Dependence of nanohardness upon indentation size and grain size - A local examination of the interaction between dislocations and grain boundaries

Pulse-electrodeposited nanocrystalline nickel was heat-treated to produce grain sizes from the nanoscale to microscale. By always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically, the dependence of nanohardness upon indentation size and grain size was studied. The plastic zone size related to the indentation size was measured quantitatively. The different dependences of hardness upon indentation depth in this work reveals clearly the local interaction between dislocations and grain boundaries in single grains. The experiments also show that the dislocations, which nucleate below the indenter tip, only interact directly with the surrounding interfaces for grains below 900 nm, where the nanohardness and pop-in width are grain size dependent.