Dislocation Density in Ceramics Processed by Severe Plastic Deformation via High-Pressure Torsion

This study investigates the dislocation density in ceramics processed by severe plastic deformation at room and elevated temperatures via high-pressure torsion (HPT) for various numbers of turns and shear strains. Ceramics, characterized by ionic or covalent bonding, typically exhibit brittleness due to limited dislocation activity. However, HPT enables significant microstructural transformations in ceramics including dislocation nucleation and accumulation. Despite recent advances in the visualization of such dislocations by transmission electron microscopy (TEM), there is a lack of comprehensive reports on the quantification of dislocation density in severely deformed ceramics. This paper addresses this gap by employing X-ray diffraction (XRD) analysis to quantify dislocation density and crystallite size in a few oxide ceramics. Results demonstrate that HPT induces exceptionally high dislocation densities comparable to theoretical upper limits of dislocation density in ceramics, on the order of 10¹⁵ to 10¹⁶ m^-2, with crystallite sizes reduced to the nanometer scale. These findings significantly enhance the understanding of dislocation behavior in ceramics and suggest a potential approach for tuning the mechanical and functional properties of these materials by dislocations.