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 Ti₅₀Cu ₃₂Ni₁₅Sn₃ 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). Ti₅₀Cu₂₅Ni₁₅Sn ₃Be₇ alloy shows enhanced glass-forming ability, enabling one to fabricate a fully amorphous bulk metallic glass sample 2mm in diameter by injection casting. With the replacement, the supercooled liquid region ΔT_x (≤ T_x-T_g, where T_x is the crystallization temperature and T_g is the glass transition temperature) decreased from 73 to 45K and the reduced glass transition temperature T_rg (≤ T_g/T₁, where T ₁ is the liquidus temperature) increased from 0.53 to 0.57. The amorphous Ti₅₀Cu₂₅Ni₁₅Sn₃Be ₇ phase showed a formation of short-range-ordered clusters 1-2nm in size, which is attributed to the strong interaction between Ti and Be. The results show that ΔT_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.