Effect of testing conditions on the nanomechanical behavior of surface and inner core of as-cast Zr-base bulk metallic glassy plates

We report the effect of testing conditions on the nanomechanical behavior of the surface and inner core of as-cast plates of Zr41·2Ti13·8Cu12·5Ni10Be22.5, Zr52·5Cu18Ni14·5Al10Ti5, Zr58·5Cu15·6Ni12·8Al10·3Nb2.8 and Zr55Cu30Ni5Al10 bulk metallic glasses (BMGs). A series of instrumented nanoindentation experiments have been performed under control loading rate (CLR) mode at various maximum applied load (Pmax) in between 100 and 500 mN, and under control strain rate (CSR) mode at strain rates in between 0.001 and 1.0/s at Pmax = 500 mN on length-width (LW) surface and thickness-width (TW) inner core of 2 mm thick as-cast plates. The solid-liquid like regions in the glassy structure affects the deformation mechanism of BMGs as the liquid like regions triggers the activation of the shear transformation zones (STZs), which promotes formation of shear bands at various testing conditions. The nano-micromechanical behavior has been evaluated in terms of indentation size effect (ISE), strain rate sensitivity (m) and activation volume (V*) under CLR and CSR modes for LW and TW planes. The effect of testing conditions on the rate sensitivity and deformation mechanism have been discussed in terms of size and dynamics of STZs by considering the presence of solid-liquid like regions in the glassy structure. It has been noticed that hardness and rate sensitivity values have decreased and STZ size has increased with increasing Pmax for both the planes of all the studied BMGs.