Recent progress on the study of the microstructure and mechanical properties of ECAE copper

Abstract

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.