The cracking growth behavior of a sensitized Alloy 800H in supercritical water

The cracking growth behavior of a sensitized Alloy 800H in supercritical water (SCW) was studied at temperatures between 450 degrees C and 550 degrees C. Crack growth rates (CGRs) were measured in SCW environments with various dissolved gasses and in inert argon environment to separate the effects of corrosion and creep on the overall cracking susceptibility. Creep cavities were widely observed at the grain boundaries ahead of the crack tip in both SCW and Ar gas environments. Results show that both corrosion and creep contribute to the cracking behavior of sensitized Alloy 800H, and the corrosion contribution depends on the corrosion potential of the SCW environment. The stress corrosion cracking and creep CGRs increase with temperature, and their apparent activation energies are similar. The data support the conclusion that cracking was mostly controlled by creep and oxidization at the crack tip.