Effect of Si addition on the glass-forming ability of a NiTiZrAlCu alloy

The effect of Si addition on the glass-forming ability (GFA) of a NiTiZrAlCu alloy was investigated by using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The maximum diameter of glassy rods increased from 0.5 mm for the Ni₄₂Ti₂₀Zr₂₅Al₈Cu₅ alloy (the base alloy) to 2.5 mm for the Ni₄₂Ti₂₀Zr_21.5Al₈Cu₅Si_3.5 alloy and to 3 mm for the Ni₄₂Ti₁₉Zr_22.5Al₈Cu₅Si_3.5 alloy, when prepared by using the copper mould casting. The GFA of the alloys can be assessed by the reduced glass transition temperature T_rg(=T_g/T_l) and a newly proposed parameter, δ(=T_x/T_l − T_g). An addition of a proper amount of Si and a minor substitution of Ti with Zr can enhance the GFA of the base alloy by suppressing the formation of primary Ni(TiZr) and (TiZr)(CuAl)₂ phases and inducing the composition close to eutectic.