Thermal Stability and Soft Magnetic Properties of Co–Fe–M–B (M=Nb, Zr) Amorphous Alloys with Large Supercooled Liquid Region

Abstract

A ferromagnetic amorphous phase with a large supercooled liquid region prior to crystallization and good soft magnetic properties was formed in melt-spun Co 40 Fe 22 Nb 8-x Zr x B 30 (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 ΔT 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 × 10 -6 -2.9 × 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 Co 40 Fe 22 Nb 6 Zr 2 B 30 glassy alloy with a diameter of 1.0 mm was prepared by the copper mold casting method. With increasing the cylindrical diameter up to 1.5 mm, the structure changes to coexistent amorphous, Co 21 Nb 2 B 6 , Co 3 ZrB 2 and Co 2 B 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 Co-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.