Hydrogen Embrittlement (HE) refers to the loss of ductility that metals and alloys undergo in the presence of hydrogen. The consequences for structural materials can be catastrophic even when hydrogen is present within the microstructure in small amounts (ppm). Given the importance of this phenomenon in many engineering applications, a lot of effort has been devoted over the last several decades to understand the mechanisms that lead to embrittlement in many different metals and alloys., In most cases HE is a consequence of diffusible hydrogen atoms trapped within the microstructure at unfavorable locations, such as grain boundaries and around dislocations. For this reason, the typical strategies to improve HE are: (i) preventing H from entering the material with special coatings and barriers; or (ii) introducing favorable trapping sites, especially near the external surface, to stop diffusible H from reaching sensitive microstructural defects within the bulk microstructure.

In this talk we will explore a different approach to improving HE resistance based on H dispersion, such that diffusible hydrogen is primarily located in a phase or domain less prone to embrittlement. In particular, we will focus on alloys with nano-crystalline domains that are either due to a different phase or induced by short-range ordering. To this end, we will show case studies for both model alloys and commercial steels recently developed in our lab. Combining tensile tests with damage analysis and hydrogen mapping, we will show how these nano-crystalline phases affect hydrogen diffusion and permeation through the bulk microstructure and hence the overall mechanical behavior.