Severe plastic deformation has become quite popular technique for production of compact ultrafine-grained materials. For better understanding of the microstructure of highly-deformed materials combination of different methods is desirable.

In present work, different samples of copper and copper composites deformed by the equal-channel angular pressing (ECAP) were studied by XRD line profile analysis, transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and positron annihilation spectroscopy (PAS).

Differences in microstructure of the samples in dependence on the number of passes (n_p = 1, 2, 4, 8) were found especially by TEM and EBSD. The latter technique is particularly useful thanks to the combination of good spatial and angular resolution. It was found that ECAP processing results in grain size reduction by a factor of about 100. Original course-grained microstructure evolves from prolate bands of cells/subgrains enclosed by lamellar nonequlibrium grain boundaries (1, 2) towards an equiaxed homogenous microstructure with equilibrium grain boundaries (8). Transition from the high fraction of the low angle grain boundaries created in the specimen during the first two ECAP passes to high angle grain boundaries as well as the pronounced increase of special coincidence site lattice (CSL) boundaries of Σ3ⁿ type after 4 and 8 ECAP passes have been observed.

PAS technique revealed the presence of high density of defects (absence of the signal from free positrons in the spectra) and slight increase of dislocation density with the number of ECAP passes n_p. PAS also revealed the presence of microvoids of the diameter increasing with np from about 0.34 nm to 0.44 nm.

XRD measurements were carried out with the aid of X’Pert Pro powder diffractometer, filtered CuKα-radiation filtered, variable divergence and anti scatter slits enhancing high-angle peaks important for line profile analysis and the PIXCel position sensitive detector that enables to obtain high-quality low-noise data at reasonable collection time. Line profile analysis was done by simplified integral breadth method and total pattern fitting by the FOX program that was modified for the analysis of crystallite size and strain including dislocation-induced line broadening. Modified Williamson-Hall plots (integral breadth β vs. sin θ) do not show significant dependence on np except slightly varying typical line broadening anisotropy of the β_hhh << β_h00 type. However, changes of  line profile shape can be clearly seen. With increasing np the tails become longer and shape is more Lorentzian. This may be a consequence of higher correlation in dislocation arrangements (which is in agreement with TEM and EBSD analysis) and results in the increase of dislocation density with n_p (in agreement with PAS).

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