The link between the indentation size effect and the density of geometrically necessary dislocations was studied by using the following approach: four indents of different depth and hardness were placed in a Cu single crystal using a conical indenter with a spherical tip. The deformation-induced lattice rotations below the indents were monitored via a three-dimensional electron backscattering diffraction method with a step size of 50nm. From these data were calculated the first-order gradients of strain and the geometrically necessary dislocations densities below the indents. This approach permitted the quantification of both the mechanical parameters (depth, hardness) and the lattice defects (geometrically necessary dislocations) that were believed to be responsible for the indentation size effect. It was found that the geometrically necessary dislocation density does not increase with decreasing indentation depth but rather drops instead. More precisely, while the hardness increases from 2.08GPa for the largest indent (1230nm depth) to 2.45GPa for the smallest one (460nm depth) the geometrically necessary dislocation density decreases from ≈2.34 x 1015/m2 (largest indent) to ≈1.85 x 1015/m2 (smallest indent).

Investigation of the Indentation Size Effect Through the Measurement of the Geometrically Necessary Dislocations Beneath Small Indents of Different Depths using EBSD Tomography. E.Demir, D.Raabe, N.Zaafarani, S.Zaefferer: Acta Materialia, 2009, 57[2], 559-69