Formation of icosahedral phase in Zr65Al7.5Ni10Cu12.5Ag5 metallic glass

Two Zr65Al7.5Ni10Cu12.5Ag5 amorphous specimens were prepared from the mother ingots with different solidification microstructures. Observation by high-resolution electron microscopy (HREM) revealed that there existed numerous nano-sized short-range order regions (SRORs) in the as-cast specimens although their amorphous nature had been verified by X-ray diffraction (XRD). The average size of the SRORs decreased significantly as the solidification microstructure of the mother ingot became finer. The transformation from amorphous to icosahedral phase (I-phase) in the Zr65Al7.5Ni10Cu12.5Ag5 metallic glass was systematically investigated by differential scanning calorimetry (DSC) under isochronal and isothermal conditions. The results indicated that the transformation kinetics slightly changed, and that the formation of I-phase was triggered by the growth of those SRORs as the pre-existing embryos. It was strongly suggested that the atomic configuration of the unit structure in the metallic glasses showed an icosahedron-like one.