TY - GEN
T1 - Microstructural and microchemical characterization of primary-side Cracks in an Alloy 600 nozzle head penetration and its Alloy 182 j-weld from the Davis-Besse reactor vessel
AU - Thomas, Larry
AU - Johnson, Brad R.
AU - Vetrano, John S.
AU - Bruemmer, Stephen M.
PY - 2005
Y1 - 2005
N2 - Cracks in Alloy 600 and Alloy 182 upper-head-penetration welded components from the Davis-Besse pressurized-water reactor (PWR) have been characterized by high-resolution analytical transmission electron microscopy (ATEM). This work complements a metallographic investigation of companion samples described separately in these proceedings. Samples containing axial cracks in the Alloy 600 nozzle material and both axial and circumferential cracks in the weld metal were prepared by ion micromilling and examined at scales ranging from mm to less than 1 nm. In both materials, the cracks occurred along high-angle grain boundaries and contained corrosion products indicating exposure to high-temperature water. Grain boundaries in the Alloy 600 were found decorated by Cr7C3 carbides and smaller Ti(C,N) particles. Cr 7C3 particles in cracks were interfacially attacked and formed Cr2O3 shells. The cracks ended in nm-wide oxide-filled zones containing S impurities and sulfide particles. These observations suggest that intergranular stress corrosion cracking in the Alloy 600 nozzle was assisted by S impurities in the primary-water environment. Microstructural characteristics of the weld metal differed greatly from those of the Alloy 600 nozzle. Welding produced dendritic microstructures with cellularly enriched Mn and intragranularly precipitated Nb-Ti carbides, Ti-Al-Mn-Si oxides and occasional MnS particles. The grain boundaries were decorated by fine MC (M = Nb + Ti) and Cr23C6 particles, but did not show evidence of impurity segregation or other second phases indicative of hot cracking. Cracking involved penetrative attack along the carbide-decorated grain boundaries as indicated by the corrosion microstructures observed near crack tips. These structures included Nb- and Cr-rich spinels from the reacted IG carbides, precipitated Ni metal, and distinctive spinel-filled corrosion tunnels containing S impurities in the metal near the tips. Comparisons with previously examined Alloy 182 welds from Ringhals 4 PWR indicated similar corrosion microstructures in primary-side cracks despite differences in grain-boundary precipitation.
AB - Cracks in Alloy 600 and Alloy 182 upper-head-penetration welded components from the Davis-Besse pressurized-water reactor (PWR) have been characterized by high-resolution analytical transmission electron microscopy (ATEM). This work complements a metallographic investigation of companion samples described separately in these proceedings. Samples containing axial cracks in the Alloy 600 nozzle material and both axial and circumferential cracks in the weld metal were prepared by ion micromilling and examined at scales ranging from mm to less than 1 nm. In both materials, the cracks occurred along high-angle grain boundaries and contained corrosion products indicating exposure to high-temperature water. Grain boundaries in the Alloy 600 were found decorated by Cr7C3 carbides and smaller Ti(C,N) particles. Cr 7C3 particles in cracks were interfacially attacked and formed Cr2O3 shells. The cracks ended in nm-wide oxide-filled zones containing S impurities and sulfide particles. These observations suggest that intergranular stress corrosion cracking in the Alloy 600 nozzle was assisted by S impurities in the primary-water environment. Microstructural characteristics of the weld metal differed greatly from those of the Alloy 600 nozzle. Welding produced dendritic microstructures with cellularly enriched Mn and intragranularly precipitated Nb-Ti carbides, Ti-Al-Mn-Si oxides and occasional MnS particles. The grain boundaries were decorated by fine MC (M = Nb + Ti) and Cr23C6 particles, but did not show evidence of impurity segregation or other second phases indicative of hot cracking. Cracking involved penetrative attack along the carbide-decorated grain boundaries as indicated by the corrosion microstructures observed near crack tips. These structures included Nb- and Cr-rich spinels from the reacted IG carbides, precipitated Ni metal, and distinctive spinel-filled corrosion tunnels containing S impurities in the metal near the tips. Comparisons with previously examined Alloy 182 welds from Ringhals 4 PWR indicated similar corrosion microstructures in primary-side cracks despite differences in grain-boundary precipitation.
KW - Alloy 182
KW - Alloy 600
KW - Cracking
KW - PWSCC
KW - Weld micro structures
UR - http://www.scopus.com/inward/record.url?scp=33745195002&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:33745195002
SN - 9780873395953
T3 - Proceedings of the Twelfth International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors
SP - 567
EP - 578
BT - Proceedings of the Twelfth International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors
T2 - 12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors
Y2 - 14 August 2005 through 18 August 2005
ER -