Thermal Stability and Mechanical Properties of Cu-Hf-Al Base Bulk Glassy Alloys with a Large Supercooled Liquid Region of Over 100 K

Abstract

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) for Cu₅₀Hf₄₅Al₅ glassy alloy increased by the addition of noble metals (Ag, Pd, Pt or Au) and the largest ΔT_x reached 110 K for Cu₄₅Hf₄₅Al₅Ag₅. The large ΔT_x of 94 to 101 K were also obtained for the alloys containing the other noble metals of 5 at%. The reduced glass transition temperature (T_g⁄T_l) of Cu₄₅Hf₄₅Al₅M₅ (M=Ag, Pd, Pt or Au) glassy alloys are in the range from 0.60 to 0.61. The selection of the quaternary compositions enabled us to form bulk glassy alloys with diameters up to 3 mm. The Vicker’s hardness, Young’s modulus, compressive fracture strength and plastic strain are 603 to 655, 119 to 125 GPa, 2220 to 2330 MPa and 0.1 to 0.6%, respectively, for the Cu₄₅Hf₄₅Al₅M₅ (M=Ag, Pd, Pt or Au) bulk glassy alloys. A different crystallization behavior is observed for Cu₅₀Hf₄₅Al₅ and Cu₄₅Hf₄₅Al₅Ag₅ glassy alloys. The final crystallization phases are Cu₁₀Hf₇ and CuHf₂ for the former alloy, and Cu₁₀Hf₇, CuHf₂ and Cu₈Hf₃ for the latter alloy.