Geometrically necessary dislocation density distributions in Ti–6Al–4V deformed in tension

We have used cross-correlation-based analysis of electron backscatter diffraction patterns to map lattice rotations in polycrystalline samples of Ti–6Al–4V before and after moderate (6%) tensile deformation. The sensitivity is improved compared to conventional Hough-based indexing and allows the density of geometrically necessary dislocations (GNDs) to be determined to ∼3×1012m−2 at a step size of 250nm. In the undeformed sample there were a few grains with GND density significantly higher than the background level. These tended to be of small area and associated with neighbouring regions of β-phase exhibiting the Burgers relation. After deformation the overall GND density increased, with 〈a〉 dislocations some 20 times more frequent than 〈c+a〉 ones. Evidence is given of elevated GND densities close to some, but not all, grain boundaries after deformation. This was also the most likely reason for the trend for the grain-averaged GND density to be higher for grains with small area on the section plane.