Effect of Si and Y Addition on Glass Transition Kinetics of ZrCu Based Bulk Metallic Glass

Zr₄₇Cu₄₄Al₉, (Zr₄₇Cu₄₄Al₉)_98.5Si_1.5 and [(Zr₄₇Cu₄₄Al₉)_98.5Si_1.5]_97.5Y_2.5 bulk metallic glass (BMG) were prepared by copper mould casting and studied using X-ray diffraction and differential scanning calorimetry. The influence of addition elements on the glass transition kinetics of the alloys were analyzed by the VFT equation. It is revealed that the glass transition behaviours of ZrCu based BMG were changed obviously by Si and Y addition, and the sensitivity of the glass transition temperature (T_g) to the heating rate is significantly increased. The fragility parameters m were reduced from 35.4 of Zr₄₇Cu₄₄Al₉ to 31.5 of (Zr₄₇Cu₄₄Al₉)_98.5Si_1.5, and that of alloy reached 30.7 after adding Y. The viscosity versus temperature relationship of alloy changes from characteristic of brittle fluid to strong fluid. The normalized glass transition temperature and heating rate show a clear VFT relationship. With the addition of Si and Y elements, the melt viscosity is close to that of the strong fluid.