Enhancement of Glass-forming Ability of CoFeBSiNb Bulk Glassy Alloy with Good Soft-magnetic Properties

Abstract

The effect of B and Si concentration ratio on the glass-forming ability (GFA) of Co46Fe20B22+xSi6-xNb6 (x=0–2) glassy alloys was investigated. By copper mold casting, bulk glassy alloys of Co46Fe20B22+xSi6-xNb6 with diameters up to 4.5 mm were synthesized in the compositions of x=1. The additions of 23at% B combined with 5at% Si was found to be effective for the extension of the supercooled liquid region (∆Tx) defined by the difference between glass transition temperature (Tg) and crystallization temperature (Tx). The ∆Tx value is 51 K for the Co46Fe20B22Si6Nb6 alloy, and increases to 55 K for the Co46Fe20B23Si5Nb6 glassy alloy. In addition, this glassy alloy exhibits a highly reduced glass transition temperature (Tg/Tl) of 0.64 and in the compositions of x=1 was found to be in approaching alloy to a eutectic point. Large ∆Tx, high Tg/Tl and in approaching alloy to a eutectic point enabled us to prepare the Co46Fe20B23Si5Nb6 bulk glassy alloy successfully with a diameter of 4.5 mm. In addition to high glass-forming ability, the bulk glassy alloys exhibit excellent soft-magnetic properties, i.e., high saturation magnetization of 0.63–0.69 T, low coercive force of 1.17–2.35A/m, high effective permeability at 1 kHz of 1.36–2.65×104. The mechanisms for the high glass-forming ability and excellent soft-magnetic properties of the Co44Fe20B22+xSi6-xNb6 (x=0–2) glassy alloys are discussed