Characterization of stress corrosion cracks in Ni-based weld alloys 52, 52M and 152 grown in high-temperature water

• Microstructure and microchemistry at the SCC tips of Ni-based weld alloys 52, 52M and 152 were examined.
• The crack densities, lengths and distributions were found to be different for different alloys.
• IGSCC and TGSCC were observed on alloy 52, only TGSCC was observed on alloy 52M and 152.
• The cracks were filled by Ni-oxides and precipitated CrCs, NbCs, TiNs and SiCs.

Ni-based weld alloys 52, 52M and 152 are extensively used in repair and mitigation of primary water stress corrosion cracking (SCC) in nuclear power plants. In the present study, a series of microstructure and microchemistry at the SCC tips of these alloys were examined with scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM) and energy filtered transmission electron microscopy (EFTEM). The specimens have similar chemical compositions and testing conditions. Intergranular (IG) and transgranular (TG) SCC was observed in all of them. The cracks were filled with nickel-oxides and partial precipitations of chrome carbides (CrCs), niobium carbides (NbCs), titanium nitrides (TiNs) and silicon carbides (SiCs), while iron (Fe) was largely dissolved into the solution. However, the crack densities, lengths and distributions were different for all three specimens.