Nano icosahedral quasicrystalline phase in Zr₆₅Al_7.5Ni₁₀Ag_17.5 quaternary glassy alloy

A nano icosahedral quasicrystalline phase was confirmed as the primary precipitation phase in the melt-spun Zr₆₅Al_7.5Ni₁₀Ag_17.5 quaternary glassy alloy with a two-stage crystallization process. The onset temperature of the first exothermic peak is 704 K at a heating rate of 0.67 Ks_-1. Although no significant X-ray diffraction peaks were observed in the sample annealed at 705 K, we confirmed the formation of the icosahedral phase by nano beam electron diffraction using FE-TEM. The icosahedral particles have an extremely fine grain size in the diameter range of 2 to 4 nm. In addition to the icosahedral phase, the nano crystalline particles corresponding to Zr₂Ag and/or fcc-Zr₂Ni structures are also observed in the annealed sample. The second exothermic peak denotes the transition from the nano icosahedral to the crystalline phase of Zr₂Ag, fcc-Zr₂Ni and Zr₄Al₃. The formation of the nano icosahedral phase as the primary phase is due to a high nucleation rate and strongly implies the existence of an icosahedral short-range order in the glassy state.