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Results on the microstructure and the tensile properties of equal channel angular extruded (ECAE) copper processed for one to 16 passes are presented and compared with the available literature data. With increasing number of passes (N), the microstructure changes from a strongly elongated shear band structure after N=1 and 2, towards a more equiaxed subgrain and grain structure. This is accompanied by a decrease in the cell wall or subgrain-boundary widths and an increase in recovered or even recrystallised grain structures with low dislocation densities. Electron backscatter diffraction measurements have indicated that for lower N, the location of Σ3 boundaries is restricted to shear bands, while at greater N, Σ3 boundaries were found to be more widely distributed. Texture measurements indicate close similarity with simple shear texture components and a spread of the orientation components with greater N. Upon comparing the tensile behaviour of as-ECAE Cu with the surveyed literature, broad agreement on the strength of the material is achieved. However, a strong variation in the percentage elongation to failure is also noted. Strain hardening and deformation kinetic analysis via strain rate jump tests indicate an evolution from stage III to V hardening during post-ECAE compression and a saturation in the strain rate sensitivity after N=4 resulting in maximum values of ∼0.02. Our results suggest that rather than a change in deformation mechanism, the increase in ductility with increasing N is associated with an increase in the mean free path of dislocations—with the grain boundaries remaining actively involved as the transmitter of plastic strain and their interaction with dislocations being the rate controlling deformation mechanism

The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via route B C for up to 16 passes have been assessed using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD) peak broadening, and texture analysis. The differences in grain size measured by these techniques allows for an understanding of microstructural evolution. A gradual decrease in grain size occurs with an increasing number of passes, while the subgrain size remains approximately constant. Up to four passes, the fraction of high-angle grain boundaries (HAGBs) (>15 deg) increases from 15 to 45pct, but remains constant thereafter. The grain boundary character distribution shows a decrease of Σ1 boundaries and an increase of Σ3 boundaries with higher passes. After 16 passes, a few regions of large 1 to 4 μm sized grains embedded in a submicrometer sized matrix were observed. These agglomerates of larger grain diameters together with the measured decrease in the dislocation density correlate with the observed decrease in yield strength of samples subjected to four and more passes. Texture evolution is adequately described under conditions of negative simple shear. The effect of increased accumulated strain results in an overall spread of orientation densities due to the absence of stable end positions post-ECAE. Detailed microstructural information suggests that strengthening mechanisms in the material can be sufficiently well described by the classical Hall-Petch relationship by applying it to the subgrain size, while the subgrain size remains smaller than the grain size