Formation, nanostructure and mechanical properties of Cu-based nanocrystal-dispersed glassy matrix alloys

Bulk glassy alloys containing cubic phase particles with a size of 3 to 5 nm were formed in Cu₆₀Zr₃₀Ti₁₀ and Cu ₆₀Hf₃₀Ti₁₀ ternary systems by copper mold casting. The cubic phase had a lattice parameter of 0.45 nm for the former alloy and 0.51 nm for the latter alloy and was analyzed to have Cu-rich compositions as compared with their nominal compositions. The mixed phase bulk alloys exhibit good mechanical properties of 2000 to 2130 MPa for tensile fracture strength, 2060 to 2160 MPa for compressive fracture strength and 0.008 to 0.017 for compressive plastic strain. The temperature interval of the supercooled liquid region prior to crystallization is 37 K for the Cu ₆₀Zr₃₀Ti₁₀ alloy and 67 K for the Cu ₆₀Hf₃₀Ti₁₀ alloy. The primary crystallization occurred by the precipitation of a cubic CuZr phase with a lattice parameter of 0.35 nm in a diffusion-controlled growth mode of nuclei and an orthorhombic Cu₈Hf₃ phase in an interface diffusion-controlled growth mode of nuclei with decreasing nucleation rate, respectively. The difference in the precipitation modes is interpreted to be the origin for the difference in the supercooled liquid region. The formation of Cu-based alloys with high strength in the nanoscale mixed phase state is encouraging for future development as a new type of structural materials.