Boron content dependence of crystallization, glass forming ability and magnetic properties in amorphous Fe-Zr-B-Nb alloys

The glass forming ability (GFA) was investigated in Fe _91-xZr₅B_xNb₄ alloys with B contents of 0-36at.%. The GFA changes with B content, and fully amorphous alloys were prepared by melt spinning for B contents between 5 and 30at.%. The amorphous alloys crystallize with a primary crystallization mode in the low B content range of 5≤x≤20at.%, but in the eutectic mode in the high B content range of 20<x<30at.%. A single new metastable Fe-Zr-B-Nb cubic phase with a lattice constant of 1.0704nm, a saturation magnetization of 137emu/g and a coercivity of 7.3Oe at room temperature is formed when crystallizing in a polymorphous mode at x=30at.%. The glass transition temperature (T_g), crystallization temperature (T_x), Curie temperature (T_c) and saturation magnetizations (M_s) of the amorphous alloys increase with increasing B content, but the coercivity (H_c) decreases. As the B content exceeds 20at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but also the concentration dependence of the T_c and M_s changes. It is concluded that the amorphous alloys have better GFA, thermal stability and soft magnetic properties for the high B contents of 25-30at.% than for the low B contents of 5-20at.%.