Effects of Ti-replacing on the crystallization mechanism of amorphous Zr-Ti-Al-Cu-Ni alloys

The crystallization behavior of the Zr65-xTixAl7.5Ni10Cu17.5 based amorphous alloys for x = 5, 10, 15 has been studied by X-ray diffractometry (XRD), differential scanning calorimetry (BSC), atomic force microscopy (AFM) with the aim of investigating the replace ment effects of Zr by Ti. It has been found that, as the amount of Ti increases, the glass transition temperature decreases gradually but the temperature interval of the supercooled liquid region remains unchanged. Of the four exothermic peaks in DSC result, the temperature width between the first and second exothermic peak markedly broadens with increasing Ti concentration, indicating that the thermal stability of a crystalline phase corresponding to the second exothermic peak increases. After the second exothermic peak in DSC, the crystallized structure of amorphous alloys consists of coexistent amorphous and nano or microcrystals, and the third exothermic peak is due to the crystallization of CuZr2. The crystallization processes we obtain take the stages of Am --> Am' + AlZr+ NiZr2 --> Am' + recrystallization (AiZr + NiZr2) --> CuZr2 + AlZr + NiZr2 + recrystallization (CuZr2). The activation energies obtained by modified Ozawa method are 5.9, 2.6, 1.5 eV at the first peak and 2.9, 3.1, 4.2 eV at the second peak; for 5, 10, 15% Ti, respectively. These indicate the replacing of Zr by Ti changes the characteristic mechanism of phase transition significantly. (C) 2001 Elsevier Science B.V. All rights reserved.