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 Ni42Ti20Zr21.5Al8Cu5Si3.5 alloy and to 3 mm for the Ni42Ti19Zr22.5Al8Cu5Si3.5 alloy, when prepared by using the copper mould casting. The GFA of the alloys can be assessed by the reduced glass transition temperature Trg(=Tg/Tl) and a newly proposed parameter, δ(=Tx/Tl − Tg). 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.