Precipitation of an icosahedral quasicrystalline phase in Hf59Ni8CU20Al10Ti3 metallic glass

The crystallization process of a Hf59Ni8Cu20Al10Ti3 metallic glass was studied using differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Two exothermic peaks are observed in the DSC curve of the as-quenched sample. It was revealed that the two reactions correspond to the phase transformations amorphous --> icosahedral phase + fee phase and icosahedral phase + fcc phase --> Hf2Cu + Al16Hf6Ni7 + Hf3Al2, where a = 0.254nm for the icosahedral phase and a = 0.53nm for the fee phase. Nanobeam electron diffraction patterns corresponding to the fivefold, threefold and twofold symmetries of a quasicrystal were obtained, revealing that the quasicrystal is an icosahedral phase. It is suggested that the present report on a Hf-based icosahedral phase is helpful for understanding the structural relationship between amorphous and icosahedral phases.