Localized corrosion resistance of high nickel alloys as candidate materials for nuclear waste repository. Effect of alloy and weldment aging at 427 C for up to 40,000 h

Ni-Cr-Mo alloys (e.g. C-22, C-4 and C-276) are considered candidate materials for nuclear waste containers because they offer excellent resistance to localized attack in conditions that can be encountered at the permanent repository site. Electrochemical and standard immersion tests showed that the most resistant of the studied alloys to localized attack was C-22 alloy and the less resistant was C-4 alloy. It was important to determine if long time exposure to low temperatures (below 500 C) would be detrimental in the resistance of these alloys to localized attack (pitting and crevice corrosion). After aging for 40,000 h at 427 C none of these alloys showed precipitation of a second phase (such as carbides or μ phase) that could promote a higher corrosion susceptibility of the alloys. Moreover, immersion and electrochemical tests showed that, after the same long term aging, the susceptibility to corrosion of both the base material and weldments remained unchanged. The effects of alloying elements on the resistance of the alloys to localized attack is discussed