Crystallization And Mechanical Property Of Cu-Zr-Based Bulk Metallic Glass

The glass forming ability, crystallization kinetics and mechanical propertiesof Cu₅₀Zr₄₀Ti₁₀,Cu₄₉Zr_39.2Ti_9.8Al₂ and Cu_47.5Zr_47.5Al₅ bulk metallic glasses havebeen investigated in this thesis.The structural characterization of three kinds of bulk metallic glasses wasperformed by XRD and the glass forming ability of them was studied by meansof DSC, the results show that Cu_47.5Zr_47.5Al₅ has the best glass forming ability inthe three kinds of bulk metallic glasses, the glass forming ability is enhanced byadding 2 at% Al to the Cu₅₀Zr₄₀Ti₁₀ bulk metallic glass.The crystallization kinetics of three kinds of bulk metallic glasses wasinvestigated by means of DSC under nonisothermal conditions. The effectiveactivation energies for the crystallization of three kinds of bulk metallic glasseswere evaluated by Kissinger′s equation. The results show that the crystallizationprocess of three kinds of bulk metallic glasses can be regarded as a kineticallymodified thermodynamic phase transformation process. Cu_47.5Zr_47.5Al₅ has thehighest effective activation energy for the crystallization temperature and thehighest thermal stability.Real-time detection of the crystallization behavior of Cu₅₀Zr₄₀Ti₁₀ bulkmetallic glass from the glassy state was studied using X-ray diffraction duringin-situ heat treatment. The results show that monoclinic CuZr metastable phaseis firstly precipitated in the glassy matrix during the continuous heating process,and the equilibrium phases are orthorhombic Cu₁₀Zr₇, orthorhombic Cu₈Zr₃ andtriclinic Cu₃Ti₂ at the final stage of crystallization.The compressive deformation behaviors of three kinds of bulk metallicglasses and Cu₅₀Zr₄₀Ti₁₀ composites with 20 nm and 30 nm crystalline at roomtemperature were investigated at strain rate of 10^-4 s^-1. The results show thatCu₅₀Zr₄₀Ti₁₀ bulk metallic glass exhibits excellent plastic deformation behavior,the strains of Cu₅₀Zr₄₀Ti₁₀ composites with 20 nm and 30 nm crystalline aremuch larger than that of Cu50Zr40Ti10 bulk metallic glass during plasticdeformation, Cu49Zr39.2Ti9.8Al2 and Cu47.5Zr47.5Al5 bulk metallic glasses exhibitembrittlement fracture pattern.The hardness of three kinds of bulk metallic glasses and Cu50Zr40Ti10composits with 20 nm and 30 nm crystalline was studied. The results show thatCu47.5Zr47.5Al5 are hardest in the five kinds of alloys, the hardness is enhancedby adding 2 at% Al to the Cu50Zr40Ti10 bulk metallic glass.