Industrially-relevant multiscale modelling of hydrogen assisted degradation

The advancement of computational modelling methods, particularly atomistic techniques, provides new opportunities for the investigation of H-metal interactions. However, there remain numerous obstacles to the application of such methods to real industrial problems. Key among these are the inability of atomistic calculations to describe long range diffusion processes and the inherent uncertainty regarding the predominant H-assisted damage mechanism in real engineering systems. The EU-FP7 project MultiHy aims to develop a robust, transferrable multiscale modelling methodology for predicting the HE susceptibility of real materials and components under actual production/service conditions. This will be demonstrated by investigating the influence of microstructure on H diffusion and trapping in three contrasting industrial case studies: (i) pulse-plated Ni coatings used in EADSs Ariane satellite launch system; (ii) advanced high strength steels for future automobile bodies; and (ii) ultra-high-strength steels used for offshore wind turbine bearings. A summary of the results from the first year of the project are presented. We have performed accurate first-principles calculations based on density functional theory (DFT) of the H binding energies and diffusion barriers in Fe and Ni as a function of lattice strain. Semi-empirical tight-binding models have also been developed, which will facilitate the evaluation of H trapping at extended crystal defects such as grain boundaries and dislocations. The atomistically-derived results have been used in mesoscale kinetic Monte Carlo (K MC) simulations to evaluate the effective H diffusivities under different strain conditions and trap densities. At the macroscopic level, we have developed a framework for the evaluation of H distribution under rolling contact conditions using the finite element method (FEM). Such FEM models will be later extended to full component scale models and will incorporate diffusivities derived using the atomistic-KMC simulations. An overview of experimental work aimed at the validation of the models at all scales will also be presented.