Structural investigations of submicrocrystalline metals obtained by high-pressure torsion deformation

• Published in: Journal of alloys and compounds 2004-09, Vol.378 (1), p.242-247
• Main Authors: Kužel, R., Matěj, Z., Cherkaska, V., Pešička, J., Čı́žek, J., Procházka, I., Islamgaliev, R.K.
• Format: Article
• Language: English
• Subjects: Metals; Positron spectroscopies; X-ray diffraction, dislocations, TEM
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2003.12.048

Different samples prepared by high-pressure torsion deformation (Cu, Cu with addition of different amounts of Al 2O 3, Fe, Mg and Mg with 10 wt.% Gd) were investigated by X-ray powder diffraction (PXRD), positron lifetime spectroscopy (PL) and transmission electron microscopy (TEM). Conventional PXRD studies were carried out in order to determine lattice parameters, texture coefficients and especially crystallite size and microstrain (and dislocation densities). In simplified analysis, the profiles were analyzed in terms of the modified Williamson–Hall (WH) plots and more sophisticated analysis was performed by total powder diffraction pattern fitting. Small grains of the order of 50–300 nm and dislocation densities within the range of 1×10 13 m −2 up to 1×10 15 m −2 were determined. Observed line broadening anisotropy could be explained well for all the materials by the dislocation-induced line broadening and elastic anisotropy. Positron lifetime spectra have shown two major components—from positrons trapped at dislocations inside the distorted regions and the one attributed to positrons trapped in microvoids with the size of 4–5 vacancies. The values of crystallite size and dislocation density agree quite well with the estimations made from TEM. It was found that the addition of more than 0.5 wt.% Al 2O 3 prevents grain growth and keeps the dislocation density high up to about 400 °C. The amount of 0.3 wt.% is insufficient for that and significant grain growth is observed at about 200 °C.