Evaluation of Mechanical and Environmental Parameters Affecting Primary Water Stress Corrosion Cracking of Nickel-based Alloys

摘要

Primary water stress corrosion cracking (PWSCC) is one of the main degradation processes of nickel-based alloys in the pressurized water reactor environments. This paper evaluates the effects of the mechanical and environmental parameters on the cracking behavior of Alloy 600 in a quantitative way. Based on two mechanistic models for SCC, including the slip oxidation (SO) and internal oxidation (IO) mechanism, we have formulated the equations for the crack growth rate (CGR) calculation. The concept of a crack-tip strain rate was embedded into the CGR equation for the IO model, as well as for the SO model, which enables us to predict the CGR. It is found that the proposed two CGR equations are of use in predicting the CGRs of Alloy 600 in high temperature water environments. Particularly, the use of oxygen diffusion rate embedded in the IO model equation produces the comparable CGRs to the measured data. From the parametric study, the significance of the mechanical parameters on the cracking behavior was examined. Since a variation of the yield strength and the strain-hardening exponent of metals might enhance or reduce the CGR, it is of importance to accurately determine the mechanical parameters. In evaluating the effect of the water chemistry on the CGR, only the SO model equation was used since the IO model dose not take the water chemistry parameters into account at present.