Effect of cast temperature, size and annealing condition on the serrated flow during nano-indentation of Zr-based bulk metallic glasses

Abstract The present work deals with mechanical properties of five multicomponent Zr-based bulk metallic glasses: Zr 58 Cu 22 Fe 2 Ag 6 Al 12 , Zr 58 Cu 22 Fe 4 Ag 4 Al 12 , Zr 58 Cu 22 Fe 4 Co 4 Al 12 , Zr 58 Cu 22 Fe 8 Al 12 , and Zr 58 Cu 22 Ag 8 Al 12 , using nano-indentation technique at very low loading rate (80 μN/s). Zr-based glasses exhibit serrated flow during nano-indentation, manifested as a stepped load-displacement curve. Systematic study on the influence of free volume and nanocrystallization on shear band formation by varying the casting temperature and cross-section of the Zr 58 Cu 22 Fe 2 Ag 6 Al 12 , and annealing above and below glass transition temperature of the Zr 58 Cu 22 Co 4 Fe 4 Al 12 alloy is carried out. Analysis of the experimental data has revealed that higher casting temperature and larger casting cross-section cause partial crystallization, which decreases the hardness by promoting multiple shear band formation. However, hardness of the annealed glasses with similar fraction of nanocrystalline phases increases due to the reduction of free volumes as confirmed through electron diffraction studies in transmission electron microscope. Moreover, both free volume and nanocrystalline phase are found to have significant influence on the mechanical properties of bulk metallic glasses investigated in the present study.