Viscous flow behaviour of supercooled liquids and mechanical properties in Zr-Cu-Ni-Al bulk metallic glasses

Viscous flow behaviour of supercooled liquids and mechanical properties in Zr_55+XCu_30-XNi₅Al₁₀ (X=0, 5 and 10 at. %) and Zr₆₅Cu₁₈Ni₇Al₁₀ bulk metallic glasses (BMGs) have been examined. Viscosity has been measured by using a penetration viscometer at a high-speed heating rate of 400 K/min. With increasing Zr-content, T_g tended to decrease and T_x tended to increase, resulting ΔT_x (=T_x-T_g) increaseing up to about 170 K under a heating rate of 400 K/min by the DSC analysis. The viscosity lowered about one order of magnitude, e.g., minimum value of the viscosity decreased from 3∼4×10⁶ Pa-s for the Zr₅₅Cu₃₀Ni₅Al₁₀ and Zr ₆₀Cu₂₅Ni₅Al₁₀ BMGs down to 5∼6×10⁵ Pa-s for the Zr₆₅Cu₂₀Ni ₅Al₁₀ and Zr₆₅Cu₁₈Ni ₇Al₁₀ BMGs under the same heating condition. Compression tests were also carried out at a slow strain rate of about 1 × 10 ^-4 s^-1 at room temperature. With increasing Zr-content, the apparent yield stress was decreased but the total strain at fracture was increased significantly, suggesting that there is a strong relationship between viscosity and the mechanical properties in these BMGs.