Nanocrystal development in Cu47Ti33Zr11Ni8Si1 metallic glass powders

The crystallization of gas atomized Cu47Ti33Zr11Ni8Si1 metallic glass powders subjected to annealing at temperatures above and below the glass transition temperature has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Nucleation occurs heterogeneously at “quenched-in” nucleation sites at temperature below the glass transition. The resulting nanocrystals are Cu rich. However, upon annealing in the supercooled liquid region, crystallization of Cu51Zr14 nanocrystals occurs homogeneously by a nucleation and growth mechanism. Crystallization in the supercooled liquid is diffusion-controlled. The activation energies for the first-order transformation have been calculated using isochronal and isothermal approaches and do not seem to be markedly affected by annealing.