Effects of high boron content on crystallization, forming ability and magnetic properties of amorphous Fe_91-xZr₅B _xNb₄ alloy

The effect of boron (B) on crystallization, glass forming ability (GFA) and magnetic properties of amorphous Fe_91-xZr₅B _xNb₄ (FZBN) was studied in the B content (X_B) ranging from 0 to 36 at.%. The GFA changes with B content and reaches maximum near eutectic composition of 27.5 at.% B. Fully amorphous FZBN was prepared by melt-spinning in the B content between 5 and 30 at.%. Amorphous FZBN crystallizes in primary crystallization mode in low B content range of X _B ≤ 20 at.%, but in eutectic mode in high B range of 20 < X_B < 30 at.% and to a new metastable Fe-Zr-B-Nb cubic phase with saturated magnetization of 137 emu/g and coercivity of 7.3 Oe at room temperature in polymorphous mode at X_B = 30 at.%. The glass transition temperature (T_g), crystallization temperature (T _x), Curie temperature (T_c) and magnetizations (M _s) of the amorphous FZBN increase with increasing B content, while its coercivity (H_c) decreases. When the B content changes from low to high range at X_B = 20 at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but T_c, M_s and H_c as well as B content dependence of them also change. The amorphous FZBN has better GFA, thermostability and soft magnetic properties in high B content of 25-30 at.%.