COMPOSITION DESIGN OF Fe-B-Si-Ta BULK AMORPHOUS ALLOYS BASED ON CLUSTER plus GLUE ATOM MODEL

The structural and compositional features of amorphous alloys can be described by cluster-plus-glue atom model, which is an effective method for the composition design of amorphous alloys. In the Fe-B binary system, Fe2B phase is an intermetallic phase related to Fe83B17 eutectic point. Under the framework of the highest radial number density and isolation principle, the local structure of Fe2B phase is characterized by a B-centered Ar-chimedean octahedral antiprism [B-B2Fe8] atomic cluster. Combined with the electron consistence criterion, the [B-B2Fe8]Fe (here the center and shell atoms are separated by a hyphen, a cluster is enclosed in square brackets, the glue atom is out square brackets) is then determined as an ideal cluster formula for Fe-B binary amorphous. To further enhance the glass-forming ability (GFA) of the alloy, the center B and shell Fe atoms in [B-B2Fe8]Fe are replaced with Si and Ta, respectively, due to their large negative enthalpy of mixing between Si-Fe and (B, Si)-Ta atomic pairs, and Fe-B-Si-Ta quaternary composition series, namely [Si-B2Fe8-xTax]Fe, are thus derived. The experimental results reveal that the bulk amorphous alloys with a diameter of 1.0 mm can be achieved for [Si-B2Fe8-xTax]Fe (x=0.4 similar to 0.7) compositions. Among them, [Si-B2Fe7.4Ta0.6]Fe (i.e. Fe70B16.67Si8.33Ta5, atomic fraction, %) is the best glass former, its glass transition temperature T-g, supercooled liquid region Delta T-x and the reduced glass transition temperatures T-rg are 856 K, 33 K and 0.584, respectively. The Vickers hardness, saturation magnetization and coercivity of the [Si-B2Fe7.6Ta0.4]Fe (i.e. Fe71.67B16.67Si8.33Ta3.33) amorphous alloy are measured to be 1117 HV, 1.37 T, and 3.0 A/m, respectively.