An atom probe tomography study of Pb-caustic SCC in alloy 800

Stress corrosion cracking (SCC) of Alloy 800 was induced in 330 °C Pb-caustic solution (pH330°C 9.5). These laboratory tests simulated extreme crevice environments in nuclear plants, but do not occur under normal operating conditions. Atom probe tomography (APT) was used to examine crack tips, a powerful but scarcely used technique for this application. APT revealed sub-nanometre scale crack chemistry: successive Ni-rich, de-alloyed regions and segregated Fe- and Cr-rich oxides. Also, APT allowed for quantification of impurities, such as Pb which segregated to oxide-metal interfaces (<4 at.%). Discussion highlights new mechanistic insights from APT, complementing prior transmission electron microscopy (TEM) analysis.