Impression of Crystalline Cu with Different Grain

At room temperature, the indentation morphologies of crystalline copper with different 13 grain size including nanocrystalline (NC), ultrafine-grained (UFG) and coarse-grained (CG) copper 14 were studied by nanoindentation at the strain rate of 0.04/s without holding time at indentation 15 depth of 2000 nm. As the grain size increasing, the height of the pile-up around the residual 16 indentation increases and then has a slightly decrease in the CG Cu, While the area of the pile-up 17 increases constantly. Our analysis has revealed that the dislocation motion and GB activities in the 18 NC Cu, some crossand multiple-slips dislocation insides the larger grain in the UFG Cu, and forest 19 dislocations from the intragranular Frank-Read sources in the CG Cu, would directly induce these 20 distinct pile-up effect. 21