High temperature melt viscosity and fragile to strong transition in Zr–Cu–Ni–Al–Nb(Ti) and Cu47Ti34Zr11Ni8 bulk metallic glasses

The molten viscous behavior of Vitreloy 106, 106a, 105 and 101 bulk metallic glass-forming alloys was investigated at temperatures above Tliq. Couette concentric cylinder viscometry was used to determine the isothermal and continuous cooling melt viscosities. Isothermal three point beam bending measurements of the viscosity in the vicinity of Tg revealed a kinetically stronger liquid at low temperatures than at high temperatures, near Tliq. This behavior is revealed to be the result of a fragile to strong transition in the undercooled liquid, possibly due to polyamorphism.