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 subgrainboundary
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
S3 boundaries is restricted to shear bands, while at
greater N, S3 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.
