Role of irradiated microstructure and microchemistry in irradiation-assisted stress corrosion cracking

Irradiation has a profound effect on the stress corrosion cracking propensity of austenitic alloys in high-temperature water. Irradiation-assisted stress corrosion cracking (IASCC) has been well documented both in the laboratory and in service over the past two decades. Numerous studies have shown that the degree of intergranular stress corrosion cracking increases with dose. However, the microstructure is simultaneously changing in several ways (dislocation loops, voids, segregation and hardening) and, not surprisingly, they all correlate with increased cracking susceptibility. As a consequence of their simultaneous development, the attribution of IASCC to one or more of these features has been difficult to establish. Mechanisms based oil each of the principal effects of irradiation in the alloy are considered. Arguments call be made in support of any one of these features as the cause of IASCC, but substantial evidence exists to refute a first order correlation. The mechanism of IASCC is more likely due to a combination of factors, or second order effects not yet considered. One such mechanism that is considered is based on the change in the deformation mode caused by the irradiated microstructure and the interaction of localized deformation bands with grain boundaries.