Formation of Ti-Zr(Hf)-Ni-Cu Amorphous Alloys and Quasicrystal Precipitation upon Annealing

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Ti₆₀Zr₁₅Ni₁₅Cu₁₀ and Ti₆₀Hf₁₅Ni₁₅Cu₁₀ amorphous alloys were prepared and the crystallization process was studied. These alloys crystallize through multiple step exothermic reactions, of which the low-temperature one corresponds to the precipitation of an icosahedral quasicrystalline phase (I-phase). The particle size of the precipitated I-phase is approximately 20 nm for the two alloys. Further annealing of the alloys at higher temperatures leads to the decomposition of the I-phase to other stable crystalline phases, implying that the present I-phase is in a metastable state. It is speculated that icosahedral atomic clusters exist in the amorphous phase, which causes high nucleation rate of the I-phase in the initial crystallization stage.