A Mechanistic Study of the Effect of Temperature on Crack Propagation in Alloy 600 Under PWR Primary Water Conditions

Stress corrosion cracking (SCC) in Alloy 600 has been studied in simulated pressurized water reactor (PWR) primary water at various temperatures. A clear correlation between temperature and crack growth rate (CGR) was found showing that the CGR increased monotonously within the range of temperatures used in this study (320–360 °C). In order to understand the temperature dependence of CGR, high-resolution characterization was used to study the crack tips. The crack tips obtained from different temperatures were analyzed by high-resolution analytical transmission electron microscopy (TEM) to reveal the crack tip morphology and chemistry, which enable the study of a thermally activated diffusion-based mechanism operating during SCC propagation. Transmission Kikuchi diffraction (TKD) was used to investigate mechanical response-based mechanisms in SCC propagation through quantifying the size and extent of plastic deformation around the crack tips. Results obtained in this study show that the thermally activated diffusion along the grain boundary increased with temperature while the changes of plastic deformation around the crack tip were small and nearly independent of temperature, suggesting that a thermally activated diffusion-based mechanism was dominant.