Formation of an Icosahedral Quasicrystalline Phase in Zr65Al7.5Ni10M17.5 (M = Pd, Au or Pt) Alloys

An icosahedral (I) phase was found to be formed as a metastable phase in the crystallization process of amorphous Zr65Al7.5Ni10M17.5 (M = Pd, Au or Pt) alloys. The three amorphous alloys show an endothermic reaction due to the glass transition, followed by two exothermic peaks. The first exothermic peak is due to the precipitation of an I-phase and the second one results from the transition from the I to crystalline mixed phases of Zr4Al3+Zr2Ni+Zr2Pd (Zr2Au or ZrPt). The I-phase consists of fine grains with a size of about 10 nm and no distinct residual amorphous phase is seen. The formation of the I-phase in the new Zr-based alloy systems with a large supercooled liquid region and high glass-forming ability is important for the future development of bulk quasicrystalline alloys as basic science and engineering materials.