Kinetics and thermodynamics of bulk glass formation in a Zr52.5Cu17.9Ni14.6Al10Ti5 alloy

Abstract

Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glasses have been prepared by copper moulding. In order to obtain a fully amorphous sample, a careful control of the atmosphere conditions in the casting chamber was necessary. In particular, the presence of oxygen contamination promotes the nucleation of a fcc "big cube" phase, reducing glass formation. The crystallisation of bulk amorphous samples has been followed by DSC and values of about 4 kJ·mol-1 have been obtained for the heat release at about 740 K. By high temperature DSC, a metastable-to-stable phase transformation has been evidenced at 938 K, which gives a heat evolution of 1.12 kJ·mol-1. Melting and solidification of the alloy have been observed at 1070 K, giving an average value for the enthalpy change of about 8.2 kJ·mol-1. The temperature dependence of the enthalpy difference between undercooled liquid and equilibrium crystal phases has been described on the basis of different models for the specific heat difference (ΔCp) between the two phases. A best fitting of experimental data gives values of ΔCp of about 21 J·mol-1 ·K-1 at the glass transition temperature (690 K), in good agreement with experimental values obtained from DSC measurements.