Annealing Effects on Viscosity of Zr₅₅Cu₃₀Al₁₀Ni₅ Supercooled Liquids

Abstract

Viscous flow behavior in supercooled liquid region of as-cast and annealed Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses has been examined by using a penetration viscometer under various heating rates of 20, 200 and 400°C/min. Applied load for the cylindrical-shaped penetration indenter with a diameter of 1 mm was varied from 0.049 N to 0.294 N. Viscosity was quite independent of these applied loads under the various heating conditions. When the sample was slowly heated at the rate of 20°C/min, viscosity exhibited relatively high values that may be mainly due to the skin effects of oxides on the sample surface. At the heating rate of 200°C/min and above, viscosity (η) largely decreased and tended to saturate. By annealing the bulk metallic glasses at 400°C, the density of the glasses increased, while the crystallization temperature (T_x), the viscosity and the activation energy for viscous flow in their soopercooled liquid decreased gradually with increasing the annealing time. The specific behaviour of viscosity has been explained by the formation of particles during annealing for relaxation.