OXIDE-INDUCED INITIATION OF STRESS-CORROSION CRACKING IN IRRADIATED STAINLESS-STEEL

Stainless steel (SS) samples were irradiated with protons at 400 degre es C and strained in 288 degrees C water to examine the role of oxide particles in the irradiation-assisted stress corrosion cracking (IASCC ) process. Oxides in the matrix acted as the predominant crack initiat ion sites, and the amount of cracking scaled with oxide density. Inter granular cracking occurred by mechanical failure of oxide particles th at created electrochemical crevices and stress concentrators from whic h intergranular cracks could propagate. Relatively few of the cracked oxide particles actually led to intergranular cracking in the matrix, which was consistent with the requirement that the crack tip solution had to be deaerated for an aggressive crevice chemistry to form and th at the cracks in the oxides had to be well aligned with susceptible gr ain boundaries, Intergranular cracking occurred only when both the SS was irradiated and when straining was conducted in high-temperature wa ter. This observation supported an IASCC mechanism that required an ag gressive environment and an irradiated microstructure.