Mechanism-Based Modeling of Hydrogen Environment Assisted Cracking (HEAC) in High Strength Alloys for Marine Applications: Prediction of Monel K-500 HEAC for Select Environmental and Mechanical Conditions

: The objective of this interdisciplinary research program was to implement quantitative predictive models of hydrogen environment assisted cracking (HEAC) of Monel K-500 in a pseudo-application specific situation. Here the crack growth behavior and component lifetime will be predicted as a function of applied stress, surface condition component geometry (summed into stress intensity variation), as well as metallurgical and environmental conditions (applied cathodic potential in seawater with local pH and potential at a crack tip). These conditions were relevant to naval components in the marine environment. Research emphasized hydrogen environment assisted cracking. The scientific goal was to improve understanding of crack tip electrochemical, H-trap interaction, and fracture processes at the microscopic scale to enable threshold and crack growth rate predictions in Ni-based alloys which differ substantially from high strength steels studied previously at UVa. The engineering goal is to transform this understanding into quantitative predictions of H uptake, H crack initiation and growth towards component lifetimes. An example of component lifetime for a generic bolt is detailed in Task 2 findings. Such models must be sufficiently flexible and implemented to accept metallurgical, mechanical and electrochemical inputs for Monel K-500 to predict cracking behavior and replace extensive empirical experimentation. The overarching goal was to provide outputs relevant to engineering that are based on proper physics of crack tip hydrogen uptake and chemo-mechanical damage. With active interactions involving US Navy laboratories, this research can impact cathodic protection system optimization (for instance, low voltage anodes) for a single material condition as well as component failure analysis/design.