The effect of nano-sized precipitates on stress corrosion cracking propagation of Alloy 718 under constant loads in PWR primary water

The stress corrosion cracking (SCC) propagation behavior of solution-annealed and precipitation-hardened Alloy 718 was investigated. The results show γ″ and γ′ precipitates are beneficial on retarding its crack growth under constant loads. Nano-sized precipitates at grain boundary (GB) tend to impede GB migration and oxidation beyond the crack tip, thereby compensating for the detrimental effect of a steeper strain gradient resulting from prominent elevated yield strength. The observed 2–40 times increase in CGR in hydrogenated water (near the Ni/NiO boundary) primarily attributes to the preferential GB oxidation and instability of the oxides during phase transition.