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

The thermal stability of supercooled liquid in the temperature range before crystallization was examined in Zr₅₅Al_45-x-yCo _xCu_y alloys without Ni element and the large supercooled liquid region exceeding 80 K was obtained at the compositions around Zr ₅₅Al₂₀Co₂₀Cu₅ and Zr ₅₅Al₁₅Co_7.5Cu_22.5. 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 T_g, ΔT _X and T_g/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.