Copper-based Amorphous Glass-forming Ability And Thermal Stability

Ribbons of amorphous Cu-Ti-Ni alloys were prepared by melt spinning method. Bulk metallic glasses, Cu₆₀Zr₃₀Ti₁₀, Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁, Cu₅₀Zr₄₅Al₅ and Cu₄₆Zr₄₂Al₇Y₅, with a diameter of 3mm were prepared by copper mold casting method. The amorphous structure of these glassy alloys was confirmed by using X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis. Glass transition, crystallization and melting behavior of these alloys were studied by differential scanning calorimetry (DSC, Netzsch404). In Cu₅₀Ti_50-xNi_x (x=0, 5, 10, 15 at.%) system, we found that the supercooled liquid region, ⊿T_X, showed the maximum value of 61℃ at x=10. And the reduced glass transition temperature, T_rg, was smaller than 0.45. The glass forming ability (GFA) of Cu-Ti alloy was not effectively promoted by Ni addition.Dilatometric measurement (Netzsch DIL 402C) was carried out on Cu₆₀Zr₃₀Ti₁₀, Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ alloy rods to obtain information about the average nearest-neighbour distance r₀ and the effective depth of pair potential V₀. A decrease of thermal expansion indicating long range topological relaxation before glass transition was observed in Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ glassy alloy. By assuming a Lennard-Jones potential, r₀ and V₀ were calculated to be 0.28nm and 0.16eV for Cu₆₀Zr₃₀Ti₁₀, 0.27nm and 0.13eV for Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ respectively. It was found that the glassy alloy Cu₆₀Zr₃₀Ti₁₀ was more stable than Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ against heating from both experiment and calculation.The addition of Y promotes the glass-forming ability of the Cu₅₀Zr₄₅Al₅ alloy by comparing the cooling rate and the reduced glass transition temperature. The theoretic critical diameters of Cu₅₀Zr₄₅Al₅ and Cu₄₆Zr₄₂Al₇Y₅ were calculated to be 4.7mm and 15.8mm respectively. By the Kissinger Equation, the activation energy for crystallization was calculated to be 412 and 353kJ/mol for Cu₅₀Zr₄₅Al₅ and...