Effect of loading rate on the serrated flow of a bulk metallic glass during nanoindentation

The nature of displacement burst features throughout the load-controlled instrumented indentation of a Mg65Cu25Y10 bulk metallic glass was investigated over four decades of loading rate with varying peak loads and tip geometry. Where observed in the load–displacement data, displacement burst frequency, size and duration were found to be inversely related to loading rate, despite hardness and stiffness being independent of this parameter. Based on this evidence, it is proposed that increasing the loading rate during nanoindentation does not change the mechanism of deformation from serrated flow via shear banding to smooth plastic flow but is a result of the inability to resolve the length of displacement bursts at high loading rates. A displacement burst model is proposed that was found to successfully fit the experimental data for the investigated range of loading rates.