In-situ investigation of thermal aging effect on oxide formation in Ni-base alloy/low alloy steel dissimilar metal weld interfaces

The thermal aging effect on the formation of oxide films at the interfaces of nickel-base alloy/low alloy steel dissimilar metal welds has been analyzed by in-situ Raman spectroscopy. Experimental conditions were controlled so as to simulate a pressurized water reactor primary water condition, with in-situ spectra recorded at 300 °C for 50 h. The results indicate the formation of Cr2O3, Fe3O4, and FeCr2O3 in as-welded samples, whereas thermal aging is found to form NiCr2O4 and NiFe2O4. In this study, therefore, it is determined that the thermal aging creates a susceptibility to stress corrosion cracking that is not present in the as-welded sample.