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. (C) 2014 AIP Publishing LLC.