Comparison of the thermal stability between electro-deposited and cold-rolled nanocrystalline copper samples

The objective of this work is to investigate the microstrain effect on grain growth and strain release processes in nanocrystalline (nc) samples. Two kinds of nc Cu samples were studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM): an electro-deposited nc Cu sample with an average grain size of about 30 nm and one after cold-rolling in which the average grain size remain unchanged but the microstrain is substantially elevated. Measurement results indicated for the electro-deposited nc Cu, grain growth occurs at about 70°C, which was prior to the major strain release process (onset at 150°C). While for the as-rolled nc Cu, the grain growth onset temperature increases up to about 150°C and that of the strain release process drops to about 115°C. These results showed an evident correlation between the grain size stability and the microstrain in the nc materials.