Contrast factors of dislocations in the hexagonal crystal system

Strain anisotropy can be well accounted for by the dislocation model of lattice distortion. In a texture-free powder or polycrystal, or if all possible Burgers vectors are equally populated, the dislocation contrast factors are a linear function of the fourth-order invariants of the hkl indices. Using this relation the dislocation contrast factors have been evaluated numerically and compiled for a number of common hexagonal materials. A procedure is presented to match experimentally determined contrast factor parameters with the numerically obtained parameter values. The procedure can be used as a tool to extract the microstructure from strain anisotropy in terms of Burgers vector populations, dislocation densities, crystallite size and size distributions in hexagonal crystals. Its practical use is illustrated by the application to plastically deformed titanium.