Development and application of a novel precession electron diffraction technique to quantify and map deformation structures in highly deformed materials-as applied to ultrafine-grained titanium

The increased spatial resolution of a new characterization technique, precession electron diffraction (PED), makes possible the very accurate and automated quantitative characterization of technically interesting materials that historically have been difficult to analyze due to their dimensions and/or degree of deformation, including specifically ultrafine-grained metallic structures with high dislocation densities. PED, when coupled with the novel post-processing techniques that have been rigorously developed and presented for the first time in this paper, such as applying a Kuwahara filter to improve the angular resolution of the technique, makes it possible to determine grain size, texture, the density and spatial distribution of geometrically necessary dislocations, crystal orientation gradients, and the character of grain boundaries at the relevant length scale (the nanoscale) for such ultrafine-grained materials. The methods detailed in this paper place the determination of key microstructural features on a quantitative, rather than qualitative footing. These techniques have been applied to a hexagonal close-packed a-titanium. The results include the correlation between defect structure and microstructure with a nanometer resolution, the identification of regions containing few geometrically necessary dislocations, the quantification of dislocation densities in cell walls, and the quantification of deformation type in a statistically meaningful fashion. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd.