Effect of time on the isothermal viscosity of metallic glass supercooled liquids

The viscosity of metallic glasses is considered to remain constant during thermoplastic forming operations. Here, we quantify the time dependent change in isothermal viscosity of Pt57.5Cu14.7Ni5.3P22.5 and Zr35Ti30Cu8.25Be26.75 glass formers in the supercooled liquid state. The samples were isothermally held prior to thermoplastic molding to probe the viscosity at different times. The viscosity values were extracted from the filling length of mold cavities. The viscosity increased with annealing time and the rate of increase was found to be largely independent of temperature and type of glass former. However, the viscosity increase was higher in the outer parts of samples which experienced higher shear rate during molding. Crystal nucleation and growth contributions are considered to explain the observed changes in effective viscosity of remaining amorphous phase. Our results suggest that thermoplastic forming is an effective tool in analyzing subtle changes in structure and viscosity of metallic glass supercooled liquids. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The viscosity of metallic glasses remains constant during thermoplastic forming operations, but increases with annealing time in the supercooled liquid state. The rate of increase is largely independent of temperature and type of glass former. Higher viscosity increase is observed in the outer parts of samples experiencing higher shear rates during molding. The changes in effective viscosity of remaining amorphous phase are attributed to crystal nucleation and growth contributions.