Influence of alloying on the formation of Zr-based quasicrystals

Glassy Zr-Cu-Ni-Al precursor alloys exhibit quasicrystal forming ability in a narrow concentration range via isothermal heating. The formation of quasicrystals has been explained by various arguments. Often, they are considered as Hume-Rothery phases, atomic size or bond strength dependent structures, or a hybrid structure built from Al2Cu- and MoSi2-type structural units. The aim of the present investigation is to find out the influence of alloying on quasicrystal formation using transmission electron microscopy and X-ray diffraction. Small addition of elements such as Sit or Mo was found to change the phase selection during the early stages of crystallization significantly. Substitution with Sri, having the same oxidation state, leads to the formation of the icosahedral phase. On the other hand, substitution with Mo, having a higher oxidation state, leads to the formation of the fcc big cube phase. However, in the present investigation substitution of atoms bigger than Zr such as Y or Ce leads to very easy formation of quasicrystals even at lower temperatures. Si, on the other hand, which is smaller than Zr leads to the formation of the tetragonal Zr2Ni phase. (C) 2004 Elsevier B.V. All rights reserved.