Analyses of shear band emission in a Mg-based bulk metallic glass deformed at different nanoindentation rates

Nanoindentation behavior of Mg57Cu31Y6.6Nd5.4 bulk metallic glass was characterized at different loading rates. The load–displacement curves exhibit significant displacement serrations, apparently associated with discrete shear band emission, at low loading rates but disappear at high rates. Analyses based on displacement serration, strain rate serration and hardness serration were carried out to determine the critical strain rate beyond which the transition from inhomogeneous to homogeneous deformation actually took place. It was concluded that the hardness serration analysis probably provides the most reasonable result as the other two were limited by the instrument noises. Based on a shear band nucleation model, the critical nucleus size was estimated to be a sphere of about 25 nm in diameter.