Structural evolution of ultrafine-grained copper and copper-based alloy during plastic deformation

The dependence of stresses on the strain level and structural evolution of ultrafine-grained copper and a copper-based alloy during active plastic deformation at room temperature is studied in detail. Existence of short linear and parabolic work-hardening stages (stages II and III) in stress-strain curves and a long stage with nearly zero work-hardening coefficient are characteristic of the materials under study. It was revealed by transmission diffraction electron microscopy that at grain size of hundreds of nanometers, the in-grain dislocation slip and overslip along grain boundaries are the basic deformation mechanisms. The shear at grain boundaries and its contribution to the total shear are estimated. Changes in the grain structure and grain boundaries with strain level are analyzed. The scalar dislocation density and the internal stress field amplitude are measured. Special attention is paid to the contribution of grains of different size from the entire grain spectrum to the strain resistance. A composite model of the strain resistance of such materials is developed.