Stress Corrosion Cracking of Zirconium and Zircaloy-4 in Iodine-Alcoholic Solutions

Stress corrosion cracking (SCC) susceptibility of Zr (UNS R60702) and one of its alloys, zircaloy-4 (UNS R60804), was studied at room temperature in 10 g/L iodine dissolved in various alcohols: methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-octanol. SCC was observed in all the systems studied and the crack propagation rate was found to vary depending on the size of the solvent molecule. As the solvent molecular weight increased, the crack propagation rate decreased. Prior to crack propagation, intergranular attack was found in all the solutions tested. The intergranular corrosion rate also varied according to the size of the solvent molecule. Since the corrosion rate of Zr single crystals was similar in all the solutions tested, it was concluded that the decrease in both the intergranular attack rate and the crack propagation rate was attributable to a steric effect that hindered the access of the corrosive species to the tip of the crack. The surface-mobility SCC mechanism accounts for the experimental observations made in the present work.