning Kelvin probe force microscopy characterized that the modified GB phase in Pr35Tb35Ni15Cu15 treated magnet exhibits a higher Volta potential than the 2:14:1 main phase, which is the main reason for the improved corrosion resistance. The present results suggest that the non-rare earth elements in the alloy diffusion sources play important roles in enhancing both coercivity and corrosion resistance of Nd-Fe-B magnets.