Grain growth and strain release in nanocrystalline copper

Grain growth and strain release processes in the electrodeposited nanocrystalline (nc) Cu specimen with a high purity were investigated by means of differential scanning calorimetry, x-ray diffraction, electrical resistance measurement, and high-resolution transmission electron microscopy. It was found that for the as-deposited nc Cu, the grain growth started at about 75 °C, at which the microstrain in (111) plane (e111) began to release, while the mean microstrain and that in (100) plane (e100) began to release at a higher temperature (150 °C). With an increment in microstrain in the nc Cu introduced by cold rolling, the grain growth onset temperature increased while the strain release onset temperature dropped obviously. These results showed an evident correlation between the grain size stability and the microstrain in the nc materials. The activation energy for the grain growth was determined by using Kissinger analysis and isothermal kinetics analysis, being about 86 kJ/mol, implying that the grain growth process is dominated by grain boundary diffusion.