Formation and Mechanical Properties of Ti-Zr-Ni-Cu Amorphous Alloy Containing Icosahedral Nanoscale Quasicrystalline Phase

Abstract

Amorphous Ti 60 Zr 15 Ni 15 Cu 10 alloy ribbons containing an icosahedral quasicrystalline phase were prepared by melt-spinning. The microstructure of this alloy strongly depends on cooling rate, which controlled by the circumferential velocity of copper roll. At a low velocity of 10 m/s, stable α-Ti/Zr, Ti 2 Ni and Ti 2 Cu crystalline phases are formed. At the velocities of 15 and 20 m/s, an icosahedral quasicrystal phase (I-phase) is formed directly. At the velocities of 25, 30 and 35 m/s, a mixed structure consisting of I- and amorphous phases is formed and the size of I-phase is in the range of 5-50 nm. At the high velocity of 40 m/s, a single amorphous phase is formed. The DSC traces of these melt-spun alloys obtained during continuous heating from room temperature to 1000 K at a heating rate of 0.67 K/s show distinct exothermic peaks. The amount of the first exothermic heat decreases with a decrease of cooling rate, indicating an increase of the precipitated I-phase in these melt-spun ribbons. For the single amorphous phase ribbon, the Vickers microhardness (H v ), tensile fracture strength (σ f ) and distinct plastic elongation (e) are 460, 1480 and 1.42% respectively. For the nano-scale 1-phase bearing amorphous composite ribbons, the σ f , H v and e depend on the volume fraction (V f ) of the I-phase. The maximum σ f (1650 MPa) and e (1.52%) was obtained at about V f = 28% with particle size of 5-20 nm.