Microstructures and properties of copper processed by equal channel angular extrusion for 1-16 passes

The influence of the microstructure and the misorientation relationship between grains on the mechanical properties is investigated in specimens of ultrafine-grained copper processed by equal channel angular extrusion (ECAE) route B C in 1, 2, 4, 8, 12 and 16 passes is described. XRD peak broadening analyses showed a decrease in the lattice strain at roughly constant domain size as the number of passes increased. Analysis by TEM showed that the microstructure evolves from lamellar boundaries and elongated cells towards a more equiaxed homogeneous microstructure. On the microscale, observed by TEM, the degree of misorientation among subgrains/cells increases and the width of boundaries decreases while the cell/subgrain size remains approximately constant as the number of passes increases. Yield stress and ultimate tensile stress reach a maximum after four passes. From 4 to 16 passes the strength of the material decreases and the uniform elongation increases. It is suggested that the increase in the ductility (and decrease in strength) are associated with the operation of recovery mechanisms which decrease the boundary volume and the total dislocation density causing an increase in the mean free path of dislocations. The application of two single parameter models describing the constitutive behavior of the mechanical properties helps in the understanding of storage and annihilation of dislocations during deformation and the microstructural observations.