Room-temperature flow in a metallic glass -- strain-rate dependence of shear-band behavior

Abstract

The rate dependence of serrated flow in amorphous Al86.8Ni3.7Y9.5 has been investigated by nanoindentation. Three samples, containing different initial amounts and distributions of free volume, were used: as quenched, cold rolled and annealed below the crystallization temperature. When the cold-rolled sample is indented at low rates, no new shear bands form, and stable, time-dependent, flow takes place at pre-existing shear bands, well below the glass transition temperature. Aside from instrumental resolution, factors that likely affect serrated flow include the magnitude of the yield drop and the shear-band propagation velocity. The trends we observe are compared with calculations based on the free-volume theory.