UNS N07718 is widely used in marine service applications and under a variety of conditions: alternate immersion, different levels of cathodic protection, freely corroding galvanic couples. Environmentally assisted cracking can significantly affect the performance of this alloy and constraint design as it needs to account for subcritical crack growth in service.
We measured subcritical crack growth rates and thresholds in different environmental conditions for two different heat treatments of UNS 07718. The first heat treatment, following AMS 5664 is typically used in the aircraft industry, and the second, following API 6A, is used in the marine and oil and gas industry. Other materials studied are UNS R30035 and UNS S66286. The material environmentally assisted cracking was studied under alternate immersion to natural seawater, and under cathodic protection in natural seawater.
Microstructural modeling of simultaneous fracture nucleation and propagation modes is presented to further understand and predict how precipitates, their volume fraction, morphology, and properties, on the evolution and accumulation of dislocation-densities within the microstructure affect the fracture process at different physical scales. Furthermore, a dislocation-density crystalline plasticity formulation is coupled to a hydrogen diffusion approach and the nonlinear fracture framework to further understand how cracks and dislocation-densities diffuse and interact.