Crystallization behavior and magnetic properties of (Nd0.4Pr0.6)9Fe76−xNbxB15 (x=0–5) flakes prepared by slow quenching

•First, (Nd0.4Pr0.6)9Fe76−xNbxB15 flakes were fabricated by slow quenching, which is different from Nd2Fe14B/α-Fe and Fe3B/Nd2Fe14B nanocomposites.•Second, we certify that Nb could suppress the formation of (Nd,Pr)2Fe23B3 and (Nd,Pr)1.1Fe4B4 phases in (Nd0.4Pr0.6)9Fe76B15 alloy.•Further, magnetic properties of (Nd0.4Pr0.6)9Fe76B15 flakes were significantly enhanced by introducing Nb.

(Nd0.4Pr0.6)9Fe76−xNbxB15 (x=0–5) flakes were fabricated by slow quenching from master alloys. Effects of Nb on crystallization behavior and magnetic properties of flakes have been systematically investigated. For the sample with x=0, the metastable compound (Nd,Pr)2Fe23B3 crystallized as a precursor from amorphous state and then transformated to the (Nd,Pr)2Fe14B and α-Fe phases, and the (Nd,Pr)1.1Fe4B4 phase was formed on further increasing annealing temperature to 700 °C. So the crystallization process of the (Nd0.4Pr0.6)9Fe76B15 alloy was as follows: amorphous phase (AP)→AP′+(Nd,Pr)2Fe23B3→(Nd,Pr)2Fe14B+α-Fe→(Nd,Pr)2Fe14B+α-Fe+(Nd,Pr)1.1Fe4B4. For the sample with x=4, the α-Fe phase was first formed from amorphous matrix, and then the (Nd,Pr)2Fe14B and Fe3B phases subsequently crystallized from residual amorphous phase. So the crystallization process of the (Nd0.4Pr0.6)9Fe72Nb4B15 alloy was as follows: amorphous phase (AP)→α-Fe+AP′ →α-Fe+Fe3B+(Nd,Pr)2Fe14B. The addition of Nb to (Nd0.4Pr0.6)9Fe76B15 alloy could suppress the formation of the metastable (Nd,Pr)2Fe23B3 phase and nonmagnetic (Nd,Pr)1.1Fe4B4 phase. Meanwhile, microstructure of (Nd0.4Pr0.6)9Fe76B15 flakes was significantly refined by introducing Nb. After optimal annealing treatment, the intrinsic coercivity increased from 397.3 kA/m for the Nb-free sample to 1297 kA/m for the 5 at% Nb-doped sample.