Formation, Thermal Stability and Mechanical Properties of Cu-Zr and Cu-Hf Binary Glassy Alloy Rods

Abstract

Glassy alloy rods with diameters up to 1.5 mm exhibiting a large supercooled liquid region before crystallization and high mechanical strength were formed in Cu-Zr and Cu-Hf binary alloy systems by the copper mold casting method. The large supercooled liquid region exceeding 40 K was obtained in the composition range of 30 to 70 at%Zr and 35 to 60 at%Hf. The largest value of the supercooled liquid region defined by the difference between glass transition temperature (T_g) and crystallization temperature (T_x), ΔT_x (= T_x − T_g), was 58 K for Cu₆₀Zr₄₀ and 59 K for Cu₅₅Hf₄₅. The reduced glass transition temperature (T_g/T_l) of the two alloys was 0.61 and 0.59, respectively. The alloys with large ΔT_x above 50 K were formed into a bulk glassy alloy form with diameters up to 1.5 mm by copper mold casting. The Cu₆₀Zr₄₀, Cu₄₅Zr₅₅, Cu₆₀Hf₄₀ and Cu₅₅Hf₄₅ glassy alloy rods exhibited high fracture strength of 1920, 1880, 2245 and 2260 MPa, respectively, Young's modulus of 107, 102, 120 and 121 GPa, respectively, a nearly constant elastic elongation of about 1.9% and plastic elongation up to 2.2%. The formation of these binary glassy alloy rods can be interpreted in the framework of the concept of the formation of the unique glassy structure consisting mainly of icosahedral atomic configuration as similar to that for special multi-component alloys with the three component rules.