The deformation around a 500-nm deep Berkovich indent in a large grained Fe sample was studied using high resolution electron back scatter diffraction. electron back-scattering diffraction patterns were obtained in a two-dimensional map around the indent on the free surface. A cross-correlation-based analysis of small shifts in many sub-regions of the electron back-scattering diffraction patterns was used to determine the variation of elastic strain and lattice rotations across the map at a sensitivity of ∼±10-4. Elastic strains were smaller than lattice rotations, with radial strains found to be compressive and hoop strains tensile as expected. Several analyses based on Nye's dislocation tensor were used to estimate the distribution of geometrically necessary dislocations around the indent. The results obtained using different assumed dislocation geometries, optimisation routines and different contributions from the measured lattice rotation and strain fields were compared. The favoured approach was to seek a combination of geometrically necessary dislocation types which support the six measurable (of a possible nine) gradients of the lattice rotations after correction for the 10 measurable elastic strain gradients, and minimise the total geometrically necessary dislocation line energy using an L1 optimisation method. A lower bound estimate for the noise on the geometrically necessary dislocation density determination was ∼±1012 m-2 for a 200-nm step size, and near the indent densities as high as 1015 m-2 were measured. For comparison, a Hough-based analysis of the electron back-scattering diffraction patterns has a much higher noise level of ∼±1014m-2 for the geometrically necessary dislocation density.

Determination of Elastic Strain Fields and Geometrically Necessary Dislocation Distributions Near Nanoindents using Electron Back Scatter Diffraction. A.J.Wilkinson, D.Randman: Philosophical Magazine, 2010, 90[9], 1159-177