Icosahedral and Amorphous Phases in Melt-Spun Ti-Zr-Ni-Cu Alloys

Abstract

Structure of melt-spun Ti₆₀Zr₁₅Ni_25−xCu_x (x=0, 5, 10, 15, 20 and 25) alloys and crystallization behavior of the amorphous alloys have been studied. The alloys have different structures depending on cooling rate. An icosahedral quasicrystal phase (I-phase) is formed directly upon cooling at a wheel velocity of 20 m/s for x=0–15, and at wheel velocities of 40 and 60 m/s for x=0. The high cooling rate at 60 m/s for x=5–25 causes the formation of a single amorphous phase. DSC traces of the amorphous alloys obtained during continuous heating to 1000 K showed distinct exothermic peaks. The first exothermic reaction at low temperatures for x=5, 10 and 15 is due to the precipitation of I-phase, and the following reactions at higher temperatures result from the formation of α-Ti and Ti₂Ni or Ti₂Cu phases. The simultaneous addition of Cu and Ni to Ti–Zr base alloys can enhance the forming ability of I-phase as well as amorphous phase.