Icosahedral quasicrystal phase in Al₁₅Mg₅₀Zn₃₅ ternary alloy by rapid quenching

Almost an icosahedral quasicrstyal phase is obtained in the Mg-riched region off the Bergman line by means of rapid quenching in a cool copper mould. The microstructures, chemical composition and atom cluster of the icosahedral phase are charactered by X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy and transmission electron microscopy (TEM). It is found that the icosahedral quasicrystal phase is obtained with the composition of 39.76 at% Mg, 18.34 at% Al, and 41.90 at% Zn, which nucleates and grows directly from the melt with icosahedral symmetries. It exhibits a characteristic faceted dendritic growth with the fastest growth direction along a three-fold axes. At the same time, the regular hexagonal-polygon icosahedral quasicrystal grains with a size of 0.2 μ m can also be observed. The atomic cluster of icosahedral phase is pentagonal dodecahedron with icosahedral symmetries and micro-lobes on the each faceted pentagonal face.