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 + fcc phase and icosahedral phase + fcc phase → Hf₂Cu + Al₁₆Hf₆Ni₇ + Hf₃Al₂, where a = 0.254nm for the icosahedral phase and a = 0.53 nm for the fcc 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 isosahedral phase is helpful for understanding the structural relationship between amorphous and icosahedral phases.