Crack Initiation Behaviour in Corrosion Fatigue of Copper Single Crystals in 1M NaNO2 Solution
Hiroyuki MIYAMOTO, Takayuki MORIKAWA, Takuro MIMAKI and Satoshi HASHIMOTO
Abstract:Corrosion fatigue of pure copper single crystals having a single activated slip system in aquious 1 M NaNO2 solutions, in which transgranular stress corrsion cracks (TGSCC) were observed in a slow strain rate technique, was investigated focusing on the effect of anodic potential and role of persistent slip bands (PSBs) on the crack nucleation. The number of cycles to fracture is lowest under 100 mV(Ag-AgCl) followed by those under 0 and 250 mV. Potential of 100 mV corresponds to where sensitivity of the TGSCC in pure copper was reported to be highest. A number of cracks were observed at PSBs under 100 mV, and plane of the cracks corresponds to [110] plane normal to applied tensile axis. Crystallographic features of the cracks formed under 100 mV were similar to TGSCC of pure copper single crystals deformed monotonically. Anodic current increased when the Bauschinger energy parameter be showed a peak, suggesting that cracks formed on the formation of the PSBs. Little cracks other than the primary crack were observed under 0 and 250mV. It is suggested that the cracks formed by the same mechanism of TGSCC in pure copper, and PSBs play an important role in nucleation of cracks under cyclic deformation. Key Words:Corrosion fatigue, Pure copper, Single crystal, NaNO2 solution, Potential, Stress Corrosion Cracking(SCC)