Search

Anisotropic strain broadening of diffraction peaks can be parameterised by dislocation contrast factors. A comprehensive software has been developed and made available through the internet to determine the individual and averaged contrast factors which are also compiled for cubic and hexagonal crystals. Using the theoretical and the measured values of contrast factor the microstructure of the specimen can be characterised in terms of active slip systems, Burgers vector populations, dislocation densities and crystallite size- and size distribution.

Ultrafine-grained titanium produced by equal channel angular pressing and subsequent cold rolling is studied by X-ray diffraction. It is found that a texture exists in which the hexagonal ...

Nanocrystalline titanium was produced by equal channel angular pressing (E CAP). It was found that during ECAP a texture evolved in the specimen in which the hexa gonal "c" axis is perpendicular to the extrusion direction. The crystallite size dist ribution and the dislocation structure were determined by fitting ab-initio theoretical functions to the Fourier coefficients of the measured X-ray diffraction peak profiles. The peak profile anal ysis provided the median and the variance of the crystallite size distribution: m=38 nm and s=0.49, respectively. The dislocation slip system population was found to be 75% type, 20% type and 5% type.

It has been shown recently that in many cases strain anisotropy in powder diffraction can be well accounted for by the dislocation model of the mean square strain. The practical application assumes knowledge of the individual contrast factorsCof dislocations related to particular Burgers, line and diffraction vectors or to the average contrast factorsC¯. A simple procedure for the experimental determination ofC¯has been worked out, enabling the determination of the character of the dislocations in terms of a simple parameterq. The values of the individualCfactors were determined numerically for a wide range of elastic constants for cubic crystals. TheC¯factors andqparameters were parametrized by simple analytical functions, which can be used in a straightforward manner in numerical analyses, ase.g.in Rietveld structure refinement procedures.