Effects of Nb and Zr additions on crystallization behavior, microstructure and magnetic properties of melt-spun (Nd,Pr)2Fe14B/α-Fe alloys

Nanocomposite (Nd,Pr)2Fe14B/α-Fe magnets were prepared by crystallizing the amorphous melt-spun ribbons. The effects of Nb and Zr additions on the crystallization behavior, microstructure, and magnetic properties of (Nd0.4Pr0.6)8.5Fe85.5−x−yNbxZryB6 (x=0,0.5,1; y=0,0.5,1) alloys were studied. The microstructure and phase analysis shows that for (Nb,Zr)-free ribbons, α-Fe first precipitates, followed by the crystallization from amorphous to metastable phase before final transformation to the 2 : 14 : 1 phase and α-Fe. However, the combined Nb and Zr additions can increase the precipitating temperature of α-Fe, restrain the formation and growth of α-Fe, avoid the formation of metastable phase, refine and uniform the grain size, and thus greatly enhance intergrain exchange coupling between the hard and soft magnetic phases (verified by δM–H plot). After optimal thermal treatment, the coercivity and maximum energy product increase from 411 kA/m, 107 kJ/m3 for (Nd0.4Pr0.6)8.5Fe85.5B6 sample to 534 kA/m, 144 kJ/m3 for (Nd0.4Pr0.6)8.5Fe84.5Zr0.5 Nb0.5B6 sample, respectively.