Formation, thermal stability and mechanical properties of bulk glassy alloys with a diameter of 20 mm in Zr-(Ti,Nb)-Al-Ni-Cu system

Bulk glassy alloy rods with a diameter of 20mm were produced for Zr ₆₁Ti₂Nb₂Al_7.5Ni₁₀Cu _17.5 and Zr₆₀Ti₂Nb₂Al _7.5Ni₁₀Cu_18.5 by a tilt casting method. The replacement of Zr by a small amount of Ti and Nb caused a distinct increase in the maximum diameter from 16 mm for Zr₆₅Al_7.5Ni ₁₀Cu_17.5 to 20 mm, accompanying the decrease in liquidus temperature and the increase in reduced glass transition temperature. The primary precipitation phase from supercooled liquid also shows a distinct change, i.e., from coexistent Zr₂Cu, Zr₂Ni and Zr ₆NiAl₂ phases for the 65%Zr alloy to an icosahedral phase for the 61%Zr and 60%Zr alloys. These results allow us to presume that the enhancement of the glassforming ability is due to an increase in the stability of supercooled liquid against crystallization caused by the development of icosahedral shortrange ordered atomic configurations. The 60%Zr specimens taken from the central and near-surface regions in the transverse cross section at the site which is 15 mm away from the bottom surface of the cast glassy rod with a diameter of 20 mm exhibit good mechanical properties under a compressive deformation mode, i.e., Young's modulus of 81 GPa, large elastic strain of 0.02, high yield strength of 1610MPa and distinct plastic strain of 0.012. Besides, a number of shear bands are observed along the maximum shear stress plane on the peripheral surface near the final fracture site. The finding of producing the large scale Zr-based bulk glassy alloys exhibiting reliable mechanical properties is encouraging forfuture advancement of bulk glassy alloys as a new type of functional material.