Influence of microstructure on the diffusivity of hydrogen in advanced steels

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Significant accumulation of Hydrogen in metallic systems is known to promote premature failure and is a primary concern in current and future nuclear reactors. In advanced steels, this happens due to their complicated microstructure, their very high strength, and the low solubility of H in steel. Extreme care is taken to prevent hydrogen absorption during processing and highly conservative and expensive approaches to degassing heat treatments are applied. Understanding how the hydrogen is absorbed, transported and trapped inside steel can yield huge improvements to the energy cost of producing these materials without compromising their structural integrity.This project is aimed at conducting fundamental studies to understand and predict the influence of the microstructure on the mobility of H in multi-phase steels. The work will involve developing microstructure-sensitive computational models describing the 3-D transport of H in alloys with multiple phases, all with different local H diffusion and trapping behaviour. It is also aimed to link this research with work on Hydrogen-induced embrittlement. The computational work will be validated using different experimental techniques including: (1) Thermal desorption spectroscopy to study the variations in H release with different microstructures. (2) Scanning Electron Microscopy - including serial sectioning - to image critical 2D and 3D features in the microstructure affecting H transport, such as morphology and size. (3) Transmission Electron Microscopy to study nano-scale features affecting H diffusion and possible loss in mechanical properties.