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 tem peratures are 780 K (T-x1) and 816 K (T-x2), respectively. The phase transi tion 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-res olution 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 D SC curve of the as-quenched sample, corresponding to the reactions of Am -- > CuTi --> Cu10Zr7 and CuTi + Cu10Zr7 + Cu3Ti + CuTi2 + Cu2Ti + CU10Zr7, re spectively. During the first-stage of crystallization, a significant redist ribution 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. Th e necessity of this long-range rearrangement of Zr and Sn in the first stag e of crystallization seems to be one of the reasons for the high stability of the supercooled liquid in the present alloy system. (C) 2000 Elsevier Sc ience B.V. All rights reserved.