Modelling H diffusion and embrittlement in multi-phase alloys: Bridging the gaps in multi-scale modelling 

Anticipating hydrogen embrittlement (HE) is critical to the viability of many materials used in safety-critical industries such as energy, aerospace and automotive but HE remains a grand challenge in Materials Science. A main reason has been that detection of H inside alloys is extremely challenging, H has the solubility of only a few ppm, and is not possible to use imaging methods in Electron Microscopy. Therefore, developing computational methods that can explain the underlying physical mechanisms of hydrogen interacting with complex materials is necessary to design better and more resilient multi-phase alloy components. In this talk we present a number of modelling strategies across the scales predicting how H diffuses and interacts with microstructure to predict material’s response to H embrittlement. We first introduce a coarse-grained Off-lattice kinetic Monte Carlo model, based on the dimer saddle-point finding method, suitable for simulating the interaction of H with crystal defects in Fe over timescales not achievable with classical atomistic methods, such as molecular dynamics. Theories for local Thermodynamic equilibrium and continuum diffusion including microstructural effects are also presented to study multi-trapping effects in ferritic and martensitic steels; H behaviour in austenite-containing steels is used as example to discuss the validity of Thermodynamic equilibrium to multi-phase alloys. Lastly, we highlight how the microstructure affects plasticity-induced H segregation under applied stress in alpha+beta Ti alloys using crystal plasticity FE coupled with H diffusion modelling. The combination of these results represents a unique framework to understand conclusively H behaviour in complex materials and design microstructures more resistant against H embrittlement.

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