INFLUENCE OF PLASTIC DEFORMATION ON THE EVOLUTION OF DEFECT STRUCTURES, MICROHARDNESS AND ELECTRICAL CONDUCTIVITY OF COPPER

Samples of pure Cu cylinder were plastically deformed by combination of cold-forging (CF) and cold-drawing (CD) under the liquid nitrogen temperature (LNT). X-ray diffraction measurements indicate that an increase of deformation strain leads to a decrease in crystallite size and an increase in twin densities for the CF and CD processed ultrafine-grained (UFG) samples. Dynamic recovery is suggested to start during the deformation process, and leads to a decrease of dislocation density at large deformation strains. The increase of twin density could compensate the loss of microhardness because of the decreasing of dislocation density. The electrical conductivities of CF+CD samples were tested through standard four-probe method, all of which are higher than 92% IACS. The results suggest that the strength of pure Cu could be improved and still keep its relatively high electrical conductivity by introducing deformation twins (DTs) into its microstructure.