Stress corrosion cracking susceptibility of ultra-fine grain copper produced by equal-channel angular pressing

The stress-corrosion cracking (SCC) of ultra-fine grain (UFG) severely pre-deformed copper immersed into 1 M NaNO2 aqueous solution is investigated in terms of transient anodic current and fracture morphology. It is found that UFG copper possesses notably better resistance to SCC when compared to its coarse-grain counterpart. In contrast to the coarse grain copper, which fractures transgranularly in a cleavage manner, SCC in UFG specimens occurs intergranularly. The primary role of grain boundaries in SCC of UFG materials is argued from both mechanical and electrochemical aspects. The relatively high resistance to stress-corrosion damage in the UFG state and the intergranular type of SCC are connected with microstructural features of ECA-processed materials. Phenomenology of SCC is discussed from the standpoint of the film rupture and slip dissolution model specified for the severely pre-deformed materials.