Thermal stability and soft magnetic properties of Co-Fe-M-B (M=Nb, Zr) amorphous alloys with large supercooled liquid region

A ferromagnetic amorphous phase with a large supercooled liquid region prior to crystallization and good soft magnetic properties was formed in melt-spun Co40Fe22Nb8-xZrxB30 (x = 0, 2. 4, 6. and 8 at%) alloys. The glass transition temperature (T-g) increases monotonously with increasing Zr content. The crystallization temperature (T-x) also increases by the dissolution of Zr up to 2% and then decreases with further increasing Zr content. The increases is more significant for T-x, resulting in a maximum DeltaT(x)(=T-x - T-g) of 98 K at 2% Zr. The Co-based amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.41 T-0.42 T, low saturated magnetostriction of 2.4 x 10(-6)-2.9 x 10(-6), low coercivity of 1.2-2.0 A/m, and high permeability of 29000-33000 at 1 kHz over the whole Zr content range. In addition, the cylindrical Co40Fe22Nb6Zr2B30 glassy alloy with a diameter of 1.0mm was prepared by the copper mold casting method. With increasing the cylindrical diameter up to 1.5 mm, the structure changes to coexistent amorphous, Co21Nb2B6, Co3ZrB2 and Co2B phases. It is noticed that the maximum thickness for glass formation is about 6 times larger than that for Co-based amorphous alloys reported up to date. The success of forming Go-based bulk amorphous alloys with high stability of supercooled liquid and good soft magnetic properties is encouraging further development of bulk amorphous soft magnetic materials.