On the formation of quasicrystals in Zr-Cu-Ni-Al metallic glasses

In a large number of metallic glasses (in particular Zr-bascd alloys) an icosahedral quasicrystalline phase is known to form first upon devitrification. This indicates at least a strong influence of the short-range order in the melt, quenched-in into the metallic glass. Observations on the influence of the quenching temperature of the melt on quasicrystat formation in melt-spun Zr-Cu-Ni-Al metallic glasses as well as on the influence of different routes of glass formation oil the phase selection in Zr-Pd alloys confirm such all assumption. Formation of quasicrystals has been explained by various arguments: Quasicrystals are often considered as Hume-Rothery phases, atomic size or bond strength dependent structures, or hybrid structures built, e.g., in Zr-Cu-Ni-Al glasses from Al2Cu- and MoSi2-type building blocks. The aim of this review paper is the discussion on quasicrystal formation in Zr-based metallic glasses on the basis of the vast amount of experimental results. Melt temperature, quenching rate, oxygen contamination, alloying with small amounts of additional elements or the exchange of the late transition metals arc assumed as ruling parameter for phase selection as well as their nucleation and growth rates.