The I-SCC behavior of N18 alloy at constant strain rate

The N18 zirconium alloy, belonging to Zr-Sn-Nb systems, is a new type of alloy developed by China to satisfy the demand of high burn-up and long lifetime PWR cores. In order to evaluate iodine-induced stress corrosion cracking (ISCC) behaviors of as-received and re-fabricated N18 alloy sheets, tensile tests were conducted at the constant strain rate in different media including air, ethanol, and iodine ethanol at room temperature and in iodine vapor at 350 C and 400 C. The effects of iodine concentration, strain rate, alloy composition and texture on ISCC behavior of zirconium alloys were investigated. The results indicate that N18 alloy would become more susceptible to SCC (stress corrosion cracking) as iodine concentration increases and strain rate decreases, and SCC sensibility of N18 alloy would be influenced not by iodine pressure but by temperature in iodine vapor. The chemical composition difference between N18 and zircaloy-4 would hardly affect SCC behavior, but the texture would have strong influence on SCC for N18 alloy although there is a little difference between transverse direction and rolling direction specimens. The stress corrosion initiation mechanism must therefore be analyzed as a corrosion-strain interaction linked to the chemical effects and mechanical effects