Precursor Evolution and SCC Initiation of Cold-Worked Alloy 690 in Simulated PWR Primary Water
EMSL Project ID
49618
Abstract
We suggest to use FIB/SEM sequential milling either manually or with the slice and view application to study stress corrosion cracking (SCC) precursors in cold-worked Alloy 690 specimens.Although to date no SCC case has been reported in alloy 690 after up to 25 years in service, laboratory tests have shown that it is not totally immune to SCC and its susceptibility has been reported to strongly depend on cold working and grain boundary (GB) carbide distribution. Extensive SCC crack growth rate (CGR) tests in PWR primary water have identified slow but stable SCC growth, but studies on SCC initiation in Alloy 690 are still very limited.
Preliminary studies at PNNL have suggested, that cavities and cellular carbides appear to enhance intergranular oxide growth and formation of small cracks locally. Both of these microstructural features can be highly localized at a small portion of a given grain boundary. 3D FIB/SEM is the only technique that can systematically reveal these features below the specimen surface. While sectioning and subsequent sequential polishing allows the characterization of grain boundary cross section (if only in one plane), these techniques destroy the specimen geometry of tensile specimens and are not suited for characterization during SCC test interruptions.
The radiological FIB/SEM (Quanta) at EMSL (3410) has the capability to run FEI Slice and View 1. With a cross-over point of 10 mm, it allows analysis of specimens with a non-flat topography such as blunt-notch and tensile SCC specimens. The research will aid our understanding of the role of (grain boundary) carbides, cavity formation and distribution, intergranular oxide growth and other localized changes in the microstructure on SCC initiation.
Project Details
Start Date
2016-10-06
End Date
2017-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Luo L., M. Su, P. Yan, L. Zou, D.K. Schreiber, D.R. Baer, and Z. Zhu, et al. 2018. "Atomic Origins of Water Vapor Promoted Alloy Oxidation." Nature Materials 17, no. 6:514-518. PNNL-SA-124752. doi:10.1038/s41563-018-0078-5
Zhai Z, MB Toloczko, K Kruska, and SM Bruemmer. 2017. "Precursor Evolution and Stress Corrosion Cracking Initiation of Cold-Worked Alloy 690 in Simulated Pressurized Water Reactor Primary Water." Corrosion 73(10):1224-1236. doi:10.5006/2470