Effect of Corrosion Potential and Microstructure on the Stress Corrosion Cracking Susceptibility of Nickel-Base Alloys in High-Temperature Water

To evaluate the effect of corrosion potential on the stress corrosion cracking (SCC) initiation lifetime of nickel-base alloys, periodically unloaded uniaxial constant load (PU-UCL) tests were conducted, simulating boiling water reactor (BWR) water chemistry conditions. Utilizing the exponential distribution model for the determination of SCC lifetime, the SCC improvement factor was assessed by comparing the statistical location parameter of SCC failure time in PU-UCL tests between the hydrogen water chemistry (HWC) condition and the normal water chemistry (NWC) condition. The improvement factor larger than 10 was obtained for the moderate HWC condition, whereas it became more than 30 under the same condition when noble metals were chemically doped on the specimen surface preliminarily. The effect of microstructure on the SCC susceptibility was discussed after creviced bent beam (CBB) tests and microstructural analysis on grain boundaries. Alloy 182 (UNS W86182) with dendrite structure exhibits notably higher intergranular stress corrosion cracking (IGSCC) susceptibility than Alloy 600 (UNS N06600) with forged structure, even though the similar chromium profile was observed at grain boundary. Alloy 82 (UNS N06082) exhibited extremely high SCC resistance due to the sufficiently high chromium concentration at grain boundary.