Detailed examinations of intergranular attack (IGA) in alloy 600 were performed after exposure to simulated PWR primary water at 325°C for 500 h. High-resolution analyses of IGA characteristics were conducted on specimens with either a 1 µm diamond or 1200-grit SiC surface finish using scanning electron microscopy, transmission electron microscopy and atom probe tomography techniques. The diamond-polish finish with very little preexisting subsurface damage revealed attack of high-energy grain boundaries that intersected the exposed surface to depths approaching ~2 µm. In all cases, IGA from the surface is localized oxidation consisting of porous, nanocrystalline MO-structure and spinel particles along with regions of faceted wall oxidation. Surprisingly, this continuous IG oxidation transitions to discontinuous, discrete Cr-rich sulfide particles up to ~50 nm in diameter. In the vicinity of the sulfides, the grain boundaries were severely Cr depleted (to
Published: July 21, 2023
Citation
Olszta M.J., D.K. Schreiber, L.E. Thomas, and S.M. Bruemmer. 2011.Electron Microscopy Characterizations and Atom Probe Tomography of Intergranular Attack in Alloy 600 Exposed to PWR Primary Water. In Proceedings of the 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, August 7-11, 2011, Colorado Springs, CO, edited by J.T. Busby, G. Ilevbare and P.L. Andresen, 1503–1517. Cham:Springer.PNNL-SA-81560.doi:10.1007/978-3-319-48760-1_93