Soft Magnetic Bulk Glassy Fe–B–Si–Nb Alloys with High Saturation Magnetization above 1.5 T

New Fe-based bulk glassy alloys were synthesized in the (Fe0.75B0.15Si0.10)100−x Nbx system by copper mould casting. The maximum diameter of the bulk glassy alloy rod was 0.5 mm at 1 at%Nb, 1.0 mm at 2 at%Nb and 1.5 mm at 4 at%Nb. No glass transition is observed at 0 at%Nb, but the addition of Nb causes the appearance of glass transition before crystallization. The glass transition temperature (Tg) and crystallization temperature (Tx) of the bulk glassy rods were 815 K and 858 K, respectively, for the 1 at%Nb alloy, and 835 K and 885 K, respectively, for the 4 at%Nb alloy. The reduced glass transition temperature (Tg/Tl) defined by the ratio of Tg to the liquidus temperature (Tl) was measured as 0.56 at 1 at%Nb, 0.57 at 2 at%Nb and 0.61 at 4 at%Nb. There is a tendency for Tg, ∆Tx (= Tx − Tg) and Tg/Tl to increase with increasing Nb content. The effect of Nb addition can be interpreted in the framework of the three component rules for the formation of bulk glassy alloys and the stabilization of supercooled liquid. The Fe–B–Si alloy satisfies the three component rules by the addition of Nb. The bulk glassy alloy rods exhibited good soft magnetic properties, i.e., high saturation magnetization (Is) of 1.47 to 1.51 T, low coercive force (Hc) of 2.9 to 3.7 A/m and Curie temperature of 593 to 684 K. The high Is and low Hc, as well as the formation of bulk glassy alloys in the simple alloy system are promising as a new type of soft magnetic bulk alloy.