Precipitation of Stable Icosahedral Phase in Ti-Based Amorphous Alloys

The crystallization behavior of bulk amorphous Ti-Zr-Be-Cu-Ni alloys has been studied by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Detailed thermal analysis showed that Ti-Zr-Be-Cu-Ni amorphous alloys with the wide composition range crystallized through two exothermic reactions followed by one endothermic reaction. At first stage, nanometer scale primary icosahedral phase (I-phase) precipitated from an amorphous matrix and then the remaining amorphous phase crystallized into cubic β-Ti(Zr) phase or hexagonal Laves phase depending on the alloy composition. Finally, I- and β-Ti(Zr) phase or I- and Laves phase mixture transformed into the Laves phase by the high-temperature endothermic reaction, indicating that the I-phase is a thermally stable phase at the lower temperature range. Reversible transformation between the I-phase and Laves phase during cyclic heating and cooling confirmed the thermodynamic stability of the I-phase in Ti-Zr-Be-Cu-Ni system.