Study of formation of nano-quasicrystals and crystallization kinetics of Zr-Al-Ni-Cu metallic glass

The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr69.5Al7.5Ni11Cu12 metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy (Ec) and frequency factor (k0) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol-1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·1019 and 1.42·1020 s-1. Ec, k0 and the Avrami exponent (n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction (x) to the crystallization data. JMAK results of Ec for the first and second crystallization peak turn out to be 270 and 290 kJ mol-1 respectively. However, k0 and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports.