INVESTIGATING Pb-INDUCED STRESS CORROSION CRACKING OF ALLOY 800 VIA IN-SITU XPS

摘要

Laboratory investigations, aimed at testing the extremesof secondary side crevice chemistry have demonstratedthat Alloy 800NG materials can be susceptible to Pbinducedstress corrosion cracking (PbSCC) in causticenvironments, provided sufficient stress is present. Morerecently, a mechanism for PbSCC of Alloy 800NG has beendeveloped. Integral to this mechanism is the assumptionthat microscopic quantities of Pb are electrodeposited inmetallic form (i.e., Pb~0) on the metal surface, at the oxidemetalinterface. The fact that only a few atomic layers ofPb are typically associated with this degradation processhas posed considerable challenges for investigations of thechemical state of Pb on the material surface. To this end,building on the previous mechanistic work, anexperimental approach was devised wherein PbSCCcracks were produced in Alloy 800NG notched pinspecimens subjected to a 3-point bend loading and,subsequently, fractured in-situ within an ultra-highvacuum (UHV) pocket chamber attached to an X-rayPhotoelectron Spectrometer (XPS). The combination of thehigh surface specificity, chemical state selectivity and UHVof XPS, allowed for unfettered analysis of the fracture facefor the presence, and oxidation state determination, of Pb.This paper includes a discussion of the results of thisexamination in the context of the mechanism of Pb-assistedSCC of Alloy 800NG.