Primary precipitation of icosahedral quasicrystal with rearrangement of constitutional elements in Zr₆₅Al_7.5 Cu_27.5 glassy alloy with low oxygen impurity

The primary transformation reaction of the Zr₆₅Al_7.5Cu_27.5 ternary glassy alloy with a low oxygen impurity of approximately 100 mass ppm was investigated. We have discovered the precipitation of the metastable icosahedral phase with a fine grain size of 50-100 nm in diameter accompanying with the formation of stable Zr₂Cu phase at the annealing temperatures ranging from 715 to 730 K. The lattice spacing of Zr₂Cu phase decreases at higher temperatures, which is attributed to the rearrangement of Zr and Cu in the decomposition of the icosahedral phase. It is suggested that the formation of the icosahedral phase in the primary stage originates from the existence of the quenched-in icosahedral local atomic configuration in the glassy state.