For achieving a global transition from fossil energy sources towards regenerative energy, hydrogen will play a leading role. Thus, more and more industry branches as well as private consumers have to deal with generation, transportation, storage and combustion of hydrogen.

However, this development potentially poses new challenges for many materials, specifically metals: Hydrogen can detrimentally affect the mechanical properties of metals and may eventually yield “hydrogen embrittlement”. In particular, bcc steels exceeding a tensile strength of 800 MPa are susceptible to “hydrogen embrittlement”, which is characterized by a brittle material failure, often within a state of elastic strain. Other types of hydrogen-induced failures include blistering and the formation of defects such as flakes, fish-eyes, hydrides etc.

Hydrogen sources are found in various different steps of a component`s life cycle. Manufacturing, welding or heat treatment may bring hydrogen into the component. Hydrogen uptake during the component´s application can be facilitated by corrosion and exposure to hydrogen-containing atmospheres as well as high-pressure hydrogen, with the latter being predominantly associated to hydrogen as an energy source.

In order to prevent “hydrogen embrittlement”, it is essential to understand the mechanisms of failure, as well as the interactions of hydrogen with metals.

Hydrogen either is trapped at energetically favorable lattice sites such as dislocations or phase boundaries or remains diffusible as an interstitial atom. Since hydrogen diffusion is directed by stress gradients and affected by the microstructure, “hydrogen embrittlement” may occur when a critical threshold concentration is exceeded.

On the other hand, fcc metals such as stable austenitic steels as well as Nickel base alloys are far less susceptible to “hydrogen embrittlement”. Therefore, fcc metals, low strength steels and specific coatings are considered as key materials for a successful transition towards a hydrogen-based energy supply.