Unusual glass-forming ability induced by changes in the local atomic structure in Ti-based bulk metallic glass

The effect of partial replacement of Cu by Be in Ti50Cu32Ni15Sn3 alloy on the thermal properties, structure, and forming ability of an amorphous phase were investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS), and high-resolution transmission electron microscopy (HRTEM). Ti50Cu25Ni15Sn3Be7 alloy shows enhanced glass-forming ability, enabling one to fabricate a fully amorphous bulk metallic glass sample 2 mm in diameter by injection casting. With the replacement, the supercooled liquid region Delta Tx (= T-x - T-g, where T-x is the crystallization temperature and Tg is the glass transition temperature) decreased from 73 to 45 K and the reduced glass transition temperature T-rg (= T-g/T-1, where T-1 is the liquidus temperature) increased from 0.53 to 0.57. The amorphous Ti50Cu25Ni15Sn3Be7 phase showed a formation of short- rangeordered clusters 1 - 2 nm in size, which is attributed to the strong interaction between Ti and Be. The results show that Delta T-x can be used as a thermal parameter reflecting the glass-forming ability of the alloy only when the phase formed during crystallization is the same as the phase competing with the glass transition during solidification.