Serrated flow behaviors of a Zr-based bulk metallic glass by nanoindentation

Instrumented nanoindentation tests were used to investigate the mechanical properties of Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass. The corresponding loading strain rates were ranged from 0.002 s−1, 0.02 s−1 to 0.2 s−1. Plastic flow of this material exhibited remarkable serrations at low strain rates and increasingly became weakening until disappearance with increasing indentation strain rate, implying strong rate sensitivity. A significant pile-up around the indents was observed through atomic force microscopy, which suggested a highly localized plastic deformation. Mechanism governing the deformation was tentatively discussed in terms of the increasing process of free volume with a negligible temperature rise under low strain rate, which well explained the declining trend of elastic modulus and hardness with an increase of indentation depth.