Formation and High Mechanical Strength of Bulk Glassy Alloys in Zr-Al-Co-Cu System

Abstract

The thermal stability of supercooled liquid in the temperature range before crystallization was examined in Zr55Al45-x-yCo xCuy alloys without Ni element and the large supercooled liquid region exceeding 80 K was obtained at the compositions around Zr 55Al20Co20Cu5 and Zr 55Al15Co7.5Cu22.5. By choosing the alloy composition of Zr55Al20Co20Cu 5 we have formed bulk glassy alloys in rod and sheet forms by copper mold casting and melt-clamp die forging. The maximum diameter and sheet thickness were 5 mm and 3 mm, respectively. The Tg, ΔT X and Tg/T1 are 746K, 84K and 0.61, respectively, being independent of sample thickness. The bulk alloy sheet exhibits Young's modulus of 92 GPa, elastic elongation limit of 2.1% and high tensile strength of 1960MPa. These strength values are considerably higher than those for the other Zr-based bulk glassy alloys reported up to date. The synthesis of the new Zr-Al-Co-based bulk glassy alloy with high glass-forming ability, large supercooled liquid region and high tensile strength approaching 2000 MPa is expected to result in a future extension of application fields as a high strength material.