Cu-based bulk glassy alloys with good mechanical properties in Cu-Zr-Hf-Ti system

High-strength Cu-based bulk glassy alloys were synthesized in Cu-Zr-Ti and Cu-Hf-Ti ternary and Cu-Zr-Hf-Ti quaternary systems by copper mold casting. The critical diameter was 4 mm for the Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Hf₂₅Ti₁₅ ternary alloys and the Cu₆₀Zr₂₀Hf₁₀Ti₁₀ and Cu₆₀Hf₁₅Ti₁₅ quaternary alloys. As the substitution amount of Zr or Hf by Ti in Cu₆₀Zr₄₀ and Cu₆₀Hf₄₀ alloys increases, the glass transition temperature (T_g), crystallization temperature (T_x) and temperature interval of supercooled liquid region ΔT_x(= T_x - T_g) decrease, while the liquidus temperature (T_l) has a minimum of 1127 K around 20%Ti, resulting in a maximum T_g/T_l of 0.63 in in the vicinity of 20%Ti. The high glass-forming ability was obtained at the compositions with high T_g/T_l. The bulk glassy alloys exhibit high fracture strength of 2040-2190 MPa and plastic elongations of 0.3 to 1.9%. The finding of the Cu-based bulk glassy alloys with high T_g/T₁ above 0.60, high fracture strength above 2000 MPa and distinct plastic elongation is encouraging for the subsequent development as a new type of bulk glassy alloys which can be used for structural materials.