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This paper studies the effects of high-pressure torsion (HPT) at ambient temperature on microstructural evolution and mechanical properties enhancement in pure copper. The aim is to introduce gradient microstructure, with various statistical distributions of grain size and grain orientations to examine their effect on strength and ductility. To this end, extruded cylindrical pure copper subjected to HPT for 1, 2, and 3-turns resulted in grain refinement down to the grain size of 500 nm. Combination of microhardness test and EBSD scans through the radial direction confirm the creation of a heterogeneous structure through the thickness and radial directions. The results demonstrate that increasing the shear strain leads to (1) ultra-fine grain (UFG) generation at deformed coarse-grain boundaries, (2) an increase in the fraction of recrystallized grains and high angle grain boundaries, and (3) a homogenous structure in the last step. A unique mixture has been obtained due to the particular shape of the anvils. The mixture included a chain of UFGs and coarse grains contain dislocations and subgrains. The highest level of gradient structure through the thickness was observed after 1-turn, which leads to the best combination of strength and ductility.

Severely plastically deformed microstructures of pure copper were produced by subjecting cylindrical copper samples to high-pressure torsion. The effects of this procedure on introducing gradient microstructure and subsequent mechanical behavior were investigated by utilizing electron backscatter diffraction and performing Vickers hardness/tensile testing. A crystal plasticity-continuum dislocation dynamics modeling effort was performed to predict the mechanical performance of these samples. The model includes mechanisms based on the gradient of dislocation density and grain size, back stress fields of grain boundaries, dislocation density transmission across grain boundaries, and stress/strain gradient effects.