Dynamic crystallization process in a supercooled liquid region of Cu₄₀Ti₃₀Ni₁₅Zr₁₀Sn₅ amorphous alloy

Recently, a new bulk amorphous system Cu₄₀Ti₃₀Ni₁₅Zr₁₀Sn₅ has been reported. The glass transition temperature T_g is 735 K and the crystallization temperatures are 780 K (T_x1) and 816 K (T_x2), respectively. The phase transition of the Cu₄₀Ti₃₀Ni₁₅Zr₁₀Sn₅ amorphous alloy annealed at 735 (T_g), 758 (T_g+T_x1)/2, 780 (T_x1), 900 and 1000 K, respectively, was studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution analytical electron microscopy (HRATEM). The crystallization of the alloy proceeds by the process Am (amorphous state) →CuTi+Cu₁₀Zr₇→Cu₃Ti+Cu₂Ti+CuTi₂ +Cu₁₀Zr₇. Two exothermic peaks are observed in the DSC curve of the as-quenched sample, corresponding to the reactions of Am→CuTi+Cu₁₀Zr₇ and CuTi+Cu₁₀Zr₇→Cu₃Ti+CuTi₂+Cu₂ Ti+Cu₁₀Zr₇, respectively. During the first-stage of crystallization, a significant redistribution of Zr and Sn was recognized by a composition analysis with energy dispersive X-ray spectroscopy (EDS), implying that the phase transition is controlled mainly by the rearrangement of the solute elements Zr and Sn. The necessity of this long-range rearrangement of Zr and Sn in the first-stage of crystallization seems to be one of the reasons for the high stability of the supercooled liquid in the present alloy system.