Amorphous and icosahedral phases in Ti-Zr-Cu-Ni-Be alloys

Abstract

Crystallization behavior of melt-spun and injection cast Ti-Zr-Cu-Ni-Be alloys have been studied by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Ti40Zr28Cu9Ni7Be16 and Ti34Zr31Cu10Ni8Be17 amorphous alloys crystallized through a two step process during heating: Nanoscaled primary I-phase precipitated from an amorphous matrix first and the remaining amorphous phase crystallized into the cubic beta-Ti(Zr) phase for Ti40Zr28Cu9Ni7Be16 alloy and to hexagonal Laves phase for Ti34Zr31Cu10Ni8Be17 alloy. The I-phase is stable at lower temperature and transforms into a Laves phase at high temperature through an endothermic reaction. Reversible transformation between the I-phase and Laves phase takes place during cyclic heating and cooling. In-situ composites consisting of I-phase embedded in an amorphous matrix can be fabricated by either heat treatment of fully amorphous phase or by controlling cooling rate during solidification. At lower cooling rate, I-phase forms as primary crystal in undercooled liquid and remaining liquid solidified into a glass. (C) 2003 Elsevier B.V. All rights reserved.