Formation of Ti-Zr(Hf)-Ni-Cu amorphous alloys and quasicrystal precipitation upon annealing

Abstract

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.