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Title: High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water

Abstract

Intergranular (IG) attack regions and stress-corrosion cracks in alloy 600 U-bend samples tested in 330C, pressurized-water-reactor water have been characterized by analytical transmission electron microscopy (ATEM). Observations of cross-sectional samples revealed short oxidized zones preceding crack tips and narrow (10-nm wide), deeply penetrated, oxidized zones along grain boundaries exposed along open cracks. High-resolution TEM imaging and fine-probe analysis were used to determine the local chemistries and structures in these corrosion-affected zones. Matrix areas surrounding the crack tips appeared highly strained, whereas the IG penetrations generally did not. The predominant oxide structure found along crack walls and just ahead of crack tips was NiO with metal-atom ratios similar to the alloy. The attacked grain boundaries off open cracks contained similar fine-grained NiO-structure oxide together with local areas of Cr-rich oxide and Ni-rich metal. In contrast, Cr-rich oxide identified as Cr2O3 predominated at the leading edges of the IG attack. Stereoscopic imaging of these tip structures revealed nm-scale porosity and tunnels within the oxide and pores along the grain-boundary plane ahead of the oxide. The general interpretation of these results is that IG attack and cracking follows local dissolution or oxidation and the formation of pores at grain boundaries. This degradation occursmore » at the nanometer scale and therefore requires high-resolution ATEM methods to reveal detailed characteristics. Experimental support for several possible IG degradation mechanisms is considered.« less

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
950749
Report Number(s):
PNNL-SA-32906
KC0201020; TRN: US0902016
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Corrosion, 56(6):572-587
Additional Journal Information:
Journal Volume: 56; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; INCONEL 600; INTERGRANULAR CORROSION; STRESS CORROSION; CRACK PROPAGATION; PWR TYPE REACTORS; PRIMARY COOLANT CIRCUITS; DISSOLUTION; GRAIN BOUNDARIES; OXIDATION; POROSITY

Citation Formats

Thomas, Larry E., and Bruemmer, Stephen M. High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water. United States: N. p., 2000. Web. doi:10.5006/1.3280561.
Thomas, Larry E., & Bruemmer, Stephen M. High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water. United States. doi:10.5006/1.3280561.
Thomas, Larry E., and Bruemmer, Stephen M. Thu . "High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water". United States. doi:10.5006/1.3280561.
@article{osti_950749,
title = {High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water},
author = {Thomas, Larry E. and Bruemmer, Stephen M.},
abstractNote = {Intergranular (IG) attack regions and stress-corrosion cracks in alloy 600 U-bend samples tested in 330C, pressurized-water-reactor water have been characterized by analytical transmission electron microscopy (ATEM). Observations of cross-sectional samples revealed short oxidized zones preceding crack tips and narrow (10-nm wide), deeply penetrated, oxidized zones along grain boundaries exposed along open cracks. High-resolution TEM imaging and fine-probe analysis were used to determine the local chemistries and structures in these corrosion-affected zones. Matrix areas surrounding the crack tips appeared highly strained, whereas the IG penetrations generally did not. The predominant oxide structure found along crack walls and just ahead of crack tips was NiO with metal-atom ratios similar to the alloy. The attacked grain boundaries off open cracks contained similar fine-grained NiO-structure oxide together with local areas of Cr-rich oxide and Ni-rich metal. In contrast, Cr-rich oxide identified as Cr2O3 predominated at the leading edges of the IG attack. Stereoscopic imaging of these tip structures revealed nm-scale porosity and tunnels within the oxide and pores along the grain-boundary plane ahead of the oxide. The general interpretation of these results is that IG attack and cracking follows local dissolution or oxidation and the formation of pores at grain boundaries. This degradation occurs at the nanometer scale and therefore requires high-resolution ATEM methods to reveal detailed characteristics. Experimental support for several possible IG degradation mechanisms is considered.},
doi = {10.5006/1.3280561},
journal = {Corrosion, 56(6):572-587},
number = 6,
volume = 56,
place = {United States},
year = {2000},
month = {6}
}