Glass-Forming Ability And Fracture Behavior Of NiTiZrAlCuSi Alloys

In this dissertation, the composition of Ni₄₁Ti_20.3Zr_21.8Al_8.4Cu₅Si_3.5 (at. %) bulk metallic glass (BMG) was designed in Ni-based alloys. The uniaxial compressive deformation and fracture behaviors at room temperature as well as crystallization behaviors in the supercooled liquid region of the Ni₄₁Ti_20.3Zr_21.8Al_8.4Cu₅Si_3.5 BMG alloy were investigated.The chemical composition of Ni₄₁Ti_25.3Zr_25.3Al_8.4 amorphous alloy was designed by a method of proportionally mixing the deep-euectic compositions of relevant binary alloys. The amorphous alloy sample with a diameter of 0.5 mm was obtained by using the arc-melting copper mould casting method. The BMG alloy of Ni₄₁Ti_20.3Zr_25.3Al_8.4Cu₅ was acquired by the addition of Cu for Ti, achieving fully amorphous sample of 1mm in diameter. The beneficial effect of Cu on the GFA of Ni₄₁Ti_25.3-xZr_25.3Al_8.4Cu_x(x = 1, 3, 5, 6,at. %) alloy system was analyzed. By further increasing the confusion degree of the amorphous alloy system, Ni₄₁Ti_20.3Zr_21.8Al_8.4Cu₅Si_3.5 BMG alloy was obtained by substituting Zr with metalloid Si, which can be synthesized into an amorphous sample with a diameter of 4 mm using copper mould casting. The role of Si addition to Ni₄₁Ti_20.3Zr_25.3-xAl_8.4Cu₅Si_x(x = 2.5, 3.5, 4.5,at. %) alloy system in enhancing GFA was also analyzed.By means of Differential scanning calorimeter (DSC), the crystallization of Ni₄₁Ti_20.3Zr_21.8Al_8.4Cu₅Si_3.5 BMG alloy under different continuous heating rates showed a single exothermic stage. The higher heating rate, the lower the crystallization degree would be. The primary crystallization activation energy is as high as 379.339 kJ/mol, which represents a larger thermal stability, and the continuous crystallization behavior of the studied BMG alloy was analyzed. The isothermal annealing crystallization DSC curve of the Ni₄₁Ti_20.3Zr_21.8Al_8.4Cu₅Si_3.5 BMG alloy in the supercooled liquid region still experienced a single exothermic stage. With the annealing time increasing, the disappearance of sphere-like crystalline phases in as-cast alloy confirmed its metastable nature. The crystallization of the studied alloy occurs via the precipitation of the nanocrystalline phase and the decomposition of the sphere-like primary phases.