Hydrogen transport in metals understood

At room temperature, hydrogen atoms may be absorbed into the metal lattice and diffuse through its grains. The hydrogen may be accumulated either as atomic or molecular form. Regardless of the form, atoms and molecules will combine to form small bubbles at the boundaries between metal grains. These bubbles build up pressure to levels where metals lose their ductility and minute cracks are formed.

The susceptibility of materials to hydrogen embrittlement depends on the characteristics of their microstructure and the presence of defects. Scientists initiated the EU-funded project MULTIHY (Multiscale modelling of hydrogen embrittlement) to develop tools to evaluate hydrogen transport in high-strength alloys with complex microstructure and a better understanding of hydrogen embrittlement.

Project scientists related the effect of micro-scale and even nano-scale structural features to measurable macroscopic hydrogen embrittlement susceptibility factors. Analytical techniques, physical testing and in-service data were used to develop a multi-scale modelling framework of hydrogen transport from the atomistic to the component level.

The MULTIHY team chose three industrial case studies, including the combustion chambers of a satellite launcher, automobile body in white components and offshore wind turbine bearings. The microstructure of advanced materials for all three case studies was analysed, and hydrogen diffusion and trapping parameters were evaluated through experiments and atomistic modelling.

To ensure accuracy without undue computational load, the scientists needed to balance and integrate the spatial and temporal differences between atomistic and finite element (FE) models. They relied on kinetic Monte Carlo simulations to facilitate use of the results of atomistic calculations as input parameters to FE-based models.

MULTIHY's multi-scale modelling framework will assist several industries in making informed decisions regarding the materials and processing methodologies they choose for their end-products. Steps that could be taken to reduce hydrogen embrittlement include reducing hydrogen exposure and low-temperature heat treatment (baking).