Retardation of Softening of Ultrafine-Grained Copper during Low Temperature Annealing under Uniaxial Tensile Stress

Abstract

It is known that pure metals having ultrafine grains (UFGs) exhibit softening and grain coarsening at temperatures about one third of the melting temperatures. When such low-temperature annealing (LTA) of UFG copper is conducted under uniaxial tensile stress, the retardation of the softening is found to occur compared with that without stress. Observations of the microstructure and texture analysis indicate that the softening and the grain coarsening are attributed to recrystallization, and the presence of uniaxial tensile stress during LTA retards recrystallization. High voltage transmission electron microscopy revealed that the dislocation density of UFG copper annealed under uniaxial tensile stress is lower than that after LTA without stress. The retardation of recrystallization is associated with the reduction of the dislocation density of unrecrystallized UFG copper induced by dynamic recovery.