Synthesis and fundamental properties of Cu-based bulk glassy alloys in binary and multi-component systems

A glassy phase containing cubic phase particles with a size of 3-5 nm was formed in cast Cu₆₀Zr₃₀Ti₁₀ and Cu ₆₀Hf₃₀Ti₁₀ bulk alloys. The cubic phase is in a metastable state and its lattice parameter (a₀) is 0.45 nm for the former alloy and 0.51 nm for the latter. These bulk alloys exhibit good mechanical properties of 2000-2130MPa for tensile strength (σ _t,f), 2060-2160MPa for compressive strength (σ_c,f) and 0.008-0.017 for compressive plastic strain (ε_c,p). The temperature interval of the supercooled liquid (SL) region prior to crystallization is 37 K for Cu₆₀Zr₃₀Ti₁₀ and 67 K for Cu₆₀Hf₃₀Ti₁₀. The primary crystallization occurred by precipitation of cubic CuZr (a₀ = 0.35 nm) in a diffusion-controlled growth mode of nuclei and an orthorhombic Cu ₈Hf₃ phase in an interface diffusion-controlled growth of nuclei with decreasing nucleation rate. The difference in the precipitation modes is interpreted to be the origin of the difference in the SL region. Furthermore, the addition of Al to Cu-Zr and Cu-Hf alloys caused the formation of a glassy single phase in the rod form with diameters up to at least 3mm, though bulk glassy alloy rods with critical diameters up to 1.5mm and σ_c,f of 1920-2260MPa were formed in Cu-Zr and Cu-Hf binary systems. The ternary bulk glassy alloys exhibited high σ_c,f of 2100-2370 MPa with ε_c,p of 0.002-0.006. The addition of Pd, Pt, Ag or Au increased ΔT_x and a large ΔT_x of 102-110 K was obtained for the Cu-Hf-Al-M (M=Pd or Ag) glassy alloys. The synthesis of Cu-based bulk glassy alloys with good mechanical properties and large ΔT_x in glassy single, and mixed glassy and cubic phase states, is important for future applications of bulk glassy alloys.