Ultrafine grained Cu processed by compression with oscillatory torsion

Purpose: The aim of this work is a study of Cu microstructure after severe plastic deformation process by using compression with oscillatory torsion test. Design/methodology/approach: Cu samples were deformed at torsion frequency (f) changed from 0 Hz (compression) to 1.8 Hz under a constant torsion angle (alpha) sim 8 degree and compression speed (v)=0.1 mm/s. Structural investigations were conducted by using light microscopy (LM) and transmission electron microscopy (TEM). Findings: The structural analysis made by TEM shows that the process lead to grain refinement by the reconstruction of the banded (laminar) structure, typical for conventional deformation (compression), into a subgrain structure. Deformation at lower (f) and higher (v) were the most effective in refining grains, while using higher (f) and lower (v) may be characterized as a recovered and coarsened structure. This method facilitates obtaining a submicrocrystalline structure with nanocrystalline elements localised in the shear bands' region. Research limitations/implications: The understanding in refinement of Cu structure could help to modify the process and design deformation parameters. Practical implications: The knowledge of the characteristic features of unconventionally deformed materials will provide the usefulness of the employed method to produce materials having the desirable functional properties.