Precipitation of nanoscale icosahedral quasicrystalline phase in Hf-Cu-(Rh, Ir) amorphous alloys

摘要

Hf_(70)Cu_(25)Rh_5 and Hf_(70)Cu_(25)Ir_5 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization processes were studied by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. For both of the two alloys, the crystallization proceeds through the reactions of Am→I-phase→Hf_2Cu+α-Hf, where am and I-phase represent the amorphous and icosa-hedral quasicrystalline phases, respectively. Under optimum annealing conditions, the particle size of the I-phase is 10-25 and 10-20 nm for Rh- and Ir-containing alloys, respectively. Considering the fact that the crystallization process of Hf_(70)Cu_(30) amorphous alloy does not accompany the precipitation of an I-phase, the present result demonstrates that the addition of Rh or Ir is significant. It is suggested that icosahedron-like atomic clusters exist in the amorphous state of Hf_(70)Cu_(25)Rh_5 and Hf_(70)Cu_(25)Ir_5 alloys, which serve as the seeds for the precipitation of the I-phase in the initial crystallization process.