Role of excessive vacancies in transgranular stress corrosion cracking of pure copper

The role of the excessive metal vacancy generation in transgranular stress corrosion cracking (TGSCC) of pure copper was studied in relation to crack initiation and growth mechanisms. Electrochemically polarized specimens were strained at room temperature in 0.3 m NaNO2 solution. Cation vacancy redistribution under applied anodic polarization took place at the p-n junction of the duplex Cu2O oxide film, resulting in cation vacancy transport in the p-type layer of the oxide to the metal substrate interface and in excessive metal vacancy accumulation in the metal substrate. The rapid initiation of TGSCC at room temperature in the cold-worked oxygen-free high-conductivity copper samples occurred during slow strain rate tests under anodic polarization in 0.3 m NaNO2 solution. The duplex Cu2O oxide film structure formed by cathodic deposition, before applying the anodic polarization, was characterized with X-ray diffraction and field emission scanning electron microscopy/electron backscatter diffraction/energy-dispersive spectroscopy. The redistribution of cation vacancies in the p-type oxide phase due to the anodic polarization and the metal vacancy accumulation in the copper substrate interface was studied by using positron annihilation spectroscopy.