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 (Tg) and crystallization temperature (T x ), ΔT x (= T x - T g ) for Cu 50 Hf 45 Al 5 glassy alloy increased by the addition of noble metals (Ag, Pd, Pt or Au) and the largest ΔT x reached 110 K for Cu 45 Hf 45 Al 5 Ag 5 . 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 1 ) of Cu 45 Hf 45 Al 5 M 5 (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 3mm. The Vicker's hardness, Young's modulus, compressive fracture strength and plastic strain are 603 to 655, 119 to 125 GPa, 2220 to 2330MPa and 0.1 to 0.6%, respectively, for the Cu 45 Hf 45 Al 5 M 5 (M=Ag, Pd, Pt or Au) bulk glassy alloys. A different crystallization behavior is observed for Cu 50 Hf 45 Al 5 and Cu 45 Hf 45 Al 5 Ag 5 glassy alloys. The final crystallization phases are Cu 10 Hf 7 and CuHf 2 for the former alloy, and Cu 10 Hf 7 , CuHf 2 and Cu 8 Hf 3 for the latter alloy.