Effects of high boron content on crystallization, forming ability and magnetic properties of amorphous Fe91−xZr5BxNb4 alloy

The effect of boron (B) on crystallization, glass forming ability (GFA) and magnetic properties of amorphous Fe91−xZr5BxNb4 (FZBN) was studied in the B content (XB) 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 XB⩽20 at.%, but in eutectic mode in high B range of 20<XB<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 XB=30 at.%. The glass transition temperature (Tg), crystallization temperature (Tx), Curie temperature (Tc) and magnetizations (Ms) of the amorphous FZBN increase with increasing B content, while its coercivity (Hc) decreases. When the B content changes from low to high range at XB=20 at.%, not only increase the Tg, Tx and GFA sharply, due to the change of crystallization mode, but Tc, Ms and Hc 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.%.