Keynote
THE ROLE OF HYDROGEN IN MATERIAL DEGRADATION

Development and validation of a lifetime prediction methodology for failure of materials used for hydrogen containment components is of significant importance to the planned hydrogen economy. With the prospect of transitioning to a hydrogen-based economy, many engineering components will be exposed to high-pressure gaseous hydrogen environments.

Hydrogen embrittlement is a severe environmental type of failure; when hydrogen is present, materials fail at load levels that are very low compared with those that a hydrogen free material can sustain.

We will review recent contributions to the understanding of mechanisms of hydrogen embrittlement. In this paper, we describe the role of hydrogen in different structural materials with an emphasis on steels. For components made of high strength steels, we propose a model of decohesion-induced failure that links the microstructural decohesion event with the macroscopic load.

Thermal desorption spectroscopy (TDS) was used to identify and quantify the types and strengths of the hydrogen trapping sites. TDS results support the notion that only the diffusible hydrogen through the lattice sites or the hydrogen residing at the traps with the lowest binding energy contributes to material embrittlement; the deeper traps were saturated in both hydrogen free and charged samples. Hydrogen trapping and diffusion will be discussed in relation with microstructure features and mechanical states. We present a model for hydrogen transport that accounts for trapping of hydrogen at microstructural defects and address the interaction of hydrogen solute atoms with material deformation.

The residual stress state in a material has an important role in the mechanism of cracking, induced or assisted by hydrogen. The hydrogen interaction with residual stresses is studied by synchrotron x-ray diffraction. The results will be discussed in detail.