Experimental investigation of distance effects between indenter and grain boundary on nanoindentation of Cu bicrystal

In order to study the effects of the distance between the indenter and the grain boundary (GB) on nanohardness and plastic deformation under micro-/nanoscale, the nanoindentation tests on copper bicrystals using a small size spherical indenter (40 nm radius) were analysed. The distance between the indenter and the GB was changed with different loads ranging from 20 to 1000 mN. The contact depth and nanohardness of the indents were calculated from load- displacement curves. The results show that the nanohardness on the GB is much higher than those of other indents inside the grains, due to the strengthening effect of the GB on material deformation realised by hindering the movement of atoms and dislocation slip. The nanohardness descends sharply when the indenter is near the GB (1 mm); however, when the indenter is far away from the GB, the nanohardness increases slightly, and then decreases. It is also found that there is load dependence on the GB; thelaw is different from those of the grain interior and other single crystal materials.