Effect of Co concentration on thermal stability and magnetic properties of (Fe,Co)-Nb-Gd-B glassy alloys

A two-stage-like glass transition phenomenon attenuated gradually with an increase in Co content in (Fe_1-yCo_y)_67.5Nb ₄Gd_3.5B₂₅ (y = 0.1-0.5) glassy alloys, and disappeared for the alloy with y = 0.5, resulting in a large supercooled liquid region of 102 K. As the Co content increases, the liquidus temperature decreases gradually, and the reduced glass transition temperature increases, indicating the enhancement of glass-forming ability (GFA). The best GFA was obtained for alloy with y = 0.5, and the full glassy sample with a diameter of 5 mm could be fabricated by copper mold casting. The (Fe,Co)-Nb-Gd-B glassy alloys exhibited good soft magnetic properties, i.e., rather high saturation magnetization of 0.86-0.91 T, low coercive force below 5.0 A/m, and low saturated magnetostriction of 6-13 × 10^-6. In addition, the glassy alloys also possessed very high compressive fracture strength of 3821-4112 MPa and high Vickers hardness of 1028-1065.