The influence of grain boundaries and grain orientations on the stochastic responses to low load nanoindentation in Cu

Mechanical properties that are considered to be deterministic in the macro-scale have been shown to be stochastic in the sub-micron length scale. The origin of such stochastic responses is not well understood. This work examines the potential influence of grain boundaries and grain orientations on the stochastic nature of pop-in and hardness measurement in annealed high purity polycrystalline Cu samples during low load nanoindentation. Statistical analysis on pop-in load and hardness showed that variations of these measurements depend on crystal orientations and is influenced by the indenter probe size. Analysis on the pop-in load statistics showed that pop-ins are likely initiate from an atomic sized precursor that leads to dislocation generation or expansion. Variation in hardness measurements near an arbitrary chosen grain boundary and the apparent grain boundary hardening effect observed may be related to the higher density of dislocations at and near the grain boundary.