Nano Icosahedral Quasicrystalline Phase in Zr<SUB>65</SUB>Al<SUB>7.5</SUB>Ni<SUB>10</SUB>Ag<SUB>17.5</SUB> Quaternary Glassy Alloy

Abstract

A nano icosahedral quasicrystalline phase was confirmed as the primary precipitation phase in the melt-spun Zr 65 Al 7.5 Ni 10 Ag 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 Zr 2 Ag and/or fcc-Zr 2 Ni structures are also observed in the annealed sample. The second exothermic peak denotes the transition from the nano icosahedral to the crystalline phase of Zr 2 Ag, fcc-Zr 2 Ni and Zr 4 Al 3 . 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.