Improving intergranular phase and enhanced coercivity: A grain boundary diffusion of non-heavy rare earth PrNdAl alloy in sintered Nd-Fe-B magnets

The optimization of microstructure is an important strategy to improve the coercivity. In this paper, non-heavy rare earth PrNdAl alloy was selected as the diffused source to enhance the coercivity and improve the microstructure. The results show that the diffusion of PrNdAl alloy can greatly enhance the coercivity, achieving an increment of 31.1% compared to that of as-prepared sample. The diffusion of PrNdAl alloy does not change the crystal structure of intergranular phase in the triple-junction region. Three factors contribute to the improvement of coercivity. One is the enhancement of magnetic hardening of main phase grain surface, owing to the formed (Nd, Pr)2Fe14B shell. The other is the weakening of intergranular exchange coupling among grains, which is aroused by the reduced Fe content in RE-rich phase. The last is that the formed continuous RE-rich phase between grains contribute to the enhancement of magnetic isolation effect. In addition, the metallurgical behavior of elements and the evolution of intergranular phase are investigated.